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Irrigation:
Irrigation is the artificial application of water to the soil to assist in the growth of crops. It is a crucial agricultural practice that ensures the availability of water to plants during periods of inadequate rainfall. Irrigation systems are designed to optimize water use and enhance agricultural productivity.
2. Importance of Irrigation
a. Agricultural Productivity
Irrigation plays a vital role in enhancing agricultural productivity by ensuring that crops receive the necessary water throughout their growing season. This leads to higher yields and the ability to cultivate crops in arid and semi-arid regions.
b. Food Security
By enabling consistent crop production, irrigation contributes significantly to food security. It helps stabilize food supplies and reduce dependence on rainfall, which can be unpredictable.
c. Economic Stability
Irrigated agriculture supports the economy by providing employment opportunities and contributing to the income of farming communities. It also supports related industries, such as food processing and distribution.
Methods of Irrigation
Irrigation methods are essential for managing water resources effectively in agriculture. Different techniques are employed based on the type of crop, soil conditions, topography, and water availability. Below is a detailed explanation of the various methods of irrigation:
1. Surface Method or Gravity Method of Irrigation
Surface irrigation, also known as gravity irrigation, is the most traditional and widely used method of irrigation. In this method, water is applied directly to the soil surface and allowed to flow over the field by the force of gravity. It can be further classified into different types based on how water is applied and managed on the field.
A. Complete Flooding of Soil Surface
In complete flooding, the entire soil surface is covered with water, allowing it to infiltrate into the soil. This method is suitable for crops that can tolerate waterlogging.
i) Wild Flooding
Description: Wild flooding involves releasing water without any control or structure, allowing it to flow over the field in a random manner.
Applications: Used in areas where land levelling is not done and for crops that are not sensitive to uneven water distribution.
ii) Border or Border Strip Irrigation
Description: Water is released into long, narrow strips of land called borders. Each border is levelled, and the water flows in a controlled manner from one end to the other.
Types:
- a. Straight Border: Borders are straight and parallel, suitable for flat lands.
- b. Contour Border: Borders follow the contour of the land, ideal for hilly or undulating terrain.
iii) Check or Check Basin Irrigation
Description: The field is divided into small basins or checks by creating levees (bunds) around them. Water is applied to each check, ensuring even distribution and minimal runoff.
Types:
- a. Rectangular Check: Basins are rectangular, suitable for flat and level fields.
- b. Contour Check: Basins follow the contour lines, ideal for sloped or uneven land.
iv) Contour Ditch / Contour Channel Irrigation
Description: Water is conveyed through small channels that follow the contours of the field. These ditches help distribute water evenly and reduce soil erosion on slopes.
Applications: Suitable for hilly areas where water needs to be controlled to prevent erosion.
B. Partial Flooding of Soil Surface
Partial flooding involves applying water to only a portion of the field's surface, which can be more efficient and reduces the risk of waterlogging.
i) Furrow Irrigation
Description: Water is applied in small channels or furrows between the rows of crops. This method ensures that water is delivered close to the root zone with minimal evaporation losses.
Applications: Commonly used for row crops like maize, sugarcane, and cotton.
C. Surge Irrigation
Description: Surge irrigation involves intermittently applying water in pulses, allowing better control over water distribution and infiltration. This technique reduces runoff and improves water use efficiency.
Applications: Effective in managing water in furrow irrigation systems, particularly in soils prone to crusting.
2. Sub-Surface or Sub-Irrigation
Sub-surface irrigation delivers water directly to the root zone of the plants below the soil surface. This method reduces water loss through evaporation and surface runoff, making it highly efficient.
i) Irrigation by Lateral Supply Trenches
Description: Water is supplied to crops through trenches or ditches placed laterally below the soil surface. The water seeps through the soil, reaching the root zone.
Applications: Suitable for soils with good permeability and for crops that can tolerate water near the roots.
ii) Irrigation by Underground Pipe or Tiles
Description: Water is delivered through a network of underground pipes or tiles. The pipes have perforations or outlets that allow water to seep into the surrounding soil, directly reaching the root zone.
Applications: Ideal for high-value crops and areas with limited water availability, as it ensures efficient use of water.
3. Micro-Irrigation
Micro-irrigation is a highly efficient method that delivers water directly to the root zone of each plant through a network of pipes and emitters. It minimizes water wastage and ensures precise water application.
A. Drip Irrigation
Description: Drip irrigation involves the slow release of water directly to the root zone through small emitters. This method ensures that water is used efficiently, with minimal loss to evaporation or runoff.
Applications: Commonly used in orchards, vineyards, and vegetable gardens where precise water application is crucial.
B. Sprinkler Irrigation
Description: Sprinkler irrigation mimics natural rainfall by spraying water over the crops using a system of pipes and nozzles. The water is distributed uniformly across the field, making it suitable for a wide range of crops.
Types:
- Center Pivot: A rotating sprinkler system that covers large circular areas.
- Lateral Move: A system that moves laterally across the field, covering rectangular areas.
Water Requirement (mm) of Crops
| Crop | Water Requirement (mm) |
|---|---|
| Puddled Rice | 1800-2000 |
| Direct Seeded Rice | 1100-1200 |
| Wheat | 350-400 |
| Rabi Maize | 400-450 |
| Jowar | 450-500 |
| Barley | 200-250 |
| Chickpea | 150-200 |
| Lentil | 120-180 |
| Field Pea | 200-250 |
| Summer Greengram | 250-300 |
| Summer/Post Kharif Black Gram | 270-330 |
| Pigeonpea | 210-280 |
| Mustard | 180-220 |
| Linseed | 250-310 |
| Groundnut | 400-450 |
| Soybean | 400-450 |
| Sunflower | 350-500 |
| Sugarcane | 1500-2500 |
| Ragi | 400-450 |
| Potato | 500-600 |
| Onion | 450-550 |
| Berseem | 500-700 |
Water Use Efficiency
Water Use Efficiency (WUE) measures how effectively applied water contributes to economic crop production. It can be evaluated in two ways:
i) Field Water Use Efficiency: This is the ratio of economic crop yield to the total water used for crop growth. Formula: Eu = Y/WR.
ii) Crop Water Use Efficiency: This is the ratio of economic crop yield to the water consumed by the crop. Formula: ECU = Y/CU or ET.
3. Types of Irrigation Systems
a. Surface Irrigation
Surface irrigation involves the distribution of water across the soil surface by gravity. It is one of the oldest and most commonly used methods, including techniques like furrow, basin, and border irrigation.
b. Drip Irrigation
Drip irrigation delivers water directly to the root zone of plants through a network of pipes, tubes, and emitters. This method is highly efficient, reducing water wastage and promoting better crop growth.
c. Sprinkler Irrigation
Sprinkler irrigation mimics natural rainfall by spraying water over the crops through overhead pipes or nozzles. It is suitable for a wide range of crops and is effective in areas with uneven terrain.
d. Subsurface Irrigation
Subsurface irrigation involves the application of water below the soil surface, close to the plant roots. This method reduces evaporation losses and is ideal for areas with limited water resources.
Scheduling of Irrigation
Scheduling of irrigation refers to the systematic planning and timing of when and how much water should be applied to crops. It's crucial for efficient water use and optimal crop growth. Here are the key aspects involved in scheduling irrigation:
1. Crop Water Requirement
Understanding how much water the crop needs at different growth stages based on factors like crop type, stage of growth, weather conditions, and soil type.
2. Soil Moisture Monitoring
Regularly measuring soil moisture content to determine when irrigation is needed. Techniques include using soil moisture sensors or simple methods like feel and appearance.
3. Climate and Weather Considerations
Taking into account factors like temperature, humidity, wind speed, and solar radiation, which affect the rate of water loss from the soil and plants (evapotranspiration).
4. Irrigation Methods
Choosing appropriate irrigation methods such as drip irrigation, sprinkler irrigation, or furrow irrigation based on crop needs, soil characteristics, and water availability.
5. Water Management
Balancing the amount of water applied to ensure it meets crop requirements without causing water stress or waterlogging, which can both adversely affect crop health and yield.
6. Scheduling Tools
Utilizing tools like crop coefficients (Kc values), weather forecasts, and irrigation scheduling models (like the FAO Penman-Monteith method) to calculate water needs and determine optimal irrigation timing.
7. Adjustments
Making adjustments to irrigation schedules based on real-time conditions and feedback from monitoring systems to optimize water use efficiency and crop productivity.
4. Challenges in Irrigation
a. Water Scarcity
In regions with limited water resources, managing water for irrigation is challenging. Efficient irrigation techniques and water conservation practices are essential to address this issue.
b. Soil Salinity
Poor irrigation practices can lead to soil salinity, where salts accumulate in the soil, affecting crop growth. Proper drainage and the use of high-quality water are necessary to prevent salinization.
c. High Costs
Installing and maintaining irrigation systems can be expensive, particularly for small-scale farmers. Government support and subsidies can help mitigate these costs and encourage the adoption of efficient irrigation methods.
5. Sustainable Irrigation Practices
a. Precision Irrigation
Precision irrigation involves the use of technology, such as sensors and automated systems, to apply the right amount of water at the right time. This approach minimizes water wastage and optimizes crop yields.
b. Water Recycling
Recycling wastewater for irrigation purposes is a sustainable practice that reduces the demand for freshwater resources. Treated wastewater can be safely used for irrigation, especially in water-scarce regions.
c. Rainwater Harvesting
Harvesting and storing rainwater for irrigation can supplement water supplies, especially during dry periods. It is an effective way to make use of natural resources and reduce dependence on external water sources.