COS 298-4 - Legacy effects of diverse cover crops on soil microbial communities and winter wheat growth

Abstract: There has been a significant loss of biodiversity in agricultural ecosystems. The lack of aboveground diversity has been shown to reduce soil microbial diversity- the main drivers of soil carbon and nutrient cycling, and ecosystem function. The implementation of cover crops is a proposed management strategy to increase agricultural diversity and cash crop productivity. In grassland ecosystems, an increase in aboveground diversity results in increased belowground diversity. However, it is relatively unknown how increasing diversity over short time scales (i.e. cover crops) in agroecosystems impacts microbial communities and a subsequent winter wheat crop. This research investigates the legacy effects of diverse cover crops on soil properties, microbial diversity and composition, and winter wheat growth. Six species of cover crops including oilseed, grass, and legume species were planted individually and in combinations with increasing levels of diversity for two years before the planting of winter wheat. Soil samples were collected once before cover crop establishment, prior to cover crop termination, and before winter wheat harvest. Winter wheat aboveground biomass was quantified, and the plant samples were analyzed for carbon and nitrogen content. We also assessed soil microbial biomass, ammonium and nitrate content and carbon mineralization rates – an indicator of bioavailable carbon. Microbial bacterial and fungal communities were analyzed using 16S and ITS Illumina sequencing, respectively, and bioinformatic pipelines. Sequences were analyzed for alpha and beta diversity and differential abundance across all treatments and sampling periods.

Here we show legacy effects of cover crops on winter wheat growth were affected by cover crop identity and diversity. Winter wheat plots with a history of diverse cover crops had greater crop biomass, microbial biomass, and carbon mineralization. Plots previously planted with a cover crop mixture, especially those including legumes, had greater soil nitrate concentrations which positively impacted winter wheat nitrogen content. Increasing cover crop species diversity from zero to six species increased alpha and beta diversity for both bacterial and fungal communities during the cover crop growing season. However, during winter wheat growth, cover crop legacy effects on microbial alpha and beta diversity were much more complicated compared to other soil-plant characteristics. These results show that the implementation of diverse cover crops can have positive effects on winter wheat biomass, nitrogen content, and soil microbial communities. This indicates that cover crops have the potential to improve cash crop growth and overall sustainability of agroecosystems.