Grassland management and conversion into grassland: Effects on soil carbon

Grasslands are heavily relied upon for food and forage production. A key co mponent for sustaining production in grassland ecosystems is the maintenanc e of soil organic matter (SOM), which can be strongly influenced by managem ent. Many management techniques intended to increase forage production may potentially increase SOM, thus sequestering atmospheric carbon (C). Further , conversion from either cultivation or native vegetation into grassland co uld also sequester atmospheric carbon. We reviewed studies examining the in fluence of improved grassland management practices and conversion into gras slands on soil C worldwide to assess the potential for C sequestration. Res ults from 115 studies containing over 300 data points were analyzed. Manage ment improvements included fertilization (39%), improved grazing management (24%), conversion from cultivation (15%) and native vegetation (15%), sowi ng of legumes (4%) and grasses (2%), earthworm introduction (1%), and irrig ation (1%). Soil C content and concentration increased with improved manage ment in 74% of the studies, and mean soil C increased with all types of imp rovement. Carbon sequestration rates were highest during the first 40 yr af ter treatments began and tended to be greatest in the top 10 cm of soil. Im pacts were greater in woodland and grassland biomes than in forest, desert, rain forest, or shrubland biomes. Conversion from cultivation, the introdu ction of earthworms, and irrigation resulted in the largest increases. Rate s of C sequestration by type of improvement ranged from 0.11 3.04 Mg C.ha(- 1) yr(-1), with a mean of 0.54 Mg C.ha(-1).yr(-1) and were highly influence d by biome type and climate. We conclude that grasslands can act as a signi ficant carbon sink with the implementation of improved management.