ECONOMIC AND ENVIRONMENTAL FEASIBILITY OF VARIABLE RATE NITROGEN FERTILIZERAPPLICATION WITH CARRY-OVER EFFECTS

Authors: Watkins, Kenton - Brad; LU, YAO; HUANG, WEN-YUAN - USDA/ERS/NR&ED

Submitted to: Journal of Agricultural and Resource Economics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/1998
Publication Date: N/A
Citation: N/A

Interpretive Summary: This study evaluates the profitability and the environmental consequences of applying nitrogen fertilizer to seed potatoes in different application rates rather than in one single application rate throughout the field. Application rates are determined based on profit maximization rather than yield goals and nutrient recommendations. An economic optimization model is used to determine profit maximizing nitrogen application rates for four different areas of a seed potato field near Ashton, Idaho U.S.A. These rates are used by the EPIC crop growth model to simulate crop yields and nitrogen losses for seed potato production under single and variable rate nitrogen fertilizer application. Economic returns are calculated and evaluated with simulated nitrogen losses. More nitrogen was required for low-yield areas than for high-yield areas to achieve profit maximizing yields. This led to large simulated nitrogen losses from the low-yield areas. The results also indicate variable rate nitrogen application is less profitable than single rate application for the field at current cost levels. Soil grid sampling and custom variable rate application charges are the largest expenses associated with variable rate nitrogen application. The study provides additional evidence to researchers, fertilizer and equipment dealers, and farm operators alike that variable rate application of one input alone may be unprofitable. In addition, the study demonstrates that variable rate nutrient application may not reduce environmental degradation in every instance.

Technical Abstract: This study evaluates the long-term profitability and environmental impacts of variable rate versus uniform nitrogen application in seed potato production with nitrogen carry-over effects included. Unique seed potato yields are simulated for four different areas of a field using the EPIC crop growth model. A dynamic optimization model is used to determine optimal steady-state nitrogen levels for each area and the field. Average nitrogen losses and economic returns are evaluated for eight nitrogen application strategies ranging from uniform application to variable rate application. Variable rate nitrogen application is found to be unprofitable relative to uniform application at current cost levels. Nitrogen losses may also be greater in low yield areas of the field under optimal nitrogen application. Removing areas with the lowest yields from production may be more environmentally sound than leaving these areas in production and applying optimal levels of nitrogen fertilizer.