Cover crops for ecological management of U.S. agricultural systems: quantifying ecosystem services across multiple scales
Date
2023
Authors
Eash, Lisa, author
Fonte, Steven J., advisor
Schipanski, Meagan E., committee member
Trivedi, Pankaj, committee member
Mooney, Daniel, committee member
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Abstract
Managing agricultural systems to provide multiple ecosystem services (ES) beyond food provisioning has gained considerable attention in recent years. The integration of cover crops (CC) into U.S. cropping systems presents an opportunity to support multifunctional agricultural systems, which alleviate negative environmental impacts of agriculture, mitigate greenhouse gas (GHG) emissions and support sustained crop production. However, CC impacts on these ES are variable and depend on management and site characteristics, contributing to uncertainty surrounding to what extent CC can improve ES. Reducing this uncertainty is critical to both identify appropriate environmental and management conditions for CC adoption and improve the estimated potential for CC to improve multifunctionality of U.S. cropping systems. This dissertation aims to quantify CC impacts on ES at multiple scales, exploring benefits to the soil microbiome, at the farm level, and nationally. Throughout this assessment I explore how these effects are influenced by climate and soil characteristics and how management can be leveraged to optimize the provision of ES. Chapter two estimates the potential for widespread adoption of CC to increase soil organic carbon (C) stocks and mitigate GHG emissions in the U.S. Analysis using current U.S. crop management data and a biogeochemical model revealed that the mitigation potential over a 20 year period is lower than previous estimates due to regional variability, decreasing rates of C accrual over time, and limited CC integration. Changes in N2O emissions did not offset C sequestration but introduced large uncertainty surrounding total national mitigation potential. Soil C gains due to CC offer important co-benefits to U.S. cropping systems, but the contribution of CC to achieving U.S. emissions targets will likely be lower than previously anticipated. Our spatially-explicit analysis also highlights regions where adoption of CC can have greater relative contributions to GHG mitigation. I then quantify a larger suite of ES in dryland wheat systems of the semi-arid western U.S., a particularly challenging context for CC due to lower potential productivity and associated economic trade-offs. I used two existing field trials to monitor CC impacts on soil health, cash crop productivity, and economics over a period of six years. No-till, CC planting window, and the sale of CC biomass as forage were also explored as strategies to optimize ES provision and economic viability. Chapters three and four demonstrate that the integration of CC amidst water limitations can benefit erosion control and soil structure, but also present significant productivity and economic trade-offs. The integration of fall-planted CC, no-till management, and the use of CC for forage provided the greatest potential for maximizing ES benefits in an economically viable manner. In Chapter five, I conducted a greenhouse study to examine the impact of CC type and functional diversity on microbial community composition and associated ES. Plant functional types (Poaceae, Brassicaceae, and Fabaceae) were associated with distinct increases in ES proxies, which appear to be mediated by shifts in microbial community composition. Specifically, Fabaceae (legume) CC enhanced the presence of copiotrophic microbes, which were associated with improvements in soil structure and high enzyme activity, a proxy for nutrient cycling. Poaceae and Brassicaceae led to improvements in microbial diversity. Ecosystem service benefits and microbial community shifts were conserved in diverse CC mixtures, contributing to increased multifunctionality. Across studies and scales, CC were observed to support a number of ES that address environmental concerns resulting from modern intensive agricultural practices. However, slight benefits and substantial productivity trade-offs in water-limited systems may limit the extent to which CC can mitigate GHG emissions and restore soil C reserves nationally. Management choices, such as CC composition and diversity, no-till management, and the sale of a portion of CC biomass as forage, can be leveraged to optimize the provision of ES in an economically viable manner. Overall, CC effectively contribute to multifunctional agroecosystems whose ES extend beyond food provisioning.
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Subject
climate mitigation
ecosystem services
cover crops
agroecology