How cost-effective are nitrogen-removal best management practices in agricultural landscapes?

Background/Question/Methods

Excess nitrogen (N) causes numerous water quality problems, and in the agricultural Midwest, much of the excess N results from landscape modifications for row crop agriculture. Several best management practices (BMPs) reduce N export, but the cost-effectiveness of these strategies has not been thoroughly evaluated. We estimated the cost per kg of N removed for three agricultural BMPs: wetlands (a riparian practice), cover crops (a field practice), and two-stage ditches (an in-stream practice). Each BMP is currently eligible for financial assistance from the United States Department of Agriculture (USDA), and we estimated the current cost of each BMP to the USDA, annualized over 10 and 50 years and under 3 interest rates.

Results/Conclusions

Two-stage ditches currently have the highest implementation costs, followed by wetlands, with cover crops the least expensive to implement. Wetlands and two-stage ditches removed more N per unit area than cover crops, resulting in wetlands being the most cost-effective practice (in $/kg N removed) over both time periods.  The other practices varied with time period: over 10 years, cover crops were more cost-effective than two-stage ditches, and over 50 years, two-stage ditches were more cost-effective than cover crops.  We also estimated the amount of land required for each BMP to achieve N reduction goals at a single farm. We found that the two-stage ditch required the least amount of area, while the cover crops required the most.  The cost of all three BMPs was generally less than the cost of N pollution, suggesting that implementation of any BMP will likely result in a net economic benefit to society.