Yield response to phosphorus fertilizer in a wheat - lentil rotation in a mediterranean environment

The effect of a single application of phosphorus (P) fertilizer on yields of wheat and a following lentil crop was studied in two-course rotational trials under rainfed conditions in a Mediterranean-type environment. Wheat was grown during the 1984/85 and 1985/86 growing seasons at three sites in north-west Syria, with P applied at rates of 0, 17.5, 35.0 and 52.5 kg ha−1. Lentil (Lens culinaris Med.) was grown during the 1985/86 and 1986/87 seasons at the same sites, following the wheat crops. During the 1985/86 season, no additional P was applied to the lentil crop. During the 1986/87 season, additional P was applied to the lentil crops grown at two of the three sites, in order to compare the residual and direct effects of P fertilizer application. Initial contents of extractable soil P (P-Olsen) were low at all sites: in the range of 2–5 ppm. The response of wheat to direct application of P and of lentil to residual P were described by a modified Mitscherlich equation accounting for the effect of rainfall on potential yield (under rainfed conditions) and on the availability of P to the crop. Under the conditions of the experiments, lentil benefited significantly from P fertilizer applied to the preceding wheat crop. It was concluded that a single application of P to the wheat crop in a wheat-lentil rotation would reduce the cost of lentil production without significantly reducing lentil yields.