MODELLING THE EFFECTS OF BIOCHAR ON SOIL CHEMICAL AND MICROBIOLOGICAL PROPERTIES USING META-REGRESSION

Abstract

The effects of biochar on soil fertility, carbon storage, and microbiological processes vary considerably depending on feedstock, pyrolysis conditions, application rate, and the initial properties of the soil. The purpose of this work is to systematize the quantitative evidence published in the literature on the effects of biochar and to establish a scientific and methodological foundation for building a meta-regression model that will subsequently incorporate individual study-level data. The primary sources underlying this work are a global meta-analysis covering 59 studies, a global meta-analysis of soil chemical properties, a microbiological meta-analysis covering 49 studies and 265 datasets, and a 2025 biochar–microorganism meta-analysis drawing on 56 studies and 356 individual data points. According to the published results, biochar application increased soil pH, cation exchange capacity, and organic carbon by 46%, 20%, and 27%, respectively, decreased bulk density by 29%, and increased porosity by 59%. For chemical indicators, Hedges' d was 0.50 for SOC, 0.44 for the C:N ratio, 0.39 for pH, 0.35 for total carbon, 0.21 for EC, and 0.20 for CEC. The microbiological effects of biochar can likewise be positive, although they depend on biochar properties and soil conditions. The 2025 meta-analysis showed that combining biochar with a microbial inoculant can increase soil nitrogen, SOC, and crop productivity relative to biochar applied alone. This article does not fabricate new experimental results; final meta-regression coefficients should only be calculated once individual study-level data have been fully digitized. This approach preserves scientific integrity while enabling the development of a predictive model for designing future field experiments and climate-adapted soil management systems.