Progress report for GW20-203
Soil carbon (C) sequestration is a top priority for regenerative ranchers, researchers, and policy makers in California. Adaptive multi-paddock (AMP) grazing, characterized by short-duration, high intensity grazing events, is a promising grazing management strategy for increasing soil C sequestration. However, the potential of AMP grazing to sequester soil C is largely unquantified in the highly temporal and spatially variable dynamics of rangelands in the Western U.S. Rangeland systems are also socio-ecological system with complex interactions among social drivers and ecological outcomes, and very little is known about the decision making frameworks utilized by AMP ranchers regarding soil health. The goal of this project is to address these gaps with a unique, interdisciplinary approach. Soil C sequestration, water holding capacity, and other ecosystem functions (i.e. biodiversity) will be measured on AMP ranches across CA. To further understand soil C stabilization and persistence (as a long term greenhouse gas mitigation strategy), a novel soil C fractionation method will be used. Semi-structured interviews with ranchers, technical assistance providers, support organizations and policy makers will also be used to address informational and network challenges facing ranchers to graze for soil C sequestration. This research will aid development of effective grazing strategies across CA rangelands to optimize soil health and rancher livelihoods, and will expand the monitoring and payment opportunities for soil C sequestration.
- Quantitative analysis of soil C sequestration on AMP grazed ranches across CA. This Spring 2020, I will be conducting a comparative “fence-line” analysis of soil C outcomes on AMP vs CONT grazed ranches across CA. To build on these data, this proposed project will allow me to conduct additional analyses that provide a more complete assessment of potential AMP benefits.
- Conduct interviews with AMP ranchers, technical assistance providers, and associated soil C advocates across CA. The goal of these interviews is to expand on the 11 AMP rancher interviews that I have already conducted. This is a necessary addition to understand the barriers to AMP grazing by identifying gaps in knowledge (e.g. with technical assistance providers) and identify opportunities to link grazing with soil C advocates.
- Produce one video to bolster communication of AMP grazing and soil health. One video will be targeted to a public, general audience, and the other will be aimed at engaging a wider population of ranchers on grazing for soil health (see Educational Outreach Plan). A primary goal of this project is to capitalize on the visual science benefit of this project, and the effectiveness of peer-to-peer knowledge dissemination.
- Host a producer workshop to disseminate information, research results, and facilitate knowledge exchange on grazing for soil health. I will host a producer workshop at Paicines Ranch with the support of the Central Coast Rangeland Coalition (see attached collaboration letter from CCRC Board Member Sheila Barry) and University of California Cooperative Extension (Collaborators Leslie Roche and Sheila Barry). The workshop will be structured to share research findings, perform an in-field soil health demonstration, play the rancher educational soil health video (Obj 3), and facilitate knowledge exchange among ranchers, technical assistance providers, soil C advocates and policy makers.
From August to December 2020, I will conduct qualitative data collection through interviews with AMP ranchers, technical assistance providers, organizational members such as NRCS and RCDs, with members of soil C advocacy organizations, and policy makers. I will also continue to process soil samples and will conduct additional lab analyses made possible through this project. In the Spring and summer 2021, I will work with a videographer to collect rancher profile footage. Fall and winter of 2021 will consist of data analysis and preparation for the producer workshop in Spring 2022. Scholarly and general audience publications will be completed by end of summer, 2022. Full timeline in Table 1.
Table 1. Timeline
In the first year of the project, I identified seven paired ranches eligible for the study. I narrowed ranch pairs on the basis of grazing management (adjacent adaptive multi-paddock and low rotational grazing systems – chosen with previously developed criteria), land-use/inputs (no compost/fertilizer application or irrigation), and location. In Fall 2019, I conducted initial ranch visits and did “pasture walks” with each rancher to identify possible sampling locations. In concert with local extension agents, I obtained ranch shape files for each property and chose ultimate sampling locations based on topography, soil type, and slope aspect.
I ultimately sampled on four ranch pairs chosen based on the above criteria. Ranch pairs (from South to North) were located in San Benito County, San Mateo County, Marin County, and Yuba County. A fifth ranch pair in Tehama County was originally planned, but we was ultimately excluded because of soil rock content, making soil sampling infeasible. Sampling began in April 2020 and ended in July, following COVID delays. At each ranch, I navigated to my pre-determined sampling location (described above), and constructed three transects based on hillslope catenal position (1 summit transect, 1 backslope transect, 1 footslope transect). Along each 50-m transect, I collected 25 30cm-deep samples and 5 1m-deep samples. These sample sizes were chosen based on an a priori power analysis informed by previously analyzed CA rangeland soils (for spatial heterogeneity of soil C). This ultimately yielded 360 individual soil samples per ranch pair, and 1440 soil samples across all ranches. Vegetation data was also collected with a combination of line-point intercept (to yield % cover) and a nested quadrat method (to yield % frequency of more rare species). To improve on historically inaccurate bulk density measures, I chose to use the equivalent soil mass method. Each soil depth was weighed in field, and a sub sample was taken and also weighed. This gives an “estimated” bulk density estimate for each sample (that will also be analyzed for C), and can be retroactively corrected with a reference soil mass. HYPROP samples (1 per transect) were also collected in-field for water retention curve analysis.
From July 2020 – February 2021, samples were air dried, sieved to 2mm, and subsamples ground on a ball-mill. Each sample was analyzed for TOC/N on an Elementar soliTOC EA (n=1440), completed in May 2021. After determining that the soliTOC was unreliable for N% analysis, only TOC was kept from these data. From February – June 2021, composited subsamples (n=240) were fractionated by size and density into MAOM (mineral associated organic matter), fPOM (free particulate organic matter), oPOM (occluded particulate organic matter), and DOM (dissolved organic matter) – to assess soil C persistence and formation in each fraction. Each fraction was subsequently ground and is awaiting analysis on an Elementar VarioEL for TC/TN%. This fractionation method was chosen because it yields information on both soil C persistence (e.g. MAOM is a more persistent form of soil C and is thought to be more important for climate change mitigation), and how soil C is forming based on longevity of management (e.g. POM is a more “leading” indicator of soil C sequestration, while MAOM may take longer to form).
July-present (2021): All composited samples were also analyzed for texture using a rapid pipette method (n=240). HYPROP samples (n=24) are currently being analyzed to build full water retention curves using a 3-step method: 1. kSAT 2. HYPROP and 3.WP4C. This method was chosen because it will yield both water holding capacity as well as water infiltration – both of which are important indicators of soil health with changing management. From now until Dec 2021, I will continue to work to finish analyzing all HYPROP samples as well as analyzing fractionated samples for TC/TN once the VarioEL is installed.
I have spent the past year processing my samples and conducting all laboratory analysis. I am currently in the data analysis phase and do not have preliminary results (expected Fall 2021). Ultimately, data will include:
- bulk soil TOC% (n=1440)
- soil C stocks determined by cumulative mineral equivalent soil mass
- fractionated soil C stocks of MAOM, fPOM, oPOM and DOM (a total of 4 fractions for each of n=240 samples)
- vegetation data, including relative abundance of different species by functional group as well as % soil cover
- soil water retention data, including water holding capacity and water infiltration
- soil texture (n=240)
Educational & Outreach Activities
Because I am still in the data analysis phase, I have not yet generated any tangible papers or education outcomes. I’ve given 1 webinar to a lab group (which was not recorded). Publications are expected later this year and into Spring/Summer 2022. In April 2022, there will be an educational workshop for this work coordinated jointly with CCRC (California Central Rangeland Coalition) at a Central Coast CA ranch to present results of this study to ranchers.
Depending on the outcome of our results, if regenerative grazing does prove to sequester soil C, this will be a promising outcome for the future of regenerative grazing. Currently, California does not include regenerative grazing in its Healthy Soils Program. If our results show positive outcomes, we hope this will catalyze state-funded action to include regenerative grazing in the Healthy Soils Program, which would ultimately increase adoption as well as improve ranchers’ financial conditions. We also hope that our social science component will help shed light on the drivers and barriers to adoption of regenerative ranching, which could better incentivize other ranchers and design effective policy measures.
The project is still ongoing (only 1-year in at the time of this progress report). My colleagues and I have learned a lot about effective sampling designs on extensive California rangelands, which we hope to share with fellow researchers. We also hope to engage with ranchers in this study in the future in order to build onto these data over time. We hope that these data (and our work in general) will facilitate more research in Western Regenerative Ranching systems in order to better understand their resiliency and climate change mitigation potential.