Agriculture is the nerve of any country as it is needed for survival of living beings. For growing crops, irrigation is major process. Irrigation is described as the artificial application of water to the land or soil. It is the substitute or supplement of rainwater with another source of water. It is used in dry areas and during periods of insufficient rainfall. It is considered as basic infrastructure and vital input required for agricultural production (Mamata Swain, 1999). Major aim of irrigation systems is to help out in the growing of agricultural crops and vegetation by maintaining with the minimum amount of water required, maintenance of landscapes, and re-vegetation of disturbed soils. Irrigation systems are also used for dust repression, removal of sewage, and in mining. Irrigation is often studied together with drainage, which is the natural or artificial removal of surface and sub-surface water from a given region. Agricultural scientists stated that irrigation also has a few other uses in crop production, which include protecting plants against frost, suppressing wild plant growing in grain fields and helping to avert soil consolidation. On the contrary, agriculture that relies only on direct rainfall is referred to as rain-fed or dry-land farming.
Irrigation has been a vital characteristic of agriculture for over centuries and the result of work of many cultures, and was the basis of the wealth and society ranging from Asia to the American Southwest.
In brief, irrigation also has many applications in crop production, which include:
Irrigation water may be applied to the crops in three basic methods that include surface irrigation, sprinkler irrigation and sub-surface irrigation method. Every irrigation method has advantages and disadvantages. Therefore before choosing a specific technique, the irrigation engineer must evaluate all the factors and choose method which is most suited for local condition (Dr. B. C. Punmia, 2009).
Techniques of irrigation
In India, the irrigated area consists of about 36 per cent of the net sown area. There are various techniques of irrigation practices in different parts of India. These methods of irrigation differ in how the water obtained from the source is distributed within the field. In general, the goal of irrigation is to supply the entire field homogeneously with water, so that each plant has the amount of water it needs, neither too much nor too little. Irrigation in India is done through wells, tanks, canals, perennial canal, and multi-purpose river valley projects.
In this technique water flows and spreads over the surface of the land. Varied quantities of water are allowed on the fields at different times. Therefore, flow of water under surface irrigation comes under wobbly flow. Consequently, it is very difficult to understand the hydraulics of surface irrigation. However, suitable and efficient surface irrigation system can be espoused after taking into consideration different factors which are involved in the hydraulics of surface irrigation.
If the surface irrigation method is perfectly selected, it fulfils following requirements:
Surface irrigation technique is broadly classified as basin irrigation; border irrigation; furrow irrigation and uncontrolled flooding.
Phases of surface irrigation:
This divided into the four component systems: (1) water supply; (2) water conveyance or delivery; (3) water use; and (4) drainage.
Basin irrigation: Basin irrigation is common practice of surface irrigation. This method is employed for watering orchards (Basak, 1999). It is useful especially in regions with layouts of small fields (Shah et al. 2002). If a field is level in all directions, is encompassed by a dyke to prevent runoff, and provides an undirected flow of water onto the field, it is herein called a basin. A basin is typically square in shape but exists in all sorts of irregular and rectangular configurations. It may be furrowed or ridged, have raised beds for the benefit of certain crops, but as long as the inflow is undirected and uncontrolled into these field modifications, it remains a basin.
Basin Method (Source: Basak, 1999)
Furrow Irrigation: In furrow irrigation technique, trenches or “furrows” are dug between crop rows in a field. Farmers flow water down the furrows (often using only gravity) and it seeps vertically and horizontally to refill the soil reservoir. Flow to each furrow is individually controlled. Furrow irrigation is suitable for row crops, tree crops and, because water does not directly contact the plants, crops that would be damaged by direct inundation by water such as tomatoes, vegetables, potatoes and beans. It is one of the oldest system of irrigation. It is economical and low-tech making it particularly attractive in the developing world or places where mechanized spray irrigation is unavailable or impractical.
Furrow technique (Source: Basak, 1999 )
In different situations, different furrow methods are used (Surajbhan 1978). They are mainly of five types:
There are numerous advantages of Furrow technique of irrigation:
Furrow irrigation is also beneficial for growing of tree crops. In the early stages of tree planting, one furrow alongside the tree row may be sufficient but as the trees develop then two or more furrows can be constructed to provide sufficient water. Sometimes a special zig-zag system is used to improve the spread of water (Basak, 1999).
Major drawback of furrow system of irrigation is ensuring uniform dispersal of water over a given field. To tackle this problem, some farmers engage in field levelling to remove any small hills that would have been bypassed by the gravity flow of the water. Other problem with furrow irrigation is the increased potential for water loss due to runoff. Building retention ponds along the edges of fields can help capture this runoff, allowing it to be pumped back to the upslope side of the field for use in further irrigation cycles.
Uncontrolled flooding: There are many cases where croplands are irrigated without regard to efficiency or consistency. These are usually situations where the value of the crop is very small or the field is used for grazing or recreation purposes. Small land holdings are generally not subject to the range of surface irrigation practices of the large industrial farming systems. The assessment methods can be applied if desired, but the design techniques are not generally applicable nor need they be since the irrigation practices tend to be minimally managed.
This flooding system of irrigation is used from ancient times. Flooding method consists in applying the water by flooding the land of rather smooth and flat topography. In current irrigation practice, several flooding methods have been developed. In free flooding method, water is applied to the land from field ditches without any check or guidance to the flow. The land is divided into plots or kiaries of suitable size depending on porosity of soil. Water is spread over the field from watercourse. The irrigation operation begins at the higher area and proceeds towards the lower levels. The flow is stopped when the lower end of the field has received the desired depth of water. The field watercourse is properly spaced, the spacing depends on the topography, oil texture, depth of soil and size of stream.
This technique is beneficial for newly established farms where making furrows is very expensive. This method is economical and can be effectively used where water supply is in plenty. This method is suitable for the fields with irregular surface in which other techniques are difficult to apply. Major drawback of this method is that there is no perfect control over the flow of water to attain high efficiency. Sometimes the flow of water over the soil is too rapid to fulfil soil moisture deficiency. On the other hand, sometimes water is retained on the field for a very long time and consequently the water is lost in infiltration or deep percolation.
In this technique of irrigation, a field is divided into number of strips. The width of strip varies from 10 to 15 metres and length varies from 90 m to 400 m. Strips are separated by low embankments or levees. The water is diverted from the field channel into the strips. The water flows gradually towards lower end, wetting the soil as it advances. The surface between two embankments should essentially be level. It assists in covering the entire width of the strip. There is a general surface slope from opening to the lower end. The surface slope from 2 to 4 m/1000 m is best suited. When the slope is steeper, special arrangement is made to prevent erosion of soil.
A well is a hole dug in the ground to get the subsoil water. Normal well is about 3-5 metres deep but deeper wells up-to 15 metres are also dug. This system of irrigation has been used in India from ancient time. Various methods are used to lift the ground water from the well for irrigation, drinking, bathing and for other purposes. Well irrigation is more popular in those regions where ground water is in ample and where there are few canals. These areas include a large part of the Great Northern Plain, the deltaic regions of the Mahanadi, the Godavari, the Krishna and the Cauvery, parts of the Narmada and the Tapi valleys and the weathered layers of the Deccan Trap and crystalline rocks and the sedimentary zones of the Peninsula. However, the greater part of the Penisnular India is not appropriate for well irrigation due to stony structure, rough surface and lack of underground water. Large dry tracts of Rajasthan, the adjacent parts of Punjab, Haryana, and Gujarat and some parts of Uttar Pradesh have salty ground water which is not suitable for irrigation and human use and hence inappropriate for well irrigation.
Tube well: A tube well is a deeper well (generally over 15 metres deep) from which water is lifted with the help of a pumping set operated by an electric motor, a diesel engine or solar power. A tube well cannot be constructed in all places and requires some geographical conditions favouring its installation. The main factors for Tube well construction are:
Advantages of Well and Tube Well Irrigation:
Well is simplest and cost effective source of irrigation and the poor Indian farmer can easily afford it. Well is an independent source of irrigation and can be used as and when the necessity arises. Several chemicals such as nitrate, chloride, sulphate, etc. are generally found mixed in well water. They make soil fertility when they reach the agricultural field along with well water. It is more reliable during periods of famine when surface water dries up.
Disadvantages of well and Tube Well Irrigation: With these methods, only limited area can be irrigated. Normally, a well can irrigate 1 to 8 hectares of land. The well may dry up and may be rendered ineffective for irrigation if excessive water is taken out. In the drought situation, the ground water level falls and enough water is not available in the well when it is needed the most.
Tube wells can draw a lot of groundwater from its neighbouring areas and make the ground dry and not suitable for agriculture. Well and tube well irrigation is not possible in areas of salty groundwater.
Canals are most important source of irrigation from the period of 1960s, but in the 1970s, they yielded first place to wells and tube wells and now constitute the second most important source of irrigation in India. Canals are most effective techniques of irrigation in areas of low level relief, deep fertile soils, perennial source of water and extensive command area. Therefore, the main concentration of canal irrigation is in the northern plain of India, especially the areas comprising Uttar Pradesh Haryana and Punjab.
The digging of canals in stony and uneven areas is difficult and unprofitable. Thus the canals are practically absent from the Peninsular plateau area. However, the coastal and the delta regions in South India do have some canals for irrigation.
Canals in India are of two types:
Inundation canals, which are taken out from the rivers without any regulating system like weirs at their head. Such canals supply irrigation mainly in the rainy season when the river is in flood and there is excess water. When the rainy season is over, the flood in the river subsides, the level of water falls below the level of the canal head and the canal dries up. Some canals taken off from the Satluj in Punjab were of this type. Since irrigation from this type of canals is unsure, they have been converted in perennial canals.
Perennial Canals are those which are taken off from perennial rivers by constructing a barrage across the river. Most of the canals in India today are perennial.
Advantages of Canal Irrigation: Most of the canals provide perennial irrigation and supply water as and when required. This saves the crops from drought conditions and helps in increasing the farm production. Canals carry a lot of residue brought down by the rivers. This sediment is deposited in the agricultural fields which make soil more fertile. Some of the canals are parts of multipurpose projects and, therefore, provide inexpensive source of irrigation. Although the initial cost involved in canal irrigation is more, it is quite cheap in the long run.
Drawbacks of Canal Irrigation: The canal water soaks into the ground and results in water-logging along the canal route. Excessive flow of water in the fields raises the ground water level. Capillary action brings alkaline salts to the surface and makes large areas unfit for agriculture. Huge areas in Panjab, Haryana and Uttar Pradesh suffer from the problem caused by canal irrigation. The muddy areas near the canals act as reproduction grounds of mosquitoes which result in widespread malaria. Many canals overflow during rainy season and flood the surrounding areas. Canal irrigation is suitable in plain areas only.
A tank act as an irrigation storage system which is developed by constructing a small bund of earth or stones built across a stream. The water impounded by the bund is used for irrigation and for other purposes. Some tanks are built partly as dugouts and partly by enclosing bunds. Tanks are of varying size but most of the tanks are of small size and are built by individual farmers or groups of farmers. Tank irrigation is more suitable in the peninsular plateau area such as Andhra Pradesh (Including Telangana) and Tamil Nadu.
Andhra Pradesh is the largest state of tank irrigation which has about 29 per cent of tank irrigated area of India. About 16 per cent of the total irrigated area of the state is irrigated by tanks. The drainage areas of the Godavari and its tributaries have large number of tanks. Nellore and Warangal are the main districts of tank irrigation.
According to reports, Tamil Nadu has the second largest area which is over 23 per cent of tank irrigated area of India and about one-fifth of the total irrigated area of the state. Tanks comprise an important source of irrigation in the Karnataka Plateau, eastern Madhya Pradesh, eastern Maharashtra, interior Orissa and Kerala. Outside the Peninsular plateau, West Bengal, Bihar, Bundelkhand area of Uttar Pradesh, Rajasthan and Gujarat have tank irrigation.
Advantages of Tank Irrigation: Most of the tanks are natural and not expensive for their construction. Even an individual farmer can have his own tank. Tanks are normally constructed on rocky bed and have long life. In many tanks, fishing is also done. This supplements both the food resources and income of the farmer.
Drawbacks of Tank Irrigation: Major problem with tanks water storage is that tanks dry up during the dry season and fail to provide irrigation when it is needed the most. Silting of the tank bed is a serious problem and it requires de-silting of the tank at regular intervals. Much water is evaporated from the large expanse of shallow water and is therefore not available for irrigation. Tanks cover large areas of cultivable land. In many areas, other sources of irrigation have been adopted and the dry beds of tanks have been reclaimed for agriculture. Furthermore, lifting of water from tanks and carrying it to the fields is a tiring and expensive effort which discourages the use of tanks as a source of irrigation.
In the area of irrigation process, drip irrigation is modern technique. It is also called trickle irrigation, which was originally developed in Israel in the early 1960s and became popular in areas of water scarcity. The drip irrigation is the most competent and it can be practised in array of crops, especially in vegetables, orchard crops, flowers and plantation crops (Mamata Swain, 1999).
Drip irrigation was used to the ancient custom in certain parts of India of irrigating a tulsi plant kept in the courtyard. During the summer months, the plant was irrigated by a hanging pitcher containing water and a minute hole at its bottom to allow the trickling of water on to the plant. The tribal farmers of Arunachal Pradesh practised a primitive form of drip irrigation system using a slender bamboo as the conduit for water flow. The use of drippers in sub-surface irrigation network was first experimented in Germany in 1869. The noticeable growth of the petrochemical industry during and after the 1950s aided manufacturing of plastic pipes at a cost much cheaper than the cost of metallic or cement concrete pipes. Plastic pipes are convenient for water conveyance under pressure and the plastic material are easily formed into the desired configuration. These features of plastic made the field-scale use of drip irrigation practicable. The drip system was developed for field crops in Israel in the early 1960s and in Australia and North America in the late 1960s. The area under drip irrigation system in the USA is about 1 M ha, followed by India, Spain, and Israel. In India, there has been a tremendous growth in the area under drip irrigation during the last 15 years. At present, around 3.51akh ha area is under drip irrigation with the efforts of the Government of India, while it was only 40 ha in 1960. Maharashtra (94,000 ha), Karnataka (66,000 ha) and Tamil Nadu (55,000 ha) are some of the states where large areas have been brought under drip irrigation. Many crops are irrigated by the drip method in India with the tree crops occupying the maximum percentage of the total area under drip irrigation, followed by vine crops, vegetables, field crops, flowers and other crops.
In drip irrigation, water is applied near the plant root through emitters or drippers, on or below the soil surface. The soil moisture is kept at an optimum level with frequent irrigations. In this method irrigation water is conveyed on the surface in 12 to 16 mm diameter tubing’s fed from large feeder pipes. The water is allowed to drip or trickle slowly through the nozzle or orifices at practically zero pressure. In this way the soil in the root-zone of crops is constantly kept wet. Drip irrigation results in a very high water application efficiency of about 90-95 per cent.
The area under drip irrigation system in the USA is about 1 M ha, followed by India and other countries.
Major component of drip irrigation:
Pump station takes water from the source and provides the right pressure for delivery into the pipe system.
Control valves control the discharge and pressure in the entire system.
Filtration system cleans the water. Common types of filter include screen filters and graded sand filters which remove fine material suspended in the water.
Fertilizer tank/venturi slowly add a measured dose of fertilizer into the water during irrigation. This is one of the major advantages of drip irrigation over other methods.
Mainlines, submains and laterals supply water from the control head into the fields. They are usually made from PVC or polyethylene hose and should be buried below ground because they easily degrade when exposed to direct solar radiation. Lateral pipes are usually 13-32 mm diameter.
Emitters or drippers are devices used to control the discharge of water from the lateral to the plants. They are typically spaced more than 1 metre apart with one or more emitters used for a single plant such as a tree. For row crops more closely spaced emitters may be used to wet a strip of soil. Many different emitter designs have been produced in recent years. The basis of design is to produce an emitter which will provide a specified constant discharge which does not vary much with pressure changes, and does not block easily.
In India, there has been a fabulous growth in the area under drip irrigation during the last many years. At present, major area is under drip irrigation with the help of the Government of India. Reports indicated that Maharashtra (94,000 ha), Karnataka (66,000 ha) and Tamil Nadu (55,000 ha) are some of the states where large areas have been brought under drip irrigation. Many crops are irrigated by the drip method in India with the tree crops occupying the maximum percentage of the total area under drip irrigation, followed by vine crops, vegetables, field crops, flowers and other crops.
Crop suitable for drip irrigation:
The National Committee on Plasticulture Applications in Horticulture (NCPAH), Ministry of Agriculture, Government of India, has approximate a total of 27 million hectares area in the country that has the potential of drip irrigation application. Through this method, crops can be grown productively over the saline lands also. This technique has been beneficial in reclaiming and developing desert and arid areas. The main disadvantage of this method is that it is expensive. But with growing realisation of the value of water this method has been introduced in other countries of the world particularly in desert areas. The method is still in preliminary stages of development in nation.
Drip irrigation layout and its parts
The advantages of drip irrigation are under:
The shortcomings of drip irrigation are:
One of the main purposes of drip irrigation is to decrease the water consumption by reducing the leaching factor. However when the available water is of high salinity or alkalinity, the field soil becomes gradually unsuitable for cultivation due to high salinity or poor infiltration of the soil. Consequently, drip irrigation converts fields in to fallow lands when natural leaching by rain water is not adequate in semi-arid and arid regions.
Most drip systems are designed for high efficiency and have little or no leakage. Without sufficient leaching, salts applied with the irrigation water may build up in the root zone. 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. Drip irrigation systems cannot be used for damage control by night frosts.
In the sprinkler technique of irrigation, water is sprinkled into the air and allowed to fall on the ground surface just like rainfall. The spray is done by the flow of water under pressure through small orifices or nozzles. The pressure is generally obtained by pumping. Through proper selection of nozzle sizes, operating pressure and sprinkler spacing the amount of irrigation water required to refill the crop root zone can be applied almost uniform at the rate to suit the infiltration rate of soil. In agriculture, almost all crops are suitable for sprinkler irrigation system except crops such as paddy and jute. The dry crops, vegetables, flowering crops, orchards, plantation crops like tea, coffee are all suitable and can be irrigated through sprinklers techniques of irrigation.
The sprinkler irrigation is categorized according to the functions which are mentioned as under:
1. The main irrigation system
2. The supplementary irrigation system
3. The protective irrigation system
The sprinkler irrigation system is effective for irrigation on uneven lands and on shallow soils. It is also suitable to coarse sandy terrain where the percolation loss is more and where as a consequence, the frequency of irrigation required is more. The sprinkler irrigation system is appropriate in rising and falling land where land shaping is expensive or technically not practicable. The elimination of fertile soil cover by land shaping is not advisable. Sprinkler irrigation system can also be espoused in hilly regions where plantation crops are grown.
Historical facts signified that though sprinkler irrigation system is known since 1946, yet the farmers started adopting it in huge scale only since 1980s. It began in the hilly areas of Western Ghats in states of Kerala, Tamil Nadu and Karnataka and in the North eastern states mainly for plantation crops like coffee, tea, cardamom, rubber. Gradually it spreads to the water scarcity and light soil states of Rajasthan and Haryana in addition to the black soil area of Madhya Pradesh.
Surge Irrigation: Surge Irrigation is an alternative of furrow irrigation where the water supply is pulsed on and off in planned time periods (e.g. on for 1 hour off for 1½ hour). The wetting and drying cycles reduce infiltration rates resulting in faster advance rates and higher uniformities than constant flow.
Ditch Irrigation: Ditch Irrigation is type of traditional method, where ditches are dug out and seedlings are planted in rows. The plantings are watered by placing canals or furrows in between the rows of plants. Siphon tubes are used to move the water from the main ditch to the canals.
Subirrigation or seepage irrigation: It is a system of irrigation where water is allowed to the plant root zone from below the soil surface and absorbed upwards. The excess may be collected for reuse. Subirrigation is used in growing field crops such as tomatoes, peppers, and sugar cane in areas with high water tables. Major benefits of this system are water and nutrient conservation, and labour-saving. The outfitting cost is comparatively high. Main problems include possibility of increased presence of disease in recycle water.
To summarize, Irrigation is a technique of supplying water to the dry land as a supplementation of rain water. It is mainly aimed for farming. There are various types of systems of irrigation practices in different parts of India. Irrigation in India is carried on through wells, tanks, canals, perennial canal, multi-purpose river valley projects. The irrigation engineer should be acquainted with the type of soil moisture, quality of irrigation water, frequency of irrigation for the proper implementation of irrigation system.