University of Nigeria Research Publications

ADAMU, Jude Uggu

Aut

hor

PG/ M.SC/93/15014

Title

Effects of Land use on Properties of Aggregates of some

Nigerian Soils

Facu

lty

Agriculture

Dep

artm

ent

Soil Science

Dat

e April, 1996

Sign

atur

e

~ ~ U , SUDE UGGU

P G / M . S c / 9 3 / 1 5 0 1 4

SCI%;IL'CX (M.SC) IN S O I L SCIXNCE.

DEPARTMENT UP S O I L S C I U f i C E

UNIV.UK;;ITY O F N I G X H I A

NSUKKA

( i i )

Jude Uggu kdamu, w poutgraduute student i n the

Depurtrient of S o i l dcience, with the Keg. No.

PG/PI.Sc/93/1!5014, has s a t i s f a c t o r i l y completed the

requ i renen ts f o r course and research work f o r the

degree of Master of Science (M.Sct) i n S o i l bcience.

This work embodied i n t h i s d i s s e r t a t i o n i s

o r i g i n a l a d has not been publivhed or submitted i n

p a t o r f u l l f o r any other diploma o r degree of t h i s ,

or any o ther Universi ty.

Jude Uggu Mamu

Dr. J: S. C. Mbagwu Supervisor

I am h i g h l y indeb ted t o t h e many people ,

c o l l e a g u e s and r e l a t i o n s and o t h e r acquain tances

wkio c o n t r i b u t e d i n one way o r t h e o t h e r t o t h e

s u c c e s s of th is work.

To tllc t y p i s t , Rr: John O. Ugwuanyi f o r t a k i n g

h i s time t o type t h e p r o j e c t , thanks a l o t .

F i n a l l y , I p r a i s e and worship God who made

a l l t h i n g s p o s s i b l e f o r me throughout the p e r ~ o d

of t h i s work.

AUhMLT, JU Di3 UGGU

(iii)

Dedicated t o my f a t h e r , M r . Uggu Adamu

and t o the memory of my l a t e mother,

M r s . Asheloben Uggu.

ACKNOWLEDG~~II!

I am g r a t e f u l t o D r . J.S.C. Mbagwu f o r no t only

guiding and supervis ing the prepara t ion of t h i s

d i s s e r t a t i o n , but a l so f o r h i s invaluable suggest ions,

const ruct ive c r i t i c i s m and above a l l , f o r being very

understanding and pa t i en t . I r e a l l y overtaxed him.

Sincere thanks a r e due t o Professor F.O.C. Ezedinaa,

D r s . P.O.B. Akamigbo and C.A. Igwe f o r t h e i r help.

I wish t o express my s incere g r a t i t ude t o

M r . J.I. Kanu and h i s wonderful family f o r t h e i r

kindness, h o s p i t a l i t y , moral support and sympathy

dur ing my frequent and most d i f f i c u l t times. I

s h a l l ever remain g r a t e f u l t o them.

The Department of S o i l Science was extremely

helpful .

I hope my dea r wife, Yacit ; my chi ldren; Ovye,

L i l i a n , Ephraim and Adigiz i p e r f e c t l y understood

we had t o s a c r i f i c e everything now so t h a t we can

succeed l a t e r . I thank them.

My good f r i ends ; O b i , C.C., Ikeh, S.G.I.,

Nnaji , G.U. and xnene, B.O.A. whose love and

encouragement helped me through the most chal lenging

per iod of my course. Thanks i n appreciat ion.

TAbLh OF CONTYNTS

TITLE PAGE ... CMTZPICATION ' , ... UkUICAIICN ... ACI(NClkLbUG~NNl ... TABLE: OX COli2EN1S ... LIST OF U&G;J ... LIST OF FIGUMS ... U8TRBC'P ...

CHAPTEB ONE

INTRO1)UC'I'IOIJ ... ... CHAPT&R ! N O

2.0 L I T ~ A T U R E n x v ~ m ... 2.1 . STRUCTUHBL PHOP~HTIJS ... 2.1.1 Aggregate s t a b i l i t y ... 2.1.2 Col lo idd, s t a b i l i t y ... 2.1.3 Aggregate s i ze d i s t r i b u t i o n

2 . 1 4 Bulk densi ty ... 2.2 PHYSICAL FBOPBH'IIES e e

2.2.1 Organic matter . ... 2.2.2 Porosity ... ... 2.2.3 Water r e t en t ion ... 2.2.4 Atterberg l i m i t s ...

P a g e

(1.)

(ii)

(iii.)

( i v >

(vi)

<xi>

( x i i i )

(xv>

( v i i )

2.3 PfiYSICO-CHKI'IICWI PRUP~H%I&S OF AGGkUGATb SUhS . . .

2.3.1 Carbon, n i t rogen and phosphorus 2.3.2 S t a b i l i t y of aggregates

2.3.3 'viater r e t e n t i o n of aggregates 2.3.4 Bulk dens i t y of aggregates

2.3.5 p a r t i c l e s i z e d i s t r i b u t i o n wi th in aggregates ...

2.4 Conclusion . . . CHASTER THWS

TlU PHY B I G U bNVIHONMJQvT

G!QWRAL UXSCXIPTICIN OF THE PHOJYCT wul;A ... . . . p la t eau S t a t e . . , Geolom and physiography

Climate ... ... Sunshine ( r a d i e t i o n ) . . . Relat ive humidity . . . Vegetation and land use

Bauchi S ta te ... Geology and physiopaphy Climate ... . . . Sunshine ( r ad i a t i ou ) ... l ie la t ive humidity ... Vegetation and land use

CHhFTER POUH

MkTEHIALS ANh i -Lirlu+ . . . FIELD MPTHODS ... LAUORA'I'OlIY METHODS .a.

DHIPERMINATIOPT ,OF AGEIiJ3GAil'E S'PAdILITY ... ~ean-wkight d i m e t e r o f dry

aggregates ... Mean-weight diameter of wet

aggregates (MWUW) ... Colloidal s t a b i l i t y ... UBT~HMINATIUN OF BULK UL;N'WPY A&U POHOSIT'I ... Bulk densi ty ... Total poros i ty ... UET~HMINk'L'ICN OF PLIY SICO-CHrnICU PHOPEHTIM OF-AGGWGATE SIZhS

Organic carbon ... Organic matter ... Total n i t rogen ... Available phosphorus . . . Moisture r e t en t ion capacity

P a r t i c l e s i z e d i s t r i b u t i o n

OTkLEH UETEHMINHTION TO FULLY C ~ C T E f i I S ~ Tllh SOILS . . . Uetermination of the Atterberg

l imits . . . p a r t i c l e s i z e ana lys i s . . . Cation exchange capacity

( v i i i )

P a ~ e

34 34 34

36

36

37 38

39 39 3'3

P a g e

4 . 2 4 4 pH determinat ion . . . 4 8

4.2.11.5 Yxchmfpable bases ... 48

4.2.4.6 Jixchangeable a c ~ d i t y . . . '49

4.2.4.7 Base s a t u r a t i o n ... 49 4. 3 DAUA ANALY G I s ... 49

CHAPTXH FIVE

K E S U L l S A.ND D I S C U S S I O N . . . C H A H U C T E B I S I I C S OY THE 0-20 CM U Y E H O F THh SOILS S T U U I M J

P m t i c l e . s i z e d i s t r i b u t i o n , organlc mat te r , t o t a l n i t rogen and ava i l ab le phosphorus o f the s o i l s

P a r t i c l e s i z e d i s t r i b u t i o n

Organic mat ter ... 'Potal n i t rogen ... Available phosghorua . . . Boi l raocbion ('11) ... E X C H A N G U B L h PROPERTIES

&changeable bases ... Catioli exchange capac i ty

Base s a t u r a t i o n ... Sxchangeable a c i d i t y . . .

AGGWGATS S T A B I L I T Y . . . Mean-weight diameter of d r y

aggregates . . . Mean-weight diameter of wet

aggregates ...

P o t e n t i a l s t r u c t u r a l deformation index ... ...

Col lo ida l s t a b i l i t y ... BULK DJLNSI'PY AND PORUSI'l'Y

PHYSICO-CHEMICAL PHOPEKTILS OF AGGWGATE SXLU . . . Organic matter content . . . T o t a l n i t rogen ... Available phosphorus ... Col lo ida l s t a b i l i t y . . . P a r t i c l e s i z e d i s t r i b u t i o n Water r e t e n t i o n . . .

CIIAPPliH SIX

B W M Y , CONCLUSION AND WCVMI"ir;NUII!CION 104

RkFhKENCk4 s: . ..a 106

Table - P t i g e

1 Rainf a l l , temperature and other meteorological information a t Joe 26

2 Rainfa l l , temperature and other meteorological information a t Bauchi 31

3 Location, c l a s s i f i c a t i o n and land use h i s t o r y of the s o i l s s tudied 35

4a P a r t i c l e s i z e d i s t r i b u t i o n , organic mat ter , t o t a l ni trogen and ava i lab le phosphorus c h a r a c t e r i s t i c s of the s o i l s s tudied ... 5 1

4b Exchangeable p rope r t i e s of the s o i l s s tudied ..- 55

5 ' Changes i n rheological p roper t i es of four s o i l s a s induced by c u l t i v a t i o n 58

6 Aggregate porosi ty , dens i ty and s t a b i l i t y of f o r e s t and cu l t i va t ed . s o i l s a s evaluated by d i f f e r e n t ind ices 60

7 Correla t ion coe f f i c i en t s ( r ) between silt + clay (%) and Dispersion r a t i o (DR), Moisture r e t a ined a t 0.01 MPa and 1.5 ma. N - 5 . . . 65

8 Corre la t iod c o e f f i c i e n t s ( r ) betweeh organic carbon (%),* and s i l t + c lay , ni trogen, phosphorus, Dispersion r e t l o (DR) and Moisture re ta ined at 0.01 Wa and 1.5 m a . N - 5 ... 76

9 Oorrelat ion c o e f f i c i e n t s ( r ) between organic carbon (%) md si l t + clay, n i t rogen, phosphorus, Dispersion r a t i o (DH) and Moisture re ta ined a t 0.01 PlPa md 1.5 m a . N = 10 . . .

LIST OF TA&L& CONT' 0

Table - P a g e

10 Correlat ion coe f f i c i en t s ( r ) between silt + cJay and t o t a l ni trogen and avai lable phosphorus. N .i 5 85

11 Correlat ion coeffici?rd:~-: ( r) between s i l t + clay and nii;m;,- .rm< phosphorus. N .; 10 . . . 0 9 - 90

' Ef fec t s of land use on the s t a b i l i t y of s t r u c t u r a l aggregates of four s o i l s (evaluated 'by the Dispersion r a t i o index) ... . . . Correla t ion coe f f i c i en t s ( r ) between s i l t + c lay and Dispersion r a t i o (UH) and Moisture re ta ined a t 0.01, MPa and 1.5 MPa. N = 10 . . Dist r ibut ion of s i l t + clay (%) i n aggregate f r ac t ions separated from s o i l s under d i f f e r e n t land uses

Moisture r e t en t ion (0.01 MPa Tension) of s t r u c t u r a l aggregates a s influenced by c u l t i v a t i o n ( e ressed as gravi- metric percentages "j.. 101

Moisture re ten t ion . (1.5 MPa Tension) of s t r u c t u r a l aggregates as influencqd by culbivat ion ( e ressed a s gravi- metr ic percentages 7 ... 102

( x i i i )

LIB2 OP FIGURES

P a ~ e

... Sample loca t ions ... 24

Uis t r ibu t ion of aggregates obtained from dry- and wet-sieving procedures on s o i l s under d i f f e r e n t land uses ,

(PSDI - Po ten t i a l S t r u c t u r a l Deforma- t i o n index) ... ... 6 3

Influence of l and 'use type on organic mat ter d i s t r i b u t i o n i n aggregate f r a c t i o n s of an Incep t i so l ... 60

Influence of land use type on organic matter d i s t r i b u t i o n i n aggregate f r a c t i o n s of an U l t i s o l . ... 69

Influence of land use type on organic matter d i s t r i b u t i o n i n aggregate f r a c t i o n s of an Ent i so l ... 71

Influence of land use type on organic' matter d i s t r i b u t i o n of a V e r t i s o l 7 2

Dis t r ibu t ion of t o t a l n i t rogen i n aggregate f r a c t i o n s of an Incep t i so l as influenced by d i f f e r e n t land uses 74

Dis t r ibu t ion of to tn? . : , : i s ro~cn i n aggregate f r a c t i o n s o.i . " ' L t i s o l as influenced *by d i f f e r e n t lwa ci;;<.r 79

Llistribution of t o t a l ni trogen i n aggregate f r a c t i o n s of an l in t i sol as influenced by d i f f e r e n t land uses 80

Di s t r i bu t ion of toba l n i t rogen i n aggregate f r a c t i o n s of a Ver t i so l as influenced by d i f f e r e n t land use8 82

Available phosphorus i n aggregate f r a c t i o n s o f an Incep t i so l us influenced by land use ... ... 84

Figure '

1 2 Available phosphorus i n aggregate f r a c t i o n s of an U l t i s o l a s influenced by land use ... ... Available phosphorus i n aggregate f r a c t i o n s of an Ent i so l a s influenced by land use ... ...

I Available phosphorus i n aggregate f r a c t i o n s of a ~ e r t i s o l a s influenced by laud use ... ...

A.ijd'PHAC'P

This s tudy waa undertaken t o evaluate the long

t e r n e f f e c t s of continuous c u l t i v a t i o n on aggregate

s t a b i l i t y , bulk denskty, poros i ty , At terberg 'e l i m i t s ,

and physico-chemical p rope r t i e s of the d i f f e r e n t

aggregate f rac t ions . Phree s o i l s from To-hoes ( Incep t i so l ) ,

Gind i r i (U l t i so l ) and Panyam '(l intisol) i n P la teau Bta te

and one s o i l from Deba ( ~ e r t i a o l ) i n i3auchi S t a t e , ' 1 I

Niger ia were used f o r t h e study. I

The land use types considered were cu l t i va t ed aud

fo re s t . The s o i l s co l lec ted from 0-20 cm depth were

seperated i n t o f i v e a g p e g u t e f rac t ions : 5-2, 2-1,

1-0.5, 0.5-0.25 and C 0.25 mu, and changes ia the

physico-chenical yroper t ieu of these aggregates due t o

c u l t i v a t i o n weL. :--!-ermined.

The aggregates i n the c u l t i v a t e d s o i l s were l e a s

s t a b l e compared t o those i n t h e ' f o r e s t s o i l s . The

p o t e n t i a l of the aggregates t o d i s i n t e g r a t e upon contact

with water was more i n the cu l t i va t ed than f o r e s t s o i l s

a d i n the order , Lu t i so l cu l t i va t ed (40 .3h)3 U l t i s o l

cu l t i va t ed ( 3 0 . 4 % ) ~ Ver t i so l f o r e s t (22.1%)7 I n c e p t i s o l

cu l t i va t ed (17.Y~) 7 U l t i s o l f o r e s t (15. Wh)p I n c e p t i s o l

f o r e s t (6.5%). The aggregates of the cu l t i va t ed s o i l a

were denser and l e s s porous than those of the, f o r e s t

so i l s . The percentage decrease i n organic matter due

to . cultivation was U l t i s o l (58%), i ih t isol (4%),

Inceyt i so l (41%) and Vert isol (33%).

The organic carbon and t o t & nitrogen concentration

i n the aggregates increased a s aggregate s i z e s decreased

i n a l l the so i l s . The higkly s i g n i f i c a n t co r re l a t ion

coef f ic ien t (PL0.001) betweeh organic carbon and t o t a l

ni trogen showed t h a t organic matter i s t h e main source

of ni trogen i n the d i f f e reu t a g ~ r e g a t e f ract ious . There

was no uniform pa t t e rn of avai lable phosphorus d i s t r ibu -

t l o n i n t h e aggregate frilctions.

Bt te rberg ' s limits and p a r t i c l e s i z e d i s t r i b u t i o n ,

were s l i e h t l y affected by cultivation. The low varia-

b i l i t y f o r Litterberg's l i m i t s aud non-sippificant

co r re l a t ion between s i l t + clay and U i s p e r ~ i o n r a t i o (DB)

showed t h a t cu l t i va t ion had only s l i g h t e f f e c t s on the

rheological p roper t ies and p a r t i c l e s i z e d i s t r i b u t i o n

of th13 s o i l s .

The low and non-significant cor re la t ion coe f f i c i en t

( r ) betweerr silt + clay und water re ten t ion , and between

organic carbon and water re ten t ion ahowed t h a t cult ivu-

t i o n had minimal e f f e c t on water r e t en t ion of the

aggregate f ract ions .

CHRPTJB ONE

INTAODUCTION

Agr icu l tu ra l development i n Nieeria has evolved

changes i n land use p a t t e r n from t h e predominant

s h i f t i n g c u l t i v a t i o n t o the more recent continuous

cropping owing t o increased population d e n s i t i e s and

hence pressure on ava i lab le a g r i c u l t u r a l lands.

Recent quest f o r increased a g r i c u l t u r a l p roduc t iv i ty

has a l so l e d t o the in t roduct ion of mechanized

fa-ng with d i f f e r e n t t i l l a g e prac t ices . A l l these

have var ious e f f e c t s on s o i l productivi ty.

I When a piece o f land i n f o r e s t condi t ion i s I*

cleared, burnt and cu l t i va t ed , bumper harves t is

obtained in the very first year; however, successive

cropping of the same piece of land r e s u l t s i n

successive decrease i n y ie ld . Most farmers a t t r i b u t e

t h i s t o f e r t i l i t y problem. A s o i l cannot be productive

un less it has d;sirable p h ~ l s i c a l c h a r a c t e r i s t i c s a s

well a s enough n u t r i e n t s t h a t w i l l meet t he p lan t

needo (Mye and Greenland, 1964.).

The physical condit ion of t h e s o i l has of ten

been considered t o be an inherent proper ty over which

there i s l i t t l e o r no con t ro l , but experience ~ n d

research have shown that physica l p r o p e r t i e s of s o i l s

mch a s bulk dens i ty , poros i ty and water r e t en t ion do

change and it is apparent t h a t c u l t u r a l p r ac t i ce s

have a profound e f f e c t upon them (Page and Willard,

t h a t c u l t i v a t i o n foilowing c u t t i n g and burning Of

t r o p i c a l f o r e s t l e d t o r ap id l o s s of n u t r i e n t s b j

leaching and erosion.

S o i l s t ruc tu re d e t e r i o r a t e s under c u l t i v a t i o n

i n t h e t r o p i c s (Sanchez, 1976). Good s t ruc tu re f o r

crop growth depends on presence of aggregates of s o i l

p a r t i c l e s 1 t o 10 am diameter which remain s t a b l e when

wetted (T i sda l l and Oades, 1982). S t a b i l i t j . a s app l ied

t o s o i l s t r u c t u r e r e f e r s t o the r e s i s t ance of the

p a r t i c l e arrangement t o change upon wet tin^ with

water and coming i n contact with farming implements

(Reeve, 1953). , S o i l s under in tens ive c u l t i v a t i o n have been

shown t o undergo some det r imenta l changes i n t h e i r

chemical and physica l p rope r t i e s (Gradwell and

Arlidge, 1971; Bourma and Hole, 1971). The7 a r e

l i k e l y t o s u f f e r a ' eradual decl ine i n aggregate

s t a b i l i t y (All ison, 1973). The s t a b i l i t y of aggregates

of a g r i c u l t u r a l s o i l s t o water inf luences many

physico-~hemic'al and b io log i ca l processes l i k e organic

carbon and exchnngeable cnt: n-? (Mbagwu, 1992a). One

of the reasons why p h y s i c ~ - , . ~ e ~ u i c ~ 1 c h ~ r a c t e r i z a t i o n

of aggregates i s important i s t h a t s ince d i f f e r e n t

aggregate f r a c t i o n s a r e s e l e c t i v e l y removed during

eros ion (Massey and Jackson, 1952; Chepil and Woodrmf,

1963), a cha rac t e r i za t i on of these aggregates i s needed

i n unders tmding n u t r i e n t dynamics during .soil

eros ion (Mbagwu and Piccolo , 1990a).

Kowalinski e t a l . (1982) noted t h a t the contents

of exchangeable ca t i ons and t o t a l organic carbon i n

d ~ y a g g ~ a g a t e s of var ious s ize0 were f a i r l y s imi la r .

Netzer and Hide (19381, Tabatabai and Hmway (1968)

repor ted a decrease i n organic carbon with decreasing

aggregate s ize . Mbagwu and Piccolo (1990a) observed

t h a t the concen$rationsof organic carbon, t o t a l

n i t rogen and ava i lab le phosphorus i n d r y micro-

and macro-aggregates, i s o l a t e d from s o i l s which had

been amended f o r severa l years with e i t h e r sewage

sludge, p i g o r c a t t l e slurries, were h igher than the

con t ro l s .

No sucu .. . " 1 , nn have bees douo with t ropica l 1 m i l e hence the rmotivati~n to do th ia work. Phero- I

I fore, the object i rss of t h i s p'roject are; 1

1. t o determine the effocfe of eontinuoua I

cultivated s o i l r e la t ive to fereat e o i l I

on s t ruotural , physical a d rheological 1 properties @f four 'contrasting s o i l r , axad

2. to evaluato the physioo-~homical yropertiea

of aggregate fractions of tkeae i n t endve ly

cult ivated s o i l s eonpared with fores t

soi ls . . I

The hypotbreeie t o be tes ted are; . I I

1. Oultivation a f f e a t a the physical, e t ruc tura l

end rheologioal proyertiee of the so i l .

2. The loss of organic matter resul t ing f r w

cul t ivat ion comes b r ie f ly f rom. the orgaaic .

material that binds individual a icro-

aggregates i n t o aacroaggre gate 8, a d

3. The physico-ohemical character is t ice o f .I. the s t ruotura l aggregates depend on the

type of eoi1 a d in tenai ty of land Us*.

repor ted t o reduce s o i l s t a b / i l i t y (LOW, 1972;

2.1.0 STRUCTURAL PROPERTIES

2.1 .I h a g r e ~ a t e s t a b i l i t x

Ploughing a permanent

Russel l , 1973). Tamhane e t a l . (1970) a r e of the ' I opinion t h a t t h e s t a b i l i t y of the aggregates (power

pas ture has been

of res i s tance againgt disintlegrtating fo rce s of

i n the conventional ly t i l l e d ) and l e a s t i n the

water and physica l a c t i on ) 2s t h e most important i n

u n t i l l e d treatments. where s o i l 8 a r e cu l t i va t ed

the s t r u c t u r a l behaviour of

s t a b i l i t y has been repor ted

a s o i l . Aggregate

t o be reduced by

wel l a s t o sharing: by impledents (LOW, 1954; Rovirti l

c u l t i v a t i o n (Moreau, 1978). Babsllola and Chelda

1 (1972) found' cu l t i va t ed s o i s t o be considerably

l e s s s t a b l e and with small ggregates than v i r g i n

s o i l s .

Mbagwu and Bazzoffi ( 1 9 89) a r e of the opinion

t h a t the p o t e n t i a l of t h e d y aggregates t o dia- 1 i n t e g r a t e upon contact with water was g r e a t e s t

f requent ly , aggregates a r e

.d i s rup t ion by r ap id wet t ing

and tirecea, 1957; Clement a d Williams, 1958). The 1

exposed t o physica l

and ra indrop impact ao

stabi1i t ;y ol' aggregates of he immediate surface i g o i l .is p a r t i c u l a r l y i m ~ o r t t n t , oi.nco i t i n those

aggregates wh.ich a r e expose t o d i r e c t i'lupact of I raindrops. If they bree.k down i n t c t h e i r const i -

t uen t p a r t i c l e s under t h i s i s 'surface s e a l

can be r e a d i l y formed, and

increas ing

s t a b i l i t y a re r e l a t e d t o decreases i n s o i l organic

carbon contents (Roone e t a l . , 1976). The in s t ab i -

J i t y of s t ruc tu re due t o s laking, f o r a given s o i l ,

i s u sua l ly more not iceable the lower . . i t s

humus content (Hussell, 1373) :

2.1.2 Colloidal s t a b i l i t x

S o i l p a r t i c l e s agaregate as a r e s u l t of glueing

by bacterially-produced '?olysaccharides and

physical-chemical i n t e r a c t i o n s between s i l i c a t e c l a y

surfaces and funct ional ~ ~ r o u p s of p a r t i a l l y decomposed

organic matter (Aspiras c't al., 1971; A r i n & h s r i

and Sequi, 1978; T i e r d e l l and Oades, 1.979; 8oronmr1,

. ..

1981). Organic matter concentrat ions i n the d i f f e r e n t

agtr;ro(~;ate f r a c t i o n s were ~.SsOciatcd w i t h t h e c l a y and

s i l t f r a c t i o n s i n th3 9011 (Christensen, 1986).

Al l i son (1973) 3bserved t h a t c l a y s t a b i l i z e s

s o i l aggregates. Also Schwertinann and Taylor (1977)

noted t h a t Fe and A 1 oxides and hydroxides a r e s o i l

aggregating mater ia ls . Panayiotopoulos and Kostopoulou

(1989) noted pos i t i ve and s ign i f i can t co r r e l a t i ons

between aggregate s t a b i l i t y and c l a y and s i l t content .

They a l so found t h a t Pe and A 1 oxides co r r e l a t ed

poni t ive ly and s i g n i f i c a n t l y with aggregate s t a b i l i t y .

Microaggregates (KC.20 nun) were held toge ther by

pe r s i s t en t binding agents such a s humic substances

and oxides of i r o n and aluminium (Mbagwu, 1989a).

T i sda l l and Oades (1982) proposed t h r e e types

of cementing agents t o be responsible f o r s o i l

aggregation. They ere:

- t r ans i en t binding agents composed of

microbial and p l an t derived polysaccharides,

which a r e r e p i d l y decomposed by microbes;

- temporary binding agents including r o o t s

and hyphae; .especia l ly mycorrhizal, and

- p e r s i s t e n t binding agents which include

aromatic huniic mater ia ls i n a s soc i a t i on

8

with amorphous Fe and A 1 compounds m d poly-

va l en t cat ions. The metals a c t a s clay-

organic matter a n d orgnnic matter - organic

matter bridges (Ed.warda and Bremner, 1967).

P e r s i s t e n t bind:.ng agents a r e thought t o be

mainly responsible f o r the i n t e g r i t y of the micro-

aggregates, which range i n s i ze from 50 t o 250Mm.

~ i c r o a g g r ~ ~ a t e s a r e uhe bu i ld ing blocks of s o i l

s t ruc tu re because' they can become un i t ed t o form

macroaggregates through t h e ac t ion of temporary and

t r a n s i e n t binding agents and a r e genera l ly 250& t o

2 urn i n s i z e ( E l l i o t t , 1986). Microbial mucilage and

polysaccharides are t h e t r a n s i e n t binding agents thought

t o be involved i n the binding toge ther of micro-.

aap;ree;ntes i n t o macroaggregates ( ~ a r r i s e t a l . , 1963;

T i ada l l and Oades, 1079; Fos t e r , 1981; Nolope e t a l . ,

1987)

2.1.3 A ~ ~ r e r < n t e s i zc d i s t r t b u t i o n

Aggregate s i z e :is a dynamic s o i l proper ty which

changes i n response :;o aggregating and disaggregat ing

forces i n the environment (Gish and Browning, 1948;

S t r i c k l i n g , 1950).

A s macroaggregates d i s i n t e g r a t e with t i l l a g e ,

the propor t ion of microaggregates inc reases , s i nce

microaggrcgates are not destroyed by c u l t i v a t i o n

( T i s d a l l and Oades, 1980a; E l l i o t t , 1986). The

e f f e c t s of in tense c u l t i v a t i o n on t h e s i z e d i s t r i b u -

t i o n of water-stable aggregates have been otudied

by Groh-n (:1960) i n .an Oxisol and U l t i s o l from

Brazi l ; The r e s u l t s i nd i ca t e t h a t c u l t i v a t i o n

reduced. the percentage of aggregates l a r g e r than

2 mm by about half i n b,oth mils. This was

r e f l e c t e d i n a uniform increase of o the r aggregate

~ i z e o i n t h e Oxisol, and a d r a s t i c increase of t h e

ap;gregntes smal ler than 0.21 mm i n the U l t i s o l .

These smal ler agp'egates can c log the l a r g e r

pores between t h e l a r g e r aggregates and decrease

i n f i l b r a t i o n .

According t o Gantzer and Blake (1978) ; Ike

(1986) ; Nesmith e t a l . (1987) ; Heard e t a l . (1988) ;

Roth e t a l . (1988); Bruce e t a l . (19901, g r e a t e r

bulk d e n s i t i e s can be expected under n o - t i l l

versus conventional t i l l a g e condit ions. Conversely,

I I I L krl l lhonr ard Moschler (1969)' and Blevins

e t a l . (1973) ind ica ted t h a t t i l l a g e treatment had

l i t t l e e f f e c t on bulk densi ty .

I n 3 t y p i c a l a]-able f i e l d , bulk d e n s i t y increases .

P a r t of the increase i n bulk dens i ty i s due t o

n a t u r a l causes (e.g,. the s lak ing of c lods on wetting;

and f i l l i n g up coarser pores) , and p a r t due t o passage ,

of c u l t i v a t i o n and harvest ing machinery, inc luding

the t r a c t c r pul ' l ing t h e implements (Bussel l , 1973).

Tabatabai and IImway (1968) assoc ia ted decreased

bulk dens i ty of s t r u c t u r a l aggregates wi th increased

organic carbon i n the aggregates.

La1 e t a l . (1904) observed t h a t s o i l bulk

dens i ty was a f fec ted by drop r o t a t i o n t i l l a g e method,

and the i n t e r ac t i on between them. The mean bulk

d e n ~ i t y values (avecage of a l l t i l l a g e methods) were

1.38, 1.24, and 1.28 ~ ~ r n - ~ f o r continuous corn,

corn-soybean, and corn-oat-meadow, respec t ive ly .

In V i r ~ i n i a (Shonr nnd Moschler, 1969.j; and i n

Kentucky (Blevins e t a l . , 1977), t i l l a g e t rea tments

were found t o have 110 s i g n i f i c a n t e f f e c t on s o i l

compaction o r bulk densi ty .

.

2.2.0 PHYSICAL PHOl'KHTILS - 2.2.1 Organic ma t to r

Granaland s o i l s a r e no-ted f o r t he i r ' h i g h l e v e l s

o f o rgan ic m a t t e r . The reduc'bion of or@;anic m a t t e r

upon c u l t i v a t i o n 2s w e l l known ( E l l i o t t , 1986).

, Long term cropping decreased t h e l e n g t h of r o o t s ,

hyyhae, and s o i l o rgan ic m a t t e r and caused a

r e d u c t i o n i n macroaggregates ( T i s d a l l and Oades,

1980b). Organic n ~ a t t e r i n macroaggregates dec reased

w i t h c u l t i v a t i o n rind t h e p r o p o r t i o n of s m a l l e r . aggrega te s i n c r e a s e d ( T i s d a l l and Oades, 1980a).

Also from s o i l s wi th a wide range of c u l t i v a t i o n

h i s t o r i e s , organic: m a t t e r concentrations i n t h e

20 t o 25CJMm s i z n aggrega te s were cons ide rab ly l e s s

t han those i n a g g ~ w g a t e s > 2 5 O A m .

E l l i o t t (1906) observad t h a t microaggrega tes

conta'ined l e s s o r ~ ; a n i c m a t t e r t h a n t h e mucro-

agkregutes . Microaggregates have lower o rgan ic

m a t t e r concentra t i .ons than macroaggregates (Uormilr,

1973), and t h i s ox-ganic ma.t-ter i s l e s s l a b i l e t han

t h a t a s s o c i a t e d wi th macroaggregates ( P l l i o . t t , 1986;

Gupta hnd Germida, 1988):

' C u l t i v a t i o n causes a d e c l i n e i n t h e c o n t e n t

of: o rganic mat te r . This d e c l i n e i s aggravated i f

. ...

bake fa l low i s included i n t h e ro - t a t ion where the

s o i l i s c u l t i v a t e d t o ensure no p l a n t growth, o r

where crop r e s idues a r e removed (Hamig and Maeurak,

1964; Xidley and I iedl in, 1968; h o n d , 1971.;

Mortal and Paul , 1974; Juo and L a l , 1977). Hegular

c u l t i v a t i o n may reduce the content of organic

mat te r and the chemical f e r t i l i t y with l i t t l e

inf luence on the phys ica l ppoper t i e s of such s o i l s

( T i s d a l l and Oades, 1982). Cu l t iva t ion reduces

s o i l organic: ma t te r c0nten.t (Jenny, 1941; Haas e t ul.,

1957) and r e s u l t s i n d e t o r i a t i o n of aggregate

s t r u c t u r e (Chaney and Swif t , 1984). The s t r u c t u r e

of the s o i l p r o t e c t s s o i l organic mat ter (van Yeen

and Pau l , 1981) and in f luences organic ma t t e r

' tu rnover and' s o i l f e r t i l i t y . Cu l t iva ted s o i l had

vary low organic mat te r content compa&d t o v i r g i n

s o i l (Uabulola and Chelda, 1.972).

2 . 2 2 Po ros i t y - 'Mbugwu and Uazzoffi (1989) repor ted .that;

aggregutes of convcritionally t i l l e d p l o t s were

s l i g h t l y denser aud l e s s pbrous than those an the

u n t i l l e d o r min ima t i l l e d p l o t s .

Thompson and .Yroeh (1973) a l s o showed t h a t

c u l t i v a t e d . s o = l s u s u a l l y have l e s s pore s p a c e s t h a n

a d j a c e n t u n c u l t i v a t e d s o i l s of t h e same type . H u s s e l l

(1973) i$ of t h e op in ion t h a t t h e volume of t h e

c o a r s e r p o r e s d e c r e h s e s from seedbed t o h a r v e s t .

O l i v e r i a (1967) r e p o r t e d a s i g n i f i c a n t d e c l l n e

i n s o i l p o r o s i t y w i th cont inuous c u l t i v a t i o n . Gumes.

e t a l . (1978) observed t h a t con t inuous c ropping of

an U l t i s o l i n Brazil . i nc reased macroporos i ty , bu t

d i d n o t a l t e r microporos i ty . Mourn and 8 u o l (1972)

concluded t h a t c ropping s h a r p l y dec reased macropores

g r e a t e r t h w 0.5 mm i n d i ame te r , whereus Che micro-

po re s remained e s s e n t i a l l y unchanged. Compaction by

machinery was cons idered t h e cause of t he dec reased

m ~ c r o p o r o s i t y .

Gantzer and Bl&e (1978) r e p o r t e d lower t o t a l

p o r o s i t y i n n o - t i l l a g e t h a n i n conven t iona l t i l l a g e .

C o n t r a s t i n g r e s u l t s were, however, r e p o r t e d i n

un t racked i n t e r r o w s by Cul ley e t al. (1987a, b).

Mbagwu (1989) i n d i c a t e d t h a t h i g h o r s m i c carbon

i s r e s p o n s i b l e f o r i he i n c r e a s e i n t o t a l p o r o s i t y of

s o i l s and aggregate:; , whereas t h e p h y s i c a l s t r u c t u r e

of s o i l s determine pore-s ize d i s t r i b u t i o i , which i n

,. - t u r n a f f e c t s w a t e r f low (White, 1985). It appears

the re foxe , t h a t the gene ra l r educ t ion i n t o t a l and

'macropcres of s o i l aggrega te s under cu1tivtit;ion i s

a 'consequence of reduced o rgan ic carbon associated

with t h i s type of land uae.

2 . ~ I . 3 b w t o t rotxuki.on --- ----- 'Tlw w r r h r : cuiilcn't; of s u r f a c e l a y e r s o f s o i l s

l u ofken higher i n undis turbed s o i l t han a f t e r

ploughing (Army e.c aL., 1961; Muody e t a l . , 1961;

Bmika und Uicks , 1968; Tr ip l e t t i e t a l . , 1968). One

of $he f a c t o r s t h a t may be r e s p o n s i b l e f o r t h i s i s

the s m a l l e r volumo of u n t i l l e d s o i l occupied by

pores which d r a i n r e a d i l y under g r a v i t y ( L h l e r s ,

1976).

~ a r t i n et; a l . (1983) r e p o r t e d h i g h e r vo lumetr ic

vru te r . conten t under n o - t i l l a g e than convent ional-

t i l l a g e . Wood (1471) .observed. t h a t mosL t r o p i c a l

s o i l ? under f o r e s t vege ta t ion have tile ability to

absorb. water at r q h l r a f e s.. Vowai ( 1968) supported

t h i s view und f u r t h e r noted t h a t u f t c r t h e f o r e s t

v e g e t a t i o n was c l e a r e d a d farmed, i n f i l t r a t i o n

r a t e decreased und h l&i e r o s i o n rate became an

important management problem i n a r a b l e croyyiog.

Mbagwu (1989b) reported t h a t inc reas ing ma'nure

add i t ions r e su l t ed i n s i g n i f i c a n t . impravements i n

water r e t en t ion and ava i lab le water capaci ty of

th ree s o i l s . A t i i e l d capaci ty (0.01 MPa tens ion) ,

addi i ion of 10% munure improved moisture contenl;

by 22,, 32 and 15% i n the Lamporecchio, Vicare l lo

and Cremona s o i l s , re ' spect ively , r e l a t i v e t o the

contrgls . .At permanent w i l t i ng po in t (1.5 Ml?a

tens ion) the r e l a t i v e improvements f o r the th ree

s o i l s were 30, 17 and 3% a t 10% manure add i t ion

ra te . ,

. ' The ' p l a s t i c l i m i t (YL) i s genera l ly regarded

a8 the upper l i m i t of water content i n s o i l f o r

ploughing. Above t h i s l i m i t , s o i l s become very

unploughable m d sometimes develop c lay pans below

the plou@ layer . Increas ing add i t ions of manure

cons i s t en t ly incruased the p l a s t i c l i m i t of s o i l s .

The p r a c t i c a l imp:Lication of the increase i n p l a s t i c

l i m i t due t o manure mendmen6 A 8 t h a t of an increase

.in the l a t i t u d e 01 cu l t i va t i on (Mbagwu, l989b).

, If a s o i l has a moisture content above i t s

lowor p l a s t i c l i m i t (which i s the moisture content

,

a t which the s o i l p a r t i c l e s begin t o s t i c k t o each

o ther ) working it m d e r moderate pressure i s l i a b l e

t o c rea te l a rge c l o ~ s devoid of coarse pores. This

is because the s o i l crumbs become r e a l l y s t i c k y and

begin t o flow under pressure as the moisture content

r i s e s above t h i s point . H a m i can be done by cu l t i va -

t i o n i f c a r r i ed out a t these moisture contents

(Russel l , 1973).

Yavies a t al . (1972) are o f the opinion tha t . at

the extremes of moisture contents cu1tivat;ion of the

s o i l i s vary d i f f i c u l t , i f not impossible. The

intermediate moisture range wi th in which'conditions

f o r cu l t i va t i on a r e good, i s known a s f r i t lb le range

and i n t o the p l a s t i c s t a t e , they a r e r ead i ly

compacted t o form iqe rmeab le l a y e r s o r pans. The

smearin'g caused by implements o r spining t r a c t o r wheels

i s p a r t i c u l a r l y damhging s ince it s e a l s off the s o i l ' s

interconneLctihg systems of pores.

Good s o i l t i l t h . i s manifested i n . the f r i a b l e

rantge of s o i l consistency. It is a dyuamic s o i l

condit ion and tends t o d e t e r i o r a t e under the usual

cropping and t i l l a g e operat ions (Baver c t a l . , 1972).

Shrinkage-ousccp~tible s o i l s pose s e r lous problems

t o t igr icul t ;ur is ts and engineers. Ver t i ca l shrinkage

~crcicks on a g r i c u l t u r a l s o i l s a c t a s channels througb

which rapid l o s s o f i r r i g a t i o n water c u occur. I T

used f o r foundation?^ f o r bui ld ings and dams without

adequate anti-shrinkage treatment , c racks w i l l

f r equen t ly occur on the wal l s a s the s o i l s con t r ac t

during dry per iods (Mbagwu, lC;)gZb). - Information on the e f f e c t s . of land u s e of the

.. . At ta rbe rg ' s l i m i t s i s not avai lable . l o the ex ten t .

t h a t the p l a s t i c l i m l t of soils i s influenced by

t h e i r orgenic mat ter contents , any land use that;

reduces s o i l orgariic matter should be expected t o

reduce the s o i l s p l a s t i c l i m i t .

PHYSICO-Ct1E;MICAL I'RUPLH'PILS OF AGGIUGATE BIZkX3 - Carbon, nitrojien mid phosphorus

Metzer and Hlde (19.38) and Tabatabai and Httnway

(1968) reported a decrease i n orgarlic carbon wi th .

decreasing aggregate ~ i z e , b u t o the r s (Uitmus and

Mazurak, 1958; iiolomon, 1962; Tamboli e t a l . , 1964;

Uebber, 1965) obtained an inverse r e i a t i o n s h i p

between organic csrbon and aggregate s ize . This

a&arent dispt lr i t ,y may be r e l a t e d t o the f ind ings

t h a t .C and N are ~lssociatied with f i n e s o i l p a r t i c l e s

( ~ h r l o t e n s e n , 1985; chr is tensen and Sorenuen, 1985)

and these p a r t i c l e s may vary among differenl- aggregate

f r a c t i o n s (Mbagwu and Piccolo , lg90a).

18 ,,-_

Mbagwu and Baz:soffi (1989) observed t h a t the

s o i l of the t i l l e d p l o t s contained l e s s carbon and

ni t rogen than tha t of the u n t i l l e d p l o t s i n a l l

aggregate s i ze f rac t ions . The d i s t r i b u t i o n 01 organic

0 and N among l a b i l e a d s t ab l e s o i l organic mat ter

pools i s affected by many f a c t o r e i nc ludmg crop

rotatlion ( ianzen, 1387), type and length of t i l l a g e . ('Piesoen and Btewarl;, 1983; Dalal and Mayer, 1987;

Balesdat e t , al. , 19tB; Carnbardella and E l l ~ o t t , 1992),

and f e r t i l i z e r a p p l ~ c a t i o n s (Stanford and Smith, 1972;

Chri'stensen, 1988). The most l a b i l e f r a c t i o n s decl ine

wi-th cu l t iva t ion .

The g rea t e s t e f f e c t s of cultivation on the

nu t r i en t and mlcrobral c h a r a c t e r i s t i c s of s o l 1 are

oberrvod i n the C- und -N enriched small macro-

~lpgregute f raq t ion 250 - 2000Am (T i sda l l and Oades,

A~IWa, b[ Uolmaur, 1383; E l l i o t t , 1986; Gugta and

Oermlde, l'jMt.31 Qmbtirdel la and E l l i o t t , 1993). S o i l

niaroorganisms, especially fungi , may play an important

ro l e i n the formation of these macroaggregates

( T i s d a l l and Oades, 1982; Molope e t a l . , 1987; Gupta

and Germida, 1988).

The C/N, O/P aud N/P r t l t ios o f water-stable

micro-aggregates were narrower than those of macro-

. aggreeates i n both cu l t i va t ed and na t ive sods

( E l l i o t t , 19.86).

Llhatnagar and K i l l e r (1985) and Uhatnagar e t a l .

(1985) observed higher available P i n the l a r g e r than

i n the smaller aggregates. Hi$her contents of p , Ca,

lt, OC and N were fou.nd i n .the no- t i l l age than conven-

t i o n a l t i l l a g e s o i l s (Lgl, 1986; Saff igna e t all.,

1989; Utomo e t a l . , 1990; Md-~boubi e t a l . , 1'39.5).

The d i s t r i b u t i o n of ava i lab le P among the

aggregates d id not reveal any consistent- pa t te rn

whatsoever and were i n no way associa ted with the

p a r t i c l e s i ze f r ac t ions (Mbagwu and dazzof f i , 1989).

Kowalinski e t a l . (1982) reported t h a t the

contents of exchanbcable ca t ions and t o t a l organic

carbon i n dry aggregates of various s i z e s were f a i r l y

s imi lar .

The d i s in t eg ra t ion of macroaggregates (wi th

cu l t i va t ion ) i n t o r iutr ient poor microaggregates md

the subsequent re lease of p lant -avai lable nu- t r i en t s

may be one explanation f o r the observed pa t t e rn of

reduced nutr ient-supplying e f f i c i e n c i e s i n cultivated

s o i l s when compared with grassland s o i l s ( P l l i o t t ,

1986).

20

,. . .

2.3.2 S t a b i l i t y bf u~;grci.a.tes

S t a b i l i t y of aggregates of f i v e d i f f e r e n t

s i z e s decreased with decreasing aggregate s ize .

Virgin s o i l s had s i g n i f i c a n t l y h igher aggregate

s t a b i l i t i e s than cu l t i va t ed s o i l s (Panayiotopoulos

and Kostopoylou, 1989). There was a l s o a s i g n i f i c a n t

r educ t ion ' i n the percentage of I - 5 am aggregates .

produced by t i l l a g e of a continuously cropped a s

compared with pas ture s o i l (Ojeniyi and Dexter,

1979)

Mbagwu and Bazzof f i (1989) no-ted t h a t aggregates

were l e s s s t a b l e .under conventional t i l l a g e on a l l

so i l s . Heduc-tions i n aggregate s k a b i l i t y a f t e r

c u l t i v a t i o n are most pronounced i n s o i l macro-

aggregates, whereas the s t a b i l i t y of s o i l micro-

aggregates remained unchanged (T iada l l and Oades , 1982 ; ..Onde 8 , 1984).

A s a r e s u l t of t i l l a g e , the re was a reduction

of the l a r g e c lods t o smallor easier-to-erode s o i l

aggregates (Mbagwu and nazzof f i , 1989). Yater

re6is:tance 'of s t r u z t u r a l aggregates increased with

docrerising' d i m e t e r (Kowalinski e t a l . , 1982).

21 . ,

- .

2.3.3 .Water r e i en t ion of a g ~ ; r o ~ c r t c s

Il'horne and Thorne (1979) showed t h a t the

degree of aggregation and the arrangement and . ,

s t a b i l i t y of aggregates mf luence watcr r e t e n t ~ o n .

The water r e t a ined a t small negat lve water

p o t e n t i a l (-0.03 increased progressively with

decreasing aggregate s i ze whereas a t -1.5 W a , the

water re ta ined appeared uninfluenced by aggregate

diameter. There were no r e a l d i f f e r ences between

t i l l e d and u n t i l l e d p l o t s i n water r e t a ined by the

d i f f e r en t . agg rega t e f r a c t i o n s (Mbagwu and bazzof f i ,

1989; Mbagwu and Piccolo , 1990b). These authors

a l s o observed t h a t the moisture r e t a ined u.t thc

-0.03 MPa p o t e n t i a l cor re la ted y o s l t i v e l y wi th the

s i l t + c lay contents while moisture r e t a ined a t

-1.5 Ml'a was l e s s influenced by s i l t + clqy contents

of the aggregates.

2.3.4 Bulk dens i t y of a g p e ~ a t e s

Benjamin and Cruse (1987) noted t h a t t i l l a g e

reduced the shear s t r eng th and bulk dens i t y of s o i l

ap;gregates. Mbagwu and Piccolo (l'j90b) concluded

t h a t organic w a s h app l ica t ion on s o i l s decreased

bulk d$nsity of e o i l aggregates.

2.3.5 P a r t i c l e s i z e d i s ' ; r i b u t i o n withi.n oy;p;re~ut;es

Metzer and Hide (1938) and Witmus.and

Mazurak (1958) found p a r t i c l e sslze distribution

f a i r l y c o n s t a n t i n a g g r e g a t e s of v a r i o u s s i z e s .

Taba taba i and Hanway (1968) observed t h a t t h e

p a r t i c l e s i z e d i s s r i b u t l o n s i n t h e d i f f e r e n t s i z e d

agg rega t e s were n o t d ~ f f e r e n t .

Chr l a t ensen (1986) r e p o r t e d t h a t t h e c o n t e n t

of s i l t and c l a y i n macroaggregates s e p e r a t e d by

d ry - s i ev ing i n c r e a s e d with d e c r e a s i n g aggrega te

s i z e , a view suppor ted by Mbagwu and P i c c o l o (199013).

2.4 Conclusion - Thi s review h a s r evea l ed inconsistent r e s u l t s

on t h e physico-chemical proper.l;ies of s o i l aggre-

g a t e s due t o l a n d use/management. The e p i c e n t r e

of t h e s e s t u d i e s A S i n t h e temperate r e g i o n where

t h e sofi ls a r e veqr d i f f e r e n t from t h o s e i n t h e

tropico:. 'The pre:jent s t u d y hopes 'to p rov ide

in fo rma t ion on the: p r o p e r t i e s of s t r u c t u r a l aggre-

g ~ t e s of t y p i c u l 1;ropical s o i l s under d i f f e r e n t

.land use sys'tems.

3.0 l!lE I'IIYSICAL ENVIRONMENT

3.1.0 General descr ip t icn of thc pro,jcct a r ea

The s o i l samplcs f o r the pro.ject were co l l ec t ed

from th ree locat ions i n Ylateau S t a t e and one

loca t ion i n Bauchi S t a t e , Nigeria (P ig . 1).

3.1.1 Platcau S t a t e

Pla teau S t a t e i s bounded by longitudes

7 ° 0 0 ' ~ and 1 0 ~ 3 0 ' ~ and l a t i t u d e s 8 ° 0 0 ' ~ and 1 0 ~ 3 0 ' ~ .

The sample locat ions a r e la-hoss, Gindir i and Panyam

a l l on the Jos Pla teau marked by 8 ° 2 2 ' ~ , 9 ° 3 0 ' ~ ,

8 ° 5 0 ' ~ ~ and 1 0 ~ 1 0 ' ~ ( H i l l and Rackman, 1973).

H i l l and Hackman (1973) and Macleod e t a l .

(1971) described the geological formations of Jos

Pla teau a s Basement complex of o lde r g ran i te and

granite-gnesis . . and the Newer b a s a l t .

The locat ion a t Gindir i f a l l s within t he

p o l o ~ ; i c & i formatjon of o lde r g ran i t e and. g ran i t e

gnesis while those a t Ta-hoss and Panyam f a l l

within the Newer k a s a l t formation. The F'unyk

Newer b a s a l t has keen descpibed as some of tho

-- ----------.I

most r e c e n t on the Joz r l a t e a u ( k c k a y e t a l . ,

The physiogr2phy has t h r e e major f e a t u r e s : t

undu la t ing t e r r a i n , h i l l s and mountains and

d i s sdc ted t e r r a i n (Hill and Hackman, 1973).

The rel- iof i s g e n e r a l l y wi th in 1500 metres

above s e a l e v e l , 'but does i n c r e a s e t o a spot iieigh'r,

of 1751 metres a t t h e Shere h i l l s .

3.1.1-2 Climat;c .

>'ul l c l i iua to log ica l d a t a a r e a v a i l a b l e orAy

f o r J o s town and no where e l s e on t h e P ia teau .

However, t h e sample l o c a t i o n s a r e covered by t h e

Jos synoptic c l i m x t i c s t a t i o n (Kowai and KrinSe ., 1972)

The mem a n m a l r a in fa ; i rcmps I r o n about

1050 mm t o about 1580 mm w i t h an o v e r a l l mean o 2

about 1413 rnm ( H i li , 1976; Kowa~ and Knabe, 1972) . Thc me,% annual r l i n f a L i f o r J o s i s 1212 am

compu-tod from l O yearn r ecords (Ta3ie 1).

T h e mecan annual temperature f o r J o s P i a t e a u ,

cnrnpltcd from t e n years record i s 22.3'~. The

I \ i j:hrta t, Len~~)eratu.-e occurs j u s t bcf ore the beginning

~ b s e r v a t ion'

t U1 0; 0 U Tu

I a April 0

1-1 0 P 0 O'! I-'.

of the r a i n s , t h a t i s i n March and k ~ j r i l ( k l i 1 1 ,

1976; Table 'I), when the m c a n monthly t e ~ y e r a t u ~ e s

reach 24.5'~. They drop t o 19.5 '~ lu D e c e m b e r which

correspond t o t h e peak of the harinaltan. The

monthly anti s easona l variations i n temperature a re

3.1.1.3 Sunshine ( ~ a d i a t i o n l

The p a t t e r n of r a d i a t i o n over &he s tudy a r e a

more o r l e s s , t a l l i s s . with t h e p a t t e r n of r a i n z a l l

wi th t h e l ' a rges t amaunt of s o l a r radiation c o r m s -

youding roughly t o thc ralny season (dowa; a a

mabe, 197.2). There 1 s a g e n e r a l a rop i n t n e

miount of radiation from October t o Eebruary . Pcak

i n t o ' n s i t i e Y of radi'l 'kion are r e ached aroulyd mld-day

wl ic lo r~ even though ~ h c a c t u a l numoer oP h v u s 01

m e r m doily u u n s h ~ n e a r e h lgher durlnli; t h e day i n

rocorded dur ing the harmattan. This c u oe a t t r l o u t e d

t o t h e b r i g h t clo'udii w n i c i l r e l i e c t raaia-Llon d u r m g

t h e r a i n y season anc the rluzjr and d u s t y l ia rant tan

which h m p e r incider,. t i n s o l u t i o n .

3.1.1.4 Hi?lat-ivc humidity

The rnaxunum va lues of t h e relative hum~dity

correspond t o the p'ak r a i n f a l l p s r i o a unu drop t o

minimum dur ing the .lry scason, thl1t i s , Noveinbcr

.LO March (Table 'I). Tne P l a t e a u has a h igner

r e l a t i v e humidity w'aen couparea with o t h e r a re a s <

along t h e s w e l a t i t u d e due t o t h e in f luence o:

. h i g h e r ground.

3.1.1. 5 Ve ge -ti a t i on m d . Lcvld.i~.:;e --- '

The 'vege ta t ion of 20s P l a t e a u has been hig11i.y

a l t e r e d by human' a c . i i v i t i e s l i k e c l e a r i n g , f arrning,

grazing. Conse quen-~;iy , t h e y r e sent-day comriun.~t-ie s

are l i t t l e more t h a n s h o r t d u r a t l o n Paiiows o f

adopted g r a s s e s and herbs a t d iPfercnL s t a g e s 01'

regrowth, w l t h a few highly p e r s i s tent; snrubs

(1ii.f ord and Tuley , 1'374). However, Groovc (1952)

had observed t h a t a r e l i c vegeta t ion on t h e E l a t e m i

shows Iorrner exister..ce of arl extensive W O L X L ~ ~ L G

of t h e nor the rn Guir.ea savannah type .

The

tmd shrubs l i k e Terrr i n a l i u anu dy;llyf;ium. Areas

i n which Zoudet ia , G t e z i u m , Microchloa and ~poroboius

s p e c i e s predommate. Areas deveiopea from b a s a l t s

have Yasualum anci - i L r a c h i a s i a spec ies . Piore i n t e n s e l y

c u l t i v a t e d a r e a s are o f t en ba re of veget;ation and

t o r r a c e s a re b u i l t on s t e e p s lopes of the escarpwent

(Grove, 1352; Alfo'rd and Tuley, 1974) t o coun te rac t

the shor tage of farmland and a l s o c i z e c ~ e r o s i o n on

these s lopes . The m a j o r c rops culLivatek incluae

maize, sorghuni, a ~ h a , I r i s h p o t a t o e s , m i l l e t , r i c e

und yams. Other c rops are c a r r o t s , tomatoes, caobage,

oni on3 arid o t n e r vegetable s.

3.1.2 Uaucn i S t a t e

Uauchi S t a t e l i e s I n t h e n o r t h e a s t e r n porJt,iun

of Nigeria . It i s bounded by long i tudes 8'45'~ and

0 11°45'k; and. latitudes g050 'h and 12 3 O ' h . The

sample i o c a t i o n ai. Deba i s boundeu o y i i G 1 5 ' s ,

1 1 ° 3 0 ' ~ , 1 0 ~ 0 0 ' h anti 1 0 ~ 1 5 ' ~ (UbUP, li)d4).

The sample l o c a t i o n a t Deoa I a l l s w l C u n t h e

geo log ica l Iormat--on of c re taceous saiiastone and

sha le ( F u ~ ~ x , l99Oa),

Thc p h y s i o g r ~ ~ p h y 01 3auchi L t a t c 1 s uurkcd b y

l l i l l s and K e r i - K e n and Golnue p l a n s ,

,

3.1.2.2 Climate

t h e n o r t h t o 1500 riiln in t h e southwest. This i s

u s u a l l y p r e c i p i t a t e d between Karch and t he enci 01

October, most ly falling i n J u l y m u ~ u p p s t ( ' 2 io lc 2 ) .

The r a i n y season v a n e s Irom about 95 days In the

n o r t h t o 170 days i n t h e south.

The mean maximum temperature i n Bauchi rises

- 0 t o 37.0'~ i n march and A p r i l , d r o p p u g t o 29.6 C

in August, w h i l s t the miniuurn temperature may drop

0 t o 22 C i n December and January because of tne cool

hurmattun wcaLher.

Bauchi S t a t e has u high c l z a r n c t ~ r i s t i c p a t t e r n

o I r a d i a t i o n because of i-Ls semi -and clin:jic,. TLX

of tho r a i n y season. The mount of raci la t ion IS

1 Observation

0 k' 03 w 4= . VrJ * b 0 !U 0 0 O 0

February .

0 8 w I V1 CT\ Lh . 4 - 0 3 <

September

. -

' lower during the r a l n y season. pea^ ~ n l i c n s i t l e s

are reached arour!.d mid-day.

3.1.2.4 lielativc: humidity

The r e l a t i v e humlaity i s highest a$ the

during the r a i n y season, drollping t o 7%

the d ry season. Relative huuialt-y Pol,lows t h e

p a t t e r n of ra infuLl i n the S ta te (Table 2).

3.1.2.5 Vep;eta:tion and La;~duse

The area of .detuchi State nor tn of i1°0r3' Ales

wi thin the Sudan Lone, and i s charac te r i zed l ~ y Acacia

t r e e v and scrub s6avannn. The bulk of t h e sta-Le i s

i n the sub-Sudan Sone. The l i e r i - ~ e r i y l a l n s i n the

e a s t and c lay y l a l n s are woouluud t r e e savannah.

The western area of Jos Pla teau wnicn l i e s i u the

Northern Guinea Zone i s woodland. PakLand nas

developed i n the nore densely s e t t i e d areas 02 t h c

. .

fa rming i s a l s o p r a c t i c e d . fi-ornadic hcrclsmun are

s c a t t e r e d all ovex the s t a t e .

Preference 1 s given t o shorter season crop

v a r i e t i e s arid mixed. cropping i n t h e north. The

main crops a r e sorghum, m i l l e t , maize, c o t t o n ,

groundnut, cowped, r i c e , sugar-cane and vcge t-ables.

,Soil namples from C - 20 cm depth were colleated

from cultivated and adjacent fores t land i n four

locations i n Nigeria (Fig. 1). C u e was t u e n t o

miniaize sample disturbance during aamyling and .

taanspor ta t ion.

The s o i l s sampled f o r the p r o j e c t .'are c l a ~ s i f i e d

according t o S o i l Twonomy as ~ l t i s i l , belonging t o

t he sub-group typic kaplustult (FDILLR, 1990b) ;

Incep t i so l , belonging to Typic Bystropeyt ( P D U ,

L990b) and .Fhtiso2, belo!lging t o Typic Troporthent

( U g w u , 1983) i n Plateau ,S ta te , while n l l e r t ieo l

belonging t o "ic Chromstert (FDBLrR, 1930a) was

colLccted from Bauchi S t a t e ( T a b l e 3).

4.2 Laborator j Methods _I.--- -_I--

The s o i l samples wefie air-dried a t room temyera-

ture and then pre-sieved through n 5.00 nn mesh.

C l o d s were c a r e f u l l y cruohed b y hand clouy, l i u e e of

n a t u r a l cleavages t o pass the mu&. Two hundred uud

f i f t y grams (250 g ) of t t .e s ieved sample, at a t ime,

was t ra~sfer red . t o the uyyermost of a seat; of- sieves

cn c - t

of s i z e s 2 , 1, 0.5 and 0.25 ma. They were shaken

mechanically f o r 10 mins. Fur the r s i ev ing by hand

was done where necessary. This procedure, s i m i l a r

t o *that described by Kemper and Chepil (1965),

resul.ted i n t he sepera t ion of t he following

a ~ g r e g a t e f r a c t i o n s 5 - 2 , 2 - 1, 1 - 0.5, 0.5 - 0.25, and < 0.25 mm. 'Phis sepera t ion continued

u n t i l enough quan t i ty of each f r a c t i o n was

co l l ec t ed f o r f u r t h e r ana lys i s .

4.2.1 Determination of ciaaregate s t a b i 1 j . t ; ~

4.2.1.1 Mcm-wci.~;ht dinmeter of dry ap;gmy~otes ( M w D D ~

The nean-weight diameter of dry aggregates

was delermined according t o t he method o f Kemper

and Chopil (1965). This method involved v i b r a t i n ~

ho r i zon t a l l y on z, mechanical shaker f o r 10 mins. ,

;'50 C: of d l y s o i l (previous ly s ieved through a

rnm mesh) bn t h c t op of n nes t of s i eves of

r l l nmo-tcro 2 , I., C1.5, ma 0.25 mm and determining

t he mass of aggrf:gates on each s ieve t h a t r e s i s t e d

4.2.1.2 Plem-ye5.r;ht diamcber o f wet a y ; ~ r e ~ n t e s (MWDW)

,. . . ' Mean-weight diame.ter of wet aggregates was

determined according t o the method o f Kemper (1965).

I n t h i s procedure 10 p; s o i l was pre-soaked f o r

5 mins. on the topmost s ieve of diameters a s i n

(1) above, then v e r t i c a l l y osc i l l a te 'd f o r 20 times

a t the r a t e of I osci . l la t ion per second. The

. resist-an% aggregates were oven-dried and t h e i r

masses recorded.

To assess the r e l a t i v e s u s c e p t i b i l i t y of the

s o i l s t o d i s in t eg ra t e upon wet-sieving a new index,

the p o t e n t i a l s t r u c t u r a l deformation index,

PSDI (Mbac;wu and Bazzoffi , 1989) was computed

thus ,

where : k 1

PSDI =

Q ~ ~ ' = mean diameter of the i t h s i ze f r a c t i o n (am;

2 (QiWi) i = 1 1 -. - I x 100 ------- (1) & 1 = 1

(Qidi),

Wi = propcrt ion of thc t o t a l mass r e t a ined i n $lie i t h s i z e f r a c t i o n (from wet-sieving; @;g-

. di = . propcrt ion o l the t o t a l mans r e t a ined i n tkc i t h s i .m f r a c t i o n (from dry- s ieving) gg-1

n = number of s ieve (s1ze)f ract ionn used.

. . 38

. . +. - - The FSDI was .ased t o normal ize t h e c h a n g e s

i n d i s t r i b u t i o n of d r y and wet a g g r e g a t e s t o

ennble a r c a l i s t i c comparison of t h e r e l n t i v c

e f f e c t s pf l and u s a c r o s s t h e d i f f e r e n t s o i l s t o

be made.

h.2.l.3 Col loid .nl . s t a b i l i t y

The procedure d e s c r i b e d by Middleton (1930)

wns used. Th i s involved de te rmin ing t h e p e r c e n t

s i l t + c3.ay i n wate r -d i spersed samples ( A ) and

t h a t i n sodium resf in-dispersed samples (B). The

index (A/B x l o o ) , known a s t h e ' d i s p e r s i o n r a t i o '

( D l < ) , i.:; a measure of t h e p o t e n t i a l of t h e i n d i v i d u a l

ngg rega t c s t o r e s i s t breakdown upon c o n t a c t w i t h

water molecules. I n t h i s s tudy , a 20 g sample from

each aggrega ted f r a c t i o n was soaked i n e i t h e r

distilled water o r ciodium hexametaphosphate s o l u t i o n

Tor '1.8 hrs, :Collowctd by end-over-end shirking on a

mechanical shaker. f o r 2 h r s . a t 10 rpm. The d i s p e r s e d

s i l t + c l n g was determined by t h e hydrometer method.

lE!CEI?.MINATIOn' OF BULB DENSITY AND POROSITY

13ullc d c n s i t y

Bulk d e n s i t y was determined by t h e c l o d

method a s desc r ibed by Blake (1965). Oven

d r i e d c l o d s were t i e d wi th s t r i n g s an& weighed

whi le suspended i n a i r . The c l o d s were d ipped

i n rnclted p a r a f i n i n a c o n t a i n e r . T h i s o p e r a t i o n

wnn rc'pcntod u n t i l t h e c l o d s wcrc complete ly

co:rl;c!cl. wi.th p a r a f f i n and weighed.

3 u l k d e n s i t y was c a l c u l a t e d a s fo l lows :

who sc :

-3 Db = d r y b u l k d e n s i t y (Mgm )

d = dens: i ty of wa te r a t t empera ture o f de t e rmina t ion (1.0)

Wodo = Ovon-dry weip;ht of s o i l sample ( c lod )

( R:)

= nei; wei.ght o f s o i l sample p lus 'hw parefifin i n water ( 8 )

LI = weif;ht o f p a r a f i n c o a t i n g i n a i r ( g ) pa

Wsa = n e t weieht of s o i l c lod i n a i r (e) d = dens i . ty o f p a r a f i n (0.9) . . P . .

, .

T o t a l p o r o s i t y

T o t a l p o r o n i t y i n t h e volumo of t h o sninple

n o t occupied by s o l i d m a t e r i a l s . It was c a l c u l a t e d

. . Prom t ' h o values of b u l k d e n s i t y u s i n g t h e method

.dcr,cri.bcd by Voniocil (1965). The ca l cu la t i . on i s

bnncd on. t h e rel .at j .onshi.p between bulk d e n s i t y

r l r l l i p:irli.i.csl.e der,::ity and. on t h e assumption of

2.b5 ~ r ; r n - ~ p a r t i c l e d e n s i t y f o r mine ra l s o i l s .

T = Total p o r o s i t y (%) P DD = Bulk d e n s i t y (M~Y')

PD = P a r t i c l e d e n s i t y (Mgm - 3 )

4.2.5 :DVJ!:I3I<1"1TNATTON OF P l J Y S Z C O - C H E M I C A L P I I O P G I 1 T I E S OF A A . 5:1.ZKX

4.2..3.1 0ry;:inic carbon

0ry;anic carbon was determined by t h e Walkley

and Black method (1974) a s modified by A l l i s o n

(,l9c5). T h i s method. i nvo lves t h e oxidat i -on o f

t h c ' s o ' i l o rgan ic m a t t e r w i th potass ium d.ichroinate

(K,Cr,,n,) u s i n r ; concon1;-rxtod nulphur ic clcj~tL .. I . / (EI~SOLI,), and t h e percentage 0rp;anic carbon found

1 l;:il:i:l;:i r w: 1 I N rcrrwu:~ am~oonj.u rn r:~:L.~)h:rtc

%his was delxrmined from Walkley and Black

. . t h o pcrcantnge o:rgani.c cwbor, b y t h e convent ional

" V n n Bemme1.m f a c t o r " of 1.724.

4.2.3.5 Total. n i t r o c e n

Total. n i t r o g e n was determined by 'the K j e l d a h l

metho3 (Bremner, 1965) u s i n g CuS04/Na2S04 c a t a l y s t

.mixture. The ammonia (NH ) from t h e d i g e s t i o n 3 was di.s.l;i.lled. wj..th 45% NaOH i n t o 2.5% b o r i c a c i d

and dotermined by t i t r a t i n g wi th 0.05N IICl.

4-.?; 3.4 Avni.l.nb1.n phosphorus

~ v a i l n b ' l e phosphorus was determined by Bray and

Kurtx (1.94-5). Bray II method (0.03N ammoni.um

flu or id^ x 0.1N IIC1). The a v a i l a b l e phosphorus

- (ppm) was read oSf from s tcmdard curve a f t e r

ohtnininy: t h e o p t i c a l densi.ty from a photo-e1ectrj.c

coi.ori.meter.

I . ? . 5. i h:i r: I . l r r . c? - 'rc1;ent;j.c.n c n p n c i t g

I l h i r l ; ~ I cram:. (30 p;) of each o f t h e : t~p;regate

r:~:~nc l;i ons were wej.ghed i n t o rubbe r bands ( r i .n r r s ) .

Thesc wcrc used Lo determine t h e wa te r con ten t o f

ngr;re;;a.te Crnc t i cns a t 1.5 PPa ( 1 5 b a r ) and ,0 .01 P"IPa

(0.1. b a r ) , u s ing Lhc p re s su re -p ln t c appa ra tus . I n

each caso tho samples were p l aced on ccramic

plate-sand soaked with water f o r 24 hrs. The p l a t e s

with t h e sanples were placed i n t h e yretluura chamber

and subjected t o the d i f f e r e n t suct ions u n t i l water

ceased t p dra in out f rou the s o i l saxpleo. The

samples were then weipJwd and oven-dried at 1 0 5 ' ~

f o r 24 hrs . and re-weighed. Moiqture r e t a ined by

each aggregate f r a c t i o n was ca lcu la ted , thus:

Y t . of moisture = W t . of wet s o i l + - conta iner - k t . of d ry s o i l + couta iner ------ (4)

'

Y t . of d r y s o i l - W t . of d ry oil + conta iner - W t . of conta iner ----------------- ( 5 )

% Moisture r e t a ined = kt . of moisture ,00-----(6) W t . of dry s o n

4 .2 .56 - P a r t i c l e s i z e d i s t r i b u t i o n - - P a r t i c l e s i z e ana lys i s was determined on t h e

s o i l aggregate fractions using the p r i n c i p l e s of

Bouyoucos hydrometer met?hod described b r D a y (1965).

The technique used was t h e dirrpersion of semple with

calgon (sodium hexametaphosphate). I n t h i s method,

20 g of t h e aggregate f r a c t i o n s were soaked i n calgon

f o r 48 hrs . and l a t e r were transferx-ed t o mechanical

s t i r r e r f o r mechanical a g i t a t i o n f o r 2 hrs. before

t h e hydrometer t e s t .

4.2.4 O'i ' l l l;;lt Dk;'l.!liViINAl?IONS TO FDZ;LY GH AII AC!PER? 5.E TIi.E SOILS

n:l.l;-i on of t h e l i t t e r b e r g L i m i t s

Thc c c t of s o i l s f o r t h e d e t e r m i n a t i o n o f t h e

c:onr~:l.r.I;cnc:f l imits were f u r t h e r sieved. u s i n g s i e v e

No. 56 ('+SO microns = 0.00Ll-5 mm) t o remove t h e c o a r s e

particles b e f o r e beinp; used t o determine t h e limits.

Approxirnntcly 200 g of each sample was weighed t o be

uncd t o dctcrmino the shr inkage l i m i t and A t t e r b e r g

l i ~ n i - t s .

The i i .qu id l i m i t (LL) was de te rmined u s i n g t h e

c1ns::icnl C~nsnp;rnncle method. (1972) and t h e procedure

ou.Lli.ncd. by Sowers (1965) making use o f t h e LL dev ice .

200 ~ ; . o i " each s t i f f p i s t e o.f t h e s o i l samples

was mixed wi th enough h i s t i l l e d wa te r t o g ive t h e

s o i l thc c o n s i s t e n c y of s o f t pu&;y. Some of t h e

mixtuFe 'bias p u t i n t o t h e cup of t h e LL device and

8mool;hen l e v e l with. . the front; of t h e cup with a sha rp

k n i f e ' to form o p a t ' tha t i s 1 cm t h i c k above t h e

p o i n t ol' c o n t a c t . A dividinp; groove was then used

t o c u t n p o o v e d i v i d i n g t h e pa$ i n t h e cup i n t o

two oqual p a r t s . 'The crank was t u r n e d a t 2 revolu-

t:i.on:; p c r second. wai1.e t h e blows ( t a p s made by t h e

cup on Lhc hard ru.>ber s t a g e ) r e q u i r e d t o cause t h e

, r ;o i l pa-i; t o flow bogether and obscure t h e bottoln of

t h e groove f o r a d i s tance of (yl inch) 1.25 cm was

noted. S o i l pas te of about 10 g of the po r t i on of ', I

the s o i l which flowed together was taken and weighed 1 and then p h 3 3 d i n the oven a t 1 1 0 , ~ ~ . f o r 24 Us t o

dry. The above s t e p s were repeuted about f i v e time^ ~ l

and a t l e a s t f ou r determinations obtained i n the ~ rt+ne;e of blows between 1.0 and 50 inolus ive with some 1 above and below the required 25 blows of the LL. -.

Af te r 24 hours of oven-drying, t h e s o i l pas tea were

re-weighed and the percentage moisture contents

determined f o r the d i f f e r e n t s o i l e x t r a c t s (por t ions ) i I us ing the formula below: i

I ;

U t . of moisture = W t . of wet s o i l + conta iner - W t . of d r y s o i l + conta iner ------ (7)

W t . of d r y s o i l W t . of d ry s o i l + c o n t a ~ n e r - k t . of c o n t a m e r ----------------- (8)

% Moisture content P -of moisture wt. onl'yiUTI'

x 100 ------ ( 9 )

P flow curve was p lo t t ed , of water oouteat aga ins t I the number of blows a t the d i f f e r e u t yoiuta. The

b e s t - f i t t i n g s t r a i g h t l i n e was drawn through t h e t e s t

p o i n t s which showed a decrease i n water content with I

i nc rea s ing number of blows. Prom the r e spec t ive curves

of the s o i l s , the LL was determined a s the water

content of t h e flow curve t h a t corresponds t o 25 blows.

The LL s o determined i s the water content a t which

, 25 blows a r e requ i red t o c lose t h e bottom o f the

groove over a d is tance of 13 mm (Craig, 1989).

The p l a s t i c limit (PL) was, a l s o determined us ing

the classical. Casagrande method as described below.

After making a homogenous mixture of t h e s o i l and

d i s t i l l e d water t o form a pas t e , some of the pas te

was spread out evenly on a g l a s s p l a t e and allowed t o -

d r ~ t o such a point t h a t it could r o l l i n t o a thread

3 mm i n diameter on the g l a s s p l a t e , us ing the palm.

This thread was co l l ec t ed and weighed aud placed i n an

oven a t 1 1 0 ~ ~ and re-weighed a f t e r ' 24 es. Two such

readings were taken and the PL ca lcu la ted ao t h e

av, r age of the percentage moisture contents of the two

determinations, thus;

W t . of moisture = kt . of wet thread + container. - W t . of d ry thread + container------ (10)

k t . of d ry thread = W t . of d ry thread + conta iner - k t . of contariner ------------------ (111

% moisture content (X) = W t . of moisture 12) E o f dry Lhread'

The same procedure was done t o ge-t ( Y ) % moisture ,

content of the second reading. .Then the mean PL was

- - c.alcul.ntcd a s fo l lows:

'!!hc p l . n s t i c i t y index (PI) was c a l c u l a t e d a s

1 . 1 1 0 r '~ : i . r ro~cncc. betvocn t h e LL nnd PL.

= L1, - pL ------- ---------- --------- (14)

Whilr? cars,yin(: ou t t h e LL t e s t ; s o i l p a s t e s

wc?rc cnl.loctcd whcn t h e groove c l o s e d a t ex:act ly

25 blows f o r t h e dotermina.t ion of , t h e shr inkage l i m i t

(SL). , The p a s t e s were p u t i n a shr inkage a o u l d 14 cm

i n l c n g t h and leve;.led t o t h e br im of t h e mouldand

placed. i : n t h e oven a t 1 1 0 ~ ~ f o r 24 h r s . A f t e r t h e . .

dryin[{ p r o c e s s , t h e new l e n g t h s of t h e s o i l s i n t h e

mold, wcrc measured. The shr inkage was c a l c u l a t e d a s

t he r a t i o 01 t h e dec rease i n l e n g t h t o t h e o r i g i n a l

Icng.kh i n peken ta i :o . S ince t h e sh r inkace was i n a

l i n c n r .:Corm, we r e f e r t o t h e c a l c u l a t e d v a l u e s

a s li.n'c?a:a chrinkogtr. I t was c a l c u l a t e d a s fo l lows : . .

s~ - - g hrinkngc! l i m i t i n pe rcen tage of i n i t i a l l e n ~ t h 01' mois t s o i l sample

L = I n i t i a l i.cnfl;th i.n cm. of mois t s o i l i n mold ( l e n g t h of mold.)

L,, = Length of oven-dried s o i l . c

4 7 . . . .

Prom t h e r c a d i n ~ s , c o e f f i c i e n t o f l i n e a r

e x t e n s i b i l i t y (COLE) was c a l c u l a t e d thus :

t h e clian(;e in. 1enp;th of t h e s o i l upon d r 7 i . n ~ .

where :

Lm = Length o f mois t s o i l sample, and

La = Length of d r y s o i l .

T'nc vo lumet r ic shr inkage (VS) was coaputed ~ from measured c o e f r i c i e n t of l i n e a r e x t e n s i b i l i t y

4 . 2 . l':rrLj.clc r,:~se a n a l y s i s

P a r t i c l e s i z e a n a l y s i s was determined w i t h '

t h e Bouyoucos (195 :~ ) hydrometer method u s i n g sodiuln

hexametaphosphate (ca lgon) a s t h e ,d i spers inp ; ap;ent.

The sizes and amounts of t h e s e t t l i n p ; p a r t i c l e s

were dctorrnined 6y' employing p rogres s ive t ime

i n t e r v a l s .

4.2.4.3 C:i-tion e x c h m ~ e c a p a c i t y

," Thc de.termi.nation. o.f t h e c a t i o n exchange cnpaci.by

was b ? ~ c i bn the p r i n c i p l e s exp la ined by Chapman

(l965), , t h e n e u t r a l ammonium a c e t a t e method i n

which'O.1N K C 1 s o l u t i o n was used t o counter-i.cnch,

and from t h e K C 1 l e a c h a t e , cati.on exchange c a p a c i t y

was dctermined by t i t r a t i o n wi th s t a n d a r d 0.1N NaOH

s o l u t i o n .

4.2.4.4 PIT dc t c rmina t ion

S o i l pII was determined i n d u p l i c a t e s i n bo th

water and 0 . 1 ~ potsss ium c h l o r i d e (KC1) so1.ution

ur,inc a : ; o i l : l i q u i d r a t i o o f 1:2.5. A f t e r s t i r r i n g

f o r 30 minutes t h e pH v a l u e s .were r e a d o f f u s i n g a

Beckman zcromntic :$I meter ( ~ e e c h , 1965).

4.?.'1..5 l3xhnny;eabl.c b a s e s

!Uhc comploxom~?tri.c 'l-i-l-rnLi.on method do::cri.borl

by Chnpmnn (1965) w a s u s e d f o r de t e rmina t ion of

cnlcium nnrl mn~nes:i.um. Sodium and po tnsnium were

dhtermined &om 1 N (NH40Ac) ammonium a c e t a t e u s ing .

t h e .Clnmc photometer.

. . I 6 Ekchnny;cnblc ac i t t iQ

Exchangeable a c i d i t y (H' and ~ 1 " ) was d e t e r -

m-incd by -tho t i t r i m e t r i c method u s i n g 1 N KC]. e x t r a c t

.(Mclean, 1965) .

4.2.11 .7 13:1!:c c t l t u r a t i o n

B a s c . s a t u r a t i o n (BS) was c a l c u l a t e d b y d i v i d i n g

t o t a l exchmgcab le b a s e s (TEB) b y t h e correspondine,

c a t i o n e x c h a n ~ e c a p a c i t y va lue and m u l t i p l y i n g by

100.

4 . 3 DATA hPJAlXSIS

The d a t a ob.l;ai.ned from t h i s r e s e a r c h were

annl;y:;od w i t h s imple l i n e a r r e g r e s s i o n and. c o r r e l a -

t i o n cmnlgs i s (Lit:i;l.e and. t I i l l . s , 1972) so a s t o

i d e n t i f y which in1 ; r in s i c and dynamic p r o p e r t i e s

in . i lucnce t h e physico-cheinical c h a r a c t e r i s t i c s of

t h e ag[;re[ptes most.

C W T m Y I V S

5.0 R.ESULTS irNB DISCUSSION ,

5.1.1 P a r t i c l e s i z e d i s t r i b u t i o n , organic matter , t o t a l ni l-rown tuld a v a i ~ r A o s p h o m of the dif fe run t 'J'~;JTT;~ -

5.1.1.1 P a r t i c l e s i ze d i s t r i b u t i o n

The laboratory particle s i ze analys is confirmed

the var ia t ions i n the parent mater ia l s of these

s o i l s . The U l t i s o l had more s a d than other s o i l 8

(Table 4a) because t h i s s o i l i s formed from a g r a n i t i c

parent material . The other three s o i l s whose parent

mater ia l s are of f i n e r grams had c l a p 7 textures .

Cultivation had no e f f e c t on the p a r t i c l e s i z e s of

t he U l t i s o l (Table 4a).

' d w , Z O C l 0 0 , W m m , . . . f

- + z w lu r n - G x . PI t-' 'r' w 2 W d - a 0 a. nlj r \ r \ - P t V U L * ' . w r v w v X ; Y P , b : O ,

U1

5.1.1.2 - Oqpn ic matter

The organic matter content of t he f o r e s t s o i l s

were general ly higher ttlan those of t he c u l t i v a t e d

s o i l s . Phis i s a c l e a r ind ica t ion t h a t c u l t i v a t i o n

l e d t o the reduction of organic mat t s r ccntent O f

theso s o i l s . E l l l o t t (1986) made s imi l a r observations

on grassland s o i l s . Also Hahalola and Chelda (1972)

repor ted s i m i l a r r e s u l t s when they compared v i rg in

s o d with cu l t i va t ed s o i l . The organic matter values

ranged from 1.03% t o 2.14% f o r the f o r e s t so118 and

0.55 t o 1.24% f o r the cu l t i va t ed s o i l s (Table 4 4 .

The values f o r the f o r e s t s o i l s are i n l i n e with the

observations made by Siagh and Ualaeubremanian (1977)

t h a t the na t ive l e v e l of o r g m i c matter iu suvanndi

s o i l s i s qui te low because of . t h e prevuiline; high

temperature and r e l a t i v e l y low r a i n f a l l , both of which

r e s u l t i n sparse vegetat ive cover.

5.1.1.3 Total n i t rogen ---- The t o t a l n i t rogen of the c u L t i v a t e d s o i l s

were lower than those of t he f o r e s t s o i l s . Cul t i -

va t ion , the re fore , reduced the t o t a l n i t rogen

content (Table 4a). ~bagwu and Hwzoff i (1989) ,, .. .. , , ' .. .

g o t a s i m i l a r r e s u l t . ' Yaniran and Areola (lC)'/8)

and Uremner (1'JbiJ) r e p o r t e d t h a t trie t o t a l n i t r o g e n

con ten t of s o i l s i s u s u n l l y very low. Yhls can be

attributed t o d i f f e r e n t i a l uptake of t h e n u t r i e n t

element by crops .

5.1.1.4 . Avai l ab le i)hosphorus

The va lues of a v a i l a b l e phosphorus a r e shown

. i n Table 4a. The a v a i l a b l e phosphorus conbent of

t h e i;ncepl;isol, L n t i s o l and V e r t i s o l were 'higher

but- t h e r e was no j.ncretise i n t h e available phooyhoms

contenl; of t he U1l;lsol compared t o the f o r e s t s o i l s .

Therefore , t h e a p p i i c u t i o n of phospha t i c f e r t i l i z e r

to c u l t i v a t e d l a n d m i g h t be r e s p o n s i o l e f o r t h e

phosphorus b u i l d up i.n t h e s e s o i l s .

5.1.1.5 Uoi l r e a c t i o n (phi)-

The pH valued f o r the c u l t i v a t e d s o i l s were

s l i g h t l y lower t h m those of t h e f o r e s t soi ls wi th

t h e except ion o i .:he V e r t i s o l which had a h i g h e r

pH value compared t o t h e f o r e s t s o i l L o r both yki

i n water and pota.;sium c h l o r i d e (Table 4a). The

r e s u l t of reduced organic m a t t e r con ten t which se rves

s o i l Tor the f o r e s t s o i l s and 0.10 an* .0 .16 meq

~ a + / 1 0 0 g s o i l Tor the c u l t i v a t e d s o i l s were

obtained. The range f o r K+ was 0.03 t o 0 ,2+ meq/

100 g s o i l f o r the f o r e s t s o i l s md 0.09 t o 0.51

rneq/100 g s o i l fo.r t h e c u l t i v a t e d oils. Yhe calcium

vulues var ied between 2 - 5 and 46.4 meq/100 g s o i l Tor

t h e f o r e s t s o i l s and 1.5 and 30.8 meq/lUO g s o i l

f o r the cul.tivc.~toti s o i l s ; wherseas t h e range i'or

magnesium was 1.1 t o 5.0 meq/100 g s o i l and 0.9 t;o

3. 5 meq/l00 6 s o i i f o r t h e .foreul; and ct1l;ivut.ed

~ i o i l s , respective3.y. 'The amouuCs and perhaps t h e

d i s h i b u t i o n of exchur~geaole c a t i o n s uro irrfluuncod

by kinds of s o i l parcrlC mute r i a i s . The da ta

i n d i c a t e that; $he exc i iu~ge comyiexcs were occupied

m i n l y by calcium and magntisiun. ' Ugw (1983j mudc

. . -. . . a s a b u f f e r i n g agent a s w e l l a s the use of a c i d i -

f y i n g f e r t i l i z e r s on these s o i l s .

5.1.2.1 E;xchangeable bascs

The va lues of t h e exchangeable buses (IVai,

~ a + + , ME++, K + ) ob ta ined f o r tho s o i l s a r e g iven

i n Table 4b. U range of 0.09 t o 0.14 meq ha*/100 g

s i m i l a r observa t jvns l o r s o w ~avannah s o i l s .

:< 09

W

P

rv C-

I-'

I-'

0

a

'4

0

\N

N

N

Q

W

\N

0

0 W

0

0 a

0

0 VI

0

I-' 0

0

P IU

0

0 a

0

n ) F

0

W I-'

5.1.2*2 Uut - ion exchuntp caycrcitx

%he c u t i o n exchange c a p a c i t y of t h e i ' o r e s t

s o i l s was s l i g h b l y h i g n e r t han those of t h e c u l t i -

vriCed s o i l s wi th t h e e x c e g t ~ o n oi' t h o Vorb iso i

(Table 4b). The v a l u e s a r e 25.0, 5.5, 22.0 and

55.5 moq/100 s o i i f o r t h e f o r e s t s o i l s a s aga ino t

1'1.0, 3.5, 21.0 imd 58.5 meq/100 6 s o i l f o r t h e

cu l t ivuLcd s o i l s (Tuble 4b). The lowes t v a l u e s

occur red i n t h e U l t i s o l . I h i s low c a t i o n exchange

c a p a c i t y could be due t o low c l a y ' c o n c e n t i n t h i s

s o i l (Table 4a). The c a t i o n exchange c a p a c i t y v a l u e s

ranged between 3.5 and 58.5 ueq/103 g s o i l . Ine

v a l u e s ' a r e s i n i i l a r Lo those ob ta ined by l i i i l and

Hackuu~ (1973) f o r some savannah s o i l s i n cen-Lral

Tor t h e c u l t i v a

5.1.2.3 Base s a t u r a t i o n

Vho va lues rted s o i l s were h i g h e r

thap t h o s e of t h e ,:orest s o l l s wi th the excep t ion

ol' Lh.0 JmGisol which had a lower vuluc coiiipii~cd Lo

the f o r e s t c o i l . ::he ndar 100% base r;;ikurution

recoydod Sor the Vt?r t i so l shows t h a t t h e o n t i r e

exchange s i - t e is s x t u r a t e d by c i i t i ons o t h e r t41.m

hydrogen i o n s ( lab ie 4b). She n l g h e r . v a l u e s f o r

, . ... . . . c u l t i v a t e d s o i l s r e f l e c t t h e i'act t h a t i n o r g a n i c

S e r t i l i z e r s are used on these s o i l s .

5.1.2.4 ' l i x c l ~ a n ~ e a b l e 9 a c i d i t y (a3+ + 11')

3+ C u l t i v a t i o n i r~cre t l sed t h e kl conzent of t he

s o i l s and consequent ly inc reased t h e i r a c i d i t y

(Table 4b) . This may be a s a r e s u l t o f decreased

organic m a t t e r con ten t i n t h e s e s o i l l ; due t o

c u l t i v a t i o n as w u l l a s the use oJ: u c i d l f y i n g

S e r t i l i z e r s on t h e s e si-Les. T h i s c o n f i r u s t h e

r e p o r t 'of Ahn (1970).

5.2 - CUNJISIPLNCY ( A ' P i ' l i ~ ~ ~ I t G ) LIMITS

The Liquid himi-t (LL), P l a s t i c l i m i t (PL) , I l l r e t i c i t y i ndex ( P I ) , Coefficient of l i n c a r

o x t c n n i b i l i t y (CULL), Shr inkage l i m i t (SL) and

Volun~ct r ic shrink:nge (VS) o l the & o i l s are givcn

I n Table 5. For the I n c e p t i s o l , c u l t ~ v a t l o r ~

decreased t h e LL, PL and PI out t hese d e c r e a s ~ s

were no t s i g n i f i c a n t at lj = 0.05.

I n t h e U l t i s o l , Lrr t isol aid Ver i i so ; c u l t i v a -

t l o n had a vcry low e f f e c t on t h c r h e o l u g l c a l

p r o p e r t i e s 8s evidenced by t h e low v a r i a t i o n s i n

t h e s e p r o p e r t i e s .

W W W 1IUwwr

. . a .

IV P t-' n>w N m v 0 - 4 w mPaP-4 . . . . . . . . . . O \ I - ' O ~ W w m r o w W www

The non-s igni f ican t e f f e c t of c u l t i v a t i o n on

tho r h e o l o g i c a l p r o p e r t l e v 01' t h e s e s o i l s u i g h t be

due ' t o t h e method of c u l t i v a t i o n . These s o ~ l s a r e

b e h g c u l t i v a t e d manually with t h e l eas - t e f f e c t s

on t h e s o i l r h e o i o g i c a l p r o p e r t i e s . u l s o t h e s e

p r o p e r t i e s a r e ai.l 'ected nrore by t e x t u r e t h a n by

any a t h e r s o i l p~:operty. Yo t h e extent; t h a t

c u l t i v a t i o n had rio efl'ecr; on texbure (Tublc 4a) ,

it- should no t be expectod t o i n l l u e n c e t h e

r h e o l o g i c a l p r o p e r t i e s .

5.3 AGGMGATL BTA!jILI:'I'Y - 5.3.1 P'oan-wei~ht ditiruoter 0 1 d r y ag[r,rega.t;es (Ylblii'l

The . mean-weight diaine tier of dry-sieved aggre-

g x t e s of t he cu lb iva ted s o i l s were g e n e r a l l y lower

than those o f t h e f o r e s t s o d s . The percentnCL;e

decrease i n d r y &ggregate s t a b i l i t y oi' t h e s e s o i J s

were 27;8, 2.5, 2.4 and 1.7% f o r t h e i n c e p t i s o l ,

UlGisoi , E n t i s o l i ~ d V e r t i s o l , respeci ; ively

($able 6 ) . The :reduction i l l d r y aggroguLe s b a b i l i t y

10 i n l l n e with t h e observation 01 Moreav (1978)

t k l n t ; ugy;regate s b a b i l i t y is reduced by c u l b i v a t i o n .

The mean-weight d iameter of d ry aggregcise i s

g o n e r a l l y not very s e n s i t i v e in d e t e c t i n g d i f f e r e n c e s

Table 6: Lg6regate ?o ros i t y , d e n s i t y and s t z y i l i t y of f o r e s t a% c u l t i v a t e d s o l l s as e ~ a l u a t e d by d i f f e r e n t ind ices .

soilsa F o r o s i t y Densi ty iTd3 D :y&%ld DZ (%I (pig ~ n - ~ ) (%I

IF 58.11 1.11 0.oi;l 0.878 . X Q 1,- 26

. . S D . 6-53 0.18 0.169 0.152. 21-57 . .

CV (%) 14.56 15.W 16.41 . 19. 10 57-64 i

%See Fable 3 f o r e x p l a a t i o n of t h e syzbols .

among t h e v a r i ~ u n land use t y p e s (Mhagwu and

Baazof T i . , 1989). The low v a r i i i b i l i t g i n aggrega te

s t a b i l i t y of t h e s e s o i l s confi rms t h i s .

5.3.2 Mc,m-wci.~ht diamater o T wet a g ~ r c ~ n t e s (IWWTIG~)

The inenn-weight d iameter of wet a ~ g r c g a t e s

of tho cul.l;ivated. s o i l s were lower than those of

t h e Corcs-b, an i ~ l t l i c a t i o n t h a t c u l t i v a t i o n reduccld

t h c :~{:;[:rcil;nte s t a b i l i t y . of t h e s e s o i l s . The r e l a t i v e

decrc:~sc:; wcre 42.6. r 20 .0 , 13.7 ad10 .6% f o r t h e

Entisol . , Ul . t iso1, I n c e p t i s o l and V e r t i s o l ,

rcopcctive1.y ,(Table 6 ) . The aggrega te s d i s i n t e -

~ r x t c fa:;t- when they come i n c o n t a c t wi.th water

neccc::i.ta.tj.ng t h e hitgher v a r i a b i l i t y compared w i t h

dry- r , icv in~; . The MWD'd i s v e r y sens i t - j~ve i n

de-l-ec%i.n,y d i f f e r e n c e s i n a(r;p;rep,ate s b a b i . 1 i . t ~ among

thcnc . t reatments , an obse rva t ion made a l s o by

Mbny;wu and BazzoSfi (1989) with temperato s o i l s .

5. 5. 5 1 0 t ; l ; 3 1 I u ; 1 1 . r1e:form;i-tlon index

'ilic p o t e n t i a l s t r u c t u r a l dePormati.on index

(13SI):i) i r u s e d t o normalise ac(~rei7;at.e i i i s t r i b u t i o n

I'r.oin I;hc dry- and wet-sicvinp, p rocedures , so on t o

ob.1;;ri.n val.i.~l comparisons between land use types.

-. . . . The lower the percentage , t h e nore r e s i s t a n t i s

t h e s o i l t o d i s r u p t i v e f o r c e s ( P i g . 2). The shaded

a r c n s undcr the; curves i n d i c a t e t h e r e s i s t a n c e of

t h c d-y ay;~rce;ates t o d i s r u p t i o n by water .

Thc o r d e r of d i s l n t e g m t i o n o f t h e aggrega tes

IC ( ~ ~ . Y / . ) > u P (15.0%) > IF (6.5%). The s o i l s

a r c g e n e r a l l y r e s i s t a n t t o deformation because

t h e PSI31 v a l u e s a r e low and t h i s was a s a r e s u l t

o f thd manual c u l t i v a t i o n of t h e s e s o i l s which i s

no t <an i n t e n s i v e procedure.

5.3.4 Ccllo.id:ll stnlj i l . i t-7

Ibc d i s p e r s i o n r a t i o (DK) 0.f all t h e c .ul t ivnted

s o i l s we.rc: h - i ~ h e r compared t o t h e f o r e s t s o i l s , . .

wh:i.ch means t h a t t h e r e was a decrease i n t h e

agKrc?y;ab,e, r ; tabi l is ;y of these s o i l s due t o culLiva-

t i o n . The smalle:: t h e DH, t h e g r e a t e r t h e

s k r u c - t u r d 2; t:lbil.i.ty o f t h c ny;p;rnr;ot;e r, (~bnp,w~i rind

~nzxoffi', 1989). The percentage cl.ecrease i n t h e

Curnulc

Aqgreggte D~stributior~ ('I.)

64 i

1 i

(Tab l e 61, .the non 1

i between silt + clay and

type:; ( P a b l e '7) snoweu

silt + clay ;or the

mine ru l p r e s e n t .

T a b l e j l : Corre la t ion between si l t + c l a y (%) and Uisyorsion r a t l o (DK) , Moistu~w r e t a i n e d a t 0.01 Ma a d 1.5 ma. N = 5.

Cor re la t iou c o e f f i c i e n t (r)

Dispersion Moisture Betent ion r a t i o (&a) I

s o i l s a L%)

0.01 KPa 1.5 MPa

'see Table 3 f o r e x p l m a t i o n of symbols

*S ign i f i c ea t a t P' . 0.05 **Sign~Sicant at p .. 0.01 NS Not y igni f icant ;

BULK DmSITY KIIiD POHOSI'PL 5-'+ ... From t h e r e s u l t s shown i n Table 6, t h r e was

genera l ly slight i n c r e a s e i n the bulk d e n s i t y Of each

s o i l fol lowing , c u l t i v a t i o n ; ' t h e r e l a t i v e i n c r e a s e was

U l t i s o l ( 1 7 % ) ~ I n c e p t i s o l (14%)> &&5aol ( l l % ) ) V e r t i s o l

(yh). S i m i l a r l y a s l i g h t decrease i n t o t a l p o r o s i t y

i n t h e order , U l t i s o l (~i3U/o) '7 I n c e g t i s o l (10%) - V e r t i s o l

( lo%)> ESltisol (9%) was obtained. ..

The low CV of 13.04%'and 14.56% f o r t h e bu lk

d e n s i t y a d ~ o r o s i t y respectively (Table 6) confirmed

these slight change8. There were s i l n i l l t r observations

by Yhetir and Moschler (1'369) and B l e v ~ n u e t a l .

(1973) ou bulk d e n s ~ t y ; Olzver ia (1967), Thoupeon and

Trooh (1973) a d Mbagm and Bazzoff i (1909) on poros i ty .

Curr ie (1966) proposed in t ra-aggregate p o r o s i t y as an

index of s t r u c t u r a l stcrtus of so i l t l because i t i s a

measure of how fur any s o l 1 management p r a c t i c e has

halped t o prevent t h e przmary p a r t i c l e s from packing

too c l o s e l y toge the r as would be t h e case i n un

uns tab le and s t r u c t u r e l e s s s o i l .

67

. . . -- -

5.5 ~ ~ l ~ y ~ ~ c ~ - ~ l ~ ~ y , ~ ~ ~ . & , ~J . {o~ .~J ,~~~~bd V v AC&ki!iGlilk 5lihs

5.5.1 Urgnni'c mat Lcr corltenl;

. The organic matl-er d i s t r i b u t i o n of t h e agg rega t e

f r a c t i o n s i n t h e i n c e p t i s o l a r e g iven i n F ig . 3.

The r e s u l t s a r e 1 - 3 8 c 1.52< 2 . 2 6 ~ 2.34> 1.8b%

f o r t h e f o r e s t s o i l and 1 . 2 8 < 1.3l.c 1.59- 1.66>

1.60% f o r t h e c u l t i v a t e d s o i l i n t h e f o l l o w i n g

aggrega te s i z e s : 5.2, 2,1, 1-0.5, 0.5-0.25 and

c.0.25 mm resyect; ively. Tne lowest c o n c e n t r a t i o n

of o rgan ic m a t t e r occur red in . t h e - 2 inru f r a c t i o n .

The percen tage d e c r e a s e r e l a t i v e t o t h e 0.5 - 0.25 mm '

aggrega te s i z e was 20.7% f o r t h e f o r e s t s o i l end

3.6% f o r the cult ivat 'eci 8011.

The c o n c d n t r a t i o n s ol ' t h e o rgan ic mat-Ler i n

che U l t i s o l (Pig. 4 ) a r e 1.03: 0.90% 0,9'/e 1 . 1 7

~2.14% f o r the l o r e s t s o i l and 0 .62- 0 . 4 8 4 0.76

= 0.76cr: 1.03% fol: t h e c u l t i v a t e d s o i l i n the

f ~ l l o w i n g aggregat.e s i z e s : 5-2, 2-1, 1-0.5, 0.9-0.25

ar1d-r 0.25 mrri r eppec t ive ly . I n i t i a l l y , t he o r g a n i c . . m a t t e r c o n c e n t r a t i o n i n t h e 5-2 mn ay;f;regate s i z e

Was h igh , but decr.ear;cd i n .the 2-1 mm 3gil;regate s i z e

f o r h e two l a n d u s e .I;yye:i. The percuntu i i ;~ decrease

r e l a t i v e t o t h e 5-.2 mi aggrega te s i z e was lz.br?/o

f o r t h e f o r e s t s o i l and 22.58% f o r t h e c u l t i v a t e d

s o i l s .

' , . '26+ - FOREST

Agg~agate sizes (mm)

Fig. 3: , I n f l u e n c e o i l and use t y p o on organic rnal-ter d i s t r i b u t i o n i n a c c r e g a t a f r a c t i o n s 01 an I n c c p t i s o l . I li

I ! , 2:2- - FOREST i I - CULTIVATED 2.0 -

. . Aggregate sizes (mm)

, Pig. 4: ' I r ~ C l u e ~ l c e 01 Land use t ype on 0re;ani.c matter < ..

distribution in aggregate fractions of an . . Ultis ..br..-.... - . . . . . ~ . . . . . . . . .

. ..

The CnLisol had t h e h i g h e s t concen t ra t ion

of o r g m i c mat t e r Ln i t s uggrcgat;a i ' ract ionu a o n g

dl .the s o i l 8 (Fig. 5). The r e s u l t s a r e 2.97 b 2.76

-3.10 r 5 . 5 7 4 3.yl"/.xi 1 ,24<. . '1 .381 1.78 -= 2.00

<2.30$/0 i n t h e 5-2, 2-1, 1-0.5, 0,53-0.25 aau . .

c 0 . 2 3 mn aggregxte f r a c t i o n s f o r t n e f o r e s t s o i i !I

b and cul t&oted s o i l s , r e spec t ive ly .

Tne orgruiic ;nut tc r d i s t r i b u l ; i o n s i n tile Verbiuoi 4

ase 1.24 > l.l'/c 1.522. L . 6 6 ~ 1.7& f o r the f o r e s t

. s o i l and 0.03 c 1 . 0 3 7 0.69~ 0.76< 1.24% f o r tho 1 t 1 c u l t i v a t e d s o i l i n t h e 5-2, 2-1, 1-0.5, 0.>-0.25

ur1d-Z 0.25 inm aggrcgutr: f r a c t i o n s , reslje c t i v e i y

(Pie;. 6 ) . $or the 2-1 rum aggregate fraci ; ion i n

t h o i o r e s t s o i l , ;here was a decrease of >,b% i n

t h e organic matte;: content r e l x b i v e t o 5-2 mm 1 t

.aggrep;ate f r a c t i o n , while i n t h e ?-0-5 rnro aggmga.te

s i z e i n t h e c u l t i v k t e d s o i l , Lhere was a decrease

of 33.0% r e l a t i v e t o t h o 2-1 run1 aggregate f r a c t i o n .

Ytlo orgar~ io iiinttcr canccnt ra t iono i n thc

. .. sgsregute fmctioi:.s of tile f o r e s t S O L L O wcrc

gencril l ly h igher i;han those o f t h c c u i f i v u ~ c d s o i l s , j 1

showing a reduct ion i n t h e organic mut ter conccntra-

L i o n s duo .to cull l ivution. d l n i l a r rol;uj.tu were

Fig . 5: Inf luence of land uoc type on orVp,iuiic ma-bter d i s t r i b u t i o n i n aggrega te f r a c t i o n s of an

I Xtxtisol.

4 1 1

, ,

' . 3.9-

' 3.7 , ,

3.5-

I ! , 3.3

3.1

f i 0

7 2.9 V

, ,,, . y 2.7- 0 ) \ 4-

c ',, 2-5- j . , ,

'

- Cultivated ' -

.

-

-

-

, . ,

1.1 . I 1 I I I

'5-2 2-1 1-0.5 05-0.25 CO.25

1 ': Aggregate sizes (mm) . %

" lSaL - F O R S ~ P L a CuN~vatcd

C

C 0 1 . 4 - U

B 1.2

2

C

0, L 0.8 - 0

0.6' I 1 1 I 5-2 2-1 1-05 05-0.25 40 .25

Aggregate sizes (mm)

xif5. 6:. I n l l u e n c e 01 1:md Lse :typo on organic matter d i a L r i b u t i o n ,in aggregate i ' raciionu of a Vert isol .

> - r e p o r t e d by Low (,1972), aoone cC n l . (197G) n r ~ d

UouC;laa arid Goss (l%;!). Genera l ly , t h e o r g m i c

m a t t e r concentrat , ions in t he uggreg~tc : fractions

inc reased a s the aggregate sizes d e c r e n > e ~ . Th l s

cxgreus wi-th the r e s u l t s of LLiiol;L (,L')86) t h a t

organic m a t t e r a s s o c i a t e d wi th macroug&regat-e i s

more r e a d i l y winera l ihea tnan t h a t a s s o c i a t e d with .

5,5.2 Totul n i t rogen

The distribution of Loft i l riitrogcrl i n t i ic

s u e t rend ao t h a t of organlc mat ter . The t o t a l I

forevC s o i l , whllo t h a t uf i c were O . O S U r O.Oby<

0.0854 0.08br 0.080% f o r the 5-2, 2-1, 1-0.5,

0.5-0.25 and<O.%ji m aggregate s i z e s , r c s p e c t i v c l y .

contr?nt decreaocd f o r bobh i'ore;;t and cu l t iv ; i t ed I

soils. The percentage dccreaucs were 15.Wy o aid , - 7%

rcsl?oc-tivoly reLa6ive L O t n ~ . 0.5-0.25 nm aggregate

s i z e . The c o r r e l a t i o n c o e f f i c i e n t (r) betweeti o r g u i i c i I

0.11 t c-. FOR EST

0.04 L ~ - ~ - ~ - - l 5- 2 2-1 I - 0.5 05 - 0.25 -.L- '

40.25 , Aggregate size (mmi

I ' ' i 6 . a 7: ~ i s t r i b u i i o i ? of i;obal n i t rogen in u(;i;regoto

i ., f r a c t i o n 8 of an I u c e p t i s o l as i n f l u e n c e d by d i f f e r e n t l a n d uses .

. ~ . . . ~. ~ ,

lJ h 0 . 0 0 ~ f o r t he Sozes t , s o l 1 a l ~ d a t l 'L0 .05 f o r

t h e ' c u l t i v a t e d s o i l ( l 'able 8). Th i s means t h a t

t h e c o n t r i ~ u t i o n of o rgan ic carbon t o t h e concent ra -

t i o n of t o t a l n i t r o s e n i n f h e agg rega t e s i x e s of i

t h i s s o i l i s high. however, t h e r e was no correlation

between o r g a n i c caroon and t o t a l n i t r o g e n wheu t h e

l a n d u s e s Here combined (Table 9 ) . Th i s shows t h a t

t h e magnitudes of t n e c o r r e l a t i o n between o r g a n i c

carbon and: t o f u 1 n i t r o g e n i s s p e c i f i c t o t h e typo

of l a n d use i n t h i s s o i l .

I n t h e U l t i s o l , t h e t o t a l n i t r o g u n c o n t e n t i n

t h e f o r e s t s o i l decreased i n i t i a i l y , but l a t e r

i n s r e a s e h p r o g r e s s i v e l y a s aggrega te s i z e s d ~ c ~ c a s e d ( F i g

The percen tage dec rease was 17.9% r e l x t i v e t o t n e

5-2 ma aggrega te s i z e . The r e s u l t ; were 0.05b- 0.046

<0.047< 6 . 0 5 1 ~ 0.078% i n t h e 5-2, 2-1, 1-0.5,

0.5-0.25 :mi6 0.25 rum aggrega te s i z e s , r e s p e c t i v e l y .

The t o t a l n i l r o g e n i n -the cuL t iva t eu oil iricreilaed

d i s t r i b u t i o n s were 0 .024< 0.025< O.03L> 0.055

4 M m D Y ct rt I-. v"' ffl ffl 0 0 I-' I P

I I 0 0

t-' 4 W W I--' t-' 3 ;

z P r3

n c t 0 S Y d. -0 "

aq I>

E

e 0 . 2 5 mm uggrega'tc s i z e s , r e s p e c t i v e l y (Yig. 8).

The c o r r e l a t i o n coei'llicieni; (r) between o r t ;u i i c

curbon and t o t a l n i t r o g e n f o r t h e U l t i s o l f o r e s t

and U l t i s o l cultivated were h i s h l y s ign i l ' i can t a t

'Y,'0.001 (Table 8). Also, t h e r e was a s i g n i f i c a n t ;

c o r r e l a t i o n b e t w e n organic carbon and t o t a l

n i t r o g e n a t P S 0 . 0 0 1 when t h e -treat;ments were

combined (Table 9 ) .

illhe r e s u l t s of t h e total . nitr.oei;en i n t h e

l h t i s o l f o r e s t werc: 0 .140b O . l 5 O r . 0 . 0 O . l ' / O C

0.1'/% i n the 5-2, 2-1, 1-0.5, 0.3-0.25 and c 0.25 mm

aggregate s i z e s , r e s p e c t i v e l y . There wus a dec rease

i n bhe t y t a l n i t h g e n con ten t ox .bhe 2-1 mm iigk:regn.i;e

concen t rn t io r~o incj?casod p r o g r e s s i v e l y a s t h e

u&grugl;ate s i z e s decreased. ,.The d i s u r i b u t i o n ; were

0.064 < 0.0'/5< O.O'J4< 0.150< 0.1i.5'$ i n the

5-2, 2-1, 1-0.5, 0.>-0.;25 and<0.2> am aggregate

s i z e s , rc::pect;ivel:i (Pig. 9). yhcro w u S ii s i~ l i i l i -

cane c o r r e l a t i o n between organic carbon and t o t a l

n i t r o p n ut P&O.OOl Tor t h e Lb' and ai; P A O.O5 f o r

t he BC (Tabie 8). Also, when t h e two t r e a l m e n t s

c-. FOREST

0.07 o'~' 1 - CULTIVATED

Aggmgate sizes (mm)

Fig. . . €3: ' U i s t r i b u t i o n of t o t a l n i t r o e e n i l l agy;regate f r a c t i o n s - o f an i J lLiso l a s - i n I l u e n c e d by

.~ d i f f c r e r i t l a n d uses.

, Aggregate sizes (mm) . ,

Pig. 9: U i s t rq ibu t ion 3f t o b i i l nit-rop,en i n age.rcgat-6 f r a c t i o n s .-.of :m i.;ntisol-&s~influenced-.-by----. ' - difforc?nt; lur id uses.

, , ... . .. - - . . - -

were combined, organic carbon cor re la ted . p o s i t i v e l y .

with t o t a l n i t rogen a t PIL 0.001 i n t h i s s o i l (Table 9).

~ o t u l nitaogen i n the Ver t i so l f o r e s t decreased

from 0,056 t o 0.051% i n the 5-2 mn'aggregute s i z e

m.d l a t e r increased a s the aggregate s i z e s decreased.

The d i s t r i b u t i o n were 0.1356 7 0.051 5 '0.077 L 0.081'

0.084 i n the 5-2, 2-1, 1-0.5, 0.5-0.25 undL 0.25 mm

f r a c t i o n s , respect ively . For the ,ireitis01 cu l t i va t ed ,

the re was an i n i t i a l increase i n t o t a l n i t rogen fram

0.038 t o 0.045% followed by a decrease up to' the

0.5-0.25 nun f rac t ions . The highest ooncentration

occurred i n the 0.25 u n f rac t ion . The r e s u l t s were

0.038 L 0.045 7 0.035 L 0.39 L b.06& i n the 5-.2, 2 4 ,

1-0.5, 0.5-0.25 and C 0.25 mm aggregite s i z e s r e spec t ive ly

(Fig. 10). There was no co r r e l a t i on between organic

carbon and t o t a l n i t rogen f o r the VE but i n the VC

organic carbon and t o t a l n i t rogen cor re la ted s i g n i f i -

c an t ly a t pf 0.001 (Taoln 8). Also there was a

s i $ R i f i c a n t pos i t ive c o r r e l a t i o ~ between o r g a i c c a b o n

and t o t a l n i t rogen ( P C 0..001) when the aggregates of

the VP and VC were combined (Tab le 9 ) .

O'OgO - Forest i u

00070 C

.- z 0050

*-

o a o 2-1 1-05 05-0.25 c0.25

Aggregate sizes (mm)

Yhe r e s u l s s of t o t a l n i t r o g e n i n (;he aggrega te

s i z e s of a l l t he s o i l s showed t h a t inicro-q;y,cagates

were enr iched wi th .a i t rogen. Yhin clgrceu with Lhc

r e s u l t s 01 Chr i s t ensen (1985) and Chr is tenson ;nd

Sorensec (1985) t h a t n i t r o g e n i s a s s o c i a t e d wi th

f i n e r s o i l ' p a r t i c l e s . Also , t h i s i s a s a r e s u l t

of t he fact t h a t t h e timount ol' n i t r o g e n r n ~ n o r a l i z e d

was t l l w c l y s g r e a t e r f o r macrooggregk~tes than n i c r o -

aggrega tes ( L U i o t t , 1986). . .

5.5.3 Avn.ilab1.c.. j i k l o s ~ ~ h o v ~ = ;

Avai lab le phosphorus concen t ra t iun ia t;he

phosphorus i n t h e 5-2 mm f r a c t i o n , fol lowed by an

incre:lue i n the &I., 1-0.5, 0.5-0.25 ald(0.25 1ra1

f r ~ c t ions . The peixen tage decrease was 59.t3%'0, f o r

Aggregate sizes (mm)

Fig. 11; ilva'ilable phosphorus i n aii;ere(l;a-Lc f r a c t i o n s of an I n c e y t i s o l as i n f l u c ~ c e d u y l i i u d use. . .

. .- ....... - . . . . . . . . . . .. -. , . . . . ..... . . .

' ~ a b ~ o ------ 101 Correlation between s i l t t clay and Total N and Avn l l t i b lo P. N - 5

Correlation coefficient (r)

Total N Available P (%) (,I?m,m>

a ~ e e Table 3 fo r explmatiou of symbols -

*Significant a t P - 0.05 . . . .

***Significant at P = 0.001

NS Not s i g u i f i c a t

86

. -. The c o r r e l a t i o n c o e i f i c i e n t ( r ) between o r e a n i c

carbon and a v a i l a b l e phosphorus were n o t s i g n i f i c a n t ' i

f o r t h e I n c e y t i s o l (Tables 8 and 9). Yhio means

t h a t t h o cont ; r ibu t icn ol' o rgan ic mat l c r t o t h e

ava i lub i l i -Ly of p h o ~ p h o r u s i n t h i s s o i l was low.

Thc h igh c o n c e n t r a t i o n s of a v a i l d b l e phouphorus l n

t h e c u l t i v a t e d s o i l compared t o t h e l ~ o r u s t s o i l

may be a s a r e s u l t of phospha t i c i 'e r? ; i i . izer ayp l i ca -

t i o n d u r i n g c u l t i v a t i o n .

From t h e r e s u l t of a v a i l a b l e phosphorus shown

i n Fig. 1 2 f o r t ho L l t i s o l , cul t iv-at lor1 decreased

i t h e phosphorus conbknt; of t11.e 5-2 rfun u ~ ; ~ r e g u t e s i z e

by loo%, had no c f f c c t on t h c phosphorus con ten t of

t h e 2-1 mm aggregate s i z e , but i n c r e a r z d L-he '

y1i.osphorus contenb cf t h e 1-0.5 mm aggrega te s i z e

by 1000/o.' C u l t i v a t i c n had no e f f e c t on t h e phosphorus

con ten t of t he 0.5-C. 25 mm and (0.25 mm ae;gregatc:

s i z e s . .The c o r r e l a t i o n coef f io ien i ; (r) between

o rgan ic carbon and s .va i lab le phosphorus i n t h e

agcregote f r ac l - ions showed no s i g n i f i c a n c e f o r t h e

up, but f o r t h e UC, it was s i K n i l ' i c a n t a t Pd 0.05

(Table 8). Organic carbon d i d n o t c o r r e l a t e With

a v a i l a b l e phosphorus when t h e two l and aye typps were

combined (Table 9). There wtls no c o r r e l a t i o n bet;ween

As19 regate sizes (mm)

s i l t + clay and avai lable phosphorus f o r t he Us and

, UC (Table 10).

Cult ivat ion and appl icat ion of yhosphhate f e r t i l i z e r s

increased the concentration of the avwiluble yhosphorus I( i n a l l the ae;gregate f r ac t ions of t he Jint isol r e l a t i v e

t o f o r e s t (Pig. 13). The percentage increases were 1 9 6 ,

l G & , Y+1%, 32% and 260% f o r t h e 5-2, 2-1, 1-0.5,

0.5-0.25 and U0.25 nun aggregate s i z e s , respectively.

Mhen the trektments were combined t b r e was no

co r re l a t ion (Table 9). bhen avai lable phosphorus wae

cor re la ted with s i l t + clay there. w&s s t i l l low

cor re la t ion (Tables 10 and 11). Organic carbon and

n i l t + c lay had small contr ibut ion t o va r i a t ion i n the

uvailable phosyhorua of t h i s '8011.

In the Ver t i so l , t he re waa a decrease i n the

avuilablo phosphorus contents of the aggregate s i z e s

i n t h e cu l t i va t ed s o i l with the exception of the 2-1 mm

aggregate s i z e (Fzg. 14). Relative t o the forevt

soil, the percentage decrease f o r the 5-2 uun aggregate

f r a c t i o n was 2076, t he percent increase f o r t h e

2-1 nun aggregate f r ac t ion was 20% and' the percent

decreases f o r o ther aggregate s i z e s were fl%, 330h,

17% f o r the 1-0.5, 0.5-0.25 and 4 0.25 mm ageregate

, Forcst

. Fig. 13: Available. &osphorus .in'a@:regat-e f r a c t i o n s . , , \ of an ti sol-.as--ihfluellced by land use.

,

Table 11: Cor re la t ion between s i l t + clay and -.-- n i t r o g e n and available phosyhorus. ii! . 10

Corre la t ion c o e f f i c i e n t (r)

S o i l T o t a l Available N ~ t r o g e n Phosphorus

(%> (sw)

I n c e p t i s o l -0.16t3*' 0.20 3NY

u l t ~ s o l . o. 50'eNs 0.204~"

. b t l s o l -0.775** 0. 27yN"

V e r t i s o l -O.O~>*' -0.608-

* S q p i f i o a n t a t P 0.05

* * S i p i f i c a n t a t P - 0.01

NS = Not s i g n i f i c a n t

,a Cultivated

Aggregate sizes (mm)

Pig. 14: ~ v a i l n b l k phosphorus i n agp,re~clte I'rac.tions of a V e r t i s o l a s i n f l u e r l c e d b y l and use .

. . .. , . .. ~ , , , , .. ... . .. .- . . . ..-... ~- ' . . . . . . . . . . . ..

n i z e o , r e s ~ e c t i v e l y . Corre la t ion c o e f f i c i e n t ( r )

between organic carbon and ava i lab le phosphorus was

s igni f isant ; at 'pg.0.001 f o r t h e Vp and at P 0.05

f o r the Yo (Table 8). There was a pos i t i ve s i g n i f i -

cant c o r r e l a t i o n a t P& 0.01 between organic carbon

and ava i lab le phosphorus when t h e two land use types

were combined (Table 9). The con t r ibu t ion

of organic mat ter t o the ava i lab le phooyhorus content ,

i n t h i s ? o i l i s high. However, ava i lab le phosphorus

co r r e l a t ed negat ively , but s i g n i f i c a n t l y with s i l t + I

c lay at- PGO..O5 f o r the Vp alone and whcn the two

land use types were combined (Tables 10 and 11).

With t h e cu l t i va t ed Ver t i so l (VC) the c o r r e l a t i o n

was low and non-signif icant (Table 10).

The ' d i s t r i b u t i o n of ava i lab le phosphorua i n t h o

aggre'ga,te. fr&ktions i n the fou r s o i l s d id not follow

a p a r t i c u l a r pat tern, o r trend, un observat ion a l s o

made by Mbagwu and flazzoffi (198')).

5.5.4 Colloidnl ;at-tibil*as evaluated with the Dj.spc?rsion r a t i o (DH) index

Cul t iva t ion decreased the s t a b i l i t y of t h e

aggregate f r a c t i o n s i n the i ncep t i so l . The decreuseo

were 3.%, 9 . ~ , 25.3%, 111.3% and 8.0% f o r the

93 ? -

' 5-2, 2-1, 1-0.5, 0.5-0.25 and< 0.25 nn aggregate

f r a c t i o n s , ' respectivttly r e l a t i v e t o the f o r e s t s o i l

( b e 12). The charige was minimal and not. s i g n i f i -

cant (Tab1e-s 7 and 1;3). Also, t h e co r r e l a t i on of

organic carbon with 211 was no t s i g n i f i c a u t (Table 8 ) .

,For the U l t i s o l , c u l t i v a t i o n decreased the

s t r u c t u r a l s t a b i l i t y of the 5-2, 2-1, 1-0.5, and

~ 0 . 2 5 mm f r a c t i o n s , but had no e f f e c t on the

s t r u c t u r a l s t a b i l i t y of the 0.5-0.25 nun aggregate

f ract iou: . (Table 12). The percent decraase s relat i ive

t o t h e f o r e s t s o i l were 18.24,?, 22.32%, 7.U% and 3 . a

f o r the 5-2, 2-1, 1-0.5 and< 0.25 mm aggregate s i z e s ,

respect ively . There was low, non-signif icant cor re la -

t i o n between s i l t + c l ay and d i spers ion r a f i o f o r tihe

U l t i s o l (Tables 7 and 13). However, correlatioar.

between organic mat te r and 1)R f o r the aggregate

f r a c t i o n s waE negative a t P S 0.05 f o r the Up and

p o s i t i v e at ~ l c . 0.01 f o r the UC (2able 8).

Cul t iva t ion decreased the s t a b i l i t y of the

.5-2, 2-1, 1-0.5, 0.5-0.25 and40.25 mm aggregate

f r a c t i o n e i d the E n t i s o l (Table 12). The percent

decreases r e l a t i v e t o $he f o r e s t were 102.6%, 2 4 . 3 , . .

30.4%, 17.1% and 22.4% f o r 5-2, 2-1, 1-0.5, 0.5-0.25

and40.25 mm f r a c t i o n s respect ively. The c o r r e l a t i o n

. .

coe f f i c i en t (r) between s ~ l t + c l a y and DR was not

s igmificant (Tables 7 and 13). The correlaClou. of

o r g d c carbon wi th DK was not s i gn l f l can t .

Cul t iva t ion a l s o decfeased t h e s t a b i l i t y of

the aggregates of t h e 5-2, 2-1, 1-0.5 and 0.5-0.25' m a , . .

but had n o , e f f e c t 'on t he . s t a b i l i t y of tha(0.25 mm

f r a c t i o n i n the Ver t i so l ('Sable 12). The percentage

decreases r e l a t i v e t o the f o r e s t s o i l were 2.3%,

26.396, '13.2% and 10.7% f o r t h e 5-2, 2 1-0.5 and

0.5-0.25 mm respect ively. There was no s i g n i f i c a n t

co r r e l a t i on between silt + c l a y and DR (Table8 7 and

13). The c o r r e l a t i o n of orgamic carbon and YR was

not s i g a i f i c a n t (Table 8).

The DB index has been s h a m t o be u se fu l i n

p red ic t ing the tendency of soils t o erode. The

higher the DR the h igher the amount of s o i l s l o s t

from simulated r a i n f a l l (Mbagwu, 1986). The non-

s i g n i f i c a n t co r r e l a t i on between silt + c l a y and DB

i n a l l the s o i l s and t h e weak co r r e l a t i on between

organic carhon and DK f o r the two land use types

(Table 8) c l e a r l y showed t h a t cultivation had 1itt.l.e

e f f e c t on the c o l l o i d a l s t a b i l i t y of the aggregate

f r ac t i one of fheee s o i l s .

97 , .. . .

5+5.5 P a r t i c l e s i z e d i s t r i b u t i o n

\ I n the Inceptiso:L, c u l t i v a t i o n increased the

silt + c lay contents of a l l the aggregate f r a c t i o n s

(Table 14). The inc reases were 7.246, 6.8';6, 6.8%,

6.8% and 46.2% f o r t h e 5-2, 2-1, 1-0.5, 0.5-0.25

and 4 0.25 nun aggregate s i g e s , r espec t ive ly r e l a t i v e

, t o t h e f o r e s t s o i l . The inc reases were minimal usd

no t s i g n i f i c a i t (Tables 7 and 13).

, Tor, the U l t i s o l , c u l t i v a t i o n increased the .

s i l t + c l ay content of the 5-2, 2-1 and 1-0.5 a m

aggregate s i z e s , but had no e f f e c t on the silt + c l ay

content of t h e < 0.25 mm aggregate s i z e compared

t o the Iy (Table 14). The percent inc reases were

18%, 22% and 28% f o r t h e 5-2, 2-1 and 1-0.5 mm

aggregate s i z e s respect ively, whlle the porcentage

decrease f o r t h e c 0.25 mm was 1w0. There was low,

non-signif icant co r r e l a t i on between silt + c l a y and

d i spers ion r a t i o (BE:) f o r the U l t i s o l (Tables 7 and

Cul t iva t ion a l s o increased t h e s i l t + c l a y

contents i n a l l t h e aggregate s i z e s i n t h e Ent iao l

with the exception of the smal les t aggregate s i z e

(Table 14). The persen t inc reases were 7.36, j .2k ,

7.2% and 16.9% f o r the 5-2, 2-1, 1-0.5 and. 0.5-0.25 nn

. .

..

93 .

I f r ac t ions , respectively. There was no increase i n

s i l t + c lay .content i n t h e 4 0.25 mm aggregate s ize .

The cor&la-tion coe f f i c i en t ( r ) between silt; + c l a y

and DBwas not s i g n i f i c a n t (Tables 7 and 13).

I n the Vertiuol., c u l t i v a t i o n had no much e f f e c t

on the silt '+ clay contents of the 'aggregate f r a c t i o n s

(Table 14) . The s i l t + cl.ay contents were lower f o r .

the following aggreg;ate s izesa 5-2, 2-1 and 0.5-0.2 nn.

The percent decrease i n these aggregate f r a c t i o n s

I were 8.l%, 8.8% and 9.6% respect ively . Cul t iva t ion

had no e f f e c i on tho 1-0.5 and the < 0.25 mm aggregate,

s izes . Tliere was nu s i g n i f i c a n t co r r e l a t i on between

s i l t + clay rund DI? (Tables 7 crnd 13).

0ulOival;ion s l i g h t l y pulverized t h e s o i l

part;icles, t h a t is, the proport ion of the macro- . .

aggregate~l were reduced and t h e proport ion of the

nicroaggregatea were increused a s a r e s u l t of

c u l t i v a t i n g the Incep t i so l , U l t i s o l and b t i s o l .

These cu l t iva ted s0:~ls had s1ie;ht increaserj i n

t h e i r silt + c lay corntents when conpared .with t h e i r

f o r e s t cour te rpar t s (Table 14). The d i s t r i b u t i o n

of p a r t i c l e s i z e was f a i r l y c0nst;fuC i n the Vert isol .

'i Metzer aud Hide (1938) and Yitnusamd Mazurak (1958)

obtained similar r e a u l t s.

. . . .- . .

t 5.5.6 Watar r e t en t ion oS tq$gre~~ ' l ; e ninea

The water re ta ined at low energy p o t e n t i a l

(0.01 MPa) i s shown i n Table 15, while t h e water

re ta ined at high e n e r a p o t e n t i a l i s shown i n

Table 16. .In t he four s o i l s s tud ied , t he re was no

unifo&m pa t t e rn of water retent-+on at the 0.01 Ml>u

by t h e aggregates, a t rend n i m i l a r t o that of s i l t +

c l a y d i s t r i b u t i o n wi thin these aggregates (Table 14).

Cul t ivat ion had very l i t t l e e f f e c t on the water

i r e t en t ion of aggregate s i z e s i n these s o i l s . I n

Table 7 it i s shown t h a t the water re ta ined a t t h i ~

tension corroltated nagat ively with the s i l t + c l a y

contents o f . IF and p o s i t i v e l y with the s i l t + c l ay

contents of Up. I n l ab l e 8 water re ta ined a t t h i s

tens ion cor re la ted pos i t i ve ly with t he organic carbon

contents of the aggregaten of Up, U and KC. When C

all aggregate f r a c t i o n s were combined f o r t he

cu l t i va t ed and f o r e s t s o i l s , water re ta inod a t t h i s

tens ion comela ted highly with silt -t c l ay contenks

f o r the U l t i s o l (Table 13). The oo r r e l a t i on between

moisture re ta iued a t 0.01 MYa and organic carbon

for t h i a s o i l was weak (Table 9).

The water re ta ined a t 1.5 MPa appeared no; t o li

be influencecl by the aggregate f r a c t i o n s of these,

d h j

k-J m OJ wl

k-' C-

OJ c.'

t-' w * m

+J o-l

-4 0

n) P

0 0

lu P

V1 0

' N P

I-' il

N F

N il

ru n) m \D

d Q

il

<o 0

a\

0) m

0

0 0

m 0 I-'

0,

in N

10 3

s o i l s . . ( T ~ b l e 16). A t t h i s t e n d o n , water ' re ta ined ... -

corre la ted p o s i t i v e l y with organic carbon f o r UC .

(Table 7), and weakly f o r IF and YG (Table 8). The fi

was highly s ipp i f i cau t correlation (P40.001) f o r

' the ~ l t i s o l when moisture a t 1.5 MPa was corre1ai;ed

with ' s i l t + @lay and weak (PS0.05) pooi t ive corre la-

t i o n s f o r the Inc.ept.iso1 and Bnt i so l when. co r r e l a t ed

with organic carbon (Table '3).

The incon8isten:y i n co r r e l a t i on analys io when

silt + clay and organic carbon were co r r e l a t ed with

water r e t en t ion showed t h a t these p rope r t i e s d id not

, contr ibute much t o the water re ta ined by theoe

aggregate f rac t ions . Considering the e f f e c t of

c u l t i v a t i o n on water re t e n t ion of the aggregates,

i t was i n the U l t i s o l (UC) and t h e 1 0.25 nm

aggregates t h a t cu l t i va t ion increased t h e water

re ta ined by these segregates a t 0.01 Ml>a (Table 15),

while. a t 1.5 m a the e f f e c t of cultivation on water

re ta ined by these aggregates was not consistent

i n any of 'the 8011s (Table 16). Mbagwu and Uazzoffl

(1909), and Mbabwu and Piccolo (l99Ob) o b t a ~ n e d

s imi l a r resu'lta. It appears there fore , l;h&t the

inf lueace o f cu l t i va t ion on the p rope r t i e s of aggre-

ga tes of these s o i l s manifested more i n t h e ckienical

than the physical proper t ies .

. - ----

. .. -.

C W T . E H 1SIX

BUMMBLiY, CONCLUSION AND WCOmKNDA'PION i

The pro jec t was undertaken t o s tudy the long term

e f f e c t s of col~tirmuous cu l t i va t ion on the physico-chemical

p roper t i es o f aggregate8 of some ~ i ~ e r i a n s o i i s . Three

s o i l s , an Incep t i so l f ~ o a !Pa-hoes, U l t i s o l from Gindi r i

end Ent i so l f r o m Panyam i n Pla teau S t a t e and a Ver t i so l

from Debs i n Bauchi Bta te were used f o r the study. Qhe

in tens ive use of agricultural land, a n e c e s s ~ f y f o r

increas ing ~ g r i c u l t u r a l production, normally has an

e f f e c t on tlie s o i i . Prom the r e s h t s of t h i s study,

/ the follovling conclusions c d b e drawn:

1. Oultivated ~ o i l a had l e s s a tab le aggregate5

and , the aggregates d i s in t eg ra t ed f a s t e r than

those of fo ren t s o i l s when khey come i n

contact with water.

2. Cult ivat ion. increased the bulk density and

decrehsed the poros i ty of the so i l s .

3. A s a r e s u l t of cu l t i va t ion the organlc matter

content of the s o i l s was decreused.

4. A s ign i f i can t corxelnt-ion bctween organic

carbon and ni t rogen i n the d i f f e r u n t a g g r e p t e

f r a c t i o n s was es tabl ished. This shows thh t

the source of t o t a l n i t rogen i n the aggregates

i s from organic matter.

5. Organic matter l o s t during c u l t i v a t ~ o n was

I the organic u a t e r i a l t h a t bound microaggregatea

i n t o macroaggrego,tan.

6. The physico-chemical charuc te r l s f icn of the

s t r u c t u r a l aggregates indeed depend on the

type of s o i l , h i s to ry of cu l t iva t ion and

i n t e n s i t y of l a d use.

7. For a b e t t e r umacrstandug of the physlco-

chemical propert t ies of Nigerian s o l l s , more

research should be ca r r l ed out u s m g other

s o ~ l s w ~ t h mult iple t l l l a g e methods.

The inclusion of conpatible and desirable upecles

of le@minoua p lan t s l i k e nucua aud cenfrosema i n the

f a ~ n i n g ~;Tsteme as green nanure c a increase the organic

mat ter coatent of t h e w isoils whev they a re ploughed i n t o

the soi ls . 3 h i u w i l l i sc rease the aggregate s t a b i l i t y

of these s o i l s f o r suata.~mable crop production.

The addit ion of orgsaic n a t e r l a l is f o m of f a m

rard m a w e is a l so e s s e n t i a l i n o d e r t o maintain a

favourable l e v e l 01 soil organlo mat;ter conkcnt-.

( Ahn, P.M. (l97O). West A f r i c a ijo&ls. 0x.Cord Univsrs i fy Press, Great B r i t a i n , 332 pp.

Alford, 'M. T. and Tuley, P. (1974). The land resourc8s of Centra l Nigeria. In ter im r epo r t om the landform, s o i l s and vegeta t ion of the Jos Plateau. Vol. 11. * 138 pp.

Al l i son, I.. (1965). Or~ganic carbon. In: C.A. Black (ed.). Methods of s o l 1 analys is . Pa r t L1. Is. 60c. Agron. 9: 136j7-1378.

Al l i son , B.E; (1973). S o i l organic n a t t u r and i t s r o l e i n crop production. x l s e v i e r Gcien1;ific Publ ishing Compw, Bmsterdm, 637 yp.

Ar inghier i , 11. and S e q w , P. ( 8 ) . ?he arrengomunt of o r g m i c mat ter i n a s o l 1 crumb. p. 145-150. In: W.W. fmerson, e t a l . (ed.). Modiflaation of s o l 1 s t ruc tu re . John Wlley and Sons, lnc. , Mew York.

Army, T.J., Wiese, A.F. and Hanks, H.J. (1961). P f f s c t of t i l l a g e and chemical weed con t ro l p r a c t i c e s on s o i l moisture l o s s e s durlng the fal low poriod. Proc. Boil Bci. Soc. An. 25: 410-413.

Aspiras, 1i.B.. Allen, O.N., Chenters, G. and H a r r i s , H.1". ( 9 . Chemical md 'phys i ca l s t a b i l i t y oi' microbia l ly s t a b i l i z e d aggregates. S o i l Sc i . Soc. An. Yroc. 35: 28.5-286.

Aylmoie, L.A.C. aud Si.L.Lo, I.D. (197U). Yore s t ruc tu re and mec;imical s ' trength of s o i l s i n r e l a t i o n t o t h e i r cous t i tu t ion . In: Modificafion of s o i l a txucturo (ed. , W.W. Fmernon o t n l . ) , 69-78. John Wi1e.y and Uono , Chichuotur.

Babalola, 0. i d CheXdn, H.R. (1372), Effcc tu of crops and management system on s o i l g t ruc ture irm a Wefitern Niger ia s o i l . Nig. 5 . of Science, 6: 29-36.

Balesdent, J., Wagner, G.H. and M a r i o t t i , A. (19882. S o i l 0rgani.c ' m a t t B r turnover i u long f e rn f l e l oqor imcnto un revealed by cnrbon-13 n a t u r a l abundance. S o i l Sci . Boc. Am. J. 521 118-124.

Bauchi &ate Agric. Devolopmcnt P r o g r m e (1984). Crop production anti food balance in Bauchi S ta te . 46 pp.

Baver, L.U., Garduer, bY.,H. und Gardnur, U.H. (1972). S o i l Yhysica. John Wiley and Sons, Inc. New York, 498 pp.

Benjamin, J . G . and Drune, H.M. (1987). T i l l ~ i g e e f f e c t s on shear ssrength m d bulk. densit-y of , s o i l ageregatea. Iioil T i l l age Besearch, 9 : 225-263.

Bhatnagar, V.K. and Mi l le r , M.B. (3985). Sorpt ion of carbon ahd phosphorus from l i q u i d pou l t ry manure by s o i l a g g r e g a t e s of d i l f e r i n g s ize . Can.. J. S o i l Gci. , 65: 467-475.

i Bhatzmgar, V.K., M i l l e r , M.H. and liatcheson, J.W. (1905). . faeaction of f e r t i l i z e r . and l i q u i d lmnure phosphorus

with .soil aggregates nnd sediments phosphoxue exirichment . J. Environ. Qual. 14: 246-251.

Blake, G.R. (1965). B ~ l k densi ty. In: C.A. Black (ed.). Plethods o f s o i l ana lys i s , P a r t 1. Am. Soc. Agron. 9: 37*+-390:

Blevins, H.L., Thomaa, G.W., Smith, J.6., $rye, U.W. and Cornelius, P.L. (1973). Changes i n s o i l p roper t i es a f t e r 10 years continuous non- t i l l ed und conventionally t i l l e d corn. & o i l T i l l age Nes., 31 135-146.

Blevins, H.L., Thomas, ,:i.W. aud Corneliuu, iP.1;. (1977). Influence of no-ti l lage and ni t rogen f e r f il.iza~l;ion on corbaj.n s o i l p r o p r b i e n a f t o r 5 y.c3nrn i n continuouu corn. Agron. 3 . 69: 383-386.

Boone T.T., 8 l q < e r , S., Niodema, 12. and Elevold, W. (1976). Some infLmnces of ze ro- t i l luge on the

, s t ruc tu re and s t q b i l i t y of a f i n e textured levee ao i l . Netherlande Journal of Agr icu l tu ra l Science 24; 305-119.

Bourma, J. and'klolo, B.U. (1971). Boi l s t r u c t u r e and hydraul ic coudu.cti.vity of adjacent v i r g i n and

1 cu l t i va t ed pedons a6 two s i t e s : A Typic Argivdoll ( s i l t lo'ai) and a Typic Uatrochrept (c lay) . S o i l Sci . Soc. Am. Proc:. 35: 316-319.

Bouyoucos, C.J. ( 1 A r e c a l l b r u t i o n of hydromcber f o r maklng mechanical ana lys l s of s o i l . Agron. J. 43: 434L438.

Bray, R . L and K~l r t z , L.T. (1945). Determination of t o . t a l organic and civailable forms of phosphorus i n s o i l s . S o i l Sc i . , 59: 39-45.

Brennor, J.M. (1965). Tota l ni t rogen: In : Methods of s o i l analys is . P a r t 11. C.A. Ulack o t al. (eda.). h e r . Soc. of Agron. 9; 1149-1178.

Bruce, R . L , ~ a n & a l o , G.W. and D i l l a rd , A.L. (1990). 'Pillage orop r o t a t i o n e f f e c t on c h a r a c t e r i s t i c s of a nmdy surface soi. 1. Boi l Sci: Soc. Bcm. J. 54: 1744-1747.

Canbardella, C.A. and . & l l i o t t , E. T. (1.932). P a r t i c u l a t e s o i l organic mat ter changes across a grass land c u l t i v a t i o n sequeace. S o i l Sc i . Soc. Am. J. 561 777-783-

Dambardella, C.A. and. E l l i o t t , E. T. (1993). Carbon anti ni t rogen d i s t r i c u t i o n i n a g g r e g ~ t e s from cu l t i va t ed and na t ive grassland ao i l s . S o i l Sci.

, SOC. Am'. J. 57: 1071-1076.

. Casagrande, A. (1932). B~f iea rch on tho A t t e rbe rg l i m i t s of s o i l s . Pub l ic Iioads, Vol. 13: 121-136.

Ghaney, K. and Swif t , H.B. (1984). The inf luence of organic matter on aggregate s t a b i l i t y i n 'some B r i t i ~ l h s o i l a . J. S o i l Sci . 35: 223-2313.

Chapman, B.B. (1965). To ta l exchangeable basea. In: U.A. Black. Methods of sol1 analys is . Par t 11. ALU. Soc. Agron. 91 702-904.

Chepil , W.Si and Woodmf, N.P. (1963). The physics of wind erosion and i t s control . Adv. Agroh. , 15r 211-302.

O;tuisternsen, B.T. (1985). Carbon and ni t rogen i n I p a r t i c i e s i z e f ruc t iona it ;olatod ,from Danish

arable s o i l s by u l t r a s o n i c d i spers ion and gravi ty- sedimentation. Acta. Agric. Bcand. 35: 175-187.

Christenkjen, B. 1. (1986). Straw i n c o r p o r a t ~ o n and s o i l organic mat te r i n macro-aggregates and par t i c le , s i z e seperatee. J . Boil Sci . , 37; 125-135.

Christensea, B. 2. (l9€18). E f f ec t# of m m a l manure armd mineral f e r t l l l e e r on the t o t a l carbon and n i t rogen contents of s o i l s i z e f r ac t i ons . Biol. F e r t i l . S o i l s 5: 304-307.

Christensen, B. T. and :;orensen, L.H. (1985). The d i s t r i b u t i o n of na t ive nnd l abe l l ed carbcn between s o i l ptlr . t icle niao f r a c t i o n s i s o l a t e d from long term incubation experiments. J. Boi l Bci. 36; 219-229.

Clement, C.R. and Wllli.ams, I.E, (1958). An examma- t i o n o f ' t h e method of. aggregate ~nn1ysi .s by

.wet-slevina i n r e l a t i o n t o the lnf luencos of d iverse l e i s on arable 8011s. J. of S o i l 8ca.

-

9; 252-266.

Coughlm, K.J . umd Loch, H.J. (1984). The re l t l t lon- hip between aggregation and o the r s o l 1 p r o p e r t i e s i n cracking c lay s o i l s . Aus t ra l i an Journal of S o i l Research 22: 59-88.

Craig, H.Y. [1989). Yozl mechanlca. 4 th ed. J.J. Press. adst tow) Ltd., Padstow, Canwall.

Culley, J.L.B., Larsor~, W.X. and lbndall . , G.U. ( 1 9 8 7 ~ ) . Phyaical p roper t~ .es of a T y p r . Ba~>laquol l undor conventional and no-tillage. b o i l Sci . Soc. Am. J. 51: L587-1>9 3.

Culley, J.L.H., L a X ~ o l l l W.EI nnd Handall, G.W. (1987b). Boi l water regimes of a Typic Haplaquoll under oonventional rmd no- t i l lage . S o i l Sci. Sot. Am. J. 51: 1064-1610.

Currie, J.A. (1966). Tho volumo and po ros i t y oS 8013 crumb. J. Sol1 ;hi., 17: 24-35. I

Dal'd, R.C. and Mayer, H.J. (1987). Long t o m t rends i n f e r t i l i t y of s o i l s under conl;inuuus c u l t i v a t i o n

r t~ and ce rea l croppine; i n Southern Queensland. VII. Dynamics of n i t rogen mineralisatioxl p o t e a t i d s and microbial biontlss. h a t . J. S o i l Res. 25: 461-472.

Davies, D.B., E ~ g l o , D.J. and Finney, J.B. . (1972). l jo i l manrr~omenl;. j rd ed i t ion . Farming P re s s Ltd.. Llhurfedale Huad, Iyewick, SufEolk, pp. 23-82.

Day, P.H. (1965). P a r t i c l e f r ac t iona t ion and p a r t i c l e s i z e onnlysis. In: Metho,ds of s o i l ana lys i s , P a t 1' (eds. C.h. JJlaclc e t al . ) . 545-567. American SoCiety 0:: Agronomy, Madison, Wisconsin.

Domaax, J.R. (1983). Chemical p rope r t i e s of s o i l s and water-stable ageregates a f t e r s i x t y years of aropping t o spr ing wheat. P l a t Sol1 75; 51-61.

Douglas, J.T. aad Goss, M.J. (1982). 8 t a b i l : i . t ~ m d organic met ter content o f surface m i l aggregates under d i f f e r e n t methods of cu1tivat;ion and i n grass. S a i l T i l l age Hesearch 2: 155-175.

a w a r d s , A.D. and Bremner, J.M. (1967). Micro- aggregate8 i n ,soil. J. Boil Sci. 18: 64-73.

Shlers! U. (1976). Wn.tor i n f i l t r a t i o n and re - dxs t r ibu t ion i n t i l l e d a d un1;illed 1.oess soil, Qot t inger Boden Kondliche Uerichte 44: 137-156.

E l l i o t t , E.T. . (19236). Aggregate s t r u c t u r e and carbon, n i t rogen and phosphorus i n na t ive and cul.t ivated s o i l s . S o i l tici. Soc. Am. J. 50: 627-633.

Wand, G.S. ' (1971). E f f ec t s of roGalions, t i l l a g e trehtments on the aggregateu of a a lay s o i l . Canadian J. of S o i l Sc. 51: 235-241.

B a n i r a , A. and b o o l a , 0. (1978). Xasentlala of oil study. Hei iWln~n Educ, Books Ltd., London.

-278 PP.

..Fed. Dept. of Agric. Ltud Hesources (1990n). S o i l s lieport Vol. . f . Btiuchi , Borno , Gongola a d . Kano

,%, 4 t a t e e . The racoruaiarjinnce s o i l survey crf f

Ni@;eria (l:65O,OOO) ; Kaduna, Nigeria, 339 py.

, Fed. Uapt. of h g r ~ c . L m d Beso~wces (199Qb). Goila Beport' Yol. TI. Xaduna, Xatslna, Kwara, XI., Plateau, Gokoto aid N i ~ e r State..:. The rcooanai- a s a c e s o l 1 survey oi: nkgeria (1;65G,OGO) i Kaduna, Nigeria. 300 py.

Foster , K.C. (1981). Yolyaaccharldcs i n s o l 1 fabrics. Science. (Washington, D.C.), 214: 665-667,

Gantzer, C.J. Blake, G.H. 9 P h ~ ~ i c a l charac tor ia t ice of a Le sooor c lay l o a m following no-l;ills.gc and conventional t i l l a g e . Agron. J. 701 853-857.

Cish, H.E. and Bramine;, G.M. (1940). Factors a f fec t ing the d x b i l i t y of o o l l aggregates. S o i l Uci. lioc. An. Proc. 128 51-55,

Gradwell M.W .. and Arl.id$e , X. 5;. (i97L). Determination . of s o i l s t ruc turu i n t he market ~ a r d e n s of the

Pukehole d . i s t r i c t , new zealand, i?.2.3. ligric. Bes. 14; 280-306.

Greenland, D.J. (19717). Gail s t ruc tu re and eros ion hazard. Xn: So:il conservation and managemonl; i n t he humid tro:yics. 1st edi t ion. J o b Wiley aad Sons Ltd., New York, pp. 17-18.

Grieve, I. C. (1979). A 'compari~on o f aggregates s t a b x l i t y t c s t procedures i n d a t s m i n m g t h o s t ' ab i l i t y of f m e uandy s o i l s i n F i f e , Scoiiland. CATENA 6: 123-129.

Grolrmann, F. (1960). Distribucao de tiamanho do poroo en t r e s t i y o s de solos do Estauo ae Sao Paulo, ' Bragantin 19: 519-328.

Grove, A.T. (1952). Stand use and s o i l conservat-ion on the Jos Plateau. Goological, 6urve.y of Xigeria. Bul l . NO. 22 , p. 5.

Gumes, A.B., Ptlttslla, J.P. and Yauletto, L A . ' (~978). E f fec t s of cropping eystea and d u r ~ t l o n o f cu l t i va t ion u the structure of red-yellow podzol. Bev. wass Ciencia Bolo 2(1): 17-21.

Gupta, V.V.S.R. and Gemida, J. J. (1988). Dis t r ibut ion of microbial biomass and i t s a c t i v i t y i n d i f f e ren t s o i l aggregates s i ze c lasses as affected by cult ivation. S o i l Biol. Biochem. 20: 777-786.

Haas, H. J., Evans, G.E. and Miles, E.F. (1957). Nitrogen and oarbon changes i n Great P la ins s o i l s a s influenced by cropping and s o i l treatments. USDA Tech. Bull. 1164 U.S. Gov. Pr in t . Office, Washington D.C.

H a r r i s , B.B., Allen, O.N., Chesters, G. and k t t o e , O.J. (1963). Evaluation of microbial a c t i v i t y i n s o i l aggregate s t a b i l i s a t i o n and degradation by the use of a r t i f i o i a l aggregates. S o i l Sci. Soc. h. Proc. 27: 542-545.

Heard, J.R., Kladiuko, E. J. and Mamering, J.V. (1988). B o i l macroporosity, hydraulic conductivity and air permeability of sil t s o i l s under long term conservation t i l l a g e i n Indiana. S o i l Ti l lage Bes., 1 1 8 1-18.

Heinonen, R. (1955). S o i l aggregation i n r e l a t ion t o texture and organic matter. Agrogeol. Julk. 64. 17 (Abstracts S o i l s and E 'er t i l izers 19, 43, 1956).

1 1 1 . (1976). Land resources of Central Nigeria. Agricultural poss ib i l i t i e s . The Joe Plateau. Vol. 2B. Draft Land Res. Study. Land Resources Division. Tolworth Tower, Surbiton, Surrey, England, 115 pp.

H i l l , I.D. and Rackman, L.J. (1973). The land resources of Central Nigeria. Interim Report on the land forms and s o i l s . Land Resources Division, Tolworth, . Tower, Surbiton, Surrey, England, 220 pp.

Hsu, P.H. (1977). Aluminium hjtdroxides and oxhydroxides. In: Minerals i n S o i l Environments. (ed. J.B. Dixan e t al.) , 99-143.

Ike, I .F. (1986). S o i l and crop responses t o d i f f e r e n t t i l l a g e prac t ices i n a ferruginous s o i l i n the Nigerian Savanna. S o i l Til lage Res., 6: 261-272.

Izaurralde, R.C., Hobbs, J.A. and Swallow, C.Y. (1986). Effects of reduced t i l l a g e pract ices on continuous wheat production and on s o i l properties. Agron. J., 78: 787-791.

Janzen, H.EI. (1987). So i l organic matter charac ter i s t ics a f t e r long term cropping t o various wheat rotations. Can. J. So i l Sci. 67: 845-856.

Jenny, H. (1941). Factors of s o i l formation. McGraw-Hill, New York. 281 pp.

Juo, A.S.R. and Lal, R. (1977). The e f fec t s of fallow and continuous cul t ivat ion on the chemical and physical properties of an a l f i s o l i n Western Nigeria. Plant and So i l 47; 567-584.

Kemper, W. D. (1965). Aggregate s t ab i l i ty . In: Methods of s o i l analysis. Par t I (ed. 6.A. Black e t al.). 511-519. h e r . Soc. of Agron., Madison, Wisconsin.

Kemper, W.D. and Dhepil, W.6. (1965). Size dis t r ibu- t ion of aggregates. In: Methods of s o i l analysis. Pa r t I1 (ed. C.A. Black). 499-510. h e r . Boo. of Agron., Madison.

Kowal, J.M. (1968). Some physical properties of s o i l s at Samaru, Zaria, Nigeria. Storage of water and its use by crops. Nigeria Agric. Journal, 5: 13-20.

Kowal, J.M. and Knabe, D.T. (1972). An agroclimatelogieal atlas of n o r t h e n s t a te8 of Nigeria. Ahmadu Bello U a i . Press, Z a r i a , 111 pp.

Kowaliaski, S., Drord, J. and Lieznar, M: (1982). Characterist ics of the phynico-chermcal properties of s t ruc tura l aggregates of various sizes. Polish J. Soi l Sci. XV: 119-127.

Lal, R. (1976). No-tillage e f f ec t s on s o i l propert ies under d i f ferent crops i n western Nigeria. S o i l Sci. Soc. Lm. Proc. 4 0 1 762-768.

La l , R., Mahboubi, A.A. md Faueey, N.R. (1994). Long tern t i l l a g e and rotat ion e f f ec t s on propert ies of a cent ra l Ohio soi l . So i l Sci. Soo. Am. J. 58: 517-522.

L i t t l e , P.M. and H i l l s , F.J. (1972). S t a t i s t i c a l methods i n agr icul tura l research. University of California, Davies, 242 pp.

Low, A.J. (1954). The study of s o i l s t ructure i n the f i e l d and the laboratory. Journal of So i l Science, 3: 57-74.

Low, A. J. (1972). The e f f ec t of cu l t iva t ion on the s o i l s t ructure and other physical properties of grassland and arable s o i l s (1945-1970). J. of So i l Sci. 23: 363-380.

Mackay, R.A., Greenwood, J. and Rockingham, T.E. (1949). The geology of the Plateau t in f i e lds - resurvey. Geological Surv. Bull. 19: 6.

Nacleod, Y.N., Turner, D.C. mid Wright, E.P. (1971). The geology of the J o s Plateau. Geo. Surv. Bull. 32: 9-100.

Mahboubi, A.A., Lal, R. and Faussey, N.R. (1993). Twenty-eight years of t i l l a g e e f f ea t s on two s o i l s i n Ohio. Soi l Sci. Soc. An. J. 571 506-512.

Martin, V.L., Eckert, D. J. and McCog, E.L. (19139). Rotation-tillage-drainage e f f ec t s on corn grown on an Aeric Fragiaqualf. p. 286. In; Agronomy Abstracts. M A , Madison, W . 1 .

Nassey, H.P. and Jackson, H.L. (1952). Select ive erosion of s o i l f e r t i l i t y constituents. So i l Sci. Soc. h e r . Proc., 16: 353-356.

Nbagwu, J.S.6. (1986). Erodibi l i ty of s o i l s formed on catenary topose quence i n Southeastern Nigeria as evaluated by d i f ferent indices. East African Agric. and I?orestry, J., 52: 74-80.

Mbagwu, J.S.C. (1989a). Effects of organic amendments on some physical properties of a t ropica l Ultisol . Biological Wastes. 28: 1-14.

Nbagwu, 5.6.0. (1989b). Influence of cat t le-feedlot manure on aggregate s t a b i l i t y , p l a s t i c l i m i t and water r e la t ions of three s o i l s i n North-Oeutral I ta ly. Biological Wastes. 28: 257-269.

Mbagwu, J.S.C. (1992a). A comparison of three micro- aggregation indices with other t e s t s s t r u c t u r a l s t a b i l i t y . Int . Agro-physics. 1992, 27-32.

Mbagwu, J.S.C. (19921,). Evaluation of shrink-swell po tent ia l of s o i l s by two procedures. Pedologie, XLII-11 69-82.

Mbagwu, J.S.C. and Baezoffi, P. (1989). Proper t ies of s o i l aggregates as influenced by t i l l a g e practices. S o i l use and management, Vol. 5, No. 4: 180-188.

Mbagwu) J.S.G. and Piccolo, A. (1990a). Carbon, nitrogen and phosphorus concentrations i n aggre- gates of organic waste-amended so i l s . Biological Wastes. Vol. 31, No. 2, 97-111.

Mbagwu, J.S.C. and Piccolo, A. (199Ob). Some physical propert ies of e t ruc tura l aggregates seperated from organic waste amended so i l s . Biological wastes 33, 2: 107-111.

Mclean, E.0. (1965). Aluminium. In: 6.A. Black e t al. (ed.). Methods of s o i l analysis. Pa r t XI. 1st ed. h. Boc. Agronomy Monograph No. 9, 986-994.

Metzger, W.H. and Hides, J.C. (19%). Effec ts of cer ta in crops and s o i l amendments on s o i l aggrega- t i o n and the d is t r ibut ion of organic carbon i n r e l a t ion t o aggregate size. bmer. Boc. Agron. J. 301 833-843.

Middleton, H. E. (1930). Propert ies of s o i l s which influence erosion. U.S. Dept. Agric. Tech. Bull. 178.

Molope, M.B., Grime, 1.0. and Page, E.R. (1987). Contribution by fungi and bac ter ia t o aggregate s t a b i l i t y of cul t ivated soi l . J. S o i l Sci. 38; 71-77. "

Moreau, R. (1978). Effect of mechanical. loosening and water i n f i l t r a t i o n on the s t r u c t u r a l s t a b i l i t y of a f e r r a l i t i c s o i l i n Central Ivory Coast. Orstom f o r Pedologie, 413-424.

Mortal , Y.A. and Paul, L A . (1974). bff"ctS Of cu l t i va t i on on t he organic matter of grassland s o i l s as tlutermine?. by f r a c t i o n and r d i o -

chirbon dating. Cm.udian J. qf S o i l Yc. 54: 419-426.

Moody, J.E., Shear , G.M. and Jones, J;N. (1961).. Crrowirlg corn without t i l l a g e . Proc. S o i l mi. SOC. m. 23: 516-517.

Mourn, P.M. and ~ u o l , s.W. (1972). , Stud ies of a l a t o s o l ~ o x o ( ~ u t r u s t o x ) i n Ur.pzi1. Gxperiontiae 13: 201-234.

Nesmith, D.S., I Iugrove, W.L., &addiffe;D.E., Collaor , E.W. and i i r ioglu, L A ; (l(j87). T i l l a g e and res idue markgelc.uut e f f e c t s on p r o p e r t i e s of an U l t i s o l md double ,cropped-soyubean production. Agron. J., 79: 5'70-576.

Nye, P.H. and Greenland, U.J. (1964). Changes i n t he s o i l afcer clearing tr .oplcul fo r e s t . .P lant S o i l XXXI, No. 1, 101-102.

O d e s , J.M. (1984). S o i l organic mat ter and s t r u c t u r a l s t n b i l l t y : Plechanioms a d i u p l i c a t i o n s :or mwugement. P lan t S o i l 76; 719-39.

Ojeniyi , 8.0. and Dexter, P.R. (1979,). Boi l f a c t o r s a f f ec t i ng the urcro:;tructurttu produced by t i l l a g e . ICrm:;actions s l a e r i c o ~ Socie ty of A&mculGur&l lingiuaers, 22: 5 9 - 3 5 .

Ol ivera , L.B. de (1967). 0 estudo f i s i o o do s o l o en applicacao nacional do tachnicas conue rvac ion i~ bus. l'esqu. Pgropoev. Brae. a w . Agron. 2 ; 281-2&3.

Page, J.B. and Willard, O.J. '(1946). Cropping systems m d s o i l proper t ies . S o i l Yci. Bmer. P C , 1 : 81-88.

panayiotopoulos, K.P. and Kostopoulou, 2. (1989). Aggregate s t a b i l i t y dependence on s i ze , cul t ivat ion and various s o i l consti tuents i n red Mediterranean s o i l s ( f i f i so l s ) . So i l Tech. Vol. 2, NO. T , 59-69.

Peech, H. (1965). HJdrogen ion act ivi ty . Xn: C.A. Black (ed.). Methods of s o i l analysis. Par t 11. Am. Society of Agron. 9: 914-926.

Bamig, B.E. and Mazurak, A.P. (1964). Wheat stubble management I. Influence on some physical properties of a ohernozem soi l . S o i l Sc. Soo. of Am. Proc. 28: 554-557.

Reeve, R.C. (1953). A method f o r determining the s t a b i l i t y of s o i l s t ructure based upon a i r nnd water permeability measurements. S o i l Sc. Boa. of Am. Proc. 17: 324-329.

Ridleg, A.0. and Hedlin, A.O. (1968). S o i l orgunic matter and crop y ie ld a s influenced by the frequency of fallowing. Canadian J. of S o i l Sc. 48; 315-322.

Roth, C.H. , Neyer, B., Frede, A.G. and Deupeh, R. (1981). Effect of mulch r a t e s and t i l l a g e systems on i n f i l t r a b i l i t y and other s o i l physical properties of an Oxisol i n Paraf la , Brazil. So i l Til lage Hes. 11: 81-91.

Revira, A.D. and Greacea, E.L. (1957). The e f f ec t of aggregate disruption on the a c t i v i t y of micro- organisms i n the so i l . Australian J. of Agricul-

. t u r a l Research 8: 659-673.

Russell, E.W. (1973). So i l condition and plant growth. 10th edi t ion, Longman Group, London. 849 PP.

Saffigna, P.G., Powlson, D.S., Brookes, P.C. and 'Phomas, G.A. (1989). Influence of sorghun residues and t i l l a g e on s o i l organic matter and s o i l microbial biomass i n an Australian Vertisol. So i l Biol. Biochem. 21: 759-765.

Sanchez, P.A. (1976). Properties and management of s o i l s i n the tropics. John Wiley and Sons. New York, 618 pp.

Sohwertinann, U. and Taylor, R.N. (1977). Iron oxides. In: Minerals i n S o i l Environment (ed. J.B. Dixon e t . a l . ) , 145-150.

Shear, G.N. and Moschler, W.W. (1969). Continuous corn by no-tillage and conventional t i l l a g e methods: a six-year comparison. Agron. J. 61: 524-526.

Singh, L. and Balasubrmanian, V. (1977). Effects of continuous application of chemical f e r t i l i z e r s on the organic matter l eve l s of s o i l s at Samaru, Nigeria. Seglaru Conference Paper 17; 1-12.

Snika, D.E. and Wicks, G.k, (1968). S o i l water storage during fallow i n the Central Great Plains as influenced by t i l l a g e and herbicide treatments. Proc. So i l Sci. Soc. Au. 32; 591-595.

'Solomon, M. (1962). So i l aggregation - organis matter relationship i n Redtop potato relations. So i l Sci. Soc. Amer. Proc. 22: 51-54.

Sorensen, L.H. (1981). Carbon-nitrogen relat ionships during the hwnification of cellwlose i n s o i l s containing d i f ferent amounts of clay. So i l Bio l . Biochem. 13: 313-321.

Sowers, G.F. (1965). Consistensy. In: G.A. Black (ed.). Methods of s o i l analysis. Part I. Amer. Soc. Agron. 91 391-412.

Stanford, G. and W t h , S.J. (1972). Nitrogen nineral isat ion potent ia ls of s o i l . S o i l Sci. Soc. Am. Proc. 36: 465-472.

Str ickl ing, E. (1950). The e f f ec t o f ~oyabeans on volume weight and water s t a b i l i t y of s o i l aggregates, s o i l organio matter content and crop yield. Boil Sci. Soc. dm. Proc. 14; 30-34.

Tabatabai, M.A. and Hanway, J.J. (1968). Some ahemical and physioal properties of d i f f e r e i t - sized natural aggregates from Iowa soi ls . So i l Boi. Soc. Amer. Proa. 32: 588-591.

Tamboli, P.M., Larson, V.E. and Unemiya, H. (1964). Influence of aggregate s i ze on s o i l moisture retention. Iowa Acad. Sci. Proc., 71: 103-108.

Tanham, R.V., Mot i r amani, D.P. and Bali, Y.Y. (1970). Soi ls : Their chemistry aad f e r t i l i t y i n t ropioal A s i a . Preatice-Hall of Iadia Private Led. 475 pP.

Thompso~, L.M, and Troeh, F.R. (1973). So i l s aud s o i l f e r t i l i t ~ . . Third edition. McGraw-Hill, Inc., U.B.A. 516 pp.

Thorae, D.W. and Thorae, M.D. (1979). Soi l , water and crop production. 'Phe A v i Publishing Coupany, Inc. Westport, Comeoticut, U.S.A. 250 gp.

Tiessen, H. and Stewart, J.W.B. (1983). Par t i c le s ize fract ions and t he i r use i n s tudies of s o i l organic matter. 11. Cultivation eff ecta on organic matter composition i n s ize fractions. Soi l Sci. Soc. Am. J. 47: 509-514.

Tisdal l , J.N. and Oades, J.N. (1979). S tabi l iza t ion of s o i l aggregates by the root system of rye grass. Aust. J. So i l Res. 17: 429-441.

Tisdal l , J.M. and Oades, J.N. (1980a). The e f fec t of crop rotat ion on aggregation i n a red-brown earth. Aust. J. S o i l Res. 18: 423-433.

Tisdal l , J.M. and Oades, J.M. (1980b). The Ranage- ment of rye-grass t o s t ab i l i ze aggregate8 01 a red-brown earth. Aust. J. S o i l Res. 18; 415422.

Tisdall , J.M. and Oades, J.M. (1982). Organic matter and water s table aggregates i n soi ls . J. So i l Sci. 33: 141-163.

Tr ip le t t , G.B., ven Doren, D.M. and Schmidt, A.L. (1968). Effects of corn (2 a m s L.) stover on no-$illage corn yield and wa e r n f i l t r a t ion . Agroa. J. 60: 236-239.

++

Ugwu, T.O. (1983). The properties, c l ass i f i ca t ion and geomorphic relationships o f some soi1.s of the Jos Plateau. M.Sc. Thesis, Bhmadu Bello Uni. , Zaria, 130 'pp.

Utomo, N., Frye, W.W. and Blevins, H.L. (1990). Sustaining s o i l nitrogen for corn using hairy vetch cover crop. Agron. J. 82: 979-983.

van Veen, J.A. and Paul, E.A. (1981). Organic carbon dynaaics i n grassland soi ls . I. Background information and computer simulation. Can. J. Soi l Sci. 61: 185-201.

Vomocil, J.A. (1965). Porosity. In ; C.A. Black (ed.). Methods of s o i l analysis, Pa r t I. Am. Soc. kgron. 9: 299-314.

Walkley, A. and Black, I.A. (1934). kn examination of the Degtjarolt method fo r determining s o i l organic matter and a propased modification of the chromic acid t i t r a t i o n method. S o i l Sci. 37: 29-38.

Uebber, L.R. (1965). So i l polysaccharides and aggregation i n crop sequences. So i l Bci. Soc. Amer. Proc. 29: 39-42.

White, R.E. (1985). The influence of macropores on the transport of dissolved and suspended matter through soi l . k v . Soi l Bci. 3: 95-120.

Yitmuss, H.D. and Mazurak, bop. (19.58). Physical and chemical properties of s o i l aggregates i n Bronizem soi l . So i l Sci. Soc. Amer. Proc. 22: 1-5.

Appendix I; Effects of land use on organic oarbon concentratione of four aoile.

Treatment Aggregate size (mm) -- aynbola 5-2 2-1 1-0.5 0.5-0.25 40.25

a~ynbols are explained i n 'Pable 3

Appendix 2: Gffec ta of l m d use on organic matter content o f f o u r ~ o i I . 8 .

Tro atment Aggregate o i z o (mm)

symbola .5-2 2-1 1-0.5 0.5-0.25 40.25

2.97 2.33 3.10 3.57 5 3 1

*C 1.24 1. M 1.78 2.00 2.30

v~ 1 2 1 . ~ 7 1.52 1.66 1.72

v~ 0.83 1.03 0.69 0.76 1.24

aaynbols are explainmi in Table 3,

Appendix 5; Effects o f lnud use on nitrogen concentrtitions of four 6011s.

Treatment Aggregate saze (ma)

syabolsa

5-2 2-1 1-0.5 0.5-0.25 d0.25

IF 0,072 0,078 0.099 0.109 0.002

IC 0.050 0.069 0.085 0.086 0.080

U~ . '0.056 0,046 0.047 0.051 0.078

Uc 0.024 0.025 0.036 0.035 0.056

% p.140 0,*130 0.150 0.170 0.173

Ec 0.064 0.075 0.094 0.105 0.1;55

0.056 0,051 0.077 0.081 0.084

v~ 0.038 0.045 0.035 0.039 0.062

a Symbols are explained in T a b l e 3.

Appendix 4: bffects 0.1 land us@ on phosphor~s concen- trations of four soils.

Tre atmeat Aggregate size (am)

symbola 5-2 2-1 1-0.5 0.5-0.25 ~ 0 . 2 5

Appendix 5: Correlation coe f f i c i en ta (r) be tween organic carbon (%) and s i l t + clag , nitrogen, phoqhorua, dispersion rlntio and moisture retained a t 0.01 &¶Pa and 1.5 MPa (a = 8).

Variables Correlatioa coeff ic ient

OC Va S i l t + Clay

00 V s Total N

OC V s Available P

00 Vs Moisture retained a t 0.01 MPa

OC V s Moisture retained at 1.50 MPa

*Significant at P = 0.05

**Eignificant a t P = 0.01 NS = Not s igni f icant

Appendix 6; Gorrelation coeff ic ient ( r ) between silt + clay and s e l e ~ t e d s o i l properties (a - 8).

Variables Correlation coef f ic ient

( r)

S i l t + clay Vs DR -0. 734"

S i l t + clay Va Moisture retained at 0.01 MPa (96) 0.737''

S i l t + clay Vs Moisture retained at 1.50 MPa (%) 0. 511"

S i l t + clay V s 2otal IN (%) 0.633'

S i l t + clay Va Available P (ppm) 0.%lm

- - - - - - - - - - - - -

*Significant a t P - 0.05

**Significant at P = 0.01

NS = Not significant

I . '

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