1. College of Water Resources and Architectural Engineering Northwest Agriculture and Forestry Sci-Tech Univ.; Yangling 712100 China
2. Key Laboratory of Agricultural Soil and Water Engineering in Arid and Semiarid Areas; Ministry of Education Northwest Agriculture and Forestry Univ.; Yangling Shaanxi 712100 China
3. Dep. of Soil Science; Univ. of Saskatchewan; Saskatoon SK S7N 3H5 Canada