Zhang Dabin^a, Yao Pengwei^a, Zhao Na^b, Cao Weidong^c,GaoYajun^{a, d}*

　　^a College of Natural Resources and Environment, Northwest A&F University, 712100, Yangling, Shaanxi;

　　^b Bayannaoer Academy of Agricultural and Animal Sciences, 015000, Bayannaoer, Inner Mongolia;

　　^c Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Beijing, 100081;

　　^d Key Laboratory of Plant Nutrition and Agri-environment in Northwest China, Ministry of Agriculture, 712100, Yangling, Shaanxi

　　Local unreasonable cultivation practices, including the shortage of organic fertilizer input and intensive soil cultivation, exacerbate the soil quality degradation, resulting in the arable dryland soil of Loess Plateau with a more fragile physical structure and low organic matter contents.Consequently, developing a sustainable cropping system to effectively build up soil C and N stocks, thus improving soil fertility and environmental sustainability is urgent for the dryland farming in China.

　　Growth of summer legumes as green manure (GM) may influence the soil organic carbon (SOC) and total nitrogen (TN) stocks, thereby affecting soil quality and productivity under dryland condition. A five-year field experiment was conducted on the Cumulic Haplustoll in the northwest region of China to (i) quantify the growth and decomposition patterns of Huai bean ( Glycine ussuriensis Regel etMaack. ), soybean [ G. max ( L. ) Merr. ], and mung bean ( Phaseolusradiatus L.),(ii)evaluate the effect of GM legumes on soil organic carbon (SOC), liable organic carbon (LOC), and total nitrogen (TN) concentrations and stocks (0-20 cm depth), and (iii) estimate thedynamics of SOC stockfor the GM systems under semiaridcondition.Results confirmed that inclusion ofGM legumesfor continuous 5-yr significantly improvedSOC, LOC, and TN concentrations and stocks at topsoil compared with the original soil.Thepercentages of remaining GM C and Nin the soil after one yeardecomposition averaged to 26% and 31% for the above-ground residues, andaveraged to 33% and52% for the below-ground residues, respectively. The SOC stocks were closelyrelated to the annual C input by crops, and a minimum C input of 0.68 Mg C·ha-1·yr-1was estimated to maintain the original SOC stock of 19.04 Mg C/ha.Based on the one-compartment model, the annual decomposition rate of SOCandthe C added by crops remained in the SOCwere estimated as 1%and 23%, respectively. The mean turnover timeofSOC at equilibrium wasestimated as 22 years, suggesting that thisloess soil was not C saturated andstill had potential for C sequestration.Consequently, cultivation of leguminous GM during summer is a better option than bare fallow tobuild upthe soil fertility and environmental sustainabilityin the Loess Plateau of China.