Effects of KMnO4-Modified Biochar Combined with Organic Fertilizer on Carbon and Nitrogen Content in Acidic Red Soil and the Growth of Chinese Cabbage

To investigate the effects of co-application of KMnO4-modified biochar and organic fertilizer on the physicochemical properties, carbon and nitrogen content, and growth of Chinese cabbage in acidic red soil. Using typical acidic red soil from Yunnan as the test substrate, this study conducted a pot experiment with four treatment groups: control (CK), organic fertilizer alone (OF), biochar combined with organic fertilizer (BOF), and potassium permanganate KMnO4-modified biochar combined with organic fertilizer (Mn-BOF), each at three application rates (1500, 3000, and 4500 kg/ha). The results indicated that KMnO4 modification significantly improved the pore structure of biochar, increasing its specific surface area by 22.776%, and successfully loaded manganese onto the biochar surface. Compared with the CK, all treatments significantly increased soil pH, organic matter (SOM), alkali-hydrolyzable nitrogen (AN), available phosphorus (AP), and available potassium (AK), with the effects gradually increasing as the application rate rose; the 4500 kg/ha treatment yielded the best results. The Mn-BOF treatment was most effective in increasing soil organic carbon (SOC), total nitrogen (TN), soluble organic carbon and nitrogen (DOC/DON), and microbial carbon and nitrogen (MBC/MBN); simultaneously, the Mn-BOF treatment significantly promoted the growth of Chinese cabbage, with yield under the 4500 kg/ha treatment increasing by 158.58% compared to CK (under pot-grown conditions), and soluble total sugars, chlorophyll, and vitamin C content also significantly increased. In summary, Mn-BOF can improve the fertility of acidic red soil, particularly demonstrating excellent performance in enhancing key carbon and nitrogen components such as SOC, TN, DOC, DON, MBC and MBN. This, in turn, promotes increased yield and improved quality of Chinese cabbage, providing feasible guidance for enhancing soil fertility in highland agricultural systems.