1. State Key Lab. of Soil Erosion and Dryland Farming on the Loess Plateau Institute of Soil and Water Conservation Northwest A&F Univ. Yangling Shaanxi 712100 China
2. USDA‐ARS, Genetics and Sustainable Agriculture Research Unit Mississippi State MS 39762 USA
3. U.S. Forest Service Pacific Northwest Research Station Corvallis OR 97331
4. Institute of Soil and Water Conservation, CAS and MWR Yangling Shaanxi 712100 China