1. Surface Irrigation

Surface irrigation is the most commonly used method worldwide. It involves the application of water by gravity flow over the soil surface. This method is suitable where land has a gentle slope and sufficient water is available.

Surface irrigation refers to a method of watering crops where water is applied directly to the soil surface. The water moves across the field by the force of gravity. This method works best on lands that are not too steep, as gently sloped land allows water to flow evenly and reach all crops. Adequate water supply is also needed to utilize this method effectively.

Imagine filling a shallow dish with water. As the water fills up, it spreads out and covers the surface evenly, especially if the dish is not too deep. Similarly, in surface irrigation, water flows over the soil like this dish filling up, ensuring that all plants get the moisture they need as long as the ground is level.

1.1 Types of Surface Irrigation

1.1.1 Basin Irrigation • Land is divided into flat basins surrounded by bunds. • Used for rice, wheat, sugarcane. • Water is allowed to flood the basin and infiltrate gradually.

1.1.2 Border Irrigation • Water is applied through long parallel strips called borders. • Width of border: 3–15 meters; Length: 100–400 meters. • Used for close-growing crops like wheat, barley.

1.1.3 Furrow Irrigation • Water flows through small, shallow channels (furrows) between crop rows. • Suitable for row crops: maize, cotton, sugarcane. • Reduces contact with foliage, thus reducing fungal diseases.

1.1.4 Wild Flooding • Water is released without defined control or channels. • Practiced in undulating lands. • Low efficiency and high water wastage.

Surface irrigation can be categorized into four main types:

1. Basin Irrigation: Fields are divided into flat areas called basins which hold water, allowing it to seep into the soil. This method is great for water-intensive crops like rice.
2. Border Irrigation: Water is applied in strips called borders that can be adjusted in size. This method is often used for crops like wheat and barley.
3. Furrow Irrigation: Water is delivered to the plants via small channels called furrows. This approach minimizes water on plant foliage, which helps prevent diseases. It’s mostly used for row crops such as maize.
4. Wild Flooding: Water is released to flow naturally without any control structures, often resulting in waste. This is generally less efficient and used in uneven terrain.

Think of basin irrigation like little swimming pools for plants. Each pool catches water and lets it slowly sink in. Border irrigation can be likened to running water down a line of small hills; it follows the edges where it can flow safely. Furrow irrigation is like rolling a ball in between a row of dominoes, making sure each gets a little water without all of them toppling over. Wild flooding resembles letting water run freely in a park—great for some spots, but it can get messy and wasteful!

1.2 Design Parameters • Soil infiltration rate • Land slope • Stream size • Field length and width • Water application depth

To design an effective surface irrigation system, several parameters must be considered:

1. Soil Infiltration Rate: This is how quickly the soil can absorb water. Faster rates mean better irrigation effectiveness.
2. Land Slope: The angle of the land influences how water flows. Steeper slopes can result in runoff instead of absorption.
3. Stream Size: This refers to how much water is being applied at one time. The right size prevents flooding or dry patches.
4. Field Dimensions: The length and width of the field affect how water will spread across the area.
5. Water Application Depth: How deep the water can soak into the soil before reaching the crop's root zone is crucial for ensuring healthy plant growth.

If you're filling up a sponge with water, you need to consider how quickly the sponge can soak it up (infiltration rate), its angle (slope), and how much water you pour on it at once (stream size). If your sponge is too flat or too small (field dimensions), it may not hold enough water, and if you pour too much too fast, it might just overflow!

1.3 Advantages • Simple and low cost • No high-tech equipment required • Utilizes gravity

Surface irrigation has several benefits:

1. Simplicity: This method is straightforward to set up and operate, making it accessible for many farmers.
2. Cost-Effective: Since it doesn't require advanced technology or equipment, surface irrigation can be less expensive than other methods.
3. Natural Flow: By using gravity, this irrigation method requires less energy, which can be a big advantage in remote areas without electricity.

Consider a simple garden hose attached to the side of a hill. Rather than using a pump to force the water upwards, you let gravity do all the work, guiding the water down to your plants. It's inexpensive and everyone can do it without needing special training!

1.4 Limitations • High water losses due to deep percolation and runoff • Waterlogging and salinity risk • Not suitable for sandy soils or steep terrains

While surface irrigation is practical, it also has limitations:

1. Water Losses: A significant amount of water can seep deep into the ground or run off, especially during heavy applications, leading to inefficiency.
2. Waterlogging: Too much water on the surface can saturate the soil and lead to waterlogging or root damage. Salinity can also increase when water evaporates, leaving salts behind.
3. Soil Type Limitations: This method is not ideal for sandy soils, which drain too quickly, or steep slopes, where water will run off instead of soaking in.

Imagine trying to fill a bucket with holes at the bottom. No matter how much water you pour in, it will always leak out. This is similar to how water can be wasted in surface irrigation, especially on porous or sloped land where it can’t be absorbed well, often leaving plants thirsty.

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