Effects of Biochar on Soil Organic Carbon Mineralization in Citrus Orchards

The primary ecological challenges in citrus orchards include soil acidification, nutrient depletion, and significant carbon dioxide emissions resulting from conventional cultivation practices. To address these challenges, citrus peel residues and cassava stalks underwent pyrolysis at 500 °C to generate biochars. Different proportions of these biochars (1%, 2%, and 4%) were applied under controlled laboratory conditions to assess their impact on the mineralization of soil organic carbon in citrus orchards. The results indicated that both types of biochar effectively regulated the soil pH to approximately 5.5. Significantly, the addition of 4% cassava stalk biochar significantly increased the levels of available phosphorus and potassium. The phosphorus levels rose by 512.55%, and the potassium levels surged by 1434.01%. Additionally, the soil organic carbon increased to 16.7 g/kg. Conversely, the citrus peel biochar decreased the availability of phosphorus but resulted in the highest increase in available potassium, at 1523.75%, and elevated the soil organic carbon content to 13 g/kg. Both types of biochar enhanced the soil organic carbon mineralization rate to varying extents with increasing application ratios, simultaneously boosting the cumulative amount of organic carbon mineralized. Among the treatments, cassava stalk biochar displayed the lowest C0/SOC ratio, of 0.169, indicating its superior carbon retention capacity. Furthermore, cassava stalk biochar showed inhibitory effects on soil catalase and urease activities within the citrus orchard. Overall, the application of 4% cassava stalk biochar appears to be more beneficial for nutrient regulation and carbon sequestration in citrus orchard soils, while also contributing to the reduction in soil acidification by adjusting pH levels.