PHOSPHORUS-SULFUR INTERRELATIONSHIPS FOR SOYBEANS ON P-DEFICIENT AND S-DEFICIENT SOIL

We investigated the P-S interrelationship in a 3-year field experiment on soybean (Glycine max) on a soil deficient in both P and S. The treatments were in a factorial combination of four levels each of P (0, 17.5, 35.0, and 52.5 kgha−1) and S (0, 20, 40, and 60 kgha−1). Combined applications of P and S showed synergistic effect up to 35 kg P- and 40 kg S-ha−1levels. The balanced P-S fertilization resulted in maximum seed yield and enhanced the process of protein and oil synthesis in soybean. Fertilizer P and S promoted the availability of native soil P and S as reflected by their percentage removal in the crop. The efficiency of native S was almost double that of native P in supply and removal by the plant. The antagonistic effect of P × S on plant growth and on cross-utilization was only observed when they were applied together at 52.5 kg P ha−1. © 1990 Williams & Wilkins.