Irrigation and it's Types

Irrigation is the artificial application of water to the soil through various systems of tubes, pumps, and sprays. Irrigation is usually used in areas where rainfall is irregular or dry times or drought is expected. There are many types of irrigation systems, in which water is supplied to the entire field uniformly. Irrigation water can come from groundwater, through springs or wells, surface water, through rivers, lakes, or reservoirs, or even other sources, such as treated wastewater or desalinated water. As a result, it is critical that farmers protect their agricultural water source to minimize the potential for contamination. As with any groundwater removal, users of irrigation water need to be careful in not pumping groundwater out of an aquifer faster than it is being recharged.

1. Besin Irrigation -

In this method the field is divided into square or rectangular plots of 4 to 4000 m² guided by bunds on all the sides (Fig. 30.4). In some cases (ring basin) the plot may also be circular. This method is usually practiced in nearly levelledlands and hence the depth of wetting is more uniform in this method. However, it is particularly useful on fine textured soils with low infiltration and percolation ratesso that the water is retained on the surface and in the root zone for a longer period of time.

(i) Check Basin - 

The size of check basins may vary from one meters square, used for growing vegetables and other intensive cultivation, to as large as one or two hectares or more, used for growing rice under wet land conditions. The shape and design of basins generally depends on the topography of the area it is being designed for. Check basins can be further divided into rectangular and contour types.

(ii) Ring Basin Method -

This method is a modification of check basin method and is suitable for sparsely grown orchard crops and cucurbits (Fig. 30.5). In this method a circular bund is constructed around each tree/plant or group of plants/trees to create a basin for irrigation. These basins are suitably connected to irrigation conveyance channels in such a way that either each basin is irrigated separately or a group of basins are irrigated at once by flowing water from one basin to another through inter- connections.

2. Furrow irrigation -

Furrow irrigation system is primarily used for vegetables. Furrows are sloping channels dug in the soil with the crops being planted on the ridges. It has advantage that water is applied only in furrows instead of being applied on the whole field. This saves water and at the same timethe plant does not come in direct contact with water which is an added advantage as some plants, like vegetable crops,are very sensitive to ponded water.

3. Sprinkler Irrigation -

The sprinkler irrigation is one of the pressurised irrigation methods, in which water is sprayed into the air and fall on the ground surface somewhat resembling rainfall. The spray of water is developed by the flow of water under pressure through small orifices or nozzles. The pressure created by the pump, which causes the water to flow out through the sprinkler nozzle. The nozzles are mounted on the pressurized pipe system. With careful selection of nozzle sizes and spacing, sprinkler pipe spacing and operating pressure the amount of irrigation water required to fill the crop root zone can be applied nearly uniform at the sprinkling rate to suit the infiltration rate of soil. Pipes used for the sprinkler irrigation system are usually light in weight hence can be conveniently installed and transported in the field from one place to another.

4. Drip Irrigation -

Drip irrigation also called as trickle irrigation is the method of applying filtered water (and fertilizers soluble in water) at a low discharge through the emitters or drippers directly onto or in to the soil. The pressure that need to maintained at the emitters, also called as operating pressure, is usually small operating pressure (20 to 200 kPa or 1 to 2 kg/cm2) compared to the operating pressure required at the nozzle or sprinkler of the sprinkler irrigation system. The discharge of the emitter varies from 0.5 to 12 lph depending on the soil type, discharge available at the source and the area to be irrigated. The low discharge of the emitter results in partial wetting of soil root zone.

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