1. Key Lab of Plant Nutrition and the Agri-Environment in Northwest China; Ministry of Agriculture/College of Natural Resources and Environment; Northwest A&F Univ.; Yangling 712100 Shaanxi China
2. Ludong Univ.; College of Resources & Environ. Engin.; Yantai 264025 China
3. Heyang Field Station of Agricultural; Environment and Farmland Conservation; Ministry of Agriculture; Fuping Shaanxi China