Page 22 - Soil Degradation, Conservation and Remediation

1.4 Soil Fertility, Soil Productivity, Soil Quality, and Soil Health 7

air quality, and support human health and habitation.” Subsequently the two terms
soil quality and soil health are used interchangeably (Karlen et al. 2001 ), although
it is important to distinguish that soil quality is related to soil function (Karlen et al.
2003 ; Letey et al. 2003 ), whereas soil health presents the soil as a fi nite nonrenew-
able and dynamic living resource (Doran and Zeiss 2000 ). The quality of soil is
rather dynamic and can affect the sustainability and productivity of land use. It is the
end product of soil degrading or conserving processes and is controlled by chemi-
cal, physical, and biological components of a soil and their interactions (Papendick
and Parr 1992 ).

1.4.4.1 Soil Quality Classes

The concluding remarks of the meeting on “Land Resources: On the Edge of the
Malthusian Precipice?” (Greenland et al. 1998 ), “if all the resources are harnessed

and adequate measures taken to minimize soil degradation, sufficient food to feed

the population in 2020 can be produced, and probably sufficient for a few billion
more,” inspired Eswaran et al. ( 1999 ) to review the soil quality status of the world.
They defined soil resilience and soil performance and divided each into low,

medium, and high categories. Combining three soil performance classes and three
soil resilience classes, Eswaran et al. ( 1999 ) divided world soils into nine land qual-
ity (in this classification land and soil are used synonymously) classes. They defi ned

land quality, soil resilience, and soil performance as:
Land Quality : The ability of the land to perform its function of sustainable agricul-
ture production and enable it to respond to sustainable land management.
Soil Resilience : The ability of the land to revert to a near original production level
after it is degraded, as by mismanagement. Land with low resilience is perma-
nently damaged by degradation.
Soil Performance : The ability of the land to produce (as measured by yield of grain,
or biomass) under moderate levels of inputs in the form of conservation technol-

ogy, fertilizers, pest, and disease control. The definitions of the land quality
classes according to Eswaran et al. ( 1999 ) are shown below:

Land quality class Performance and resilience
Class I High performance, high resilience
Class II High performance, medium resilience
Class III Medium performance, high resilience
Class IV High performance, low resilience
Class V Medium performance, medium resilience
Class VI Low performance, high resilience
Class VII Low performance, low resilience
Class VIII Low performance, medium resilience
Class IX Low performance, low resilience