EFFECT OF LONG-TERM APPLICATION OF FERTILIZER AND CROP SEQUENCES ON PHOSPHORUS IN AN USTOCHREPT IN PUNJAB

The effect of fertilizer application and different crop sequences on t he utilization, accumulation, and depletion of Olsen extractable P and other fractions of P in the soil after 10 cycles of cropping are repo rted. The apparent recovery of P declined in the sequence rice-wheat, rice-berseem, cotton-wheat, maize-wheat, groundnut-wheat, and pearl mi llet - berseem. Application of P increased Olsen extractable P in the soil profile under ail the crop sequences. The increase was less under rice-based sequences. The differences in Olsen extractable P in the c ontrol (no NPK) and fertilizer treated plots were large up to upper 45 , and beyond that the differences were small and decreased with depth. The P uptake by crops was significantly related to Olsen extractable P in the 0-15 cm soil depth.