Soil and crop management to promote formation of stable soil organic matter

土壤有机质（SOM）是陆地有机碳（C）的三分之二，是大气中或植物生物量中碳含量的两倍以上。有机质对于支持植物、动物和微生物的生命至关重要，因为它在增强调节土壤质量的物理和化学特性方面发挥着重要作用。这包括保持基本植物养分和提高用水效率，促进聚合从而减少侵蚀，并直接促进土壤肥力。 农业土壤的集约化耕作加上一年生粮食作物的种植，使土壤有机质水平比当地同行减少了30-50%。 土壤管理（耕作方法）和种植制度影响植物残体投入的质量和数量，以及植物残体腐烂和有机质周转的速度。 虽然农业土壤占全球有机碳的约10%，是大气CO2排放的重要贡献者，但它们有可能成为大气二氧化碳C的主要全球储存库，在那里它可以作为数百至数千年的稳定腐殖质被隔离。采用适当的文化和管理措施，包括复杂的作物轮作和保护性耕作（减少或免耕）系统，并返回作物残留物和有机废物正在积极促进保护和提高SOM水平。近年来，农业土壤中有机质组分的定量和定性测定已成为一个主要的研究热点，因为它们具有减缓气候变化的潜力。

Two-thirds of the terrestrial organic carbon (C) in soil is contained as soil organic matter (SOM), a pool of C more than twice the size of that in the atmosphere or in the living plant biomass. SOM is critical for supporting plant, animal and microbial life because of its role in enhancing the physical and chemical properties that regulate soil quality. This includes retention of essential plant nutrients and increasing water-use efficiency, promoting aggregation thereby reducing erosion, and its direct contribution to soil fertility. Intensive soil cultivation for agriculture combined with the growing of annual crops for food production have depleted SOM levels by 30-50% compared to that in their native counterparts. Soil management (tillage practices) and cropping systems influence the quality and quantity of plant residue inputs, and the rates of plant residue decay and SOM turnover. Although agricultural soils, which account for ~10% of global organic C, have been a significant contributor to atmospheric CO2 emissions, they have the potential to be a major global reservoir for atmospheric carbon dioxide C where it can be sequestered as stable humus that is hundreds to thousands of years old. Adoption of appropriate cultural and management practices, including complex crop rotation and conservation tillage (reduced or no-till) systems, and returning crop residues and organic wastes are being actively promoted to protect and enhance SOM levels. Recently quantitative and qualitative measurements of the components of SOM in agricultural soils have become a major research focus due to their potential for mitigating climate change.