Review of grassland management practices for carbon sequestration.

About 400 million ha grassland in China is a large potential carbon sink.However,grassland carbon sequestration is not fully understood.This paper reviews the effects of meteorological factors(CO2,temperature and rainfall change),grassland management(grazing,native grassland conversion to cropland,mowing,fertilization,irrigation,reseeding,abandoned cropland,exclosure,establishment of artificial grassland and ploughing),and degradation on soil carbon content,to guide grassland management for carbon sequestration.Changes of temperature and precipitation play different roles in the function of grassland carbon sequestration,which should be taken into account in grassland management.Degraded grassland with low productivity and soil organic matter content and a worse soil physical and chemical environment has great carbon sequestration potential.Appropriate grassland management measures will greatly improve soil organic carbon.One report suggests that the application of exclosure in degraded grassland in China could sequester over 12.01 Tg C/year.Heavy grazing can reduce carbon sequestration due to changing grassland plant community diversity,net primary productivity reduction,lower litter production and nitrogen limitation in soil.Proper grazing management has been estimated to increase soil carbon storage.Native grassland conversion to cropland has caused negative carbon sequestration,as a result of soil erosion,soil organic matter decomposition and lower litter production.Because high mowing intensity reduced soil organic matter,proper mowing height and frequency,application of manure and fertilizer to balance nutrient loss was needed on hay grassland.Fertilization,reseeding,ploughing and irrigation increased soil organic matter storage by promoting revegetation and net primary productivity.Abandoned cropland and exclosure associated with fertilization and reseeding could promote restoration and soil nutrient content,and increase carbon sequestration efficiency.Carbon sequestration capability of forage was: mixed perennial legume and grasslegumeperennial grassannual grass.