Jump to Main Content
A Comparison of Two Nitrogen Credit Methods: Traditional vs. Difference
- Lory, John A., Russelle, Michael P., Peterson, Todd A.
- Agronomy journal 1995 v.87 no.4 pp. 648
- nitrogen fertilizers, estimation, accuracy, crop rotation, continuous cropping, Zea mays, field crops, legumes, cover crops, Trifolium incarnatum, Glycine max, crop yield, fertilizer requirements, application rate, grains
- Cereals and other nonlegumes typically require less fertilizer N when grown following a legume. Nitrogen credits for a previous legume crop often are used to reduce fertilizer N recommendations in combination with other site-specific information. Researchers continue to use two methods of determining N credits, the and techniques, which often produce unequal estimates. Our objective was to clarify when each method provides accurate N credit estimates. The traditional method compares yield of a nonfertilized nonlegume crop grown in rotation to the fertilizer N response curve of the continuously cropped nonlegume. This approach assumes that fertilizer N compensates for all benefits of rotation. The difference method compares the economic N rate of the nonlegume crop grown in rotation with that of the continuously cropped nonlegume. We use examples from the literature to demonstrate that when non-N rotation effects are present, N credit estimates from the two methods will differ. The difference method is more accurate and should be used unless it has been demonstrated that non-N rotation effects are not present.