2. UNIT II Irrigation Methods

Unit 2: Irrigation Methods

Tank Irrigation

1. Definition: Tank irrigation refers to the use of large, man-made or natural water bodies (tanks) to collect and store water for agricultural purposes.
2. Components: Tanks, channels, embankments, and sluice gates.
3. Advantages:
   • Suitable for undulating terrain.
   • Provides water during dry periods.
   • Helps in groundwater recharge.
4. Disadvantages:
   • High initial cost for construction.
   • Requires regular maintenance to prevent siltation.
5. Examples:
   • Eri systems in Tamil Nadu, India.
   • Village ponds in rural areas.

Well Irrigation

1. Definition: Well irrigation involves extracting groundwater through wells for irrigation purposes.
2. Types:
   • Dug wells.
   • Tube wells.
3. Advantages:
   • Reliable source of water.
   • Independent of surface water sources.
4. Disadvantages:
   • High cost of drilling and maintenance.
   • Risk of groundwater depletion.
5. Examples:
   • Use of bore wells in arid regions.

Irrigation Methods

1. Surface Irrigation:

   • Definition: Water is distributed over the surface of the soil by gravity.
   • Types:
     • Basin irrigation.
     • Border strip irrigation.
     • Furrow irrigation.
   • Advantages:
     • Low initial cost.
     • Simple technology.
   • Disadvantages:
     • Inefficient water use.
     • Soil erosion risk.

2. Sub-Surface Irrigation:

   • Definition: Water is applied below the soil surface, directly to the root zone.
   • Types:
     • Buried drip lines.
     • Sub-surface pipes.
   • Advantages:
     • Efficient water use.
     • Reduces evaporation losses.
   • Disadvantages:
     • High installation cost.
     • Maintenance challenges.

3. Micro Irrigation:

   • Definition: Water is applied directly to the plant root zone in small quantities.
   • Types:
     • Drip irrigation.
     • Sprinkler irrigation.
   • Advantages:
     • High water use efficiency.
     • Reduced weed growth.
   • Disadvantages:
     • High initial cost.
     • Potential clogging of emitters.

Design of Drip and Sprinkler Irrigation

1. Drip Irrigation Design:

   • Components: Mainline, sub-mainline, lateral lines, emitters.
   • Design Steps:
     • Determine water requirements.
     • Design layout.
     • Select appropriate emitters.
     • Calculate flow rates and pressure.
   • Advantages:
     • Water savings.
     • Suitable for all soil types.
   • Disadvantages:
     • High initial setup cost.
     • Maintenance required to prevent clogging.

2. Sprinkler Irrigation Design:

   • Components: Pump, mainline, lateral lines, sprinklers.
   • Design Steps:
     • Determine crop water needs.
     • Design system layout.
     • Select sprinkler heads.
     • Calculate pressure and flow rates.
   • Advantages:
     • Uniform water distribution.
     • Can be used on varied topographies.
   • Disadvantages:
     • Wind can affect distribution.
     • Higher energy requirements.

Ridge and Furrow Irrigation

1. Definition: Water is applied in furrows and crops are planted on the ridges.
2. Advantages:
   • Reduces water runoff.
   • Enhances soil moisture retention.
3. Disadvantages:
   • Labor-intensive.
   • Not suitable for all crops.
4. Examples:
   • Used in row crops like maize and cotton.

Irrigation Scheduling

1. Definition: Planning the timing and amount of water application to crops.
2. Methods:
   • Soil moisture monitoring.
   • Crop water stress indicators.
   • Climate data-based scheduling.
3. Advantages:
   • Optimizes water use.
   • Increases crop yield.
4. Disadvantages:
   • Requires accurate data and monitoring.

Water Distribution System

1. Definition: Infrastructure for conveying irrigation water from the source to the field.
2. Types:
   • Canal systems.
   • Pipe distribution networks.
3. Advantages:
   • Efficient water transport.
   • Reduces losses in transit.
4. Disadvantages:
   • High initial construction cost.
   • Maintenance challenges.

Irrigation Efficiencies

1. Field Efficiency: Ratio of water used by the crop to water delivered to the field.
2. Application Efficiency: Ratio of water stored in the root zone to water delivered by the irrigation system.
3. Conveyance Efficiency: Ratio of water delivered to the field to water taken from the source.
4. Overall Efficiency: Combined effect of all efficiencies in the irrigation system.
5. Improvement Methods:
   • Use of lined canals.
   • Drip and sprinkler systems.
   • Proper scheduling and management.

Summary

Understanding various irrigation methods, their design, advantages, and limitations is crucial for efficient water management in agriculture. Implementing suitable irrigation methods and systems, along with proper scheduling and maintenance, can significantly enhance water use efficiency and crop productivity.