Quantitative and Qualitative Responses of Soil Water-Extractable Organic Matter to Carbon and Nitrogen Management Practices in Loess Soil oleh Qin Chen, Zheng-kui Ge, Rong Chai, Yuan Li, Yu-long Li, Yan-jiang Zhang, Zhi Qu, Ai-qing Zhao, Xiao-hong Tian, Min Duan, Ming Li