Optimizing phosphorus fertilization in an intensive vegetable-rice cropping system

A study was conducted in a sweet pepper-maize-rice cropping system in six farmers' fields in Batac, Ilocos Norte, the Philippines, to determine the optimum P fertilizer rate for sweet pepper that will benefit the succeeding crops, maximize system-level productivity and profitability, and reduce the excessive accumulation of P in the soil. Single super phosphate was applied to sweet pepper at rates of 0, 28, 56, 84, 112, and 140 kg P ha(-1) and the succeeding crops were grown without P fertilization. Maize residue was incorporated into the soil at puddling of soil for rice. Phosphorus fertilization at 56 kg P ha(-1) and above had a residual effect on maize and rice. A reduction in the P applied to sweet pepper from 140 to 84 kg P ha(-1) reduced extractable P in the soil at rice harvest from 52 to 29 kg P ha(-1). Phosphorus applied at 111 kg P ha(-1) to sweet pepper was optimum for maximum productivity and economic returns of the sweet pepper-maize-rice cropping system. This rate of P also significantly reduced P accumulation in the soil, thereby reducing the chances of negative effects on soil nutrient balance/availability. The results suggested the need for a cropping systems approach to conserve and effectively use native and fertilizer P in the sweet pepper-rice cropping system.