Assessing compost application and grazing management in California rangelands: Impacts on soil microbial ecology and drought resilience

Project Overview

Project Type: Graduate Student
Funds awarded in 2023: $29,608.00
Projected End Date: 06/30/2025
Grant Recipient: UC Davis
Region: Western
State: California
Graduate Student:
Principal Investigator:


  • Animals: bovine
  • Animal Products: fiber, fur, leather, meat


  • Animal Production: feed/forage, grazing management, range improvement, rangeland/pasture management
  • Education and Training: extension, farmer to farmer, networking, on-farm/ranch research, workshop
  • Natural Resources/Environment: biodiversity, carbon sequestration, habitat enhancement, soil stabilization, wildlife
  • Production Systems: holistic management
  • Soil Management: composting, organic matter, soil analysis, soil microbiology, soil quality/health
  • Sustainable Communities: partnerships, sustainability measures

    Proposal abstract:

    Rangelands in California provide essential ecosystem services such as water purification, wildfire fire prevention, and food and fiber production. Rangelands also serve as the economic base of many rural communities. Because rangelands are rain-irrigated systems, these regions are vulnerable to drought conditions, which are expected to increase in severity due to climate change. Severe droughts pose significant threats to rangelands, including decreased livestock forage production, reduced biodiversity, and soil degradation. These ecological impacts also place significant socio-economic strain on ranchers. Previous initiatives have found that compost amendments provide benefits to soils and forage productivity within agricultural cropping systems, including greater resilience to drought. However, there are potential limitations to applying compost amendments to rangeland soils, and research thus far has demonstrated mixed results, particularly for soil health with key knowledge gaps remaining for the soil microbiome. It is essential to understand the ecological and social implications of compost application before implementing these practices on a large scale. This research will examine how compost application impacts soil microbial abundance and community composition on ranches. Soil microbes are essential in key processes that determine soil quality and health; soil health can, in turn, impact forage productivity and improve rangeland resilience to drought conditions. Throughout this project, I will work with ranchers and UCCE advisors to communicate results via on-ranch research and extension workshops. Project outcomes will be (1) determine impacts of compost applications to soil microbial ecology, (2) assess social barriers to adoption, and (3) collaborate and share results with stakeholders. 

    Project objectives from proposal:

    My overarching goal for this research is to determine the potential of rangeland compost application as a climate smart ranching practice to manage soils for increased resilience to prolonged drought and water scarcity in California.

    Objective 1: Measure impacts of compost application to soil microbial biomass and community composition 

    I will work with ranchers and UC Cooperative Extension (UCCE) collaborators who have previously applied compost amendments to their land at a variety of sites managed under a gradient of livestock grazing intensities. Soil microbes are essential drivers of numerous soil processes (Wagg et al. 2021), and have previously been found to improve resilience to climate change induced drought and prolonged water scarcity (Umezawa et al. 2006). A primary objective of this work will therefore be to determine how compost amendments impact the soil microbiome. I will collect soil samples from each site to measure variation in total soil microbial biomass and microbial community composition between sites. I will then analyze these results to assess the potential impacts of compost application practices to the soil microbiome. 


    Objective 2: Determine potential of compost application to increase drought resilience in rangelands via key soil health metrics 

    There is substantial evidence that high soil microbial diversity, and microbial community composition impacts soil health metrics and large scale ecosystem processes (Wagg et al. 2021) Examining impacts of soil microbial diversity to key soil health metrics can potentially serve as a proxy for drought resilience. I will therefore analyze soil samples collected from all sites for key soil health metrics relevant to improving resilience to drought and increasing water uptake and retention. I will measure variation in soil organic matter, soil organic carbon, bulk density, and gravimetric water content, between sites. This will allow me to determine if variation in microbial abundance and community composition have an impact on soil health metrics. 


    Objective 3: Assess adaptive capacity and potential barriers to adopting compost application as a climate smart ranching practice 

    I will collaborate with UCCE advisors to create and distribute surveys in order to assess adaptive capacity of implementing compost amendment practices, as well as other potential climate smart ranching practices (e.g., prescribed burning, strip seeding, livestock species rotation). I will build on previously successful initiatives within my lab group using surveys to gauge rancher perspectives on barriers to adopting sustainable ranching practices(Roche et al. 2015). I will base these surveys on previously successful work applying the four key components of adaptive decision making: information sources, management capacity, goal setting, and previous experience (Lal et al. 2001). 


    Objective 4: Collaborate with and communicate results to ranchers, and key stakeholders 

    In order to facilitate project collaboration and communicate results to key stakeholders, I will leverage established relationships with UCCE professionals to provide workshops, demonstrations, and resources for ranchers in counties across California. This project will include collaborations with UCCE researchers who currently have partnerships with ranchers who have applied compost to their land, or have expressed interest in implementing composting practices on their land. 

    Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.