Question

Choose the correct answer from the given below terms in decreasing order of irrigation requirement:
A. Consumptive Irrigation Requirement (CIR)
B. Net Irrigation Requirement (NIR)
C. Field Irrigation Requirement (FIR)
D. Gross Irrigation Requirement (GIR)

• A. CIR $>$ FIR > GIR $>$ NIR
• B. CIR $>$ GIR > FIR $>$ NIR
• C. GIR $>$ FIR > CIR $>$ NIR
• D. GIR $>$ FIR > NIR $>$ CIR

Hint:

Remember the water flow sequence:
$\text{Gross (Source)} \rightarrow \text{Field (Surface)} \rightarrow \text{Net (Root Zone)} \rightarrow \text{Consumptive (Crop Use)}$.
Because efficiency losses occur at each step, the water quantities must decrease along this path.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Irrigation requirements describe the depth of water needed at different stages of the delivery system to meet crop water needs.
As water moves from the source to the field and down into the soil, some of it is lost to evaporation, seepage, and deep percolation.
Because these losses accumulate at each stage of the system, the gross volume of water diverted from the source must always be larger than the net amount used by the crop.

Step 2: Detailed Explanation:
Let us define and calculate each irrigation term from the crop root zone back to the water source:
1. Consumptive Irrigation Requirement (CIR):
This is the depth of water required to meet the crop's evapotranspiration ($ET_c$) needs, minus the amount supplied by effective rainfall ($P_e$):
\[ \text{CIR} = ET_c - P_e \] This is the smallest water requirement term.
2. Net Irrigation Requirement (NIR):
This is the total water depth that must be stored in the root zone to satisfy the crop's needs.
It includes the consumptive requirement plus water needed for leaching ($LR$), pre-sowing tillage ($W_{ps}$), and nursery operations:
\[ \text{NIR} = \text{CIR} + \text{Leaching} + \text{Pre-sowing requirements} \] Thus, $\text{NIR} \ge \text{CIR}$.
3. Field Irrigation Requirement (FIR):
This is the depth of water that must be applied to the field surface.
It includes the net irrigation requirement plus water lost to surface runoff and deep percolation during application on the field:
\[ \text{FIR} = \frac{\text{NIR}}{\text{Field Application Efficiency } (\eta_a)} \] Thus, $\text{FIR} \ge \text{NIR}$.
4. Gross Irrigation Requirement (GIR):
This is the total depth of water diverted from the source (such as a river, canal, or well).
It includes the field irrigation requirement plus water lost to seepage and evaporation during conveyance through the canal network:
\[ \text{GIR} = \frac{\text{FIR}}{\text{Conveyance Efficiency } (\eta_c)} \] This is the largest water requirement term.
Arranging these terms in decreasing order gives:
Gross Irrigation Requirement (GIR) $>$ Field Irrigation Requirement (FIR) $>$ Net Irrigation Requirement (NIR) $>$ Consumptive Irrigation Requirement (CIR).

Step 3: Final Answer:
The correct decreasing order of the irrigation requirement terms is GIR $>$ FIR $>$ NIR $>$ CIR.
Hence, the correct option is (D).