Sustainable woody biochar application for improving net ecosystem carbon budget, yield and soil properties in red pepper cropping systems: a two-year field study

Abstract Woody biochar (WB) is a low carbon (C)-emitting organic resource that can be used to increase C sequestration by effectively storing C in the soil. However, there is a lack of research on optimal WB application levels for improving the annual net ecosystem C budget (NECB) in red pepper cropping systems. In this study, WB was applied annually at 0, 2.5, 5, and 10 Mg d.w ha −1 for 2 years in a red pepper cropping field. The annual NECB, including C input and output, red pepper biomass productivity, and soil properties, was investigated. The total C input from fertiliser and WB application over the two years was the highest at WB10, followed by WB5 > WB2.5 > WB0. In both years, CO 2 emissions increased with increasing WB application levels, whereas CH 4 emissions exhibited negative fluxes across all treatments, with a negligible impact on C output. WB application increased the cumulative fruit productivity and total biomass productivity. The optimal and sustainable WB application levels for improving the annual NECB were estimated to be 7.3–11.4 Mg d.w ha −1 when removing the whole biomass after harvest and 1.8–6.7 Mg d.w ha −1 when returning it to the soil. Increasing WB application levels significantly improved soil physicochemical properties, such as bulk density and soil organic carbon (SOC) content. Optimising the WB application level may improve organic matter management by enhancing NECB, red pepper productivity, and soil properties. Our results offer guidance for sustainable optimisation of WB application in red pepper cropping systems. Graphical Abstract