Legacy effects of alfalfa monocultures or annual crop/alfalfa mixtures on subsequent corn yield and quality

Authors: Whippo, Craig; Hendrickson, John; Clemensen, Andrea; Grusak, Michael

Submitted to: Agrosystems, Geosciences & Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/5/2025
Publication Date: 5/14/2025
Citation: Whippo, C.W., Hendrickson, J.R., Clemensen, A.K., Grusak, M.A. 2025. Legacy effects of alfalfa monocultures or annual crop/alfalfa mixtures on subsequent corn yield and quality. Agrosystems, Geosciences & Environment. 8. Article e70114. https://doi.org/10.1002/agg2.70114.
DOI: https://doi.org/10.1002/agg2.70114

Interpretive Summary: Planting annual crops into alfalfa is gaining interest. One reason for this may be that alfalfa lowers the nitrogen needs of the next crop. But not much is known about how alfalfa-annual crop mixtures affect the production of corn. We examined grain yield and quality of corn grown one year after 1) a mixture of alfalfa and annual crops, 2) an alfalfa alone, or 3) an annual crop without alfalfa. We found that corn yield was lower after annual crop without alfalfa than after alfalfa alone or a mixture of alfalfa and annual crops. Alfalfa density, the cation exchange capacity, and the organic matter in the soil improved corn yield and quality. We did not find differences in the amount of protein or starch in the grains between the treatments. However, the amount of oil in the grains was higher after the mixture of alfalfa and annual crops than annual crops alone. The amount of zinc in corn grain was linked to the density of alfalfa and the amount of chlorophyll in corn ear leaves. These results show that growing only alfalfa or growing alfalfa along with annual crops can have different effects on corn yield, near-surface soil properties, and grain quality. Based on these results, future studies that aim to find the best annual crop/alfalfa mixtures in the northern Great Plains should be structured to look at how these mixtures affect corn crops that come after.

Technical Abstract: Interseeding annual crops into existing alfalfa (Medicago sativa L.) stands is gaining interest and one reason may be that alfalfa lowers nitrogen requirements for subsequent crops. However, little is known about the legacy impact of this practice on subsequent corn (Zea mays, L) production. A study comparing grain yield and quality of corn planted one year after; 1) alfalfa and annual crop polyculture, 2) alfalfa monoculture, or 3) annual crop monoculture found that corn yield was lower following annual monocultures compared to corn following alfalfa monoculture and polyculture plots. Alfalfa stand density, soil cation exchange capacity, and soil organic matter significantly influence corn yield. This study found no significant differences in grain protein or starch between treatments, but grain oil content was higher following polyculture compared to annual monoculture. Corn grain Zn concentration was positively associated with previous alfalfa density and corn ear leaf chlorophyll content. These findings suggest that alfalfa monoculture and alfalfa-annual crop polycultures can have different positive legacy effects on corn yield, near-surface soil attributes, and grain quality. These results suggest future research aimed at optimizing annual crop/alfalfa mixtures in the northern Great Plains should be designed to capture the legacy effects on subsequent corn crops.