1. College of Water Resources and Civil Engineering, China Agricultural University, Beijing 100083, China
2. National Field Scientific Observation and Research Station on Efficient Water Use of Oasis Agriculture, Wuwei 733000, China
3. Department of Soil and Water Sciences, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot P.O. Box 12, Israel
4. Department of Civil and Environmental Engineering, The University of Tennessee, Knoxville, TN 37996, USA