Does biochar application improve soil aggregation? A meta-analysis

Biochar as a potential soil amendment has been widely used in agricultural soils for improving soil physical properties. However, the effects of biochar addition on soil aggregation are inconsistent in many individual studies. Therefore, we conducted a meta-analysis of 641 comparisons from 119 published studies to assess the combined effects of biochar application on soil aggregation through biochar attributes, initial soil properties, and experimental conditions. Overall, our results indicate that biochar application significantly improved soil aggregation by 16.4 ± 2.5 %, regardless of biochar/experimental/soil conditions. The response ratio (lnR) of biochar-induced soil aggregation had significant variability across different studies. In the context of biochar attributes, there was a higher favorable influence of wood biochar with higher pyrolysis temperature (> 600 °C). With the amount of biochar increased, the effects of biochar on soil aggregation significantly improved (P < 0.001). Considering experimental conditions, the advancement of soil aggregation was more significant over a longer period of time (> 3 years). In particular, the wet sieving method (18.2 %) is better than the dry sieving method (4.05 %) for assessing soil aggregation. Moreover, soil aggregation intensified in neutral and acidic soil, while alkaline soil was not significantly changed. Also, biochar amendment strengthened soil aggregation in the loam-textured (19.9 %) soils relative to sandy soils (13.4 %). Our meta-analysis demonstrates that biochar as a soil amendment can improve soil aggregation through the combination of experimental conditions with specific biochar, and soil properties.