Determining fertilizer phosphorus requirement of upland rice

Assessing the fertilizer phosphorus requirement (FPR) of crops is an import ant component of research for efficient and rational use of fertilizers. So il and plant tests are used to determine the FPR of crops. Two methods were evaluated for determining the FPR of upland rice grown on an Ultisol in th e humid forest zone of Cote d'Ivoire. The first method used a simple model based on P uptake using the equation: FPR=(Up-U0)/PRF, where Up is P uptake at a given yield, Uo is P uptake from unfertilized soil, and PRF is the P recovery fraction of applied P. The parameters, U0, Up, and FPR were determ ined in field experiments for the rice cultivars grown on an Ultisol under rainfed upland conditions. The second method was based on the P applied, P uptake, and grain yield relationships for upland rice. First, P uptake at a given rice yield was determined from the relationship between total P upta ke and grain yield. The amount of fertilizer P applied for the given P upta ke and grain yield was then, determined from the relationship between P app lied and P uptake. There was a good agreement between the observed values o f FPR and the predicted values of FPR determined by the two methods. The re sults suggest that the simple model based on P uptake can be utilized for d etermining the fertilizer P requirements of crops.