Relationships between antioxidant capacity and microbial activity in a soil amended with biochar, green compost and vermicompost

The aim of the study was to evaluate the relationships between the antioxidant capacity and the microbial activity in a soil amended with different organic materials. In a 1-year laboratory incubation, biochar, green compost and vermicompost were added to soil at the dose of 2.5% w/w. Antioxidant capacity (TEAC), dissolved organic carbon (DOC), water- and alkali-soluble phenols and microbial activity, as measured by the fluorescein diacetate hydrolysis (FDA), were monitored during incubation. Greater TEAC was in green compost and vermicompost than in biochar treated soil and it was directly related on the TEAC values of the added materials. The application of organic materials caused a marked increase of DOC and water- and alkali-soluble phenols, with values reflecting the amount of these compounds present in the amendments. The relationships between values of TEAC and phenols in the treatments suggest that these substances may be involved in determining the antioxidant capacity of soil. Compared to control, FDA was not influenced by B at each sampling time, probably because the inhibiting activity of TEAC of the material. The two types of compost, particularly vermicompost, stimulated FDA throughout the whole experimental period. Any possible inhibition of the microbial activity induced by TEAC of vermicompost and green compost could have been masked by the considerable supply of organic soluble compounds of composts, that may have stimulated strongly the microorganisms. These results suggest that the soil microbial activity can be defined by the balance between the stimulating activity of DOC and antioxidant activity of the phenols.