AFRIKA FOCUS Vol . 2. Nr. 2, 1986, pp . 127-138

THE USE OF ROCK PHOSPHATE AS A SOURCE OF PHOSPHORUS ON A SLIGHTLY ACID CLAYEY SOIL IN TANZANIA

MSAKY, J .J .T. (1), B.M. MSANYA (2) & A.P. URIYO (3) Soko ine Un ive rs i t y o f A g r i c u l t u r e , D e p a r t m e n t o f Soil Sc ience , P.O. Box 3008, Morogoro , TANZANIA.

SUMMARY

The e f f e c t i v e n e s s o f r o c k phospha te as a phosphorus n u t r i e n t s ou r c e was s t u d i e d as c ompa r ed t o t r i p l e s upe r pho spha t e (TSP), a common f e r t i l i z e r used in Tanzania. In i t i a l r e su l t s showed t h a t r o c k phospha te can be used as a P s ou r ce f o r g row ing maize. I t s app l i c a t i on i n c reased b o t h g ra in y ie lds and so lub le f l o r i d e e x t r a c t a b l e P in t h e so i l . TSP s t i l l p r o ved t o be s upe r i o r t o r o c k phospha t e f o r t h e d i r e c t e f f e c t e x pe r imen t s in t e r m s o f b o t h g ra in y ie ld and so lub le f l u o r i d e e x t r a c t a b l e P. However, f o r t h e res idua l e f f e c t s e x pe r imen t , r o c k phospha te was equal ly e f f e c t i v e as TSP. Gr ind ing r o c k phospha te beyond -40+60 mesh d i d no t r e s u l t in an inc rease in so lub le P. However, i nc rease in levels o f app l i c a t i on r e s u l t e d i n t o i n c reased so lub le P in so i l . A comb ina t i on o f f i neness and level o f app l i c a t i on r e s u l t e d i n t o an i n c reased amount o f so lub le P. This c omb i na t i on shou ld thus be used as a c r i t e r i o n in t h e use o f r o c k pho spha t e as a P n u t r i e n t s ou r c e f o r p l an t g r o w t h .

KEYWORDS : Rock Phospha te , phosphorus sou r ce , soi ls, Tanzania '

INTRODUCTION

W i t h t h e poss ib le e x c e p t i o n o f n i t r o g en , no o t h e r e l emen t has been as c r i t i c a l in t h e g r o w t h o f p l an t s in t h e f i e l d as has phosphorus (Brady, 1974). A lack o f t h i s e l emen t is e x t r e m e l y

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ser ious as i t may even p r e v e n t t h e u p t a k e o f o t h e r n u t r i e n t s by p lan t s . The impo r t a n c e o f phosphorus f o r p l an t g r o w t h has r e ce i v ed spec ia l c on s i d e r a t i o n in t h e f o rmu l a t i o n o f commerc i a l f e r t i l i z e r s .

In Tanzania, s upe rphosha t e a c coun t s f o r abou t 90 pe r c e n t o f t h e f e r t i l i z e r phosphorus used . T r ip l e s upe r pho spha t e (TSP) is be ing m a n u f a c t u r e d f r o m r o c k phospha te i m p o r t e d f r o m overseas. The local ma te r i a ! o c c u r r i n g in abundance a t Minj ingu, N o r t h e r n Tanzania, cou ld be advantageous ove r t h e i m p o r t e d r o c k phospha te . I t s e x p l o i t a t i o n wi l l n o t r e qu i r e much f o r e i g n exchange i n ve s tmen t espec ia l l y in t h e long run .

One o f t h e d i sadvantages o f t h e local ma te r i a l is t h e low phospha te (24.5 'I. t o t a l BL 0, ) and high s i l i ca (29.9 7. as Si 0, ) c o n t e n t wh i ch impl ies t h a t i t may become r a t h e r expens ive t o c o n c e n t r a t e t h e o r e as f e e d ma te r i a l t o w a r d s t h e i ndus t r i a l m a n u f a c t u r e o f t r i p l e s upe rpho spha t e f e r t i l i z e r . However, cons i de r i ng t h e avai lable phospha te s t a t u s and t h e f a i r l y high ca l c ium and magnesium c o n t e n t , i t may be used as a raw phospha t i c ma te r i a l in wel l p owde r ed f o r m in p lace o f t r i p l e s upe r pho spha t e t o some e x t e n t . I t should also be s t r e s s e d t h a t t h e use o f t h e local ma te r i a l in t h e i ndus t r i a l m a n u f a c t u r e o f TSP c anno t be ru l ed ou t a t t h i s moment .

E xpe r imen t s c o n d u c t e d in Tanzania b e t w e e n 1959 and 1970 w i t h r o c k phospha te along w i t h s upe rpho spha t e on g r oundnu t s as a t e s t c r o p showed t h a t t h e w a t e r so lub le s ou r c e o f phospha t i c f e r t i l i z e r s a re genera l l y a more e f f i c i e n t sou r ce o f phospha te t han t h e g round r o c k phospha te , t hough t h e l a t t e r has much t h e same res idua l e f f e c t (Le Mare, 1959 and Anderson , 1970).

The g row ing energy p rob l em and soar ing p r i c e s o f i m p o r t e d r o c k phospha te c oup l ed w i t h Tanzania 's i nadequa te f o r e i g n exchange cal ls f o r a need f o r b e t t e r eva lua t ion and u t i l i z a t i o n o f local r e sou r ce s . The c u r r e n t s t u d y compr i s i ng o f a ser ies o f e x pe r imen t s was c a r r i e d o u t w i t h t h e fo l l ow ing o b j e c t i v e s :

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i - t o i n ve s t i ga t e on t h e use o f t h e r o c k phospha te d e p o s i t as a s ou r c e o f phosphorus t o c r op s

ii - t o mon i t o r res idua! e f f e c t s o f app l i ed r o c k phospha te on c r o p y ie lds

iii - t o i n ve s t i ga t e on t h e r e l a t i v e e f f i c i e n c y o f t h e o r e as c ompa red w i t h t h e commonly used t r i p l e s upe r pho spha t e f e r t i l i z e r .

MATERIALS AND METHODS

The soi l on wh i ch t h e e x p e r i m e n t s w e r e c o n d u c t e d was c h a r a c t e r i z e d and c l a s s i f i ed as Typ ic Rhodus tu l t a c c o r d i ng t o Soil Taxonomy (U.S.D.A.-S.C.S., 1975), based on i t s morpho log i ca l c h a r a c t e r i s t i c s and t h e phys i co - chem i ca l d a t a p r e s e n t e d in t a b l e 1.

Powde red Minj ingu r o c k phospha te o f t h e meshes g iven in t a b l e 2 was p rov i ded by t h e S t a t e Mining C o r p o r a t i o n (STAMICO) and was analysed f o r t o t a l and avai lable phosphorus by s t a nda r d me thods . TSP was used t o m o n i t o r t h e p e r f o r m a n c e o f t h e r o c k phospha te in inc reas ing c r o p y ie lds .

A s imple c omp l e t e l y r andom i zed b lock des ign w i t h t h r e e r ep l i c a t i on s was used and inc luded f o u r r a t e s o f f e r t i l i z e r app l i c a t i on : 0, 20, 40 and 60 kg P/ha f o r each mesh s i ze . The t r i a l s w e r e c a r r i e d o u t on t h e Un ive r s i t y Farm (Morogoro, du r i ng 1976, 1977 and 1978 c r o p p i n g seasons (March-Augus t ) using maize as a t e s t c r o p . The year l y w e a t h e r c ond i t i o n s on t h e a rea rema ined q u i t e s t a b l e du r i ng t h e pe r i od o f e x p e r i m e n t a t i o n .

The p e r f o r m a n c e o f t h e r o c k phospha te was mon i t o r e d t h r o u g h (a) d i r e c t e f f e c t s e x p e r i m e n t t o c he ck t h e immed ia te e f f e c t o f t h e r o c k phospha te app l i c a t i on on c r o p y ie lds and (b) res idua l e f f e c t s e x p e r i m e n t t o see t h e e f f e c t o f t i m e on t h e re lease o f phosphorus f r o m r o c k phospha te .

Fo r t h e d i r e c t e f f e c t s e x pe r imen t , b o t h r o c k phospha te and t r i p l e s upe rpho spha t e w e r e b r o a d c a s t e d and i n c o r p o r a t e d i n t o t h e soi l t w o weeks b e f o r e p l an t i ng . No phospha te

Table 1 : Physico-chemical properties of the soil

Depth (cm. )

Sand i

Silt Clay

B.D. g/cc

„III pH 1:2.5 soil-

liquid H.,0 IM KCl

total ..V

Avail. P V I

ppm.

Exch. cations meq./lOOg

Mg

C E C ™ meq./ 100 g soil

Ap 0- 20 42 6 8 4 49 0 1 21 6 5 6 1 1 63 0 15 14.9 8 23 4 81 0 58 1 38 9 14 25 2 59 5

B l t 20- 45 33. 9 8 1 58 0 1 34 6 3 4 3 0 72 0 13 n.d. 4 00 2 84 0 08 0 18 n d. 30 0 23 5

B21t 45- 75 31. 6 8 1 60 3 1 18 6 1 4 4 0 58 0 11 n.d. 3 20 2 84 0 16 0 07 n d. 25 2 24 9

B22t 75-110 29 3 10 4 60 3 1 18 6 0 4 4 0 55 0 09 n. d. 2 00 3 24 0 23 0 0 7 n d. 28 0 19 8

B23t 110-200+ 2 7 1 12 6 60 3 1 16 6 1 4 2 0 39 0 08 n. d. 3 60 2 43 0 47 0 09 n d. 30 6 21 6

I.Hydrometer method (Day, 1965x) II. Core method (Blake, 1965x)

III. Modified glass electrode method (Peech, 1965x) IV. Wet combustion method - Walkley and Black (Allison, 1965x) V. Macro-Kjeldahl method (Bremner, 1965x)

VI. Bray and Kurtz method (1945)

VII. C a 2 + and M g 2 + EDTA titration (Head, 1965x) N a + and K +-Flame photometry H +-Menlich's method (1953)

VIII. NHÎ-saturation method (Chapman, 1965x) 4

X : In Black, C.A. et al. (1965). n.d. : not determined.

c a r r y i n g ma te r i a l was app l i ed in t h e res idua l e xpe r imen t a l f i e l d and t h e p l o t boundar ies f r o m t h e 1977 d i r e c t e f f e c t s e x p e r i m e n t w e r e ma in ta ined du r i ng t h e t i l l age ope r a t i on s .

T a b l e 2. M i n j i n g u r o c k phospha te mesh s i z e s and t h e i r phospha te forms

Mesh s i z e (*) 7 t o t a l P i n 7. P c i t r i c a c i d

(*) F i n e n e s s o f r o c k phospha te i n c r e a s e s downwards

Maize v a r i e t y I longa c ompos i t e was sown a t 75 cm b e t w e e n t h e rows and 30 cm w i t h i n t h e row spac ing . For t h e res idua l e f f e c t , t h e same v a r i e t y o f maize was g rown du r i ng 1978 c r o p p i n g season on t h e r e s p e c t i v e t r e a t m e n t p l o t s used in 1977. N i t r o g en a t 40 N kg/ha was t o p d r e s s e d a t knee he igh t f o r b o t h d i r e c t and res idua l e xpe r imen t s . Fo r p l an t analysis, a c ompos i t e sample cons i s t i ng o f ear leaves ( the u p p e r m o s t l ea f o p p o s i t e t h e t o p m o s t cob) f r o m t e n randomly s e l e c t e d p l an t s was c o l l e c t e d f r o m t h e p l o t s a t c ob f o r m a t i o n . The samples w e r e d r i e d in an oven a t 105* C t o c o n s t a n t mo i s t u r e and g round in a Wi l ly mi l l . The g round ma te r i a l was ashed and analysed f o r P by t h e v anada t e -mo l y bda t e ye l low co l ou r me t hod (Chapman and P r a t t , 1961).

RESULTS AND DISCUSSION

r o c k phospha te s o l u b l e

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11 + 22 22 + 40 40 + 60 80 + 100

10.50 11 .00 11 .40 1 1 .70 11.70

9 .75 10 .50 10.10 10.50 9 .62

(a) D i r e c t and res idua l e f f e c t s

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Table 3 shows t h e e f f e c t o f app ly ing P c a r r y i ng mate r i a l s on t h e ava i lab i l i ty o f soil P a t c ob f o r m a t i o n s t age f o r 1976 and 1977 (average f o r t w o years) .

T a b l e 3 . Mean a v a i l a b l e phospho rus l e v e l s (ppm) i n the s o i l a t cob f o r m a t i o n

Sou r ce s Meshes L e v e l s o f a p p l i c a t i o n ( kg P/ha) 0 20 40 60 Means

Rock -11 +22 10. 7 12.5 12. 9 12. 8 12.2 phospha te -22 +40 13 . 7 14.8 15. 7 17. 5 15.4

-40 +60 12. 8 14.0 14 . 9 19. 8 15.4 -80 +100 11 . 1 14.3 19. 7 18 . 1 15.8 -100 14 . 2 16.9 15. 6 15. 0 15.4

T r i p l e 15 . 8 17.4 18 . 6 22 . 4 18.6 s u p e r ­phospha te

Means 13. 1 15 ,0 16 . 2 17 . 6 15.5

Increas ing r a t e o f P app l i c a t i on r e s u l t e d in i nc reased levels o f so lub le f l u o r i d e e x t r a c t a b l e phosphorus in t h e soi l sampled a t c ob f o r m a t i o n . There was a s l i gh t i nc rease in so lub le f l u o r i d e e x t r a c t a b l e phosphorus f r o m - 1 1 +22 t o - 40 +60 mesh r o c k phospha te . However, i t appears t h a t g r i nd ing t h e ma te r i a l i n t o f i n e r p a r t i c l e s does no t necessar i l y r e su l t in an inc rease in f l u o r i d e e x t r a c t a b l e phosphorus . S t a t i s t i c a l analysis on t h e e x t r a c t a b l e phosphorus d a t a revea led t h a t t h e inc rease in so lub le f l u o r i d e e x t r a c t a b l e phosphorus f r o m t h e p l o t whe r e t r i p l e s upe rphospha t e had been app l i ed , when compa red t o t h e t r e a t m e n t s t h a t had r e c e i v ed -11 + 22 mesh r o c k phospha te we r e highly s i gn i f i c an t .

The c o n c e n t r a t i o n o f P in t h e leaves i nc reased s i gn i f i c an t l y w i t h inc reas ing P r a t e s in t h e case o f t r i p l e s upe rpho spha t e t r e a t m e n t . A s imi lar b u t s l i gh t l y less c on s i s t e n t t r e n d was obse r ved f o r t h e r o c k phospha te t r e a t m e n t s ( tab le 4).

Tab l e 4. Mean phospho rus c o n c e n t r a t i o n (7.) i n ma i ze l e a v e s a t cob f o r m a t i o n

P Sou r ce s Meshes L e v e l s o f a p p l i c a t i o n (kg P/ha) 0 20 40 60 Means

Rock -11 + 22 0. 19 0 .22 0.21 0 .20 0 .21 phospha te -22 +40 0. 21 0.21 0. 20 0 . 25 0 .22

-40 +S0 0. 19 0 .22 0.21 0 . 25 0 .22 -80 +100 0. 19 0.21 0 .20 0 .20 0. 20 -100 0 . 12 0.21 0.19 0 .25 0 .19

T r i p l e 0. 17 0 .20 0 .22 0 .25 0.21 s upe r pho spha t e

Means 0. 18 0.21 0.21 0 .25 0.21

S i g n i f i c a n t e f f e c t s : L e v e l s Meshes LSD P = 0 01 0.011 0. 015

W i t h r ega rd t o mesh s izes o f app l i ed r o c k phosphate , t h e r e was only a s l i gh t inc rease in l ea f P c o n c e n t r a t i o n f r o m -11 + 22 t o - 40 +60 mesh, and th i s was only in t h e case o f t h e h ighes t level o f r o c k phospha te app l i c a t i on (60 kg P/ha).

Table 5 shows gra in y ie ld d a t a f o r 1976 and 1977 as a f f e c t e d by f e r t i l i z a t i o n w i t h d i f f e r e n t sources o f phosphorus . In b o t h years inc reas ing levels o f P app l i c a t i on r e s u l t e d in i nc reased y ie lds o f maize. The y ie lds ob t a i n ed f r o m t h e app l i c a t i on o f t r i p l e s upe rpho spha t e w e r e supe r i o r t o t ho se ob t a i n ed a t s imi lar r a t e s o f Minj ingu r o c k phospha te app l i c a t i on . Mesh s izes also a f f e c t e d t h e y ie ld o f maize in b o t h years a l though t h e increases in y ie ld w i t h inc rease in mesh s i ze w e r e n o t c on s i s t en t . Fo r t h e d i r e c t e f f e c t i t wou ld appea r t h a t unde r t h e p r e s e n t c i r c ums t an ce s g r i nd ing t h e o r e beyong - 40 +60 mesh may no t necessar i l y give supe r i o r p e r f o r m a n c e . F u r t h e r m o r e , g r i nd ing t h e ma te r i a l i n t o t h e f i n e r meshes beyong - 40 +60 mesh may inc rease t h e r a t e o f P f i x a t i o n because o f t h e

Table 5 : Grain yield (Kg./ha) of maize as affected by fertilization with different sources of phosphorus

P Sources Meshes 19 76 Meshes 1977

Levels of application Levels of appli rat i on (Kg P/ha) (Kq IV ha )

0 20 40 60 0 20 40 60 Mean

Rock phosphate -11+22 3051 3050 2 7 50 3463 3076 233 7 2592 2939 2346 2553

-22+40 298 7 3750 3951 3 580 3592 2538 3 209 3 36 5 3121 3058

-40+60 3919 3805 3 74 3 3838 3830 3045 3150 3224 3270 31 72

-80+100 3950 3532 33 71 3884 3629 2 760 3000 3334 3301 3098 -100 3403 3958 402 8 4215 2896 3350 3 3 50 34 38 3587 3317

Triple 3 790 4166 3619 Superphosphate 35 3 4 4181 4468 4874 4264 2978 3542 3 790 4166 3619

Means 3474 3713 3685 3991 2759 3140 3348 3298

Significant effects : Levels Meshes Levels Meshes LSD p = 0.01 246 720 510 622

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i nc reased t o t a l s u r f a c e area o f t h e r o c k phospha te . In such c i r c ums t an ce s t h e r e wi l l be cons i de rab l e c r o p imp rovemen t in y ie ld mos t l y in subsequen t years as t h e P r a t e g e t s s lowly re l eased .

Table 6 shows t h e e f f e c t o f res idua l P on t h e y ie ld o f I longa c ompos i t e maize in 1978. S i gn i f i c an t y ie ld inc reases due t o P app l i c a t i on f o r all levels w e r e ob t a i ned ove r t h e c o n t r o l (0 level).

T a b l e 6. E f f e c t o f r e s i d u a l P on t he y i e l d o f I l o n g a c o m p o s i t e ma i ze (kg P/ha)

P Sou r ce s Meshes L e v e l s o f a p p l i c a t i o n (kg P/ha) 0 20 40 60 Means

Rock -11 + 22 1375 1563 1800 1856 1649 phospha t e -22 +40 1632 1743 2095 1904 1844

-40 +60 1868 2007 2184 2142 2050 -80 +100 1803 2009 1910 1931 1913 -100 1647 1966 2075 2176 1966

T r i p l e 1562 2290 224 1 2253 2087 s upe r pho spha t e

Means 1648 1930 2051 2044

S i g n i f i c a n t e f f e c t s LSD P = 0.01

A l though cons i de rab l e v a r i a t i on in y ie ld was ob t a i ned due t o mesh s izes, t h e e f f e c t s w e r e no t c on s i s t e n t . The y ie lds f r o m t h e p l o t s whe r e t r i p l e s upe r pho spha t e had been app l i ed w e r e genera l l y h igher t han t ho se f r o m t h e t r e a t m e n t s t h a t had r e c e i v ed r o c k phospha te app l i ca t i ons . Prev ious e x p e r i m e n t s have genera l l y shown t h a t t h e d r y m a t t e r y ie ld response t o r o c k phospha te is less t h an t h a t t o s upe r pho spha t e in t h e s h o r t t e r m , e x c e p t on ac id soi ls ( F i t z p a t r i c k , 1961). In t h e l a t e r years o f long t e r m

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e xpe r imen t s , in wh i ch t h e f e r t i l i z e r s a re added in a s ingle in i t ia l app l i c a t i on , t h e cumu la t i ve y ie ld response t o r o c k phospha te may o r may no t be as g r e a t as t h a t ob t a i ned w i th , s upe rpho spha t e (McLachlan, 1960 ; Russel l , 1960). Russell (1960) sugges ted t h a t r o c k phospha te might be used t o more advantage whe re t h e labi le phosphorus c o n t e n t o f t h e soi l had been inc reased by prev ious f e r t i l i z a t i o n t o t h e e x t e n t t h a t f u r t h e r supp l ies a re needed only t o mainta in t h e labi le s t o r e o f phosphorus , and t h a t t hey might be pa r t i c u l a r l y u se fu l whe r e w a t e r so lub le phospha te is read i l y l eached .

( b ) I n t e r a c t i o n e f f e c t

S t a t i s t i c a l analysis f o r t h e 1977 r e su l t s showed a d e f i n i t e i n t e r a c t i o n p a t t e r n b e t w e e n mesh s i ze and levels o f app l i c a t i on o f r o c k phospha te . The i n t e r a c t i o n e f f e c t was ve ry highly s i gn i f i c an t (F = 6.142***). This means t h a t f o r t h e e f f e c t i v e use o f r o c k phospha te b o t h t h e f i neness and t h e r a t e o f app l i c a t i on should be c on s i de r ed as i m p o r t a n t f a c t o r s and t h e main f a c t o r s c on t r o l l i n g t h e amount o f avai lable P f o r p l an t u p t a k e . However, t h e res idua l e x p e r imen t d i d n o t show any s i gn i f i c an t i n t e r a c t i o n e f f e c t (F = 0,94).

CONCLUSIONS AND RECOMMENDATIONS

The r e su l t s ob t a i n ed in t h i s s t u d y c lea r l y i nd i c a t e t h a t t h e local r o c k phospha te can be used in p owde r ed f o r m t o improve c r o p y ie lds . I t was also a ppa r en t t h a t unde r t h e cond i t i on s o f t h e e xpe r imen t s , f i neness o f t h e phospha te mate r i a l is a c on t r o l l i n g f a c t o r in P re lease f o r p l an t s . In th i s r e s p e c t , g r i nd ing o f r o c k phospha te up t o - 40 +60 mesh s i ze is r e commended f o r op t imum y ie lds . Gr ind ing t h e mate r i a l i n t o f i n e r p a r t i c l e s izes may be un j u s t i f i a b l y c o s t i y and may no t necessar i l y improve c r o p y ie lds pa r t i c u l a r l y in t h e s h o r t run .

As f o r t h e r a t e s o f phospha te app l i c a t i on , i t was also obvious t h a t i nc reased levels o f phospha te improved c r o p y ie lds .

-Ha**-

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Cons ider ing t h e r e su l t s ob t a i n ed f r o m b o t h t h e d i r e c t and res idua l e f f e c t s o f phospha te app l i c a t i on , t h e r a t e o f 40 kg P/ha can be r e commended as an ideal one.

Las t l y t h e au tho r s wou ld s t i l l l ike t o u rge t h e gove rnmen t o f Tanzania t o f u r t h e r a s t udy on t h e poss ib i l i t i es o f using t h e local r o c k phospha te in f u t u r e as a f e e d mate r i a l f o r t h e m a n u f a c t u r e o f s upe rpho spha t e f e r t i l i z e r s by t h e Tanzania F e r t i l i z e r Company. The a rguments aga inst i t s use f o r t h a t pu rpo se (i.e. high c o s t s o f c o n c e n t r a t i n g t h e ore) need t o be s u b s t a n t i a t e d by a mu l t i - d i s c i p l i n a r y s tudy) .

NOTES

MSAKY, J.J.T. (1) ; B.M. MSANYA (2) and A.P. URIYO (3) L e c t u r e r s (1 and 2) and P r o f e s s o r (3) r e spec t i v e l y . P r e sen t addresses : .1. S c i ence du Sol , I n s t i t u t Nat iona l Agronomique Pa r i s -

Gr ignon, 78850 Thiverval Gr ignon, FRANCE. 2. S t a t e Un ive rs i t y Ghent , Depa r tmen t o f General Pedology,

Kr i jgs laan 281, 8 -9000 Ghent , BELGIUM. 3. I n t e r na t i o na l I n s t i t u t e o f T rop i ca l Ag r i c u l t u r e , P.M.B. 5320

Ibadan, NIGERIA.

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ACKNOWLEDGEMENTS

The au tho r s wish t o exp re s s thanks t o t h e S t a t e Mining Co r po r a t i o n (STAMICO) o f Tanzania f o r p rov id ing t h e r e s ea r ch f unds .