Research advances on the effect and mechanism of green manure on improving soil carbon sequestration in cropland
Soil carbon sequestration plays an important role in mitigating global climate change and maintaining farmland productivity.There are many determinants for soil carbon sequestration in cropland,such as climate(precipitation,temperature),soil biotic property(microbial communities and enzyme activities),and soil abiotic properties(physiochemical properties,agronomic management practices,aggregates).Cropland became carbon sink(positive sequestration)through increasing carbon input,reducing carbon output,and increasing carbon retention time in the soil.Green manures show multiple functions in such as nitrogen fixation,carbon sequestration,and regulation of soil microbial community structure.Incorporating green manure into crop production system could reduce the mineralization of soil organic carbon,increase the sources of soil organic carbon,regulate the process of soil aggregation,promote the accumulation of microbial biomass and residues,and improve the composition and metabolic activity of microbial communities,and these functions could be concluded into physical fixation(physical protection of aggregates),chemical fixation(chelating with soil minerals),and microbial carbon pump.The currently used key technologies to strengthen soil carbon sequestration efficiency of green manures mainly include:1)Selecting appropriate green manure varieties;2)Construction of'main crop+green manure'planting pattern to match the regional soil and climate conditions;3)Nutrient management technology to form synergic effect of green manure and other fertilizers;4)Optimized tillage methods.In the future,more researches should be focused on:1)The mechanism of soil carbon sequestration mediated by green manure;2)Breeding of high-efficiency carbon-fixing green manure germplasm resources;3)Establishing a long-term research system for the utilization of green manure;4)Construction of organic carbon management framework based on the application of green manure.