Compost amendment to enhance carbon sequestration in rangelands

Rangelands contain 20% of global soil carbon (C). Past management of rangelands has resulted in significant losses of soil C, threatening the long-term productivity and sustainability of these ecosystems. Compost amendments have been proposed as a means to increase soil C sequestration while providing important cobenefits to rangeland ecosystems and land managers. Here, we review the literature on the effects of compost amendments on soil and plant characteristics and rates of soil C storage. We extracted values related to biological, physical, and chemical responses to compost applications in rangelands in eight countries and on five continents. Studies reported both short (<1 y) and long-term (>12 y) effects with compost types derived from green waste, food waste, manure, and biosolids. Generally, we found that compost amendments improved aboveground production by >40%, and belowground C content by 50%. Further benefits of compost additions included increasing aggregate stability (~42%), water retention (~18%), nutrient availability (~37% and 126% for nitrogen [N] and phosphorus [P], respectively), as well as generally reducing erosion but with high variability. We found little to no effect of compost amendments on plant diversity and very few studies investigated effects on soil microbial community and function. Both field and modeling studies demonstrated that the changes in soil C from compost amendments can result in long-term C storage. Overall, results suggest that compost amendments may contribute to rangeland resilience to climate change with the additional benefit of climate mitigation via soil C sequestration.