Trade-offs of Conservation Practices in the US Corn-belt: Balancing Soil Organic Carbon, Water Quality, and Crop Yield

Agricultural conservation practices (e.g. conservation tillage, cover crops) are critical measures to mitigate nutrient loss and greenhouse gas emissions, enhance soil organic carbon (SOC), and maintain crop yield. Despite these benefits, recent studies indicate that switching to conservation tillage (e.g. no-till) can inadvertently increase nitrate leaching, thereby degrading water quality.  This study presents a meta-analysis of field experiments to elucidate the conflicting outcomes of conservation tillage—increasing SOC levels but simultaneously exacerbating nitrate loss. For instance, SOC in the top 30 cm of soil under no-till (NT) was 14.2% and 4.7% higher than under high-intensity tillage (HT) and intermediate-intensity tillage (IT), respectively. In contrast, nitrate leaching under NT exceeded that under HT and IT by 4.9% and 0.6%, respectively.

By leveraging high-resolution datasets of soil characteristics, weather, water quality, land use, and topography, we utilized a comprehensive watershed model, the Terrestrial-Aquatic Sciences Convergence (TASC) to evaluate the combined effects of tillage and cover crops (e.g., winter wheat, rye, and oats) on SOC sequestration, nitrate loading, and crop yield in the Upper Mississippi River Basin (492,000km²). We found that conservation tillage  and cover crops could complement each other. The combined adoption significantly affects water availability, nitrate leaching, SOC, and crop yield. While the integration of cover crops enhances biomass production and SOC, their ability to absorb soil inorganic nitrogen during the non-growing season helps mitigate nitrate leaching. Notably, crop yield under scenarios combining tillage and cover crops surpasses those involving only tillage. However, cover crops can also enhance evapotranspiration, which could potentially aggravate the water availability issues for crop production under future climate conditions. These results underscore the critical need for careful evaluation of the trade-offs between conservation tillage and cover crops when developing policies to address environmental challenges in agricultural ecosystems over the coming decades.