[Effect of Biochar on Agricultural Soil Aggregates and Organic Carbon: A Meta-analysis]

As a soil amendment, biochar has been widely used to ameliorate agricultural soil. To ensure the effect of biochar on the carbon sequestration of farmlands in China, a Meta-analysis was carried out via collecting published literatures. We quantitatively analyzed the response of biochar application to soil aggregates, aggregate carbon, and soil organic carbon to different experimental conditions. The results showed that the application of biochar significantly increased the proportion of soil macroaggregates(10.8%) and MWD(13.3%) but had no significant effect on soil microaggregates and silty-clay compared with those in the non-biochar-added treatment. Moreover, biochar addition significantly increased soil organic carbon content(56.9%), with the largest increased area in North China(39.4%), and enhanced intra-aggregate carbon contents of each particle size. Biochar could significantly increase soil organic carbon content under different experimental designs. Compared with that under non-fertilization, biochar combined with fertilization could also significantly improve soil structure and soil fertility. We also found that more than two years of biochar application significantly increased the proportion of macroaggregates(15.7%), MWD(21.2%), macroaggregate carbon(31.7%), and soil organic carbon(40.0%). Meanwhile, biochar produced from crop straw had better soil improvement effects than that of wood and sawdust. Biochar applied in high-nitrogen soil was more beneficial to improve soil stability. Thus, we concluded that biochar could meliorate soil structure and promote the accumulation of soil organic carbon, which was of importance for the fertility maintenance and improvement of the farmland.