Effect of Biochar, Green Compost, and Vermicompost on the Quality of a Calcareous Soil: A 1-Year Laboratory Experiment

Changes in the chemical and biological characteristics of a calcareous soil by the addition of green compost (GC), vermicompost (VC), biochar, biochar + GC, and biochar + VC were evaluated during a 360-day laboratory incubation. The GC and the VC treatments lowered the soil pH and increased the total and dissolved organic C, microbial biomass C, microbial quotient, alkaline phosphatase (AP-ase) and specific AP-ase, dehydrogenase (DH-ase) and specific DH-ase, and metabolic potential. The improvement in the biological activity of the soil was more notable and permanent with VC than GC. The biochar treatment temporarily increased the pH of the calcareous soil (pH 8.2) up to a maximum of 8.57, showed the greatest increase of total organic C, did not change dissolved organic C and microbial biomass C, and induced small effects on soil biological activities. When mixed with biochar (biochar + GC and biochar + VC), composts led to higher organic C mineralization; dissolved organic C, biomass C, and DH-ase activity; and did not change the metabolic quotient, specific AP-ase, and specific DH-ase activities. The AP-ase activity of biochar was enhanced only by the addition of VC, although in a nonadditive way. Metabolic potential was more than halved by the GC and was not changed by the VC. Overall, our study shows that the incorporation of both composts, particularly VC, into calcareous soils may improve soil quality, whereas biochar could have benefits for C sequestration. In addition, the mixing of GC, and especially VC with biochar, increased some soil quality parameters compared with the biochar-only treatment.