Application of holm oak biochar alters dynamics of enzymatic and microbial activity in two contrasting Mediterranean soils

The application of biochar in Mediterranean region has been considered a promising mean to enhance the soil quality and health. However, the results of previous studies are inconsistent and the effects of biochar on biological activity seem to depend on the initial soil properties. To elucidate this relation, the evolution of microbial and enzymatic activity in two contrasting soils was evaluated in the course of 12 weeks of greenhouse incubation after biochar application and fertilization with nitrogen, phosphorus and potassium. Biochar enhanced the activity of soil biota in an acid Acrisol as a result of soil pH neutralization which was observed as an increase of microbial biomass carbon (MBC) and soil basal respiration (SBR) during the initial six weeks of the incubation. On the other hand, in an alkaline Calcisol, the effect of biochar application on SBR and MBC was short-term (three weeks) and seemed to be related to the nitrogen availability. Dehydrogenase and urease activity in Acrisol were enhanced by biochar application while the activity of all the other enzymes decreased or remained unaffected by biochar application. Biochar application enhanced the aggregates stability in both soils. In summary, general decrease of the enzymatic activities and the inconsistency of the soil biological properties, specifically MBC and SBR, highlight the need of long-term investigation and periodic sampling to target the dynamic changes induced by biochar application. Nevertheless, the improved aggregation of both soils could indicate biochar as a useful mean to combat soil degradation in Mediterranean areas.