Monday, November 13, 2006

Economically Optimal Nitrogen Rate Reduces Soil Residual Nitrate.

Nan Hong, Univ of Missouri-Columbia, Columbia, MO 65211, Peter Scharf, Univ of Missouri-Columbia, Div. of Plant Science, Columbia, MO 65211, J. Glenn Davis, USDA-NRCS, Columbia, MO 65203, Newell Kitchen, Univ. of Missouri/USDA-ARS, 243 Agricultural Engineer Bldg, Columbia, MO 65211, and Kenneth A. Sudduth, USDA-ARS, Cropping Syst. and Water Quality Res. Unit, Columbia, MO 65211.

Practices that minimize post-harvest residual soil NO3-N (RSN) can reduce N loss to the environment. Our objectives were to determine if the RSN after corn ( Zea mays L.) harvest can be reduced if N fertilizer is applied at the economically optimal N rate (EONR) as compared to current producers’ practices in the midwestern U.S., and to compare RSN levels if no N fertilizer is applied to RSN levels if N fertilizer is applied at a rate below, at, or above the EONR. Six experiments were conducted in producers’ fields over 2 yrs. At four transects in each field, six treatment N rates from 0 to 280 kg ha -1 were applied, the EONR was determined, and the RSN was sampled to a 0.9-m depth from five treatment plots. The EONR at sampling sites varied from 49 to 228 kg ha -1 depending on site-year. Estimated average RSN at the EONR was 27 kg ha -1 in the 0.9-m profile. Applying fertilizer N at the EONR reduced the RSN by at least 11 kg ha-1 compared to the producer’s rate. The RSN increased with increasing ΔEONR (total N applied – EONR). When ΔEONR < 0, average RSN was 21 kg ha-1 and was not different than if total N applied was zero or equal to the EONR. When 0 < ΔEONR < 50 kg ha-1, average RSN increased to 39 kg ha-1, but was not greater than when ΔEONR = 0. When 50 < ΔEONR < 100, average RSN increased to 49 kg ha-1, and was greater than when ΔEONR = 0. When ΔEONR > 100 kg ha-1, average RSN significantly increased to 91 kg ha-1. Our results suggest that applying the EONR will produce environmental benefits in an economically sound matter.

Handout (.pdf format, 137.0 kb)