Biochar effects on soil organic carbon sequestration and acidity amelioration persist after 10 years

Intensive cropping and long-term ammoniacal nitrogen (N) fertilization have degraded soil health in eastern Oregon dryland wheat systems, leading to soil acidification and declining soil organic carbon (SOC) stocks, which poses a critical threat to sustainability. This study assessed the impacts of a one-time biochar application on soil acidity, SOC sequestration, and nutrient dynamics over 10 years in a winter wheat–spring pea rotation. Biochar, derived from forest waste and applied only once in 2013 at rates of 11.2, 22.4, and 44.8 t ha −1 , was evaluated against both non-amended control plots and plots receiving nitrogen fertilizer alone. Key soil properties, including pH, SOC, labile carbon (POXC), cation exchange capacity (CEC), electrical conductivity (EC), nutrient concentrations, and mineralization rates, were measured. Results showed biochar significantly increased soil pH by up to 0.9 units, with improvements persisting for a decade, particularly at higher rates. Elevated pH positively correlated with improved CEC, indicating enhanced nutrient retention and better macro/micronutrient availability (Zn, Ca, Mg, K), reducing Fe solubility. Biochar instantly increased SOC stocks by 95–207% and maintained the stocks for more than 10 years, demonstrating long-term persistence, particularly at higher application rates. Biochar effectively maintained a higher labile carbon content (POXC), although a declining POXC/SOC ratio suggested a shift to more stabilized carbon pools. Mineralization changes were moderate, with non-significant increases in CO 2 efflux at higher biochar rates and no consistent net N mineralization trends, suggesting limited direct stimulation of microbial N cycling. Overall, a single alkaline biochar application provided sustained, long-term benefits, playing a dual role in mitigating acidity and enhancing carbon sequestration, thereby supporting a sustainable strategy for restoring soil fertility and ecosystem function and strengthening dryland agroecosystem resilience.