EFFICIENCY OF P UTILIZATION BY PIGEONPEA AND WHEAT GROWN IN A ROTATION

Field experiments were conducted for three years to investigate the ef fect of direct, residual and cumulative P application on the grain yie ld, P removal and P use efficiency of pigeonpea and wheat grown in rot ation. Four levels of P, i.e. 0, 13, 26, and 39 kg P ha(-1) were appli ed to either pigeonpea (Cajanus cajan L., cv. AL 15) or wheat (Triticu m aestivum, cv. WL 711) or to both crops. Maximum increase in wheat gr ain yield ranged from 1.5 to 1.9 t ha(-1) and in pigeonpea from 0.28 t o 0.36 t ha(-1). On average, the grain yield of pigeonpea was 8-15% hi gher in the residual P treatment than by direct application. In wheat, cumulative P application (to both crops) resulted in highest grain yi eld, but it did not differ significantly from the direct effect. Howev er, the residual effect of P (applied to previous pigeonpea) on wheat proved to be significantly inferior to direct application. Percent rec overy of P from applied fertilizer decreased with P level. Total recov ery in the complete rotation was higher where P was directly applied t o wheat compared to pigeonpea. The P use efficiency was also highest i n the treatment comprising direct application to wheat. Pigeonpea coul d utilize the residual P more efficiently, indicating that fresh appli cation to this crop can be omitted without any reduction in yield.