1. National Engineering Laboratory for Efficient Utilization of Soil and Fertilizer Resource College of Resources and Environment, Shandong Agricultural University Tai'an Shandong 271018 PR China
2. Key Laboratory of Humic Acid Fertilizer Ministry of Agriculture and Rural Affairs of the People's Republic of China Feicheng Shandong 271600 PR China
3. Engineering Technology Research Center of Shandong Province for Efficient Utilization of Humic Acid Shandong Agricultural University Fertilizer Science and Technology Co. Ltd. Feicheng Shandong 271600 PR China