Long-term phosphorus fertilizer effects on phosphorus uptake, efficiency, and recovery by upland rice on an ultisol

Phosphorus (P) deficiency is a major constraint to upland rice production on highly weathered, low activity clay soils in the humid zone of West Africa. There is a paucity of information on the long-term fertilizer P effects on rice on these soils. A field experiment was conducted for six years (1993-1998) to determine the response of four upland rice cultivars to fertilizer P applied at 0, 45, 90, 135, and 180 kg P ha(-1) only once in 1993, and to residual P in 1994, 1995, 1996, and 1998. The experimental site was located on an Ultisol, low in available P, in the humid forest zone of Cote d'Ivoire, West Africa. This paper discusses long-term P effects on P uptake and efficiency of upland rice cultivars. The cultivars evaluated differed in cumulative agronomic and physiological P efficiencies, and the efficiencies were higher at lower P rates for the P-efficient cultivars. The P uptake response and P harvest index were affected by P rate and its residual effect, which decreased with time after P was applied. The mean cumulative recovery of applied P in five crops of four rice cultivars varied from 5.5 to 9.4%. The results suggest that the variation in P efficiency of the cultivars is due to differences in the efficiency of utilization of P for grain production.