Adaptive Multi-paddock Grazing Increases Organic Carbon in Grassland Soils

Abstract

Grasslands cover 30% of the planet’s terrestrial surface and provide habitat and forage for livestock and wildlife. In addition, grasslands have the potential to mitigate climate change by sequestering substantial amounts of carbon (C) in the soil. However, the ability of grassland soils to sequester C varies greatly depending on the grazing management system adopted. This study examined the difference in soil organic C (SOC) mass between two different grazing systems, including adaptive multi-paddock (AMP) grazing, which involves rotating livestock through many small paddocks based on forage availability and allowing extended rest periods between grazing events, and conventional grazing (i.e., neighboring to AMP, hereafter n-AMP, varying from continuous to slow or fast rotational grazing, representative of the typical variation in grazing practices observed on-farm). I evaluated the effects of diverse grazing practices on SOC in soil depths up to 1 meter, using equivalent soil mass (ESM) to offset differences in soil bulk density among different paddocks, thus ensuring the proper comparison of grazing system effects on SOC mass. Soil samples were collected from 26 ranch pairs, where one ranch practiced AMP while the other n-AMP grazing across the Canadian prairies. In addition to assessing differences in equivalent SOC mass between grazing systems at the treatment level (AMP vs. n-AMP), I used an information theoretic model selection approach to assess the influence of nuanced grazing management practices, including stocking rate, animal stock density, and rest intervals, on SOC. My results show AMP grazed grasslands with higher stocking rates and extended rest periods sequestered significantly more SOC in the 10-30 cm ESM soil layer than n-AMP grazed grasslands. Conversely, n-AMP can sequester more SOC than AMP grazing at stocking rates lower than 3.5 AUM ha-1. These results highlight the importance of using sampling protocols that encompass deeper soil layers to adequately quantify the effect of grazing management on SOC. This study emphasizes the potential for enhancing soil C sequestration in grazed grasslands through the use of rotational grazing systems at adequate stocking rates.