Hillslope position affects soil nitrogen dynamics and maize fertilizer needs following a cereal rye cover crop

Authors: PESSOTTO, MILA - Iowa State University; LICHT, MARK - Iowa State University; ADJUIK, TOBY - Iowa State University; MARCOS, FERNANDO - Iowa State University; MATTHIESEN, RASHELLE - Iowa State University; O'Brien, Peter; ROBERTSON, ALISON - Iowa State University; MCDANIEL, MARSHALL - Iowa State University

Submitted to: Field Crops Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2026
Publication Date: 5/6/2026
Citation: Pessotto, M.V., Licht, M.A., Adjuik, T.A., Marcos, F., Matthiesen, R., O'Brien, P.L., Robertson, A.E., McDaniel, M.D. 2026. Hillslope position affects soil nitrogen dynamics and maize fertilizer needs following a cereal rye cover crop. Field Crops Research. https://doi.org/10.1016/j.fcr.2026.110516.
DOI: https://doi.org/10.1016/j.fcr.2026.110516

Interpretive Summary: Cover crops are plants grown during times of the year that corn and soybean are not growing. These crops can reduce soil erosion and nutrient losses while suppressing weeds and helping soil organisms. However, yields of corn grown are sometimes lower when a cover crop is used than when it is not used. This reduction is inconsistent, and the underlying causes are still unclear. We conducted an experiment to determine: (1) if reduction in corn yields is related to the hillslope position (top, middle, and bottom) and (2) if higher fertilizer rates could help offset the reduction. We found that corn grown after a cover crop had consistently lower yields at all points on the hillslope, but it was more severe at the top (12%) and middle (19%) locations where less soil organic matter is present, compared to the bottom (8%). We also found that nitrogen processes were very different in the three hillslope positions, which indicates that soil properties related to corn yields change across the field. Overall, this research shows that corn should be managed differently following a cover crop, and that management plans should consider landscape variability for the greatest yields. These results can help farmers, researchers, and crop advisors make the best decisions about use of cover crops while maintaining highly productive cropping systems.

Technical Abstract: Context: Winter cover crops, like cereal rye (Secale cereale), are one of the most promising solutions to environmental sustainability in the maize (Zea mays L.)-soybean (Glycine max L. merr.) cropping systems of the Midwestern U.S. However, one of the largest barriers to adoption is the “yield drag,” or decrease in cash crop yield that occurs when following cereal rye (especially with maize). Reports of maize yield drag are inconsistent, and the underlying mechanisms are unclear. Objective: Our primary research questions were: i. Does fertilizer N alleviate maize yield drag? ii. does hillslope position change soil N dynamics and maize N needs after cereal rye cover crop? iii. what factors across site-years and hillslopes best predict maize yields? Methods: We conducted a split-plot experiment [cover/no-cover × six nitrogen (N) rates] across three hillslope positions (summit, backslope, and toeslope) over three site-years. Fertilizer N rates ranged from 0 to 336 kg N ha'' 1. In response, we measured soil N dynamics (net N mineralization, inorganic and organic N pools), crop grain yield, and response to N fertilizer. We also ran a random forest model to identify the most important factors affecting yield drag. Results: There were few, weak interactive effects of hillslope position and cover crops on soil N dynamics. Toeslope positions tended to increase soil N pools. Cover crops had weaker effects on soil N dynamics but did decrease soil nitrate by 26%, on average, across the field. There were more complex hillslope × cover crop interactions on maize yield response to N fertilizer. While fertilizer N partially alleviated maize yield drag, yields remained consistently lower under cover crops compared to winter fallow, particularly at summit and backslope positions characterized by lower soil organic matter (SOM). Random forest modeling identified N application rate, cereal rye biomass, soil test phosphorus, and SOM as key predictors of maize yield, and revealed complex interactions between management and hillslope factors (i.e., soil properties). Conclusions: Our findings emphasize the importance of considering landscape variability when optimizing N management in cereal rye-maize systems to mitigate yield penalties and enhance nutrient use efficiency.