Table 3: Soil quality indicators, scoring curve, and threshold and baseline limits used for evaluating eight LUSMS in northern Ethiopia.

IndicatorScoring curveThresholdBaselinecOptimumdSlope at baselineSource of limits
LoweraUpperb

Sand (%)Optimum 060L, 30360.440Natural ecosystem, best managed soils
U, 50
Silt (%)More is better 038190.249Best managed soil, natural ecosystem
Clay (%)More is better031150.268Natural ecosystem
SAS (%)More is better 1060300.296Harris et al. [17]; natural system
BD (g cm−3)Less is better12.21.51.2−0.323Harris et al. [17]; natural ecosystem
A-horizon depth (cm)More is better020100.318Natural ecosystem
MWHC (%)More is better2058300.198Gregory et al. [41]; natural system
OCe (%)More is better16.53.51.046Kay and Angers [42]; natural ecosystem
CEC (cmolc kg−1)More is better646200.245Natural ecosystem, best managed soil
TN (%)More is better0.050.540.3025.408Natural ecosystem,
TP (mg kg−1)More is better20013166500.005Natural ecosystem
Pav (mg kg−1)More is better529150.433Mausbach and Seybold [43]; natural ecosystem
Zn (mg kg−1)Optimum 220L, 10140.855 Mausbach and Seybold [43]; natural system
U, 18
Fe (mg kg−1)Optimum 1050L, 20260.577Harris et al. [17]; natural system
U, 40
Earth worm count
per m2
More is better01150.470 Natural ecosystem

Soils at or below the threshold values are prone to structural destabilization, erosion, and low productivity; so the scoring value is 0.
bSoils at or beyond this values no further increase in productivity or decrease in erosion rate are achieved the upper threshold; values at and above this level thus receive a score of 1.0.
cValues receive a score of 0.5 and are generally regarded as the minimum target values.
dThe value is given a score of 1.0 if the desired relationship is bell-shaped.
eAccording to Kay and Angers [42], irrespective of soil type if SOC contents are below 1%, it may not be possible to obtain potential yields.
L: lower; U: upper; SAS: soil aggregate stability; BD: bulk density; MWC: maximum water holding capacity; OC: organic carbon; CEC: cation exchangeable capacity; TN: total nitrogen; TP: total phosphorous; Pav: available phosphorous; Zn: available Zinc; Fe: available iron; —: implies not applicable.