African Journal of Agricultural Research Vol. 2(10), pp. 521-527, October, 2007

ISSN 1991- 637X­© 2007 Academic Journals

Full Length Research Paper

Use of pruning and mineral fertilizer affects soil phosphorus availability and fractionation in a gliricidia/maize intercropping system

D. E. Mweta^1,2, F. K. Akinnifesi^2*, J. D. K. Saka¹, W. Makumba^2,3, N. Chokotho¹

¹University of Malawi, Chancellor College, P.O. Box 280, Zomba, Malawi.

²World Agroforestry Centre (Malawi), P.O. Box 30798, Lilongwe, Malawi.

³Chitedze Agricultural Research Station, P.O. Box 158, Lilongwe, Malawi.

*Corresponding author. E-mail: fakinnifesi@africa-online.net .

Accepted 26 September, 2007

Leguminous tree species are known to replenish soil nutrients through biological N fixation, mulch effect and recycling of other nutrients from the deeper soil layer to the topsoil, when managed in agroforestry systems. The soil available phosphorus (P) status and inorganic P-forms (fractionation) in a long-term gliricidia-maize trial was studied to understand the effect of additions of gliricidia prunings combined with and without inorganic fertilizers (N and P). Addition of gliricidia prunings and inorganic N and P fertilizers significantly increased phosphorus uptake by maize. Bray P1 had strong correlation with P uptake by maize in gliricidia/maize intercropping (r = 0.81, p<0.001). Both the Olsen and Bray P1 methods of extraction were strongly correlated (r = 0.80). Phosphorus fractionation data of the soils from the maize and gliricidia-maize plots indicated that the Fe-P fraction was the most dominant form of inorganic P. The addition of gliricidia prunings significantly reduced the Fe-P and Al-P forms. We conclude that iron phosphate acts as a sink for applied inorganic P in Lixisols and the increased soil organic matter through addition of gliricidia prunings solubilizes fixed P in the soil.

Key words: Agroforestry, fertilizer trees, available P, P-uptake, inorganic P fractions.