Grouping of soil based on their suitability for irrigation

Based on the suitability, the soils are grouped into 5 classes as I to V for the purpose of irrigation, survey and mapping as follows.

Group I – It is indicated in green colour in soil mapping. The soil has the characteristic features of:

• Good available moisture holding capacity

• Low water table

• Low salts either soluble or exchangeable

• No soil crust and pan formation

• Negligible sodium amount.

• Negligible sub soil salinity.

• Good Internal permeability.

Group II – Group II is marked in yellow colour. The soil has the following characteristics of:

• Moderately suitable for irrigation

• Relatively higher, salt and exchangeable sodium content is more than group I

• Deep soil with loamy sand texture; some permeable clay may be there

• Subsoil is also permeable in nature.

Group III – It is indicated in red colour.

• Limited irrigation is practiced with limited cropping intensity

• Available soil moisture holding capacity is medium

• Medium water table

• Moderate salt content and exchangeable sodium percentage

• Moderate internal permeability

• No soil crust or pan formation within the root zone

• Sub soil water may be slightly to moderately saline.

Group IV – It is indicated in blue colour. This soil group is usually not suitable for irrigation. Reclamation work such as addition of organic manures, sand, silt, and application of gypsum may bring the soil under irrigation. It has the characteristic features of:

• shallow depth due to rocky substrata

• hard impervious pan formation

• high soil pH

• more soluble salt content (0.5%)

• low moisture supplying capacity

• low internal permeability.

Group V – It is indicated in dark green colour.

• The soil is shallow in depth

• Total soluble salt and exchangeable sodium percentage is high (more than 25%)

• Stony impervious layers

• Severe crust and pan formation are common

• It cannot be reclaimed by normal reclamation work The soil grouping may be again grouped based on the following limitation

• Erosion/drainage which is indicated by the symbol (O)

• Drainage, wetness or overflow indicated by (W)

• Root zone limitation indicted by the symbol (S)

• Climate limitation indicated by the symbol (C) Based on the dominance, the limitation will be ranked serially.

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