*2.4. Biological Fertility Index*

The Biological Fertility Index (BFI) is a comprehensive indicator by composing six biological variables, such as SOM, BSR, CSR, MBC, qCO2, and qM. Five intervals of values were set for each parameter, and scores increasing from 1 to 5 were assigned to each interval (Table 2) based on the available evidences from previous research [13]. The algebraic sum of scores for all the parameters providing the proposed classes of biological fertility are shown in Table 2


**Table 2.** Scores of the intervals of values for the different parameters.

## *2.5. Soil DNA Extraction*

The FastDNA® SPIN Kit for Soil (MP Biomedicals, Solon, CA, USA) was used for DNA extraction. Briefly, 0.5 g of soil was added into Lysing Matrix E tubes, and the samples were homogenized in a FastPrep® at setting 6.0 m s−<sup>1</sup> for 40 s. All extraction steps were performed according to the manufacturer's instructions for kit. Nucleic acid concentration was evaluated using a Nanodrop spectrophotometer (ND-1000, EuroClone, Milan, Italy).
