Abstract

Estimating demand for nitrogen (N) fertilizer in corn cropping systems has traditionally used yield goals. Data published by the United States Department of Agriculture National Agricultural Statistic Services indicated yields from the top five corn producing states increased approximately 117 kg ha ⁻¹ yr⁻¹ from 1965 to 2005. When this rate was adjusted by yearly increases in plant population densities the grain weights per plant remained stable. The temporal increases in yield have been from increasing plant densities while maintaining grain weight per plant. Nitrogen management techniques being developed aim at detecting variability in yield at a range of spatial scales. Grain weights collected on individual corn plants in the Central Platte River Valley revealed a normal distribution with 38–54% of plants having a grain weight between 151–200 g plant⁻¹ . Less than 1% yielded >250 g plant⁻¹ while another 1% was barren.

Data were collected to estimate how much N fertilizer, when applied to a target plant, was acquired by its neighbors using depleted ¹⁵N ammonium-nitrate. Results indicate the target plant acquired over 70% of the total depleted fertilizer that was taken up by all the plants. Adjacent plants accounted for 20–30% of the total depleted ¹⁵N taken up while the second nearest plants accounted for >10%. Based on the plant density employed in this study, data revealed an individual corn plant acquires most of its N from within a radius of less than 0.5 m. Relative emergence date impacts a plant’s potential to achieve maximum grain weight and its response to applied N. Plants lose yield potential by emerging as little as three days after their neighbors. Large doses of N fertilizer could not increase the yield of late emerging corn plants. Kernel weights were unaffected by the N management schemes employed. Once a plant produces 35 g of stover it maintains a harvest index between 50–55%. Small spatial resolution N management techniques should be focused on determining the N demand of the early emerging plants.