INTERCEPTED RADIATION AT FLOWERING AND KERNEL NUMBER IN MAIZE - SHADE VERSUS PLANT-DENSITY EFFECTS

The number of grains produced in maize (Zea mays L.) is altered by environmental conditions during growth. The response occurs primarily during flowering. The objective of this work was to study the relationship between intercepted radiation during a 31-d period bracketing flowering and final kernel number per unit area in maize and to analyze the effect of plant density on that relationship. Shading and population density experiments were conducted at Balcarce, Argentina, under no limitations of water and nutrients. A significant and positive association between number of kernels per square meter and intercepted radiation during this 31 d was found for the shading experiments. The slope of this relationship was 5.39 kernels MJ-1 of intercepted radiation. When intercepted radiation at flowering was modified by varying plant density within suboptimal values, the response of number of kernels per unit area was larger than that observed in the shading experiments (28 vs. 5.39 kernels MJ-1; P less-than-or-equal-to 0.001). At supraoptimal densities, the number of kernels per unit area was significantly reduced even though the amount of radiation intercepted by the crop was not affected. This work indicates that a model developed from shading experiments and based on the amount of radiation intercepted by the crop at flowering does not predict the effect of altered plant density on kernel number. Suboptimal and supraoptimal densities produced a strong negative effect on the efficiency with which the crop or plant converts intercepted radiation into grain sink capacity.