Assessment of drainage nitrogen losses on a yield-scaled basis

Subsurface nitrogen (N) losses represent a major environmental concern in agriculture, particularly from fields containing artificial drainage to prevent saturated soil conditions and increase crop production. To develop sustainable intensification strategies and achieve high yields with minimal environmental impacts, N losses are increasingly evaluated with respect to crop productivity on a “yield-scaled” basis, yet little information is available to address the current challenge of balancing crop yields and drainage N losses from intensive maize production systems in the U.S. Midwest by using this metric. In the present study, a meta-analysis was conducted using 31 studies with 381 observations from a publicly available nutrient loss drainage database (Measured Annual Nutrient loads from Agricultural Environments, MANAGE) to address this issue. Results showed that increasing N rates enhanced yields but had weak effects on area- and yield-scaled drainage N losses. In contrast, yield-scaled drainage N losses responded exponentially to N surplus (estimated as N application rate minus above-ground crop N uptake). Relative precipitation during the drainage monitoring period strongly influenced area- and yield-scaled drainage N losses. Maize-soybean rotations and silt loam soils had lower yield-scaled drainage N losses compared to continuous maize and clay loam soils, respectively, whereas tillage practices had little impact on yield-scaled drainage N losses. To meet the growing challenge of achieving high yields with minimal impacts on water quality, these results suggest that evaluating drainage N losses on a yield-scaled basis may complement the more conventional approach of evaluating N losses on an areas basis for maize systems in this region.