Contents preface (VII) introduction 1—37

(vi) Forest Soils: These soils contain high percentage of organic and vegetable matter and are also called humus. These are found in forests and foothills.
Soils suitable for agriculture are called arable soils and other soils are non-arable. Depending upon their degree of arability, these soils are further subdivided as follows:
(i) Class I: The soils in class I have only a few limitations which restrict their use for cultivation. These soils are nearly level, deep, well-drained, and possess good water-holding capacity. They are fertile and suitable for intensive cropping.
(ii) Class II: These soils have some limitations which reduce the choice of crops and require moderate soil conservation practices to prevent deterioration, when cultivated.
(iii) Class III: These soils have severe limitations which reduce the choice of crops and require special soil conservation measures, when cultivated.
(iv) Class IV: These soils have very severe limitations which restrict the choice of crops to only a few and require very careful management. The cultivation may be restricted to once in three or four years.
Soils of type class I to class IV are called arable soils. Soils inferior to class IV are grouped as non-arable soils. Irrigation practices are greatly influenced by the soil characteristics. From agricultural considerations, the following soil characteristics are of particular significance.
(i) Physical properties of soil,
(ii) Chemical properties of soil, and (iii) Soil-water relationships.