Direct and residual effect of different sources and levels of phosphorus in rice-wheat sequence under rainfed condition of Assam
Gowsami, J.; Baroova, S.R.
Annals of Biology 14(2): 149-153
Field experiment was conducted on acid soil of upper Brahmaputra Valley zone of Assam to study the direct and residual effects of single super phosphate (SSP), diammonium phosphate (DAP), Mussorie rock phosphate (NW) and Purulia rock phosphate (PR.P) each at 30, 60 and 90 kg P2O5/ha level applied to rice in a rice-wheat sequence. Both direct and residual effects of P as judged by grain and straw yield along with relative profitability were found superior over no P fertilization to either of the crops in the sequence. In rice, SSP was found to be the best source in respect of both grain and straw yield. Both NW and PRP recorded higher yield in wheat than SSP and DAP. However, in no case did the residual value of P fertilization match the benefit of directly applying P to the wheat crop suggesting that in a rice-wheat sequence in acid soil under rainfed condition, phosphatic fertilizer should preferably be applied to the wheat crop. In both the crops increasing P levels from 30 to 90 kg/ha recorded increasing yield level. The total rice equivalent grain yield from the sequence was found highest with SSP (33.96 q/ha) followed by DAP (33.52 q/ha) and then NW (32.95 q/ha). The optimum level of SSP was found to be 70.83 kg/ha. Highest net return (Rs. 3692.05) and return per rupee investment (0.69) were recorded with MRP at 90 kg P2O5/ha.