Abstract
An experiment was conducted during the wet seasons of 1990-91 and 1991-92 to study the effects of four levels of S (0, 30, 60, and 90 kg ha-1) and three levels of P (0, 30, and 60 kg ha-1) on seed, oil yield, and oil content of raya (Brassica juncea var. Varuna) seeds. Seeds and oil yield increased significantly with application of S and P2O5 up to 60 kg ha-1. With S addition of 30, 60, and 90 kg ha-1, the increases in seed yield over the control were 121, 157, and 176%, respectively. Similarly, the increases in seed yield with P2O5 applications at 30 and 60 kg ha-1 compared to 0 P2O5, were 36 and 82%, respectively. There was a positive significant interaction between the two nutrients in increasing the seed and oil yield. The highest seed (2.15 t ha-1) and oil (0.95 t ha-1) yield resulted from S and P addition at their highest rates (90 kg S ha-1 and 60 kg P2O5 ha-1, respectively). The oil content was minimum where the highest level of S was used without P and maximum where either no S or P (S0P0) was applied or from the highest rates of their application. Maximum (1.051 t ha-1) and economic (1.050 t ha-1) oil yield levels as calculated from empirical quadratic equations, were expected to be obtained from an S dose of 62.8 and 60.8 kg ha-1, respectively, in combination with P2O5 level of 30 kg ha-1, which earned maximum (U.S. $22.0 and U.S. $22.8, respectively), for each dollar spent on S fertilizer. The pattern of increase in seed and oil yield and content was the same in both the years (1990-91 and 1991-92) when studied separately, and these deserve mention owing to two differences. Significant increases in seed and oil yields remained restricted up to 30 kg S ha-1 in both the individual years, and interaction effects of S and P on seed and oil yields were seen during the first year and those on oil content during the second year only. High residual effects of S and P fertilizers were seen at the end of the experiment. Both SO42- and PO43- benefitted each other in appreciating their carry-over effects.
