Soil organic carbon content affects the stability of biochar in paddy soil

[Display omitted] •Rice straw biochar addition decreased total carbon mineralization in paddy soils.•Rice staw biochar carbon cumulative mineralization rates were relatively low in paddy soils.•Mean residence time of stable carbon components of rice straw biochar were 617–2829 years.•Rice straw biochar carbon stability was significantly impact by native soil total organic carbon content. Recalcitrant biochar application appears to be a promising method to decelerate global warming through increasing long-term carbon sequestration in soil. Stability of biochar carbon (C), which is the major determining factor of C sequestration effect, depends mainly on biochar physiochemical characteristics and soil properties. However, little is known about biochar C stability in paddy soil. In this study, 13C labeled rice straw (RS) biochar produced at 500°C was incubated with five types of paddy soils to determine the key soil characteristics involved in biochar-C stability. Results showed that cumulative mineralization rates of RS biochar-C incubated with different paddy soils were relatively low (0.17–0.28%) during 390days of incubation. The cumulative mineralization rates of RS biochar-C increased with the increasing native soil total organic carbon (TOC) content. The estimated mean residence time (MRT) of stable C components of RS biochar in paddy soil, varying from 617 to 2829 years, decreased with the increase of soil TOC content. In addition, greater atomic O/C ratio and oxygen-containing functional groups were observed in biochar samples incubated in paddy soils with higher TOC content. These results suggest that RS biochar application could be an effective method for C sequestration in paddy soil. However, the stability of RS biochar in paddy soil would be significantly impacted by soil TOC content. From the perspective of long-term C sequestration, RS biochar is more suitable for applying in paddy soils with lower TOC content.