Monday, November 5, 2007
102-5
N Fertilizer Recommendations for Second-Year Corn after Alfalfa.
Thomas Morris1, Jianli Ping1, and Alfred Blackmer2. (1) 1376 Storrs Rd. Box U-4067, University of Connecticut, University of Connecticut, Plant Science Department, Storrs, CT 06269-4067, (2) Iowa State University, Department of Agronomy, Ames, IA 50010
There is no general guidance on how to make N fertilizer recommendations when the N response is erratic. The primary objective of this study was to develop a method for making N fertilizer recommendations for second-year corn (Zea mays L.) after alfalfa (Medicago sativa L.) that had been cropped as alfalfa for three or more years. We also evaluated the influences of model selections and different approaches to calculating the economic optimum rate of nitrogen (EORN) on N recommendations, the influences of price changes in N and corn on profit and EORN, and the relationships between EORN and the nitrate concentrations in soil and cornstalks. Twenty-four trials in Iowa having 10 rates of N at sites receiving no fertilizer N for the first-year corn after alfalfa were considered. Significant grain yield increases were observed at 8 of the 24 trials (33.3%). Our results suggest a two phased procedure for making a N recommendation for second-year corn: 1) using a logistic regression model to identify the N responsive fields based on PSNT values and the amount of rainfall in the spring before collection of soil samples for the PSNT, and 2) applying N only to those responsive fields at a rate of N that maximizes the total profit across all the fields using a Mitscherlich model. With the prices of corn and N at $98.33 Mg-1 and $0.66 kg-1, the recommended N rate (96 kg ha-1) estimated with the Mitscherlich model results in N savings of 34 and 21 kg ha-1 compared with the rates estimated by use of the quadratic and quadratic plus plateau models. The average cornstalk nitrate concentration was in the optimum range for the plots when 96 kg ha-1 was applied. More N response trials in second-year corn are needed to improve N recommendations for this crop.