Climate solutions from the ground up: The science behind sustainable grazing
By Dr. Jessica Murray
This fall, partners of the National Grazing Lands Coalition from the Western Grazing Network (WGN) traveled to 10 ranches in New Mexico and Colorado to dig holes – but these holes were not for fence posts nor wells!
With the help of NatGLC coordinators, a team of scientists from Working Lands Conservation dug over 950 holes and collected that many soil samples to determine the amount of soil organic carbon held on ranches within the WGN. We collected soil samples from lush hay fields, range ruled by prairie-dogs, green pastures, riparian areas, and land cloaked in prickly pear. Why collect so much soil?
Dr. Megan Nasto, Soil Science Program Director of Working Lands Conservation in the field gathering soil in the Western Grazing Network’s New Mexico hubs.
Because measuring soil carbon is part of the WGN mission to “regionally pilot a new model of natural resource management, conservation and market-derived financing that values landscape functionality for both agriculture commodity production and a full suite of ecosystem services, including GHG benefits.”
Greenhouse gas (GHG) benefits are derived from climate-smart practices that “reduce greenhouse gas emissions or sequester carbon." (1) In other words, GHG benefits are associated with activities that decrease the overall amount of planet-warming GHGs in the atmosphere.
The WGN is working to normalize climate-smart practices and increase their profitability by 1) providing financial and technical assistance to interested ranchers and 2) advancing local markets to increase the value of climate-smart, ranch-derived goods. The science team at Working Lands Conservation is supporting this work by quantifying the GHG benefits of the climate-smart practices implemented through the WGN. That way we can provide data on the benefits of regenerative practices to producers, consumers, and decision makers and explore the potential for additional ranch revenue sources through carbon markets.
To start, the WGN is focusing on GHG benefits through practices that build soil organic carbon.
Soil has been receiving a lot of attention lately due to its ability to store carbon, and rightfully so: globally, there is more carbon in the soil than in the atmosphere and all land plants combined! (2)
Plants draw carbon dioxide out of the atmosphere through photosynthesis and use that carbon to produce roots, shoots, and leaves. Plant carbon eventually becomes soil carbon through the decomposition of dead plant parts or the manure of grazing animals. Soil organic carbon is sequestered (stored) when the inputs of carbon to the soil are greater than the losses of carbon due to soil erosion and the carbon dioxide produced during decomposition.
Researchers and policy makers have asked whether we can increase the amount of carbon stored by soils to reduce or offset GHG emissions. It turns out there is a lot of potential to do this on agricultural lands. In fact, if we can increase global soil carbon stocks on agricultural land by an average of just 0.4% each year, we can offset our annual GHG emissions from fossil fuel burning. (3)
The advantages of building soil carbon on agricultural lands extend far beyond GHG benefits. In grazing systems, increases in soil carbon can lead to healthier animals, greater soil health, and increased drought resistance. Why? Because soil carbon and soil health are very much connected. Building soil carbon can increase forage production (4,5) increase the amount of water soils can hold (6,7,8) and support healthier, more abundant communities of soil microbes. (9) This can translate to higher profits for producers thanks to lower inputs, higher AUMs, higher valued commodities, and voluntary carbon markets.
Despite all the hype for soil carbon, we don’t totally have it figured out. We estimate that rangelands in the U.S., which cover about 1/3 of its land area, store 33.3 billion tons of carbon.10 That’s five times the amount of carbon emitted by the U.S. each year (11). There are many ways that grazing can build soil carbon (12) but we need more on-the-ground data to predict how specific grazing strategies might affect soil carbon in western working lands. (13) A barrier to collecting more data, however, is the expense of accurate soil carbon estimates.14 There’s the labor for collecting and processing soils (did I mention we dug 950 holes?!) as well as the costs of analyzing the samples for soil carbon.
So back to digging holes. Working Lands Conservation has partnered with the WGN to quantify the GHG benefits of climate-smart practices, generate more on-the-ground data about soil carbon on western working lands, and explore more cost-effective ways of analyzing soil carbon in the lab. We are excited to continue sampling soils throughout central and southern Colorado, northern New Mexico, and the Navajo Nation. Through this work, we hope to answer some of the remaining questions about soil carbon in western grazing systems. How much soil carbon can western grazing lands store? How do the timing, intensity, and duration of grazing affect soil carbon? Can we make it more affordable to accurately estimate soil carbon stocks on rangelands? And most importantly, how can we use scientific tools to support good land stewardship? Stay tuned!
Working Lands Conservation (WLC) is a non-profit that aims to empower the stewardship of working lands by bringing science to collaborative partnerships. To learn more about WLC, visit www.workinglandsconservation.org. To learn more about the Western Grazing Network, visit https://www.grazinglands.org/western-grazing-network.
References
https://www.usda.gov/sites/default/files/documents/usda-partnerships-climate-smart-factsheet-22.pdf
USGCRP, 2018: Second State of the Carbon Cycle Report (SOCCR2): A Sustained Assessment Report [Cavallaro, N., G. Shrestha, R. Birdsey, M. A. Mayes, R. G. Najjar, S. C. Reed, P. Romero-Lankao, and Z. Zhu (eds.)]. U.S. Global Change Research Program, Washington, DC, USA, 878 pp., https://doi.org/10.7930/SOCCR2.2018
Minasny, B., Malone, B. P., McBratney, A. B., Angers, D. A., Arrouays, D., Chambers, A., ... & Winowiecki, L. (2017). Soil carbon 4 per mille. Geoderma, 292, 59-86.
Vendig, I., Guzman, A., De La Cerda, G., Esquivel, K., Mayer, A. C., Ponisio, L., & Bowles, T. M. (2023). Quantifying direct yield benefits of soil carbon increases from cover cropping. Nature Sustainability, 6(9), 1125-1134.
Bauer, A., & Black, A. L. (1994). Quantification of the effect of soil organic matter content on soil productivity. Soil Science Society of America Journal, 58(1), 185-193.
Minasny, B., & McBratney, A. B. (2018). Limited effect of organic matter on soil available water capacity. European journal of soil science, 69(1), 39-47.
https://water.unl.edu/article/animal-manure-management/connection-between-soil-organic-matter-and-soil-water
Donahue, R. L., Miller, R. W., & Shickluna, J. C. (1977). Soils: an introduction to soils and plant growth, 133.
Anderson, T. H., & Domsch, K. H. (1989). Ratios of microbial biomass carbon to total organic carbon in arable soils. Soil biology and biochemistry, 21(4), 471-479.
Follett, R. F., Kimble, J. M., & Lal, R. (2001). The potential of US grazing lands to sequester soil carbon. The potential of US grazing lands to sequester carbon and mitigate the greenhouse effect, 65.
https://www.epa.gov/ghgemissions/inventory-us-greenhouse-gas-emissions-and-sinks
Stanley, P. L., Wilson, C., Patterson, E., Machmuller, M. B., & Cotrufo, M. F. (2024). Ruminating on soil carbon: Applying current understanding to inform grazing management. Global Change Biology, 30(3), e17223.
Brown, J., Angerer, J., Salley, S. W., Blaisdell, R., & Stuth, J. W. (2010). Improving estimates of rangeland carbon sequestration potential in the US Southwest. Rangeland Ecology & Management, 63(1), 147-154.
Stanley, P., Spertus, J., Chiartas, J., Stark, P. B., & Bowles, T. (2023). Valid inferences about soil carbon in heterogeneous landscapes. Geoderma, 430, 116323.
