Economically Optimal Nitrogen Rates of Corn: Management Zones Delineated from Soil and Terrain Attributes

Abstract

Much of the NO3 found in streams in the Midwest comes from leaching of N fertilizers applied to corn (Zea mays L.). To reduce this leaching, N fertilizer must be used more effectively. Dividing fields into areas that respond more uniformly to management is one approach for improving N fertilizer use. The objective of this study was to determine and compare economically optimal N fertilizer rates for corn in a corn–soybean [Glycine max (L.) Merr.] rotation within management zones. A method based on soil and landscape characteristics was used to divide three fields into management zones roughly equivalent to toeslope, footslope, backslope, and shoulder landscape positions. We applied N fertilizer at six rates within replicated small plots (15.1 by 4.5 m) located within each management zone. Yield vs. N rate for each management zone was fitted to the Mitscherlich equation using nonlinear methods. Final Mitscherlich parameters, economically optimal N rates, and their confidence limits were computed for each management zone. Yields at the highest N rate generally followed the pattern of toeslope ≥ footslope ≥ backslope >> shoulder among the management zones. Conversely, economically optimal N rates followed the reverse pattern and varied from 23 to 247 kg ha−1. Thus, yield at the highest N rate was a poor predictor of the optimal N rate for the management zones delineated in this study and N fertilizer application would have been optimized by applying relatively less to the toeslope and footslope management zones and relatively more to the shoulder and backslope management zones.