Requirement of phosphorus and its use efficiency by sunflower in high phosphorus soils

Field experiments were conducted during Kharif, 2008, 2009 and 2010 to find out the phosphorus requirement to Sunflower crop grown in a soil with high initial available phosphorus (110–119 kg P2O5 ha−1). Three years pooled data revealed that application of 100% RDP resulted highest seed yield of 12.18q ha−1. The seed yield increased significantly by about 9.51, 11.75, 12.50 and 13.62 percent due to application of 25(11.74q ha−1), 50 (11.98 qha−1), 75 (12.06 qha−1) and 100 (12.18 qha−1) per cent RDP respectively over control (10.72qha−1). However, the differences in seed yields observed at 50, 75 and 100% RDP are narrow and imperceptible. The % Pdff and Puse efficiency decreased significantly from 21.10 to 19.93% and 24.19 to 6.67% respectively due to increase in P level from 25 to 100% RDP, where as the fertilizer P uptake and soil P uptake increased from 1.58 to 1.75 kg ha−1 and 5.93 to 7.03 kg ha−1 respectively with increase in P level from 25 to 100% RDP. The extent of saving in P fertilizer in these soils is ranged from 75 to 100 per cent depending upon the P build up in the soil.