Fig. 4. Relationship between maize grain yield and rainfall from 30 d before to 20 d after flowering (W₄) in shallow soils. The baseline function derived from Exp. [1] is shown for comparison. Parameters of the fitted curves for shallow soil data are a = 9107 ± 579, W₀ = 31.4 ± 14, and b = 93.5 ± 30 (P < 0.001).