Effects of Organic Farming on the Biotic and Abiotic Properties of Soil: A Meta-Analysis and Meta-Regression from Central Europe

Organic farming can increase the sustainability of farming and support biodiversity and soil health. The aim of this work was to conduct a meta-analysis to evaluate the effects of organic farming on selected soil biotic and abiotic properties in Central Europe and to quantify the possible influences of sampling characteristics, soil type and crop husbandry on these effects. Overall, we integrated data from 59 peer-reviewed studies into our analysis, including 1365 pairwise comparisons (log-response ratios; LRR) that covered carbon and nutrient contents, soil organic matter (SOM), soil microbiology and physicochemical properties. Organic farming increased the levels of microbial activity and this effect decreased with soil depth, whereas generally positive but less robust effects on microbial biomass quantity and soil pH were observed across analyses. In addition, a decrease in cation exchange capacity was observed, but this result should be interpreted with caution due to the limited number of studies. The LRR for the bulk density was affected by the sampling season, while soil type influenced the LRR for the nitrogen contents (with negative values for Chernozems). Tillage modified the LRR for pH and bulk density, as did animal fertilizer for microbial biomass quantity. These differences can be attributed to the differences in pairwise comparisons in these moderators rather than to the use of different farming systems themselves. The lack of effects of organic farming for some categories (SOM, carbon, phosphorus, other macroelements and microbial biomass quality) could be attributed to opposing input–decomposition processes, high variability in site conditions across studies or large scatter in the data. Our results highlight the importance of considering soil characteristics and moderators related to crop husbandry when evaluating the effects of farming systems on soil health.