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

Little attention has been devoted to calibrating soil tests for phosph orus (P) in the field for upland rice in West Africa. The information is needed to improve fertilizer P recommendations. A field experiment was conducted in the rainy season of 1994 to establish the relationshi p between extractable P by Bray 1 and grain yield of four upland rice cultivars grown on an Ultisol in the forest zone of Ivory Coast. The c ritical limit of Bray 1 P in the soil at 90% relative rice grain yield varied from 12.5 to 15.0 mg P/kg of soil for the four cultivars teste d. The P critical limit in the soil tended to be lower for the cultiva rs of rice earlier found to be efficient at converting applied P into grain yield.