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

摘要

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.