PLANT PHOSPHORUS AND RICE YIELD IN AN ULTISOL OF THE HUMID FOREST ZONE IN WEST-AFRICA

Little attention has been devoted to calibrating plant tissue tests fo r phosphorus (P) in the field for upland rice in West Africa, although information is needed for improving crop production through efficient P nutrition. A field experiment was conducted under rainfed condition s in the 1994 season to establish the relationships between plant P co ntent and grain yield of upland rice grown on an Ultisol, having a ran ge in extractable P, in the humid forest zone of Ivory Coast. The crit ical limit of P content in the whole rice plant tops at the tillering stage, at 90% relative grain yield, was found to be 2 g kg(-1) P for t he four upland rice cultivars tested. Total P uptake in the biomass wa s significantly correlated with rice grain (r=0.81, n=20) and straw (r =0.79) yields of the cultivars.