Multi-state, multi-seeding rate evaluations of three cool season cover crop mixes: Effects on cover crop performance, soil health indicators, and an analysis of costs

Authors: STARR, LAURA - Natural Resources Conservation Service (NRCS, USDA); DOUGLAS, JOEL - Natural Resources Conservation Service (NRCS, USDA); BRYON, KIRWAN - Natural Resources Conservation Service (NRCS, USDA); CASEY, ALLEN - Natural Resources Conservation Service (NRCS, USDA); Mirsky, Steven; ENGLERT, JOHN - Natural Resources Conservation Service (NRCS, USDA); ACKROYD, VICTORIA - University Of Maryland; THAPA, RESHAM - Tennessee State University

Submitted to: Journal of Soil and Water Conservation
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2025
Publication Date: 9/12/2025
Citation: Starr, L., Douglas, J.L., Bryon, K., Casey, A., Mirsky, S.B., Englert, J.M., Ackroyd, V.J., Thapa, R. 2025. Multi-state, multi-seeding rate evaluations of three cool season cover crop mixes: Effects on cover crop performance, soil health indicators, and an analysis of costs. Journal of Soil and Water Conservation. 1-14. https://doi.org/10.1080/00224561.2025.2457181.
DOI: https://doi.org/10.1080/00224561.2025.2457181

Interpretive Summary: Cover crops (CCs) provide many benefits to cropping systems such as increased soil health, improved soil water infiltration and storage, decreased nitrogen (N) leaching, reduced erosion, and increased weed suppression. The more biomass (i.e. plant material) a cover crop produces, the greater the extent to which it provides these services. This study evaluated the effects of cover crop mixes and seeding rates on cover crop performance and soil health indicators at five NRCS Plant Materials Centers from 2013-2016. Cover crop mixture composition and seeding rate had no detectable effect on measured soil health parameters or cash crop yield. Increasing number of species in the mix increased cover crop biomass in six of nineteen site-years. Increased seeding rates had a variable effect on cover crop biomass and biomass nitrogen content dependent on site-year. An economic analysis revealed an average 260% increase in cost to plant four or six species mixes compared to a two species grass/legume mix. This work reinforces the recommendation that growers should weigh expected benefits versus costs when designing their cover crop mixtures and determining seeding rates.

Technical Abstract: Cover crops (CCs) provide many benefits to cropping systems such as increased soil health, improved soil water infiltration and storage, decreased nitrogen (N) leaching, reduced erosion, and increased weed suppression. Increasing CC biomass is often associated with an increase in these ecosystem services. This research was conducted at five NRCS Plant Materials Centers from 2013-2016 to investigate the effects of CC mixes and seeding rates on CC performance and soil health indicators. In each site-year, experiments were laid out in a randomized complete block design with two, four, and six-way species CC mixtures seeded at 215, 430, and 645 seeds per m2. There was no treatment effect detected of CC mixture composition and seeding rate on total soil organic carbon, permanganate oxidizable carbon, Mehlich-III/Olsen phosphorus, total soil nitrogen, or cash crop yields in any of the site-years. Increasing number of species in the mix increased CC biomass in six of nineteen site-years. Increasing the CC seeding rates had a variable effect on CC biomass and biomass N dependent on site-year. An economic analysis revealed an average 260% increase in cost to plant four or six species mixes compared to a two species grass/legume mix. The cost of increasing the seeding rate from 215 to 645 seeds/m2 ranged from $72 ha-1 to $277 ha-1. We conclude that CC mixture composition nor seeding rate do not consistently improve CC performance, soil health, or cash crop yields. Growers should weigh expected benefits versus costs when designing their CC mixtures and determining seeding rates.