Phosphorus fertilization in a tropical acid soil under simulated slash and burn conditions: effects on uptake and adsorption of phosphorus

A greenhouse and P adsorption studies were carried out to assess the influence of P fertilization on availability and adsorption of phosphorus, in a tropical acid soil sample submitted to simulated slash and burn conditions, by adding 4 g.kg(-1) wood ash to the soil. Corn (Zea mays L.) was used as a plant-test for the pot experiment. Plants were harvested four weeks after sowing. The dry matter, P uptake as well as soil extractable P were determined. Phosphorus adsorption was investigated on soil samples of the pot experiment. Application of a P-fertilizer increased extractable P and decreased the P adsorption capacity of the soil. This resulted in increased P uptake by plants. The beneficial effects brought about wood ash, notably the increased pH neutralisation of exchangeable Al in the soil, enhanced P response similar to that found in lion acid soils. In these conditions, P uptake was correlated positively to extractable P and negatively to P adsorption maxima. The close relationships obtained between P adsorption maxima and extractable P can be used as a means of estimating P- fertilizer recommendations. This presumes a positive response to P-fertilizers in tropical acid soils after slash and burn. Field studies must be undertaken to confirm this findings and to determine the influence of some factors