Corn (Zea mays L.) grain yield is closely related to plant density and is typically maximized in the northern Corn Belt when planting occurs in late April. However, spring rainfall events often result in wet soil conditions that delay planting. From 2008 to 2010, experiments were conducted at two locations in southern Minnesota to determine whether the agronomic responses of corn to plant density differ with planting date. Six plant densities ranging from 38,400 to 107,900 plants ha -1 were evaluated within three planting dates that occurred on 2-wk intervals beginning in late April to early May. Yield and net return to seed cost were not affected when planting was delayed 2 wk, but were 15 and 18 to 30% lower when planting was delayed 4 wk, respectively. Yield loss due to late planting was associated with a 7% decrease in kernel weight and no change in kernels per square meter. Responses to plant density for stalk diameter, intercepted photosynthetically active radiation (IPAR) and leaf area index (LAI) at silking, lodging, grain yield and components, and net return to seed cost for 25 economic scenarios did not differ with planting date. There was a quadratic-plateau response of grain yield to plant density with yield maximized at ≥81,700 plants ha -1. These results from a 102-d relative maturity hybrid over six site-years in southern Minnesota show that increased plant density may not be able to offset the yield and economic losses associated with late planting.
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