Crop responses to residual phosphorus and economic evaluation in soybean – wheat system on Vertisols

Abstract

Field experiments at Jabalpur and Bhopal on Vertisols were conducted to study the residual effects of P applied to either soybean or wheat in a soybean - wheat system in terms of the changes in soil test P values and benefit: cost rations. Phosphorus was applied at rates of 0,13,26.39 and 52 kg P/ ha to soybean 0,13,26 and 39 kg P/ ha to wheat during the first year and in the subsequent years the residual effects were compared with 39 kg P/ ha to each crop as recommended dose. Both soybean and wheat crops, during the three rotations, responded to residual and 39 kg P/ ha applied during 2nd and 3rd crop cycles at Bhopal due to low Olsen P status. But at Jabalpur, residual and freshly applied P had significant influence on soybean and wheat yields only after two annual rotations when Olsen P was below the critical limit. At both the sites, benefit: cost ratios of fertilizer P applied at rates of 13-39 kg P/ ha to first soybean or wheat were high and almost similar upto two crops