Long-Term Low-Rate Biochar Application Enhances Soil Organic Carbon Without Affecting Sorghum Yield in a Calcaric Cambisol

Biochar has gained significant attention for its potential in carbon sequestration, soil health improvement, and crop production sustainability. However, the existing studies predominantly focus on short-term experiments conducted in acidic or neutral soils. This study investigates the long-term effects of biochar application in a calcaric cambisol in a field experiment with four treatments: CK (no fertilizer or biochar), B (only biochar), NPK (chemical fertilizer), and NPKB (combination of chemical fertilizer and biochar). This study assessed soil organic carbon (SOC), sorghum yield, soil bacteria, plant nutrient accumulation in 2020 and 2022, and soil chemical properties after 12 years of consecutive application in 2022. The results revealed a significant increase in SOC due to biochar application in both 2020 and 2022 compared to the treatments without biochar. The 12-year biochar application also significantly enhanced soil total nitrogen (N), available phosphorus (P), and available potassium (K), irrespective of chemical fertilizer application. Notably, sorghum plant N and P accumulation remained unaffected by biochar, and plant N accumulation induced by NPKB was even lower than that of the NPK treatment in 2022. Furthermore, soil bacterial diversity and composition, as well as sorghum yield, showed no significant alterations due to biochar application in both years, despite increased soil nutrient content. These findings affirmed the benefits of carbon accumulation through long-term biochar application in calcaric cambisols, but the positive effects on crop production were found to be negligible.