Large discrepancies in soil carbon sequestration following biochar application

The addition of biochar, an almost pure and stable C product, to soil is proposed as a method to enhance soil carbon (C) sequestration, yet evidence from research studies suggest variable results. This study reassesses biochar research by reviewing 16 laboratory studies from prominent biochar reseachers, that lead the field to compare the theoretical and actual soil carbon increase post-biochar application. Our analysis, which included 116 data points, reveals large discrepancies between the expected (i.e. estimated by mass balance) and measured soil carbon content after biochar addition. Our results show that 66% of the reported results demonstrate a net loss (mean of -56%) of biochar-derived carbon, while 34% of the reported results observed carbon gains of 505% in average, which was well above the total amount of biochar C added. Such large discrepancies in the results together with the existence of unexplained huge soil C gain puts into question the applicability of these studies and potentially the ability of biochar to enhance soil C stock. Until sound research is performed, particularly by prominent scholars at the forefront of the field, on the underlying reasons of such discrepancies, models and policies should consider with more caution the use of biochars as a panacea for soils. Possible ways forward for biochar research are finally suggested.