2.5. Irrigation efficiency

 

Calculating Irrigation Efficiencies: A Step-by-Step Guide

Irrigation efficiency measures how effectively water is used in an irrigation system, comparing the amount of water delivered to the crops with the amount applied. It is crucial for optimizing water use, reducing waste, and improving crop yields.

Types of Irrigation Efficiencies

1. Application Efficiency (Ea)
2. Conveyance Efficiency (Ec)
3. Distribution Efficiency (Ed)
4. Overall Irrigation Efficiency (Eo)

Let's go through each type of efficiency with numerical examples.

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1. Application Efficiency (Ea)

Definition: Application efficiency refers to the ratio of the water that is actually used by the plants to the water applied to the field. It accounts for water lost due to evaporation, runoff, and deep percolation.

Formula: $Ea=\left(\frac{\text{Water stored in the root zone}}{\text{Water applied to the field}}\right)\times 100$

Real-Life Example: Surface Irrigation in a Wheat Field

Context:

• Location: Punjab, India
• Water Applied: 100 mm of water
• Water Stored in the Root Zone: 75 mm

Calculation: $Ea = \left(\frac{75 \text{ mm}}{100 \text{ mm}}\right) \times 100 = 75\%$

Interpretation:

• 75% Efficiency: 75% of the water applied is effectively stored in the root zone for the crop to use, while 25% is lost.

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2. Conveyance Efficiency (Ec)

Definition: Conveyance efficiency refers to the ratio of the water delivered to the field to the water released at the source. Losses occur due to leakage, seepage, and evaporation in the conveyance system.

Formula: $Ec=\left(\frac{\text{Water delivered to the field}}{\text{Water released at the source}}\right)\times 100\mathrm{<br>}\mathrm{<br>}\mathrm{<br>}\mathrm{<br>}\mathrm{<br>}\mathrm{<br>}\mathrm{<br>}\mathrm{<strong><strong\; style="display:\; inline\; !important;"><br></strong></strong><strong><strong\; style="display:\; inline\; !important;"><br></strong></strong>}$

$\mathrm{<strong><strong\; style="display:\; inline\; !important;">Real-Life\; Example:\; Canal\; Irrigation\; in\; California,\; USA</strong></strong>}$

Context:

• Water Released at the Source: 1,000 m³
• Water Delivered to the Field: 900 m³

Calculation: $Ec=\left(\frac{900{\text{ m}}^3}{1,000{\text{ m}}^3}\right)\times 100=90\mathrm{\%}$

Interpretation:

• 90% Efficiency: 90% of the water released from the source reaches the field, while 10% is lost in the conveyance system.

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3. Distribution Efficiency (Ed)

Definition: Distribution efficiency refers to the uniformity with which water is distributed across the field. A low distribution efficiency indicates that some areas of the field receive more water than others, leading to inefficiencies.

Formula: $Ed=(1-\frac{\text{Average deviation from mean application}}{\text{Mean application}})\times 100$

Real-Life Example: Sprinkler Irrigation in a Corn Field

Context:

• Mean Application: 30 mm
• Average Deviation from Mean: 3 mm

Calculation: $Ed=(1-\frac{3\text{ mm}}{30\text{ mm}})\times 100=90\mathrm{\%}$

Interpretation:

• 90% Efficiency: The water distribution is fairly uniform, with only 10% deviation from the mean application across the field.

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4. Overall Irrigation Efficiency (Eo)

Definition: Overall irrigation efficiency combines application efficiency, conveyance efficiency, and distribution efficiency to give an overall measure of how effectively water is used in an irrigation system.

Formula: $Eo=Ea\times Ec\times E\mathrm{d<span\; class="base"><br></span>}$

Real-Life Example: Drip Irrigation in a Vineyard in Spain

Context:

• Application Efficiency (Ea): 85%
• Conveyance Efficiency (Ec): 95%
• Distribution Efficiency (Ed): 92%

Calculation: $Eo=0.85\times 0.95\times 0.92=0.742=74.2\mathrm{\%<span\; class="base"><br></span>}$

Interpretation:

• 74.2% Efficiency: The overall system is fairly efficient, with 74.2% of the water released at the source effectively used by the plants. The remaining 25.8% is lost due to various inefficiencies.

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Summary of Calculations

1. Application Efficiency (Ea):

   • Example: Surface Irrigation in Punjab, India
   • Efficiency: 75%

2. Conveyance Efficiency (Ec):

   • Example: Canal Irrigation in California, USA
   • Efficiency: 90%

3. Distribution Efficiency (Ed):

   • Example: Sprinkler Irrigation in a Corn Field
   • Efficiency: 90%

4. Overall Irrigation Efficiency (Eo):

   • Example: Drip Irrigation in a Vineyard in Spain
   • Efficiency: 74.2%

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Conclusion

Calculating irrigation efficiencies helps in identifying areas of water loss and optimizing irrigation practices. By improving these efficiencies, farmers can conserve water, reduce costs, and improve crop yields, contributing to more sustainable agriculture