Alfalfa-livestock system promotes the accumulation of soil organic carbon in a semi-arid marginal land

Developing cropland in marginal lands presents a potential solution to address food security challenges. However, the low organic carbon (C) content in these soils severely constrains crop productivity, and developing cropland aggravates the loss of soil organic carbon (SOC). Therefore, it is essential to elevate the SOC content via a profitable solution for food production. In this study, we examine the impacts of land use changes (fallow, cropland, and Alfalfa-livestock system [AL]) over 12 years on SOC content, composition, and mineralization rate in a semiarid marginal land. SOC was categorized into three components: plant necromass C, microbial necromass C, and "other C." We utilized lignin and amino sugars as biomarkers to assess plant and microbial necromass C content, respectively, and the remaining component was other C. We found that AL increased SOC contents in 0-15 cm by 142 % and 123 % compared to fallow and cropland. Other C was the main factor driving SOC accumulation in AL compared to fallow and cropland, which contributed 2 times more than microbial necromass C (63 % VS 31 %), while plant necromass contributed less than 7 %. Furthermore, AL decreased C mineralization per unit of SOC than fallow and cropland due to increased soil available N contents. In conclusion, AL facilitated a rapid increase in SOC contents on marginal lands by fostering the accumulation of microbial necromass C and other C while inhibiting SOC mineralization. This finding helps improve the productivity and sustainability of marginal croplands.