Nitrogen Deficiency in Maize: II. Carbon‐Nitrogen Interaction Effects on Kernel Number and Grain Yield

Abstract

Assimilate and N supply at flowering are determinants of the number of kernels set in maize (Zea mays L.). The objectives of this work were (i) to evaluate the effect of N shortage on grain yield and its numerical components, particularly potential grain number, determining kernel losses due to morphogenesis d fertilization‐abortion, (ii) to analyze the combined effects and interactions of assimilate and N availability on kernel set, and (iii) to determine the existence of direct effects of N deficiencies on this yield component. Three experiments were conducted with a commercial hybrid (DK636) under field conditions at the INTA Balcarce Experimental Station, Argentina, without water limitations. The treatments consisted of different radiation levels, obtained by shading, combined with different levels of N availability obtained by the addition of N fertilizer or organic matter of high C/N ratio in the soil. Nitrogen stress reduced kernel number(K N) without a significant effect on morphogenesis of reproductive structures. Under normal incident radiation, kernel number was associated with crop and ear growth rate at flowering following linear + plateau functions. Under shading this relationship presented an optimum, indicating that the widely accepted linear and direct relationship (with or without plateau) between KN and crop or ear growth rate is not valid under high N rates and light stress at flowering. No direct effects of N were detected. Nitrogen deficiencies affected KN because of reductions in C assimilation.