Agronomic Responses of Corn to Planting Date and Plant Density in Minnesota.

Recent increases in the price of corn (Zea mays L.) seed and in the tolerance of modern hybrids to high plant densities have stimulated interest in the agronomic responses of corn to plant density, and in whether these responses are influenced by cultural practices such as planting date. In 2008 at two locations in southern Minnesota, the hybrid DKC52-59 was evaluated at six densities ranging from 38,400 to 107,900 plants ha^-1 at three planting dates spaced on 2-wk intervals. Across locations and plant densities, grain yield and economic return were similar with each planting date. There was a quadratic response of both grain yield and economic return to plant density, and these responses were not affected by planting date. Yield was maximized at a density of 89,700 plants ha^-1, but densities ranging from 71,300 to 81,500 plants ha^-1 produced economic returns within $2.50 ha^-1 of the maximum. As plant density increased from 38,400 to 107,900 plants ha^-1, kernel weight decreased by 26% and the number of kernels per unit area increased by 65%. These yield components were not influenced by planting date. Ear height increased linearly by 15% as plant density increased from 38,400 to 107,900 plants ha^-1, but overall plant height was not affected. These responses were consistent across planting dates, even though ear and plant height were 10 and 4% shorter with early planting than with late planting, respectively. Across planting dates, stalk diameter decreased linearly from 27 to 20 mm as plant density increased from 38,400 to 107,900 plants ha^-1, but stalk lodging was rare at high plant densities. These results indicate that plant density can have a greater influence on grain yield than planting date, and that planting date has little effect on the agronomic responses of corn to plant density.