Requirement of phosphorus and its use efficiency by sunflower (Helianthus annuus L.) in high phosphorus soils

Abstract

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