Among the countries using a capability classi 
fication system the United States is unique in the extent 
to which the soils of the country have been surveyed. 
This allows a further modification, which is not possible 
in countries with less detailed soil survey information. 
When the soils of a state or country are well known it 
may be found that the land falling within a particular 
capability class usually consists of one of a group of soil 
types, which is sufficiently different to be recognized 
and identified. These would then be classified land 
capability units, and land would be classified into these 
smaller more precise categories as well as into the broad 
capability classes. The land capability unit is often the 
same as a soil series in the pedological sense, but need 
not necessarily be so. Even when soils have not been 
broken down into series, the principle of smaller 
divisions within 'capability classes can be applied 
whenever distinctive combination of physical 
characteristics can be identified. 
Two case studies from Chandigarh area and 
Chamba Block, Tehri district are presented here. In our 
country class I land is not very common because of 
climatic factors. 
Land irrigability classification 
The aim of land irrigability classification is to 
categorise the different land units to bring the land under 
sustained irrigation which is one of the most important 
activity to increase productivity. Considerable 
importance has been given to the development and 
extension of irrigation since the time of green revolution. 
This is accomplished by the interpretation of soil 
survey data for grouping the soil and land units for 
sustained use under . irrigation. The interpretative 
groupings of soil and land characteristics for irrigation 
suitability is primarily concerned with predicting 
behaviour of soils under the greatly altered water regime 
brought about by irrigation practices. The requisite 
criteria are soil depth, soil texture, soil permeability/ 
infiltration, coarse fragments, chance of water logging 
etc. This is accomplished in two steps: (1) soil 
irrigability classification which is based on the 
permeability; (2) by integrating soil irrigability 
properties, topography and irrigation water quality, land 
irrigability classes following the contextual approaches 
in GIS environments. The detailed methodology 
followed here is as suggested by AIS&LUS (1970). 
Soil Irrigability Classes 
According to the suitability of soils for sustained 
use under irrigation, they are grouped into different soil 
irrigability classes. This grouping is carried out without 
taking into consideration the available quantity or 
quality of water or even non-soil related factors like land 
development costs, drainage facilities etc. 
Land Irrigability Classes 
The suitability of land for irrigation depends on 
physical factors like quality and quantity of irrigation 
water and socio-economic factors like land development 
costs, provision of drainage facilities and production 
costs of individual crops. The definition for classifying 
soils into different irrigability classes and land 
irrigability classes are shown in Table 5 and 6 (AIS and 
LUS, 1970). 
The criteria adopted for irrigability classification of 
soils are given in Table 7, and for land irrigability in 
Table 8. Overlaying soil, drainage and topography using 
GIS one can derive these classes through querry shell. 
Table 6. Soil irrigability classes and their definitions. 
Class 
Definition 
A 
None to slight limitations for sustained use under 
irrigation 
B 
Moderate soil limitations for sustained use under 
irrigation 
C 
Severe soil limitations for sustained use under 
irrigation 
D 
Very severe soil limitations for sustained use 
under irrigation 
E 
Not suitable for irrigation 
Table 7. Land irrigability classes and their definition. 
Class 
Definition 
Class 1 
Lands that have few limitations of soils, topo 
graphy or drainage for sustained use under irrigation. 
Class 2 
Lands that have moderate limitations of soil, topo 
graphy or drainage for sustained use under irrigation. 
Class 3 
Lands that have severe limitations of soil, topo 
graphy or drainage for sustained use under irrigation. 
Class 4 
Lands that are marginal for sustained use under 
irrigation because of very severe limitations of either 
soil topography or drainage. 
Class 5 
Lands that are temporarily classed as not suitable for 
sustained use under irrigation. 
Class 6 
Lands not suitable for sustained use under irrigation.