While agricultural soils account for a large portion of nitrogen pollution in the US, sustainable soil management practices present unmatched potential to slow global warming and counteract environmental externalities. Planting cover-crops is part of a set of recommended practices in conservation agriculture, a management approach that encourages farmers to decrease N losses by keeping living plants and plant cover in the soil during the off-season. Despite their promise in reducing sources of N loss through denitrification and leaching, the functional impact of cover-crops on microbially-driven soil N-cycling remains a mystery. At a time when cover-crops are gaining increased interest across the country, including in the Upper Midwest, leveraging below-ground interactions with microbes to tighten nutrient cycles presents the next big challenge for climate-friendly farming.
This project contributes to an existing SARE project aimed at engaging minority farmers in summer cover crop systems. Under the current project, optimal management of a variety of summer cover crop species is being investigated to maximize ecosystem services such as providing habitat for pollinators and plant-available mineral N. The objective of this proposal is to understand how summer cover-crop management impacts key soil microbial groups.
Cover crop management decisions such as species selection and termination date can influence microbial groups responsible for transforming soil N in ways that are not well-understood. Agriculturally-relevant sources of N loss that contribute to water pollution and greenhouse gas emissions are controlled by the key microbial processes of nitrification and denitrification. The objectives of this project are to 1) identify summer cover crop species and species mixtures that minimize soil N loss via impacts on key microbial communities, and 2) contribute to resources for underserved farmers to assess summer cover crop management trade-offs for ecosystem services. Farmer collaborators will assist in evaluating seven cover crop species mixture treatments, each at two different planting dates. Soil samples will be collected from on-farm trials at key timepoints to determine cover crop impacts on microbial populations. Information on how cover crop management interacts with microbial communities will be paired with qualitative farmer evaluation of the cover crop systems under study. This project will ultimately engage small-scale vegetable producers and minority farmers in making informed decisions on the unseen, below-ground impacts of planting cover-crops.
Project objectives from proposal:
Objective 1. Identify summer cover crop species and species mixtures that minimize soil N loss through impacts on specific microbial communities. Learning outcome: 5 educators/researchers will learn about the impact of at least three summer cover-crop species on soil microbial groups that play a central role in soil N cycling. Action outcome: Educators will develop and distribute recommendations to 200 farmers for using summer-cover crops to functionally impact soil microbial communities.
Objective 2. Contribute to resources for immigrant and minority farmers to assess management trade-offs with summer cover crop ecosystem services. Learning outcome: 50 growers will learn to weigh impacts on soil microbial populations in their decision to adopt summer cover crop mixtures. Action outcome: Growers contribute to the preservation of plant-available soil N and reduce losses from leaching and denitrification by cultivating beneficial microbial communities through cover crop selection.