PHOSPHORUS REQUIREMENT OF A MAIZE-COWPEA SEQUENTIAL CROPPING ON A PALEUDULT

A field experiment was conducted for 6 growing seasons on a Paleudult to assess the influence of P rate and frequency on crop yield and P fr actions in a maize-cowpea sequential cropping system. Although croppin g depleted soil organic P by up to 42.1% over the cropping seasons per haps through mineralisation, the major portion of added P and minerali sed P were not utilised by the crops. Transformations were probably mo re to the insoluble Fe-P than A1.P. Cumulative recovery of P in maize and cowpea was never above 75% at a single application of 30kg P ha(-1 ) over a period of 6 seasons while cumulative recovery of annually app lied P ranged from 17.1 to 31.8% over the same period. Lower values we re recorded for seasonally applied P plots. Annual application of P at 30kg ha(-1) kept the available P above the critical level and maintai ned maize and cowpea yields at near maximum over the cropping periods.