1. Key Lab. of Agricultural Soil and Water Engineering in Arid and Semiarid Areas of Ministry of Education; Northwest A&F Univ.; Yangling Shaanxi 712100 China
2. College of Water Resources and Architectural Engineering, Northwest A&F Univ.; Yangling Shaanxi 712100 China
3. Dep. of Soil Science; Univ. of Saskatchewan; Saskatoon SK S7N5A8 Canada
4. New Zealand Institute for Plant & Food Research Limited; Private Bag 4704 Christchurch 8140 New Zealand
5. Dep. of Renewable Resources; Univ. of Alberta; Edmonton AB T6G2H1 Canada