1 Key Laboratory of Western China's Environmental Systems (Ministry of Education), College of Earth and Environmental Sciences, Lanzhou University, Lanzhou 730000, China.
2 National Engineering Research Center for Water Saving Irrigation at Yangling, Institute of Soil and Water Conservation, Northwest A&F University, Yangling 712100, China. Electronic address: gjzwpt@vip.sina.com.
3 National Engineering Research Center for Water Saving Irrigation at Yangling, Institute of Soil and Water Conservation, Northwest A&F University, Yangling 712100, China.