Agriculture's Nitrogen Legacy. Metaxogolou, K. & Smith, A. 2022.
Agriculture's Nitrogen Legacy [pdf]Paper  abstract   bibtex   
Nitrogen pollution of waterways is a large global problem, especially in regions with intensive cropland agriculture such as the Mississippi River Basin that drains 40% of the continental United States. In contrast to prior studies, which mostly apply agronomic and hydrologic models, we collect detailed data from water quality monitors and use panel data econometric methods to estimate how land use affects nitrogen pollution. We find a strong positive effect of corn acreage on nitrogen concentration in nearby streams and rivers that is an order of magnitude smaller than those implied by the agronomic and hydrologic models. Our findings are consistent with a new line of research documenting accumulation of large amounts of nitrogen in subsurface soil and groundwater over several decades; this is excess nitrogen that was applied to fields but has yet to appear in waterways. This legacy nitrogen will eventually leach into streams and rivers exacerbating further nutrient pollution. In the presence of large amounts of legacy nitrogen, land retirement and other on-farm mitigation policies are uneconomic. Downstream off-farm practices, such as the creation and restoration of fluvial wetlands, which can remove both legacy and new nitrogen, however, are cost-effective.

Downloads: 0