2.3.3. Indicator scoring
For the comparability of each MDS indicator with different
units, data were transformed and normalized to a value ranging
from 0 to 1 using a standard scoring function (SSF) (Andrews et al.,
2002; Qi et al., 2009). Soil indicators could be divided into four
types according to their functions on soil quality: upper limit,
lower limit, peak limit, and descriptive limit (Qi et al., 2009). SSF
equations for soil indicators are listed in detail in Qi et al. (2009). In
addition, the variables without certain threshold values were
ranked by the linear scoring technique described in Liebig et al.
(2001).