1. Shaanxi Key Laboratory of Earth Surface System and Environmental Carrying Capacity, College of Urban and Environmental Science Northwest Univ. Xi'an 710127 China
2. State Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation Chinese Academy of Sciences and Ministry of Water Resources Yangling 712100 China
3. USDA‐ARS, Northern Plains Agricultural Research Laboratory 1500 North Central Avenue Sidney MT 59270 USA
4. Agricultural Science Center New Mexico State Univ. 2346 State Road 288 Clovis NM 88101 USA