1. College of Urban and Environmental Sciences, Northwest University, Xi’an 710127, China
2. Shaanxi Key Laboratory of Earth Surface System and Environmental Carrying Capacity, Northwest University, Xi’an 710127, China
3. Inner Mongolia Key Laboratory of Soil Quality and Nutrient Resource, College of Grassland, Resources and Environment, Inner Mongolia Agricultural University, Hohhot 010011, China
4. Alabama Transportation Institute, 248 Kirkbride Lane, Tuscaloosa, AL 35487, USA