Irrigation
What is Irrigation?
The artificial application of water to land to supplement rainfall and meet the water requirements of crops.
Key formula / rule: Duty
Key points
- Understand the necessity and benefits of irrigation.
- Identify and differentiate various irrigation methods.
- Calculate crop water requirements and irrigation water needs.
- Analyze the design principles of different irrigation systems.
Common exam trap
Over-irrigation leading to waterlogging and nutrient leaching.
Definitions
- Term
Irrigation
- Meaning
The artificial application of water to land to supplement rainfall and meet the water requirements of crops.
- Term
Duty
- Meaning
The area of land that can be irrigated by a unit discharge of water flowing continuously throughout the base period of the crop.
- Term
Δ
- Meaning
The total depth of water required by a crop during its entire base period.
- Term
Base Period
- Meaning
The total period between the time of sowing of the crop and the time of its harvesting.
- Term
Waterlogging
- Meaning
The condition where the soil pores are saturated with water, leading to a lack of aeration for plant roots, usually due to a high water table.
- Term
Salinization
- Meaning
The accumulation of soluble salts in the soil, which can be detrimental to crop growth.
- Term
Consumptive Use (CU)
- Meaning
The total amount of water absorbed by the plant and evaporated from the soil surface and transpired by the plant during its growth period.
Learning objectives
Understand the necessity and benefits of irrigation.
Identify and differentiate various irrigation methods.
Calculate crop water requirements and irrigation water needs.
Analyze the design principles of different irrigation systems.
Recognize the factors affecting irrigation efficiency and water management.
Formulae
- Name
Duty
- Note
D = Duty (hectares per cumec), A = Area (hectares), Q = Discharge (cumecs)
- Expression
D = A / Q
- Name
Δ
- Note
Δ = Δ (cm), B = Base Period (days), D = Duty (hectares per cumec)
- Expression
Δ = 8.64 * B * D
- Name
Crop Water Requirement
- Note
CWR = Total volume of water required (ha-m or m³), Δ = Δ (m), A = Area (ha)
- Expression
CWR = Δ * A
- Name
Irrigation Interval
- Note
I = Irrigation Interval (days), FC = Field Capacity, PWP = Permanent Wilting Point, γb = Bulk Density, Drz = Root Zone Depth, ET = Daily Evapotranspiration (consumptive use)
- Expression
I = (FC - PWP) * γb * Drz / ET
- Name
Water Application Efficiency
- Note
Measures how effectively water is stored in the root zone.
- Expression
Ea = (Water stored in root zone) / (Water delivered to the field) * 100%
- Name
Water Conveyance Efficiency
- Note
Measures losses during water transport.
- Expression
Ec = (Water delivered to the field) / (Water diverted from the source) * 100%
Prerequisites
Hydrology
Soil Mechanics
Fluid Mechanics
Engineering Mathematics
Common mistakes
Over-irrigation leading to waterlogging and nutrient leaching.
Under-irrigation resulting in water stress and reduced yields.
Applying water at inappropriate × (e.g., during peak sunlight hours, leading to high evaporation).
Ignoring soil type and drainage characteristics when designing irrigation systems.
Using inefficient irrigation methods that result in significant water loss.
Keywords
Irrigation
Duty
Δ
Base Period
Crop Water Requirement
Irrigation Methods
Waterlogging
Salinization
Sprinkler Irrigation
Drip Irrigation
Flood Irrigation
Consumptive Use
Practice preview
If the duty of water for a crop is 1000 hectares/cumec and the base period is 120 days, what is the delta for the crop in meters?…
medium
Which of the following factors does NOT significantly influence the consumptive use of water by a crop?…
medium
A canal system delivers 10 cumecs of water at the headworks. If 2 cumecs are lost due to seepage and evaporation before reaching the field, what is the water conveyance efficiency?…
medium