Marginality Principle - Principles of Sustainable Soil Management in Agroecosystems - page 25

TABLE 2.2
Types of Soil Degradation

Type Degradation Process

Biological Decline in spoil biological activity

Decline in soil biodiversity
Depletion of SOC pool
Increase in soilborne pathogens

Physical Breakdown in soil structure

Crusting and surface sealing
Compaction: surface and subsoil
Reduction in water infiltration capacity
Increase in runoff rate and amount
Decrease in soil water holding capacity as a result of reduced SOC
Inundation, waterlogging, and anaerobiosis
Accelerated erosion by water and wind
Desertification

Chemical Leaching of bases

Acidification
Elemental imbalance with excess of Al, Mn, Fe
Salinization, alkalinization
Nutrient depletion
Increased contamination, pollution

Source: Adapted from Lal, R., Philos. Trans. R. Soc. Biol. London , 352, 997-1010, 1997.

soil biological methods to determine differences among techniques. They found
that the metabolic quotient (ratio of respiration to microbial biomass) had value as a
potential index to evaluate ecosystem disturbance or its maturity. From their analy-
sis, they concluded that any framework for assessing soil quality should incorporate
some aspect of soil biological status or function as an indicator of soil quality or soil
degradation.
Any factor that modifies water and air exchanges in the soil will lead to changes
in the physical conditions linked with soil-atmosphere interactions. Degradation of
the soil structure as a result of impaired soil biological activity will no longer allow
soil particles to maintain their ability to withstand either mechanical or hydrologi-
cal forces. Once this breakdown in soil structure begins, a reduction in aggregate
strength or stability occurs, resulting in a promotion of slaking, crusting, and bulk
density (compaction). Changes in soil structure affect soil porosity and diminish gas
exchange, leading to less oxygen and increasing carbon dioxide concentrations in
the soil profile. When there is a diminished soil structure at the surface, the poten-
tial for erosion increases, because under rainfall events, the stability of the soil sur-
face decreases, and the infiltration rate of water can no longer be maintained. With
subsequent rainfall, the instable soil particles begin to move, and if rainfall events
continue long enough, there will be erosion. Compaction is a result of the lack of
soil structure and poor aggregate stability. Hamza and Anderson (2005) suggest that