Full‐Season Retrospectives on Causes of Plant‐to‐Plant Variability in Maize Grain Yield Response to Nitrogen and Tillage

Abstract

Maize (Zea mays L.) plant‐to‐plant variability at different plant densities and N fertilizer rates has been studied previously, but little attention has been devoted to consequences of different N placement and tillage management on plant variability in kernel number (KN) and grain yield. This study investigated effects of pre‐plant N placement relative to intended maize rows on the origin and magnitude of plant‐to‐plant variability in per‐plant grain weights (GW). Field studies compared two “shallow” anhydrous ammonia (NH3) placement directions (diagonal to future row vs. parallel but 15‐cm offset from the row) in both no‐till and conventional tillage systems at two N rates (145 and 202 kg N ha−1). Maize was planted with starter fertilizer (20 kg N ha−1) within 6 d following NH3 application. Aboveground growth and development was monitored on bar‐coded plants from seedling emergence to maturity. Plant‐to‐plant uniformity in GW and KN was not improved by parallel NH3 placement, conventional tillage, or a higher N rate; however, all three factors resulted in a slight shift towards higher mean GW and KN. Within‐row plant spacing and relative seedling emergence time had little influence on relative GW. Within‐row differences in silk emergence timing and estimated stem volumes were the most highly correlated parameters to per‐plant GW. Regression models confirmed that either of these mid‐silking factors explained >50% of such GW variations within most treatment combinations. Even in management systems with conventional tillage and precision N fertilizer placements, precision seed placement alone will not guarantee low variability in per‐plant GW.