Question

The field irrigation requirement is computed as ___.

• A. Consumptive use + field application losses
• B. Net irrigation requirement + field application losses
• C. Net irrigation requirement + conveyance losses
• D. Consumptive use + conveyance losses

Answer 1

The correct option is B Net irrigation requirement + field application losses

Field Irrigation Requirement (FIR): It is defined as the amount of water required to meet the 'net irrigation requirements' plus the amount of water lost as surface runoff and through deep percolation.
$FIR=\frac{NIR}{{\eta }_a}$

Net Irrigation Requirement (NIR): It is defined as the amount of irrigation water required to be delivered at the field to meet the evapotranspiration needs of a crop as well as the other needs such as leaching, presowing requirement and nursery water requirement.
NIR = CIR+ LR + PSR + NWR
where, LR = leaching requirement
PSR = pre-sowing requirement
NWR = nursery water requirement
CIR = consumptive irrigation requirement

Consumptive irrigation requirement (CIR): It is defined as the amount of irrigation water that is required to meet the evapotranspiration needs of a crop during its full growth.
$CIR=C_u-R_e$
$C_u=\text{Evapotranspiration or consumptive use of water}$
$R_e=\text{Effective rainfall during the growth of the crop}$

Gross irrigation requirement (GIR): It is defined as the amount of water required to meet the field irrigation requirement plus the amount of irrigation lost in conveyance through the canal system by evaporation and by seepage.
$GIR=\frac{FIR}{{\eta }_c}$
GIR > FIR > NIR > CIR