Eating the metaphorical elephant: Meeting nitrogen reduction goals in Upper Mississippi River Basin states

Authors: Feyereisen, Gary; HAY, CHRISTOPHER - Iowa Soybean Association; CHRISTIANSON, REID - University Of Illinois; HELMERS, MATTHEW - Iowa State University

Submitted to: Journal of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/15/2022
Publication Date: 3/13/2022
Citation: Feyereisen, G.W., Hay, C.H., Christianson, R.D., Helmers, M.J. 2022. Eating the metaphorical elephant: Meeting nitrogen reduction goals in Upper Mississippi River Basin states. Journal of the ASABE. 65(3):621-631. https://doi.org/10.13031/ja.14887.
DOI: https://doi.org/10.13031/ja.14887

Interpretive Summary: Twelve states in the Mississippi River Basin (MRB) have published Nutrient Reduction Strategies (NRS) to cut nitrogen (N) loads from their state by 45%. Progress to date has been limited. This study was conducted to estimate N load reductions at increasingly challenging implementation levels of conservation practices identified in the NRS of Iowa, Illinois, and Minnesota, Upper MRB states that contribute 36% of MRB N load. The conservation practices were grouped by strategy: infield practices, land use changes, and edge-of-field practices. Benchmark-, low-, medium-, and high-levels of implementation were established and reductions were calculated for each state and across states on an area-weighted basis. Since implementing multiple practices on the same area reduces cumulative effectiveness, adjustments were made using an N load calculator. For high-level implementation, N load reductions were 72, 49, and 37% for Iowa, Illinois, and Minnesota, respectively. When accounting for overlaps of stacking practices on the same area, N load reductions across the states were 26, 40, and 55% for the low-, medium-, and high-level implementation scenarios, respectively. Under the assumptions made, edge-of-field practices become increasingly important at higher levels of implementation. Meeting reduction goals and maintaining productivity requires market and/or technology breakthroughs.

Technical Abstract: Progress meeting the Gulf of Mexico Hypoxia Task Force’s target reduction of 45% for nitrogen (N) loads from the Mississippi River Basin (MRB), proposed over a decade ago, has been limited. This study was conducted to estimate nitrate-N reductions at increasingly challenging levels of implementation for 1) individual infield practices, land use changes, and edge-of-field conservation practices, and 2) the combining or stacking of these practices. The evaluation was done for three Upper MRB states – Iowa, Illinois, and Minnesota, which have science assessments as part of their nutrient reduction strategies and contribute 36% of the MRB N load to the Gulf of Mexico. Benchmark-, low-, medium-, and high-levels of implementation were established and reductions were calculated for each state and across states on an area-weighted basis. The Iowa N load estimator was used to account for overlapping benefits of stacking multiple practices on a given land area. State-combined N reductions for the individual practices ranged from 0 to 9, 2 to 10, and 4 to 17% for the low-, medium-, and high-level implementation scenarios. Nitrogen load reductions across the states, accounting for potential overlaps when stacking practices, were 26, 40, and 55% for the low-, medium-, and high-level implementation scenarios, respectively. Results by state for high-level implementation varied; reductions were 72, 49, and 37% for Iowa, Illinois, and Minnesota, respectively. Under the assumptions made, edge-of-field practices become increasingly important at higher levels of implementation. Meeting reduction goals and maintaining productivity requires market and/or technology breakthroughs.