Multi-decadal grazing effects on soil organic carbon and nitrogen concentrations in a semiarid rangeland

Authors: Derner, Justin; Taylor, Kalyn; Mortenson, Matthew; Stewart, Catherine; Hoover, David

Submitted to: Drylands
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/22/2026
Publication Date: N/A
Citation: N/A

Interpretive Summary: Interactions among weather/climate factors, vegetation characteristics, and soils present numerous permutations for soil organic carbon (SOC) and nitrogen (N) dynamics in semiarid rangeland ecosystems. As a result, assessing livestock grazing impacts on SOC and N are difficult to categorize given this complexity and site-specificity of conditions. Moreover, long-term studies in semiarid rangelands with consistent grazing treatments and repeated soil samplings are lacking to understand the influences of grazing with respect to environmental influences such as directional trends in climate factors. This study capitalizes on a multi-decadal grazing experiment in the semiarid North American Great Plains, northern mixed-grass prairie, with grazing season (June-late September) grazing treatments of season-long light and heavy stocking rates, and exclosure (non-grazed) established in 1982 and soils sampled in 1993, 2003, and 2013. Increasing grazing intensity from non-grazed to heavy grazed, reduced annual aboveground standing crop biomass and shifted the plant community dominance from cool-season (C3) to warm-season (C4) perennial grasses, but did not affect SOC and N. Soil dynamic findings demonstrate that concentrations of SOC and N decreased over 20 years (from 1993 to 2013) irrespective of grazing treatments (ranging from no grazing to light to heavy stocking) for the top 12 inches of soil. Climatic influences, such as an observed decreasing trend in precipitation but no temperature trends, likely impact SOC and N dynamics more than livestock grazing, suggesting that expectations of increased SOC and N with livestock grazing are not reasonable in semiarid rangeland ecosystems of the North American Great Plains with a long evolutionary grazing history.

Technical Abstract: Grazing impacts on soil organic carbon (SOC) are vexingly difficult to predict due to intricate interactions among site-specific weather, vegetation, and specified grazing treatments. This study capitalizes on a multi-decadal grazing experiment in the semiarid northern mixed-grass prairie of the North American Great Plains with grazing treatments of season-long light and heavy stocking rates, and exclosures (non-grazed) established in 1982 and soils sampled in 1993, 2003, and 2013. Increasing grazing intensity from non-grazed to heavy grazed reduced annual aboveground standing crop biomass and shifted the plant community dominance from cool-season (C3) to warm-season (C4) perennial grasses. Concentrations of SOC and soil nitrogen (N) decreased from 1993 to 2013 for the 0-5, 5-15, and 15-30 cm depths for all grazing treatments, but grazing intensity did not affect SOC and N. Annual precipitation decreased 4.2 mm yr-1 from 1982 to 2013; conversely, mean annual maximum and minimum temperatures did not change. Observed directional trends in precipitation likely impact ecosystem functioning for soil SOC and N concentrations more than grazing-induced changes in plant communities and aboveground production in this semiarid rangeland resulting in reducing expectations of increased SOC and N with livestock grazing in semiarid rangeland ecosystems of the North American Great Plains.