Table 8. Criteria for classifying soils into irrigability classes in semi-arid and arid regions. 
S.No. 
Soil Properties 
Irrigable Classes 
N on-irrigable Classes 
A 
B 
C 
D 
£ 
1. 
Effective soil depth 
(useful to crops) 
More than 
100 cm 
51-100 cm 
25-50 cm 
10-25 cm 
less than 10 cm 
2. 
Texture of surface 
(upto 30 cm) 
Sandy loam 
to clay 
Loamy sand, 
clay 
Sand, Clay 
Sand, Clay 
or any texture 
Skeletal, fragmental 
3. 
* Soil permeability 
(of least permeable layer) 
5-50 mm/hr 
1.3-5 mm/hr, 
50-130 mm/hr 
0.3-1.3 mm/hr 
130-250 mm/hr 
Less than 
0.3 mm/hr 
greater than 
250 mm/hr 
Not applicable 
4. 
Available water holding 
capacity to depth of 90 cm 
12 cm 
9-12 cm 
6-9 cm 
2-6 cm 
Less than 2 cm 
5. 
Coarse fragments 
Cobbles and stones 
(more than 75 cm) 
Less than 5% 
5% 
5-15% 
15-35% 
35-65% 
More than 65% 
6. 
Gravel and Kankar 
(less than 25 to >5 mm) 
Less than 15 
5-35 
35-55 
55-70 
More than 70 
7. 
Rock out crops 
(distance apart in m) 
40 
20 
15 
5 
Less than 5 
8. 
* * Salinity E.C. x 10 ’ 
(in saturation extract) 
Less than 
4 mmhos/cm 
4-8 mmhos/cm 
8-12 mmhos/cm 
12-16 mmhos/cm 
More than 
16 mmhos/cm 
9. 
Salt affected (visual) 
(% of area affected) 
Less than 20 
Less than 20 
20-50 
20-60 
More than 50 
10. 
Severity of Alkali problem 
- ESP less than 15 - 
ESP more than 15 
11. 
Sub-soil or sub-strata 
drainage characteristics 
Lower sub-soil is atleast moderately 
permeable or a permeable layer of atleast 
6" thickness occurs immediately below 
the soil, but within 10" (sand, gravel) 
No moderately permeable sub-oil or 
other permeable layer of atleast 6" 
thickness occurs within depth of 10" 
12. 
Soil erosion status 
Effects of sheet and rill erosion are reflected in effective 
soil depth available moisture holding capacity and in some 
other factors shown above. Moderately or severely gullied 
soils may be classified based on local experience. 
* Soil permeability as a criteria is not applicable to deep black soils because of their unique properties. Deep black soils 
Vertisols which arc inherently slowly permeable due to expanding 2:1 lattice type minerals do not quality for irrigability soil class 
A. They would qualify for being placed in B, C and D class. 
** The method recommended by the soil testing laboratories in India prescribe 1:2 Soil Water Ratio for soil salinity 
determination and hence corresponding conductivity figures are given here 
Salinity in Less than 1-1.5 1.5-2.5 2.5-3.0 More than 
1:2 dilution 1 mmhos/cm mmhos/cm mmhos/cm mmhos/cm 3 mmhos/cm 
(The criteria for salinity and alkalinity refer to equilibrium conditions under irrigation with specified irrigation water).