Evaluating the impacts of alternative grazing management practices on soil carbon sequestration and soil health indicators

Authors: KIM, JUNGJIN - Texas A&M University; ALE, SRINIVASULU - Texas A&M University; KREUTER, URS - Texas A&M University; TEAGUE, RICHARD - Texas A&M University; Del Grosso, Stephen - Steve; DOWHOWER, STEVEN - Texas A&M Agrilife

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/18/2022
Publication Date: 10/25/2022
Citation: Kim, J., Ale, S., Kreuter, U., Teague, R., Del Grosso, S.J., Dowhower, S.L. 2022. Evaluating the impacts of alternative grazing management practices on soil carbon sequestration and soil health indicators. Agriculture, Ecosystems and Environment. 342. Article e108234. https://doi.org/10.1016/j.agee.2022.108234.
DOI: https://doi.org/10.1016/j.agee.2022.108234

Interpretive Summary: About 40% of the Earth's land base is used for grazing; in addition to supporting livestock production, grazed soils contain large amounts of carbon. However, improper use of these ecosystems can degrade their soils and their carbon storage capacity. Specifically, prolonged high stocking rates in livestock production can deplete soil carbon and soil fertility. The objective of this study was to identify the impacts of alternative grazing management practices, including heavy continuous (HC), light continuous (LC), and adaptive multi-paddock (AMP) grazing, on soil carbon and soil health indicators at the ranch and watershed scales in Northwest Texas. We combined ranch level measurements with the SWAT model which represents plant-soil system dynamics and hydrological processes such as erosion. First, we showed that SWAT could reproduce measurements of vegetation, soil carbon, and erosion related metrics such as sediment load. Then we ran the model across the watershed to compare AMP, HC and LC grazing; AMP and HC had similar animal stocking rates which were reduce by half for LC grazing. At the watershed-scale, when the grazing management was changed from the baseline HC grazing to AMP grazing, the simulated average annual soil carbon increased from 35.6 to 38.3 Mg/ha (a 7.5% increase). Forage production, soil carbon, and soil nutrients increased, while C losses from runoff, and sediment loads decreased under AMP grazing. These results indicate that compared to HC, AMP grazing performed better with respect to soil carbon storage, and improvement of soil ecosystem and hydrological functions at both the ranch and watershed scales in the study watershed.

Technical Abstract: Globally, grazing lands represent a major carbon (C) sink. However, improper use of these ecosystems can degrade their soils and their C storage capacity. Specifically, prolonged high stocking rates in livestock production can result in significantly less soil organic carbon (SOC) and soil fertility in grazing lands. This underlines the need to assess key soil health indicators to determine the ecological efficacy of grazing management. The objective of this study was to identify the impacts of alternative grazing management practices, including heavy continuous (HC), light continuous (LC), and adaptive multi-paddock (AMP) grazing, on SOC and soil health indicators at the ranch and watershed scales in the Lower Prairie Dog Town Fork Red River Watershed in Northwest Texas. The stocking rate was the same under AMP and HC grazing, and it was reduced by half under LC grazing. The Soil and Water Assessment Tool-Carbon (SWAT-C) model was modified and used to conduct this assessment over a 40 year period (1979-2018), after a 900-year spin-up simulation (800 years under natural condition and 100 years under the HC grazing) to initiate the SOC pool. The simulated SOC was validated using observed data from several sampling locations. The study results indicated that when grazing management at the study ranch was changed from the current AMP grazing to hypothetical HC grazing, simulated average annual SOC decreased from 84 to 81.8 Mg/ha (a 2.6% decline). At the watershed-scale, when the grazing management was changed from the baseline HC grazing to AMP grazing, the simulated average annual SOC increased from 35.6 to 38.3 Mg/ha (a 7.5% increase). The net primary productivity (NPP), evapotranspiration (ET), biomass C, and soil nitrogen (N) increased, while C losses from runoff, and sediment loads decreased under AMP grazing. These results indicate that compared to HC, AMP grazing performed better with respect to SOC increase, and improvement of soil ecosystem and hydrological functions at both the ranch and watershed scales in the study watershed. Our findings suggest the need to shift from continuous to AMP grazing in order to improve soil health at multiple spatial scales.