Plant population and row spacing effects on corn: Phenotypic traits of positive yield-responsive hybrids

Corn (Zea mays L.) hybrids differ in their yield response to plant population and/or row spacing changes. The objective of this study was to identify the hybrid phenotypic traits underlying intensive plant population and row spacing yield responses to help breeders select for hybrids to be placed in these possible management systems. In 2017 and 2018, six commercial hybrids were planted at 94,000, 109,000, 124,000, and 139,000 plants ha⁻¹ in a 76-cm or 51-cm row spacing at two locations in Illinois. In general, the more recently released hybrids and full-season hybrids tended to have greater yields in response to both higher planting population and narrower row spacing. Of the 46 measured phenotypic traits, those related to shoot biomass had more plasticity than many of the leaf traits (i.e. total leaves, leaf length, leaf angle, etc.) in response to plant spatial arrangement, but root traits had even greater plasticity. While the hybrids had inherently distinct phenotypic traits, there was no difference between hybrids in the plasticity extent of their shoot or root traits in response to plant population and/or row spacing alterations. Stepwise multiple logistic regression was used to identify the key phenotypic traits (predictors) of hybrids with increased yield in response to greater planting populations and narrower row spacing. These key traits for increased yields were related to capturing more sunlight (leaf angle, width, length, and area per plant), plant size (stover biomass per hectare, shoot biomass per hectare, and plant width), and root weight per plant.