Irrigation methods adopted throughout the world

Irrigation is the supply of water to land or crops to help growth, typically by means of channels or the artificial application methods of water to land to assist in the production of crops.

Methods of irrigation: There are several methods of irrigation. They vary in how the water is supplied to the plants. The goal is to apply the water to the plants as uniformly as possible, so that each plant has the amount of water it needs, neither too much nor too little.

• Surface irrigation

Surface irrigation is the oldest form of irrigation and has been in use for thousands of years. In surface ( flood, or level basin) irrigation systems, water moves across the surface of an agricultural lands, in order to wet it and infiltrate into the soil.

• SUB division of Surface irrigation

Surface irrigation can be subdivided into furrow, border strip or basin irrigation and Furrow Irrigation. It is often called flood .irrigation when the irrigation results in flooding or near flooding of the cultivated land. Historically, this has been the most common method of irrigating agricultural land and is still used in most parts of the world.

• Basin Irrigation

Basins are flat areas of land, surrounded by low bunds. The bunds prevent the water from flowing to the adjacent fields. Basin irrigation is commonly used for rice (paddy) grown on flat lands or in terraces on hillsides. Trees (e.g. citrus, banana) can also be grown in basins, where one tree is usually located in the middle of a small basin.

• Furrow Irrigation

Furrows are small channels, which carry water down the land slope between the crop rows. Water infiltrates into the soil as it moves along the slope. The crop is usually grown on the ridges between the furrows. This method is suitable for all row crops and for crops that cannot stand in water for long periods.

To manage the irrigation with the traditional breach system, the farmer has to open and close the embankment of the water-conveying channel. This is the most common method of releasing water from a channel, but it can also be the most damaging.

Not only is it difficult to control the discharge, but there can be serious erosion of the channel embankment. If other more controllable methods are available, then these should be used in preference to this.

• Border Irrigation

Borders are long, sloping strips of land separated by bunds. They are sometimes called border strips. Irrigation water can be fed to the border in several ways: opening up the channel bank using small outlets or gates or by means of siphons or spiles. Siphons are small curved pipes that deliver water over a ditch bank.

Spiles are small pipes buried in the ditch bank. A sheet of water flows down the slope of the border, guided by the bunds on either side. When the desired amount of water has been delivered to the border, the stream is turned off. However, if the flow is stopped too soon, there may not be enough water in the border to complete the irrigation at the far end.

If it is left running for too long, the water may run off the end of the border and be lost in the drainage system. Border irrigation is best suited to the larger mechanized farms as it is designed to produce long uninterrupted field lengths for ease of machine operations.

Borders can be up to 800 m or more in length and 3 – 30 m wide depending on a variety of factors. Border slopes should be uniform, with a minimum slope of 0.05% to provide adequate drainage and a maximum slope of 2% to limit problems of soil erosion.

Deep homogenous loam or clay soils with medium infiltration rates are preferred. On heavy clay soils, border irrigation may cause problems because of the low infiltration rates (basin irrigation is more suited on these soil types). Close growing crops such as pasture or alfalfa are preferred.

Advantages and Disadvantages

Advantages which are follows:

• Irrigation management is very easy and does not require modern technology and can largely build on local traditional knowledge;
• Adapts well to small land holdings and does not require high financial input;
• Adapts easily to flat topography and can function without outlet drainage facilities;
• Works well with short-term water supplies;
• Irrigation allows full utilization of rainwater and can achieve high application efficiencies;
• Adapts well to moderate to low infiltration rates and allows easy leaching of salts.

Disadvantages of level surface irrigation are:

• Requires level land to achieve high efficiencies (maximum land elevation fluctuation should not be greater than half the applied irrigation depth);
• Soils with high infiltration rates require small field sizes, which interferes with mechanization.
• Difficulty to apply small irrigation quantities, excess water is difficult to evacuate, particularly during times of excess rainfall;
• Plants are partly covered with water sometimes over extended periods (in low infiltration rate soils
• Small basins require extensive delivery channels and are not easily adaptable to tractor mechanization.

Residential flood irrigation

• Drip irrigation

Micro-irrigation, sometimes called localized irrigation, low volume irrigation, or trickle irrigation is a system where water is distributed under low pressure through a piped network, in a pre-determined pattern, and applied as a small discharge to each plant or adjacent to it.

Traditional drip irrigation using individual emitters, subsurface drip irrigation (SDI), micro-spray or micro-sprinkler irrigation, and mini-bubbler irrigation all belong to this category of irrigation methods.

• Drip irrigation

Drip (or micro) irrigation, also known as trickle irrigation, functions as its name suggests. In this system water falls drop by drop just at the position of roots. Water is delivered at or near the root zone of plants, drop by drop.

This method can be the most water-efficient method of irrigation, if managed properly, evaporation and runoff are minimized. The field water efficiency of drip irrigation is typically in the range of 80 to 90 percent when managed correctly.

In modern agriculture, drip irrigation is often combined with plastic mulch, further reducing evaporation, and is also the means of delivery of fertilizer. The process is known as fertigation

Advantages and disadvantages

• • Pot irrigation by On-line drippers

• Pressure compensated integral dripper on soilless without growing channels

Advantages of drip irrigation:

• Fertilizer and nutrient loss is minimized due to a localized application and reduced leaching.
• Water application efficiency is high if managed correctly.
• Field leveling is not necessary.
• Fields with irregular shapes are easily accommodated.
• Recycled non-potable water can be safely used.
• Moisture within the root zone can be maintained at field capacity.
• Soil type plays a less important role in the frequency of irrigation.
• Soil erosion is lessened.
• Weed growth is lessened.
• Water distribution is highly uniform, controlled by the output of each nozzle.
• Labour cost is less than other irrigation methods.
• Variation in supply can be regulated by regulating the valves and drippers.
• Fertigation can easily be included with minimal waste of fertilizers.
• Foliage remains dry, reducing the risk of disease.
• Usually operated at lower pressure than other types of pressurized irrigation, reducing energy costs.

The disadvantages of drip irrigation:

• Initial cost can be more than overhead systems.
• The sun can affect the tubes used for drip irrigation, shortening their lifespan.
• The risks of degrading plastic affecting the soil content and food crops. With many types of plastic, when the sun degrades the plastic, causing it to become brittle, the estrogenic chemicals (that is, chemicals replicating female hormones) which would cause the plastic to retain flexibility have been released into the surrounding environment
• If the water is not properly filtered and the equipment not properly maintained, it can result in clogging .
• For subsurface drip the irrigator cannot see the water that is applied. This may lead to the farmer either applying too much water (low efficiency) or an insufficient amount of water, this is particularly common for those with less experience with drip irrigation.
• Drip irrigation might be unsatisfactory if herbicides or top dressed fertilizers need sprinkler irrigation for activation.
• Drip tape causes extra cleanup costs after harvest. Users need to plan for drip tape winding, disposal, recycling or reuse.
• Waste of water, time and harvest, if not installed properly. These systems require careful study of all the relevant factors like land topography, soil, water, crop and agro-climatic conditions, and suitability of drip irrigation system and its components.
• In lighter soils subsurface drip may be unable to wet the soil surface for germination. Requires careful consideration of the installation depth.
• Most drip systems are designed for high efficiency, meaning little or no leaching fraction. Without sufficient leaching, salts applied with the irrigation water may build up in the root zone, usually at the edge of the wetting pattern. On the other hand, drip irrigation avoids the high capillary potential of traditional surface-applied irrigation, which can draw salt deposits up from deposits below.
• The PVC pipes often suffer from rodent damage, requiring replacement of the entire tube and increasing expenses.
• Drip irrigation systems cannot be used for damage control by night frosts (like in the case of sprinkler irrigation systems.

SPRINKLER IRRIGATION

It is a system of irrigation in which water is distributed in the form of spray like natural rainfall. In this technique, water is delivered through a system of pipe by pumping and then sprayed to the entire field

ADVANTAGES OF SPRINKLER IRRIGATION:

1. Suitable for all types of field condition (except heavy clay soil).
2. Uniform distribution of water with high efficiency.
3. Less land loss provides more land area for cultivation.
4. Loss of water is minimum.
5. Accurate and easy measurement of distributed water.
6. Soluble fertilizers, herbicides and fungicides can be added in water before distributing to the crops.
7. Reduces labor cost.
8. Easy to operate.

DISADVANTAGES OF SPRINKLER IRRIGATION:

1. High initial cost.
2. The water must be clean and free of sand, debris and dissolve salts.
3. Cannot be used in windy climate.
4. Fruits/crops can be damaged due to excessive water.
5. Requires high and continuous power supply.