Fig. 1. Relationship among N rate and grain yield as a function of preceding crop in a rainfed wheat. Mean data from 6 yr. Vertical bars indicate LSD at P < 0.05 for comparison N rates: (a) within a preceding crop, and (b) between preceding crops. *, **, *** Significant at the 0.05, 0.01, and 0.001 probability level, respectively.