Final report for GW23-254
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 examined how compost application impacted soil microbial abundance and community composition on ranches. Soil microbes are essential in key processes that determine soil quality and health; soil health, in turn, impacts forage productivity and improves rangeland resilience to drought conditions. Throughout this project, we worked with ranchers and UCCE advisors to communicate results via on-ranch research and extension workshops. Project outcomes were 1) determining impacts of compost applications on soil microbial ecology, 2) assessing social barriers to adoption, and 3) collaborating and sharing results with stakeholders.
Our overarching goal for this project was to determine the potential of rangeland compost application as a climate-smart ranching practice to manage soils for increased resilience to prolonged drought, water scarcity, and other environmental challenges in California.
Objective 1: Measure impacts of integrated compost application and clover seeding on soil microbial biomass and community composition
We worked with ranchers and UC Cooperative Extension (UCCE) collaborators who had previously applied compost and clover seeding amendments to their land at a variety of sites. 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 was therefore to determine how compost amendments and clover seeding impacted the soil microbiome. We collected soil samples from each site to measure variation in total soil microbial biomass and microbial community composition between sites. We then analyzed these results to assess the potential impacts of compost application practices on 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 impact soil health metrics and large-scale ecosystem processes (Wagg et al. 2021). Examining impacts of soil microbial diversity on key soil health metrics could potentially serve as a proxy for drought resilience. We therefore analyzed soil samples collected from all sites for key soil health metrics relevant to improving resilience to drought and increasing water uptake and retention. We measured variation in soil organic matter, soil organic carbon, soil nitrogen, bulk density, and gravimetric water content between sites. This allowed us to determine whether variation in microbial abundance and community composition had an impact on key soil health metrics.
Objective 3: Assess adaptive capacity and potential barriers to adopting compost application as a climate-smart ranching practice
We collaborated with UCCE advisors to create and distribute surveys in order to assess adaptive capacity for implementing compost amendment practices, as well as other potential climate-smart ranching practices (e.g., prescribed burning, strip seeding, livestock species rotation). We built on previously successful initiatives within our lab group using surveys to gauge rancher perspectives on barriers to adopting sustainable ranching practices (Roche et al. 2015). We are currently developing these surveys based 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, we leveraged established relationships with UCCE professionals to provide workshops, demonstrations, and resources for ranchers in counties across California. This project included collaborations with UCCE researchers who had partnerships with ranchers who had applied compost and clover seeding to their land or had expressed interest in implementing composting practices on their land.
A no cost extension for this project (GW23-254) was approved on April 29th, 2025. The approved project end date following this no cost extension was December 31st, 2025. The approved project modification form, including the new timeline, is attached here: Project Modification Form
Cooperators
- - Producer
- - Producer
- - Producer
Research
Project Sites: PT Ranch (Ione, CA) , Curran Ranch (Ione, CA), Dell’Orto Ranch (Jackson, CA), Brownlie Ranch (Jackson, CA)
Research Methods for Objective 1: Soil Microbial Analysis
To investigate how compost amendments affected soil microbial biomass and community structure, we collected 98 soil samples across four ranches in Amador County, California. This work was conducted in close collaboration with UC Cooperative Extension, which facilitated connections with local ranchers and supported site selection. The chosen ranches represented a gradient in elevation and soil productivity (low to high). Sampling locations built upon a previous Western SARE project (OW19-349), allowing for continuity and comparative analysis.
Soil sampling occurred between March and June 2024, coinciding with peak aboveground biomass to best capture seasonal microbial activity. At each site, soil was collected from plots representing four different treatments: 1) compost application only, 2) compost application and seeding mixture, 3) seeding only, and 4) control (no compost or seeding).
Sampling locations were randomly selected within each of the 12 treatment plots at each site. No samples were taken from beneath tree cover to account for variability due to islands of fertility. Soils at each location were collected from surface soils (0-15cm depth), and subsurface soils (15-30cm depth). Samples for microbial analysis were placed in ice coolers during the collection period. All samples used for enzyme assays and PLFA were composited by plot and depth (4 samples per plot, 2 depths), and placed in a -20 °C freezer immediately upon arrival to the lab. Composited samples were thoroughly homogenized, and 200g of soil was weighed to ship to Ward Laboratories (Kearney, NE) for PLFA and enzymatic assays. Frozen samples were shipped within a week of collection on dry ice to maintain adequate temperatures for analysis.
Phospholipid Fatty-Acid Analysis (PLFA):
Phospholipid Fatty-Acid Analysis (PLFA) allowed for the identification of key microbial functional groups. Samples were analyzed at Ward Laboratories (Kearney, NE) to quantify total living soil microbial biomass and the presence of microbial functional groups using extraction and identification of phospholipid fatty-acid biomarkers (Cavigelli et al. 1995; Dierksen et al. 2002). Phospholipids were separated using solid-phase extraction before undergoing transmethylation, which released fatty acid methyl esters (FAMEs). FAMEs were then used to create fatty acid profiles for functional group identification and quantification via gas chromatography.
The functional groups identified from FAMEs were: 1) gram-positive bacteria, 2) actinomycetes, 3) gram-negative bacteria, 4) rhizobia, 5) arbuscular mycorrhizal fungi, 6) saprophytes, 7) protozoa, 8) saturated:unsaturated fatty acids, and 9) monounsaturated:polyunsaturated fatty acids. These functional groups were then used to create community composition ratios, which provided information about functional changes in soil conditions such as C:N ratios, organic matter decomposition, soil moisture, nutrient cycling, and levels of environmental stress and soil disturbance (Dierksen et al. 2002).
Extracellular Enzyme activity
Extracellular enzyme activity was used to quantify microbial activity and further identify community composition (Ward Laboratories, Kearney, NE; Sinsabaugh et al. 2009; Yao et al. 2023). Soil microbes release extracellular enzymes as a mechanism to digest and break down organic compounds such as carbon, nitrogen, and phosphorus into simpler inorganic forms (e.g., through decomposition and mineralization). Quantifying the activity of different enzymes in the soil therefore provided salient information about the functional diversity and activity of the soil microbiome.
Samples were tested for: 1) beta-glucosidase (indicative of carbon cycling), 2) N-acetylglucosaminidase (indicative of nitrogen cycling), and 3) phosphodiesterase (indicative of phosphorus cycling). Analysis was conducted via substrate consumption and product fluorescence. Calibration of enzyme activity was conducted by producing standard curves for each sample using Ward Laboratories’ standard methods.
Working with our collaborators, we compiled all data into the project database, which included pre- and post-treatment plant community data, management treatment information, and results of soil microbial, chemical, and physical analyses. All soil chemical and physical lab analyses where completed by our collaborators in the California Soil Resources Laboratory. Working with the project team, we analyzed how management treatments affected soil microbial abundance and composition across ranches spanning a range of ecological sites. We used a variety of statistical tools, including analysis of variance, linear mixed models, and multivariate methods (e.g., Principal Component Analysis, NMDS, PERMANOVA), to determine variation in microbial ecology between sites and the degree to which management drove changes in soil microbial ecology and soil health. Analysis of soil microbial data was completed, and results were finalized. A full draft manuscript of this study, led by Ava-Rose Beech, was scheduled to be completed by April 2026 and submitted for publication by June 2026.
Research Methods for Objective 2: Analysis of soil health metrics related to drought resilience
Sample collection and analysis for soil health metrics were completed in the summer of 2024 in partnership with our collaborators in the UC Davis California Soil Resources Laboratory. Statistical analyses of key soil health metrics relevant to drought resilience—including soil organic matter, soil organic carbon, bulk density, gravimetric water content, aggregate stability, total NPK, MAOM, and POM—were completed in summer 2024. These results were synthesized by our collaborator, PhD student Alyssa Flores, in the California Soil Resources Laboratory. The manuscript led by Alyssa Flores outlining these soil health results was completed and was in preparation for publication.
Statistical analysis determining how key soil health metrics (see above) vary based on soil microbial abundance and diversity at each site is currently in progress. We are currently conducting statistical analysis in R, using linear mixed models as well as an array of multivariate statistical methods, to assess the degree to which variation in soil health characteristics is related to microbial abundance, microbial diversity, and management practices. Results to date from this analysis are included in the results section below, and these finalized results will be included in the manuscript led by Ava-Rose Beech, to be submitted in April 2026. This analysis will help determine whether soil microbial communities contribute to enhanced rangeland drought resilience, with soil health metrics related to water uptake and retention used as indicators of drought resilience.
Research Methods for Objective 3: Assess rancher receptivity and barriers to adoption
Data analysis and results for this study have been finalized as of January, 2026. We are now planning a UC Cooperative Extension Soil Health Field Day on March 20, 2026 in Jackson, California in collaboration with UC Cooperative Extension, the California Soil Resources Laboratory, and the UC Davis Functional Ecology Lab to share key results and findings with local operators and community members. As part of this event, surveys will be shared and used to assess rancher receptiveness towards adopting compost amendment practices in California rangelands. We are collaborating with UCCE advisors to develop these surveys. This objective is based on previously successful initiatives using surveys to evaluate rancher decision making (Roche, 2016). Surveys topics will include: 1) assessment of ranchers’ interest in adopting compost application practices, 2) priority concerns from ranchers to adopting these practices, 3) evaluating rancher perspectives on the socioeconomic barriers of greatest importance to implementing compost application, and 4) assessing ranchers’ perspectives on the ecological and socioeconomic feasibility of implementing compost application practices. We will deliver surveys both in person during our UC Cooperative Extension Soil Health Field Day, as well as electronically, via Qualtrics, to reach as broad an audience as possible. Working with UCCE collaborators, we will also share these surveys at other relevant local soil health workshops, allowing us to gain further insight into rancher and stakeholder perspectives. Since receiving this Western SARE grant, we have completed IRB application and SOW, and received IRB approval for the project (IRB ID No. 1995095-1).
Research Methods for Objective 4: Collaborate with and communicate results to ranchers, and key stakeholders
Recommendations for ranchers and land managers will be based on results and statistical analyses from the UC Rangelands Lab and the California Soil Resources Laboratory. We have already shared these findings at multiple conferences and will continue discussing them with ranchers and stakeholders at our in-person Cooperative Extension Soil Health Field Day, which will take place on March 20, 2026, in Amador County, CA. Additionally, results from this work have already been shared with ranchers and fellow researchers at eight conferences. Most recently, completed results from this study were presented to scientists, ranchers, and stakeholders at the 2026 Society for Range Management Annual Meeting. Please see the Educational Outreach Plan below for our complete methods, outlines, and plans for Objective 4.
References:
Bastida, F., Torres, I. F., Hernández, T., & García, C. (2017). The impacts of organic 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.
Cavigelli, M. A., Robertson, G. P., & Klug, M. J. (1995). Fatty acid methyl ester (FAME) profiles as measures of soil microbial community structure. Plant and Soil, 170, 99–113.
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.
Dierksen, K. P., Whittaker, G. W., Banowetz, G. M., Azevedo, M. D., Kennedy, A. C., Steiner, J. J., & Griffith, S. M. (2002). High resolution characterization of soil biological communities by nucleic acid and fatty acid analyses. Soil Biology and Biochemistry, 34(12), 1853–1860.
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.
Hogberg, P., Nordgren, A., Buchmann, N., Taylor, A.F.S., Ekblad, A., Hogberg, M.N. et 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.
National Agricultural Statistics Service. California. California agricultural statistics, crop year 2022. Available at: http://www.nass.usda.gov/Statistics_by_State/California/ Publications/California_Ag_Statistics/2012cas-ovw.pdf.Accessed 23 Nov 2022.
Pachauri, R.; Reisinger, A.; Barros, V.R.; Broome, J. (2014). Climate Change: Synthesis 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.
Sinsabaugh, R. L., Hill, B. H., Follstad, Shah, J. J. (2009). Ecoenzymatic stoichiometry of microbial organic nutrient acquisition in soil and sediment.
Umezawa, T.; Fujita, M.; Fujita, Y.; Yamaguchi-Shinozaki, K.; Shinozaki, K. (2006). 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.
Yao, B., Wang, X., Li, Y., Lian, J., Li, Y., Luo, Y., & Li, Y. (2023). Soil extracellular enzyme activity reflects the change of nitrogen to phosphorus limitation of microorganisms during vegetation restoration in semi-arid sandy land of northern China. Frontiers in Environmental Science, 11, 1298027.
Objective 1 Results: Measure impacts of compost application and forage seeding to soil microbial biomass and community composition
Across all microbial variables and treatments, soil characteristics were consistently the strongest driver of significant variation in microbial community composition. We assessed ordination of soil microbial communities across treatments and soil series using Non-Metric Multidimensional Scaling (NMDS) analyses based on a Bray–Curtis dissimilarity metric. Our NMDS results demonstrated a high degree of ordination by soil series (Figure 1), but not by treatment (Figure 2).
We statistically confirmed our NMDS results with a PERMANOVA using the same Bray–Curtis dissimilarities to test the effects of treatment and soil series on PLFA variables. Our PERMANOVA analysis indicated that treatments did not drive significant community-level differences in microbial composition (PERMANOVA, F₃,₄₄ = 0.59, R² = 0.039, p = 0.816). However, soil series did significantly shape differences in soil microbial communities (PERMANOVA, F₃,₄₄ = 18.57, R² = 0.559, p = 0.001).
Results from our linear mixed-effects models confirmed these findings. In upper depth soils (0–15 cm), soil type had a significant impact on shaping soil microbial community structure (p < 0.05), and treatment effects on PLFA variables were site-specific. Across all variables, soil type had a stronger effect than treatment on PLFA indicators.
However, clover seeding treatment alone (t = 2.728, df = 24.000, p = 0.011722) significantly increased the predator-to-prey ratio, specifically in soils from the Nedsgulch series (Figure 3). Clover seeding treatment alone also increased the predator-to-prey ratio at the site consisting of Pentz soils (t = 2.338, df = 24.000, p = 0.028). Protozoan biomass likewise increased with seeding treatment specifically in the Nedsgulch soil series, but not at other sites (t = 2.353, df = 24.00, p = 0.02716, Figure 4).
However, clover seeding treatment alone (t = 2.728, df = 24.000, p = 0.011722) significantly increased the predator to prey ratio, specifically in soils from the Nedsgulch series (Figure 3). Clover seeding treatment alone also increased the predator to prey ratio at the site consisting of Pentz soils (t =2.338, df =24.000, p = 0.028). Protozoan biomass also increased with seeding treatment specifically in the Nedsgulch soil series, but not at other sites (t = 2.353 , df = 24.00, p = 0.02716, Figure 4).
Of the four PLFA variables indicative of environmental stress, we found significant differences in the pre-16:cyclopropane fatty acid ratio across sites. Compost application alone (t = -3.228, df = 24.00, p = 0.00359) and seeding treatment alone (t = -3.228, df = 24.00, p = 0.03171) decreased the pre-16:cyclopropane fatty acid ratio (Figure 5). Pairwise comparison results for the pre-16:cyclopropane fatty acid ratio demonstrated that the direction of treatment effects varied when considering interactions between treatments and sites. In Nedsgulch soils, compost application alone increased the pre-16:cyclopropane fatty acid ratio (t = 2.111, df = 24.00, p = 0.045). Similarly, the interaction between seeding treatment alone and site in the Auburn soil series increased the pre-16:cyclopropane fatty acid ratio (t = 2.351, df = 24.00, p = 0.02728), differing from the non-interactive negative effect of seeding treatment.
Objective 1 Results: Measure the effect of compost application and forage seeding on soil extracellular enzyme activity
Results from linear mixed-effects modeling of soil extracellular enzyme activity indicated greater variation in lower-depth soils compared to upper-depth soils. We analyzed both the separate and interactive effects of treatment and site on beta-glucosidase, N-acetylglucosaminidase (NAG), and phosphodiesterase activity in both upper and lower depth soils. Analysis of soil enzyme activity provided important information about microbial activity and nutrient cycling, including carbon breakdown (indicated by beta-glucosidase activity), nitrogen processing (indicated by NAG activity), and phosphorus release (indicated by phosphodiesterase activity).
We found that integrated compost and seeding treatment significantly lowered beta-glucosidase activity in lower-depth soils, but only in Auburn soils (β = -24.667, SE = 10.729, df = 24.000, t = -2.299, p = 0.0305). Overall, however, beta-glucosidase activity was significantly higher in Auburn soils compared to Pardee soils, the lowest productivity site (β = 28.667, SE = 9.957, df = 24.000, t = 2.879, p = 0.008; Figure 6).
Additionally, N-acetylglucosaminidase activity varied significantly across soils, but not treatments. NAG activity was significantly greater in Nedsgulch soils (β = 7.067, SE = 2.902, df = 28.211, t = 2.436, p = 0.021) and in Auburn soils (β = 6.733, SE = 2.902, df = 28.211, t = 2.321, p = 0.028) compared to Pardee soils (Figure 7). Neither treatment application nor site had a significant effect on beta-glucosidase, NAG, or phosphodiesterase activity in upper-depth soils.
These results indicate that soil type and depth strongly influence patterns of carbon and nutrient cycling. Although treatment did not play a major role in altering soil enzyme activity across most sites, the finding that compost and seeding reduced beta-glucosidase activity in Auburn soils alone further emphasizes the importance of soil context in driving these effects. The strong influence of soil series suggests that responses to compost and seeding management may vary depending on baseline soil morphology and biological conditions, and that these inherent characteristics should be considered when applying treatments. Furthermore, the depth-dependent patterns in soil enzyme activity highlight the importance of long-term monitoring and evaluating subsurface soil conditions when assessing the effects of management practices on soil health metrics.
Objective 2 Results: Determine potential of compost application to increase drought resilience in rangelands via key soil health metrics
Field work and all soil analysis of key soil health metrics was completed in June, 2024. Analysis of soil samples and statistical analyses was completed by our collaborating partners in the California Soil Resources Laboratory. These analyses indicated that differences in ecological site characteristics, including elevation and soil morphology, influence the effects of compost applications (California Soil Resources Lab, In prep). Higher elevation sites exhibited the greatest increases in soil carbon and nitrogen, as compared to lower elevation sites. Overall, soil and site level characteristics had a stronger effect in shaping soil chemical and physical properties than treatment effects. These results have been finalized and the completed manuscript of this data, prepared by PhD student Alyssa Floress, will be submitted for publication in the coming month.
Preliminary analysis is in progress to assess the relationship between soil health metrics, and soil microbial community composition. To date, we have observed strong trends in soil microbial variables associated with higher organic matter and carbon, which correlate with soil chemical and physical properties characteristic of more productive soil types (Figure 8). These preliminary findings are consistent with results from Objective 1, and with finalized analyses from our collaborators outlined above, indicating that relationships among soil health indicators and microbial metrics vary more strongly by soil series than by treatment.
Impact of compost and seeding treatments on plant functional groups
Working with collaborator UCCE advisor Scott Oneto, we analyzed data from the Western SARE project OW19-349 and collected additional plant species community composition data in 2024. This collaboration allowed us to build upon and continue research from previously funded Western SARE work. We found that baseline abundances of plant species functional groups from 2020, immediately preceding treatment application, differed across all four ranches included in the study, reflecting variation in the soil types represented in our sites.
We employed generalized linear latent variable model (GLLVM) analysis to assess variation in plant functional groups across treatments. These analyses demonstrated that both treatment and soil series significantly influenced plant functional group composition (Table 1, Figure 9). Highly invasive species decreased significantly under combined compost and seeding treatments, with lower expected abundances relative to control plots (β = –0.48 ± 0.15, p = 0.001). Across all sites and treatment applications, seeded clover species increased significantly relative to the control, with the strongest increase observed in integrated compost and seeding plots (β = 1.55 ± 0.24 SE, p < 0.001).
Additionally, plots that received compost application showed decreases in both nonnative naturalized grasses (β = –0.42 ± 0.16, p = 0.01) and native grass abundance (β = –0.46 ± 0.23, p = 0.049). Nonsignificant decreases in highly invasive species occurred across all treatments, indicating a general trend toward reduced invasive species abundance, with negative estimates observed under compost-only treatments (β = –0.107) and seed-only treatments (β = –0.246).
Table 1. Significant results from the Generalized Linear Latent Variable Model (GLLVM) assessing treatment effects on plant functional group abundances.
| Functional Group | Seed Only (β ± SE) | Compost Only (β ± SE) | Compost + Seed (β ± SE) |
| Highly Invasive | −0.25 ± 0.14 | −0.11 ± 0.14 | −0.48 ± 0.15 |
| Native Forb | −0.14 ± 0.32 | 0.36 ± 0.29 | 0.38 ± 0.29 |
| Native Grass | −0.36 ± 0.23 | −0.46 ± 0.23 | −0.31 ± 0.23 |
| Nonnative Forb | 0.07 ± 0.24 | 0.03 ± 0.24 | 0.10 ± 0.24 |
| Nonnative Grass | 0.00 ± 0.15 | −0.42 ± 0.16 | −0.28 ± 0.16 † |
| Seeded Clover | 0.72 ± 0.25 | 0.74 ± 0.25 | 1.55 ± 0.24 |
Objective 3 Results: Assess adaptive capacity and potential barriers to adopting compost application as a climate smart ranching practice
The analysis of results for objective 3 (assessing adaptive capacity and identifying potential barriers to adoption) will be completed following the conclusion of our March 20 Cooperative Extension Soil Health Field Day, and the distribution and collection of rancher surveys in Spring, 2026.
The delay in completing and finalizing results for Objective 3 is due to the reasons previously outlined by our project team in the no-cost extension and project modification form submitted in April 2025. We requested this extension to accommodate delays resulting from the federal funding freeze that began in January 2025. As a result of the freeze, we paused spending on the grant, which in turn impacted the timeline for project activities related to outreach workshops, survey distribution, and assessments of rancher adaptive capacity. These final activities for Objective 3 are currently in progress, and final results for this objective are expected by August 2026.
Objective 4 Results : Collaborate with and communicate results to ranchers, and key stakeholders
As of January 2026, we have shared results and project updates with a range of stakeholders at multiple outreach, extension, and education events, including the Western SARE CAPS Summit, the UC Davis Institute for the Environment Symposium, the California Native Grassland Association Seminar Series, the 2025 Society for Range Management Annual Meeting, the 2026 Society for Range Management Annual Meeting (posters and presentations presented by Ava-Rose Beech), and the California Rangeland Conservation Coalition (poster presented by Alyssa Flores).
Additionally, our project team collectively presented results from this project at the Rustici Rangeland Science Symposium, led by Dr. Leslie Roche. Dr. Anthony O’Geen delivered a keynote talk on this research, while Ava-Rose Beech and Alyssa Flores presented research posters.
All project collaborators, including Dr. Leslie Roche, Dr. Anthony O’Geen, Scott Oneto, Ava-Rose Beech, and Alyssa Flores, along with participating ranchers, will be hosting a Soil Health Field Day on March 20 to share final project results, findings, and recommendations.
Research outcomes
Integrated compost and forage seeding are valuable management practices with potential benefits for improving soil organic matter, water infiltration, and forage productivity, all of which can enhance rangeland resilience to drought stress. Recommendations for sustainable rangeland management informed by this project are based on our comprehensive analysis of soil microbial, chemical, and physical characteristics.
Our results from this study demonstrated that integrated compost and clover seeding altered key indicators of soil food web structure, including predator-to-prey ratios and protozoan biomass. The integrated treatment also influenced microbial stress responses and growth states, suggesting that compost and seeding can drive meaningful changes in soil food web composition and function. Predator-to-prey ratios reflect the balance between microbial predators, such as protozoa, and their bacterial prey, providing insight into the overall activity and efficiency of nutrient cycling in the soil. Microbial stress ratios indicate the proportion of microbes experiencing environmental or resource stress, which can provide salient information regarding limitations in soil nutrient availability or physical conditions. These bottom-up effects are highly relevant to rancher productivity, as soil microbial dynamics strongly influence soil organic matter accumulation, nutrient cycling, and forage productivity.
Although microbial responses varied across sites, observed changes in predator-to-prey ratios and protozoan biomass indicate that these treatments may be effective management strategies for nutrient-depleted soils or for enhancing nutrient mineralization. However, our results underscore that responses to compost and seeding are highly dependent on soil type, and these site-specific effects should be carefully considered before ranchers implement similar management strategies. It is important to note that this study reflects the results of a single, one-time application of compost and seeding. We therefore strongly recommend further research on the long-term impacts of repeated treatments in order to fully understand the potential benefits and limitations of these rangeland management methods. Importantly, soil series had a stronger influence on whole-community microbial composition than treatment alone, emphasizing that ecological site and inherent soil characteristics are critical factors to consider when designing management plans or applying compost and seeding treatments.
Collaborative analyses from the California Soil Resources Laboratory indicated that treatment effects on soil carbon and nitrogen dynamics were highly site-specific. These findings reinforce that while integrated compost application and clover seeding can improve soil biological and chemical metrics, outcomes depend strongly on soil series and the ecological context of each ranch. Managers should carefully consider these site-specific characteristics when planning and implementing treatments.
In addition, working with our collaborator Scott Oneto, our results aligned with previous Western SARE work from project OW19-349. Integrated compost and seeding treatments led to a significant decrease in highly invasive species and a significant increase in clover forage species. These effects were site-specific and varied across the soil series included in the study. These findings offer promising indication that integrated compost and clover seeding may be an effective tool to reduce invasive species in California's annual grasslands, increase beneficial forage species, and potentially provide benefits to soil microbial communities that drive soil health processes. However, we recommend further long-term studies to gain a more comprehensive understanding of these results.
Further recommendations for these practices will be refined based on rancher survey responses regarding receptiveness and barriers to adoption, which will be collected following the March 2026 Cooperative Extension Soil Health Field Day. These combined results provide a clear, science-based foundation for sustainable rangeland management practices that integrate soil health, forage production, and ecological resilience to environmental stress.
Education and Outreach
Participation summary:
We have shared all results and key findings from this project with stakeholders, rangeland managers, and other researchers at a total of eight conferences and events over the past two years. We will synthesize the data from this work to make it clear, accessible, and easy to reference, and share these resources via multiple online sources, and via publication in multiple academic journals. All event planning and preparation for our UC Cooperative Extension Field Day has been finalized by our team. We have prepared for and met multiple outreach and educational milestones for these outreach efforts based on the timeline below.
July-August 2025: Began initial planning of extension workshops and developing materials for outreach events for ranchers and local community members.
September- October 2025: Worked with UC Cooperative Extension partners, and collaborators in the California Soil Resources Laboratory to coordinate extension events. This included preparing all materials, creating informational pamphlets and handouts, and setting dates and locations for extension events.
November-December 2025: Finalized all details for extension events. Print and prepare materials, finalize all event logistics, materials, and agendas. Send out advertisements for the event, schedules, and agendas.
In collaboration with Cooperative Extension, we will coordinate one extension event to share results from this project with a range of stakeholders . The itinerary for these events 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 sustainable rangeland management 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 sustainable rangeland management, and (4) Social and networking opportunities for ranchers interested in sustainable rangeland management practices to connect and share ideas.
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 sustainable rangeland management 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 additionally develop presentation materials to share at professional and scientific meetings (e.g., Society for Range Management).
Participation Summary:
Our project team shared has shared results and project updates with a range of stakeholders at multiple outreach and extension events, including the Western SARE CAPS Summit, the UC Davis Institute for the Environment Symposium, the California Native Grassland Association seminar series, the 2025 and 2026 Society for Range Management Annual Meeting, and the California Rangeland Conservation Coalition. We collectively presented results from this project at the 2025 Rustici Rangeland Science Symposium. Dr. Anthony O’Geen presented a keynote talk on this research, and Ava-Rose Beech and Alyssa Flores presented research posters. We will be hosting a Soil Health Field Day with multiple speakers and collaborators in March, 2026. This event will provide a comprehensive overview of results as our final outreach and extension education event. Additionally, ranchers have been actively involved in the research since its inception, due to the on-ranch nature of the project.