国家自然科学基金项目41271299西北农林科技大学国家级大学生创新实验项目20140712004;黄土高原土壤侵蚀与旱地农业国家重点实验室项目A31402143-C2资助 Supported by the National Natural Science Foundation of China41271299;the Northwest A&F University National Foundation of College Students Innovation ProjectNo.20140712004.and Special-Funds of Scientific Research Programs of State Key Laboratory of Soil Erosion and Dryland Farming on the Loess PlateallA314021403-C2