Biochars improve agricultural production: The evidence base is limited

Biochar application to soil is commonly recognized to improve soil fertility and consequently biomass and food production sustainably. We re-examined the robustness of the underlying data and found that, of the 12 000+ publications on “biochar and agriculture” used in meta-studies, only 109 Institute for Scientific Information (ISI) papers (or 0.9%) provide experimental data on the impacts on crop yield and/or biomass production. Our analysis revealed that none (0%) of these studies compared a biochar treatment to a treatment adding to the soil the same amounts of easily accessible nutrients as found in biochar, 0.9% evaluated the toxicity of biochar, and 5.5% considered at least two cropping cycles after a single biochar application, which in all cases are major shortcomings. Finally, when computed only for agricultural soils ( n = 65), the mean biomass or grain yield gain, which was 16.1% (median at 7.1%) for all available experiments, decreased to -0.64% (median at 5.2%). Consequently, the underlying evidence base to support biochar application in agricultural soils to enhance biomass production and grain yield is so far limited.},