Managing Ecosystem Services with Cover Crop Mixtures on Organic Farms

Abstract

Core Ideas Mixtures provided BNF while maintaining non‐BNF services equivalent to cereal rye. Winter pea in mixture with a brassica provided the same N input as sole‐planted pea. Crimson clover fixed more N than red clover in the overwintering cover crop period. Brassica mixtures matched or exceeded rye N retention and weed suppression in fall. Participants supported use of cover crop mixtures on diversified vegetable farms. Cover crops are central to an ecological approach to nutrient management that could reduce N losses from agroecosystems. Mixed‐species cover crops that include multiple functional groups, such as legumes and non‐legumes, may improve sustainability by supplying an organic N source to fields while providing other ecosystem services, such as N retention and weed suppression. This on‐farm experiment determined the contributions of two‐ and three‐species cover crop mixtures, which combined legumes, brassicas, and cool‐season grasses, to management‐relevant ecosystem services. In August 2015, we planted mixture treatments of interest with participating farmers on nine Michigan vegetable farms. We also included a cereal rye (Secale cereale L.) monoculture treatment, which is the most common overwintering cover crop in the region. In fall 2015 and spring 2016, we measured aboveground biomass production, biological N fixation (BNF), N assimilation and N retention in aboveground biomass, and weed suppression and compared the results with a no–cover crop control. Overall, we did not find consistent benefits of cover crop mixtures compared with cereal rye for individual services other than BNF. However, several mixtures that included legume species provided BNF while maintaining the same level of weed suppression and N retention as sole‐planted cereal rye. Farmers indicated support for the use of cover crop mixtures on diversified vegetable farms, although some expressed concerns about legume seed costs and disease risk with brassica cover crops. On‐farm experimentation allowed us to address ecological questions of direct relevance to farmers within actual social and environmental contexts.