Modelling the effect of variation of in-row spacing on kernel m-2 in maize

Abstract

Maize (Zea mays L.) yield is often reduced when the in-row plant spacing is not uniform. I used a variant of the KNMAIZE model to investigate the mechanisms responsible for the reductions. KNMAIZE determines kernels per plant from the relationship between the proportion of the assimilate supply from photosynthesis that is partitioned to the kernels and the assimilate required to sustain kernel growth. Kernels abort when their assimilate requirement exceeds the supply. Algorithms were developed to create variation of in-row plant spacing (characterized by CV) and emergence percentage. The effect of spatial variation on kernels m−2 depended upon the ability of the dominant plants (higher plant growth rates associated with larger in-row spacing’s) to increase kernels per plant to compensate for the reduction on the dominated plants (lower plant growth rates resulting from smaller in-row spacing’s). When the ability of the dominant plants to respond was zero (kernels ear−1 = florets ear−1, excess capacity = 0), kernels m−2 started decreasing as soon as the CV > 0. When the dominant plants had excess capacity (i.e., kernels per ear < florets per ear), the beginning of the decline occurred at progressively larger CVs depending upon the magnitude of the excess capacity. Populations greater than the minimum needed for maximum yield provide the excess capacity on dominant plants to buffer kernels m−2 and yield against variation of in-row spacing and reductions in emergence.