1 METHODS OF IRRIGATION BY NAVANITA CHOUDHURY ASSISTANT PROFESSOR RSET
2 CLASSIFICATION OF IRRIGATION METHOD A.Surface Irrigation: Water moves over and across the land by simple gravity flow in order to wet it and to infiltrate into the soil. B.Sprinkler Irrigation or overhead irrigation: Water is piped to one or more central locations within the field and distributed by overhead high- pressure sprinklers or guns. Higher pressure sprinklers that rotate are called rotors. C.Sub-irrigation: Also sometimes called seepage irrigation. Used for years in field crops in areas with high water tables. It is a method of artificially raising the water table to allow the soil to be moistened from below the plants' root zone. Often those systems are located on permanent grasslands in lowlands or river valleys and combined with drainage infrastructure.
3 1. SURFACE METHOD OF IRRIGATION Flooding methods Furrow methods Contour farming Uncontrolled or wild flooding Control Flooding Flooding from field channels Border strip method Check Basin Method Ring basin method
4 A1.a. Uncontrolled or wild flooding Ditches are excavated in the field Water is applied from field ditches without any levee to guide its flow. Movement of water is not restricted, it is sometimes called wild flooding It is suitable for close growing crops, pastures etc. Practiced where irrigation water is abundant and inexpensive. It involves low initial cost of land preparation, extra labour cost in the application of water. Application of efficiency is low. This method may be used on rolling land (topography irregular) where borders, checks, basins and furrows are not feasible. A1. FLOODING METHODS
5 A1.b. Control Flooding In this method the irrigation water is applied by spreading it over the land to be irrigated with proper control on the flow of water as well on the quantity of water applied.
6 A1.b.i. BORDER STRIP FLOODING The farm is divided into a number of strips (width 10 ~ 20 m and length 100 ~ 400 m) separated by low levees or borders. Water is turned from the supply ditch into these strips along which a flow slowly toward the lower end, wetting the soil as it advances. When the advancing water front reaches the lower end, the stream turned off. The surface is essentially level between levees and lengthwise slope is somewhat according to natural slope of the land (0.2 ~ 0.4%) It is suitable to soils having moderately low to moderately high infiltration rates and to all closely growing crops. Large streams can be used efficiently. It involves high initial cost. Ridges between borders should be sufficiently high The land should be perpendicular to the flow to prevent water from concentrating on either side of the border.
7 The essential feature of the border irrigation is to provide an even surface over which the water can flow down the slope with a nearly uniform depth. Each strip is irrigated independently by turning in a stream of water at the upper end as shown in Figure
8 A1.b.ii. Check Basin Method The check basin method is the most common method of irrigation used in India. In this method, the land to be irrigated is divided into small plots or basins surrounded by checks, levees. Each plot or basin has a nearly level surface. The irrigation water is applied by filling the plots with water up to the desired depth without overtopping the levees and the water retained there is allowed to infiltrate into the soil. The levees may be constructed for temporary use, semi permanent for repeated use as for paddy cultivation. The size of the levees depends on the depths of water to be impounded as on the stability of the soil when wet. Basin irrigation is suitable for many field crops. Paddy rice grows best when its roots are submerged in water and so basin irrigation is the best method for use with the crop.
9 This method has the following advantages: 1. It is the best method of irrigation for leveled fields. 2. It does not require any technical knowledge. 3. Useful in soils having lesser infiltration. 4. Rain water stays in basins, hence soil erosion is not caused. 5. It has lesser economic investment. 6. It irrigates more area. 7. Crops gets sufficient water. Following are disadvantages of check basin method: 1. Due to seepage in drains, wastage of water is caused. 2. Machines cannot be used m this method because during spray of insecticides or fertilizers, the earthen walls of basins are damaged. 3. After growth of crops, water reaches the basins in disproportionate quantity thereby causing wastage of water. 4. Creation of problem of water logging.
10 A1.b.iii Ring basin method Sometimes, basin sizes are made larger to include two more trees in one basin. Water to the basins is supplied from a supply channel through small field channels conveyed the basins with the supply channel. Trees which can be irrigated successfully using the ring basin method include citrus and banana. Basins can also be constructed on hillside. Basin irrigation is suitable for many field crops. Paddy rice grows best when its roots are submerged in water and so basin irrigation is the best method for use with this crop.
11 A2.FURROW METHOD 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 ridges between the furrows, as shown in Figure. This method is suitable for all row crops and for crops that cannot stand water for long periods, like 12 to 24 hours. Water is applied to the furrows by letting in water from the supply channel, either by pipe siphons or by making temporary breaches in the supply channel embankment. The length of time the water is to flow in the furrows depends on the amount of water required to replenish the root zone and the infiltration rate of the soil and the rate of lateral spread of water in the soil.
12 Furrow irrigation is suitable to most soils except sandy soils that have very high infiltration water and provide poor lateral distribution water between furrows. As compared to the other methods of surface irrigation, the furrow method is advantageous as: Water in the furrows contacts only one half to one-fifth of the land surface, thus reducing puddling and clustering of soils and excessive evaporation of water. Earlier cultivation is possible methods of irrigation. It is commonly used for row crops such as maize, cotton, potatoes, sugar cane, groundnut, tobacco etc.
13 A3.CONTOUR FARMING It is practiced in hilly areas. It controls erosion due to rainfall In this method the land is divided into a series of strips known as terraces or benches. The borders are sometimes laid along the elevation contours of the topography when the land slope is excessive.
14 B. SPRINKLER IRRIGATION METHOD Sprinkler irrigation is a method of applying water which is similar to natural rainfall. It spreads uniformly over the land surface just when needed and at a rate less than the infiltration rate of the soil so as to avoid surface runoff from irrigation. Water is distributed through a system of pipes usually by pumping which is then sprayed into the air through sprinklers so that it breaks up into small water drops which fall to the ground. No land leveling is required as with the surface irrigation methods. This method is not suitable for soils which easily form a crust.
15 The following conditions are favorable for sprinkler irrigation # Very previous soils which do not permit good distribution of water by surface methods # Lands which have steep slopes and easily erodible soils # Irrigation channels which are too small to distribute water efficiently by surface irrigation # Lands with shallow soils and undulating lands which prevent proper leveling required for surface methods of irrigation Types of sprinkler system The most common types of sprinklers that are used are: i. Perforated pipe system: This consists of holes perforated in the lateral irrigation pipes in specially designed pattern to distribute water fairly uniformly. The sprays emanating from the perforations are directed in both sided of the pipe and can cover a strip of land 6 m to 15m wide.
16 ii. Rotating head system: Here small sized nozzles are placed on riser pipes fixed at uniform intervals along the length of the lateral pipe. The lateral pipes are usually laid on the ground surface. The nozzle of the sprinkler rotates due to a small mechanical arrangement which utilizes the thrust of the issuing water. Sprinkler irrigation has high efficiency. It however, varies according to climatic conditions; 60% in warm climate; 70% in moderate climate and 80% in humid or cool climate.
17 . Advantages: Low water loss (efficiency up to 80%) Saving in fertilizer Suitable for any topography No soil erosion Better seed germination, free aeration of root zone Disadvantages High initial cost, cannot adopt by ordinary farmers Poor application efficiency in windy weather and high temperature High evaporation losses Water should be free of debris Equipment need careful handling Uniform application of water Physical damage to crops by application of high intensity spray Power requires for running pumping unit
18 C. SUB SURFACE IRRIGATION SYSTEM Drip Irrigation system (Trickle) is sometimes called trickle irrigation and involves dripping water onto the soil at very low rates (2-20 litres per hour) from a system of small diameter plastic pipes filled with outlets called emitters or drippers. Water is applied close to the plants so that only part of the soil in which the roots grow is wetted, unlike surface and sprinkler irrigation, which involves wetting the whole soil profile. With drip irrigation water, applications are more frequent than with other methods and this provides a very favorable high moisture level in the soil in which plants can flourish.
19 Advantages: Low water loss and hence saves water Enhances plant growth and plant yield Saves labor and energy Control weed growth No soil erosion Improves fertilizer application efficiency Disadvantages: High skill in design, installation, and subsequent operation Clogging of small conduits and openings in emitters due to sand, clay particles, debris, chemical precipitates and organic growth Not suitable for closely planted crops such as wheat and other cereal grains The drip irrigation is mainly used to irrigate crops as such: Grapes Bananas Pomegranates Mangoes Sugarcane and Coconut.