Persistent effects of biochar on soil organic carbon mineralization and resistant carbon pool in upland red soil, China

Biochar as a soil ameliorant has generated great interest for scientists in improving soil quality and carbon sequestration. The objective of this study was to investigate the persistent effects of biochar application on soil organic carbon (SOC) mineralization and soil-resistant carbon ( C r ) in upland red soil. This experiment was conducted from September 2011 to May 2016. Biochar was applied only once in September 2011 at rates of 0, 2.5, 5, 10, 20, 30 and 40 t/ha in the field experiment, designated as treatments B 0 , B 1 , B 2 , B 3 , B 4 , B 5 and B 6 . The chemical properties, dynamics of SOC mineralization and soil-resistant carbon ( C r ) were measured at the 1st and 6th year after biochar application. The results were as follows: biochar application at rates of 30 and 40 t/ha (B 5 and B 6 treatments) distinctly increased soil pH value and available P relative to B 0 in 2011. The pH value, available P, SOC, total N and C / N ratio in B 4 , B 5 and B 6 treatments were significantly higher compared with the B 0 treatment, where the B 6 treatment increased the pH value by 0.80 and C / N ratio by 3.88 while increasing available P, SOC and total N by 24.18, 76.29 and 19.78%, respectively, compared with the B 0 treatment in 2016. The cumulative SOC mineralization ( C m ) occupied around 4.62–6.91% of total organic carbon ( C t ), which showed a declining trend in 2016 as compared to 2011. The C m / C t ratio also showed a declining trend with biochar amendment at both samplings. The C r occupied around 26–46% of SOC and showed obviously increasing trends both in 2011 and 2016. We further found that C m / C t showed highly significant ( p < 0.01) negative correlations with the rates of biochar application both in 2011 and 2016. The C r , however, showed very significant ( p < 0.01) positive correlations with the rates of biochar application both in 2011 and 2016. This study suggested that biochar application to upland red soil persistently improved soil properties and resistant carbon. Cumulative SOC mineralization was clearly restrained by biochar amendment. This study can provide scientific support for improving soil fertility and enhancing carbon sequestration by application of large amount of biochar (40 t/ha) in upland red soil.