1. College of Water Resources & Civil Engineering China Agricultural Univ. Beijing 100083 China
2. State Key Laboratory of Hydroscience and Engineering, Dep. of Hydraulic Engineering Tsinghua Univ. Beijing 100084 China
3. Wuwei Experimental Station for Efficient Water Use in Agriculture Ministry of Agriculture and Rural Affairs Wuwei 733000 China
4. Dep. of Plant and Environmental Sciences New Mexico State Univ. MSC 3Q, P.O. Box 30003 Las Cruces NM 88003‐8003 USA