Variable Response of Food Crops to Banded and Broadcast Residual Fertilizer P on an Ultisol

Abstract

In a sequence of ten crops on a Torres clay, an Ultisol, variable responses to fertilizer P were obtained. Rice and soybeans did not respond to fertilizer P. In three corn crops out of six, and in two field bean crops, there was response to banded fertilizer P but not to broadcast residual P. In the first corn crop, near maximum yields were obtained with 90 kgjha of banded P and with 359 kg/ha of broadcast P. The residual effect of large applications of broadcast P on successive crops was almost nil. In field experiments, soil tests indicated a sharp P drop in the broadcast P treatments after three years, perhaps due to P fixation. Organic P mineralization appears to be rather important in the highly weathered soils of the humid tropics. Apparently, P is mineralized more rapidly during. the summer months.