CARBON. NITROGEN AND PHOSPHORUS DYNAMICS INDUCED BY LONG-TERM CULTIVATION AND MANAGEMENT
CARBON. NITROGEN AND PHOSPHORUS DYNAMICS INDUCED BY LONG-TERM CULTIVATION AND MANAGEMENT
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Date
1997-09
Authors
THOMAS, GOLADI JUDAH
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Abstract
Several s t u d i e s in the savanna c o n t i n u e to justify the
benefits of inorganic f e r t i l i z e r s. Parallel s t u d i e s on the l o n g - t e rm effects
of f e r t i l i z e r s on t h e soils a r e scanty. The objective of t h i s study was to
determine t h e impact of inorganic f e r t i l i z e r s with or without farmyard
manure on carbon (C), n i t r o g e n (N) and p h o s p h o r u s (P) in a savanna alfisol
a f t e r 45 y e a r s of continuous cultivation. Soils for t h e s t u d y were fertilized
with N;N+P. N+P+K. farmyard manure (FYM) FYM+N. FYM+Pr FYM+NP and
FYM+NPK.
Continuous cultivation caused significant losses of C.N and P. The
N+P or N+P+K f e r t i l i z a t i on could not mitigate t h e s e losses. Losses of N and
P o c c u r r e d mainly in organic forms. However, combination of farmyard
manure with N+P and N+P+K fertilization maintained C.N and P at par with
or g r e a t e r t h a n the n a t i v e site soil.
Inorganic f e r t i l i z e r s s t r e s s e d microbial a c t i v i t y , evidenced by the low
microbial biomass C.N and P compared to t h e soil under native vegetation
and soils fertilized with FYM+N a n d FYM+NPK.
The study f u r t h e r examined the dynamics of inorganic P(P,) and
organic (P0) pools of the soils using a modified Medley Fractionation.
Continuous cultivation without P, fertilization decreased the concentration
of P1 and P0pools including residual P fraction. Fertilization with P, or in
combination with FYM (P.N+P+K. FYMP+P, FYM+NP a n d FYM+NPK) increased
the concentration of labile P1 pools, but decreased the concentration of P0
pools and the residual P fraction. The t e n d e n c y of t h e residual P fraction
to decrease along with P0 pools suggested that the residual P fraction was
largely P0, consistent with the correlation between residual P fraction and
total P0 (r = 0.74**) and with organic carbon (r = 0.47**). Path analysis of
the relationships between resin extractable P and the more stable Pt and P0
pools indicated that 85% of the variations in resin-P were explained by
hydroxide extractable P, (OH-P1) and HC1-P, which acted as sinks for
fertilizer-P. The contribution of residual P fraction to resin-P was indirect
via bicarbonate extractable P„ (HC03-Po) and 0H-Po suported by the
significant path coefficients between them. Thus, the hypothesis that
considers residual P fraction stable and inactive needs to be revised.
The study thus concluded that from the perspective of soil quality
maintenance and sustainable landuse systems a rational fertilization
strategy in the savanna is one that combines inorganic fertilizers with FYM
or organic/crop residue management to maintain SOM.
Description
A THESIS SUBMITTED TO THE POSTGRADUATE SCHOOL AHMADU BELLO
UNIVERSITY, ZARIA, IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR
THE AWARD OF THE MASTER OF SCIENCE (M.SC) DEGREE IN SOIL SCIENCE
Department of Soil Science
Faculty of Agriculture
Ahmadu Bello University
Zaria. Nigeria
Keywords
CARBON,, NITROGEN,, PHOSPHORUS,, DYNAMICS,, INDUCED,, LONG-TERM,, CULTIVATION,, MANAGEMENT