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

Progress report for GW23-254

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:
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Project Information


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:

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. 


Click linked name(s) to expand/collapse or show everyone's info
  • Morgan Doran
  • Scott Oneto
  • John Brownlie - Producer
  • Tim Curran - Producer
  • Molly Taylor - Producer
  • Stan Delorto
  • Scott Stone
  • Bruce Rominger
  • Kary Roulote
  • Liesel Finley


Materials and methods:

Project Sites: PT Ranch (Ione, C.A.) , Curran Ranch (Ione, CA), Dell’Orto Ranch (Jackson, C.A.) 

Research Methods for Objective 1: Soil Microbial Analysis 

To determine how soil compost amendments affect microbial biomass and community structure, I am currently collecting  soil samples at 4 ranches in Amador County, C.A. I worked in close collaboration with UC Cooperative Extension to connect with local ranches and select sites that were included in this study. These sites vary along an elevation and soil productivity gradient (low-high), and I am collecting soil samples from plots building upon a previous Western SARE project (project OW19-349). Soil sampling began in early March and will be completed by June, 2024 to overlap with peak biomass growth. The next stage of analysis for this project will include conducting microbial analysis on soils collected from each treatment: 1) compost application only, 2) compost application and seeding mixture, 3) seeding only, 4) control (no compost or seeding). The first round of soil samples have been sent for microbial analysis to Ward Laboratory in Kearney Nebraska, and the remaining samples will be sent throughout May and June, 2024. Soil samples are being analyzed for microbial biomass and diversity via PLFA (phospholipid fatty acid) analysis to estimate living soil microbial biomass, and analyzed for the presence of microbial functional groups (e.g., Andrews et al. 2024). To quantify changes in soil nutrient cycling processes and understand how compost and seeding alter soil nutrient supply, samples will be analyzed for soil enzymatic activity (e.g., Piotrowska-Długosz et al. 2022). 

Once microbial data has been obtained, I will determine how management treatments impact soil microbial abundance and community composition via statistical analysis in R. I will use a variety of statistical tests including analysis of variance (Girden 1992) and linear mixed models (Kuznetsova et al. 2017) to determine baseline variation in microbial ecology between field sites, and the degree to which compost applications influence changes in microbial ecology.

Research Methods for Objective 2: Analysis of soil health metrics related to drought resilience 

To determine how compost and seeding treatments affect soil health, soil samples are currently being collected (March-June, 2024) following the same sampling design outlined in objective 1. Analysis of key soil health metrics (soil organic matter, soil organic carbon, bulk density, gravimetric water content, aggregate stability) as the response variable has begun and soil analysis will be completed by late Fall, 2024. Soil collection and analysis of all soil health metrics is being completed in partnership with new collaborators in the UC Davis California Soil Resources Laboratory. 

I will analyze the degree of variation between treatments in key soil health metrics based on (1) soil microbial abundance and diversity at each site, and (2) management treatment at each site (compost application and seeding). I will complete statistical analysis in R ( analysis of variance and linear mixed models), to determine the degree to which variance in soil characteristics are related to microbial abundance, and compost application. This will provide further information into determining if soil microbial abundance and diversity can help to increase drought resilience in rangeland soils. Drought resilience will be quantified via variation in soil health metrics relevant to water uptake and retention.

Research Methods for Objective 3, Assess rancher receptivity and barriers to adoption 

Surveys will be used to assess rancher receptiveness towards adopting compost amendment practices in rangelands. I will work in close collaboration with UCCE and UCANR advisors to develop these surveys. This objective is based on previously successful initiatives utilizing surveys to evaluate rancher decision making (Roche et al. 2016). Surveys topics will specifically cover: assessment of ranchers’ interest in adopting compost application practices, priority concerns from ranchers to adopting these practices, evaluating rancher perspectives on the socioeconomic barriers of greatest importance to implementing compost application, and assessing ranchers’ perspectives on the ecological and socioeconomic feasibility of implementing compost application practices. I will deliver surveys both electronically and via mail to reach as broad an audience as possible.
Surveys will be sent to ranchers once data and analysis have been completed for this project. Surveys will focus on gaining insights into rancher perspectives and reception to climate-smart ranching practices. I will begin sending surveys to ranch managers in Amador, Plumas, Sierra, Yuba, and Butte Counties in Fall and Winter, 2024. will coordinate with UCCE partners to distribute surveys online via Qualtrics. Since receiving this Western SARE grant, I have completed my IRB application and SOW, and received IRB approval for the project (IRB ID No. 1995095-1).
In the Fall and Winter of 2024, I will assess adaptive capacity and rancher openness to compost application practices, and analyze survey results via a variety of statistical methods in R. Specifically, I will determine how different facets of ranching operations (e.g., geographic location, access to compost application resources, economic sustainability, rancher interest) impact barriers to adoption utilizing multiple logistic regression with model averaging following Kachergis et al. (2014), and Lubell et al. (2018).

Research Methods for Objective 4, Collaborate with and communicate results to ranchers, and key stakeholders 

Please see the Educational Outreach Plan below, for Objective 4 research methods. I will begin addressing objectives outlined in my Education and Outreach Plan, and sharing research results following soil sampling and analysis (in the Fall-Winter of 2024).



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amendments: Do they confer stability against drought on the soil microbial community? Soil Biology and Biochemistry, 113, 173–183. 

Breshears, D. D., Knapp, A. K., Law, D. J., Smith, M. D., Twidwell, D., & Wonkka, C. L.
(2016). Rangeland Responses to Predicted Increases in Drought Extremity. Rangelands, 38(4), 191–196. 

Buckley Biggs, N., Hafner, J., Mashiri, F. E., Huntsinger, L., & Lambin, E. F. (2021). Payments
for ecosystem services within the hybrid governance model: Evaluating policy alignment and complementarity on California rangelands. Ecology and Society, 26(1), art19.

Cusack, D. F., Kazanski, C. E., Hedgpeth, A., Chow, K., Cordeiro, A. L., Karpman, J., & Ryals,
R. (2021). Reducing climate impacts of beef production: A synthesis of life cycle assessments across management systems and global regions. Global Change Biology, 27(9), 1721–1736. 

Dubey, R.K. et al. (2020). Methods for Exploring Soil Microbial Diversity. In:
Unraveling the Soil Microbiome. SpringerBriefs in Environmental Science. Springer, Cham. 

Girden, E. R. (1992). ANOVA: Repeated measures. Sage.

Gravuer, K., Gennet, S., & Throop, H. L. (2019). Organic amendment additions to rangelands: A
meta‐analysis of multiple ecosystem outcomes. Global Change Biology, 25(3), 1152–1170. 

Havstad, K.M., Peters, D.P.C., Skaggs, R., Brown, J., Bestelmeyer, B., Frederickson, E.,Herrick,
J., Wright, J., (2007). Ecological services to and from rangelands of the United States. Ecology Economics 64, 261–268.

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al. (2001). Large-scale forest girdling shows that current photosynthesis drives soil respiration. Nature, 411, 789–792.


Howitt, R.E.j, Medellín-Asuara, D., Macewan, J.R., Lund, Sumner, D.A. (2015).
Economic analysis of the 2015 drought for California agriculture. Davis, California, USA: Center for Watershed Sciences, University of California, Davis: p. ES-2, 12.

Kachergis, E., J. D. Derner, B. B. Cutts, L. M. Roche, V. T. Eviner, M. N. Lubell, and K. W. 7
Tate. (2014) . Increasing flexibility in rangeland management during drought. Ecosphere 5. 8. 

Kuznetsova, A., P. B. Brockhoff, and R. H. B. Christensen (2017). lmerTest package:
Tests in linear mixed effects models. Journal of Statistical Software. 82:1–26.

Lal, P., H. Lim-Applegate, and M. Scoccimarro. (2001). The adaptive decision-making process as a tool for integrated natural resource management: focus, attitudes, and approach. Conservation Ecology 5(2): 11.

Lubell, M. N., Cutts, B. B., Roche, L. M., Hamilton, M., Derner, J. D., Kachergis, E., &
Tate, K. W. (2013). Conservation Program Participation and Adaptive Rangeland Decision-Making. Rangeland Ecology & Management, 66(6), 609–620.

Macon, D. K., Barry, S., Becchetti, T., Davy, J. S., Doran, M. P., Finzel, J. A., George, H.,
Harper, J. M., Huntsinger, L., Ingram, R. S., Lancaster, D. E., Larsen, R. E., Lewis, D. J., Lile, D. F., McDougald, N. K., Mashiri, F. E., Nader, G., Oneto, S. R., Stackhouse, J. W., & 

Roche, L. M. (2016). Coping With Drought on California Rangelands. Rangelands, 38(4), 222–228.

McFarland, M. J., Vasquez, I. R., Vutran, M., Schmitz, M., & Brobst, R. B. (2010). Use of
Biosolids to Enhance Rangeland Forage Quality. Water Environment Research, 82(5), 455–461. 

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year 2022. Available at: Publications/California_Ag_Statistics/2012cas-ovw.pdf.Accessed 23 Nov 2022.

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Report. Contribution of Working Groups I, II and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. J. Roman. Stud. 2014, 4, 85–88.

Piotrowska-Długosz A., Długosz J., Frąc M., Gryta A., Breza-Boruta B. (2022). Enzymatic
activity and functional diversity of soil microorganisms along the soil profile – a matter of soil depth and soil-forming processes. Geoderma 416:115779.

Rillig, M.C. & Mummey, D.L. (2006). Mycorrhizas and soil structure. New Phytol., 171, 41–53.

Roche, L. M., Schohr, T. K., Derner, J. D., Lubell, M. N., Cutts, B. B., Kachergis, E.,
Eviner, V. T., & Tate, K. W. (2015). Sustaining Working Rangelands: Insights from Rancher Decision Making. Rangeland Ecology & Management, 68(5), 383–389.

Roche, L.M. (2016). Adaptive rangeland decision-making and coping with drought.
Sustainability. 8:1334. Rangelands, 38(4), 191–196. 

Saitone, T.L. (2020). Chapter 9. Livestock and Rangeland in California. California Agriculture:
Dimensions and Issues. 207-223. 

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Engineering drought tolerance in plants: Discovering and tailoring genes to unlock the future. Curr. Opin. Biotechnol, 17, 113–122.

van der Heijden MGA, Bardgett RD, van Straalen NM. 2008. The unseen majority: soil
microbes as drivers of plant diversity and productivity in terrestrial ecosystems. Ecol. Lett, 11:296–310. 

Wagg, C., Yann H., Pellkofer, S., Banerjee, S., Schmid, B., van der Heijden, M.A.,
(2021) Diversity and asynchrony in soil microbial communities stabilizes ecosystem functioning. eLife 10(62) 813.

Wang et al. (2007) Wang Q, Garrity GM, Tiedje JM, Cole JR. Naive Bayesian classifier for rapid
assignment of rRNA sequences into the new bacterial taxonomy. Applied and Environmental Microbiology. 2007;73(16):5261–5267.

Xiao F, Li Y, Li G, He Y, Lv X, Zhuang L, Pu X. (2021) . High throughput sequencing-based
analysis of the soil bacterial community structure and functions of Tamarix shrubs in the lower reaches of the Tarim River. PeerJ 9. 

Yahdjian, L., Sala, O. E., & Havstad, K. M. (2015). Rangeland ecosystem services: Shifting focus from supply to reconciling supply and demand. Frontiers in Ecology and the Environment, 13(1), 44–51. 

Research results and discussion:

Field work (soil sampling) and soil analysis (PLFA and enzyme assays) are currently in progress. Soil sampling will be completed by June, 2024, and soil microbial analysis will be completed by July, 2024

Participation Summary
8 Producers participating in research

Research Outcomes

Recommendations for sustainable agricultural production and future research:

Recommendations for sustainable ranching informed by this project will be made once data collection and analysis has been completed (Fall 2024). Additionally, recommendations from this work will be based on analysis of surveys for rancher receptiveness and barriers to adoption. This information will be obtained by Winter 2025. Once soil sampling and analysis has been completed, recommendations will be made based on how compost and seeding practices alter soil microbial community composition as well as rancher receptiveness to adopting these practices.

3 Grants received that built upon this project
2 New working collaborations

Education and Outreach

Participation Summary:

Education and outreach methods and analyses:

Follow soil microbial analysis, I will communicate all results and key findings from this project with stakeholders and producers starting in the Winter of 2024. I will do this by synthesizing the data from this work so that it is comprehensible, and can be quickly and easily accessed.

Winter 2024: Begin planning extension workshops and outreach events for ranchers and local community members. 

January 2025: Host extension workshops to communicate results to ranchers

I will host two workshops to share results from this project with collaborating ranchers, and other ranchers in Northeastern California. I will work closely with UCCE professions to plan extension workshops. Specifically, I will focus on ensuring that all workshops are focused on information and data obtained from this study that is most relevant and helpful for ranchers interested in applying climate smart agricultural practices such as compost applications and seeding. 

The itinerary for these workshops will include: (1) Overview of the data and results from this study, and implications of these results for ecological and economic sustainability, (2) break out sessions for ranchers to discuss and develop protocols for integrating climate smart ranching practices into their management regimes that maintain economic sustainability, (3) Open forum style Q & A, and discussion of the results and adaptive capacity to apply climate smart ranching practices, and (4) Social and networking opportunities for ranchers interested in climate smart practices to connect and share ideas.

At these workshops, all participants will receive (1) a one-page, synthesized summary of key results from this study, (2) a one-page resource sheet containing information with resources to find further information about compost application practices, other groups currently investigating compost application practices (e.g., The Working Lands Innovation Center, CalCal Healthy Soils initiative), and access to information about other climate smart ranching practices (e.g., prescribed burning, strip seeding). Information on these handouts will also be uploaded to the UC Rangelands Research and Information Center, which receives ~2K page views/month from 160 countries around the world. Preceding these extension workshops, ranchers will be sent follow-up surveys to determine the efficacy of the information and resources provided, and areas for improvement at future outreach events.

Additionally, we will work with partners such as California Cattlemen’s Association, state and federal agency partners, and nonprofits to provide outreach via legislative bulletins, newsletters, and trade magazines (e.g., Progressive Cattleman). We will develop presentation materials to share at producer meetings (California Cattlemen’s Association & Cattle Women's Inc Convention), local UCCE workshops, and professional and scientific meetings (e.g., Society for Range Management).

Summer 2025: Education & outreach for land owners, land managers, and NGO staff
I will collaborate with ranchers involved in this research and UCCE advisors to create presentation materials to share at producer meetings, local UCCE workshops, and professional and scientific meetings (e.g., Society for Range Management) for land owners, land managers, and NGO staff. I will also develop a non-academic article that will be published in an advisor newsletter to clientele. I will communicate the results of this research, and provide information about goals and future directions for research related to soil health and drought resilience in California.

Education and outreach results:

Following completion of soil microbial analysis (to be completed in June, 2024), I will begin planning and executing educational outreach and extension workshops for ranchers and stakeholders starting in Winter 2024. 

Workshops will focus on communicating results and findings once I have completed all soil microbial analysis. I will host two workshops to share results from soil analysis with collaborating ranchers, UCCE advisors, and other ranchers in Northeastern California. I will work closely with UCCE professions to plan extension workshops. Specifically, I will focus on ensuring that all workshops are focused on information that is most relevant and helpful for ranchers interested in applying climate smart agricultural practices. Once workshops have been attended by ranchers, I will conduct and send out follow-up surveys to quantify the efficacy and experiences of ranchers and stakeholders who attended these workshops, and determine methods to improve upon outreach activities I host moving forward.  

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.