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Kernel Number Prediction in Maize under Nitrogen or Water Stress

Unidad Integrada INTA Balcarce, Facultad de Ciencias Agrarias UNMP. CC276, 7620 Balcarce, Buenos Aires, Argentina

View larger version (16K): [in a new window]   Fig. 1. Relationship between kernel number per uppermost ear and plant growth rate during a period bracketing silking for maize plants (Dekalb hybrid 636) growing without nutrient nor water limitations, in which plant growth rate was modified by plant density, year and shading level. Values are means of 3 or 4 replications. The inverse equation (solid line) was KNP = 594-753/PGR (R2 = 0.88, n = 34). See Andrade et al. (1999) for more details.

View larger version (24K): [in a new window]   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.

View larger version (17K): [in a new window]   Fig. 3. Relationship between kernel number per plant and plant growth rate during a 30-d period bracketing silking for maize hybrid Asgrow 777 growing with and without fertilization in three growing seasons with different water availability during the period bracketing silking (Exp. 5a, 5b, and 5c). Plants did not show prolificacy, so kernel number per plant was equal to kernel number per uppermost ear. Each point is the average of four replications. The control corresponds to fertilized treatments in the wettest year (Exp. 5b). Reduced N corresponds to non fertilized treatments in the wettest year (Exp. 5b). Reduced W corresponds to fertilized treatments in the years with lowest and intermediate available water (Exp. 5a and 5c). Reduced N and W corresponds to non fertilized treatments in the years with lowest and intermediate available water (Exp. 5a and 5c). Inverse equations were KNP = 667-705/PGR (R2 = 0.99, n = 4) for variable N at high water availability; KNP = 699-837/PGR (R2 = 0.92, n = 6) for variable available water in fertilized treatments and KNP = 699-862/PGR (R2 = 0.95, n = 6) for variable water and N supply. Standard error of the means varied from 0.11 to 0.26 g d-1 for PGR and from 15 to 16 kernels for KNP.

View larger version (21K): [in a new window]   Fig. 4. Relationship between kernel number per plant (expressed as relative values) and plant growth rate during a 30-d period bracketing silking for maize hybrids Asgrow 777 (Exp. 5), SPS 240 (Exp. 6), Dekalb 636 (Exp. 7), and Dekalb 639 (Exp. 8) growing under variable levels of nitrogen or water availabilities. KNP values for each hybrid are expressed relative to those obtained for the control without deficiencies. PGR is expressed per unit time (a) or per unit thermal time (b). Each point is the average of three replications. Plants did not show prolificacy, so kernel number per plant was equal to kernel number per uppermost ear. The reference data from Fig. 1 (with KNP data also expressed as relative values), the equation fitted to these data (solid line) and its 95% prediction interval (dashed lines) are also shown. KNP values corresponding to a relative value of 1 were 520, 385, 465, and 600 for Exp. 5 (a, b, and c), 6 (a and b), 7, and 8, respectively. SE of the means in absolute values ranged from 0.11 to 0.40 g d-1 for PGR and from 4 to 16 kernels for KNP. Equations fitted to reference data (n = 34) were KNP = 1.0(PGR-1.17)/[1+0.67*(PGR-1.17)] (R2 = 0.88) for Fig. 4a; and KNP = 8.97(PGR-0.06)/[1+5.36(PGR-0.06)] (R2 = 0.83) for Fig. 4b.