Combining meta-analysis and local assessment: An in-depth approach on biochar use towards soil carbon sequestration

This study evaluates the impact of biochar, produced by valorizing waste sewage sludge, on soil carbon (C) sequestration, combining a global meta-analysis with a four-year tropical field trial. Biochar application can enhance soil C and mitigate climate change, contributing to sustainable resource management. The meta-analysis of 586 paired comparisons from 169 studies showed increases in total C (TC) and various soil C fractions post-biochar application. In order to compare global results with local data, the effects of sewage sludge biochar (SSB) obtained at contrasting temperatures were evaluated in a field experiment conducted over five years. The field trial using SSB pyrolyzed at 300°C (SSB300) and 500°C (SSB500) showed modest TC increases (7.7 % with SSB300, 0.7 % with SSB500) and minimal changes in other C fractions. Importantly, the absolute TC gain with SSB300 surpassed those from practices like no-till farming. These results underscore the need to tailor biochar applications and optimize pyrolysis conditions to local settings to improve soil C sequestration. Adopting such context-specific strategies can enhance waste recycling, promote sustainable agriculture, and aid in climate change mitigation.