Better Recommendation Systems for Nitrogen Fertilization of Corn.

Nitrogen (N) represents the second largest input cost for corn (Zea mays L.) production. Accurate N recommendations are needed to maximize grower’s profitability and minimize environmental impact. The objectives of this study were to: i) develop two new N recommendations systems for corn fertilization based on the N requirement (kg N/Mg grain) for maximum economic yield (MEY) and Delta Yield (DY, i.e. yield response), ii) to compare these systems with the new (Corn Nitrogen Rate Calculator or CNRC) and traditional (Yield Goal) extension N recommendation systems. Experiments were conducted on 66 production fields located in IN, IL, IA, MN, NE and ND over 3 growing seasons. Six N rates (0 to 280 in 56 kg N/ha increments) were applied in 6-8 blocks within fields with commercial applicators. Grain yield was obtained with calibrated yield monitors. Grain response to N fertilizer was analyzed with quadratic-plateau and linear models and the economically optimal N rate (EONR) was determined for each field. Two N requirement coefficients were calculated, one based on the MEY and the other based on DY. The N recommendation error was estimated as the difference between the observed EONR and the predicted N rate by each system. The DY system resulted in the smallest average error, followed by the use of a variable N coefficient for the MEY approach. The CNRC had a higher average error than these two systems but lower than the Yield Goal system which tended to over predict the recommended N rate. The DY provides the most accurate N recommendation and maximizes the economic value of N fertilization, but requires estimating the yield of unfertilized corn. Alternatives to estimate unfertilized corn will be discussed.