Origins of Plant-to-Plant Yield Variability in Corn.

Corn (Zea mays L.) plant-to-plant variability at different plant densities and nitrogen (N) fertilizer rates was studied previously, but little attention has been devoted to the consequences of alternate N placements on plant variability in growth and development. This study investigated the effects of pre-plant N placement relative to intended corn rows on the origin and extent of plant-to-plant variability. Field studies between 2010 and 2012 near West Lafayette, IN compared two “shallow” anhydrous ammonia (NH₃) placement directions (diagonal to the row vs. parallel but 15-cm offset from the row) in both no-till and conventional tillage systems at different N rates (145 and 202 kg N ha^-1). All corn was planted with starter N (20 kg N ha^-1) within 6 days following NH₃ application, and above-ground growth and development was monitored on individual plants from seedling emergence to maturity. Corn plant populations (averaging 80,700 ha^-1) and seedling emergence uniformity were little affected by N placement or N rate. Parallel NH₃ placement did not improve plant-to-plant uniformity; however, it resulted in a slight shift towards higher mean per-plant grain yields. Time of silk emergence, estimated stem volumes at V15 or at R1 growth stages, and an "N index" (product of leaf area of ear leaves and SPAD readings from the ear leaves at mid-silking) were the factors that most influenced individual plant yields. Parallel NH₃ placement was more likely to benefit yield per unit area at the lower N rate; the parallel NH₃ placement method may provide opportunity to decrease N application rate without yield penalty.