Economic returns and environmental impacts of variable rate nitrogen fertilizer and water applications

Several studies have evaluated the profitability of variable rate application of one type of input, but few have investigated the profitability of variable rate application of two or more types of inputs. In addition, most studies ignore the impact of variable rate input application on the environment. This study evaluates the profitability and environmental outcomes associated with spatial variation of nitrogen fertilizer and irrigation water in seed potato production. Seed potato yields and nitrogen losses are simulated for four different areas of a 63 ha field using the EPIC (Environmental Policy Integrated Climate) crop growth model. A dynamic optimization model is used to determine optimal levels of N fertilizer for each area of the field. Average nitrogen losses and economic returns are evaluated for both uniform and variable rate application of nitrogen and water. The results indicate greater economic and environmental benefits may be achieved from varying water application than from varying nitrogen application across the field.