A Global Meta-Analysis of Grazing Impacts on Soil Health Indicators.

Grazing lands support the livelihoods of millions of people across nearly one-half of the globe. Soils are the backbone of stability and resilience in these systems. To determine livestock grazing impacts on soil health, we conducted a global meta-analysis of soil organic carbon (SOC), total N, C/N ratio, and bulk density responses to grazing strategies (continuous, rotational, and no grazing) and intensities (heavy, moderate, and light grazing) from 64 studies around the world. Across all studies and grazing intensities, continuous grazing significantly reduced SOC, C/N, and total N compared with no grazing. Soil compaction (i.e., increased bulk density) was greater under both continuous and rotational grazing compared with no grazing; however, rotational grazing had lower bulk density than continuous grazing. Rotational grazing had greater SOC than continuous grazing and was not different from no grazing. The positive responses of SOC to rotational grazing could create climate change mitigation opportunities. Grazing strategy comparisons were minimally conditioned by aridity class (i.e., arid, subhumid, and humid); however, complete observations were notably limited or missing for many rotational grazing comparisons. For continuous and no grazing strategy comparisons, we found that grazing management can significantly influence soil function and health outcomes; however, site-specific environmental factors play important moderating roles. Greater coordination across regional, national, and global efforts, as well as consistent guidelines for soil health evaluation, would help overcome these knowledge gaps and vastly improve our collective understanding of grazing impacts on soil health, providing greater management and policy impacts.