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Foreign Exchange

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a complete thesis paper on foreign exchange

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1. Introduction About 10% of the non-ice covered landmass of the world is occupied by “wet soils”. Of  this, 0% is caused by !round water and "0% by surface water sta!nation. #ydrolo!ical function of the wetlands refers to the vital function of flood control and !round water  rechar!e and dischar!e $ishat et al. 1&&'(. )etlands constitute a part of natural herita!e for human bein!. *or thousands of years wetlands have played a si!nificant part in the development of human society. +n humid climate, particularly with a concentration of rainfall durin! the rainy season, favours seasonal seasonal saturation saturation of soil with water water and seasonal seasonal floodin! floodin! of low-ly low-lyin! in! lands. lands. An abundance of low-lyin! lands therefore contributes to the eistence of wetland areas. any of the wetlands of the tropical Asia are the result of a combination of humid climate with a heavy concentration of rainfall and an abundance of low-lyin! land lie floodplains, deltas and wide coastal low-land $/yuma, 1&(. he proportion of wetland soils to total land area is probably hi!her in 2outh and 2outheast Asia than in any other ma3or tropical re!ion of the world. ost of these soils, which are already producin! rice, are very  productive $urthy, $urth y, 1&4(.

5an!ladesh has the hi!hest wetland to total land ratio in the world. )et soils are ac6uirin! increasin! importance in land development and environmental protection. /nowled!e of  the duration and periodicity of wetness is important in evaluatin! possible use of soils and formulatin! remedial measures for chemical and physical chan!es caused by floods. +n most cases such chan!es are apt to impose permanent characteristics. 7ariations in the rainfall rainfall re!ime re!ime and seasonal seasonal fluctuat fluctuations ions stron!ly stron!ly influenc influencee perched perched water water table. table. he impact of wetness also depends on the period of the year durin! which it occurs, either  durin! the !rowin! period or the “dead season”. )etlands constitute about 40% of the territory of 5an!ladesh $2aheed, 1&8(. *ertility level of the wetland soils in the country is low to moderate and is believed to be enriched by siltation durin! floodin!. he land use in wetland soils is basically traditional dependin! on the timin! and duration of floodin!. 5an!ladesh is a land 9 hun!ry country with a hi!h pressure of population leadin! to incre increasi asin! n! number number of people people that that are are landl landless ess.. +ts +ts wetl wetlan and d resou resourc rces es have have suff suffer ered ed consider considerably ably from the impacts impacts of increased increased population population..

)etlands tlands of our country country are

-1-

shrinin! fast but these soils are principally used for rice cultivation. :ressure from increasi increasin! n! populat population ion demands demands to brin! brin! more more land under under paddy paddy cultivat cultivation. ion. Another  Another  important important feature is that wet soils of the ma3or area in 5an!ladesh are problematic such as  peat soil, saline soil, acid sulfate soil, sodic soil etc. etc . +t is thus obvious that study s tudy of wetland soil in 5an!ladesh occupies an important position so far as their characteristics and mana!ement are concerned because &% of the total rice area of 5an!ladesh is on wetland soils. 5rahmanbaria 5rahmanbaria was formerly a sub-division sub-division of ;omilla ;omilla district. +t lies between "'< '&= and "8<1>= north latitudes and between &0< 88= and &1< 1= east lon!itudes. he total area of  this district is 1&"4 s6. m. About ' % of the area is sub3ect to seasonal floodin!. he 2urma-/usiyara flood plain eists in this district and is seasonally flooded but in most  places remains flooded for the !reater part of the dry season. 5asins are moderate to deeply flooded. 2oils are moderately fine and medium tetured which has developed on unconsolidated alluvial sediments. ?ice is by far the most etensive crop in this district. 5roadcast 5roadcast Aman partly mied with Aus occasionally followed followed by ?abi crops is !rown on about 8'% of the land. @nfortunately @nfortunately,, wet land soils of the 5rahmanbaria 5rahmanbaria district as a whole have been sub3ect to the least amount of scientific study. hou!h recently 2?+ has done some analysis at upaBila level but researches on these soils are inade6uate. +n fact, low land soil of the 5rahma 5rahmanbar nbaria ia district district is a!ricult a!ricultural urally ly product productive ive and contains contains hi!h 6uantit 6uantity y of soil nutrients. Our present nowled!e on the characteristics of these soils is, therefore, very limited. A more intensive and detailed study is needed at the present time to determine the  potentialities of these soils for a!ricultural production. he present investi!ation is underta undertaen, en, therefore, therefore, to mae mae a detailed detailed study of the soil resourc resources es in wetland wetlandss of  5rahmanbaria district of 5an!ladesh.

he ob3ectives of this study were as followsC i.

o stud study y some some selec selecte ted d wetl wetlan and d soil soilss with with refer referen ence ce to their their morph morphol olo! o!ic ical al,,  physical, chemical, physico-chemical physico -chemical and mineralo!ical mineralo! ical properties.

ii. iii. iii.

o furnish furnish informa information tion on clay clay minera mineralo!i lo!ical cal composi compositio tion n of the soils. soils. o inve invest sti! i!at atee the the chan chan!e !ess in sele select cted ed char charac acte teri rist stic icss of the stud studie ied d soil soilss with with reference to their physical, chemical and physico-chemical properties.

iv. iv.

o shed shed li!ht li!ht on !ene !enesis sis and class classif ific icati ation on of the soils. soils. -"-

shrinin! fast but these soils are principally used for rice cultivation. :ressure from increasi increasin! n! populat population ion demands demands to brin! brin! more more land under under paddy paddy cultivat cultivation. ion. Another  Another  important important feature is that wet soils of the ma3or area in 5an!ladesh are problematic such as  peat soil, saline soil, acid sulfate soil, sodic soil etc. etc . +t is thus obvious that study s tudy of wetland soil in 5an!ladesh occupies an important position so far as their characteristics and mana!ement are concerned because &% of the total rice area of 5an!ladesh is on wetland soils. 5rahmanbaria 5rahmanbaria was formerly a sub-division sub-division of ;omilla ;omilla district. +t lies between "'< '&= and "8<1>= north latitudes and between &0< 88= and &1< 1= east lon!itudes. he total area of  this district is 1&"4 s6. m. About ' % of the area is sub3ect to seasonal floodin!. he 2urma-/usiyara flood plain eists in this district and is seasonally flooded but in most  places remains flooded for the !reater part of the dry season. 5asins are moderate to deeply flooded. 2oils are moderately fine and medium tetured which has developed on unconsolidated alluvial sediments. ?ice is by far the most etensive crop in this district. 5roadcast 5roadcast Aman partly mied with Aus occasionally followed followed by ?abi crops is !rown on about 8'% of the land. @nfortunately @nfortunately,, wet land soils of the 5rahmanbaria 5rahmanbaria district as a whole have been sub3ect to the least amount of scientific study. hou!h recently 2?+ has done some analysis at upaBila level but researches on these soils are inade6uate. +n fact, low land soil of the 5rahma 5rahmanbar nbaria ia district district is a!ricult a!ricultural urally ly product productive ive and contains contains hi!h 6uantit 6uantity y of soil nutrients. Our present nowled!e on the characteristics of these soils is, therefore, very limited. A more intensive and detailed study is needed at the present time to determine the  potentialities of these soils for a!ricultural production. he present investi!ation is underta undertaen, en, therefore, therefore, to mae mae a detailed detailed study of the soil resourc resources es in wetland wetlandss of  5rahmanbaria district of 5an!ladesh.

he ob3ectives of this study were as followsC i.

o stud study y some some selec selecte ted d wetl wetlan and d soil soilss with with refer referen ence ce to their their morph morphol olo! o!ic ical al,,  physical, chemical, physico-chemical physico -chemical and mineralo!ical mineralo! ical properties.

ii. iii. iii.

o furnish furnish informa information tion on clay clay minera mineralo!i lo!ical cal composi compositio tion n of the soils. soils. o inve invest sti! i!at atee the the chan chan!e !ess in sele select cted ed char charac acte teri rist stic icss of the stud studie ied d soil soilss with with reference to their physical, chemical and physico-chemical properties.

iv. iv.

o shed shed li!ht li!ht on !ene !enesis sis and class classif ific icati ation on of the soils. soils. -"-

2. Review of Literature )ith the tar!et of carrin! out morpho!enic investi!ation on the soils of the wetlands of  5rahmanbaria district, it was felt necessary to review the available literatures on similar  soil elsewhere so as to provide information on their nature and properties.

2.1 Definition and concept of wetlands he RAMSAR he RAMSAR Convention has Convention has defined wetland as “ areas of marsh, fen, peat land or water, whether natural or artificial, artificial, permanent or temporary temporary,, with water that is static or flowin!, flowin!, fresh, bracish or salt, includin! areas of marine water the depth of which at low tide does not eceed si meters”. meters”. hus term “wetland” !roups “wetland” !roups to!ether a wide ran!e of inland, coastal

and

marine

habitats

which

share

a

number

of

common

features

$u!an, 1&&0(. As defined by the convention, wetlands include a wide variety of habitats such as marshes,  peatlands, floodplains, rivers and laes la es and an d coastal co astal areas such s uch as salt marshes, mars hes, man!roves man!r oves and sea!rass beds but also coral reefs and other marine areas no deeper than si meters at low tide, as well as human9made wetlands such as waste- water treatment ponds and reservoirs. he he ran! ran!ee of wetl wetlan and d habi habita tats ts whic which h come come unde underr the the mand mandat atee of the the ?A2 ?A2A?  A?  ;onvention is enormous. Accordin! to their basic biolo!ical and physical characteristics [email protected]; has identified identified a total of '& cate!ories of wetlands of which '0 are natural wetlands and 10 are man-made $u!an, 1&&0(. )etland soils can be defined as “soils whose development and properties are stron!ly influenced by topo!raphy or permanent saturation in the upper part of the land”. +n fact, wetland soils or wet soils are nown under different namesC hydric soils, sta!nosols, meadow soils, a6uic soils etc. $udal, 1&&"(. #aor, boar, beels and 3heels are commonly identified as freshwater wetlands in 5an!ladesh and they have the characteristics of four landscape units 9floodplain, 9floodplain, freshwater marshes, laes and swamp forests. *loodplains are the areas that under!o periodic floodin! as a river channel overflows with flood water. *reshwater *reshwater marshes are more or less permanent shallow water dominated dominated by reeds etc. Daes, natural or man-made, are deep waterbodies waterbodies $u!an, 1&&0(. 5eels may be taen to be a combination of freshwater marshes, laes and -'-

swamp forest. 5oars are beels which are actually obow laes and 3heels are freshwater  marshes. #aors are combination of floodplains and beels which in monsoon season !o under water and in dry months are isolated as the floodplains dry up. #uman society derives aesthetic en3oyment, inspiration and a feelin! of relaation from their scenic beauty. Archaeolo!ical findin!s confirm that many of the earliest human settlements such as those of the esolithic period were dependent on wetlands for food, water, clothin! and shelter. he civiliBation in Asia and the *ar East developed in floodplain environment. he ma3or river systems of the world have supported the development of rich and sophisticated civiliBations, and many diverse societies have evolved effective systems for derivin! benefits from the rich natural productivity of the wetlands. he rich biodiversity, which these lands support, is of particular international si!nificance. One noteworthy eample of !reat important to human society is the deep water rice that has evolved in the Ganges- Brahmaputra river basins, containin! !enes which enable these paddy plants to rise above flood waters providin! even under severe flooded conditions $ishat et al. 1&&'(.

2.2 Classification of wetlands ost wetland soils are classified as either A6uents or A6uepts or as #istosols where the decomposition of or!anic matter is retarded because of pera6uic conditions. +n a sense, they are totally immature or only wealy developed as soils and have poorly epressed  profile morpholo!y. A classification of wetland is !iven belowC Classification of wetlands (Nishat et al. 1993) 1. alt water 1.1. !arine

1.2. #stuarine

1. u"tidal

$i( :ermanent unve!etated shallow waters less than >m depth at low tide, includin! sea bays, straits.  $iii( ;oral reefs.

2. Intertidal

$i( ?ocy marine shores, includin! cliffs and rocy shores. $ii( +ntertidal mobile unve!etated mud, sand or salt flats, salt marshes and man!roves.

1. u"tidal

$i( Estuarine watersF permanent waters of  estuaries and estuarine systems of deltas.

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2. Intertidal

$i( +ntertidal mud, sand or salt flats, with limited ve!etation, marshes, man!rove swamp, snipa swamp.

1.3. La$oonal

$i( 5racish to saline la!oons with one or  more relatively narrow connections with the sea.

1.%. alt la&e

$i( :ermanent and seasonal, bracish, saline or alaline laes, flats and marshes.

2. 'reshwater 2.1. Riverine

erennial

$i( $ii(

:ermanent rivers and streams, includin! waterfalls. +nland deltas

e*porar+

$i(

2easonal and irre!ular rivers and streams, riverine floodplains, includin! river  flats, flooded river basins, seasonally flooded !rassland.

2.2. Lacustrine

er*anent

$i( $ii(

:ermanent freshwater laes. :ermanent freshwater ponds.

2.3. alustrine

easonal

$i(

2easonal freshwater laes. :ermanent freshwater marshes and swamps. 2easonal freshwater marshes on inor!anic soil, seasonally flooded meadows. :eatlands, includin! acidophilous, ombro!enous, or  soli!enous mires.

#*er$ent

$i(

$ii(

'orested

$i(

$ii( $iii( 3. !an,*ade -etlands 3.1. /uaculture0!ari culture 3.2. $riculture

$i( A6uaculture ponds, includin! fish  ponds and shrimp ponds. $i( $ii( $iii(

3.3. alt #ploitation

2hrub swamps, includin! shrub-dominated freshwater  marsh. *reshwater swamp forest. *orested peatlands.

:onds, includin! farm ponds. +rri!ated land and irri!ation channels. 2easonally flooded arable land.

$i( 2alt pans and salines. --

$i(

3.%. r"an0Industrial

$ii(

Ecavations, includin! !ravel  pits, borrow pits and minin!  pools. )astewater treatment areas,

$i(

3.. -ater stora$e areas

$ii(

?eservoirs holdin! water for   irri!ation andGor human consumption. #ydro-dams.

2.3 -etlands in 4an$ladesh he wetland soils in 5an!ladesh can be !rouped into two broad classesC or!anic and mineral. he or!anic !roup $peats( consists of around 48000 ha. hese peats $#istosols( are distributed over 5an!ladesh in different depressions, of which the Hopal!an3-/hulna  basin areas have the lar!est areal etent. #emists, 2aprists, and *ibrists occur in 5an!ladesh. 2even soil series have been established for #istosols $2?+ 2taff, 1&>->(. ineral soils formin! under the wetland conditions are the most etensive in 5an!ladesh $2?+ 2taff, 1&>->(. ineral soils formin! under the wetland conditions are the most etensive in 5an!ladesh $2?+ 2taff, 1&>->(. Out of total of 8' soil series, around 81> have developed under a6uic moisture re!ime $able- "(

Of the soil orders +nceptisols occupy more than 0% of the total area. #ydra6uents are the deeply flooded soils $2aheed and #ussain, 1&&"(. #apla6uepts $Enda6uepts( are the most etensive wetland soils in 5an!ladesh. Aeric and ypic #apla6uepts are the most dominant wet sub!roups of 5an!ladesh, followed by ypic and Aeric *luva6uents. Around 14 soil series have been classified under the Aeric Alba6uept sub!roup where ferrolysis is the dominant pedo!enic process. Aeric #apla6uents and ypic :samma6uents also occur  in 5an!ladesh. ypic sulfa6uepts and 2ulfic #apla6uepts occur alon! the sea coasts near  ;oIs 5aBar and also in areas ad3oinin! the man!rove forest of the 2undarbans in the southwest. 2ome ;ambic Arenosols and Hleyic alisols in 5an!ladesh have also been occurrin! under a6uic moisture re!ime.

Table- 1: Possible wetland classification system based on application of  land type definitions easonalit+ :erennial wetland

2easonal wetland

Classification )0

Definition Area under water throu!hout year includin! dry

)1

season. Area flooded to depth of 1.m to 'm durin! ->-

)"

 pea floodin! Area flooded to depth of 0.&m to 1.m durin!

)'

 pea floodin! Area flooded up to depth of 0.&m durin! pea  floodin!

J2ourceC ishat et al. 1&&'K

Table- 2: Characterization of the wetland soil series of Bangladesh in the U.. oil Ta!onomy 5rder

6reat $roup

u"$roup

No. of   series

#ntisols

*luva6uents

ypic *luva6uents Aeric *luva6uents ollic *luva6uents 2ulfic *luva6uents hapto-#istic *luva6uents

'" " " " >

#apla6uents

ypic #apla6uents Aeric #apla6uents

 

#ydra6uents :samma6uents

#aplic hydra6uents ypic :samma6uents Aeric :samma6uents ypic 2ulfa6uents A6uic @difluvents A6uic @stipsamments

2ulfa6uents @difluvents @stipsamments

2ulfa6uepts @strochrepts

ypic Alba6uepts Aeric Alba6uepts A6uic ystrochrepts *luva6uentic ystrochrepts A6uic Eutrochrepts A6uic ystric Eutrochrepts ypic #apla6uepts Aeric #apla6uepts Aeric Dithic #apla6uepts #umic #apla6uepts 2ulfic #apla6uepts hapto-#istic #apla6uepts ;umulic #uma6uepts *luva6uentic #uma6uepts ypic 2ulfa6uepts A6uic @strochrepts

!ollisols

#apla6uolls

Aeric #apla6uolls

lfisols

Alba6ualfs

Aeric Alba6ulfs

Inceptisols

Alba6uepts ystrochrepts Eutrochrepts #apla6uepts

#uma6uepts

1  " 1 " 8

1 14 ' " 4 > 0 1>> 1 " > 8 " 1 " " 1 8

-4-

ltisols

#aplustults :alea6uults :aleustults

A6uic #aplustults Aeric :alea6uults Albic :aleustults A6uic :aleustults

7istosols 8

@ndifferentiated 2

@ndifferentiated 38

1 1 1 4 %18

J2ourceC *[email protected]E2;O, 1&K

Table- ": #etland soils of Bangladesh in relation to their Classification in the U$% oil Ta!onomy and the &%'-U()C' *egend D oil aono*+ 6reat $roups u"$roups *luva6uents ypic, Aeric 2ulfic, ollic

'5,N#C5 Le$end ;alcaric *luvisols Eutric *luvisols

;alcareous Alluvium  oncalcareous Alluvium

#apla6uents #ydra6uents :samma6uents 2ulfa6uents @stipsamments Alba6uepts

ypic, Aeric #aplic ypic, Aeric ypic A6uic ypic, Aeric

ystric *luvisols Eutric *luvisols ;alcaric *ulvisols hionic Hleysols ;ambic Arenosols Eutric :lanosols

 oncalcareous Alluvium  oncalcareous Alluvium ;alcareous Alluvium Acid 2ulphate 2oils ;alcareous Alluvium 2hallow Hray errace 2oils

#apla6uepts

Eutric Hleysols

#uma6uepts 2ulfa6uepts

ypic, Aeric #umic, 2ulfic ;umulic ypic

ollic Hleysols hionic Hleysols

 oncalcareous Hray *loodplain 2oils Acid 5asin ;lays Acid 2ulphate 2oils

#apla6uolls

Aeric

ollic Hleysols

Acid 5asin ;lays

#istosols

:eat

#istosols

6eneral oil +pe

J2ourceC *[email protected]E2;O, 1&K

2.% Distri"ution of wetland soils of the world he wetland soils of the world mae up about 10% of the worldIs land mass. he principal suborders of wetland soils and their distribution are !iven is able- 8. oorman $oorman, 1&4( reviewed the classification of rice soils in a recent paper includin! the classification of most wetland soils of the tropics. 5ecause climate is a ma3or factor in a!ricultural production the wetlands divided into two parts, such asC

a. on tropical wetland soils.  b. ropical wetland soils.

--

a. Non tropical wetland soils Dar!e areas of A6uepts and #istosols dominant landscapes in Alasa, ;anada, ?ussia, but these soils have little or no potential for food production. 2hort !rowin! seasons followed  by lon! periods when the !round is froBen mae it impractical to drain these soils and impossible to !row crops other than ve!etables on them.

Table- +: $istrib,tion of principal wetland soils of the world oil rea (ha 18) A6uent 44.4 A6uult 1. A6uept &8." Alboll 1. A6uod 4. #istosol 1"&. J2ourceC @2A, 1&4K

'raction of world land *ass (:) 0.> 0.8 4. 0.' 0.1 0.&

)etland soils occupy lar!e areas in the middle latitudes of the northern hemisphere. One of the lar!est areas is in the delta of the ississippi ?iver in the @nited 2tates. ost of the land in this area has been drained and is now producin! crops. #apla6uepts, Ochra6ualfs and @difluvents $5artelli, 1&48( are the dominant soilsF they are fertile, !enerally flat and variable in teture. #istosols and #ydra6uents are etensive in the southern part, where a lar!e percenta!e of the land remains in forest. a3or cultivated crops are rice cotton L soybean. he Atlantic and Hulf ;oastal plains are is the lar!est area of wetland soils in the @nited 2tates and is the area with the most potential cropland $5artelli, 1&48(.

b. Tropical Wetland Soils )etland soils are fairly etensive throu!hout the humid tropics. 2outh and 2outheast Asia have the hi!hest percenta!e, althou!h lar!e areas eist in 2outh America. Africa has a few lar!e areas, but they constitute only a small percenta!e of the landmass. Os born $Osborn, 1&'( represents one 9 fifth of the worldIs land is about one 9 third desert, and that all of  its irri!ated land maes up only 0.1% of the continent. )etland soils occupy a lar!er area than irri!ated land, but compares to the total the area is still 6uite small. here are, however, several lar!e areas, principally in central Africa, where wetlands are common. ropa6uepts and ropa6uents dominate both areas, althou!h soils with better natural

-&-

draina!e are intermin!led. hese soils vary in teture and chemical properties and have limited suitability for conversion to productive use. ropical 2outh America probably has more wetland with hi!h potential for development than any other continent. A hi!h percenta!e of its wetland soils lie in the AmaBon basin, which occupies approimately 80% of the continent $Osborn, 1&'(. ropa6uents and  plintha6uults are associated with Oisols and other @ltisols on the flood plain and terraces of the AmaBon. +n northern 2outh America, coastal areas in 7eneBuela, Huyana L 2urinam are dominated  by wetland soils. +n Huyana and 2urinam, most wetland soils are planted to su!arcane and other food crops, includin! rice. +n this area, lar!e epanses of 7ertisols are associated with ropa6uepts and :lintha6uulls. he ?upununi 2avanna in 5raBil and, Huyana is a re!ion typified by a lon! wet season and dry season. As a result, most soils are either  flooded or waterlo!!ed, or both, for many months. his re!ion, which occupies more than "400 /m" in Huyana alone $Eden, 1&40(. +n +ndia, west 5en!al has a lar!e concentration of Ochra6ualfs, #apla6uepts, and #apla6uents $urthy, 1&4(, ran!in! in teture from 2andy loam to clay and formed mostly in old alluvium. )etland soils in 2ri Dana are located mainly in inland valleys, althou!h some are on coastal plains $:anaboe, 1&4(. any of the inland valleys, where most of wetland soils  produce rice, are dominated by A6ualfs and A6uults. A6uepts and #emists are locally etensive on minor flood plains and of coastal plains. ost of these soils have low p#, low ;E;, and low base saturation. he ma3or wetland soils in alaysia are A6uepts and A6uents $:aramananthan, 1&4(. ost are formed in marine or alluvial sediments and are the least productive rice soils in the country. Dow p# in some areas and sulfate retard rice production. A6uepts dominate the wetland soils of +ndonesia $2oeprapthohard3o et al, 1&4(, some of  the lar!est areas bein! on the north coasts of Mava and on the east coast of 2umatra. 2ulfur  deficiency may be a problem in some of these rice soils. Other countries where wetland soils are important are the :hilippines, /ampuchea, Daos, 7ietnam and hailand $udal, 1&>8(.

2. Distri"ution of wetlands in 4an$ladesh

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L#6#ND



Wetland

'i$. 1; Distri"ution of wetlands in 4an$ladesh J2ourceC ;EH+2, "00'K

- 11 -

'i$. 2; !a<or wetlands of 4an$ladesh

J2ourceC )orld ?esources +nstitute, 1&&0K

- 1" -

Table- : eographical distrib,tion of wetlands and their areas in  

Bangladesh Location

Open water$inland (

+pes of wetlands

( in ha )

a. ?ivers

84&,4'

 b. Estuarine area

1,"

c. 5eels and haors

118,1>1

d. +nundable floodplains ;losed water

,8>,>0&

e. /aptai lae a. :onds

>,00 18>,&0

 b. 5aors

,8

c. 5racish water farms

10,000 otalC >,&>1,11

J2ourceC Ali . N. 1&&0K

Table- /: %rea of different types of wetlands in Bangladesh +pe :ermanent rivers and streams Estuaries and man!rove swamps 2hallow laes and marshes Dar!e water stora!e reservoirs 2mall tans and fish ponds 2hrimp ponds 2easonally-flooded floodplains J2ourceC Aonda, 1&&K

rea in thousand hectare 80 >10 1"0-"&0 &0 10-10 &0-11 ,440

2.8 oil processes in wetlands +??+ $1&( published some soil process mechanisms in wetland soils lie physical  processes $dynamics of water movementF !as echan!e and seasonal fluctuation of  !roundwaterF alternate wettin! and dryin! conditionF re!eneration of structureF formation

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of restrictive pans, surface crusts and clodsF !al!ai formationF tetural differentiation(, chemical processes $redo processesF mi!ration, transformation, se!re!ation of *e, n, Al and other micronutrients and macronutrientsF saliniBation, alaniBation carbonate accumulation, ferrolysisF p# chan!esF chelation and compleation( and different  biolo!ical processes $or!anic matter transformation and humus formationF decomposition and nutrient cyclin!F 5iolo!ical nitro!en fiation and immobiliBationF nitro!en losses throu!h volatiliBation and denitrification processesF rhiBosphere effect such as eudation, ion echan!e etc.(

2.= 6enesis and sta$es of soil for*ation under seasonall+ flooded  

condition

he soils in the wetland areas remain seasonally water saturated or permanently are in waterlo!!ed condition. 2easonally saturated soils are dry in some of the year if not irri!ated. he periods of water saturation vary from soil to soil dependin! on location in the landscape. he !round water table in these soils fluctuates very widely. he fluctuatin! !round water tables play important role in the !enesis of theses soils. he sta!es and  pedo!enic processes are varied and comple in the seasonally flooded soils. Hleyans is the name !iven to the shiny surfaces of soil cracs and pores formed by the deposition of material washed from the soil surface or the topsoil under seasonally flooded condition. hese coatin!s !enerally are continuous, thic and of a uniform !rey colour. he colour of the !leyans !enerally is that of the topsoilC mid!rey where the topsoil is mid!rey $when wet(F dar !rey where the topsoil is dar !rey. +n En!lish gley is “yellow and !rey mottlin! in the soil produced by partial oidation and reduction of iron caused by intermittent waterlo!!in!”. he definition in Herman, 2panish, :ortu!uese, +talian and utch lan!ua!es is essentially the same as above. *eatures of partial !leiBation are epressed by the presence of mottles, which are caused  by alternate wettin! and dryin! i.e. oidation and reduction conditions. he main morpholo!ical features of hydromorphic soils are dar coloured or!anic mineral horiBons in the surface soils, 5rown or !rayish brown 59 horiBon enriched in ses6uioide mottles, cloddy structure in the topsoil and absence of structure in the subsoil. 5rammer, 1&&> noted the sta!es of soil formation in the wetland soils of 5an!ladesh are !iven belowC a. +nitial deposition of alluvium  b. ?ipenin! - 18 -

c. Early Early devel developm opment ent of mott mottle less d. #om #omo!en o!eniB iBat atio ion n e. evelop evelopmen mentt of structu structure re in in the the subsoi subsoill f. *orm *ormati ation on of subsoi subsoill coati coatin!s n!s !. Acidifi Acidificati cation on and decal decalcif cificat ication ion of topso topsoils ils h. *err *erroly olysis sis,, if the the soil soil is is acidic acidic i.

*orm *ormat atio ion n of plo plou! u!hp hpan an

 3.

Oidation of subsoil

. *ormat *ormation ion of of peat peat $ speci speciall ally y in some some soils( soils( he most important horiBon in a hydromorphic soil is the !ley horiBon. horp and 2mith $1&8&( introduced the new name “!leys” as a !reat soil !roup in the soil classification system of the @nited 2tates. +t was defined as, “an intraBonal !roup of poorly drained #ydromorphic soil with dar coloured or!anic horiBon of moderate thicness underlain by mineral !ley horiBons”.

Accordin! to Moffe $1&8&( the popular ?ussian idea of !ley is “a more or less compact, sticy sticy loam loam or clay clay mater materia iall which which is not, not, howeve however, r, as sticy sticy as the the loam loam or clay clay,, fre6uently with more or less clearly pronounced li!ht !reenish blue tin!e”.

+n the 2oil 2urvey annual $2oil 2urvey 2taff, 2taff, 1&1(, a !ley horiBon has been defined as “a layer of intense reduction, characteriBed by the presence of ferrous iron and neutral !rey colour that commonly chan!e to brown upon eposure to the air”. he !leiBation process involves saturation of the soils with water for lon! periods in the presence of or!anic matter. +n En!lish !ley is “yellow and !rey mottlin! in the soil produced by partial oidation and reduction of iron caused by intermittent water lo!!in!”.

2oil 2urvey 2taff $1&4( reported that when reducin! condition prevails due to water  saturation for a lon! period of time, and the re!ime is defined as a6uic moisture re!ime. he a6uic soil moisture re!ime implies a reducin! re!ime that is virtually free of dissolved oy!en because the soil is saturated with !round water or by water of the capillary frin!e. udal udal and and oorm oormann ann $1&>8( $1&>8( term termed ed the the artif artific icial ial man-i man-indu nduced ced wate waterr re!im re!imee as “anthra6uic” and the superficial soil horiBon that formed under this water re!ime was called “anthra6uic epipedon”. Anthra6uic epipedon may comprise both the cultivated layer  and the underlyin! plou!hpan. 5oth the layers have !rey base colours and are stron!ly

- 1 -

iron stained alon! root channels. he cultivated layer becomes stron!ly reduced when water lo!!ed or flooded.

2mith 2mith $1&'( $1&'( stated stated that reduction reduction and !leyin! !leyin! processe processess that result from biolo!ical biolo!ical activity under anaerobic environments environments constitute only part of the properties properties dia!nostic for  soils soils with with a6uic a6uic moistur moisturee re!ime. re!ime. “2urface “2urface water water !ley” !ley” or “pseudo! “pseudo!ley ley”” or “invert “inverted ed !leys” are the principal principal morpholo!ical features of soils that develop under a6uic moisture moisture re!ime. /armanov $1&>>(, )ada and atsumeto $1&4'( and itsuchi $1&48( noted that  poorly drained low land soils do not chan!e much, when used as paddy land. land .

+n the waterlo!!ed soils of 5an!ladesh, there is commonly a stron!ly oidiBed layer and in  places a coatin! of iron oides, but no iron pan, at the base of the plou!hpan $5rammer, 1&41(.

5rin 5rinma man n $1&44 $1&44(( noted noted that that surfac surfacee water water !ley !ley soils soils are etens etensive ively ly devel develope oped d on seasonally flooded landscapes. hey may be acid hydromorphic soils with albic horiBons and containin! less clay than the deeper horiBons, and with a seasonally seasonally fluctuatin! p# in the surface horiBon. he oldest of the #olocene floodplain landscapes landscapes in 5an!ladesh 5an!ladesh have soils in which only the upper 10 or 1 cm have less clay and contain some albic materials. materials. #e considered it premature to attempt a classification classification of paddy soils with an epression of  ferrolysis.

he he surf surface ace water water !ley !ley soils soils also also occur occur on many many other other floodp floodpla lain inss in 5an!l 5an!lade adesh sh $5rammer and 5rinman, 1&44(. he ista, the old 5rahmaputra and the northeastern part of the e!hna river floodplains as well as the old e!hna estuarine floodplains contain soils in which the surface horiBon has an anomalously low clay content and seasonally fluctuatin! p#. 5rammer and 5rinman $1&44( correlated surface water !ley soils in 5an!ladesh with the hydromorphic hydromorphic soils developed on the floodplain landforms occurrin! occurrin! widely in south east Asia $e.!. 7ander /evie, 1&4"(, the de!raded rice soils of 5urma $/armanov, 1&>(F the “a6uariBems” of Mapan $/yuma and /awa!uchi, 1&>>(, and the “anthrasols” $udal and oorman oorman,, 1&>8( 1&>8( that that form in areas areas lon! used for seasonal seasonal wetland wetland rice cultiva cultivation tion.. #ydromorphism is the common soil formin! process in all these soils.

- 1> -

#assan #assan $1&8( $1&8( studied studied the soil formatio formation n in the floodplain floodplain areas areas of 5an!lad 5an!ladesh esh and observed that the soil formation in this re!ion taes place in several sta!es. +nitially, the sediments sediments have low bul density and hi!h water content. +n the ripenin! sta!e moisture moisture is lost irreversibly resultin! in an increase in bul density. 2ubse6uently, the sediments  become homo!eniBed due to bioturbations. At this sta!e the formation of soil structure  be!ins due to alternate seasonal shrinin! and swellin! caused by wettin! and dryin! in the wet and dry seasons, respectively respectively.. 2oils of this re!ion possess either A-; type profile, or locally an A-$5(-; type profile. 5iotic factors, dependin! on the duration of dry and wet  periods, contribute to the soil structure formation. Effects of other soil formin! factors  become diffused due to hi!h !round water table and 3ubenility of these soils. +t is interestin! to note that in most cases, the attributes of the parent materials dominate the soil properties.

Accordin! to 5lume $1&(, in a typical pseudo!ley the a!!re!ate surfaces of the clayey 5 horiBon are bleached and depleted of *eGn oide, whereas the pores are enriched with  brown to oran!e *e and blacish n oides. he matri of the less clayey andGor less dense topsoil, however, is !rey and *e and n are concentrated in concretions of different siBes. hus the distribution pattern of *eGn oides is internally oriented a!ainst the ped and the soils surface.

2aheed and #ussain $1&&"( reported that in many floodplain soils influence of an a6uic soil moisture re!ime were imposed in the upper part of the profiles, while the lower  horiBons reflect that of the free draina!e.

Ali $1&&8( noted that an anthra6uic epipedon forms in the floodplain soils of 5an!ladesh under an imposed a6uic moisture re!ime havin! rice cultivation for a lon! time. 2easonally flooded soils of 5an!ladesh show special features such as coatin!s $!leyans(, ferrolysed layers and anthra6uic horiBons which have not been reco!niBed in the @2A 2oil aonomy $2oil 2urvey 2taff, 1&4(. 2o, the classification of these soils is tentative and sub3ect to chan!e as new information becomes available.

+n the !eneral sol type system of classification in 5an!ladesh the oncalcareous wetland soil soilss are are clas classi sifi fied ed into into nine nine !ene !enera rall soil soil type typess ableble- 10. 10. he he tabl tablee show showss that that noncalcareous !rey floodplain soils occupied the hi!hest proportion and occupied around

- 14 -

'" percent. oncalcareous ar !rey floodplain soils covered 11 percent. A ma3or part of  these two soils are seasonally flooded.

Table- 0: aor soil gro,ps in the non calcareo,s wetland areas of  Bangladesh 6eneral soil t+pe*

No. of soil series

rea (ha)

roportion (:)

 on calcareous alluvium

>

>","8"

'.&

 on calcareous !rey floodplain soils

104

','4,1'

"'.8

 on calcareous dar !rey floodplain soils

8

1,&&,>8

11.0

 on calcareous 5rown floodplain soils Acid 5asin ;lays Acid 2ulfate 2oils Hrey 7alley soils

""

'','1"

".>

1>

'8,&&8

".8

11

"">,>84

1.>

10

118,"4

1.

:eat



1'0,00

0.&

 oil Classification* * ypic *luva6uent

ypic #apla6uept, Aeric #apla6uept Aeric Endoa6uepts, ypic #apla6uept Aeric Endoa6uepts, @dic @stochrept ypic #apla6uept 2ulfic #apla6uept A6uic ystrudepts

ypic #aplohemists 5lac erai & ',808 0.> Aeric soils Endoa6uepts  oteC * 5rammer, 1&&>F ** @2 2oil aonomy 2ub!roup J2ourceC *[email protected]: $1&(K he wetland soils are mainly classified as A6uepts because of the occurrence of !leyed coatin! on ped faces or dominant !rey colours in the subsurface layers. ost of these soils fall in the typic or aeric sub!roups dependin! on the de!ree of oidation or reduction. All the floodplain soils have !rey matri colours $chroma "( and mottles. any of these soils have dar-!rey coloured topsoils and their subsoil coatin!s are also dar-!rey coloured. Or!anic matter content are not hi!h but dar humus stainin! was developed under natural ve!etation. 2oils on the old e!hna estuarine floodplain and most basin soils on the old 5rahmaputra floodplain are classified as oncalcareous ar Hrey *loodplain 2oils. - 1 -

2.> Characteristics of wetland soils; 2.>.1 !orpholo$ical characteristics and properties C )etland soils cover a relatively important area of the worldPs land mass and may be found in practically every climatic Bone. hey may point to the presence of a hi!h !roundwater  table or to an impermeable layer close to the surface, or they may result from natural or  artificial floodin! of the soil durin! part of the year. )etland soils are characteriBed by hydromorphic features $halomorphic, !ypsimorphic, calcimorphic or redoimorphic ones, dependin! on the volume of the catchment area( whose arran!ement corresponds to differences in redo or water potentials in space and to their chan!es in time. #ydromorphic features often coincide with but are not identical to redoimorphic features $e.!. iron Q sulfides, iron R oides. )etland soils may be submer!ed soils or floodwater soils or !round-water soils or surface- water soils. he best micromorpholo!ical indicator of hydromorphism is the presence of typic ses6uioidic features. an!anese se!re!ation $mainly coatin!s and hypocoatin!s( dominate in sli!htly hydromorphic materials. )ith increasin! hydromorphism, iron hydroide se!re!ations appear in the !roundmass and low chromas in the peds. 2awy and sade $1&&( studied morpholo!ical properties of some poorly drained soils from the ile delta. hey found that the soils had lar!e void structures, such as compound  pacin!, vu!hs and channels and preserved illuviation ar!illans and ferriar!illans. he translocation of clay was found to be a very active process at the be!innin! of profile development. 2mith and 5eecroft $1&'( from the study of the morpholo!y and water re!imes at three recent alluvial soils of ew Sealand found that with increased duration of saturation, mottles tend to decrease in siBe and abundance and have more diffused boundaries. he matri colors of the soil horiBon, in con3unction with the nature of the mottles, broadly reflect the different moisture re!imes at the three sites althou!h the distinction between imperfectly and poorly drained soils was not clear. as $1&44( reported that the soils of 5rahmaputra valley are formed both old and new alluvium of the river 5rahmaputra and its tributaries. he materials were of mied ori!in.

- 1& -

he soils of the old alluvium were in two different relief environments, namely, upland with !ood draina!e and lowlands with nearly hydromorphic conditions sub3ect to submer!ence. he soils are acidic which mi!ht be due to the nature of the alluvium itself. hese soils showed si!ns of release of iron under !leyin! conditions.

2.>.2 h+sical properties; :hysical properties of soils do not chan!e their pattern easily in comparison to the morpholo!ical and chemical properties. he soil physical properties thus impart stable and most useful contribution in soil classification purposes and in the dia!nosis, mana!ement and improvement of cultivated soils.

oil colour Amon! the conspicuous features of soil, colour is the most important and is hi!hly useful for its identification and characteriBation. 2oil scientists commonly use !rey colours $;hroma  "( as an indicator of seasonally or permanently saturated and reduced soil conditions. he colour of the topsoils of Acid basin clays is !rey to dar !rey, and has numerous  brown and yellow mottles alon! root channels $#ussain, 1&&"(. 5ecause of plou!hin! the topsoil is sometimes compacted. hese soils developed lar!e poly!onal blocs when dry. 2oils of the haor areas of 2ylhet and ymensin!h district, Arial beel and ;omilla basin have heavy tetured soil. he subsoil is !rey to dar !rey heavy clay and has stron! yellow to red mottles $#ussain, 1&&"(. he a!ricultural potential of these soils is limited  by the moderately deep to very deep seasonal floodin!. 2?+ 2taff $1&>->( noted that overall soil colour ran!ed from olive to olive brown on rid!es and !rey to very dar !rey in inter rid!e depressions and basins. 2eh!al et al. $1&>( studied the soils of the 2utle3 floodplain area and found that these soils were li!ht !rey to li!ht yellowish !rey even when the soils were mostly poorly drained. 5rammer $1&41( noted that the tetures of soils are nown to affect the bri!htness of  colour in some soils of 5an!ladesh. @sually the li!ht tetured soils tend to have li!hter  colours and the heavy tetured soils tend to have darer colours. he reduction and se!re!ation of iron in the soil, however, had been intense enou!h to produce horiBons

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dominated by !rey or olive !rey colours with chroma of " or less. +n the heavy tetured soils, or!anic matter mi!ht have a role in producin! dar !rey colour. 2in!h et al. $1&&( found variation in soil color in some imperfectly drained soils which were attributed to different characteristics of the parent materials. :oorly drained soils have hue of ".N with a chroma of less than ". icromorpholo!ically, medium to coarse structure in ar!illic horiBons reflected varyin! de!ree of plasma se!re!ation and accumulation. aniels et al. $1&4'( have indicated that reducin! conditions result in !rayish colour in  poorly drained soils and oidiBin! conditions are responsible for the bri!hter colours in  better drained soils. A study of seasonal fluctuations of water table in soils have shown that soil colours can be used as a !eneral indicator of saturated and reduced conditions, as well as movement of !round water table $acintosh and #ust, 1&4F Sobec and ?itche, 1&8F :icerin! and 7eneman, 1&8F Evans and *ranBmeir, 1&>(. 5uol et al. $1&4'( stated that since colours are !ood indicators of soil behaviour, and the environment in which they form, they may be helpful in arrivin! at conclusions concernin! their best uses and mana!ement. 2?+ 2taff $1&48( surveyed the soils of the 5rahmaputra floodplain area and noted that soils formed in the seasonally flooded old 5rahmaputra floodplain have surface soil colours ran!in! from olive to !rey and olive !rey in rid!es and !rey to dar !rey in lower  slope of rid!es and basins. 2ubsoil colour ran!es from !rey to dar !rey in rid!es and !rey to mied dar !rey in basins. @sually in youn! soils colour is an indication of parent materials while in freely drained mature soils, it is an indication of climate. Henerally low colour development e6uivalent in the floodplain soils is an interestin! feature $#ussain et. al. 1&1(. his is due to their poor  draina!e conditions and annual floodin!. urin! floodin! there is a net loss of iron from these soils which helps in developin! a !rey to yellowish !rey hue. HleiBation is thus a !eneral soil formin! process in these soils $#ussain and a3umder, 1&&"(. ;oventry and )illiams $1&8( studied the 6uantitative relationships between morpholo!y and current soil hydrolo!y in some +nceptisols in Australia and observed a stron! - "1 -

relationship between the soil colour and the current !round water table. hey also found that the !rey colours occurred when there was saturation of at least five for at least "1 wees. 2harma and ev $1&( studied different !eomorphic surface in the riverine plain of the :un3ab and found that the soils showed wide variation in hues ran!in! from 4. N? to  N dependin! on their physio!raphic location. 2oils located in the lower terrains showed !rey colours $hue N( with low chromas su!!estin! poor draina!e conditions and a fluctuatin! !round water table. 2in!h et al. $1&&( found variations in soil colour which were attributed to differential characteristics of the parent materials. On the basis of morpholo!ical characteristics they concluded that the poorly drained floodplain soils have hues !reyer than 10 N?, value -> and chroma less than "F whereas moderately to well drained soils have redder hues and hi!her chromas. Ousami and ?ust $1&&"( the hydromorphic soils from some inland depressions, alluvial  plains and coastal sediments. A 10N? hue was observed in addition to other typical morpholo!ical features of hydromorphic soils. ?edder hues within a 10N? matri colour  indicated an iron accumulation Bone which reflected the aerobic or anaerobic fluctuation Bones. 2Bo!i and #udnall $1&&"( emphasiBed that in studyin! the seasonally wet soils the terms “episaturation” and “endosaturation” must be differentiated because the different nature and duration of perched and !round water tables. he endosaturation conditions are related to the occurrence of horiBons with oidiBin! conditions above reduced horiBons. +n saturated Bones of soils that have true water tables, the redo potentials are low,  particularly if the water table is not very mobile.

/han $1&&( studied some benchmar soils from the seasonally flooded recent floodplains of 5an!ladesh and observed that the top soil colours !enerally ran!ed from !rey to dar  !rey while the sub soil colours ran!ed from olive !rey to !rey.

aBumder $1&&>( and Ali $1&&8( studied some soil series developed on the 5rahmaputra alluvium and found that topsoil colour ran!ed from !rey to dar !rey to dar !rey while the subsoil colour is olive is olive to !rey with abundant mottles.

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Concretions and *ottlin$ ;harrabarti et al. $1&8( eamined the morpholo!ical features of five profiles of alluvial soils from 5rahmaputra and 2urma valleys of Assam and found that upland leveled soils were devoid of mottlin!s and concretions and were moderately developed. 2oils affected  by hi!h water table resulted in the formation of iron mottlin!s and were wealy developed. :rofiles of 5rahmaputra valley indicated the development of a wea ar!illic horiBon, and the 2urma valley soils, which remained submer!ed for most part of the year, did not have iron concretions.

+n the floodplain soils of 5an!ladesh, mottles are the most common redoimorphic feature. hey are the reliable indicators of a6uic moisture re!ime $2aheed and #ussain, 1&&"(.they can be formed by both epia6uic and endoa6uic mechanisms in these soils. 2idhu et al. $1&4( have reported the movement of reduced *e and n by mass flow and diffusion durin! the rainy months, and their precipitation after the rainy season, when conditions are favourable for oidation, to be the possible sta!es in the alluvium in the !enesis of *e-n concretions and mottles in the soils developed on seasonally flooded alluvium in the :un3ab.

*rom the study of the morpholo!y and water re!imes of three recent seasonally flooded soils developed on a floodplain in ew Sealand, 2mith and 5eecroft $1&'( found that with increased duration of saturation, mottles tend to decrease in siBe and abundance and have more diffuse boundaries. he matri colours of the soil horiBons, in con3unctions with the nature of the mottles, broadly reflect the different moisture re!imes at the three sites althou!h the distinction between imperfectly and poorly drained soils was not clear.

Coatin$s A coatin! is an important property in the seasonally flooded soils in the floodplain areas. 5rammer $1&41( called these as flood coatin!s that has shiny surface is formed by deposition of material washed from the soil surface or the top soil under seasonally flooded conditions. hese coatin!s are typically continuous, thic and of a !rey colour. 5rammer $1&41(, further reported that the colours of the coatin!s were same as that of the top soils, !rey where the top soil is !rey $moist(F dar !rey when the top soil is dar !rey. his indicates that the materials have been derived from the top soil and not from - "' -

suspended materials in the flood water. +t also indicates that the flood coatin!s are not  pressure coatin!s. ;oatin!s of the lowland soils may develop in soils under cultivation, forest and !rass land, and on floodplain as well as terrace landF the common factor in their  occurrence bein! seasonal floodin!. Accordin! to 7eneman et al, soil materials that are sub3ect only from time to time to short  period s of saturation shows little or no mobility of the iron. herefore the hi!h chroma of  the matri is preserved. an!anese is more readily reduced than iron and can be translocated to the ped surfaces, where it is precipitated as man!anese coatin!s and hypocoatin!s. 2oil materials saturated durin! several consecutive days show a clear  mobility of the iron present. Only the lar!est pores are filled most of the time with air, and the ped interior remains practically constantly wet and is the seat of reduction of iron and man!anese compounds which !ive rise to low chromas inside the peds. +n wetter  conditions coatin!s of iron oyhydrates are deposits on the walls of voids. an!anese is more readily reduced than iron and leached down the profile or may be present as blac  diffuse nodules. )hen the soil material remains completely wet durin! several months, much of the iron and man!anese is removed from the profile. +nside the peds low chromas are therefore observed. +ron and man!anese are deposited as coatin!s around voids. :article orientation in flood coatin!s has not been studied well in the seasonally flooded soils of 5an!ladesh. hey are 6uite etensive in the soils of the Han!es, e!hna and 5rahmaputra floodplains. 5rammer $1&41( proposed the name !leyans for these coatin!s since the coatin! materials are always !leyed and usually have a !rey colour $reduced(. 2?+ 2taff $1&40 and 1&4( studied the nature of flood coatin!s in the seasonally flooded soils developed on the floodplains of ymensin!h district by the old 5rahmaputra ?iver. +n these soils cracin! is common, flood coatin!s are enormously present.

oil eture 2oil teture is one of the most fundamental and permanent characteristics that has direct  bearin! on structure, porosity, adhesion, consistency and physico-chemical behavior of  soils. 2?+ 2taff $1&>->( worin! on the soils of ;omilla districts stated that the soils developed in the e!hna and 5rahmaputra floodplains almost everywhere showed a distributional pattern of friable silt loams to silty clay loams on the rid!es and clays in the

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 basins. 2ome clays in older floodplain areas were very heavy and craced widely when dry and flood coatin!s were also 6uite common in them. Henerally, the alluvia of most rivers passin! throu!h 5an!ladesh are predominantly silty. 5ut sediments of rivers show some distributional trends. 2andy materials usually occur  near active and abandoned river channels, and clayey materials occur in the basin sites. As one moves from the river bans towards the bac-swamps the teture of the soil materials !ets !radually finer. :eat may sometimes accumulate in the depressional sites, if it is  permanently wet. he ma3or river systems in 5an!ladesh are reported to have varied in their etent of sandy, silty and clayey deposits. he sediments of the north 5en!al rivers drainin! directly from the #imalayas are relatively coarse tetured and those of river  e!hna drainin! the central parts of 2ylhet basin are relatively fine tetured. +n !eneral, the proportion of fine tetured sediments increases from north to south across 5an!ladesh $*AO, 1&41(.

he teture of the substratum of Acid basin clays is usually silty and sometimes clayey and is permanently reduced $#ussain, 1&&"(. 5rammer $1&41( stated that silt loams and silty clay loams predominate on the old e!hna estuarine floodplain, whereas silty clays and clays occur etensively on the old 5rahmaputra floodplain. #e noted that loam was the dominant tetural class in 5an!ladesh soils followed by clay. #ussain and ;howdhury $1&0( reported the physical properties of a number of cracin! clay soils and observed that clay was the dominant fraction followed by sand and silt. he mean clay content of the soils was  percent. 2?+ staff $1&40( found that most rid!e soils in old 5rahmaputra floodplain are silt loam to silty clay loam and inter rid!e depressions they are mostly silty clay loam to silty clay. Ousami and ?ust $1&&"( pointed out that the soil teture varied 6uite widely with land types in their study of hydromorphic soils from inland depressions, alluvial plains and coastal sediments.

oil tructure

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he importance of soil structure in soil classification and soil productivity can hardly be overemphasiBed $2oil 2urvey 2taff, 1&4(. Alternate wettin! and dryin! situations play an important role in soil structure formation. )ettin! which leads to epansion and !elation and dryin! which leads to construction and de!elation are etremely important phenomena in structure formation, and hence, in profile differentiation with respect to one another and also with respect to structure development. )ettin! and dryin! and epansion and construction affect structure formation because they affect orientation of the clay particles with respect to the plant roots $5ear, 1&>(. he structure of the soils of acid basin clays is coarse prismatic to blocy. 2ome structural units have shinny pressure faces. he pressure faces are occasionally wed!e-shaped $#ussain, 1&&"(. 2?+ 2taff $1&4( found that the moderately well to imperfectly drained subsoils have wea to moderately stron! prismatic and blocy structure in the old 5rahmaputra floodplain area. he imperfectly to poorly drained soils have moderately stron! to very stron! prismatic structureF and the poorly to very poorly drained soils have stron!  prismatic and blocy structures. 5rammer $1&&>( stated that poly!ons provide the prismatic structure which is typical of  most loamy and clayey floodplain soils. ;lay material cracs horiBontally and usually develop both blocy and prismatic structure. :rismatic structure may be broen to an!ular   blocy or suban!ular blocy in less clayey materials. aBumder $1&&>( studied some 5rahmaputra floodplain soils land found that prismatic to an!ular blocy structure developed in the subsurface horiBons of the profiles whereas the surface soils were massive.

oil !oisture 2oil moisture retention is stron!ly related to the surface area per unit mass of the soil. +t is also related to the teture of the soil and the clay mineral types. as et al. $1&48( studied water retention characteristics of 1" alluvial soil profiles from )est 5en!al. 2oil varyin! in tetures from sandy loam to sandy clay loam showed increasin! trend of water holdin! capacity with depth $8".&-.4%( and the available water ran!ed from 4.1 to "'.' percent in Hheora and from 4.4 to 1>.0 percent in ehrauli  profile.

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2.>.3 Che*ical properties; 2ubmer!ence causes chan!es in the nutrient status of the surface soils. 2o the nutrient dynamics in wetland soils are in a complicated situation. here is not only a vertical and lateral redistribution of various nutrient species includin! or!anic matter but a chan!e in the forms of the individual nutrients as well.

oil Reaction (p7) 2oil reaction is the most important sin!le chemical characteristic which has a !reat influence on different physical, chemical and mineralo!ical property of the soils. 2uitability of soil as a medium for the plant !rowth and desirable micro-or!anisms depends upon whether the soil is acid, neutral or alaline and therefore this property play an important role in pedo!enesis and classification. +n most of the wetland soils of 5an!ladesh, p# value, in !eneral, is around 4.0 which  become alaline on dryin! when the soils are calcareous and the noncalcareous soils  become acidic. Han!etic alluvium, bein! calcareous and the noncalcareous, has hi!her p# when dry than other river alluvia. )ith depth, in almost all soils, there is an increase in p# $2aheed and #ussain, 1&&"(. Die or!anic matter, the total nitro!en contents in the mineral wetland soils ran!e from 0.0 to 0.1 percent. :onnamperuma $1&> and 1&4"( observed that when an aerobic soil was submer!ed, its  p# decreased durin! the first few days, reached a minimum, and then increased asymptotically to fairly stable value of >.4 to 4." a few wees later in a 1C1 soil water  suspension. #e reported that the overall effect of floodin! is an increase in p# of most acid mineral soils. he increase in p# of most acid mineral soils was due to the reduction of *e'T to *e"T and a decrease in p# of alaline soils which was due to ;O " accumulation. 2eh!al et al. $1&>( reported p# in some soils of the 2utle3 floodplain of :un3ab ran!es from 4.& to &.1. +t is possible that these soils were calcareous. u3ib $1&>&( and 5rammer  and 5rinman $1&44( concluded that the increase of p# with depth is a common feature in the seasonally flooded soils of 5an!ladesh. #ussain and 2windale $1&48( noted that the increase of p# with depth is a characteristic  property of the hydromorphic soils in #awaii.

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#ussain et al. $1&0( studied the properties and !enesis of some pedons from the ippera surface and observed that the soils were stron!ly acidic at the surface and the p# !radually increased with depth. he !radual increase of p# with depth was an important characteristic feature of all the floodplain soils in 5an!ladesh $5rammer, 1&41(. ;haraborty et al. $1&8( studied the morpholo!y and physico-chemical properties of  some alluvial soils of Assam and reported that the p# of the soils increased with profile depth. #ussain and ;howdhury $1&0( studied some soils from Han!es delta in 5an!ladesh and found that the reaction $p#( of the soils neutral to sli!htly alaline with a p# in the ran!e of >.4-.0. he p# values increased with increasin! depth. ?ahman et al. $1&&"( also reported similar feature in some calcareous Han!etic alluvial soils. +n the noncalcareous soils this feature is even more re!ular $5rammer, 1&41(.

5r$anic !atter and C0N Ratio +n wetland soils or!anic matter is the substrate for anaerobic microbial activity that results in oy!en depletion and characteristic chan!e in redo potential, p#, and nutrient availability. 2oil or!anic ; accounts for 0.1-80% of wetland soils. ost mineral wetland soils of tropical Asia have only up to '% or!anic matter content is very low. ore than half of the soils have or!anic matter in the ran!e of 1 to "% $#u6 et al. 1&&'(. 2?+ $1&>->( analyBed a lar!e number of samples from many representative soil  profiles coverin! almost all the areas of 5an!ladesh and found that the or!anic matter  contents of soils were !enerally lowF ran!in! from 0.' to 1. percent in upland soils, 1. to ".0 in medium low land areas and ".0 to '. percent in the low land areas. +n beel areas, the or!anic matter content was about 8.0 percent $?ahman, 1&&0(. #ussain and ;howdhury $1&1( studied the pedochemistry of some cracin! clay soils in the basin areas of haa and ;omilla districts and observed that or!anic matter in the surface horiBon was 6uite hi!h and decreased with profile depth. Accordin! to the classification proposed by 5A?; $1&&(, the percenta!e of or!anic matter within the limit of 1.0-1.4 fell in the low ran!e. #u6 $1&&0( commented that most a!ricultural soils of 5an!ladesh have low or!anic matter content.

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u3ib $1&>( found 1.'4 percent or!anic matter in some soils of 5rahmaputra floodplain of 5an!ladesh. 2idhu et al. $1&&8( noted that the or!anic carbon content in some floodplain soils decreased irre!ularly with depth due to their fluvial nature. hese soils were Entisols. 2aheed and #ussain $1&&"( reported that both or!anic carbon and total nitro!en contents in the mineral wetland soils in 5an!ladesh were low.

2.>.% h+sico,che*ical properties; Cation #chan$e Capacit+ (C#C) ;ation echan!e phenomena are the most important properties in soils. ;ation echan!e  phenomena are considered as an inde of soil fertility as well as soil 6uality. +t plays an important role in the !enetic processes of soils. 2?+ 2taff $1&4( reported that ;E; of the top soil of most of the 5rahmaputra floodplain area havin! less than "% or!anic matter ran!ed from &-"'meG100! soil. he ;E; of  subsoils was usually sli!htly hi!her ran!in! from 10-"meG100! of soil. he values of  ;E; sli!htly increased with depth due to their increased clay content. he ;E; in the wetland surface soils of 5rahmanbaria district is "1."" cmol $p T( /!-1. ;hatter3ee and alal $1&4>( reported that the ;E; value of some soils from 5ihar and )est 5en!al decreased with depth from 8.1 to 10."meG100!. /arim and +slam $1&>( reported that the avera!e ;E; of clay and silt fractions of some soils and sediments of 5an!ladesh were "4 and 1" cmol $pT( /!-1 respectively. 2?+ staff $1&>&( reported an increase in ;E; values with the increase of clay contents in the 2ara and Hhior series.

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#chan$ea"le Cations )ri!ht et al. $1&( stated that the cations such as ;aTT, !TT, aT and / T are nown to be sensitive to leachin! durin! weatherin! and soil formation. +n well drained normal soils ;aTT  is the dominant cation. /anehiro and ;han! $1&>( noted that as the !leiBation  process pro!resses, the echan!eable ;aTTG!TT ratio tends to approach unity. +t has been reported that under the !leiBation process of soil formation, echan!eable !TT becomes the dominant cations in the echan!e comple $2unders, 1&&(. :onnamperuma $1&>8( reported that submer!ence of soil causes an increase in the concentration of ions in the soil solution, as indicated by the rise in specific conductance. +n a reduce soil, these ions are chiefly ;aTT, !TT, / T and aT which are not involved in the reduction process, the increase in their concentration is a secondary effect of  submer!ence and reduction. *errolysis is a process of soil de!radation of silicate minerals under alternate cycles of  oidation and reduction with removal of basic cations from the soil and eventually destroyin! the clay particles $5rinman, 1&40(. his process is dominant in the wetland soils of old floodplain areas of 5an!ladesh $/arim et. al. "001(.

#ussain and 2windale $1&48( studied the !rey hydromorphic soils of #awaii and reported that the avera!e echan!eable ;aTTG!TT  ratio was 1.. +slam and +slam $1&4'( studied some submer!ed soils of 5an!ladesh and found that the echan!eable ;aTT concentration first increased after submer!ence and then decreased. #e noted that the velocity and ma!nitude of increase of echan!eable ;aTT varied in different soils. +n all soils, the pea  values were obtained in the ninth wee of submer!ence. )alia and ;hamuah $1&&"( found that the echan!e comple of the flood affected soils of  5rahmaputra valley are dominantly saturated with ;aTT and !TT cations followed by aT and / T.

4ase aturation ercenta$e 5ycheno and /omarovaya $1&41( reported &0% base saturation in the floodplain soils of Afanasiev area of /irvo re!ion. +ncrease of base saturation with depth was reported by aBumder $1&4>( in some deep water rice soils of 5an!ladesh. Ali $1&&8( observed hi!h de!ree of saturation in some alluvial soils of 5rahmaputra and Han!etic floodplains.

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!acro,Nutrients #abibullah et al. $1&0( reported that the total / in the soils of the 5rahmaputra floodplain and in the Hrey errace soils ran!ed from 1.'& and "."& percent, respectively. 5rar and 2ehon $1&( studied a lar!e number of soils from the +ndus basin belt in the :un3ab and @ttar :radesh. hey studied reserve / levels in soils in relation to or!anic carbon, clay and teture. Accordin! to +slam et al. $1&( the total soil / in "& rice !rowin! soils from 5an!ladesh ran!ed from 1.08 to '.1" percent. #ussain et al. $1&&( indicated that available  showed a si!nificant positive correlation with or!anic matter and total  in some submer!ed soils of 5an!ladesh. 2?+ 2taff  $1&&1( studied soil series of e!hna floodplain and observed that the mean amount of  nitro!en is below the critical level $4 ppm(, the mean phosphorus content is medium $1'" ppm( and the mean potassium content is hi!h. #ussain et al. $1&&"( studied the properties of four pedons from 5hola district and observed that the available nitro!en ran!ed from 8" to & ppm, available phosphorus from > to 1" ppm and available potassium ran!ed from "00 to 8" ppm. he concentration of  available nitro!en, phosphorus and potassium were hi!her near the surface and decreased downward in the profile. +slam et al. $1&( indicated that soils of 5an!ladesh are rich in total / but 6uite poor in available /. hey further pointed out that the readily echan!eable potassium varied  between  and 1& ppm with an avera!e of ' ppm. Echan!eable potassium accounted for 0.'' to 0.> percent of total / and had si!nificant correlations with the clay contents and ;E; values of the soils. Elahi et al. $1&&'( studied / status of 1" etensively occurrin! a!ricultural soils from northern re!ion of 5an!ladesh and showed that total / "O content in soils ran!ed from 1.' to '.08 percent.

!icro nutrients he amounts of free oides in soils are very important in evaluatin! mineral weatherin! and pedo!enic chan!es in soils $cea!ue and ay, 1&>>F 5lume and 2chwertmann, 1&>&(. Orlov $1&&"( stated that the forms of iron and man!anese in soils and their vertical distribution in the profiles reflect the trend and peculiarity of the soil formation process. Uuantity of free *e"O' in soils is important in determinin! their !enesis. - '1 -

Arduino et al. $1&8, 1&>( indicated that the free *e"O'  G total *e"O'  ratio is a !ood criterion for indicatin! the relative a!e of soils and its development. hey noted that the  percenta!e of total iron $*et( etracted by dithionite $*ed( iron increased with increasin! a!e of the soils. Moffee $1&>0( stated that the surface enrichment of free iron oide was probably due to the fact that ferrous iron is oidiBed easily to form ferric oide at the surface, while in the sub soil ferrous oides does not chan!e. cea!ue $1&>( stated that the low free iron oide is neither due to the leachin! of iron nor to the accumulation of iron in mottles but presumably resultin! from reduction. 5rinman $1&40( reported that durin! the anaerobic phase of soils free iron is reduced with continuous oidation of or!anic matter and formation of hydroyl ions. he ferrous iron displaces other cations and the displaced cations are leached from the soils. #ussain et al. $1&&"( stated that the free iron oide content in the floodplain soils of  5an!ladesh was low due to loss of iron when reduced alon! with drainin! water thus main! the colour of the surface soil !rey or dar !rey. #e reported that at a depth of  around 80-0 cm in all the studied pedons an enrichment of free iron oide occurred, which was probably due to their fiation in the profiles in the form of mottles. his is very common feature in the floodplain soils !rowin! rice. Moffee $1&>0( noted that the movement and deposition of man!anese dioide and its distribution in the soil profiles were si!nificant criteria in pedo!enic study as it behaves more or less lie iron oide. +n !eneral man!anese oide is more easily soluble than iron oide. aniels et al. $1&>"( stated that, poor draina!e condition was probably the important factor  that caused the decrease in free iron and man!anese oides contents of the top soil. /arim $1&8( identified aluminium substituted !oethite in some seasonally flooded rice soils in 5an!ladesh.

2.>. !ineralo$ical properties; 5rammer $1&&>( reported that floodplain sediments of the 2urma and other eastern rivers contains low amount of feldspars and micas and their total content of easily-weatherable

- '" -

minerals usually is about 10 percent. #owever some rivers such as 2omeswari and atamuhuri brin! the deposits richer in amphiboles. eposits in the 2ylhet basin are also richer in amphiboles $"- percent of the heavy fraction( than most alluvium derived from the ertiary hill sediments. At the same time, they are richer in heavy minerals lie epidote $"0-80 percent( and Bircon than 5rahmaputra deposits. he clay mineralo!y of  floodplain sediments is also striin!ly different from that of hill sediments and the adhupur ;lay. eesta and 5rahmaputra river sediments and old e!hna deposits have a miture of aolinite, illite and chlorite. Noun! e!hna estuarine deposits have these same clay minerals but they also contain si!nificant amounts of smectite.

5rinman $1&44( wored with the surface water !ley soils in 5an!ladesh. #e noted that in the soils of the old 5rahmaputra sediments easily weatherable minerals comprise about '0%, a third of which was mica. *rom V-ray diffracto!raphic data he found that vermiculite account for about 8% of the clay fraction in the lowest horiBon and this was  pro!ressively replaced by soil chlorite, which increases to '0% in the surface horiBon. #e rou!hly estimated " % illite, "0% aolinite and 10-"0 % inter-stratified minerals in those soils. #assan and ?aBBa6 $1&1( and #ussain et al. $1&&( reports hi!h content of mica, aolinite and smectite in the clay fraction of soils formed on the Han!etic alluvium. he variation in the content of smectite with depth was reported to be insi!nificant which led them to conclude that this mineral was allo!enic in ori!in and the post-depositional chan!es are very small. *loodplain deposits of the 2urma-/usiyara and other small eastern rivers have characteristically low content of feldspars and micas. heir weatherable mineral content is reported to be around 10 percent $#ussain, 1&&"(. +n the floodplain soils of 5an!ladesh there is little evidence of any chan!e in clay mineralo!ical composition due to pedo!enesis, ecept in the topsoils of some older, noncalcareous soils where ferrolysis reactions appear to have destroyed some of the ori!inal clay minerals formin! a small amount of amorphous silica-alumina-iron mineral $5rammer, 1&&>(. ;lay synthesis possibly taes place in some poorly drained soils. 2mall 6uantity of  montmorillonite is reported to have been synthesiBed in some samples taen from a basin - '' -

clay on the 2urma-/usiyara as well as the Han!etic floodplains to!ether with aolinite and illite $5rammer, 1&&>(.

- '8 -

Table- 3: inerals in the sand and silt fractions and the weatherable mineral contents in some noncalcareo,s floodplain soils of Bangladesh oil racts

and

 t*

and !inerals $%( ica *eldspar UuartB

ilt

and !inerals $%( *eldspar Amphiboles ica

-eathera"le

;hlorite

+ **

$2oil 2eries(

%

2ylhet 5asin

10

18

18

1

"

1

'

1

8

">

1

"

% "

4



1"

"0

8

>

8&

"0

8

1

1"

--

"

'0

18



"'

8>

8

"

1

8

18

11

1

"&

$:ha!u( e!hna *loodplain $ebidwar( 5rahmaputra *loodplain $2onatala(

%

UuartB

*inerals

ource; #uBin!, 1&41F E!ashira, / and Nasmin, . $1&&0( and #ussain, . 2. $1&&(  t* =  on-transparent; +** = +nterstratified minerals

- ' -

/apoor et al. $1&"( studied the clay mineralo!ical composition of soils from four profiles developed on alluvium by suin! V-ray diffraction techni6ue and found dominance of illite followed by mied-layer minerals, chlorite, smectite, chloritiBed smectite and vermiculite. he illite present in the soils was found to consist of both the dioctahedral and trioctahedral varieties and the latter appeared to have under!one transformation to smectite-lie minerals throu!h intermediate sta!es of $10-18 A( interstratifications. :uri et al. $1&'( studied the silt and clay mineral composition in soil samples from nine different locations representin! five soil !roups of Han!etic alluvium. hey found that these soils were coarse to moderately fine tetured and moderately to poorly drained with a predominance of mica followed by chlorite, smectite and vermiculite. hey concluded that these minerals were relatively hi!h. 7inaya $1&8( investi!ated the clay mineralo!y of three typical saline-sodic soils if the +ndo-Han!etic alluvial plains by V-ray diffraction and chemical techni6ues. #e found that illite was the dominant clay mineral in all the soils. #e characteriBed the saline sodic soils  by the presence of smectite as a second dominant mineral. +t was, however, not detected in

/apoor et al. $1&"( studied the clay mineralo!ical composition of soils from four profiles developed on alluvium by suin! V-ray diffraction techni6ue and found dominance of illite followed by mied-layer minerals, chlorite, smectite, chloritiBed smectite and vermiculite. he illite present in the soils was found to consist of both the dioctahedral and trioctahedral varieties and the latter appeared to have under!one transformation to smectite-lie minerals throu!h intermediate sta!es of $10-18 A( interstratifications. :uri et al. $1&'( studied the silt and clay mineral composition in soil samples from nine different locations representin! five soil !roups of Han!etic alluvium. hey found that these soils were coarse to moderately fine tetured and moderately to poorly drained with a predominance of mica followed by chlorite, smectite and vermiculite. hey concluded that these minerals were relatively hi!h. 7inaya $1&8( investi!ated the clay mineralo!y of three typical saline-sodic soils if the +ndo-Han!etic alluvial plains by V-ray diffraction and chemical techni6ues. #e found that illite was the dominant clay mineral in all the soils. #e characteriBed the saline sodic soils  by the presence of smectite as a second dominant mineral. +t was, however, not detected in the associated cultivated soil. inor amounts of chlorite and aolinite were present in all cases. #e reported that imperfect draina!e mi!ht have resulted in the transformation of  illite to smectite. +llite, aolinite and chlorite in these soils were probably inherited. )hite $1&( studied the clay mineralo!y of some representative soils from the 5rahmaputra and the Han!es floodplains of 5an!ladesh. *rom the V-ray diffracto!raphic data he reported that amon! the 5rahmaputra floodplain soils an eclusive combination of  mica-aolinite vermiculite has been found in the youn!er member of the soils. #e stated that apparently most of these aolinite and vermiculite minerals are part of the ori!inal alluvial deposition, while chlorite and smectite are the products of in-situ weatherin!. he relatively older soils of the old 5rahmaputra floodplain, with a mild acidic environment in the pedons, have traces of chlorites, but not smectite. Ali $1&&8( studied the effects of alternate wettin! and dryin! cycles on pedo!enic  processes of some representative 5an!ladesh soils. #e stated that the Han!etic alluvial soils were found to contain clay minerals lie smectite, illite chlorite and aolinite. heir  contents varied with respect to soils and their mana!ement. +n 5rahmaputra alluvium soils, he observed that the dominant clay minerals were illite, chlorite and aolinite. - '> -

+n a study of some 5rahmaputra floodplain soils a3umder $1&&>(, observed that the dominant clay minerals were mica, aolinite, chlorite and a small amount of vermiculite. A small amount of smectite was also detected in the subsoils of 2onatala soil series.

3. -etland conditions and characteristics of 4an$ladesh 3.1 $ro,#colo$ical Re$ions (#R) he Dand ?esources Appraisal of 5an!ladesh $*AO 1&( classified the whole of the 5an!ladesh into '0 different a!ro-ecolo!ical re!ions in which depth and duration of  seasonal floodin! has been one of the component information layers. Amon! them "8 AESs have floodplain soils. istribution of various land types in different a!ro-ecolo!ical re!ions has been incorporated as an Anneure. )etlands occupy about 0% of the areas of  these a!ro-ecolo!ical re!ions and about 14% of the total areas of 5an!ladesh. #owever, these estimates eclude the water bodies lie rivers. *i!ure- ' indicates the various a!roecolo!ical re!ions where WwetlandI and Wwetland soilsI are present. he re!ions ', 10, 11, 14, "" and " also contain some medium to lowlands which at times of the year become wetlands. +t is interestin! to note that wetlands occur at contour lines as hi!h as 1 meters. his phenomenon is principally due to local hydrolo!y and !eomorpholo!ic formations.

3.2 6eo*orpholo$+? $eolo$+ and ph+sio$raph+ of wetland soils of  4an$ladesh ependin! on the land levels in relation to seasonal floodin! $depth of floodin! and duration of floodin!( si broad land types $able- 4( are reco!niBed in 5an!ladesh $*AO, 1&(. Of these land classes medium lowland throu!h bottomland are to be considered “wetlands” and “wetland soils”. hese lands have constraints of various de!rees so far as their uses are concerned. A !eneraliBed map of the inundation land types is shown in fi!ure 8. he area distribution of various land classes are shown in able- .

- '4 -

'i$. 3; $ro ecolo$ical re$ion in 4an$ladesh (4RC? 1999)

- ' -

Table- 4: *and Types in Bangladesh on the basis of 5n,ndation $epth Land Level #i!hland $#( edium #i!hland $#(

edium Dowland $D( Dowland $D(

+pe *0 *1

cale and duration of inundation Dand which is above normal flood level Dand which normally is flooded up to &0 cm deep

*"

durin! flood season Dand which normally is flooded up to 10 cm deep

*'

durin! flood season Dand which normally is flooded up to '00 cm deep durin! flood season. uration of floodin! is &

7ery Dowland $7D(

*8

months. Dand which normally is flooded deeper than '00 cm durin! flood season. uration of floodin! is X&

5ottomland $5(

*

months. epression sites in any land level class that remains wet throu!hout the year. hese constitute the  perennial wetlands.

J2ourceC *[email protected]:, 1&K

Table- 16: %rea distrib,tion of 7ario,s *and Classes Land Classes #i!hland edium hi!hland edium lowland Dowland 7ery lowland and bottomland 2ettlements and water bodies otal J2ourceC 2?+ 2taff $1&>->(K

rea (@*2) 8144 010> 14>0& 10&" 1&"1 "1>

: of total area "& ' 1"  1 1 100

- '& -

'i$. %; Inundation land t+pe *ap (4RC? 1999)

- 80 -

3.2.1 6eolo$+; here are three ma3or !eolo!ical formations in 5an!ladesh which are important to the contet of soils in !eneral and WwetlandsI and Wwetland soilsI in particular. hese areC ertiary hill sediments in the northern and eastern hills, the odhupur clay of the odhupur and 5arind tract in the center and west and recent alluvium in the floodplains and estuarine areas. Heolo!ically, the 5en!al basin is an active tectonic re!ion where some areas are believed to be under!oin! subsistence, thus causin! the formation of a few synclines $or!an and c+ntire, 1&&(. *lood water stands in synclines have !iven rise to many WwetlandsI in areas which are topo!raphically at hi!her elevations. hus, one can see the occurrence of wetlands in the inland valleys inside older land formations of terraces and hills $2aheed and #ussain, 1&&"(. @nconsolidated floodplain sediments occupy the !reater part of the country. he floodplains of the Han!es, the 5rahmaputra and the e!hna cover approimately 80% of  5an!ladesh $/han, 1&&1(. he floodplain sediments are far from homo!enous in a!e, teture and mineralo!y. hey have been deposited under piedmont, meander floodplain, estuaries and tidal conditions in different areas, new alluvium in still bein! deposited near  active river channels, but most floodplain land has apparently received little new alluvium for hundreds years of more. ?ivers have chan!ed their courses from time to time in the  past, abandonin! and re-occupyin! various parts of their floodplains and thus providin! sediments of different a!es in different areas. 2ome floodplains areas have also been uplifted in 2ylhet and ymensin!h areas, and there are numerous sand filled earth6uae fissures in part of these areas. ost floodplain sediments have hi!h silt content. his is particularly true in the case of  5rahmaputraGMamuna and e!hna sediments. ista floodplains and west of Han!es floodplains have sandy sediments in the sub-surface horiBons while most of the Han!es floodplains have clay deposits on the surface. :eat has accumulated in some permanent wet basins throu!hout the country. +n most areas they are at shallow depthF it can be up to m thic as in the Hopal!an3-/hulna peat basins.

3.2.2 6eo*orpholo$+; Each year ".8 billion tons of sediments are transported by the ma3or rivers to 5an!ladesh, havin! a profound effect on the !eomorpholo!y of the floodplains and the coastal plains. - 81 -

remendous amount of sediments is deposited on the floodplain areas which plays an important role in case of chan!in! its !eomorpholo!ical features. An understandin! of !eomorpholo!y is especially important in 5an!ladesh where differences between soils are partially related to their positions in the landscape. he country comprises hill, terrace and floodplain areas. +t may be classified into four distinct re!ionsC 1.

he eastern and northern frontier hilly re!ions comprisin! of the eastern hilly re!ions, hills of Dalmai and northeastern 2ylhet district and a narrow strip of a series of low hill ran!es and isolated circular and elon!ated hillocs represented by recent alluvium alon! the northern frontiers of the districts of 2ylhet and ymensin!h. $#ills(

". he Hreat able Dand $erraces( '. *loodplains of the Han!es, the 5rahmaputra and the e!hna river systems 8. he elta $?eef *loodplains( he floodplains of the Han!es, the 5rahmaputra and the e!hna cover approimately 0% of 5an!ladesh. umerous swamps have developed in the floodplains of the 5rahmaputra and the e!hna. he ;halan 5eel is the lar!est wetland of the area. he floodplains and the delta are studded all over with clusters of wetlands or swamps,  both bi! and small, commonly called haors or beels. hese freshwater swamps appear to  be tectonic in ori!in. hose of the districts of ?a3shahi and :abna and the elta seem to have formed due to chan!in! stream courses at short intervals and rapid buildin! up of  hi!h levees by the streams. he swamps have also developed in many of the valleys of the hilly re!ions due mainly to poor draina!e.

3.2.3 h+sio$raph+ and edi*entation; he term physio!raphy includes combination of the !eolo!ical material in which  particular inds of soil have formed and the landscape on which they occur. hirty four   physio!raphic units and subunits are reco!niBed in 5an!ladesh $*AO, 1&(.

- 8" -

he main wetlands and their physio!raphic units are as followsC . Lower trai 4asin 4. Lower unar"ha"a 'loodplain C. 6opal$an<,@hulna 4eels D. rial 4eel #. ur*a,@usi+ara 'loodplain;

he meander floodplains of the rivers flowin! into the upper e!hna catchment area are included in this unit. he rivers include the 2urma, /usiyara, anu, halat and /howai as well as smaller rivers flowin! from 2hillon! plateau on the northern side. All these rivers ori!inate in hill areas in +ndia. hese rivers pour into a vast low-lyin! area, the 2ylhet  basin. his basin seems constantly of have been sinin! due to earth movements. he lowest parts, even in the north ad3oinin! the +ndian border and '00 m from the coast, are less than  meters above 2D $ishat et al. 1&&'(. 2easonal floodin! is very deep in this sub-unit. he alluvial sediments deposited in this sub-unit are predominantly silts and clays. erived from tertiary hill sediments, the alluvium has a much lower content of  weatherable minerals. espite the sudden floods that occur, brin!in! with them vast 6uantities of sediments, the main river channels appear to be much more stable in their  courses than 5rahmaputra and Han!es channels probably because the eastern rivers carry little sand by the time they reach this area and because silt and clay floodplain sediments are themselves denser than the less consolidated, mied-tetured sediments of the Han!es and the 5rahmaputra floodplains. 2ylhet 5asin mainly comprises etensive, low-lyin!  basins $the haors( bordered by relatively narrow, hi!h rid!es. he relief is locally irre!ular  due to erratic deposition of new sediments. ;lay soils predominate, and peat occurs locally. 2easonal floodin! is mainly deep, more than  meters in the basin centres. )ater  6uicly drains from the floodplain rid!es after the rainy season, but lar!e areas in the  basins remain wet or submer!ed for most or all of the dry season. '. 'loodplains;

he floodplains contain noncalcareous recent alluvial sediments rich in weatherable minerals with illite as the dominant clay mineral. he eception is the Han!es alluvium which is calcareous at youn!er sta!e and montmorillonite forms an important part of its clay fraction. On lower sites, most of the soils are seasonally flooded, poorly to imperfectly drain with loams and clays as sediments. *looded topsoils are near-neutral upon dryin!. hey become acidic in non-calcareous soils and alaline in calcareous soils. - 8' -

he floodplain soils have formed in river and piedmont alluvium ran!in! from very recent to several thousand years old. etually, these soils are silt loams or sandy loams on intermediate sites to silty clays or clays in basins. *loodin! with silty water occurs in lands close to river channels, hill foot areas and on unembaned parts of tidal and youn! estuarine floodplains. *loodin! depth varies with physio!raphy, bein! deepest in basins.

Table-11: $istrib,tion of wetland soils in 7ario,s physiographic locations8 drainage and hydrology h+sio$raph+0Landfor*

#illy areas #ills 7alleys

: of  Draina$e total land area 1" 11 )ell to ecessive 1 :oor to imperfect

errace areas issected erraces erraces 7alleys Devel terrace areas erraces

 ' " 1  8.

7alleys *loodplain areas :iedmont alluvial :lains andGor meander  ?iver floodplain Devees

0. 0

:oor 

" 1'

5asinGepressions

1

:oor to imperfect, Docally moderately well ainly poor, locally very poor

eander floodplains Devees

7+drolo$+

 on-flooded +ntermittent 2easonal shallow

+mperfect to well :oor 

ainly nonflooded 2easonal shallow to deep

:oor to imperfect

+ntermittent to seasonal 2hallow 2easonal shallow

+ntermittent to seasonal shallow seasonal shallow moderately deep

to

riversG "> &

5asinsGepressions

14

idalGestuarine *loodplains Dow levees 2hallow basins

"0 > 18

eep basins

>

ainly poor 

seasonal shallow to moderately deep ainly poor locally seasonal moderately deep to very poor  deep

:oor  ainly poor  Docally very poor  :oor to very poor 

2easonal shallow $tidal( 2easonal shallow moderately deep $tidal( 2easonal deep to very eep

J2ourceC ishat et al. 1&&'K

- 88 -

to

3.3 I*portance of wetlands for 4an$ladesh )etlands in 5an!ladesh have !reat ecolo!ical, ecolo!ical, economic, commercial and socio-economic importance and values. hey contain very rich components of biodiversity lie flora and fauna of important local, national and re!ional si!nificance. he principal functions of wetlands areC Hround water rechar!e, !round water dischar!e, stora!e of flood water, shoreline stabiliBation and reduction of erosion, sediment trappin!, nutrient retentionGremoval, support for food chains, fisheries production, habitat for  wildlife, recreation, natural herita!e values, biomass production, water  transport, bio-diversity preservation and micro-climate stabiliBation $+)?5( 1&&", u!an 1&&0(. )et lands in 5an!ladesh are a very rich depository of ve!etations, a6uatic plants, reeds and al!ae. he floral composition is relatively uniform throu!hout the haors, 3heels, beels, and boars but the dominance varies seasonally. )etland soils have distinctive advanta!es and disadvanta!es for food production. +n addition to their ample water supply, they are usually level and often occur in lar!e land units, main! lar!e 9 scale farmin! feasible. Other advanta!es include low erosion disadvanta!es include cost of development L difficulty of mana!ement. 2ome wetland soils have special problems such as salinity, hi!h  a-content, low p#, or poor physical properties followin! draina!e. )etlands are essential  breadin!, rearin!, and feedin! !rounds for many species of fish L wildlife. hey are also important for producin! food for humans and domestic animals. +nternational reco!nition of these some times conflictin! values have led to an ever increasin! need to classify and characteriBe wetland soils in relation to food production. )etlands are nationally important for a variety of reasonsC  Biodiversity he lar!e and varied wetland environment is rich in species diversity. Of more than ,000 species of flowerin! plants and 1,00 species of vertebrates, of which approimately 40 are birds and over 00 are coastal, estuarine and freshwater fish, some 800 vertebrate species and between "00 and '00 plant species are 3ud!ed to be dependent on wetlands for  all or part of their life spans. )etlands provide habitat for a rich variety of resident and mi!ratory waterfowls, a number of endan!ered species of international interest, and a lar!e number of species of commercial importance. - 8 -

 !ish he inland capture fishery is the important subsector in terms of total catch, source of  employment and supply of animal protein. +t is based on the countryIs vast freshwater  resources and some "40 species of fin and shellfish which inhabit them. Essential habitats for the inland fisheries comprise open and closed water habitats, includin! rivers, canals, floodplains, haors, beels, baors and small roadside depressions. Althou!h discrete in the dry season, these water bodies become interconnected durin! the monsoon and provide critical habitats for completion of the life cycles of a lar!e number of fish species.  Agri"ultural diversity here are many local varieties of rice, conservatively estimated to number in the thousands, as well as other eistin! or potential commercially-important plants, which  provide a valuable !ene pool to ensure continued development of improved varieties for  the future. All wetlands are sub3ect to sedimentation composed of clay soils rich in or!anic matter, and the vast flooded areas of wetland are covered by crops which can tolerate waterlo!!in! and inundation. 5efore the introduction of mechaniBed dry- season irri!ation in the sities, deepwater rice and the broadcast aman rice $floatin! rice( used to be the ma3or crop in the wetlands durin! the rains. his crop was sometimes mied with short duration Aus rice to be harvested in Mune allowin! broadcast Aman to !row till ovember. *i!.  shows a typical croppin! pattern alon! with the time and duration of occurrence of  floods and need for irri!ation water.

'i$. ; Relation of crops with flood and irri$ation (Nishat et. al.1993)

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#ourism +t remains an infant if not non-eistent economic activity, but there is substantial foundation for the view that the countryIs natural resources, especially the 2undarbans, could support the development of this sector. $ther e"onomi" a"tivities he countryIs wetland resources support a si!nificant ran!e of economic activities other  than fishin!, such as etraction of reed and other plant products, harvestin! of a6uatic ve!etation, herbs, etc.

3.% De$radation of wetland soils 2ince independence in ecember, 1&41 there has been an accelerated epansion of   physical infrastructure in the floodplains and hoar areas. +n recent years, decentraliBation of administration at the upaBila level also led to a rapid epansion of roads and feeder  roads evenin! the rural areas of the hoar basins. hese infrastructures were often done without proper plannin! or due re!ard to natural water flows. hese poorly planted roads and draina!e structure created water lo!!in! and also had serious impact on the water  re!imes in the flood plains. he de!radation of wetlands in 5an!ladesh was mainly due toC+ncreased of population and epansion of human habitatsF epansion of a!riculture and subse6uent conversion of wetlands throu!h draina!e into rice fieldsF flood control and irri!ation pro3ects for enhancement of a!ricultural productivityF national, local and rural infrastructures lie ill-planned roads, narrow culverts etc.F over-fellin! of wetland treesF over-!raBin! by livestocF over-fishin! and associated disturbancesF siltation due to de!radation of the watershed areas which are often transboundary in natureF indiscriminate controlG re!ulationG use of waterflows of main river systems in the upper riparianF and  pollution of water due to industrial, urban, a!rochemical and other types of pollutants includin! pollution from transboundary sources. e!radation of the wetlands in 5an!ladesh has created the followin! impactC $a( 2erious reduction in fish habitat, fish population and diversityF $b( Etinction and reduction of wildlife includin! birds and reptilesF

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$c( Etinction of many indi!enous varieties of rice with the propa!ation of hi!h yieldin! varieties. $d( Doss of many indi!enous a6uatic plants, weeds and shrubsF $e( Doss of natural soil nutrients and loss of natural reservoirF $f( +ncrease in the recurrence of flashfloodsF $!( eterioration of livin! condition.

3. trate$ies and plan for "etter use of wetlands; he followin! strate!ies and research plans are envisa!ed for a better understandin! and conse6uently better use of the wetlands $ishat et al.1&&'(C $a( A thorou!h inventory of the various types of freshwater wetlands under different a!ro-ecolo!ical re!ions. $b( horou!h physical, physico-chemical and chemical analyses of water, soil and ve!etation of the wetland ecosystemF this has to be done initially every month for  three consecutive years and then to be continued periodically as a monitorin! worF this will help loads brou!ht in by the ma3or rivers and their tributaries to the various catchment areas and the 6uanta leavin! the systemF this will help assess the dynamics in a macro levelF $c( Uuantify the total loads brou!ht in by the ma3or rivers and their tributaries to the various catchment areas and the 6uanta leavin! the systemF this will help assess the dynamic in macro levelF $d( Evolve water mana!ement pro!rammes efficient for both rainy season and dry  periodsF creatin! dams around the basin areas mi!ht help protect lands from floodin! but not allowin! water to be stored will create adverse effect, lie soils  becomin! acids, in non-calcareous floodplains and or!anic wetlandsF however, in calcareous floodplains where the waterbodies become dry durin! the dry season, the wetlands could be reclaimed by creatin! dams etc. so that the croppin! intensity could be increasedF $e( iversification of the use of water bodies needs to be attempted throu!h an efficient water mana!ement pro!rammeF $f( 2urvey and monitorin! for various pollutants in the wetlands, particularly in areas where intensive a!riculture is practised or near the industrial and urban peripheryF $!( Assess the possibility of usin! the mucy clay or clayey muc for various soil amendments other than its use as fuelF and $h( evelop personnel and manpower trained in the wetland systems of the country.

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%. #nviron*ental conditions of the area under stud+ %.1 6eolo$+ and landfor*s of 4rah*an"aria district; Ecept for a minor area of the low hills and terrace in the etreme east, the whole of the district is occupied by a relatively smooth, nearly level to !ently undulatin! landscape of floodplain rid!es and basins. he subunits are !iven belowC i. ii.

iddle e!hna floodplain Old e!hna estuarine

iii.

2alda floodplain

iv.

2ylhet basin a. 2urma-/usiyara floodplain  b. itas floodplain

ii.

:iedmont alluvial plain

+lhet "asin is a vast depressed area lyin! between the 2urma-/usiyara floodplain and

the Old 5rahmaputra floodplain. he sediments appear to have been derived mainly from the hills to the north and from the 2urma and /usiyara rivers. he relief comprises hi!h river levees surroundin! etensive basins $haors(, the centres of which stay wet throu!h the dry season. he whole area is sub3ect to flash floods, and most of the land is deeply or  very deeply flooded in the monsoon season. he difference in the elevation between river   bans and haor centres can be five meter or more. ;lays predominate in the basins, with  peat in some basin centres $5rammer, 1&&>(. ur*a A @usi+ara floodplain   is formed by the sediments brou!ht in by the rivers

drainin! into the e!hna catchment area from the orthern and Eastern hills $?ahman, "00(. 2ome small hill and piedmont areas near 2ylhet, too small to map separately, are

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'i$. 8; Location *ap of 4rah*an"aria district $2ourceC 552, 1&&1(

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4rah*an"aria District +nundation land types

Le$end 1. ". '. 8. . >.

#i!h land 2hallowly flooded land oderately deeply flooded land eeply flooded land 7ery deeply flooded land ied shallowly flooded and nonflooded land 4. ied shallowly and moderately deeply flooded land . ied deeply and moderately deeply flooded land &. ied shallowly and very deeply flooded land 10. ied very deeply and moderately deeply flooded land

'i$. =; Distri"ution of land t+pes on the "asis of floodin$ depth

$2ource, 2?+, 1&4'( - 1 -

included within the boundaries. Elsewhere, the relief !enerally is smooth, comprisin!  broad rid!es and basins, but it is locally irre!ular alon!side river channels. 2urma/usiyara unit occupies minor areas in the etreme north. +t comprises alternate narrow lon! rid!es and deep narrow inter- rid!e depressions with some broad basins. he relief is !enerally is smooth, comprisin! broad rid!es and basins, but it is locally irre!ular  alon!side river channels. he soils are mainly heavy silt on the rid!es and clays in the  basins $5rammer, 1&&>(. !iddle !e$hna floodplain consists of a comple, rather irre!ular landscape of 

floodplain rid!es and inter-rid!e depressions, cut offs, o-bow laes with fresh spill deposits alon! active channels $2?+ 2taff, 1&4'(. he whole landscape is seasonally flooded by the e!hna and eposed to river erosion by fresh deposits in each monsoon season. 2easonal floodin! from the e!hna ?iver is mainly deep. 5asin sites are submer!ed early and drain late $5rammer, 1&&>(. 5ld !e$hna estuarine  comprises smoothed out rather low rid!es with broad basin areas.

he relief is almost level, with little difference in elevation between rid!es and basins $5rammer, 1&&>(.

%.2 Cli*ate; a. he area has a pronounced tropical monsoon climate. hree main seasons found hereC the monsoon $or rainy( season from ay to October durin! which about 8 percent of the total annual rainfall is receivedF the dry season $or winter( from ovember to *ebruary which has very little rainfall and has the lowest temperatures and humidities of  the yearF and the pre-monsoon $or hot( season from arch to April which has the hi!hest temperatures and evaporation rates of the year and durin! which occasional thunder  showers fall. otal annual rainfall is "8"0 mm $in "00( and "8'0 mm $in "008( $552, "00>(. he rainy season ecess of rainfall over evaporation is about 88 inches and in dry season ecess of evaporation over rainfall is about 11 inches. here is plenty of rainfall durin! monsoon and most of this rainfall occurs durin! the months of ay, Mune and Muly.  ormal duration of the rainy season $monsoon( as well as distribution of the rainfall vary from year to year and no ind of periodicity could be established between a drou!ht year 

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and a per humid or flood year. +n some years short spells of drou!ht and flood alternate $which have si!nificant influence on a!riculture( was found.

". he climatic condition of the district is similar to that of other districts in the eastern re!ion of the country. #ot summer, lon! rainy season and pleasant sprin!-cum-winter are the main noticeable seasons prevailin! in the locality. he summer be!ins at the end of  arch and mer!ed with the rainy season which continues up to 2eptember. )inter lasts from early ovember to late *ebruary. he hi!hest and lowest mean temperatures are ''.<; $in "00( and 1".'<; $in "00( $552, "00>( in the months of ay to Manuary respectively.

c. he avera!e relative humidity is around 4%.

%.3 7+drolo$+; he main rivers in the 5rahmanbaria district are the e!hna, the haleswar, the itas, the 5ansi, the 5alia!uri, the :a!la, the 2aldha and the 5uri.he e!hna river flows alon! of  the mar!in area. he e!hna is navi!able throu!hout the year. All other rivers are navi!able durin! the rainy season. he flowin! len!th of the rivers is about 18 /ms. he river area is &.>8 /ms $552, "00>(. he itas tain! off from the e!hna several miles north of 5hairab baBar has meandered throu!h the study area and finally has 3oined the e!hna near abina!ar several miles downstream of 5hairab baBar. 2everal crees drainin! ripura hills 3oin the itas.  ormally the flood- level of the e!hna ?iver starts risin! from ay due to increased dischar!e of its tributaries viB. Old 5rahmaputra, haleswar rivers. ?iver-level and dischar!e are usually at their hi!hest ion Muly to 2eptember, from ovember it starts recedin! and finally touches lowest dischar!es in Manuary-arch. ;rees drainin! the ripura #ills swell rapidly and flow in spate for a few days at a time after heavy premonsoon rainfall in its catchment areas i.e. ripura #ills. he dry season dischar!e of  most rivers is very small.

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Climatic components

Av. ?ainfall $mm( Av. a. emp. $° ;( Av. ini. emp. $° ;( Av. #umidity $%(

"00 "8"0 ''. 1".'

"008 "8'0 '8.8 1".&

"00' 1" '&.' 10.&

"00" "0'" '"." 1'.

"001 1&"& ''. 10.&

"000 "0"> '".' 1".'

1&&& "0 '8.' 14.>

+ear 1&& 1&&4 "8' "1'8 ''. ''." 11.4 11."

1&&> "0"> '0.8 "0.

1&& "10" ''.8 &.

1&&8 1'8 ''.1 10.>

1&&' ">> 8>. 14.4

1&&" 1"80 ''." 1&."

1&&1 "0& "&.4 "0.4

1&&0 ""14 '". 1&.8

4

4&

0

0

4"

0

0

0

'

1

8



8



8

'

Table- 12: Climatic $ata of Comilla eteorological tation J2ourceC 5an!ladesh eteorolo!ical epartment, "00>K

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-  -

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On the Old e!hna estuarine floodplain, floodin! is mainly due to sta!nation of rain water. #owever flood levels are controlled by chan!es in rainy-season water-levels of the e!hna, its tributaries and distributaries. hese chan!es are usually !radual and even in deep basins broadcast aman can be !rown without much dan!er of crop dama!e or loss. 5asin depressions or abandoned channels that remain wet for the !reater part or all of dry season are normally used for 5oro rice. he piedmont alluvial plain comprises mainly  basins, basin depressions and valleys. hese are !enerally shallow to moderate or deeply flooded. he 2ylhet basin subdivided into the 2urma-/usiyara floodplain and itas floodplain  because of its lower elevation receives run-off from the ripura #ills, nei!hbourin!  piedmont apron and ad3oinin! Old e!hna estuarine floodplain as well as spillin!s from the e!hna river. +n the rainy season it becomes a enormous lae more than 1" feet deep. eep floodin!, sudden rise of flood level and current water prevent the cultivation of  /harif crops in most of the area. #owever 5oro rice is etensively !rown because lar!e areas remain wet for most or all of dry season $2?+ 2taff, 1&4'(.

On the Old e!hna estuarine floodplain, floodin! is mainly due to sta!nation of rain water. #owever flood levels are controlled by chan!es in rainy-season water-levels of the e!hna, its tributaries and distributaries. hese chan!es are usually !radual and even in deep basins broadcast aman can be !rown without much dan!er of crop dama!e or loss. 5asin depressions or abandoned channels that remain wet for the !reater part or all of dry season are normally used for 5oro rice. he piedmont alluvial plain comprises mainly  basins, basin depressions and valleys. hese are !enerally shallow to moderate or deeply flooded. he 2ylhet basin subdivided into the 2urma-/usiyara floodplain and itas floodplain  because of its lower elevation receives run-off from the ripura #ills, nei!hbourin!  piedmont apron and ad3oinin! Old e!hna estuarine floodplain as well as spillin!s from the e!hna river. +n the rainy season it becomes a enormous lae more than 1" feet deep. eep floodin!, sudden rise of flood level and current water prevent the cultivation of  /harif crops in most of the area. #owever 5oro rice is etensively !rown because lar!e areas remain wet for most or all of dry season $2?+ 2taff, 1&4'(.

%.% Draina$e; About &% of the area is affected by seasonal floodin!. epth and duration of the floodin! vary with topo!raphical position and are mainly controlled by the rainy- season waterlevels of the main rivers and their tributaries. ?id!es are mainly seasonally flooded from few wees up to 8- months. 5asins and basin depressions are flooded more deeply and for a lon!er time. hey receive run-off water from ad3acent rid!es and usually are sub3ect to rapid rise of the flood level. he 2urma-/usiyara floodplain is seasonally very deeply flooded and in most places remains flooded for the !reater part of the dry season. his area is sub3ect to flash floods in the pre-monsoon, monsoon and post monsoon seasons, so the etent and depth of floodin! can vary !reatly within a few days. ormal floodin! is mainly shallow on the rid!es and deep in the basins, with flood depths tendin! to increase towards the mar!in with the 2ylhet basin. he centres $haor( stay wet in the dry season $5rammer, 1&&>(. 2ylhet basin is also sub3ect to early flash flood and basin centres stay wet for most or all of the dry season $5rammer, 1&&>(.

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%. Be$etation; +rri!ated boro paddy is the main cropC local 5oro in basin centres sub3ect to early floodin!F #N7 boro on the hi!her mar!ins of basins. Aus followed by transplanted Aman are the main practice on shallowly flooded rid!e, with some mied Aus plus Aman alone on basin mar!ins. he cultivation of dryland rabi crops is mainly confined to loamy river-ban  soils. 2ome basin land that cannot be irri!ated is under red swamp or !rassland used for  dry season !raBin! $5rammer, 1&&>(. he main constraints on improved a!ricultural  production in both areas areC the heavy rainfall eperienced susceptibility to flash flood, deep and prolon!ed floodin! of basin sites and the prevalence of heavy soils that are difficult to cultivate when wet or when dry $5rammer, 1&&>(.

he land use in this area is mainly depends on the duration and depth of seasonal floodin! and by the suitability of soil moisture in the dry season. On shallowly flooded land farmers !row aus followed by transplanted aman. )here sufficient dry season moisture is available, a dry-land crop is often !rown after the main harvest. ryland rabi crops cannot  be !rown in soils which remain wet for some wees after the end of rainy season. )here floodin! become too deep transplanted aman is cultivated and where rapid rise of the flood level occur, broadcast aman or sometimes mied with aus is !rown. 5asin depressions with sufficient water for dry season irri!ation are used for boro cultivation. On comparatively hi!h land where water cannot be ept on the land, only aus is !rown, followed by a dryland crop at the end of the rainy season. ?abi crops mainly include hesari, mustard, till, !ram, sweet potatoes and potatoes.

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Table- 1": Crop s,itability ratings by soil series8 phase or land type in different wetlands of Brahmanbaria district  oil series

5.

nnual wetland crops %ithout irrigation %ith irrigation . 5. 5oro Mute . . 5. 5oro

Aus Aman Aman 5ala!an3, mll " 8 '  abina!ar, vll 8 8 8  asirna!ar, vll 8 8 8 :ha!u, vll 8 8 ' J2ourceC 2?+ staff, 1&4'K

8 " " 8

" 8 8 8

Aus " 8 8 8

Aman 8 8 8 8

Aman ' 8 8 '

" " " 1

Mute " 8 8 8

Note;  mll =  medium lowland, vll =  very lowland, 5. Aus = 5roadcast Aus, . Aus

=ransplanted Aus, 5. Aman = 5roadcast Aman, . Aman =ransplanted AmanF uita"ilit+ class; )ell suited = 1, moderately suited= ", poorly suited = ', not suited =

8

%.8 oil; ost of the soils of 5rahmanbaria district are seasonally flooded, have silt to clayey tetures and moderate or low contents of or!anic matter. Ecept in a minor area of hills and terrace in the eastF all soils are developed in recent and sub recent alluvium. he  orthern part of the district has !rey silty loam of the non-saline phase of the old lower  e!hna estuarine floodplain. he central part of the district is covered with dar !rey clay of the itas floodplain. he soil in the eastern re!ion contains silty clay loam. he piedmont alluvium admiture of sandy and silty alluvium of middle e!hna floodplain is prevailin! in the southern re!ion. he overall basin is poorly drained and deeply flooded in the monsoon season. +n the different parent materials, the soils have developed different properties, mainly due to difference in teture, draina!e, ind of sediment, a!e of the deposits and ve!etation. ost soils are dar !rey or very dar !rey but mottled to varyin! de!rees with brown or  yellowish red. op soils are !enerally puddled for rice cultivation and usually have a compact plou!hpan at a depth of '-8 inches. ost top soils are near neutral in seasonally reduced condition and become medium to stron!ly acid when dry. he soils have moderate content of or!anic matter and soil reaction is mainly acidic $5rammer, 1&&>(. *ertility level is medium to hi!h.

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he soils of the ur*a,@usi+ara alluviu* are mainly heavy silts on the rid!es and clays in the basins. his area is sub3ect and depth of floodin! can vary !reatly within a few days.  ormal floodin! is mainly shallow on the rid!es and deep in the basins, with flood depths tendin! to increase towards the mar!in with the 2ylhet 5asin. he basin centres $haors( stay wet in the dry season $5rammer, 1&&>(. ainly silty clay loam rid!e soils coverin! about " percent of the total soil area on the 2urma-/usiyara floodplain and only 10  percent in the 2ylhet basin. ost soils of the +lhet "asin have subsoil with mied !rey and dar brown colors, stron! prismatic and blocy structure and the reaction of soils ran!es from stron!ly acidic to near neutral. Or!anic matter content of the soils is moderate $5rammer, 1&&>(. 2oils in basin depression are !rey or dar !rey in color and remain wet for most or all of the dry season. 2oils of the itas floodplain are poorly drained and blac  to !rey clay soil which remains wet in most of the dry season. 2oils formed in the Old !e$hna estuarine  floodplain have dar !rey or very dar !rey subsurface soil. early all

soils have subsoil with mied dar !rey and yellowish brown colours, stron! prismatic structure, conspicuous dar !rey coatin!s and a sli!htly acid to mildly alaline reaction. 2oils in basin depressions are dar !rey to very dar !rey in colour and remain wet for  most or all of the dry season. he soils of the !iddle !e$hna floodplain  are poorly drained and have !rey or olive!rey as dominant matri colour. About one half of the area is occupied by finely stratified sandy and silty alluvium. oderately shallow loamy soils over a stratified substratum cover most of the rid!e and inter-rid!e depression sites. +n relatively sheltered parts, where no river erosion or thic deposition has taen place for the last decades, loamy soils have developed moderate to stron! prismatic structure with !rey cutans alon! ped faces. he subsoil reaction varies from sli!htly acid to mildly alaline.

5asin soils of the 5ld

!e$hna estuarine floodplain are poorly drained and have a humous dar !rey to very

dar !rey A horiBon between the plou!hed layer and the subsoil. 2ilty clay loam teture  predominates in the basin soils. :art of the soils has very dar !rey or blac coatin!s alon!  ped faces in the subsoil. About three-fourths area of the 2alda floodplain is deeply flooded and sudden rise in flood level taes place. 2ediments carried by the e!hna water have produced fine tetured very dar !rey basin soils. 2oils occupyin! rid!es are shallowly to deeply flooded, mied olive and !rey or dar !rey colours and loamy teture. - & -

. !aterials and *ethods .1 election of soil sa*plin$ sites and sa*ple preparation; On havin! a preliminary idea about the different location of 5rahmanbaria district, the net 3ob for its soil study was to select the individual soil samplin! sites as accurately as  possible to have a homo!enous and representative samplin! of soil pedons. 2oil samplin! sites was based mainly on the land type i.e, it must be low to medium low land which are seasonally flooded, the a!e of the soil materials and ve!etation. he soil samplin! sites are recorded in able- 18 with some of their respective environmental characteristics. *our  soil series were collected from 2arail upaBila which is shown in *i!ure- . After studyin! soil profile soils are collected for laboratory study.

.2 !ethods of the field stud+ of soils; A pit of 1m

 "m up to a depth of 1'0 cm was ecavated for each soil profile. *or 

×

understandin! the soil properties, the soil profiles were studied and described morpholo!ically in the field accordin! to the system of 2oil 2urvey 2taff $1&1(. he environmental conditions of the study area is !iven in able - 18. he horiBons of each  pedon were described morpholo!ically.

- >0 -

:-1 - 5ala!an3 series :-" - :ha!u series :-' - asirna!ar series :-8 - abina!ar series

'i$. >; !ap of arail upaila showin$ the location of soil sa*plin$ sites - >1 -

Table- 1+: oil sampling sites and their en7ironmental characteristics District

paila

Billa$e

Latitude and lon$itude "8 < 0> = 8&8  9 &1 < 04 = >"" E

oil eries 5ala!an3

opo$raph+

Draina$e

' loodin$

Landuse

Hently slopin! rid!e

:oor

*looded up to '-8 feet about 8- months

ransplanted Aman, 5oro

"8 < 0 = &18  9 &1 < 0> = >8' E

:ha!u

/aliascho

2lope of basin

:oor

*looded up to >-4 feet about -> months *looded up to 4- feet about -> months *looded up to -10 feet about 4- months

5oro-fallow

"8 < 0 = 4"  9 &1 < 0 = '8 E

 asirna!ar early level  basin

7ery poor

iorona

"8 < 04 = &>>  9 &1 < 0 = 1>1 E

 abina!ar

7ery poor

horanti!hat

horanti!hat

5rahmanbaria 2arail

5asin depression

5oro-fallow

5oro-fallow

- >" -

Table- 1+: oil sampling sites and their en7ironmental characteristics District

paila

Billa$e

Latitude and lon$itude "8 < 0> = 8&8  9 &1 < 04 = >"" E

oil eries 5ala!an3

opo$raph+

Draina$e

' loodin$

Landuse

Hently slopin! rid!e

:oor

*looded up to '-8 feet about 8- months

ransplanted Aman, 5oro

"8 < 0 = &18  9 &1 < 0> = >8' E

:ha!u

/aliascho

2lope of basin

:oor

*looded up to >-4 feet about -> months *looded up to 4- feet about -> months *looded up to -10 feet about 4- months

5oro-fallow

"8 < 0 = 4"  9 &1 < 0 = '8 E

 asirna!ar early level  basin

7ery poor

iorona

"8 < 04 = &>>  9 &1 < 0 = 1>1 E

 abina!ar

7ery poor

horanti!hat

horanti!hat

5rahmanbaria 2arail

5asin depression

5oro-fallow

5oro-fallow

- >" -

.3 'ield description of the studied soils;  he soils were sub3ected to detailed study in the field. he environmental characteristics and !eneral morpholo!ical properties of the soil profiles are presented belowC

.3.1 4ala$an< eries (,1) 5ala!an3 series are seasonally shallowly flooded, poorly drained soils developed in mied tetured alluvium occupyin! upper part of rid!es. hey have a mied !rey and dar brown, friable, silt loam to loam subsoil with stron! to moderate suban!ular blocy structure and  patchy to continuous !rey cutans on ped faces.

+pical profile

; 5ala!an3 2eries

hase

; edium hi!hland phase

Location

; "8Y 0>P 8&8 - &1Y 04P >""E

Billa$e

; horanti!hatF :. 2.- 2arail, istrictC 5rahmanbaria

opo$raph+

; Hently slopin! rid!e.

Landuse

; ransplanted Aman, 5oro.

Draina$e

; :oor. *looded up to '-8 feet about 8- months

.3 'ield description of the studied soils;  he soils were sub3ected to detailed study in the field. he environmental characteristics and !eneral morpholo!ical properties of the soil profiles are presented belowC

.3.1 4ala$an< eries (,1) 5ala!an3 series are seasonally shallowly flooded, poorly drained soils developed in mied tetured alluvium occupyin! upper part of rid!es. hey have a mied !rey and dar brown, friable, silt loam to loam subsoil with stron! to moderate suban!ular blocy structure and  patchy to continuous !rey cutans on ped faces.

+pical profile

; 5ala!an3 2eries

hase

; edium hi!hland phase

Location

; "8Y 0>P 8&8 - &1Y 04P >""E

Billa$e

; horanti!hatF :. 2.- 2arail, istrictC 5rahmanbaria

opo$raph+

; Hently slopin! rid!e.

Landuse

; ransplanted Aman, 5oro.

Draina$e

; :oor. *looded up to '-8 feet about 8- months

a*plin$ date

; "'rd arch, "00>

rofile Description; 7orion na*e

Ap1

7orion depth (c*) 0-10

7orion description

Di!ht yellowish brown $10 N? G( moistF few distinct stron! brown mottlesC ilt loa*F massiveF sli!htly sticy, sli!htly plastic when wetF friable when moistF very fine tabular poresF common fine

5"1!

10-""

rootsF abrupt smooth boundaryF p# >.8. ar yellowish brown $10N? G>( and dar brown $4. N? 8G8( moistF few fine distinct reddish brown mottlesF silt loa*F stron! coarse and medium sub an!ular blocyF friable moistF sticy, plastic wetF !rey cutans alon! ped faces F many very fine tabular   poresF few fine rootsF abrupt smooth boundaryF p#

5""!

""-'4

>.&. Hrey $10N? G1 ( and dar brown $ 4.N? 8G8 ( - >' -

moistF few fine distinct dar reddish brown $moist ( mottlesF silt loa*F medium suban!ular blocyF friable moistF sli!htly sticy, sli!htly plastic wetF continuous !rey cutans alon! ped faces and poresF few very fine rootsF abrupt smooth boundaryF p# 5"'

>.&. Hrey $10N? G' ( and dar brown $ 4.N? 8G8 (

'4- 4

moist F silt loa*F stron! medium suban!ular blocyF friable moistF sli!htly sticy, sli!htly plastic wetF continuous !rey cutans alon! ped faces and poresF 5'

few very fine rootsF clear smooth boundaryF p# >.&. Hrey $10N? G" ( and stron! brown $ 10N? 8G" (

4-0

moistF common fine distinct dar reddish

brown

$moist ( mottlesF silt loa*F stron! medium and fine suban!ular blocyF friable moistF sli!htly sticy, sli!htly plastic wetF continuous thic !rey cutans alon! ped faces and pores, clear smooth boundaryF ;1

0-1"0

 p# >.&. Hrey $10N? G1 ( and dar yellowish brown $ 4.N?   G" ( moistF few fine prominent dar reddish brown $moist ( mottlesF silt loa*F p# >..

Ran$e in Characteristics a. rofile characteristics;

eture of the both topsoil and subsoil are silt loam. ;olour of the topsoil is li!ht yellowish  brown and subsoil varies from !rey to dar !rey. 2tructure of the soil is fine suban!ular   blocy. ". #nviron*ental characteristics;

hese soils occupy upper to lower part of rid!es and narrow levees on the 2urma-/usiyara floodplain. edium hi!hland phase is flooded up to 1-' feet in the monsoon season for  about "-' monthsF medium lowland flood haBard phase is flooded up to 8-> feet for about 8 months in the monsoon season and become drou!ht in the dry season flood haBard taes  place. Dowland flood haBard phase is flooded deeply in the monsoon season and become drou!ht in the dry season and flood haBard taes place.

- >8 -

c. Be$etation and Landuse;

At present these soils are used for transplanted aman- rabi crops.

 

755-

.3.2 ha$u eries (,2)

- > -

:ha!u series consists of poorly drained, seasonally deeply flooded soils developed in the  basins and basin mar!ins in the 2urma-/usiyara floodplain. hey have a !rey to dar !rey, clay subsoil usually with stron! prismatic and an!ular blocy structure and continuous !rey or dar !rey cutans alon! ped faces.

+pical profile

; :ha!u 2eries

hase

; Dow land

Location

; "8Y 0P 4" - &1Y 0P '8E

Billa$e

; ioronaF :. 2.- 2arail, istrictC 5rahmanbaria

opo$raph+

; early level basin.

Landuse

; 5oro 9 fallow.

Draina$e

; *looded up to 4-> feet deep for about -> months.

a*plin$ date

; "8th arch, "00>

rofile Description; 7orion na*e Ap1!

7orion depth (c*) 0-10

7orion description Hrey $  N G1( moistF common fine distinct

yellowish brown and yellowish red iron stainin! alon!

root

channelsF ilt loa*F

massiveF firm moistF sli!htly sticy, sli!htly  plastic wetF common very fine tabular poresF many very fine rootsF abrupt smooth boundaryF Ap"!

10-"0

 p# >.1. Di!ht !rey $  N G"( moistF few fine distinct reddish brown mottlesF silt loa*F massiveF friable moistF sticy, plastic wetF !rey cutans alon! ped facesF many very fine tabular pores F few fine roots F abrupt smooth boundaryF p#

5"1!

"0-'0

>.&. ar !rey $N 8G1 ( moist F common fine distinct stron! yellowish brown mottles F silt+ cla+ loa*  F stron! coarse prismatic breain!

to medium an!ular blocyF firm moistF very

- >> -

sticy, plastic wetF continuous thic !rey cutans alon! ped faces and poresF many very fine tabular poresF few very fine rootsF abrupt 5""!

'0-1

smooth boundaryF p# 4.0. Hrey $N G1 ( moistF common fine distinct yellowish brown mottlesF silt loa*F

stron!

coarse and medium an!ular blocyF firm moistF very sticy, plastic wetF continuous thic !rey cutans alon! ped faces and poresF clear smooth ;1!

1-4>

 boundaryF p# 4.". Hrey $N G1 ( wetF many fine distinct yellowish brown mottlesF loa*F firm moistF

++;"!

4>-1""

sli!htly sticy, sli!htly plastic wetF p# 4.0. Hrey $N G1( wetF common fine distinct yellowish brown mottlesF silt loa*F firm moistF sticy, plastic wetF p# 4.0.

Ran$e in Characteristics a. rofile characteristics;

hese soils have a !rey to dar !rey in colour, finely mottled !enerally firm to very hard clay topsoil with medium an!ular blocy structure, overlyin! !rey mottled yellowish brown, firm clay subsoil with stron! an!ular blocy to prismatic structure and sli!htly acid in reaction.

". #nviron*ental characteristics;

hese soils occur on the 2urma-/usiyara floodplain and in itas basin. hey are seasonally flooded up to &-1" feet for about > months.

c. Be$etation and Landuse;

he present landuse of these soils is for boro cultivation.

755-4

- >4 -

.3.3 Nasirna$ar eries (,3) - > -

 asirna!ar 2eries comprises seasonally very deeply flooded, very poorly drained, moderately fine tetured soils developed in the itas valley of the 2ylhet basin. hey are deeply flooded in the monsoon season and remain wet for most of the dry season. hey have a dar !rey to very dar !rey, mottled brown, silty clay loam subsoil.

+pical profile

; asirna!ar 2eries

hase

; Dow land phase

Location

; "8Y 0P &18 - &1Y 0>P >8'E

Billa$e

; /aliaschoF :. 2.- 2arail, istrictC 5rahmanbaria

opo$raph+

; 2lope of basin.

Landuse

; 5oro 9 fallow.

Draina$e

; :oor. *looded up to >- 4 feet for about -> months.

a*plin$ date

; "8th arch, "00>

rofile Description; 7orion na*e Ap1!

7orion depth (c*) 0-4

7orion description 7ery dar !rey $10 N? 'G"( moistF common

fine distinct dar brown mottlesF 2ilt  loa* massiveF firm moistF sli!htly sticy, plastic wetF Ap"!

4-14

abrupt smooth boundaryF p# 4.0. ar !rey $10 N? 8G1( moistF common fine distinct dar yellowish brown mottlesF silt loa*F medium an!ular blocyF firm moistF

sticy, plastic wetF abrupt smooth boundaryF 5"'

14-"

 p# >.&. Hrey $10N? 8G" ( moistF common fine distinct reddish brown mottlesF silt loa*F firm moistF sticy, plastic wetF clear smooth boundaryF p#

;1!

"->"

4.1. ar !rey $10N? 8G1 ( moistF common fine distinct red and yellowish brown mottlesF silt

- >& -

loa*F firm moistF sticy,

;"!

>"-1'0

plastic wetF clear 

smooth boundaryF p# >.8. Di!ht yellowish !rey $10N? G'( moistF silt loa*F firm moistF sli!htly sticy, sli!htly

 plastic wetF p# 4.0.

Ran$e in Characteristics a. rofile characteristics;

he colour of the topsoil ran!es from very dar !rey to dar !rey and that of subsoil !rey to li!ht yellowish !rey. eture of both subsoil and topsoil is silt loam.

". #nviron*ental characteristics;

hese soils occur on the 2urma-/usiyara floodplain and in itas basin. hey are seasonally flooded up to -1" feet in the monsoon season and remain wet for most of the dry season.

c. Be$etation and Landuse;

hese soils are mainly used for boro-fallow. :art of the area is covered by !rasses.

755-C

- 40 -

423

C1$

C2$

.3.% Na"ina$ar eries (,%) - 41 -

 abina!ar 2eries comprises seasonally very deeply flooded, very poorly drained soils developed in fine tetured alluvium on the itas valley of the 2ylhet basin. hey have a very dar !rey, silty clay to clay A horiBon with common brown mottles overlyin! a silt loam to silty clay loam oidiBed substratum. +pical profile

; abina!ar 2eries

Na"ina$ar eries

; Dowland phase

Location

; "8Y 0&P &>> - &1Y 04P 1>1E

Billa$e

; horanti!hatF :. 2.- 2arail, istrictC 5rahmanbaria

opo$raph+

; 5asin depression.

Landuse

; 5oro 9 fallow.

Draina$e

; 7ery poor. *looded up to -10 feet about 4- months.

a*plin$ date

; "'rd arch, "00>

rofile Description; 7orion na*e Ap!

7orion depth (c*) 0-1

7orion description 5lac $  N "G1( moistF silt+ cla+F massiveF

firm moistF sticy,

plasticF common fine

tabular poresF few very fine rootsF clear  A11!

1-'0

smooth boundar yF p# >.1. ar !rey $  N 8G1( moistF common fine distinct

yellowish

brown

mottlesF cla+F

massiveF firm moistF very sticy, plastic wetF common fine tabular poresF few very fine 5"'

'0-8'

rootsF clear smooth boundaryF p# >.&. ar $N ".G1( moistF clayF medium sub an!ular blocyF firm moistF very sticy,

;1

8'-

;"

-11'

 plastic wetF clear smooth boundaryF p# 4.8. Olive brown $".N 8G1( moistF common fine distinct !rey mottlesF cla+F stron! medium and fine sub an!ular blocyF firm moistF very sticy, plastic wetF clear smooth boundaryF p# 4.8. Hrey $N G1( moistF silt+ cla+ loa*F friable moistF sticy, plastic wetF p# 4.8.

Ran$e in Characteristics a. rofile characteristics;

- 4" -

he colour of the topsoil ran!es from very dar !rey to blac and that of subsoil olive brown to !rey. eture ran!es from silty clay loam to silty clay. ;olour of the subsurface A horiBon is dar !reyF the mottle colour ran!es from dar brown to !rey, it usually occupies less than "0% of the soil mass. he contrastin! layer is mostly bri!htly oidiBed olive to li!ht yellowish brown and is usually medium to moderately fine tetured.

". #nviron*ental characteristics;

hese soils occupy basin depressions, infilled cut-offs on the itas valley of the 2ylhet basin. hey are seasonally flooded up to 10-1" feet for about 4- months in the monsoon season and remain so!!y for most of the dry season.

c. Be$etation and Landuse;

hese soils are mainly used for a sin!le croppin! of boro-fallow.

- 4' -

755-D

423

.% La"orator+ *ethods;

- 48 -

2oil samples from each horiBon of the profile were collected in polythene ba!s. he ba!s were sealed properly precludin! moisture loss from the samples and transferred as 6uicly as possible to the laboratory for relevant analyses. :rior to analysis, the representative soil samples were air dried under shade. he soil samples were then !ently !round with rollin! wooden rod and passed throu!h "mm $10 mesh( sieve and mied thorou!hly. he samples were then preserved in plastic pot for  laboratory analyses.

Table- 1: Parent material of the selected soil series and their e!pected areas oil series   4ala$an<   ha$u   Nasirna$ar   Na"ina$ar J2ourceC 2?+ staff, 1&4'K

arent *aterial 2urma-/usiyara alluvium 2urma-/usiyara alluvium 2urma-/usiyara alluvium 2urma-/usiyara alluvium

rea (ha) "''01 '0&0 48 >01

.%.1 !ethods for h+sical nal+sis і. 7+$roscopic *oisture

#y!roscopic moisture content of soils was determined by dryin! the air-dried soils in an oven at 10<;-110<; for "8 hours $5lac, 1&>(. іі. article sie distri"ution

he particle siBe analysis of soils was carried out by combination of sievin! and hydrometer  methods as described by ay $1&>(. etural classes were determined by arshallIs trian!ular coordinate curve as devised by @2A $1&1(.

.%.2 !ethods for Che*ical nal+sis і. oil reaction (soil p7)

he p# $#"O( of soils was determined at a soil-water ratio 1C". usin! a pye p# meter. A same ratio of soil-1 /;l solution was used for determination of p# $/;l(. іі. 5r$anic car"on

he or!anic carbon content of soils was determined volumetrically by wet oidation method as described by Macson $1&>4(. ііі. otal N

- 4 -

he total nitro!en in soils was determined by /3eldahlIs method as described by Macson $1&>4(.

.%.3 !ethods for ph+sico,che*ical nal+sis і. Cation echan$e capacit+ (C#C)

;ation echan!e capacity of soils was determined with 1 #8OAc method buffered at p# 4 $Macson, 1&>4(.  

іі. #chan$ea"le cations (Ca EE? !$EE? NaE? @ E)

he echan!eable cations were determined from 1 #8OAc $p# 4.0( etract as described  by Macson $1&>4(. ;aTT and !TT were determined by atomic absorption spectrophotometer, while aT and / T were analyBed by Hallenamp flame photometer.  ііі. 4ase saturation percenta$e (4)

he percent base saturation was calculated by usin! the followin! formula.

% 5ase saturation Z

Echan!eable CaEEE !$EEE NaEE @ E ;ation echan!e capacity

[ 100

.%.% !ethods for !ineralo$ical nal+sis 2urface soil samples representin! the A $top( horiBon from each of the five soil profiles were selected for the determination of mineralo!ical composition in the clay fraction. o achieve successful dispersion the followin! pretreatments were used for the removal of flocculatin! and cementin! a!ents. he soil samples were treated with in aOAc-acetic acid buffer $p# .0( to destroy the free carbonates and or!anic matter was destroyed by '0% #"O" treatment $Macson, 1&>4(. *ree oides of *e L n were removed from soils by citrate-bicarbonate-dithionite etraction method as described by A!uilera and Macson $1&'( and ehra and Macson $1&>0(. After removin! soluble salts, carbonates, or!anic matter, nO"  and *e"O' the soils were dispersed with dilute sodium carbonate solution at p# &. $Macson,1&4( and the clay fraction $ "\( was separated by sedimentation L decantation processes as described by Macson $1&4(.

- 4> -

+dentification of mineralo!ical composition was carried out by V9ray diffraction $V?(. he separated clay fraction was treated by 1 /;l and 0. !;l " respectively to mae / T and !T saturated clay and wash them with ethanol to remove ecess salts. 2uitable amount $0.8 ml( of sol was dropped on a !lass slide coverin! two third of its area, air dried, and V9  rayed $parallel powder mount(. +n addition to the air dried specimen, the ! saturated clay was V 9 rayed after saturation with !lycerolF and / 9saturated clay after heatin! at '00° ; and 0Y; for "h. he V? pattern were obtained usin! 2himadBu V? >000 diffractometer with i 9 filtered ;u / 



radiation at 80 7 and '0 mA and at a scannin!

speed of ".0YGmin over a ran!e of '-'Y"θ. Approimate mineral contents of clay fraction estimated on the basis of the relative pea  intensities in the V? patterns $+slam and Dotse, 1&>(. he intensities ratio of two components : and U in a multi 9 component miture can be related to their wei!ht ratio as followsC +pG+6 Z /p.6.)pG)6 )here +p and +6 are the intensities of the : and U components in V?, )p and )6 are the wei!ht proportion of : and U components and /p.6, a constant value is the intensity 9  wei!ht coefficient : and U components.

8. Results and discussion 8.1 !orpholo$ical properties

- 44 -

he coded morpholo!ical properties of the wetland soils of 5rahmanbaria district have been  presented in able- 1>. Amon! the morpholo!ical characteristics color, mottlin!, consistence, structure, teture, and root distribution have been recorded and discussed.

Colour ;olour is the most obvious characteristic of any soil that is easily seen by even a lay-man. An enthusiastic observer in a !iven area can often relate soil colour to specific  physio!raphic location of the soil in that area. +t is also possible to mae some !eneraliBed statements. *or eample, in temperate climate dar-coloured soils are related with hi!h  presence of or!anic matter than li!ht coloured soil. he red colour soil is related with the  presence of free iron oide $unhydrated(. Nellow colour of the soil indicates the presence of  iron oide. Hrey or whitish colours of soil caused by the presence of 6uartB, aolinite and other clay minerals, carbonates of lime and man!anese and ferrous iron. @nder reducin! conditions, the soils usually appear !rey or bluish !rey in color. +n some instances relict colour that is those inherited from the parent materials, may be present in the soil. he variation of soil colours may be related to variation in submer!ence time, reduction and movement of iron from the surface downward. hus the variation on draina!e condition is responsible for variation in soil colours. he matri colour of the soils was found to be a miture of !rey, dar !rey, blac and yellowish brown. he dominant hue, when moist, in two profiles was 10N? while in the other two profiles it was N. hese hues in these soils have been developed due to prolon!ed submer!ence durin! rainy season and dryin! condition durin! the dry months. hese hues are related to the loss of free iron in these soils. @nder moist condition, the colour of the surface horiBon in the studied soils were found to be !rey $N G1(, blac $N "G1(, very dar  !rey $10N? 'G"(, and li!ht yellowish brown $10N? G(. 2oils of the e!hna floodplains become increasin!ly oidiBed in the subsoil, so that yellow or brown colour dominates over !rey colour in many soils which are not permanently wet. 2ome of these soils show dar coloured topsoil and subsoil coatin!s, probably developed under natural ve!etation $swamp( before the soils were cleared for cultivation. *loodplain and poorly drained soils of 2urma-/usiyara floodplain soils have !rey matri colours and their mottles and ped coatin!s are indicative of seasonal wetness $2?+ staff, 1&4'(.

- 4 -

+t was noted earlier that the studied soils are basically poorly drained. ost of the soils have low chroma. On the basis of chroma these studied soils can be classed as “hydromorphic soils” $2oil 2urvey 2taff, 1&&8(. he causes of hydromorphism are that these soils are inundated for a considerable part of the year by rain water as well as river waters which cause the reducin! condition of these soils. he reducin! condition is the cause of formation of !rey colour in the studied soils. his !rey colour of the soils is caused by removal of free iron oides from these soils by drainin! water. Amounts of free iron oide in the seasonally flooded soils have been reported to be low $/han et. al., 1&&4F Ali, 1&&8F uBib et al., 1&>&(

!ottles he formation of various coloured mottles is !enerally associated with seasonal fluctuation of !round water table $cea!ue, 1&>(. ue to alternate wettin! and dryin! conditions abundant 6uantities of mottles have formed in all the four soil profiles of the studied area. he colours of mottles were a combination of dar reddish brown to dar yellowish brown $able- 1>(. ottled horiBons occur in the subsoil Bone in these soils. ottles were present most of the profiles but 5ala!an3 and :ha!u contains mottles throu!hout the profile. he siBe and contrast of the mottles show variation from soil to soil. he occurrence of !ley horiBons in the features of most hydromorphic soils $#ussain et al., 1&&(. he hydromorphic soils are nown by different names in various parts of the world but they have mottles dependin! on the de!ree of hydromorphism $#ussain and 2windale, 1&48F 7ander, 1&4"(. hese soils are nown as de!raded rice soils in 5urma $/armanov, 1&>( and a6uariBems in Mapan and in some other 2outheast Asian countries $/yuma and /awa!uchi, 1&>>(.

Consistence 2oil consistency desi!nates the manifestation of the physical forces of cohesion and adhesion actin! within the soil at various moisture contents. hese manifestations includea( the behaviour towards !ravity, pressure, pull or thrust. b( the tendency of the soil mass to adhere to forei!n bodies or substances, and c( the sensations which are evidenced as feel by the fin!ers of the observer. *inally, it may be concluded that consistency represents the composite epression of the forces of cohesion and adhesion that determine the ease with which a soil can be reshaped or ruptured.

- 4& -

?esults of soil consistence are important for soil mana!ement especially durin! tilla!e. his assumes importance when the soils are plou!hed in wet conditions. he consistence of the soils under study has been determined under two moisture conditions 9 moist and wet. Ecept for the soils of the abina!ar series consistence of surface soils of all the studied  profiles was found to be sli!htly sticy and sli!htly plastic when wet. +n subsurface soils of  :ha!u series very sticy consistence also found. +n moist condition, the consistence of the soils of 5ala!an3 series was friable, while in abina!ar, asirna!ar and :ha!u series it was firm $able- 1>(.

eture 2oil teture means the siBe distribution of soil particles. atural soils are comprised of soil  particles of varyin! siBes. he soil particles called soil separates $i.e, sand, silt and clay(. 2oil teture refers to the relative proportion of soil separates in a !iven soil. +t also refers to the fineness or coarseness of the soil. he field teture of the soils was determined by “feelin! method”. he field teture ran!ed from silt loam to silty clay loam ecept in the abina!ar series in which the teture ran!ed from silty clay to clay $able- 1>(. Doamy and clayey teture of the soils of 5rahmanbaria district is an indication that they are hi!hly suitable for a!ricultural use especially for rice cultivation under waterlo!!ed condition. he variation in clay, silt and sand content in most  profiles su!!ests that teture is mainly due to sedimentary variations rather than a result of  soil formin! processes. 2ilty clays and clays are predominate, with mainly silty clay loam soils coverin! about "% of the total soil area on the 2urma-/usiyara floodplain and only about 10% of the 2ylhet  basin$5rammer, 1&&>(. eture of the soils of 2urma-/usiyara and Old e!hna estuarine floodplain soils are silt loam and silty clay loam to silty clay and topsoils are heavier in teture $2?+ 2taff, 1&4'(. )etlands are not, however, confined to low-lyin! lands. @nder  heavy concentration of rainfall, even terraces and fans are flooded or saturated with water, as lon! as the land surface is level or depressional and soils are heavy tetured and impervious $#u6 and /amal, 1&&'(.

Table- 1/: Coded * morphological properties of the st,died soils !unsell Colour

oil eries

7orion

Depth

Consistence

4**

- 0 -

5"'

'0-8'

 N ".G1 !

;1

8'-

". N 8G1 ob

;"

-1"0

 N G1 !

4. N? G1 fd! 4. N? G1 fd! ----

;

sb

mfi mfi

wvs, wp ws,wp

;

smGfsb

2i;D

----

;s ;s

mfr

ws,wp

--

*Accordin! to the method of 2oil 2urvey 2taff $1&(F 5**=5oundary

tructure 2oil structure is the arran!ement of soil particles into a!!re!ates and the forces between them and the conse6uences of the arran!ement on soil pores. +t also refers to the a!!re!ation of individual soil particles into lar!er units or peds with planes of weaness between them. +n the surface layer of all the studied soil profiles, the structure was found to be massive. 2tructure could not develop in the surface horiBon as they have been plou!hed for many years with puddlin! as an usual feature. he subsoil of 5ala!an3 and abina!ar series showed stron! medium and medium suban!ular blocy and fine suban!ular blocy structure. he subsoil of :ha!u series showed stron! coarse prismatic and medium an!ular   blocy structure. +n asirna!ar series, medium an!ular blocy structure was found. *rom the studied soils, it may be concluded that medium suban!ular blocy and medium an!ular   blocy structure dominate in the wetland soils of 5rahmanbaria district. 2?+ staff $1&4'( durin! the reconnaissance survey with lar!e number of soils of the studied area $5rahmanbaria( reported almost similar structures in the studied soils. )et basins of the 2ylhet basin soils have blocy or prismatic structure which is developed below the surface layer and brown mottle colour showin! some oidation $2?+ 2taff, 1&4'(.

Coatin$s 5rammer $1&&>( defined coatin!s as the shiny surfaces of soil cracs and pores formed by deposition of materials washed from the surface soils under seasonally flooded condition. he sides of cracs and pores in most of the wetland soils of 5an!ladesh are coated with such materials. hese coatin!s are called !leyans are uniformly !reyF mid-!rey if the surface soil layer is !rey $when wet(F dar !rey if the surface layer is dar !rey.

- 1 -

;ontinuous thic dar !rey to continuous dar !rey cutans alon! ped faces are found in 5ala!an3 and :ha!u series. he coatin!s on ped faces may possibly be due to mechanical downward washin! of material from the soil surface throu!h cracs when the soils are in waterlo!!ed condition and plou!hed.

ost of the soils of Sylhet basin are poorly or imperfectly drained havin! conspicuous cutans alon! ped faces and pores in the subsoil $2?+ 2taff, 1&4'(.

7orion "oundaries +t is the important morpholo!ical feature in soil profiles. ;lear smooth boundary was found in 5ala!an3, :ha!u and abina!ar series. Abrupt smooth boundary was found in 5ala!an3 and :ha!u series. )ith respect to horiBon boundaries, the soils under the present investi!ation are more or less similar.

8.2 h+sical properties he physical parameters of soils are important criteria in the land use and also land mana!ement. 2ome of these properties were studied in the field as well as in the laboratory. ?esults of physical properties of the studied soils are presented in able- 14.

8.2.1 article sie distri"ution he studied soils were !enerally fine tetured and showed 6uite a narrow ran!e in tetural class from silt loam to clay amon! the horiBons $able - 14(. eture varies both within the  profile and on different parts of the relief. he topsoil was much li!hter in teture. 2ubsoil teture was closely related to position on the relief, with silt loam on the slope and silty clays or clays in basins. ost of the studied soils were located near the basin mar!ins and  bottom lands of seasonally flooded areas, the soils were mostly silt loam and clayey in teture.

and fraction 2and fraction of the studied soils varies from ' to "& percent with a mean value of 10  percent $able - 14(. he surface horiBons of the four studied profiles have 1>, >, 4 and 

- " -

 percent sand, respectively. his indicates that sand is not the dominant siBe fraction in these soils and its 6uantity is 3ust not sufficient to provide a con!enial physical condition of the soil for plant !rowth. he hi!hest value of sand was found in the soils of the 5ala!an3 series while the lowest value wass found in the soils of the abina!ar series.

Table- 10: Particle size distrib,tion and te!t,ral class of some wetland  soils ,nder st,dy oil series

4ala$an<

7orion

Depth (c*)

ilt0 Cla+ ratio

7!* (:)

and $%( 1>

ilt $%( >"

Cla+ $%( ""

2ilt loam

0."

".1

8."0

"0 1& 1 " "& 21

>4 >> >& >8 >' 8

1' 1 1>   1%

2ilt loam 2ilt loam 2ilt loam 2ilt loam 2ilt loam ,,

0."& 0."& 0."" 0.88 0.8> .32

.1 8.80 8.'1 .00 4. .%3

'.8 8.10 8.80 ".4> 1.'4 3.%%

5"1!

10-""

5""!

""-'4

5"'

'4-4

5'

4-0

;1

0-1"0

Ap1!

0-10

>

40

"8

2ilt loam

0.0

".4

8.1

Ap"!

10-"0

5"1!

"0-'0

4 &

40 >>

"' "

0.10 0.1'

'.00 ".>8

8." ."

5""!

'0-1

;1!

1-4>

Q;"!

4>-1"0

11 1" 18 9

> >8 >" 8=

"8 "8 "8 2%

2ilt loam 2ilty clay loam 2ilt loam 2ilt loam 2ilt loam --

0.1> 0.1 0."" .1

".40 ".>4 ". 2.=%

'.8" 8.1" '.&8 %.2>

Ap1!

0-4

4

4'

"0

2ilt loam

0.10

'.>

8.1>

Ap"!

4-14

5"'

14-"

;1!

"->"

;"!

>"-1'0

1" 11 18 4 1

40 4" > 44 =1

1 14 1 1> 1>

2ilt loam 2ilt loam 2ilt loam 2ilt loam ,,

0.14 0.1 0."0 0.0& .1%

'. 8."' '.44 8.1 %.1

"."0 .8 ".1 ".& 3.%

Ap!

0-1



8

0

2ilty clay

0.11

0.&0

>.0"

A11!

1-'0

5"'

'0-8'

> 8

80 '4

8 &

;lay ;lay

0.1 0.11

0.48 0.>'

>.10 .80

 ean

Na"ina$ar

and0 silt ratio

0-10

 ean

Nasirna$ar

etural class

Ap1

 ean

ha$u

article sie distri"ution

- ' -

;1

8'-

;"

-1"0

' 

'4 41

>0 "8

 ean



%8

%9

rand  ean

12

82

28

;lay 2ilty clay loam ,,

0.0 0.04

0.>1 ".&>

.00 ".0

.1

1.18

.

.1=

3.38

%.3

7!* F #y!roscopic oisture

5ased on the sand content, the studied pedons show the followin! !radation.  Balagan > (asirnagar

> Phag, >  (abinagar

he trend of vertical distribution of sand fraction in the various soil profiles is presented in *i!ure- 1'. he vertical distribution of sand indicates that its content is almost similar in :ha!u and asirna!ar series. +n 5ala!an3 series, the sand percent in the ;-horiBon was "&  percent and very lower content of sand fraction was found in the ;-horiBon of abina!ar  series. Ecept abina!ar series sand percenta!e were !radually hi!her in lower horiBon than those of the upper horiBon. his irre!ularity in sand distribution pattern is thou!ht to be related to the depositional process of the parent material. +n other words the irre!ularity is !eo!enic rather than pedo!enic in nature. +t may be concluded that the parent materials of  the present soils were homo!eneous. he very low percenta!e of sand fraction in the studied soils indicates the !eneral characteristics as observed by 5rammer $1&41(.

ilt fraction 2ilt was the dominant fraction of the soils of 5rahmanbaria districts. he silt content of the studied soils ran!ed from '4 to 44 percent with a mean value of >" percent. he result  presented in able - 1 shows that ecept abina!ar series, silt was the dominant siBe fraction. #owever, the vertical distribution of silt fraction is more or less similar in the soil  profiles $*i!ure- 18(. 2uch a hi!h level of silt content is possibly the conse6uence of nature of the parent material. 5ased on the percent silt content, the studied pedons show the followin! !radation.

 (asirnagar > Phag, > Balagan > (abinagar

- 8 -

he sandGsilt ratio of the studied soil profiles ran!es from 0.04 to 0.8> with a mean of 0.14 $able - 14(. he hi!hest mean of sandGsilt ratio is found in the 5ala!an3 series whereas the lowest ratio is found in the abina!ar series.

Cla+ (colloidal) fraction  he colloidal fraction represents the clay fraction. he clay content of the studied soils varied from  to >0 percent with a mean value of "> percent $able - 14(. his indicates that clay was one of the dominant siBe fractions in most of the investi!ated soils. he hi!hest avera!e value for clay was observed in the abina!ar soil $8&%( and the lowest value was in

-  -

  e    h    t   n    i   n   o    i    t   c   a   r   n    f   o    d   i   n   t   a   a   !    2   i    f    t   s   o   e   n   v   n   o   i    i    t   r   u   e    b    d    i   r   n    t   s   u    i   s    d   l    l    i   a   o   c   s    i    t   r   e    7   C    &  .   !    i    *

- > -

  e    h    t   n    i   n   o    i    t   c   a   r   n    f   o    t    l    t    i    i    2   a   !    f    i   o   t   s   n   e   v   o    i   n    t    i   u   r    b   e    i   r    d    t   s   n    i   u    d   s    l    l   a   i   c   o   s    i    t   r   e    7   C    0    1  .   !    i    *

- 4 -

  e    h    t   n    i   n   o    i    t   c   a   r   n    f   o    t    l    t    i    i    2   a   !    f    i   o   t   s   n   e   v   o    i   n    t    i   u   r    b   e    i   r    d    t   s   n    i   u    d   s    l    l   a   i   c   o   s    i    t   r   e    7   C    0    1  .   !    i    *

- 4 -

  e    h    t   n    i   n   o    i    t   c   a   r    f   n   o   y   i   a   t    l   a    ;   i   !    f    t   o   s   e   n   v   o   n    i    t    i   u   r   e    b    i   r    d   n    t   s   u    i   s    d   l    l    i   a   o   c   s    i    t   r   e    7   C    1    1  .   !    i    *

-  -

  e    h    t   n    i   n   o    i    t   c   a   r    f   n   o   y   i   a    t    l   a    ;   i   !    f    t   o   s   e   n   v   o   n    i    t    i   u   r   e    b    i    d   r    t   n   s   u    i   s    d   l    l    i   a   o   c   s    i    t   r   e    7   C    1    1  .   !    i    *

-  -

the 5ala!an3 profile $18%(. 5ased on the percent clay content, the studied pedons show the followin! !radation.  (abinagar > Phag, > (asirnagar

> Balagan 

he hi!h clay content in the abina!ar soil may be attributed to the hi!her clay content in their parent materials. +t has been stated that these soils have formed in the lower part of  the depressions where more clay is accumulated compared to that in the levees. he vertical distribution pattern of clay in the soil profiles is shown in *i!ure - 1. +t is evident that the distribution of clay in the profiles is very much irre!ular. his irre!ularity in clay distribution may be attributed to !eolo!ical processes rather than the pedolo!ical ones. +ncrease in clay content in lower horiBons is found in abina!ar series. #i!h accumulation of clay in the lower horiBons is a common feature of the seasonally flooded wetland soils of 5an!ladesh. +mpoverishment of clay in the upper horiBons of the soil profiles is an important feature in some seasonally flooded soils where ferrolysis is a common soil formin! process $5rammer, 1&>8F 5rinman, 1&41(. he siltGclay ratio of the studied soils varies from 0.>1 to .00 with a mean value of '.'>. he hi!hest decrease in clay content was observed in top 1 cm of 5rahmaputra

the 5ala!an3 profile $18%(. 5ased on the percent clay content, the studied pedons show the followin! !radation.  (abinagar > Phag, > (asirnagar

> Balagan 

he hi!h clay content in the abina!ar soil may be attributed to the hi!her clay content in their parent materials. +t has been stated that these soils have formed in the lower part of  the depressions where more clay is accumulated compared to that in the levees. he vertical distribution pattern of clay in the soil profiles is shown in *i!ure - 1. +t is evident that the distribution of clay in the profiles is very much irre!ular. his irre!ularity in clay distribution may be attributed to !eolo!ical processes rather than the pedolo!ical ones. +ncrease in clay content in lower horiBons is found in abina!ar series. #i!h accumulation of clay in the lower horiBons is a common feature of the seasonally flooded wetland soils of 5an!ladesh. +mpoverishment of clay in the upper horiBons of the soil profiles is an important feature in some seasonally flooded soils where ferrolysis is a common soil formin! process $5rammer, 1&>8F 5rinman, 1&41(. he siltGclay ratio of the studied soils varies from 0.>1 to .00 with a mean value of '.'>. he hi!hest decrease in clay content was observed in top 1 cm of 5rahmaputra *loodplain, e!hna ?iver *loodplain and Old #imalayan :iedmont :lains$about 0%( followed by ista *loodplain, 5arind ract, adhupur ract and ;hitta!on! ;oastal :lain$'0-80%(. 5ut in lowland situation, decrease in clay content in ur*a @ush+ara 'loodplain is comparatively low $about "0%( $5A?;, 1&&&(.

o sum up the results of particle siBe distribution in the investi!ated wetland soils, it may  be stated that 9  a. 2ilt is by far the dominant siBe fraction in the studied wetland soils and therefore,  played a si!nificant role in mouldin! the physical properties of these soils.  b.

;lay is the dominant siBe fraction in the abina!ar series.

c. he vertical distribution of sand and clay fractions in the profiles is irre!ular. d. Ecept abina!ar series the vertical distribution of silt content in the studied  profiles are more or less re!ular. e. he mean sand, silt and clay contents in the studied soils are 1", >" and "> percent respectively.

- & -

f. he sand content is much lower in these soils $avera!e 1"%(. his is the common feature in many of the wetland soils in the seasonally flooded basin areas of  5an!ladesh. !. *inally it may be concluded that the parent materials of the soils under the investi!ation can be considered as more or less homo!eneous.

8.2.2 7+$roscopic !oisture he amount of moisture retained by air-dry soils $#y!roscopic oisture( has been  presented in able - 14. he hy!roscopic moisture in the soils ran!ed from 1.'4 to >.10  percent. he mean value of hy!roscopic moisture in the soils is '.4 percent. he hi!hest hy!roscopic moisture percent was recorded in the :ha!u series. he soils of the 5ala!an3 series contain the lowest hy!roscopic moisture. 2uch a variation in moisture content retained by air- dry soils is possibly due to the difference in their clay and or!anic matter  content. A hi!hly si!nificant positive correlation was found between percent clay and  percent hy!roscopic moisture content in the studied soils, the WrI value bein! T 0.> $*i!. 1&(.

8.3 Che*ical properties

>.'.1 2oil reaction $p#( 2ol reaction is the most important characteristics of soils in the wetland area. here can be three types of soil reactionC acid, alaline and neutral. 2oil acidity is common in all re!ions where precipitation is hi!h enou!h to leach appreciable amount of echan!eable bases from the surface layers of the soils so that the echan!e comple is dominated by hydro!en ions. he soil p# plays a very important role in !roupin! the soils into different classes. +t has direct influence on the availability of nutrients to plants and hence special emphasis is !iven on it. +t has a profound influence on many factors connected with the suitability of a soil for a!ricultural use and hence special importance has been !iven to it $ruo!, 1&>1(. he p# value of the studied wetland soils ran!ed from >.1 to 4.8 with a mean of >.& $able- 1(. he soils, therefore, have sli!htly acidic to neutral in reaction. +n each soil  profile there is a trend of increasin! p# with depth $*i!- "0(. evertheless, the surface soil

- &0 -

of each profile shows a sli!htly acidic in reaction. he increase of p# with depth is a common feature in many of the seasonally flooded soils of 5an!ladesh. his has been

7    ) 6    %    (   e   r   u 5    t   s    i   o 4   m   c    i   p 3   o   c   s 2   o   r   g   y 1    H

r = +065!!  " = 277 + 005#

0 5

15

25

35

45

55

65

Percent clay content

*i!. 1"C ?elationship between clay content and hy!roscopic moisture in the studied soil.

- &1 -

attributed to the alternate oidation and reduction conditions in the seasonally flooded,  poorly drained soils $:onnamperuma, 1&(. ost of the wetland soils of 5an!ladesh contain low or!anic matter ran!es from 1 to "%. he decomposition and mineraliBation of  or!anic matter are interrelated with successive microbial chan!es and are accompanied by a stepwise bio-chemical and chemical reduction of the soils resultin! in the lowerin! of  redo potential and chan!in! of p# to near neutral $#u6 et al.1&&'(.

+n most wetland soils of 5an!ladesh the p# value, in !eneral, is around 4.0 $2aheed and #ussain, 1&&"(. ry topsoil p# of 2urma-/usiyara floodplain and estuarine ran!ed from 8. to >.'. +t is lower in tertiary sediments which ran!ed from 8." to 8.&. he subsoil p# of  2urma-/usiyara floodplain ran!es from 8. to >.", in the estuarine floodplain it is .' to 4.1. he substratum of 2urma-/usiyara floodplain soils ran!es from . to >., in estuarine floodplain it is . to 4." $2?+ staff, 1&4'(.

)hen an 1 /;l solution was used in place of water for determination of p# in the soils there was a decrease in p# value $*i!. - 1(. his chan!e in p# value has been denoted as ]p#. he ]p# values of all the soils under study were ne!ative. his indicates that the clay minerals havin! permanent ne!ative char!e are more than those havin! p# dependant ne!ative char!e. he ]p# value of the soils ran!es from -0.> to -0.&, indicatin! that the soils contained very small 6uantity of reserve acidity $able- 1(. his indicates that the studied wetland soils of the basin area contain clay minerals havin! more permanent ne!ative char!e than the p# dependent ne!ative char!e. his is epected as the soils remain inundated with water both from rain or river durin! the monsoon season and some  part of the dry season, when the #T in the echan!e phase is washed out. he low ]p# value may also be indicative of the low cation echan!e capacity which is a notable feature of these soils. he distribution pattern of ]p# value within the soil profiles was more or less re!ular. he ]p# value was lower in the surface soils than in the subsoils.

- &" -

Table- 13: oil reaction of the st,died soil oil series

7orion

Depth (c*)

4ala$an<

Ap1

0-10

5"1!

10-""

5""!

""-'4

5"'

'4-4

5'

4-0

;1

0-1"0

Ap1!

0-10

Ap"!

10-"0

5"1!

"0-'0

5""!

'0-1

;1!

1-4>

Q;"!

4>-1"0

Ap1!

0-4

Ap"!

4-14

5"'

14-"

;1!

"->"

;"!

>"-1'0

Ap!

0-1

A11!

1-'0

5"'

'0-8'

;1

8'-

;"

-1"0

 ean

ha$u  ean

Nasirna$ar  ean

Na"ina$ar  ean rand 

Δp7

p7 725

@Cl

>.8 >.& >.& >.& >.& >. 8.= >.1 >.& 4.0 4." 4." 4.0 8.9 4.0 >.& 4.1 >.8 4.0 8.9 >.1 >.& 4.8 4.8 4.8 =. 8.9

.> >." >.1 >." >." . 8. . >." >.' >.' >.' >.1 8.1 >." >.0 >.' >.0 >.1 8.1 .' >." >. >. >. 8.2 8.1

-0. -0.4 -0. -0.4 -0.4 -0.4 ,.= -0.> -0.4 -0.4 -0.& -0.& -0.& ,.> -0. -0.& -0. -0. -0.& ,.> -0. -0.4 -0.& -0.& -0.& ,.> ,.>

 ean Δp7 = pH (KCl) – pH ( #"O(

One of the main ob3ectives of ]p# determination was to !et a measure of echan!eable #T on the surface of the soil colloids. A portion of the echan!e sites on the surface of soil colloids is occupied by echan!eable #T. @nder this circumstance, when 1 /;l is added to the soil, the dissociated / T  ion replaces the absorbed #T and the replaced #T ion on comin! to the solution phase depresses the p# value of the soil suspension.

he vertical distribution of p# $#"O( in all of the studied profiles showed an increasin! trend with the increase in depth $*i!. 14(. he p# of the studied soils was sli!htly acidic near the surface horiBon and !radually became neutral in the deeper layer. his increase

- &' -

has been attributed to the alternate oidation and reduction conditions in the seasonally flooded, poorly drained soils $:onnamperuma, 1&(. he increase of p# with depth is a common feature in many of the seasonally flooded soils of 5an!ladesh $u3ib, 1&>&F 5rammer, 1&41 and atin, 1&4"(. 5ut the p# values of the asirna!ar series did not show the increasin! trend with depth. )ith the recedin! of the !round water table, the ferrous iron is oidiBed and the p# naturally drops first in the surface horiBon or up to oidiBed Bone. +n the subsoil Bone the soluble bases have only restricted movement where the internal draina!e is poor. *or this reason, the p# in the subsoils tends to remain at a hi!her  level as compared to that in the surface soils. A hi!hly si!nificant positive correlation was found between p# $#"O( and p# $/;l( in the studied soils, the WrI value bein! T 0.&8 $*i!. - 1&(.

- &8 -

  s    l    i   o   s   e    h    t   n    i    (    O    "    #    $

  n   o    #   i    t   p   a    f   !   o    i    t   n   s   e   o    i    t   v   n   u    i    b   r    i   r   e    t    d   s   n    i    d   u    l   a   c    i    t   r   e    7   C    '    1  .   !    i    *

- & -

- &> -

- &> -

$ 7 6 5 4

pH (H2,)

3

pH (*l)

2

$ 7 6 5 4

pH (H2,)

3

pH (*l)

2 1 0 alagan&

P'agu

asirnagar ainagar  

'i$. 1%;  co*parison of p7 (7 25) with p7 (@Cl) in the studied wetland soils

- &4 -

*i!. 1C ?elationship between p# $# "O( and p# $/;l( in the studied soil.

8.3.2 5r$anic *atter

- & -

Or!anic matter is the store house of all plant nutrients. +t influences physical, chemical and  physico-chemical properties of soils far out of proportion to the small 6uantities present. Or!a Or!ani nicc matte atterr supp suppli lies es ener ener!y !y and and body body-b -bui uild ldin in! ! cons consti titu tuen ents ts for for most most of the the microor!anisms which is important for soil. ?ole of or!anic matter in improvement of soil structure, structure, water and nutrient holdin! capacities capacities in li!ht soils, release of available nutrients from native sources, control of soil erosion and supply of food and ener!y for beneficial soil microbes are well established facts $+slam, 1&&'(. +n most of the mineral wetland soils of 5an!ladesh, or!anic matter content is very low. ore than half of the soils have or!anic matter in the ran!e of 1 to "% $#u6 et al. 1&&'(. 2?+ has analyBin! about 11,000 11,000 samples from "00 representative representative soil profiles coverin! a!riculturally important areas of 5an!ladesh found that the or!anic matter contents of  soils were !enerally lowF it ran!es from 0.' to 1.% in upland soils, 1. to " in medium lowland and " to '.% in the lowland areas. +n beel areas, this fraction is about 8% $?ahman, 1&&0(. Dow-lyin! areas of most floodplains have a !ood reserve of or!anic matter, hi!her than that in hi!h land or medium-hi!h medium-hi!h land. hese soils remain under water for a considerable considerable  period of time of a year. 2o, little decomposition of or!anic matter can c an occur. occu r. oreover a lar!e number of a6uatic weeds !row which add or!anic matter to these soils $*[email protected]:, 1&(. he rapid decomposition and loss of or!anic matter from the soil are the usual  process in tropical climatic condition. any reports show rapid depletion of the soil or!anic matter resultin! in decline in soil fertility and subse6uent decrease in crop yield $:ortch and +slam, 1&8F 5huiya, 1&4 and 5A?;, 1&&4(.

Or!anic Or!anic carbon percenta percenta!e !e in the 2urma2urma-/usi /usiyar yaraa floodpla floodplain in ran!es ran!es from 0.' to 1.  percent in the topsoil of the floodplain and rid!e soils and from 1. to .> percent in basin soils $2?+ 2taff, 1&4'(. he or!anic carbon was found in the studied soils ran!es from 0.'8 to 0.&0 with a mean value of 0.>' percent. ?esults of the or!anic matter content of the studied soils from the wetland areas of  5rahmanbaria district indicate that the percenta!e of or!anic matter ran!es from 0. to 1. with a mean of 1.10 percent $able- 1&(. he abina!ar series contains hi!h amount

- && -

Table- 14: 'rganic matter and nitrogen contents of the st,died soil  oil eries

7orion

Depth

: 5C*

: 5!**

otal N

C0N***

(:)   Ratio Ap1 0-10 0 . 8 1 .8 8 0.11 4 5"1! 10-"" 0 .4  1 .' 0 0.10 4 5""! ""-'4 0 .4 0 1 ." 0 0.11 > 5"' '4-4 0 . > 0 .& > 0.0  5' 4-0 0 . 0 0 .& > 0.0 > 4ala$an< ;1 0-1"0 0 .' 8 0 .  0.0   ean .82 1.1 .9 8 Ap1! 0-10 0 . > 1 .8  0.0&  Ap"! 10-"0 0 .4 0 1 ." 0 0.04 11 5"1! "0-'0 0 . > 0 .& > 0.0 11 5""! '0-1 0 . > 0 .& > 0.04  ; 1 !  1 4 > 0 .' 8 0 .  0.04  ha$u Q;"! 4>-1"0 0 .' 8 0 .  0.04   ean .8 .98 .= > Ap1! 0-4 0 .  1 . 1 0.10  Ap"! 4-14 0 .4 0 1 ." 0 0.10 4 5"' 14-" 0 .>  1 .1 " 0.04 & Nasirna$ar ;1! "->" 0 . > 0 .& > 0.0 4 ;"! >"-1'0 0 . 0 0 . > 0.0&   ean .8 1.13 .9 = Ap! 0-1 0 .& 0 1 .  0.10 & A11! 1-'0 0 .4 ' 1 ." > 0.0&  5"' '0-8' 0 .>  1 .1 " 0.0  Na"ina$ar ;1 8'- 0 . > 0 .& > 0.0> & ;" -1"0 0 . > 0 .& > 0.0> &  ean .8> 1.1= .> 9 rand ean .83 1.1 .> > 5CG Z Or!anic carbonF 5!GG ZOr!anic matterF C0NGGG Z ;arbon G itro!en (c*)

of or!anic matter throu!hout the profile. All the soil profiles contained hi!her amount of  or!anic matter in the surface than the subsoil $able- 1&(. *rom the results it may be concluded that the studied soils contain low amount of or!anic matter $5A?;, 1&&(. his findin! was in a!reement with the findin!s of #u6 $1&&0(, who reported that most a!ricultural soils of 5an!ladesh have low or!anic matter content. edium content of or!anic matter was found in the surface soils of 5ala!an3, abina!ar,  asirna!ar and :ha!u series which contains 1.88, 1., 1.1 and 1.8 percent or!anic matter. 2ince these soils remain flooded for >-4 months every year, the or!anic matter  decomposition is bein! retarded seasonally. oreover the medium amount of or!anic

- 100 -

matter at the surface may be attributed to maimum root activities of !rowin! crops as well as natural and artificial artificial addition of fresh and partly decomposed or!anic materials materials in the form of farm yard manures and crop residues. he hi!hest mean value of or!anic matter was found in the soils of the abina!ar abina!ar series. Dow content of or!anic or!anic matter may  be caused by rapid decomposition of or!anic residues because of hi!h temperature and rainfall, rainfall, hi!her croppin! intensity under tropical conditions. 5ased on the percent or!anic matter content, the studied pedons show the followin! !radation.  (abinagar > Phag,> (asirnagar

> Balagan

he or!anic matter content in the studied soils show a !eneral tendency of decrease with depth in all the pedons and the decrease is more or less !radual which is a si!n of their  maturity $able- 1&(.

8.3.3 otal Nitro$en and C0N ratio otal otal nitro!en contents in the studied wetland soils ran!ed from 0.0 to 0.11 percent with a mean of 0.0 percent $able- 1&(. he hi!hest mean value of nitro!en content amon! the  profiles was found f ound in the 5ala!an3 and asirna!ar series whereas the lowest amount was found in the :ha!u series. he total nitro!en contents in the mineral wetland soils ran!es from 0.0 to 0.1 percent $#u6 et al. 1&&'(. +n 2urma-/usiyara 2urma-/usiyara floodplain and old e!hna estuarine floodplain soils nitro!en ran!es from 0.0" to 0.0& percent in topsoils. 5oth carbon and nitro!en contents !enerally decreases re!ularly with depth $2?+ 2taff, 1&4'(. hese features were also similar in the studied soils.

he vertical distribution pattern of total nitro!en follows closely the se6uence of or!anic matter $*i!. "0(. #i!her amount of nitro!en content are found in the surface horiBons than the underlyin! horiBons. A positive correlation was found between or!anic matter and total nitro!en contents of the soils with a correlation $r( of T0.4> $*i!. "1(. he 6uantities of  or!anic matter and total nitro!en are low in the seasonally flooded wetland soils of  5an!ladesh $2?+ 2taff, 1&4'(.

he ;G ratio of the studied soils ran!ed from  to 11 with a mean value of  $able$able- 1&( his indicates that the or!anic matter fraction is hi!hly oidiBed even if these soils remain flooded for more than  months or more in a year. he microbial activity in these soils

- 101 -

appears to be 6uite vi!orous. he ;G ratio within the soil profiles showed irre!ular   patterns.

his sort of irre!ular pattern is 6uite common in the floodplain soils of 

5an!ladesh $a3umder, 1&&>, #ussain et al., 1&&(. Menny $1&>0( also noted that in some !reat soil !roups the ;G ratio was variable within the sin!le soil profile. he ;G ratio of  the soils of 2urma-/usiyara and old e!hna estuarine floodplain soils was mainly  between > and 1 $2?+ 2taff, 1&4'(.

- 10" -

  e    h    t   n    i   n   e   !   o   r    t    i    %  n    l    i   o   a   t    t   o   a   !       i    f    t   o   s   e   n   v   n   o   i    i    t   r   u   e    b    d    i   r   n    t   s   u    i   s    d   l    l    i   a   o   c   s    i    t   r   e    7   C    >    1  .   !    i    *

- 10' -

*i!. 14C ?elationship between or!anic matter and total nitro!en in the studied soils

8.% h+sico,che*ical properties of the soils - 108 -

8.%.1 Cation echan$e capacit+ he cation echan!e capacity $;E;( is an important soil physico-chemical property that is used for classifyin! soils in 2oil aonomy and for assessin! their fertility $5rady, "00"(. ;E; is defined as the amount of a cation species bound at p# 4 or another suitable p# dependin! on the method used for its measurement. 2ometimes it is called otal Echan!e ;apacity or 5ase Echan!e ;apacity. ;E; is a very important property of soils for   predictin! their 6uantity and types of clay minerals and their nutrient holdin! capacity $Dandon, 1&&1(. +t also plays a vital role in determinin! the trend and type of pedo!enic  processes of soils $5uol et. al., 1&0(. he weatherin! sta!e of soils can also be conveniently determined or predicted by their cation echan!e capacity. he cation echan!e capacity of the studied wetland soils ran!es from 1'.18 to "8.> cmol $pT( /!-1 with a mean value of 1&.1 cmol $pT( /!-1 $able- "0(. hese results indicate that the clay rich soils have hi!her ;E; values. 5ecause fine tetured soils tend to have hi!her  ;E; than sandy or coarse tetured soils. 2andy soils have lower ;E; than clayey soil  because the coarse tetured soils are commonly lower in both clay and humus content. +ncrease in ;E; values with increase in clay contents in soils has been reported by many authors $Hupta and isra, 1&40 and :atha et. al., 1&0(. A!ain the cation echan!e capacity of most soils increases with increasin! p#. he cation echan!e capacity of the soils is p# dependent $Macson, 1&F ;hapman, 1&>(. ;ation echan!e capacity of soils are influenced by a number of factors, which may be enumerated as or!anic matter  content, clay content, free iron oides etc. $;ampbell and ;larid!e, 1&4F awson et. al., 1&&1(.

At low p# values, the cation echan!e capacity is also !enerally low $5rady,

"00"(. he hi!hest mean value of the ;E; amon! the profiles was found in the abina!ar series $"1.&8 cmol $pT( /!-1( and the lowest in the 5ala!an3 series $1>.>0 cmol $pT( /!-1(. he variation of ;E; values of the pedons studied reflects the influence of both the clay and or!anic matter content of these soils. he ;E; of mineral wetland soils ran!es between 10 and "0 cmol $pT( /!-1. ore than >0% of the mineral wetland soils have ;E; values ran!in! from 10 to "0 cmol $pT( /!-1 and these values rarely eceed the value 8 cmol $pT( /!-1. he ;E; of or!anic soils may eceed "00 cmol $pT( /!-1 $)ilander, 1&>(.

Table- 26: Cation e!change capacity and e!changeable cations of the st,died soil  - 10 -

oil eries

7orion

Depth

C#C

CaEE

!$EE

NaE E

C*ol (p ) @$

0-10

"0.8'

&.>8

>.8"

0.4

0.'

14.1'

5"1!

10-""

5""!

""-'4

5"'

'4-4

5'

4-0

;1

0-1"0

Ap1!

0-10

Ap"!

10-"0

5"1!

"0-'0

5""!

'0-1

;1!

1-4>

Q;"!

4>-1"0

Ap1!

0-4

Ap"!

4-14

5"'

14-"

;1!

"->"

;"!

>"-1'0

Ap!

0-1

A11!

1-'0

5"'

'0-8'

;1

8'-

;"

-1"0

1.'0 14.00 1>."0 18.4 1'.18 18.8 1&.&" "1.>8 "1.8" 1>.4 1&.00 1>.41 19.2% "0. "0.0 "0.41 "".0 14.18 2.28 "".14 "0.84 "'.0 "8.> 1&.8" 21.9% 19.1

4.0 >. 4.1" >.'& ."' =.2 10."8 11."0 10.> .'8 &.0 .80 9.=1 11.0 11."> 11.0 11." .84 1.=8 10."> &."& &.44 10.10 .8' 9.= 9.31

.0 8.&0 ."1 8."1 '.&0 .2 4.8" 4.>0 4.1 .80 >.8 .>4 8.= >." >.0" .&4 4.'> 8.44 8.2 4.>0 >.4' 4." .0 >.& =.% 8.33

0.& 0.& 1.08 1.10 1.14 1.1 0.&0 0.& 1.01 1.0' 1.0& 1.00 1. 1.00 0.&0 1.0> 1.08 1.11 1.2 1.0' 1.0 1.10 1."1 1." 1.13 1.%

0.8" 0.8 0. 0.' 0.> . 0.'> 0.' 0.8 0.>8 0.>& 0.41 . 0." 0.'0 0.'0 0.'' 0.'' .31 0. 0.&8 0.&0 0.4 0." .> .%>

18.40 1'.1 1'.&" 1"."' 10.& 13.=2 1.&" "0.1' 1&.>" 1.81 14." 1. 1=.98 1&.>0 1.8 1.' "0." 18.> 1>.23 1&.48 14.&" 1&.8 "0.18 14.0& 1>.9 1=.2

0 4  ' 8 >3 & &' &" &" &' &8 93 &" &"  &0  >9 &   "  >8 >>

 ean

Nasirna$ar  ean

Na"ina$ar  ean rand 

4*

Ap1

 ean

ha$u

#4*

,1

* 

(c*)

4ala$an<

@ E

 ean #4G Z otal echan!eable basesF 4GG Z 5ase saturation percenta!e

- 10> -

  e   !   n   a    h   n   o   c   i   ,   t    E   a   !    i   n   t   s   o    i    t   e   a   v   n    ;   i    f   r   o   e   n   d   o   n    i    t   u   s   u   l    i    b    i   r   o   s    t   s   e    i    d   h    l    t   n   a   i   c    i   y    t   r    t   e   i   c    7  a   C   p       a    1   ;  .   !    i    *

- 104 -

*i!. 1&C ?elationship between ;lay and ;E; in the studied soils

- 10 -

30    0 25   g    * 20    )    +   p    (    l 15   o   m   c    . 10            5    1   /

r = +046!!  " = 143$ + 46#

0 0

05

1

15

2

,rganic matter (%)

*i!. "0C ?elationship between or!anic matter and ;E; in the studied soils

- 10& -

he ;E; is relatively hi!her in or!anic wetland soils than mineral wetland soils because of substantial presence of clay $around >0 percent( in addition to the or!anic matter $#u6, 1&&'(. 5rinman found ;E; of clay around "4 cmol $p T( /! -1F and of silt T sand around  cmol $pT( /!-1  in the soils of 2urma-/usiyara floodplain $2?+ staff, 1&4'(. he distribution patterns of cation echan!e capacity in the studied profiles showed more or  less an irre!ular trend with depth $*i!.-""(.

8.%.2 #chan$ea"le cations ?esults of echan!eable cations in the studied soils are presented in able- "0. he amount of echan!eable ;aTT ran!es from ."' to 11." cmol $pT( /!-1 with a mean of  &.'1 cmol $pT( /!-1. Echan!eable ;aTT is by far the most dominant metal ion in the soils. 2imilar result was also reported by 2?+ 2taff in most of the soils of 5rahmanbaria district $2?+ 2taff, 1&4'(. he hi!hest echan!eable ;a TT  was found in the soils of   asirna!ar series while the lowest value was found in 5ala!an3 series. he predominance of  ;aTT was reported by Heor!e et. al. $1&( in some humic !ley soils of Ohio. he vertical distribution of echan!eable ;aTT in the profiles shows an irre!ular trend. +t was observed that all the profiles contain hi!her amount of ;a TT in their surface soils due to their seasonal submer!ence. he percenta!e composition of the echan!eable ;aTT varies from 8 to >0 percent with a mean of 8 percent $able- "1(. he echan!eable !TT content in the soils ran!ed from '.&0 to .0 cmol $pT( /! -1 with a mean of >.'' cmol $pT( /! -1. On the 6uantitative basis, echan!eable !TT comes after  echan!eable ;aTT. he hi!hest mean value of echan!eable !TT amon! the profiles was found in the abina!ar series J4.80 cmol $pT( /! -1K and the lowest in the 5ala!an3 series J.0" cmol $pT( /! -1K. he percenta!e composition of the echan!eable !TT varies from '" to 80 percent with a mean of '> percent $able - "1(. he ;aTTG!TT ratio of the studied soils varies from 1." to 1.& and the mean ratio was 1. $able- ""(. +n almost all the soils of the 2urma-/usiyara and old e!hna estuarine floodplain, ;a TT eceeds !TT,  but the ratios are variablesF most of them lie between " and 8 and the trend of ;aTTG!TT ratio down the profile often irre!ular $2?+ 2taff, 1&4'(.

- 110 -

he hi!hest mean ;aTTG!TT amon! the profiles was found in asirna!ar series and the lowest in the abina!ar series. #ussain and ;howdhury $1&0( reported an echan!eable ;aTTG!TT ratio of around " in some poorly drained wetland soils of 5an!ladesh. he ;a T T

G!TT ratio in soils decrease with increasin! maturity of the soils $5uol et. al., 1&0(. he

echan!eable ;aTTG!TT ratio of a!ricultural soils of ;alifornia was ".8& and of Danna soil in 2weden was '.0> $5ohn et. al., 1&4&(. +t appears that the seasonally flooded soils of 5an!ladesh are similar to those of the other countries in respect of ;a TTG!TT ratio. he above results of echan!eable ;aTTG!TT ratio indicate that the seasonally flooded soils in 5an!ladesh are immature.

he amount of echan!eable aT ion varied from 0.4 to 1." cmol $pT( /!-1 with a mean of 1.08 cmol $pT( /! -1. he hi!hest mean echan!eable aT within the profile was found in abina!ar series J1.1' cmol $pT( /!-1K whereas the lowest was found in the :ha!u series J1.00 cmol $pT( /!-1K. he seasonally flooded soils are so intensely washed that Echan!eable aT can never be a problem. he vertical distribution pattern of  echan!eable aT in all the profiles was more or less irre!ular.

he amount of echan!eable / T in the studied soils ran!ed from 0." to 0.&8 cmol $p T( /!-1 with a mean value of 0.8 cmol $pT( /!-1. he hi!hest mean echan!eable / T within the profile was found in abina!ar series J0. cmol $pT( /!-1K whereas the lowest was observed in the asirna!ar series J0.'1 cmol $pT( /! -1K. he echan!eable / T content in the studied wetland soils indicates that these soils are not deficient in / T and little amount of potassic fertiliBer will be needed. he percent composition of echan!eable / T ran!es from 1 to > with a mean of 8 $able- "1(. he hi!hest percenta!e was found in the soils of  the abina!ar series and the lowest in those of the asirna!ar series. +n an “ideal soil” the cationic composition in the echan!e comple was as followsC ;aTT > percentF !TT 10 percentF / T  percentF #T "0 percent $oth, 1&>(. On this basis the wetland soils under the present investi!ation may be considered as very close to the “ideal soil”. Henerally in the studied soils, the value of ;a TT and !TT increased !radually from basin to basin depressions. Echan!eable aT and / T content were hi!h in basin depressions.

- 111 -

Table- 21: 9es,lts of percent composition of the e!changeable metal  ions in the e!change comple! of the st,died soils oil eries

4ala$an<

7orion

Depth (c*)

Ap1

0-10

5"1!

10-""

5""!

""-'4

5"'

'4-4

5'

4-0

;1

0-1"0

Ap1!

0-10

Ap"!

10-"0

5"1!

"0-'0

5""!

'0-1

;1!

1-4>

Q;"!

4>-1"0

Ap1!

0-4

Ap"!

4-14

5"'

14-"

;1!

"->"

;"!

>"-1'0

Ap!

0-1

A11!

1-'0

5"'

'0-8'

;1

8'-

;"

-1"0

 ean

ha$u

 ean

Nasirna$ar

 ean

Na"ina$ar

 ean rand ean

EE

Ca > ' " 0 " 8 2 8  8 8 ' ' % & >0 >0 4  9 " 1 0 0 0 1 %

ercent co*position !$EE NaE '4  ' > '4 4 '  '8 10 '> 10 3= > '  '  '  ' 4 '4 > ' 4 38 = '  ''  '" > '>  '"  33 8 '&  ' > '& > 80 > ' 4 39 8 38 =

@ E " ' 8 8 8 > % " " ' 8 8  3 1 " " " " 2 8   8   %

Table- 22: ome important Chemical properties of the st,died soils oil eries

4ala$an<

7orion

Depth (c*)

Ap1

0-10

5"1!

10-""

5""!

""-'4

5"'

'4-4

5'

4-0

Ratio

;aTTG!TT 1.

 aTG/ T ".'

1.8 1.8 1.' 1.

".' ".1 1.& ".1 - 11" -

;1

0-1"0

1.'

1.4

- 11' -

 ean

1.%

2.1

- 118 -

Ap1!

0-10

1.8

".

- 11 -

Ap"!

10-"0

1.

".

- 11> -

5"1!

"0-'0

1.8

1.&

- 114 -

5""!

'0-1

;1!

1-4>

Q;"!

4>-1"0

Ap1!

1. 1.8 1. 1.

1.> 1.> 1. 1.9

0-4

1.4

'.>

Ap"!

4-14

5"'

14-"

;1!

"->"

;"!

>"-1'0

1.& 1. 1.> 1. 1.>

'.0 '. '." '.8 3.3

Ap!

0-1

1.8

1."

A11!

1-'0

5"'

'0-8'

;1

8'-

;"

-1"0

 ean

1.8 1.' 1." 1.' 1.3

1." 1." 1.> 1. 1.3

rand ean

1.

2.2

ha$u  ean

Nasirna$ar

 ean

Na"ina$ar

- 11 -

*i!. "1C ?elationship between p# $# "O( and percent base saturation in the studied soil.

- 11& -

8.%.3 4ase saturation percenta$e he percenta!e of the ;E; of any soil that is satisfied by the base formin! cations is termed as the base saturation percenta!e $52:(. he 52: of a soil is very important for   predictin! the runnin! !enetic processes in soil as well as its sta!e of development. he 52: values have also been used in soils for their classification $2oil 2urvey staff, 1&4(.

he percent base saturation of the studied soils ran!ed from 4 to & with a mean value of  $able- "0(. he hi!h base saturation may be due to rapid replenishment of bases from the weatherin! minerals. he hi!hest mean value amon! the profiles was found in the :ha!u series $&'( and the lowest in the 5ala!an3 series $'(. he 52: was found to be lower in the surface horiBon of the soils and hi!her in the underlyin! horiBon. +n 5an!ladesh, Ali $1&&8( noted that the base saturation was hi!h in some alluvial soils of the 5rahmaputra floodplains. A ne!ative correlation was found between p# $#"O( and  percent base saturation in the studied soil, the WrI value bein! - 0.1' $*i!. - "1(.

8. Cla+ *ineralo$ical co*position ;lay mineral contents can be used as important criteria for soil classification $2oil 2urvey 2taff, 1&4(. he use of clay mineral data in the comprehensive soil classification system as well as soil family differentiation characteristics was noted by $5uol et. al., 1&0(. hese minerals are best determined by V-ray diffraction analysis and some other  techni6ues. hey also provides physical support for plants and the presence or absence of   particular mineral which !ives clues to how soils have been formed.

V-ray diffraction techni6ue was used to identify the minerals in the clay fraction. V-ray diffracto!rams of clay fraction of some selected soil samples under the present investi!ation have been presented in *i!s. ">-"&. *or the identification of minerals in the

 Ǻor 1  Ǻ pea in the !lycerol solvated samples clay fraction it was assumed that the 14 were an indication of the presence of smectite $ontmorillonite( mineral. he pea at - 1"0 -

 Ǻ which collapsed when heated to 0<; indicates the presence of vermiculite. he 18  Ǻwhich does not collapse on heatin! at 0<; is due to chlorite. he pea at  pea at 18 10  Ǻin the !lycerol solvated clay samples was caused by the presence of mica. he pea  at 4.1  Ǻdisappearin! on heatin! the sample at 0<; confirmed the presence of aolinite

 Ǻto 18  Ǻ, some of which persist on mineral. A number of small peas in the re!ion of 10 !lycerol solvation of the clay, su!!ested the presence of interstratified minerals most liely of the aolinite, illite and vermiculite. :resence of 6uartB is indicated by the

 Ǻ.  presence of '.'

Amounts of minerals determined by the above method are presented in able- "'. +n the  present soils /aolinite is the dominant mineral closely followed by mica. A small 6uantity of 6uartB is present in all the soils. 2mall 6uantities of montmorillonite and interstratified minerals are present in some specific soils. hese results appear to be in conformity with the findin!s of )hite $1&( and /han et. al. $1&&4( for some soils of  5an!ladesh.

he studied soils contain around "> percent mi"a with around " percent vermi"ulite. *annin! and /eramidas $1&44( pointed out that mica in most soils ori!inate mainly from soil parent materials and tend to weather to other minerals with time. hey are more  prevalent in clay fraction of youn!er and less weathered soils $Entisols, +nceptisols, Alfisols(.he studied soils contain " percent vermiculite which indicates that the transformation of mica is considerable. ou!las $1&44( stated that soil vermiculites are always reported to occur as an alteration product of muscovite, biotite and chlorite. Accordin! to ou!las et. al. $1&44( the transformation se6uence isC

!ica → Ber*iculite → 7+dro+l -lu*iniu* -interla+ered Ber*iculite ,,,,,,,,,,,,,,,,,,,,,,,,,, > @,content decreases ,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, >

- 1"1 -

e!ree "θ  *i!. ""C V-ray diffraction patterns of the clay samples from surface horiBon of 5ala!an3 soil. reatmentC a( !- saturation and !lycerol-solvin!F b( !saturation and air- dryin!F c( /- saturation and air- dryin!F d( /- saturation and heatin! at '00<;F e( /- saturation and heatin! at 0<;.

- 1"" -

e!ree "θ  *i!. "'C V-ray diffraction patterns of the clay samples from surface horiBon of :ha!u soil. reatmentC a( !- saturation and !lycerol-solvin!F b( !saturation and air- dryin!F c( /- saturation and air- dryin!F d( /- saturation and heatin! at '00<;F e( /- saturation and heatin! at 0<;.

- 1"' -

e!ree "θ  *i!. "8C V-ray diffraction patterns of the clay samples from surface horiBon of asirna!ar soil. reatmentC a( !- saturation and !lycerol-solvin!F b( !- saturation and air- dryin!F c( /- saturation and air- dryin!F d( /saturation and heatin! at '00<;F e( /- saturation and heatin! at 0<;.

- 1"8 -

e!ree "θ  *i!. "C V-ray diffraction patterns of the clay samples from surface horiBon of abina!ar soil. reatmentC a( !- saturation and !lycerol-solvin!F b( !saturation and air- dryin!F c( /- saturation and air- dryin!F d( /- saturation and heatin! at '00<;F e( /- saturation and heatin! at 0<;.

- 1" -

he soils under study contain around 1" percent &aolinite and ' percent sme"tite $able"'(. 5rady $1&&8( and Macson $1&>8( stressed that aolinite represents a more advanced sta!e of weatherin! than those of any other ma3or types of silicate clays and formed from the decomposition of silicates under conditions of moderate to stron! acid weatherin! environment which results in the removal of the alalies and alaline earth metals. Hupta et. al. $1&8( stated that aolinite usually forms throu!h the weatherin! of feldspars. +n the floodplain soils of 5an!ladesh the aolinite mineral is thou!ht to be allo!enic in nature.

he semi-6uantitative estimation of clay minerals shows that the dominant mineral in the clay fraction of the studied soils was mica occupyin! more than "> percent of the clay fraction $able- "'(. he second dominant mineral in the clay fraction was vermiculite. he clay fraction is found to contain interstratified minerals of mica-vermiculite and mica-vermiculite-smectite respectively. he mean chlorite content in the clay fraction of  the present soils was 1' percent.

2aheed $1&( reported that there were three !roups of mineralo!ical association in 5an!ladesh soilsC mica, vermiculite and aolinite in most floodplain soilsF smectite alon! with mica in Han!es *loodplain soilsF and mica and halloysite in terrace soils.

)hite $1&( conducted an eperiment on the 6ualitative estimation of clay mineralo!ical composition of a lar!e number of soils of 5an!ladesh and reported that mica $muscovite( and aolinite were the predominant minerals in the clay fraction of  most floodplain soils. #e speculated that mica was transformed to vermiculite under  acidic condition in the 5rahmaputra, e!hna and ista *loodplain soilsF while under

- 1"> -

Table- 2": emi-,antitati7e estimation of minerals in the clay fraction of st,died soils

oil eries

7orion

(:) !inerals1

Depth



2

7t

;h

/

7t-;h

G7t

G7tG2

U

H

0-10

1& '

" '

14 

11 11

1" 1'

" -

'

-

"'

8 4

(c*) 0-10

1. ".

5ala!an3 :ha!u

Ap1 Ap1

'.

asirna!ar

Ap1

0-4

14

'

"

1

-

-

1

1

-

1

8.

abina!ar

Ap!

0-1

'0

'

80

-

&

-

-

-

1

-

!ean

-

">

'

"

1'

1"

-

-

-

-

-

1

""reviations;   Z icaF 2 Z 2mectiteF 7t Z 7ermiculiteF ;h Z ;hloriteF / Z /aoliniteF 7t9;h Z 7ermiculite 9 ;hlorite inter!rade,

G7t and G7tG2 Z +nterstratified minerals of ica 9 7ermiculite and ica 9 7ermiculite 9 2mectite respectivelyF U Z UuartBF H Z Heothite.

- 1"4 -

neutral to alaline reaction and poor draina!e conditions mica was transformed to smectite $montmorillonite( in Han!es *loodplain soils.

+slam and Dotse $1&>( studied on the mineralo!y of silt, fine and coarse clays of four soil  profiles by usin! V-ray diffraction $V?(, ion echan!e and selective dissolution techni6ues. ica was found to be dominant in 5atra and Hhior series of Han!es ?iver  *loodplain, whereas mica and aolinite were dominant in araiba! and Hhatail series of  $ld Meghna 'stuarine !loodplain  and Old 5rahmaputra *loodplain, respectively.

*inally, it can be stated that an admiture of "> percent mi"a, " percent vermi"ulite, 1"  percent &aolinite, 1' percent "hlorite and ' percent sme"tite and interstratified minerals occur in the clay fraction of the soils under study. )ith such a combination of clay mineralo!ical composition, the soils are epected to demonstrate a physical condition 6uite close to ideal for the a!ricultural use.

neutral to alaline reaction and poor draina!e conditions mica was transformed to smectite $montmorillonite( in Han!es *loodplain soils.

+slam and Dotse $1&>( studied on the mineralo!y of silt, fine and coarse clays of four soil  profiles by usin! V-ray diffraction $V?(, ion echan!e and selective dissolution techni6ues. ica was found to be dominant in 5atra and Hhior series of Han!es ?iver  *loodplain, whereas mica and aolinite were dominant in araiba! and Hhatail series of  $ld Meghna 'stuarine !loodplain  and Old 5rahmaputra *loodplain, respectively.

*inally, it can be stated that an admiture of "> percent mi"a, " percent vermi"ulite, 1"  percent &aolinite, 1' percent "hlorite and ' percent sme"tite and interstratified minerals occur in the clay fraction of the soils under study. )ith such a combination of clay mineralo!ical composition, the soils are epected to demonstrate a physical condition 6uite close to ideal for the a!ricultural use.

- 1" -

=. Chan$in$ scenario of the studied soils 5an!ladesh possesses enormous areas of wetland and about half of the country turns into wetland durin! the rainy season. A!ain wetland soils are invaluable components of the environment, ecolo!y, a!riculture and biodiversity of 5an!ladesh. hese soils are  principally used for rice cultivation. ainly two rice crops are usually !rown in shallow flooded as well as in the low to very low wetland soils which is very important for our  increasin! food demand. ;han!es in morpholo!ical, physical and chemical properties of  wetland soils occur continuously throu!h human activities, re!ular cultivation and !radual siltation. 5ecause of natural and human causes, land de!radation is wide spread not only in 5an!ladesh but also all over the !lobe. *or 5an!ladesh, this is of serious concern, as we have land scarcity, declinin! productivity and soil nutrient balance is !ettin! worse  because of continuous depletion and disturbance. Over the last two or three decades, croppin! intensity has increased many fold startin! with the introduction of inor!anic fertiliBer in 1&0=s and “!reen revolution “ in early 1&>0=s. his has resulted in si!nificant a!!re!ate a!ricultural production but at the cost of different inds of land de!radation. Dand de!radation leadin! to chan!e in croppin! and a!ricultural productivity and vice versa is threatenin! the a!ricultural sustainability of our country. Dand de!radation and a!ricultural land use are delicately poised to an e6uilibrium which, unless properly and very carefully dealt with may create serious problem on the issue of  land productivity in 5an!ladesh. Over the last two or three decades, enormous pressure has been eerted on land resources of the country to derive necessary food, fibre and fuel for its vast population. +ntensification of a!ricultural land use in particular has increased remarably alon! with considerable epansion of modern crop varieties replacin! the traditional ones. hese chan!es apparently loo !reat. 5ut, in reality, it inflicted serious in3ury to the land 6ualities due to non3udicious etraction of plant nutrients by !rowin! crops without proper replenishment thus destroyin! and erodin! valuable !ermplasm base. As a result, plant nutrient deficiency or imbalance, soil or!anic matter depletion, soil salinity, toicity, soil compaction leadin! to the development of firm plou!hpan, top soil erosion, landslide, siltation of river beds and water reservoirs etc., river ban erosion, flash flood, waterlo!!in! etc. have emer!ed as ma3or problems as the conse6uence of irrational land use.

- 1"& -

orpholo!ical characteristics of the soil profiles and their associated soil properties have  been lar!ely depends on hydrolo!y cum draina!e conditions that is soils developed under  non-inundated conditions and those which have been developed under inundated conditions differ si!nificantly in their overall properties. *loodplain soils are the ma3or  eample which is developed under seasonal inundated conditions. ue to seasonal wettin! and dryin! in association with hi!h temperature involvin! alternate reduction and oidation processes, rapid chan!es tae place within the ori!inal soil materials resultin! in soils with different physical and chemical properties.

=.1 Chan$es in so*e properties of the studied soils ?esults of the studied soils in "00> and those from ?econnaissance 2oil 2urvey $?22( report of 1&4' were compared to asses the chan!es that have taen place durin! this interval. ;han!es in properties of the studied soils on the basis of physical, chemical and  physico-chemical nature are described belowC

=.1.1 Chan$es in ph+sical properties of the studied soils )hen compared the data sets, it was found that sand content was decreased in the surface soils of 5ala!an3 and :ha!u soil series. he hi!hest decrease in clay content was observed in the surface and subsurface layers of asirna!ar series. 5ut the clay content was increased in the surface soils of 5ala!an3 series. *rom the result, it was clear that clay content was decreased in the lowland areas.

)hen the percent wei!hted avera!e to whole soil profile the hi!hest decrease in sand $84%( and silt content $88%( was observed in case of 5ala!an3 soil $able- '0(. he silt content was increased si!nificantly in each of the soil profile of the studied area.

- 1'0 -

Table- 2+: Changes in particle size distrib,tion ;<= in the fo,r selected soil series of the st,died area oil series

5ala!an3 :ha!u  asirna!ar  abina!ar

and

ilt

Cla+

R*

R**

Chan$e

R*

R**

Chan$e

R*

R**

Chan$e

19=3 . 8." '.4 --

28 ".& ".' '." 1."

: -84 -8 -18 --

19=3 &.& 10. .1 --

28 1".& 1".1 1&.' .'

: T'0 T1 T1' --

19=3 8.' .1 8. --

28 ".8 8. 8.' &."

: -88 -> -11 --

?22*C ?econnaissance 2oil 2urveyF ?:2**C ?esults of :resent 2tudyF --C ot found

   )    %    (    4   n   a    3    l   a    t   o    2

10  $ 7 6 5 4 3 2 1 0

 173 P 2006

%alagan&

P'agu

(asirnagar  

'i$. 28; Chan$es in sand

   )    %    (    t    l    i    3    l   a    t   o    2

20 1$ 16 14 12 10 $ 6 4 2 0

 173 P 2006

%alagan&

P'agu

(asirnagar  

'i$. 2=; Chan$es in silt

- 1'1 -

10

   )    %    (   y   a    l        l   a    t   o    2

$ 6  173 4

P 2006

2 0 %alagan&

P'agu

(asirnagar  

'i$. 2>; Chan$es in cla+

=.1.2 Chan$es in che*ical properties of the studied soils +n case of p# it was clear that, p# increased in the soils of 5ala!an3, :ha!u and  asirna!ar series durin! the periods 1&4'-"00> $able- '1(. he hi!hest increase was observed in the surface soils of asirna!ar series $'%( and lowest in :ha!u series $'%(. ;han!es in p# showed a decrease of 0.1 units within the upper 100 cm of e!hna ?iver  *loodplain durin! the period 1&>4-1&&4 $5A?;, 1&&&(. Or!anic carbon was decreased in the soils of asirna!ar and :ha!u series but in the soils of 5ala!an3 series opposite situation was observed $able- '1(. #i!hest depletion of  or!anic carbon was observed in the soils of asirna!ar series $"%(. Almost the same situation was observed in case of -content of the soils of asirna!ar and :ha!u series whereas hi!hest depletion was taen place in the soils of asirna!ar series $'%(. Accordin! to a recent study $Ali, 1&&4( almost similar situation lie depletion of or!anic carbon and total  depletion were observed in different intensive croppin! areas of  5an!ladesh durin! 1&>4-1&&4. #i!hest depletion of or!anic carbon $X"0%( was observed in 5rahmaputra floodplain and e!hna ?iver floodplain areas of 5an!ladesh. iah et. al. $1&&'( outlined that in 5an!ladeshF crop residues are widely used as fuel and fodder and usually not returned to the soil. Even cowdun! is widely used as fuel in rural areas. his results in a decrease in soil or!anic matter content. +n 5an!ladesh, the avera!e or!anic matter content of top soils have !one down, from about "% to 1% over the past "0 years due to intensive cultivation, which means a decline by "0-8>%. - 1'" -

Table- 2: Changes in p>8 'rganic carbon ;<= and total nitrogen ;<= in the s,rface horizon of fo,r selected soil series oil series

p7 (1;2.) Chan$e

5r$anic Car"on (:)

otal N (:)

R*

R**

Chan$e

R*

R**

Chan$e

R

R*

Chan$e

19=3

28

:

19=3

28

:

*

*

:

28 0.1"

T''

5ala!an3

.1

>.8

T">

0.4'

0.8

T1

19=3 0.0&

:ha!u

8.>

>.1

T''

1."

0.>

-''

0.1"

0.0&

-"

 asirna!ar

8.0

4.0

T4

8.

0.

-"

0.&

0.10

-'

 abina!ar

--

4.0

--

--

0.&0

--

--

0.10

--

?22*C ?econnaissance 2oil 2urveyF ?:2**C ?esults of :resent 2tudyF --C ot found

   6   /   /   /   /   /   /   /   /   /    H   p

10  $ 7 6 5 4 3 2 1 0

 173 P 2006

%alagan&

P'agu

(asirnagar  

'i$. 29; Chan$es in p7

5

   6   /   /   /   /    )    %    (   n   o       r   a    

4 3  173 2

P 2006

1 0 %alagan&

P'agu

(asirnagar  

'i$. 3; Chan$es in car"on

- 1'' -

   6   /   /   /   /    )    %    (        l   a    t   o    2

1 0 0$ 07 06 05 04 03 02 01 0

 173 P 2006

%alagan&

P'agu

(asirnagar  

'i$. 31; Chan$es in nitro$en

=.1.3 Chan$es in ph+sico,che*ical properties of the studied soils Echan!eable ;aTT increased in case of 5ala!an3 and asirna!ar series and echan!eable !TT increased in 5ala!an3, asirna!ar and :ha!u soils $able- '0(. he ;E; of 5ala!an3 soils increased and in case of asirna!ar and :ha!u series it showed decreasin! features.

Table- 2/: Changes in cation e!change capacity8 e!changeable Ca and g in the s,rface horizon of fo,r selected floodplain soils

oil series

Chan$e in C#C

Chan$e in #. !$

Chan$e in #. Ca

Hc*ol (pE) @$,1 R*

R**

19=3

28

Chan$e

R*

R*

:

19=3

*

Chan$e

R*

R**

:

19=3

28

T"18

0.&4

>.8"

T>"

Chan$e :

5ala!an3

&.>&

"0.8'

T110

'.04

28 &.>8

:ha!u

"'.1

1&.&"

-18

10.48

10."8

-

0.''

4.8"

T"18&

 asirna!ar

''.>1

"0.

-'

&.0"

11.0

T"

8.

>."

T8'

 abina!ar

--

"".14

--

--

10.">

--

--

4.>

--

?22*C ?econnaissance 2oil 2urveyF ?:2**C ?esults of :resent 2tudyF --C ot found

- 1'8 -

50

   0   g    *    )    +   p    (    l   o   m   c    .               1   /

40 30  173 20

P 2006

10 0 %alagan&

P'agu

(arirnagar  

'i$. 32; Chan$es in C#C 20

   0   g 15    *    )    +   p 10    (    l   o   m   c 5    .   a     0    1   /

 173 P 2006

%alagan&

P'agu

(asirnagar  

'i$. 33; Chan$es in echan$ea"le Calciu*

10     0 $    1   /   g 7    *    ) 6    +   p 5    (    l 4   o   m 3   c    . 2   g 1    7 0

 173 P 2006

%alagan&

P'agu

(asirnagar  

'i$. 3%; Chan$es in echan$ea"le !a$nesiu*

5oth physical and chemical properties of soils under!one some chan!e due to intensive croppin! in the same land year after year without proper soil mana!ement practices.

- 1' -

>. 6#N#I ND CLI'ICI5N 5' 7# DI#D 5IL >.1 6enesis of the soils On the basis of the information, which is obtained from the field and laboratory analysis of  the wetland soils, an attempt has been made to loo into the !enetical processes in the studied soils. )ith the consideration of the !eolo!ical history of the area wherefrom the soils have been collected, they may be considered to be of recent ori!in. he morpholo!ical, physical, chemical and physico-chemical properties $able 1> to "0( of these soils clearly show that the parent materials of these soils are of alluvial ori!in. ?esults of the studied soil profiles show that their development did not proceed too far. All the soils under investi!ation appear to be incompletely developed which means that they are still immature and their  !enetic processes are also wea. his may be attributed to the time factor which also includes human activities, re!ular cultivation and !radual siltation that are occurrin! durin! the floodin! period. he soils may, therefore, be reasonably considered to be in the incipient sta!e of their development. he parent materials and the prevailin! environmental conditions lie poor draina!e and a6uic moisture re!ime due to re!ular submer!ence durin! the monsoon season and some  part of the dry season are probably the factors responsible for developin! the morpholo!ical characteristics of the soils. he soils are at the youthful sta!e and  presumably at this sta!e the parent materials will play a ey role in ehibitin! the  properties of the soils. he direct influence of poor draina!e is the retardation of leachin! and little alteration of soil materials. )ithout that, the soils have been under cultivation for a lon! time which disturbed the normal pedo!enic processes and caused the puddlin! of the soil materials at the surface to some etent and may helped the mechanical translocation of finer fractions downward throu!h cracs formin! flood coatin!s. A plou!hpan also formed in most of the studied soil profiles. he finer fraction mi!ht have bloced the pore spaces and restricted the movement of the products of weatherin! if there was any.

- 1'> -

2easonal submer!ence followed by dryin! set the condition of oidation-reduction reactions in the soils. he elements susceptible to oidation and reduction would therefore, impart certain characteristics to the soils. he soil reaction closely followed the course of  oidation-reduction conditions because the soils initially contained considerable amounts of *e and n bearin! minerals which are sub3ect to oidation and reduction reactions. he !rey colour of the both topsoils and subsoils is probably due to the above reason. Another  interestin! feature of these soils is the presence of mottlin!s of brown to yellowish brown throu!hout the soil profiles and sometimes alon! the pores. he various shaped, siBed and coloured mottlin! may be considered as due to alteration of oidation and reduction conditions in the soils. :resence of mottlin!s may also be attributed to evidences of a wea  type of !leiBation process in the studied wetland soils. he development of coatin! alon! the ped faces, fissures and pores in the subsoil are typical characteristics of these soils. hese coatin!s are not clay sins but are flood coatin!s or gleyan as called by 5rammer $1&41(. hey appear to have developed rapidly from the materials that were taen down from the surface under flooded condition. he vertical distribution pattern of sand, silt and clay of these soils $able-14( support the  precedin! statement that the parent material of the soils was of mied ori!in. he annual deposition of silts by floodin! affects the eistin! pedo!enic processes. he soil profile with an!ular to suban!ular blocy structures su!!ests the formation of altered 5 $;ambic( horiBon. #owever the soils in the surface horiBon have mostly massive structures. +n most of the soil profile, there is a trend of increasin! p# with depth $able-1(.  evertheless, in all the soils the surface horiBons have sli!htly acidic reaction. he surface soil acidification is due to the alteration oidation-reduction cycles in the floodplain areas $5rammer, 1&41(. he colloidal comple of the soils is well supplied with echan!eable metal ions $able"0(. he base saturation of the studied soils is hi!her in the surface horiBon than the subsoils and the values are increasin! with increasin! depth. ;alcium and ma!nesium are the dominant bases in the echan!e comple $able-"1(. Echan!eable ;aTT G !TT ratio was in !eneral, around 1. $mean value(.

- 1'4 -

V-ray diffraction analysis indicates the dominance of non-epandin! types of minerals in the clay fraction. ;racin! as a result was usually wea. *rom the mineralo!ical point of  view, alteration of mica to vermiculite may be a common :edochemical weatherin!  process in the soils under investi!ation. epotassification process may be thus a common weatherin! process. he mared similarities in the clay mineralo!y of these soils su!!est that the parent materials of the soils were more or less similar, and the mineral weatherin! andGor synthesis have been similar as well. *rom the characteristics discussed in the above para!raphs, it appears that the soils under  the present investi!ation are liely to be !enerally desi!nated as seasonally hydromorphic in nature. #owever the absence of well developed !ley horiBons and the ;aTT G !TT ratio in these soils may lead one to cast doubt about the true hydromorphic nature of these soils. he wea !leyin! represented by the occurrences of mottles which is due to the seasonal wettin! and dryin! of the soils. A wea type of !leiBation seems to be the dominant  process of soil formation in these soils.

>.2 Classification of the soils he most important ob3ective of the present investi!ation to classify the studied wetland soils on the basis of morpholo!ical, physical, chemical properties. )hen these properties of the soils are nown, it is now appropriate time for main! an attempt to characteriBe the soils in some international soil classification systems. At the present time soils will be characteriBed by matchin! with the criteria set out in the @2A soil taonomy $2oil 2urvey 2taff, 1&4' and 1&&(. *rom the final result which was studied in the present investi!ation, there were variations in the surface and subsurface colours, tetures, structures, p#, base saturation and clay mineral composition. he variation in the properties of the studied wetland soils was very important in differentiatin! the soils into the various orders, suborders, !reat !roups and families. hese soils have well developed structures in the subsoil. he presence of stron! coarse  prismatic and medium suban!ular blocy structures distinctly coated with clay on ped faces in the subsoils in the studied profiles indicates the destruction of alluvial stratification and their aeration. +n addition, this subsoilIs are devoid of any rocy structure. - 1' -

All the studied soils are poorly or imperfectly drained soils and have conspicuous cutans alon! ped faces and pores in the subsoil. hese cutans are not re!arded as true clay sins. +n the subsoil yellow or brown colour dominates over !rey colour, which is not perennially wet. he structural 5-horiBon in the subsoils of these soil profiles alon! with the redo concentration and the re!ular decrease of or!anic matter may be desi!nated as the “Cambi"” horiBon. A cambic horiBon has been defined as havin! soil structure development and absence of any roc structure in con3unction with the occurrence of  mottlin! $2oil 2urvey 2taff, 1&4(. he presence of “ stru"tural B” $;ambic 5( horiBons, su!!ests that all profiles $5ala!an3, :ha!u, asirna!ar and abina!ar( may 6ualify to be classed in the “+nceptisol order”. hese soils developed on the fresh alluvium and wet  basins of 2ylhet basin have prismatic andGor blocy structure has developed below the surface layer. he properties of the topsoils are often altered by mechanical manipulation durin! cultivation when wet. ost of these soils have been used for rice cultivation for centuries. As a result, structure formation in the surface soil has been disturbed constantly and conse6uently it has wealy developed. hese soils are seasonally and often show iron stains alon! root channels. ypical !ley horiBons are present in 5ala!an3 and :ha!u series and all the studied soils have a6uic moisture re!ime. 2oils belon!in! to the +nceptisol order are subdivided into suborders on the basis of  difference in soil moisture re!ime, and some other etreme physical and chemical  properties. he studied soils may be placed in the A6uept suborder and Enda6uept !reat !roups because of little horiBon differentiation and relative immaturity in the profile development. All the studied soils were under ypic Enda6uept sub!roup. ineralo!ical studies indicate that all the soils are mied mineralo!y as they do not have any particular clay mineral, which constitute more than 0%. On the basis of soil reaction the studied soils can be placed under sli!htly acidic to neutral in nature. +t should be noted that all the above soils have hyperthermic temperature re!ime and have medium to heavy tetured soils. On the basis of particle siBe classes 5ala!an3, :ha!u and asirna!ar series are classed as silt loam and abina!ar series is silty clay to clay.

- 1'& -

herefore, accordin! to the @2 2oil aonomy the studied wetland soils have been characteriBed into the +nceptisol order, A6uepts suborder and Enda6uepts !reat !roup. At the sub!roup level they are classed as ypic Enda6uept $able- "4(. As indicated in the above table the soils have been placed into two soil families.

Table- 20: Classification of the st,died wetland ;seasonally flooded= soils D soil taono*+*

5rder

u"order

6reat $roup

u"$roup

oil series

'a*il+ ** Doamy, ied,

5ala!an3

 onacid, #yperthermic, ypic Enda6uept Doamy, ied,

:ha!u

 onacid, ypic +nceptisol A6uept

Enda6uept

Enda6uept

#yperthermic, ypic Enda6uept Doamy, ied,

 asirna!ar 

 onacid, #yperthermic, ypic Enda6uept ;layey, ied,

 abina!ar 

 onacid, #yperthermic, ypic Enda6uept

*2oil survey 2taff $1&& and 1&&( 2oil aonomy, **#ussain, . 2. $1&&"(

9. u**ar+ and conclusion

- 180 -

he present investi!ation was undertaen to study some basic properties of some wetland soils of 5rahmanbaria district of 5an!ladesh. he ob3ectives of this investi!ation were firstly, to study the characteristics of some wetland soils with reference to their  morpholo!ical, physical, chemical, and physico-chemical and clay mineralo!ical  properties. On the basis of the above information, the second sta!e was to throw li!ht on the probable !enetic processes that have been in operation for the formation of these soil  profiles. he third sta!e is to study the chan!in! features with respect to soil series on the  basis of physical, chemical and physico-chemical nature. *inally, an attempt has been made to characteriBe these soils in the @2A soil taonomic system. *our representin! wetland $seasonally flooded( soil series of 5an!ladesh each representin! a typical soil profile were studied in the field as well as in the laboratory. 2oil samples were collected from the appropriate horiBons from each of the profiles. he collected soil samples were carried to haa for their laboratory analysis in the epartment of 2oil, )ater and Environment, @niversity of haa. . he salient *orpholo$ical features of the soils under investi$ation *a+ "e su**aried as follows; 1. Colour;

a. he top soils were !enerally !rey to very dar !rey in colour when moist ecept the 5ala!an3 soil.  b. he sub soils were !enerally !rey to dar !rey in colour. 2. eture;

a. he teture of both top soils and subsoils was silt loam ecept abina!ar  series.  b. he teture of the soil of abina!ar series is from silty clay and clay. 3.

tructure;

a. he subsoil of 5ala!an3 and abina!ar series showed stron! medium and medium suban!ular blocy and fine suban!ular blocy structure. he subsoil of :ha!u series showed stron! coarse prismatic and medium an!ular blocy structure. +n asirna!ar series, medium an!ular blocy structure was found.  b. assive structure was found in the surface horiBons of all the soil profiles.

- 181 -

%. Coatin$s; ;ontinuous thic dar !rey to continuous dar !rey cutans alon! ped

faces are found in 5ala!an3 and :ha!u series. All the soils under present study developed flood coatin!s and variously coloured mottles alon! the old root channels and pores. . Draina$e;  raina!e conditions of the studied soils are poor to very poor and

remained flooded durin! the monsoon season and also some part of the dry season. 4. he ph+sical properties of the soils *a+ "e su**aried as follows;

1. 2ilty clay loam is by far the dominant fraction in all of the profiles ecept the  abina!ar series, which plays a si!nificant role in mouldin! the tetural character  of the soils. ".

he vertical distribution of the silt and clay fraction is more or less re!ular in all of  the soil profiles reflects the homo!eneous nature of the parent materials from which these soils have developed.

'. he fine tetured soils of abina!ar soils have more hy!roscopic moisture  percenta!e than that of 5ala!an3, asirna!ar and :ha!u soils with a li!hter teture.

C. he che*ical properties of the soils *a+ "e su**aried as follows; 1. oil reaction;

a. 2oil reaction was sli!htly acidic in the surface and neutral in the subsurface and showed a tendency of increasin! p# with depth.  b. All Δ p# values were ne!ative and ran!ed from -0.& to -0.> ph unit. he Δ p# values showed a si!nificant positive correlation with p# in water.

2. 5r$anic *atter and total nitro$en;

a. he or!anic matter content of the soils are in !eneral low and showed a !radual decrease with depth.  b. otal nitro!en contents in the studied wetland soils ran!es from 0.0 to 0.11 percent and showed a !radual decrease with depth. c. he ;G ratio of the studied soils ran!es from  to 11. d. he vertical distribution patterns of both or!anic matter and nitro!en are almost irre!ular.

- 18" -

%. Cation echan$e capacit+;

a. he cation echan!e capacity of the studied wetland soils ran!es from 1'.18 to "8.> cmol $pT( /!-1. he abina!ar soils have hi!her ;E; than the other three soil  profiles. he variation of ;E; values of the pedons studied reflects the important influence of both the clay and or!anic matter content of these soils.  b. 2i!nificant positive correlations are found between ;E; and percent clay content and ;E; and or!anic matter.

. 4ase saturation;

a. he base saturation is hi!h and showed a steady decrease with depth in all of the soil profiles.  b. ;alcium and ma!nesium are the dominant echan!eable bases in all the soil  profiles. ;alcium alone occupied more than 0% of the echan!e position. c. 5ase saturation has a ne!ative relationship with p# $#"O(.

D. !ineralo$ical properties;

All the soils contained hi!h amount of mica, vermiculite and small amount of  smectite. ica and vermiculite are the dominant clay mineral in the studied wetland soils. Other minerals include chlorite, chlorite-vermiculite inter!rade, 6uartB and interstratified minerals. he above minerals are considered allo!enic ecept vermiculite. he presence of vermiculite in the soils indicated that mica was possibly  bein! !radually transformed to vermiculite.

#. 2ince the studied soils remain re!ularly inundated for few months in every year, the

moisture re!ime in there is a6uic. All these soils have been characteriBed as “#ydromorphic” and amon! the soil formin! processes “HleiBation” is the dominant  process of soil formation.

'. 2ince the soils remain re!ularly inundated for few months every year, the moisture

re!ime there is a6uic. All these soils have been characteriBed as hydromorphic where !leiBation is the dominant process of soil formation.

- 18' -

6. he he studie studied d wetl wetland and soil soilss have have been been class classif ifie ied d accor accordin din! ! to the @2A @2A 2oil 2oil

aonomic system. All the soils under the present investi!ation meet the re6uirements of the (n"eptisols the (n"eptisols order  order of the above system. 7. At the sub!roup level all the soils belon!s to ypic Enda6uepts.

 !inally,  !inally, on the basis basis of the morphol morpholo!ic o!ical, al, physica physical, l, chemic chemical al and mineral mineralo!ic o!ical al  properties of the wetland soils under the present investi!ation the followin! conclusions are hereby drawnC



he soils have been classified in the +nceptisols order.



HleiBation appears to be the dominant pedo!enic process.



he soils are re3uvenated every year by fresh siltation durin! the monsoon season.



All the studied soils remain under flood water in most of the time in each year.



All All the the stud studie ied d soil soilss are are prod produc ucti tive ve and and will will have have seas season onal ally ly hi!h hi!h  productive potentiality potential ity under improved mana!ement practices.

- 188 -

1. References $uilera? N. 7. and !. L. Jac&son.  1&'. +ron oide removal from soils and clays. 2oil

2ci. 2oc. Amer. :roc. 14C '&-'>8. &onda? .-. 1&&. 5an!ladesh. +nC .A. 2coot $ed.(. A irectory of Asian )etlands.

[email protected];, Hland, 2witBerland and ;ambrid!e. pp. 81-1. li? !. '. 1&&8. Effects of alternate wettin! and dryin! cycles on pedo!enic processes processes of 

some representative 5an!ladesh soils. :h. . dissertation, @niversity of haa, haa, 5an!ladesh. 1&&4. 2oil 2oil e!radat e!radation ion durin! durin! the period 1&>4-1&& 1&>4-1&&  in 5an!lad 5an!ladesh esh :h. li? !. !. 1&&4. .hesis, 2himane @niversity, atsue, Mapan. li? !. K. 1&&0. Open )ater *isheries and Environmental ;han!es +nC ?ahman A. A.,

#u6, 2., ;onway ;onway,, H. ?. $eds.(. $eds.(. Environ Environmen mental tal Aspects Aspects of 2urface 2urface )ater )ater 2ystem 2ystemss of  5an!ladesh. he @niversity :ress Dimited, haa, pp 18-1>8.

Estimatin! relative a!es rduino? #. #. 4ar"eris '. Carraro and !. 6. 'orno.  1&8. Estimatin! from iron-o iron-oideG ideGtot total al iron rates rates of soils soils in the western western :O 7alley, lley, +taly +taly.. Heoderm Heoderma, a, ''C '&-". rduino? #. #. 4ar"eris '. . !arsan and !. 'ranchini. 1&>. +ron oides and clay

minerals within profiles as indicators of soil a!e in northern +taly. Heoderma. '4C 8-. 1&&. *ertil *ertiliBer iBer recomme recommendat ndation ion !uide, !uide, 5an!lad 5an!ladesh esh A!ric A!ricultu ultural ral ?esearc ?esearch h 4RC. 1&&. ;ouncil, *arm!ate, haa. 1&&4. *ertil *ertiliBer iBer recomme recommendat ndation ion !uide, !uide, 5an!lad 5an!ladesh esh A!ric A!ricultu ultural ral ?esearc ?esearch h 4RC. 1&&4. ;ouncil, *arm!ate, haa. 4RC $5an!ladesh A!ricultural ?esearch ;ouncil(. 1&&&. Dand de!radation situation in

5an!ladesh, 2oils ivision, haa, 5an!ladesh.

- 18 -

44 $5an!ladesh $5an!ladesh 5ureau of 2tatistics(. 1&&1.5rahmanbaria 1&&1.5rahmanbaria district statistics. inistry of 

*inance. Hovt. of 5an!ladesh, haa. $5an!ladesh desh 5ureau 5ureau of 2tatist 2tatistics( ics(.. "00>. "00>. 2tatist 2tatistica icall Nearboo arboo of 5an!lad 5an!ladesh. esh. 44 $5an!la inistry of *inance. Hovt. of 5an!ladesh, haa. 4ear? '. #. 1&>. ;hemistry of the 2oil. ?einhold :ublishin! ;ompany, ew Nor. 4hui+a? . 7. 1&4. Or!anic atter 2tatus and Or!anic ?ecyclin! in 5an!ladesh 2oils.

?esources and conservation 1', 114-1"8. 4lac&? C. . 1&>. ethods of 2oil Analysis. :art-1 and ". Am. 2oc. A!ron.F adison,

)isconsin. 4lu*e? 7. . and . chwert*ann.  1&>&. Henetic evaluation of the profile distribution

of Al, *e and n oides. 2oil 2ci. 2oc. Am. :roc. ''C 8'-888. 1&.. he conc concep eptt of :seu :seudo do!l !ley ey.. :roc :roc.. of the the int inth h +nte +nterr. 2oil 2oil 4lu* 4lu*e? e? 7. . 1& ;lassification )orshop. )orshop. :. 1"&-1'4. 4ohn? 7. L. 4. L. !c Neal and 6. . 5MConnor. 5MConnor. 1&4&. 2oil ;hemistry. Mhon )iley and

2ons, ew Nor. Nor. ""4 p. 1&&8.. he he atu ature re and and :rop :roper erti ties es of 2oil 2oils, s, 10th Edition. Edition. acillan acillan 4rad 4r ad+ +? N. C. 1&&8 :ublishers, Dondon.

Edition. :earson Education, Education, 4rad+? N. C. "00". he ature and :roperties of 2oils, 1'th Edition. elhi, +ndia. 4ra**er? 7. 1&>8. An outline of the Heolo!y and Heomorpholo!y of 5an!ladesh in

relation to soil development. 5an!ladesh M. 2oil sci.1C 1-"'. 4ra**er? 7. 1&41. ;oatin!s in seasonally flooded soils. Heoderma, >C -1>. 4ra**er? 7. 1&41. 5an!ladeshC 2oil resources. echnical ?eport '. *AO, ?ome.

- 18> -

4ra**er? 7. 1&&>. he Heo!raphy of the soils of 5an!ladesh. he @niversity :ress

Dimited. haa. :. '-1"1. 4ra**er? 7. and 4rin&*an. 1&44. 2urface-water !ley soils in 5an!ladeshC

Environment, landforms and soil morpholo!y. Heoderma. 14C &1-10&. 4rar? !. . and 6. . e&hon.  1&. :otassium status of five benchmar soil series from

northern +ndia. :otassium ?esearch. 1C "-'. 4rin&*an? R. 1&40. *errolysisC A hydromorphic soil formin! process. Heoderma.

'C1&&-"0>. 4rin&*an? R. 1&44. 2urface-water !ley soils in 5an!ladeshC Henesis. Heoderma.

14C 111-188. 4uol? . -. '. D. 7ole and R. J. !cCrac&en.  1&0. 2oil Henesis and ;lassification.

+owa 2tate @niversity :ress, Ames, lowa. 4+chen&o? 6. . and . I. @o*arovs&a+a.  1&41. Sonal soils of the Afanasiev area of 

/irov re!ion and their characteristics. :ochvoved. :robl. 2el. /hoB. 148-1.

Ca*p"ell? I. 4. and 6. 6. C. Clarid$e.   1&4. orpholo!y and A!e ?elationship of 

Antarctica 2oils. +nC ?. :. 2u!!ate and . . ;resswall $Editors(, Uuaternary studies. he ?oyal 2ociety of ew Sealand, )ellin!ton. C#6I $;enter for Environmental and Heo!raphic +nformation 2ervices(. "00'. i!ital

+ma!e of ;EH+2. 5anani, haa. Cha&ra"ort+? . @. 7. inha and 4.. !athuri. 1&8. orpholo!ical and

 physicochemical properties of some alluvial soils of Assam. M. +ndian, 2oc. 2oil 2ci. '"C 1"-1'>. Chap*an? 7. D. and . '. ratt.  1&>1. ethods of analysis for soils, plants, and waters.

@niv. of ;alif., iv. of A!r. 2ci. p. '0&. Chatter<ee? R. @. and R. C. Dalal.  1&4>. ineralo!y of ;lay fraction of some profiles

from 5ihar and )est 5en!al. M. +ndian 2oc. 2oil. 2ci. "8C 1'-">". - 184 -

Coventr+? R. J. and J. -illia*s. 1&8. Uuantitative relationships between morpholo!y

and current soil hydrolo!y in some Alfisols in semiarid tropical Australia, Heoderma. ''C 1&1-"1. Daniels? R. 4. J. '. 4rasfield and '. '. Riec&en. 1&>". istribution of sodium

hydrosulfite etractable man!anese in lowa soil profiles. 2oil 2ci. 2oc. Am. :roc. ">C 4-0. Daniels? R. 4. #. #. 6a*"le and . -. 4uol. 1&4'. Oy!en content in the !round water 

of some orth ;arolina A6uults and @dults. $eds.( 5ruce ?. ?. 2oil 2ci. 2oc. Am. 2pecial :ublications 2eries no. . :. 1'-1>>. 2oil 2ci. 2oc. Am., adison. )isconsin. Das? D. @. 4. Das and 6. C. Nas&ar. 1&48. )ater retension and stora!e characteristics

of alluvial soils. M. +ndian 2oc. 2oil 2ci. ""C '4&-'". Das !. 1&44. :hysical properties of some soils of Assam in relation to soil clay

mineralo!y. :h. . thesis, A!ricultural ?esearch +nstitute, ew elhi. 11. Dawson? 4. . -. J. L. 'er$usson Ca*p"ell? . . and #. J. 4. Cutler.   1&&1.

epletion of first row-transitional metals in a ;hronose6uence of soils in the ?eefton area of ew Sealand. Heoderma. 8 p.

Da+? . R. 1&>. :article formation and particle-siBe analysis. +nC ethods of soil analysis

$eds. ;. A. 5lac et al.( American 2ociety of A!ronomy, adison, )isconsin, :. 8->4. Diwar&er? D. . . and R. N. i$n.  1&&". al land soils of 5ihar. +++C A!!re!ation and

)ater retension characteristics. M. +ndian 2oc. 2oil 2ci., 80C >>4->4'. Dou$las? R. 4. #. #. 6a*"le and . -. 4uol. 1&4'. Oy!en content in the !round water 

of some orth ;arolina A6uults and @dults. $Eds. ?. ?. 5ruce et. al. 2oil 2ci. 2oc. Am. 2pecial :ublications series no. . :. 1'-1>>. 2oil 2ci. 2oc. Am., adison, )isconsin. Dudal? R. and '. !oor*ann. 1&>8. a3or soils of 2outheast Asia. M. rop. Heo!.

1C 8-0.

- 18 -

Du$an? .J. $ed.(. 1&&0. )etland conservationC a ?eview of ;urrent +ssues and ?e6uired

Action. [email protected];, Hland, 2witBerland. &> pp. #den? !. J. 1&40. 2avanna 7e!etation in the orthern ?upununi, Huyana. M. rop. Heo!.

'0C 14-". #lahi? '. . !. . 7ussain and !. . Chowdhur+. 1&&'. :otassium status of some soils

from the northern district of 5an!ladesh. haa @niv. M. 5iol. 2ci. "$"( C 14 $Muly(. #vans? C. B. and D. . 'ran*eir. 1&>. 2aturation, aeration and colour patterns in a

topose6uence of soils in north-central +ndiana. 2oil 2ci. 2oc. Am. M. 0C &4-0.

'annin$? D. . and B. . @era*idas.  1&&4. icas. +nC ion, M. 5. and 2. 5. )eed $Eds.(

inerals in soil environments. ::C 1&-". 2oil 2cience 2ociety of America, adison, )isconsin, @. 2. A. 4& p. '5. 1&41. 5an!ladesh 2oil ?esources. AHDC 2*G:A/>, ech. ?ep.', *AO, ?ome, pp.

"0&.

'5.1&. Dand ?esources Appraisal of 5an!ladesh for A!ricultural evelopment.

?eport o ", A!ro ecolo!ical ?e!ions of 5an!ladesh. *AO, ?ome, pp 40. '5,ND. 1&. A!roecolo!ical re!ion of 5an!ladesh, ?oport-", *AO, ?ome, 40 p. '5, N#C5.  1&. *AO- @E2;O soil map of the world. ?evised le!end. *AO,

?ome. 6eor$e? !. N. chafer and N. 7oloa+chu&. 1&. ;haracteristics of medium and fine

tetured humic !ley soils of Ohio. 2oil 2ci. 2oc. Amer. :roc. ""C">". 6upta? 6. . and B. @. !isra.  1&40. A comparative study of the methods of estimation of 

;E; in soils of Hwalior district. +ndian M. A!ric. ;hem. 'C &4-100. 6upta? R. D. @. @. Jha and 4. . ahi.  1&8. :roc. +ndian ational 2cience Academy.

1C>8'->8&.

- 18& -

7a"i"ullah? . @. !. D. J. 6reenland and 7. 4ra**er. 1&41. ;lay mineralo!y of 

some seasonally flooded soils of East :aistan. M. 2oil 2ci. ""C 14&-1&0. 7assan? !. !. 1&>8. 2oil formation in the recent deltaic re!ion of 5an!ladesh.

5an!ladesh Mour. 2oil. 2ci. "0C '4-8. 7assan? !. !. and !. . Raa&.  1&1. A preliminary evaluation of the clay mineralo!y

of the 2undarban soils. 5ano 5i!an :atria. 10C 1->.

7u/? !. 1&&0. +mportance of or!anic matter in 2oil *ertility. 2?+ $emo(. 7u/? . !. I. and 6. !. @a*al.  1&&'. “;haracteristics and dynamics of wetland soils”.

*reshwater )etlands in 5an!ladeshC +ssues and Approaches for ana!ement. [email protected];, [email protected]; 5an!ladesh ;ountry Office, haa, 5an!ladesh. 7ussain !. . and . !. Chowdhur+. 1&0. 2tudied on some cracin! clay soils from

+)?5. 1&&". Action :ro!ramme for the ;onservation of )etlands in 2outh and )est Asia. 7ussain? !. . 1&&". 2oil ;lassification with 2pecial ?eference to the soils of 

5an!ladesh. @niversity of haa, haa, 5an!ladesh. 7ussain? !. . and . !. Chowdhur+.  1&1. 2tudies on some cracin! clay soils from

5an!ladesh. ++. :edochemistry and !enesis. M. 2oil 2ci. 5an!. 14C 1-1". 7ussain? !. . @. Nahar . @. !. #. Isla* and . '. #lahi.  1&&. A morpholo!ical

and clay mineralo!ical study of some soils from 5hola district in 5an!ladesh. haa @niv. 2tud. $:art-E( 8C &'-108. 7ussain? !. . . Rah*an . . had . . !. !ohiuddin and . R. !a<u*der.

1&&". :hysical and chemical properties of four pedons from 5hola. haa @ni. M. 5iol. 2ci. 1$1(C &-10". 7ussain? !. . and L. D. windale.  1&48. :hysical and chemical properties of the Hray

#ydromorphic soils of the #awaiian +slands. 2oil 2ci. 2oc. Amer. :roc. 'C &'-&81.

- 10 -

I/"al? . 1&&. 2tate of Dand )ater and :lant utrition ?esources in 5an!ladesh.

:roceedin!s of the 3oint re!ional worshop on land 7ulnerability assessment for food security usin! AESGDand resources information system. ?A:A, *AO :ub. o. ?A: 1&&G1>.5an!o. :a!e 11-1. IRRI $+nternational ?ice ?esearch +nstitute(. 1&. )etland 2oilsC ;haracteriBation,

;lassification and @tiliBation. Dos 5anos Da!una, :hilippines. Isla*? . 1&&'. 2oil ?esources and +rri!ated A!riculture in 5an!ladesh. *ood and

A!ricultural or!aniBation of the @nited ations. @:G *AO- 5HG &G 0'&. echnical ?eport. Isla*? . @. !. #. and #. 6. Lotse.  1&>. Uuantitative mineralo!ical analysis of some

5an!ladesh soils with V-ray, ion echan!e and selective dissolution techni6ues. ;lay iner. "1C '1-8". Isla*? !. . and -. Isla*.  1&>. utrient status of East :aistan $5an!ladesh( soils.

irectorate of A!riculture, Hovt. of East :aistan $5an!ladesh(, haa, 5ulletin o. 1C " p. Isla*? . and -. Isla*.  1&4'. ;hemistry of submer!ed soils and !rowth and yield of 

rice. :lant and soils. '&C ->. Isla*? . . 7o/ue R. !andal and . . Chowdhur+. 1&. ;omparison of method to

evaluate potassium availability in rice soils. 2ri. Danan M. A!ri. 2ci. "C >4-4. I-R4.  1&&". Action pro!ramme for the ;onservation of )etlands in 2outh and )est

Asia. Jac&son? !. L. 1&. 2oil ;hemical Analysis. :rentice #all, +nc. En!le )ood ;liffs. .

Mersey. @2A. Jac&son? !. L. 1&>8. Aluminium bondin! in soils. A unifyin! principle in 2oil 2cience,

2oil 2ci. 2oc. Amer. :roc. "4C 1-10. Jac&son? !. L. 1&>4. 2oil ;hemical Analysis. :rentice #all of +ndia :vt. Dtd. ew elhi.

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Jac&son? !. L.  1&4. 2oil ;hemical Analysis Advanced ;ourse. :ublished by the Author.

epartment of 2oils, @niversity of )isconsin, adison. &&1 p. Joffee? J. .  1&>0. :edolo!y. :edolo!y publications, ew 5runswic, ew Mersey. >>"p. @anehiro? K. and . . Chan$.  1&>. ;ation echan!e properties of the #awaiian !reat

soil !roups. !roups . #awaii A!r. Ep. 2ta.F ech. ech. 5ull. '1, p. "4. @apoor? 4. . . C. 6oshwa*i and B. B. La*i.  1&". V-ray studies on the distribution

and characteriBation of layer silicates in some alluvial soils. M. +ndian 2oc. 2oil 2ci. '0C 404. @ari*? . and . Isla*.  1&>. A study of ion echan!e properties of silt. 2oil 2ci. "C

8''-8'>. @ari*? . 1&8. *ormation of aluminium substituted !oethite in seasonally waterlo!!ed

rice soils. 2oil 2ci. 2oc. Amer. M. 8C 810-81'. +mpact of Dand Dand e!rada e!radatio tion n in 5an!lad 5an!ladesh, esh, ;han!in! ;han!in! @ari*? @ari*? . . . I/"al I/"al.. 21. 21. +mpact 2cenario in A!ricultural Dand @se. 5A?;, *arm!ate, haa, 5an!ladesh. @ar*anov? I. I.  1&>>. ;han!es in tropical soils under a!ricultural use. 2oviet 2oil 2ci.

1C '1-&". 1&>. 2oil 2oilss of 5urm 5urma, a, :art :art-1, -1, #ydro #ydrophy physic sical al proper properti tiesF esF :art :art-". -". @ar*an @ar*anov ov?? I. I. 1&>. :eculiarities of cultivated soils. +nC 7. /ovda and E. 7. Doboval $Editors(, Heo!raphy and classification of the soils of Asia. +srael :ro!ram for 2ci. ranslation, Merusalem, :. "1'"'>. @ate"i? !. N. . and . 4ari.  1&&. ;oastal Afforestation in 5an!ladesh. +nC ational

)orsho rshop p on ;oast ;oastal al Area ?esou ?esourc rcee evel evelopm opment ent and and ana!e ana!eme ment nt $:ar $:artt Q. :. 101-10'(. @han? '. 7. 1&&1. Heolo!y of 5an!ladesh. @niversity :ress Dimited, haa. @han? . 7.  1&&. A !enetic study of some 5enchmar soils of 5an!ladesh. . 2c.

hesis, haa @niversity, haa, 5an!ladesh. - 1" -

@han? . 7. . R. !a<u*der !. . 7ussain and . !. aheed.  1&&4. ;hemical and

mineral mineralo!ic o!ical al propert properties ies of some some 5enchm 5enchmar ar soils soils in the floodpla floodplains ins of 5an!lade 5an!ladesh. sh. Mournal of the +ndian 2ociety of 2oil 2cience 8 $"(C 8-8&. @+u*a? @. 1&. *undamental characteristics of wetland soils. pp 1&1-"0>. +nC )etland

2oilsC ;haracteriBation, ;lassification and @tiliBation. +??+, Dos 5anos, :hilippines. @+u*a? @. and @. @awa$uchi. 1&>>. a3or soils of 2outheast Asia and the classification

of soils under rice cultivation. 2outheast Asia 2tud. 8C "&0-'1". 1&&1. 5ooer 5ooer ropic ropical al anual. anual. Don!ma Don!man n 2cienti 2cientific fic and echnic echnical al Land Landon on?? J. R. 1&&1. Don!man Hroup, @. /. Dtd. !ac&intosh? #. #. and J. B. D. 7ust.   1&4. 2oil draina!e classes and water table

relations in medium and coarse tetured soils in 2outhern Ontario. ;an. M. 2oil 2ci. C "4-'01. !au*der? . R. 1&4>. 1&4>. A study on some some deep-wat deep-water er rice soils soils of 5an!la 5an!ladesh desh.. . 2c.

hesis. ept. of 2oil 2ci. @niversity of haa, haa. !au*der? . R.  1&&>. A pedo!enic study of soils from the 5rahmaputra floodplain. :h.

. dissertation, @niversity of haa, haa. !atin? !. . 1&4". Henesis and :edochemical :edochemical properties of some 7ertisols 7ertisols 5an!ladesh.

. 2c. hesis. ept. of 2oil science. @niversity of haa, haa, 5an!ladesh. ?elationship of water table and Eh to properties of three clay soils !c&ea$ue? J. . 1&>. ?elationship in the Ottawa Otta wa 7alley. 7alley. ;an. M. 2oil 2ci. 8C 8&->". !c&ea$ue? J. . and J. 7. Da+.  1&>>. ithionite and Oalate etractable *e and Al as

aids in differentiatin! various classes of soils. ;an. M. 2oil 2ci. 8>C 1'-"". !ehra? 5. . and !. L. Jac&son.  1&>0. +ron oide removal from soils and clays by

dithionite-citrat dithionite-citratee system buffered with sodium bicarbonate. :roc. 4th atl. ;onf. on clays and clay minerals. :erman!on :ress. ew Nor. Nor. :. '14-'"4.

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!iah? !. !. . . @. !. 7a"i"ullah and !. '. li.  1&&'. epletion of Or!anic matter 

in @plan @pland d soils soils of 5an!l 5an!lade adesh. sh. :roce :roceed edin! in!ss of +nter +nternat natio ional nal 2ymp 2ymposi osium um on “2oi “2oill ?esilience and 2ustainable Dand @se” held in " 2eptember " October, 1&&", 5udapest, #un!ary, pp 40-4. characteristics of paddy soils and their si!nificance si!nificance in soil !itsuchi? !. 1&48. :edo!enic characteristics classification $Mapanese, En!lish 2ummery(. 5ull. atl. +nst. A!ric. 2ci. 5 "&C "&-11. !oor*ann? '. R.  1&4. orpholo!y and classification of soils on which rice is !rown.

:a!es :a!es "-"4" "-"4" +nC soils soils and rice. rice. +nternat +nternationa ionall ?ice ?ice ?esearc ?esearch h +nstitut +nstitute, e, Dos 5anos, :hilippines. !or$ !or$an an?? J. . and and !cIn !cInti tire re.. 1&&. 1&&. Uuarte Uuarternar rnary!eo y!eolo!y lo!y of the 5en!al 5en!al 5asin, 5asin, East East

:aistan and +ndia. :p '1&-'8". 5ull. Heol. 2oc. Amer., 40. 1&>. :edoche :edochemic mical al properti properties es of the soils develope developed d on the ippera ippera !u<i"? !. . 1&>. surface, East :aistan. . 2c. hesis, epartment of soil 2cience. @niversity of haa. haa. !u<i"? !. . !. . 7ussain and . Rah*an.   1&>&. istribution of free iron and

man!anese oides in the soils of the ippera surface, East :aistan. :a. M. 2oil 2ci. 7ol. ,  o. ". !urth+? C. .  1&4. ?ice soils in +ndia. :a!es '-14 +nC 2oils and rice. +nternational ?ice

?esearch +nstitute, Dos 5anos, :hilippines. Nishat? . . 7ussain !. @. Ro+ and . @ari*.  1&&', $Eds.(, *reshwater )etlands in

5an!ladeshC +ssues and Approaches for ana!ement. he [email protected]; )etland :ro!ramme. [email protected];. characteristics and classification classification of  5&usa*i? . . and R. 7. Rust. 1&&". Occurrences, characteristics some hydromorphic hydromorphic soils from south i!eria. +nC M. . /imble $1&&"(. :roceedin!s :roceedin!s of the th +ntl. +ntl. 2oil 2oil correla correlation tion meetin meetin! ! $7+++ $7+++ +2;O( +2;O(FF charact characteris eristic tics, s, classifi classificati cation on and utiliBation of wet soils, @2A 2oil conservation service, ational 2oil 2urvey ;enter, Dincoln, :. 1-1&.

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5rlov? D. .  1&&". an!anese and iron in soil. +nC 2oil ;hemistry. Oford and +5

:ublishin! ;o. :vt. Dtd. ew elhi. 5s"orn? '. 1&'. he limits of the earth. Dittle, 5rown and ;o., 5oston. "' p. ana"o&&e? C. R. 1&4. ?ice soils of 2ri Dana. :: 1&-'' +nC 2oils and rice. +nternational

?ice ?esearch +nstitute, Dos 5anos, :hilippines. ara*ananthan? . 1&4. ?ice soils of alaysia. :: 4-&4 +nC 2oils and rice.

+nternational ?ice ?esearch +nstitute, Dos 5anos, :hilippines. atha&? . R. and N. @. atal.  1&0. 2tudy of some physico-chemical characteristics of 

salt affected soils of /aiBa district, Hu3rat 2tate. M. +ndian 2oc. 2oil 2ci. "C '1-'4. ic&erin$? #. -. and . L. !. Bene*an. 19>%.   oisture re!imes and morpholo!ical

characteristics in a hudrose6uence in central assachusetts. 2oil 2ci. 2oc. Am. onna*peru*a? '. N.  1&>8. he mineral nutrition of the rice plant. :roceedin! of a

symposium at the +nternational ?ice ?esearch +nstitute. *ebruary. 1&>8. :. "&-'". onna*peru*a? '. N.  1&>. ynamic aspects of flooded soils. :a!es "&-'". +nC he

mineral nutrition of rice plant. :roceedin! of a symposium at the +nternational ?ice ?esearch +nstitute, Dos 5anos, Da!una, :hilippines. onna*peru*a? '. N. 1&. ;hemical inetics of wetland rice soil relative to soil

fertility. +nC wetland soilsC characteriBation, classification and utiliBation. +nternational ?ice ?esearch +nstitute, Dos 5anos, Da!una, :hilippines. onna*peru*a? '. N. 1&4". he chemistry of submer!ed soils. Adv. A!ron. "8C "&-&>. ortch? . and !.. Isla*. 1&8. utrient 2tatus of 2ome of the ore +mportant

A!ricultural 2oils of 5an!ladesh. +nC “:roceedin!s of +nternational 2ymposium on 2oil est ;rop ?esponses ;orrelation 2tudies.” Ed. . A. annan, A. /. . #abibullah and 2am :ortch. 5A?; and 2oil 2cience 2ociety of 5an!ladesh. uri? 6. R. in$h . @u*ar and @. B. Ra*an.  1&'. ineralo!ical studies on alluvial

soils of ecrut district in @ttar :radesh. ;lay ?esearch, "C 1>-1&.

- 1 -

Rah*an? ..  1&&. 5an!ladesh ;oastal Environment and ana!ement, +nC ational

)orshop on ;oastal Area ?esource evelopment and ana!ement $:art Q(, p.1-"". Rah*an? !. !. 1&&0. utrient 2tatus of 2ome of the ore +mportant A!ricultural 2oils

of 5an!ladesh. +nt. 2ymp. On soil test crop response correlation studies 5A?;, haa. ?ahman, . #., /han, . #. and #o6ue, 2. 1&&". 2tructural attributes of soils under rice  based croppin! pattern in the Han!es /obada :ro3ect area of 5an!ladesh. 5an!ladesh M. 2oil 2ci. "'C 4&-&1. aheed? . !.  1&8. 2oils of 5an!ladesh. :p. 104-1"&. :roc. +nt. 2ymp. 2oil est ;rop

?esponse ;orrelation 2tudies. 5A?; and 2225, haa, 5an!ladesh.

aheed? . !.  1&. ;lay mineralo!y study of some ma3or river and estuarine floodplain

and terrace soils of 5an!ladesh. :roc. )ors. 2oil ineralo!y, haa. :p. 8&-. aheed? . !. and !. . 7ussain.  1&&". )etland soils of 5an!ladesh. :p ""0-""&. :roc.

Ei!hth

+nternational 2oil ;orrelation eetin! $7R +2;O(C ;haracteriBation,

;lassification, and @tiliBation of )et 2oils. Douisianan and eas, Oct. >-"1, 1&&[email protected]A, 1&&". pp. ""0-""&. har*a? . @. and 6. Dev. 1&. :hysio!raphy and soil relationship in a transect in

north-east :un3ab. M. +ndian. 2oc. 2ci. ''C >08->1". ihdu? . . 6. . undeer and 6. '. 7all. 1&4. *erroman!anese concretions from the

alluvial derived soils of :un3ab. M. +ndian 2oc. 2oil 2ci. ">C ">-"4'. aw+? . and . . ade/. 1&&. orpholo!y and classification of some soils of the

northern part of ile elta. E!yptian M. 2oil. 2ci. "& C 801-814. eh$al? J. L. R. 4hu*"la and D. R. Dhin$ra.  1&>. 2oils of the 2utle3 flood basin area

in the :un3ab. M. +ndian 2oc. 2oil 2ci. 1>C "81-"84. idhu? . . Ra<&u*ar and 4. D. har*a.  1&&8. ;haracteriBation and classification of 

Entisols in different soil moisture re!imes of :un3ab. M. +nd. 2oc. 2oil 2ci. 8"C >''->80. in$h? 6. N. 7. . $arwal and !. in$h.  1&&. Henesis and classification of soils in

an alluvial pedo!enic comple. M. +ndian. 2oc. 2oil 2ci. '4C '8'-'8.

- 1> -

*ith? . !. and 4eecroft.  1&'. 2oil morpholo!y and water re!imes in three recent

alluvial soils on the aieri plains. 2outh +sland, ew Sealand. M. 2ci. ">C 80'-811. oeprapthohard<o? !. and 7. uhard<o. 1&4. ?ice soils of +ndonesia. :a!es &&-11' +nC

2oils and rice. +nternational ?ice ?esearch +nstitute, Dos 5anos, :hilippines. oil urve+ taff. 1&1. 2oil 2urvey anual. @2A #andboo o. 1. @2 Hovt.

:rintin! Office, )ashin!ton, . ;. oil urve+ taff.  1&4. 2oil aonomyC A basic system of soil classification for main!

and interpretin! soil surveys. @2A, #andboo o. 8'>, @2 Hovernment :rintin! Office, )ashin!ton, . ;. RDI taff. 1&40. etermination of physical properties of some soils on Old 5rahmaputra

and Old e!hna estuarine floodplain of 5an!ladesh. 2oil ?esource evelopment +nstitute. haa. RDI taff. 1&4'. ?econnaissance 2oil 2urvey reports of 5rahmanbaria 2ubdivision

$;omilla istrict( of 5an!ladesh. Hovt. of 5an!ladesh, *arm!ate, haa. RDI (oil Resource Develop*ent Institute) taff.   1&>-1&>. ?econnaissance 2oil

2urvey ?eports. '8 volumes, Hovt. of 5an!ladesh, haa. RDI taff. 1&&1. hana Dand and 2oil ?esource @tiliBation Huide. oil urve+ taff.   1&&8. /eys to 2oil aonomy. @2A, 2oil ;onservation 2ervice,

)ashin!ton . ;. unders? -. !. 7. 1&&. On !leyin!. . S. 2oil ews. "C ->0. o$i? . . and -. 7. 7udnall.  1&&". ;lassification of soils in Douisiana accordin! to

“Endoa6uic” and “Epia6uic” concepts. :roc. th +ntl. 2oil ;orrel. eetin!. 5aton ?ou!e. :. "41-"4. horp? J. and 6. D. *ith. 1&&. #i!her cate!ories of soil classification- Order,

2uborder and Hreat 2oil Hroups. 2oil 2ci. >4C114.

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oth? . J. I. 1&>. he physical chemistry of soil. +nC *. E. 5ear $ed.(. ;hemistry of the

2oil. ?einhold :ublishin! ;orporation, ew Nor. :. 18"-1>". ruo$? #. 1&>1. 2oil as a edium for plant !rowth. +nC ineral utrition of plants. :. "'-

. he @niversity of )isconsin :ress. 8'0 2terlin! ;ourt, adison >, )isconsin. D oil urve+ taff.  1&4. 2oil taonomyC a basic system of soil classification for 

main! and interpretin! soil surveys. @2A A!ric. #andb. 8'>. @. 2. Hovernment :rintin! Office, )ashin!ton, .;. 48 p. Bander? @. -. 1&4". escription le!end for the !eneral soil map of the eon! basin.

Appendi +. *inal report of soils consultant. @. . ;ommittee for coordination of  investi!ations of the lower eon! basin 5an!o, "> p. Bina+a&? . @. L. eh$al and . . idhu.  1&8. ;lay minerals in some saline 9sodic

soils of the indo-!an!etic alluvial plain in :un3ab. M. +ndian 2oc. 2oil 2ci. '"C 84-8". -ada? 7. and !atsu*eto.  1&4'. :edo!enic processes in paddy soils. pedolo!ist. 14C "-

1. -alia C. . and 6. . Cha*uah. 1&&". *lood affected soils of 5rahmaputra 7alley and

their suitability for land use plannin!. M. +ndians 2oc. 2oil. 2ci. 80C ''-'80. -hite? J. L. 1&. 2ummary of results of ineralo!ical study of clay fractions of 

5an!ladesh soils. +nC :roceedin!s of the worshop on soil mineralo!y. 5A?;, haa, 5an!ladesh. -i&lander? L. 1&>. ;ation and anion echan!e phenomena. +nC *. E. 5ear $ed.(

;hemistry of the soil. ?einhold :ublishin! ;orporation, ew Nor. :. 1>'-"0. -orld Resources Institute? ;entre for +nternational evelopment and EnvironmentF

5an!ladesh Environment and atural ?esources Assessment, raft ?eport. )ashin!ton ;, @2A. Manuary. 1&&0, pp >. -ri$ht? J. R. R. Levic& and 7. J. t&inson.  1&. :roc. 2oil 2ci. Am. 1&C '80. o"ec&? . !. and . Ritchie.   1&8. Analysis of lon!-term water table depth records

from a hudrose6uence of soils in central Ohio. 2oil 2ci. 2oc. Am. M. 8C11&-1'. - 1 -

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