Irrigation: Meaning and Types

Irrigation refers to artificial application of water to crops.  It is one of the most important critical inputs for enhancing the productivity that is required at different critical stages of plant growth of various crops for optimum production. There are four main methods of irrigation. First one is irrigation using buckets and water cans, useful for small gardens and is out of our purpose of study. The three other types of irrigation viz. Surface irrigation, Sprinkler Irrigation and Drip Irrigation are of importance to agriculture and economy.

Surface irrigation

This refers to application of water by gravity flow to the surface of the field. This can be of three types depending on if the entire field is flooded (basin irrigation) or the water is fed into small channels (furrows) or strips of land (borders). The three types include Basin, Furrow and Border Irrigation.

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 grown on flat lands or in terraces on hillsides. Trees can also be grown in basins, where one tree is usually located in the middle of a small basin.
• In general, the basin method is suitable for crops that are unaffected by standing in waterfor long periods such as 12-24 hours.

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 are affectedin water for long periods such as 12-24 hours.

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. A sheet of water flows down the slope of the border, guided by the bunds on either side.

Surface irrigation is a simple and effective method of irrigation but it should be used under correct management practices only. This is because over and incorrect surface irrigation would result in issues such as water logging, deep drainage, and salinization.

Sprinkler Irrigation

It involves applying irrigation water which is similar to natural rainfall. Water is distributed through a system of pipes usually by pumping. It is then sprayed into the air through sprinklers so that it breaks up into small water drops which fall to the ground.

• The pump supply system, sprinklers and operating conditions must be designed to enable a uniform application of water.
• Sprinkler irrigation is suited for most row, field and tree crops and water can be sprayed over or under the crop canopy.

However, large sprinklers are not recommended for irrigation of delicate crops such as lettuce because the large water drops produced by the sprinklers may damage the crop.

Drip Irrigation

With drip irrigation, water is conveyed under pressure through a pipe system to the fields, where it drips slowly onto the soil through emitters or drippers which are located close to the plants. Only the immediate root zone of each plant is wetted. Therefore this can be a very efficient method of irrigation. Drip and Sprinkler Irrigation involves irrigating crops at the root zone as per the crop requirement. It greatly enhances water use efficiency and can also be used for fertilizer application. Drip irrigation is sometimes called trickle irrigation.

^^Rainguns

Rainguns are high performance impact sprinklers designed for a variety of uses and applications where relatively high flows and extended radius of throw are desired. Rainguns are available with operating pressure of 2.0 to 7.5 kg/cm2 and flows of 3 to 30lps usually with nozzle diameters ranging from 10 to 30 mm and with a wetting radius of 27 to 60 metre^^