Soil organic carbon, nitrogen, and enzyme activity in glaciated-derived agricultural landscapes of the U.S. Midwest

Authors: AMORIM, HELEN - University Of Arkansas; Ashworth, Amanda; Stott, Diane; Wills, Skye; Winzeler, Hans; Owens, Phillip; Libohova, Zamir

Submitted to: Catena
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/23/2025
Publication Date: 1/21/2026
Citation: Amorim, H.C., Ashworth, A.J., Stott, D.E., Wills, S.A., Winzeler, H.E., Owens, P.R., Libohova, Z. 2026. Soil organic carbon, nitrogen, and enzyme activity in glaciated-derived agricultural landscapes of the U.S. Midwest. Catena. https://doi.org/10.1016/j.catena.2025.109770.
DOI: https://doi.org/10.1016/j.catena.2025.109770

Interpretive Summary: Landscape features can have a big impact on how soils store and release nutrients, but that is not very well known for agricultural lands in the US Corn Belt. In this study, researchers investigated soils under corn-soybean rotations in northern Indiana to evaluate how where crops are grown on the landscape (low lands middle slope, hill top) impacts soil organic carbon, nitrogen, and soil microbial activity They collected over 200 surface soil samples across various landscape positions and analyzed nutrient concentration and soil respiration, which is an indicator of how active microbes are in soils. They found that lowlands and wetter areas had between 55-76% more organic matter than drier areas and surrounding uplands. Soils with poor drainage also released 2 times more carbon in the soil respiration tests, indicating greater biological activity. Despite releasing more carbon, these lowland soils are rich in organic matter and store most of the soil carbon in this region, while hilltop soils stored much less. This research shows that nutrient distribution in agricultural soils is highly affected by landscape and soil drainage, and this knowledge can help farmers to choose more tailored practices that protect soil health, store more organic matter, and support sustainable row crop agriculture in the US.

Technical Abstract: The extent to which terrain and landscape modify soil C and nutrient dynamics remains largely unknow for agricultural lands. This study assessed total soil organic carbon (SOC), mineralizable SOC (Cmin), total N, and beta-glucosidase (BG) activity affected by landscape position in glaciated-derived agricultural soils of northern Indiana. Soil samples from the 0-25 cm surface layer (n = 210) were collected along 10-point transects following the soil catena. Total SOC and N distribution in the landscape was generally driven by soil wetness and organic matter accumulation. Depressional areas, poorly and very poorly drained soils stored 42-188 Mg C ha-1, or between 55 to 76 % more SOC than surrounding upland areas. After 28 days of incubation, depressions, poorly and very poorly drained soils released 1.4 Mg C ha-1 as Cmin, nearly 2 times more than upland areas (p < 0.05; 0.8 Mg ha-1), likely owing to greater enzyme activity. Mean C-CO2 evolution decreased exponentially after 28 days (1.5 to 0.2 µg g-1 h-1). At day 28, C-CO2 evolution differed (p < 0.05) between depressions and summits/side slopes, and very poorly drained soils. Soils with high contents of relatively less decomposed organic matter (e.g, histic epipedon) had the highest total SOC stock (188 Mg C ha-1) compared to mollic and ochric epipedons (51 and 32 Mg C ha-1, respectively). Findings from this study can inform land managers about the best management practices to enhance SOC retention based on soil type and relief, being critical to support long-term soil health and sustainability of crop production systems.