Managed grazing incrementally increased soil organic carbon amid larger temporal trends in a temperate pasture system

Soil carbon sequestration offers potential to decrease levels of atmospheric carbon dioxide (CO₂) and help mitigate the climate impacts of livestock greenhouse gas emissions. Low-cost management changes that can quickly increase soil organic carbon (SOC) are needed for widespread implementation. Grazing management, which can be implemented across extensive pasture systems, is often promoted to increase SOC. A grazing trial was established in 2012 to investigate the effect of stocking rate, rest length, and number of paddocks in rotation on SOC stocks. Plots were sampled regularly for pasture composition and biomass, and approximately every three years for SOC to a depth of 30 cm. All treatments increased SOC, primarily reflecting land-use conversion from cropping to permanent pasture three years prior to the start of the experiment. Differences between grazing treatments were also detected. Continuously grazed treatments had lower SOC stocks relative to rotationally grazed treatments. However, no consistent differences were detected in SOC stocks between rotationally grazed treatments with 15 or 30 paddocks, or different rest periods (56 or 112 days between grazing events). Paddocks that were rotationally grazed also had greater ground cover and pasture production relative to the continuously grazed treatments. These results suggest that allowing pasture recovery from grazing through a greater number of paddocks and rest periods likely enhanced pasture productivity, leading to marginally greater SOC stocks relative to continuous grazing. While land-use change from cropping to pasture was the dominant factor influencing SOC stocks, rotational grazing management provided additional carbon storage potential.