Organic production reduces subsurface nitrate leaching and maintains crop yields in a U.S. Mollisol

Authors: Rogovska, Natalia; Ruis, Sabrina; Carney, Derek; DELATE, KATHLEEN - Iowa State University; Wacha, Kenneth; Kovar, John; O'Brien, Peter; Cambardella, Cynthia

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2025
Publication Date: 9/25/2025
Citation: Rogovska, N.P., Ruis, S.J., Carney, D., Delate, K., Wacha, K.M., Kovar, J.L., O'Brien, P.L., Cambardella, C.A. 2025. Organic production reduces subsurface nitrate leaching and maintains crop yields in a U.S. Mollisol. Journal of Environmental Quality. https://doi.org/10.1002/jeq2.70085.
DOI: https://doi.org/10.1002/jeq2.70085

Interpretive Summary: In this study we investigate how organic farming affects nitrate losses in artificially drained soils of the U.S. Midwest, an area where such studies are few. We evaluated changes in nitrogen (N) loading and crop yields for the diversified organic rotation (corn-soybean-oat/alfalfa-alfalfa), and organic perennial pasture systems compared with the conventional corn-soybean rotation system. The results showed that the 4-year organic rotation reduced nitrogen losses by 50% and organic pasture by 93% compared with the conventional corn-soybean rotation system. These reductions are largely attributed to crop diversification and the use of organic fertilizers such as composted manure. Despite some variability due to precipitation, the study results show that crop yields in organic systems were comparable to or higher than conventional yields in most years. This research provides strong evidence that organic farming systems, when designed with diverse rotations and organic nutrient sources, can substantially reduce nitrogen pollution in surface waters without sacrificing productivity. The findings of this work can aid farmers and policymakers in understanding how organic farming systems impact water quality and crop yields in regions with artificial drainage.

Technical Abstract: Organic production aims to diversify crop rotation and use organic fertilizer sources to build soil fertility and improve soil health indicators. The impact of organic farming on water quality in artificially drained midwestern Mollisols, however, has received limited attention. A replicated plot experiment was initiated to investigate the impact of conventional corn (Zea mays L)-soybean (Glycine max L.) rotation, organic corn-soybean-oat (Avena sativa L.)/alfalfa (Medicago sativa L)-alfalfa rotation, and an organic perennial pasture on NO3- losses via subsurface drainage and crop yields. Nitrogen fertilization consisted of sidedress UAN for conventional corn (168 kg N ha-1) and spring-applied composted manure for organic corn (168 kg N ha-1) and oats (56 kg N ha-1). Overall, the 4-year organic rotation reduced N loads by 50% and pasture reduced loads by 93% compared with the conventional 2-year corn-soybean rotation. Reductions in N loads were related to the diversified cropping system as no difference in N losses were detected when only corn-soybean phases of the organic rotation were compared with the conventional system. Annual variations in N loads were explained by precipitation and varied by crop. Soil health indicators sampled in the fall showed minimal influence on N losses. Organic corn yields were equivalent or higher than conventional in 4 of 7 years and soybean in 6 years. Results of this study suggest that organic farming practices that combine use of animal manure and inclusion of small grains, forage legumes, and green manures can improve water quality in artificially drained landscapes while maintaining crop yields.