Co-application of biochar and potassium fertilizer improves soil potassium availability and microbial utilization of organic carbon: A four-year study - Hao Xia; Jiyuan Wang; Muhammad Riaz; Saba Babar; Yuxuan Li; Xiangling Wang; Xiaoyang Xia; Bo Liu; Cuncang Jiang (Journal of Cleaner Production, 2024)