Human Impact On Soil Quality

Soil quality may be defined as the capacity of a soil to function for human survival and for the related biogeocycling. Four basic soil functions contribute to such  ecosystemic maintenance:

    1. Sustenance of biological activity, diversity, and productivity

    2. Storage and cycling of nutrients

    3. Water and solute partition and regulation

    4. Filtration, buffering, decomposition, immobilization  and detoxification of organic and inorganic materials

These functions apply to any ecosystem that comprise soil as a component, whether directly or indirectly altered by man. When any of these functions are hampered, soil quality decreases.

Soil degradation is a  major consequence of ecosystem destruction and soil disturbance. It refers to the decline in soil productivity through adverse changes in nutrient states, organic matter, structural stability and concentrations of electrolytes and toxic chemicals  (Lal and Stewart 1990).

Soil degradation incorporates a number of environmental problems, some of which are interrelated. The extent of soil degradation is influenced by a number of factors, namely soil characteristics, relief, climate, land use and socio-economic and political controls. Management of soil degradation represents one of the most challenging environmental problems existing today. Emphasis needs to be placed on sustainable rather than exploitative land use.

Listed below are the physical, chemical and the anthropogenic causes of soil degradation

Physical Causes: 

1. Erosion - rate of removal of soil by water/wind exceeds the rate of soil formation
2. Compaction - compression of a mass of soil into a smaller volume and is usually expressed in terms of  dry  bulk density, porosity and resistance to infiltration Ex. Heavy agricultural machinery
3. Water excess and deficit - either can have a detrimental effect on soil performance

Chemical Causes:

1. Acidification- the main causes are long term leaching and microbial respiration.
2. Salinisation- the accumulation of salts in the soil  (e.g.. irrigation)
3. Sodification- alkalization, the dominance of the soil exchange complex by Na⁺   ions

Anthropogenic Causes:

1. Deforestation
2. Misuse of agricultural land
3. Overgrazing
4. Needleleaf afforestation
5. Excessive use of inorganic nitrogen fertilizers
6. Poor land drainage
7. Acid Deposition/ Acid Rain
8. Improper Irrigation techniques
9. Construction and demolition waste
10. Metalliferous Wastes / Heavy Metals
11. Power generation emissions- Sulfur dioxide, Radionuclides

References: Salvatore Engel Di-Mauro, July 2001, Assessing Soil Quality, Manuscript
Ellis, S., and A. Mellor (1995). Soils and Environment.  Longdon:  Routledge, Chapter 8: "Soils and Environmental problems," pp. 238 - 297