Determination of irrigation requirement of crops

Consumptive Use or Evapotranspiration

Irrigation requirement of crops depends upon the total amount of water used by the plant in transpiration ( building of plant tissues, etc.) and evaporation from adjacent soils or from plant leaves, in any specified time.

Consumptive use may be different for different crops and may be different for the same crop at different times and places

Values of daily consumptive use or monthly consumptive use.

Used to determine the irrigation requirement of the crop

Determination of irrigation requirement of crops

1.Effective rainfall(Re)

Precipitation falling during the growing period of a crop that is available to meet the evapotranspiration needs of the crop.

It does not include precipitation lost through deep percolation below the root zone or the water lost as surface runoff.

2.Consumptive Irrigation Requirement(CIR)

It is the amount of irrigation water required in order to meet the evapotranspiration needs of the crop during its full growth 

It is, therefore nothing but the consumptive use itself, but exclusive of effective precipitation, stored soil moisture or groundwater 

C.I.R = Cu-R

3.Net Irrigation Requirement(NIR)

It is the amount of irrigation water required in order to meet the evapotranspiration need of the crop as well as other needs such as leaching

N.I.R = Cu-R + Water lost in deep percolation for the purpose of leaching etc.

4.Field Irrigation Requirement (FIR)

It is the amount of water required to meet ‘net irrigation requirements’ plus the water lost in percolation in the field water courses, field channels and in field applications of water.

5.Gross Irrigation Requirement (GIR)

GIR is the sum of water required to satisfy the field irrigation requirement and the water lost as conveyance losses in distributaries up to the field.