On the impact of grassland management on soil carbon stocks: a worldwide meta-analysis

International audienceGrasslands occupy 70% of whole agricultural land and hold significant amounts of carbon, a key element in the regulation of Earth's soils fertility, biomass production and climate. Previous work has shown that carbon stocks of grassland soils have been largely depleted worldwide due to missuse or mismanagement but that shifts in management could also potentially increase soil carbon stocks and mitigate against the degradation of natural ecosystems. However, the existing literature points to large discrepancies in the impact of grassland management practices on soil carbon, which the present study investigated. Here we considered 235 experimental sites in 18 countries across the world where shifts in grassland management involved different grazing strategies (free, F vs controlled, C; high, H vs low, L density grazers), grazers exclusion (E), mowing (M) and burning (B). The best performing practice was controlled grazing with high density of grazers (CHG) with an average soil organic carbon content (SOCC) increase of 21% and with 100% of the studies pointing to a SOCC increase. This was followed by E (14.9%; 60%) and FLG (13.3%; 80%). On average, burning grasslands, decreases SOCC by 9.3% but 31% of the studies pointed to an increase, thus indicating discrepancies in the impact of grassland management. CLG and mowing did not significantly impact SOCC. These results also indicated that B decreased SOCC the most under moist to humid climates (−10.9% vs −1.7% under arid to semi-arid), while that E was only beneficial in arid to semi-arid grasslands. Adoption of rotational high-intensity grazing in place of free grazing grasslands, should be seriously considered by policy and decision makers to mitigate against climate change while fostering economic and social development