Abstract

P. K. Ghosal, B. Bhattacharya, D. K. Bagchi and T. Chakraborty

A study was conducted on rainfed rice to find out the efficiency of phosphate rocks (PRs) as P-fertilizer. Four sources of phosphatic (P) fertilizers namely, triple superphosphate (TSP), Morocco rock phosphate (MORP), partially acidulated phosphate rock (PAPR) and Mussoorie rock phosphate (MRP) were used. Both the direct and residual effect of different P-sources on rice yield, P-uptake, phosphorus availability in soil and balance of soil P in the direct-residual system of P application in rice were recorded. The result on yield showed significant best effect by direct application of water-soluble TSP (2.77 t ha-1 ) followed by PARP (2.50 t ha-1 ) in the first crop. The best residual effect on the yield of rice was obtained by insoluble and slowly available rock phosphates, MORP (3.87 t ha-1 ) followed by PARP (3.81 t ha-1 ) and MRP (3.74 t ha1 ). The yield also increased with the increase of phosphate dose at 40 or 80 kg P ha-1 , applied once in three years and residual effect was better than the direct one. TSP and PARP gave linear response whereas MORP and MRP showed quadratic response to P-application. MRP also depicted highest P-balance in soil, (29.53 kg P ha-1 ) and better economic benefit was received in favour of PARP and MORP in the three-crop system.