Fig. 2. Relationship between kernel number per plant and plant growth rate during a 30-d period bracketing silking for maize hybrid Dekalb 636 growing under (i) variable incident radiation at optimum N and water availabilities and (ii) variable N or water availabilities without shading, in Exp. 1 to 4. Plants did not show prolificacy, so kernel number per plant was equal to kernel number per uppermost ear. Each point is the average of three replications. When N or water were variable, best fit was given by the rectangular hyperbola equation: KNP = 375(PGR-0.82)/[(1 + 0.58(PGR-0.82)] (R² = 0.83, n = 12). When radiation was variable, best fit was given by the inverse equation: KNP = 598-757/PGR (R² = 0.82, n = 10). Reference equation from Fig. 1 is also shown. Standard error of the means were 0.22, 0.16, 0.11, and 0.30 g d^-1 for PGR and 17, 19, 20, and 28 kernels for KNP, for Exp. 1, 2, 3, and 4, respectively.