Row Arrangement, Phosphorus Fertility, and Hybrid Contributions to Managing Increased Plant Density of Maize

Inter-plant competition must be carefully managed to realize the yield potential of increased plant density of maize (Zea mays L.). Twin row planting arrangement, P fertility, and hybrid selection may be important components of managing increased plant density. Our hypotheses were (i) that twin row planting arrangement would be superior to traditional 0.76-m rows at ultra-high densities and (ii) that supplemental P fertility would alleviate inter-plant competition. In 2010 and 2011, twin row planting arrangement was compared to single 0.76-m rows across densities ranging from 61,775 to 160,615 plants ha(-1) and P fertility treatments ranging from 0 to 168 kg P2O5 ha(-1). Twin rows did not increase yield relative to single rows, and twin rows often yielded significantly less at plant densities greater than 111,195 plants ha(-1). Mean responses to supplemental fertility were 1.0 and 0.3 Mg ha(-1) in 2010 and 2011, respectively. There was no interaction between plant density and P fertility suggesting that extra resource availability does not necessarily overcome inter-plant competition. In 2011, two hybrids of contrasting ear type were included to explore the role of hybrid selection in plant density response. Maximum yields of each hybrid were achieved at contrasting densities, and genetic differences in plant density tolerance appeared to be related to (i) kernel number response on a per-area basis and (ii) stability of individual kernel weight. These results highlight the importance of independently optimizing row spacing and soil fertility while understanding the plant density response characteristics of maize hybrids.