Page 19 - Soil Degradation, Conservation and Remediation

4 1 Soil Resources and Soil Degradation

30
25
20

% 15
10
5

0
No significant Permafrost Soils too wet Soils too Chemical Soils too dry
limitation shallow problems
Categories of land

Fig. 1.1 Global soil conditions (Based on data from FAO 1998 )

degree of limitation imposed by its biophysical properties. It is based primarily on
climate, a number of soil properties, (e.g., depth and stoniness), wetness, erosion
risk, and slope.
The USDA Soil Conservation Service devised the land capability classifi cation
system (Helms 1977 ) during the late 1930s and early 1940s. Some form or adapta-

tion of land capability classification is used throughout the world (Olson 1974 ; FAO
1999 ). Scientists are continually refining and improving land classifi cation systems

(Eswaran et al. 2000 ; Fischer et al. 2000 ). Land capability classification is a system
of grouping soils primarily on the basis of their capability to produce common cul-
tivated crops and pasture plants without deteriorating over a long period of time.

The land capability classification is one of the interpretive groupings made also
primarily for agricultural purpose. USDA Nature Conservation Service grouped
soils into following 8 land capability classes.

Class I. Class I soils have few limitations and are suited to a wide range of plants;
they can be safely used for cultivated crops, pasture, range, woodland, and wild-
life. Soils are nearly level with low erosion hazard. Soils are deep, fertile, and
responsive to fertilizers.

Class II. Soils of this class have some limitations reducing choice of crops and may

require moderate conservation practices. These soils require careful management
and conservation to prevent deterioration or to improve air and water relations
when the soils are cultivated. The limitations are few and the practices are easy
to apply .
Class III. Soils have severe limitations that reduce the choice of plants or require

special conservation practices or both. Soils have more restrictions than those in
Class II, and when used for cultivated crops, the conservation practices are

usually more difficult to apply and to maintain. They may be used for cultivated
crops, pasture, woodland, range, or wildlife food and cover.