Nitrogen Fertilizer Effects On Corn Grain Nutrient Composition.

Nitrogen fertilizer recommendations for corn to achieve maximum profit are determined by corn grain prices and N fertilizer costs. Recent substantial fluctuations in grain and fertilizer prices have resulted in a wide range of fertilizer N recommendations in the past 3 years.  Grain nutrient composition is an important component of nutrient management planning and animal ration formulation.  Utilization of N fertilizer rates less than those needed to maximize yield may alter grain nutrient composition, thereby impacting nutrient management planning and ration formulation. Corn was grown on 7 Purdue Agricultural Centers located throughout the state of Indiana from 2006-2009 with a range of 5 to 6 N rates from zero to as much as 286 kg N/ha (varying by location). Of the 41 site-years, 25 were corn after soybean, 14 were corn after corn, and 2 were corn after a rye cover crop following watermelon. A hybrid or its near isoline was grown on all 29 of the trials in 2006-2008, whereas 2 hybrids were grown in 2009. Grain was collected after physiological maturity and analyzed for N, P, K, S, and Mg.  Grain concentrations of N and S were consistently increased by increasing N fertilization rate, resulting in a consistent N:S ratio (g:g) of about 13:1. Phosphorus and K were frequently decreased by increasing N rate. Magnesium was infrequently impacted by N rate. Variation in grain composition within the range of N rates likely to produce maximum profit will have limited impact on nutrient management plans and ration formulation.