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®at-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-.
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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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