Types

Irrigation

There are several methods of irrigating fields viz

• Wild flooding,

• Border Irrigation,

• Basin Irrigation,

• Furrow Irrigation,

• Contour Furrow Irrigation,

The method should allow conservation of soil and should also provide enough water to satisfy the needs of plants but not cause waste and damage.

1. Flow

• Wild Flooding

It is the oldest and the most primitive method of irrigation. It consists of opening a water channel in the field so that water can flow freely in all direction. In this method considerable quantity of water is wasted by run-off, deep seepage and evaporation, high lying patches remain dry and low lying ones are sub merged under water, resulting in ununiform stand of the crop and low yields.

• Border Irrigation

This may also called Sara Method. In this method, field is irrigated by dividing it into a number of strips, varying from 6-18 m. in width and 30-150 m. in the length and levelling the land and separating the strips by earth bund about 30 cm high. When sufficient water has been applied to one border strip, the irrigation stream is turned into another strip.

• Basin Irrigation

It consists of letting water into level square plots of 3.6 m. X 3.6 m., size surrounded by small bunds to retain the desired depth of water. This method is especially adopted for orchards and other high value crops viz., leafy vegetables, onions, lucerne etc. It is suitable for all types of soils. It is also efficient in the use of water.

• Furrow Irrigation

Row crops such as potatoes, maize, jowar, sugarcane, cotton, vegetables etc., can be irrigated by the furrow method. Furrows are either run directly down the slope or they can be run on contour to control erosion from rainfall or irrigation water. On slopes of 1 to 3 p.c., furrow irrigation with straight furrows is quite successful but on steeper slopes contour furrows not only check erosion but also ensure uniform water penetration. Fixed curvature syphon tubes to carry water from the head ditch down each furrow, ensure a uniform supply of water and also help in reducing soil erosion. It is necessary to adjust the height of the spiles so as to keep the rate of flow uniform in all the furrows. In heavy black cotton soils a combination of border strip irrigation with furrows may be useful.

• Contour Furrow Irrigation

With contour furrow irrigation, the direction of flow is across a sloping field rather than down the slope to reduce water velocity. Head ditches are run across the slope or down hill using drop structures as needed to feed the individual furrows. The contour furrow method can be successfully used in nearly all irrigable soils. Light soils can be irrigated successfully across slope upto 5 p.c.

This system involves the slow application of water, drop by drop, to the root-zone of a crop. The equipment consists of a pumping-unit to create a pressure of about 2.5 kg/sq.cm, pipe lines which may be of PVC tubing with drip type nozzles or emitters, and a filter unit to remove the suspended impurities in the water. The amount of water dripping from the nozzles can be regulated, as desired, by varying the pressure at the nozzles, and the size of the orifice of the nozzles. Water supply may be continuous or intermittent. In this method, water is used very economically, since losses due to deep percolation and surface evaporation are reduced to the minimum. This method is very suited to arid regions. The successful growing of orchards even on saline soils has been made possible by the drip system of irrigation. The system can be used for applying fertilisers in solution. The initial high cost of the equipment and its maintenance are the major limitations of this system. Pitcher Method: Porous pitcher inserted near the pit or pocket or base of the plant, water that comes out of the pitcher, irrigates the root-zone of the crop. The pitcher is refilled. This method is a most important and easy method of applying water in arid and semi-arid zones with light soil and wide spaced crops such as cucurbits or orchards.

This method consists of application of water to soil in the form of spray. It is particularly useful for sandy soils because they absorb water too fast. Soils that are too shallow, too steep, or too rolling to be irrigated by surface method, can be effectively irrigated with sprinklers. Urea and potash fertilisers as well as pesticides can also be successfully applied to crops through sprinklers. It also saves about 30 to 40% of water and water losses are kept to the minimum. Sprinkler system has some limitations such as (a) distribution may be affected by wind, (b) power requirement is usually higher than for other methods of irrigation and (c) the initial cost is very high.

Drainage is removal of excess gravitational water from the soil by artificial means to enhance crop production. The drains may be opened or closed. In heavy rainfall areas, surface drainage for the speedy disposal of water. In a high water- table areas there should be sub-soil drainage. Close drains may be of mole or tile type. A mole drain is an unlined channel in the sub-soil made with a tractor-drawn mole plough and suitable only on heavy clay soils.

• Surface Drains

These consist of providing channels through which free water is carried away to natural drains such as nalas and rivers. These drainage channels in medium and deep soils may have bed width of 60 cm., side slope 30 to 45 cm., and depth 60 cm. The bed slope should not exceed

1 p.c. The distance between two drains may be 15 to 45 m., depending upon the type of soil, slope, intensity of rainfall etc., so that the excess water is removed within about 12 hours. Such drains are less costly to construct but need maintenance every year. One disadvantage with these drains is that it divides the field into small blocks and affects tillage and cultural operations. Some land is also wasted. Farming operations should be carried out parallel to the drain channels.

• Closed Drains

In order to drain away excess water, trenches may be dug 90 to 120 cm., in depth at a distance of 15 to 45 m. about 7.5 cm., layer of sand is spread in the trench and a bed slope of about 1 p.c. is given. Boulders are then spread over the sand and covered with 10 to 15 cm., layer of small stones and rubble over it upto about 30 cm., from the surface. The trenches are then covered with silt. Trenches have to be opened once in 8 to 10 years to remove any soil that might have accumulated within the boulders.

• Tile Drains

In heavy rainfall areas, there should be adequate arrangements for surface drainage for the speedy disposal of water. In areas with more phreatic water both surface and subsurface drains (trenches) should be provided. In high water-table areas, there should be subsoil drainage. The drains may be open or closed. A tile is made of clay or concrete and it is about 30 to 50 cm in length and 7 to 12 cm in diameter. These are placed end to end, with a gap of two to three mm between them. Excess water enters the system through this space and is conveyed along the gradient. To avoid obstruction, it is necessary to remove soil or roots or grasses also outlets should be checked to prevent rodents from plugging them.

With proper planning and designing the drainage water of one field may be used as irrigation water for another. On a mild gradient (about 0.1 to 1%) a shallow common channel may be constructed for irrigation and drainage purposes. Such channels are very available to mainstreams and without much effort can increase the level of water for discharge.

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