Principles of Soil Management - Principles of Sustainable Soil Management in Agroecosystems - page 8

Soil quality
Physical
Chemical
Biological Climate

Precipitation
Te mperature
Growing season
Erosivity
Extreme events

Land
Slope (gradient,
aspect, length)
Drainage
Ve getation cover

Interactive
effects

Management
Land use
Land management
(i) Soil
(ii) Crop/vegetation
(iii) Water

FIGURE 1.3 Natural and anthropogenic factors affecting the extent and severity of soil
degradation.

impacts (Moges and Holden 2007). Wind erosion is an important feature of deserti-
fication on cultivated fields in regions receiving <500 mm/year of rainfall. In the
Sahel, Toure et al. (2011) observed that the absence of crop residue cover is a major
factor exacerbating the wind erosion hazard on cultivated millet fields. Stocking rate,
grazing intensity, and uncontrolled grazing are important factors affecting erosion
on grazing lands (Keay-Bright and Boardman 2007).
The slash-and-burn agriculture, with a short fallow period, is another cause of deg-
radation (Styger et al. 2007) by erosion and nutrient and soil organic C (SOC) deple-
tion. Desertification, soil degradation in arid climates, can alter both the patch index
and the Shannon landscape diversity index. The latter is affected by a severe decline
in the vegetation cover (Hirche et al. 2011). In a chronosequence study conducted in
Western Kenya, Moebius-Clune et al. (2011) reported that physical, chemical, and
biological soil quality indicators (e.g., SOC, aggregation, available water capacity,
pH, electrical conductivity, cation exchange capacity). Thus, soil management must
be done to ensure and sustain soil quality over decadal to millennial scales.

1.4 KEY SOIL PARAMETERS IMPORTANT TO SOIL SUSTAINABILITY
Soil physical, chemical, and biological properties relevant to sustainable manage-
ment are outlined in Table 1.6 . Key soil physical properties are texture, structure,
available water capacity, rooting depth, water transmission, soil strength, crusting,
and erodibility. Important soil chemical properties include pH, total acidity, elec-
trical conductivity, total soluble salts, effective cation exchange capacity, total and
available plant nutrients, and concentration of heavy metals (Pb, Hg, As, etc.).
Similarly, relevant soil biological characteristics comprise total SOC and different
fractions, microbial biomass C (MBC), activity and species diversity of soil fauna,
soil enzymes, and other rhizospheric properties and processes. Threshold/critical
levels of these key soil parameters must be maintained to sustain numerous ecosys-
tem services and functions.