Soil responses to inclusion of corn, soybean, and cover crops under rainfed conditions in the Northern Great Plains

Authors: Liebig, Mark; Archer, David; Halvorson, Jonathan; Clemensen, Andrea; Hendrickson, John; Tanaka, Donald

Submitted to: Canadian Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/7/2023
Publication Date: 2/6/2024
Citation: Liebig, M.A., Archer, D.W., Halvorson, J.J., Clemensen, A.K., Hendrickson, J.R., Tanaka, D.L. 2024. Soil responses to inclusion of corn, soybean, and cover crops under rainfed conditions in the Northern Great Plains. Canadian Journal of Soil Science. https://doi.org/10.1139/cjss-2023-0092.
DOI: https://doi.org/10.1139/cjss-2023-0092

Interpretive Summary: Corn and soybean are being included in crop rotations more frequently in the northern Great Plains. Use of cover crops is also increasing throughout the region. However, these shifts in cropping patterns can influence the soil in ways that affect long-term sustainability. Therefore, a study was conducted to investigate the effects of three crop rotations (spring wheat–soybean, spring wheat–corn–soybean, and spring wheat–corn–cover crop), each under two forms of tillage (minimum- and no-tillage), on soil properties six years after the rotations were established. Soil responses to corn, soybean, and cover crops were subtle and concentrated at the soil surface. Spring wheat was found to enhance soil cover and aggregate stability, while soybean increased soil acidification and lowered levels of exchangeable potassium. Accordingly, frequent soil monitoring is recommended when soybean is grown every other year, as adjustments in crop choice and/or rotation length may be needed to maintain suitable soil conditions for crop growth. Furthermore, the lack of a positive soil response to cover crops in the study suggests more research is needed to develop cover crop practices that meet production goals while improving the soil.

Technical Abstract: Crop rotations in the northern Great Plains of North America increasingly include warm season crops, such as corn and soybean. Use of cover crops, while less extensive, is also increasing throughout the region given their purported agronomic and environmental benefits. To date, soil responses to the inclusion of corn, soybean, and cover crops in rainfed cropping systems have not been well documented in the region. To address this gap, soil properties were evaluated six years after establishment of three crop rotations [spring wheat–soybean (SW-S), spring wheat–corn–soybean (SW-C-S), and spring wheat–corn–cover crop (SW-C-cc)] each split by no- and minimum tillage treatments on a Temvik-Wilton silt loam soil near Mandan, ND USA. Soil responses to corn, soybean, and full-season cover crops were subtle and exclusive to the 0-7.6 cm depth. Soil pH was lower in SW-S than SW-C-cc (5.28 vs. 5.48; P = 0.05), SO4-S was greater under SW-C-cc than SW-C-S (13.4 vs. 11.6 g/kg; P = 0.03), exchangeable K was greater under SW-C-S and SW-C-cc than SW-S (0.83 cmol/kg vs. 0.52 cmol/kg; P = 0.05), and water-stable aggregates were greater in SW-S than SW-C-S (26 vs. 19%; P = 0.08). Soil C and N pools did not differ among crop rotations, while particulate organic matter N was greater under no-tillage compared to minimum tillage (P = 0.08). Between 2012 and 2018, soil pH decreased and soil organic C increased under SW-C-S. Frequent monitoring of near-surface soil conditions in rotations with soybean every other year is recommended, and innovative management practices are needed to enhance soil C and N pools in rotations with full-season cover crops.