Corn Physiology, Morphology, and Yield Response to Hybrid and Seeding Rate in Mid-Missouri on a Claypan Soil: Potential Application for Variable Rate Seeding.

Corn hybrids exhibit variable response of physiological, morphological, and yield parameters due to interactions with management factors such as seeding rate. The objective of this study was to examine corn development and physiological response across the growing season of multiple hybrids at a range of seeding rates. We implemented a measurement protocol in a field scale strip-trial design at multiple locations in the Central Claypan Areas of Northeast Missouri (7 locations in 2013, 5 locations in 2014). The design of the experiments included four different hybrids at three different seeding rates: 74,100, 83,980, and 93,860 seeds ha^-1. Individual locations serve as replicates in a spatially distributed analysis of variance design. Treatments are laid out in field length strips, six or eight rows wide at 30-inch spacing. Measurements were tracked regularly in small plot areas including: population at emergence, plant growth stage, plant height, canopy photograph, normalized difference vegetation index and red edge, leaf area index, plant biomass, leaf and canopy temperature, and stomatal conductance. Measurements at maximum vegetative mass included the above plus ear height and stem diameter. Field scale spatial measurements that incorporated these plot locations included multispectral aerial imagery, and bulk soil electrical conductivity. Grain yield was measured by hand sampling small plot areas and by yield monitor at field scale. We measured yield components of hand harvested sub-samples including harvest index, barrenness, kernel rows, kernels per row, kernel mass, and kernel count. Initial results show some potential interactions among leaf area index, hybrid and seeding rate.  These preliminary findings about the mechanisms of interplant competition suggest opportunities exist to develop variable rate seeding in the Central Claypan Areas of Missouri.