Cover crop effects on the soil microbiome and microbially mediated soil functions

Cover crops can improve soil health and there is growing interest in identifying how soil microbes mediate some of the benefits provided by cover crops. However, most studies analyzing cover crop short-term effects on the soil microbiome have been conducted in controlled settings such as greenhouses, while field studies have focused on accumulated, longer-term effects. We conducted a short-term field experiment in northern Colorado with four different cover crop species (Secale cereale, Vicia villosa, Brassica napus, and Sorghum bicolor) and a fallow control grown from August 2022 to May 2023. Maize was then planted in all plots and subsequently harvested in fall 2023. Soil samples collected at cover crop termination and peak maize biomass were analyzed for soil extracellular enzymes, organic carbon, nitrogen, soil aggregate stability, and microbial community metrics. Prior to cover crop termination, Secale cereale (rye) and Brassica napus increased aggregate stability and nitrogen-cycling enzyme activity, respectively, relative to other treatments. The cover crop treatment effects only persisted into the following corn crop for the rye treatment via increased carbon and phosphorus cycling enzyme activity relative to Sorghum bicolor. While microbial community diversity indices did not differ by cover crop treatment, microbial community richness was correlated with soil enzyme activity under different cover crops. Our research shows that within a single season, cover crops can modify the soil microbiome at an organismal level and influence soil functions, demonstrating the potential scalability of findings from controlled studies to more complex field environments. Highlights: Single season cover crops can modify microbially-mediated soil functions Cereal rye and rapeseed cover crops influenced soil functions more than other species Enzyme activity effects persisted into the following maize cash crop Cover crop treatments did not result in different soil microbial communities But, both bacterial and fungal communities correlated with soil enzyme activity Key words: soil health, rhizosphere, microbiome, extracellular enzymes, aggregate stability