Read this essay to learn about the methods of irrigation adopted in India. The methods are: 1. Surface Irrigation 2. Sub-Surface Irrigation 3. Sprinkler Irrigation 4. Localized Irrigation.
1. Essay on the Surface Irrigation:
In this method, water from an irrigation channel is allowed to reach a part or whole of the field and spread by the gravitational flow incidental to the slope of the land. Water may be distributed to the crops in border strips, check basins or furrows.
The important requirements to obtain high efficiency in surface method are:
i. Properly constructed water distribution systems to provide adequate flow of water to the fields; and
ii. Proper grading and leveling of land to achieve uniform distribution of water.
(a) Border Strip Method:
The border method of irrigation makes use of parallel ridges to guide a sheet of flowing water as it moves down the slope. The land is divided into a number of long parallel strips called borders that are separated by low ridges. The border strip has little or no cross slope but has a uniform gentle slope in the direction of irrigation. The essential feature of 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 into a stream of water at the upper end. The water spreads and flows down the strip in a sheet confined by the border ridges. The irrigation stream must be large enough to spread over the entire width between the border ridges without over topping them. When the advancing water front either reaches the lower end, or a few minutes before or after that, the stream is turned off.
The water temporarily stored in the border moves down the strip and infiltrates into the soil, thus completing the irrigation. It is adapted to most soils where depth and topography permit, 1 the required land leveling at a reasonable cost and without any permanent reduction in soil fertility. It is, however, more suitable to soils having moderately low to moderately high infiltration rates.
It is generally not used in coarse sandy soils that have very high infiltration rates. It is also not well suited to soils having a very low infiltration rate. This method is suitable to irrigate all close growing crops like wheat, barley, fodder crops and legumes. It is, however, not suitable for crops like rice which requires standing water during most part of its growing season.
Advantages:
(i) It is easy to construct border ridges even with some simple farm implements like a bullock drawn A-frame ridger or tractor-drawn disc ridger.
(ii) Labour requirement in irrigation is greatly reduced as compared to the conventional check basin method of irrigation.
(iii) Uniform distribution and high water application efficiencies are possible if the system is properly designed.
(iv) Large irrigation streams can be efficiently used.
(v) Operation of the system is simple and easy.
(vi) Adequate surface drainage is provided if outlets are available.
Disadvantages:
(i) It requires an extensive land grading which is too expensive.
(ii) It is mainly suitable for deep soils with the availability of large flow of water.
(iii) Drainage may be essential.
(iv) Water wastage is frequently observed.
If the borders are constructed along the general slope of the field, they are known as straight borders or slope borders, and if they are constructed across the general slope of the field they are called contour borders. When fields can be leveled to desirable land slopes economically and without affecting its productivity, graded borders are easier to construct and operate.
In case where land slope exceeds safe limit, fields are undulating and leveling is not feasible, borders may be laid across the slope. The design of a contour border is the same as that of a straight border. Each contour border is level crosswise and has a uniform longitudinal gradient as in a straight border. The width and length of a contour border are identical to that of-a straight border for a particular set of conditions.
In laying contour borders, the field is divided into a series of strips on the approximate contour, and each strip is leveled as an independent area. Thus, a series of strips are formed in successive elevations around the slope. The vertical interval between the adjacent benches should, as far as possible, be limited to 30 cm, but should not exceed 60 cm. The height of ridge should be sufficient to check both the normal irrigation stream and run-off.
(b) Check Basin Irrigation:
Check basin irrigation is the most common method of irrigation in India and in many other countries. This is the simplest in principle of all methods of irrigation. There are many systems in its use, but all involve dividing the field into smaller units so that each has a nearly level surface. Ridges-are-constructed around the areas forming basins within which the irrigation water can be controlled. The basins are filled to the desired depth and the water is retained until it infiltrates into the soil. The depth of water may be maintained for considerable periods of time by allowing the water to continue to flow into the basins.
The distinguishing features of various uses of check basin method of irrigation involve the size and shape of the basins and “whether irrigation is accomplished by intermittent or continuous” collection of water in the basins. The ridges or bunds may be temporary for a single irrigation as in the pre-sowing irrigation of seasonal crops. They may be semi-permanently constructed for the repeated use in the case of paddy fields. The size of ridge will depend on the depth of water to be impounded as well as on the stability of the soil when wet.
Water is conveyed to the field by a system of supply channels and lateral field channels. The supply channel is aligned on the upper side of the area and there is usually one lateral channel for every two rows of check basins. Water from the laterals is turned into the beds and is cut off when sufficient water has been administered into the basin. Water is retained in the basin until it soaks into the soil.
The size of the irrigation stream is not critical as long as it is sufficient to provide a coverage of the entire strip in a relatively short time span required to apply the desired amount of water into the soil. As the infiltration rate of soil increases, stream size must be increased or the size of the basins reduced in order to cover the area within a short period of time. A large size irrigation stream will permit a comparatively larger size of the basin.
The size of check basin may vary from one square metre, used for growing vegetables and other intensive cultivation, to as large as two hectares or more, used for growing rice under wet land conditions. When the land can be graded economically into nearly level fields, the basins are rectangular in shape.
In rolling topography the ridges follow the contours of the land surface. The contour ridges are connected by cross ridges at intervals. The vertical interval between contour ridges usually varies from 6 to 12 cm in case of upland irrigated crops like wheat and 15 to 30 cm in case of low land irrigated crops like rice.
In irrigating orchards, square to contour basins may be used as in other crops. When the plants are widely spaced the ring method of basin irrigation is adopted. The rings are circular basins formed around each tree. The ring basins are small when the plant is young. The size is increased as the plant grows.
Check basin irrigation is suited to smooth, gentle and uniform land slopes and for soils having moderate to slow infiltration rates. Steep slopes require complex layouts and heavy land leveling. Both row crops as well as close growing crops are adapted to basins as long as the crop is not affected by temporary inundation.
The method is especially adopted for, irrigation of grain and fodder crops in heavy, soils where water is absorbed very slowly, it is also suitable in very permeable soils which must be covered with water rapidly to prevent excessive deep percolation loss of water at the upstream end.
Advantages:
(i) Since in this method the entire area is not flooded, it ensures -high water use efficiency.
(ii) Excessive seepage loss can be avoided by adopting this practice.
(iii) Damage to plants and loss of soil nutrients do not occur in this practice.
Disadvantages:
(i) The major disadvantage of check basin method of irrigation is that the ridges interfere with the movement of animal drawn or tractor drawn implements for inter culture operations or harvesting of crops.
(ii) Considerable land is occupied by ridges and lateral field channels and crop yields are substantially reduced.
(iii) The method impedes surface drainage.
(iv) Precise land grading and shaping are required.
(v) Labour requirement in land preparation and irrigation are much higher.
(c) Furrow Irrigation:
The furrow method of irrigation is used in irrigation of row crops with furrows developed between the crop rows in the planting and cultivating processes. The size and shape of the furrow depends on the crop grown, equipment used and spacing between crop rows. Water is applied by running small streams in furrows between the crop rows. Water infiltrates into the soil and spreads laterally to, irrigate the areas between the furrows.
The length of time water takes to flow in the furrows depends on the amount of water required to replenish root zone and the infiltration rate of the soil. Both large and small irrigation streams can be used by adjusting the number of furrows irrigated at anyone time to suit the available flow. In areas where surface drainage is necessary, the furrows can be used to dispose off the run-off from rainfall rapidly.
Furrow irrigation can be used to irrigate all cultivated crops planted in rows, including orchards and vegetables. Among the common cultivated crops of India, the method is suitable for irrigating maize, sorghum, sugarcane, cotton, tobacco, groundnut, potato and other vegetables.
Furrows are particularly well adapted to irrigating crops which are subject to injury from accumulated surface water or susceptible to fungal root rot. Furrow irrigation is suitable to most soils except sands that have a very high infiltration rate and provide poor lateral distribution of water between furrows.
Advantages:
(i) Water in the furrows contacts only one half to one fifth of the land surface, thereby reducing puddling and crusting of the soil, and evaporation losses.
(ii) Early sowing is possible which is a distinct advantage in heavy soils.
(iii) It can be safely adopted on the sloppy lands by opening the furrows across the slope.
(iv) This method reduces labour requirement in land preparation and irrigation.
(v) Compared to check basin method, there is no wastage of land in field ditches.
Disadvantages:
(i) It requires skilled labourers to operate.
(ii) It may cause serious erosion, if excess water flows over the ridges.
(iii) Difficult to carry on mechanical operations.
Irrigation furrows may be classified into two general types is based on their alignment. They are:
(i) Straight furrows,
(ii) Contour furrows.
Based on their size and spacing furrows, may be classified as deep furrows and corrugation.
Deep furrows are of two types i.e., straight furrows and contour furrows:
(i) Straight Furrows:
Straight furrows, like borders, are laid down across the prevailing land slope. They are best suited to sites where the land slope does not exceed 0.75 per cent. In areas of intense rainfall, however, the furrow grade should not exceed 0.5 % so as to minimise the erosion hazard.
(ii) Contour Furrows:
Contour furrow method is similar to the graded furrow method in that the irrigation water is applied in furrows, but the furrows carry water across the sloping field rather than down the slope. Contour furrows are curved to fit the topography of the land. The furrows are given gentle slope along its length as in the case of graded furrows. Field supply channels rundown the land slope to feed the individual furrows and are provided with erosion control structures.
2. Essay on the Sub-Surface Irrigation:
In this method of irrigation water is supplied below the ground surface by maintaining an artificial water table at some depth depending upon the soil texture and the depth of the plant roots. Water reaches the plant roots through capillary action. Water may be introduced through open ditches or underground pipelines such as tile drains or mole drains.
The depth of open ditches varies from 30 to 100 cm and they are spaced about 15 to 30 metres apart. This water application system consists of field supply channels, ditches or trenches and drainage ditches for the disposal of excess water. The irrigation ditches should be suitably spaced to cover the whole field adequately.
This method is suited to soils having reasonably uniform texture and are permeable enough for water to move rapidly both vertically as well horizontally within and for some distance below the crop root zone. The soil profile must control a barrier against excessive loss through deep percolation. Topography must be smooth and nearly level or slight slopes very gentle and uniform.
Advantages:
(i) In soils having low water capacity and a high infiltration rates where surface methods cannot be used and sprinkler system is very expensive, sub-surface irrigation method can be used effectively.
(ii) Evaporation loss from ground surface are minimum.
(iii) In this method, it is possible to maintain the water level at optimum dephs for crops required at different growth stages.
Disadvantages:
(i) It is quite expensive and labour intensive in the beginning.
(ii) The method requires an unusual combination of natural conditions, therefore its scope is limited.
(iii) Frequent removal of accumulated soil and other materials from channels is necessary.
In India, this irrigation is practiced to a limited extent for growing vegetable crops around Dal Lake in Kashmir and for irrigation of coconut palms in the organic soils of Kuttanad area in Kerala.
3. Essay on the Sprinkler Irrigation:
In the sprinkler method of irrigation, water is applied above the ground surface as spray. The spray is developed by the flow of water under pressure through small orifices or nozzles. The pressure is obtained by pumping with careful selection of nozzle sizes, operating pressures and sprinkler spacing. High efficiency in water application/distribution can be obtained with sprinkler system.
Sprinkler systems are of generally two major types viz.:
(i) Rotating head system, and
(ii) Perforated pipe system.
In case of rotating head system small nozzles are placed on riser pipes and these riser pipes are fixed at an even interval along the length of lateral pipes which are placed on the ground surface. However, they can be mounted on posts exceeding the crop height and made rotating through 90 degree. In rotating sprinkler, the most, important device to rotate the sprinkler head is a small hammer activated by the trust of water striking the vane connected to it.
In case of perforated pipe system, holes are perforated in lateral irrigation pipes which is especially designed to distribute water with a good deal of uniformity. This system is usually designed for low operating pressures (i.e. 0.5 to 2.5 kg/sq cm). Due to this low pressure, the system is attached to an overhead tank to achieve the requisite pressure head. The sprays are directed on both sides of the pipe which cover a strip of land from 6 to 15 metres wide.
Nearly all cultivable soils can be sprinkler irrigated. It is, however, not suitable in very high textured soils where the infiltration rates are very low (i.e. less than 4 mm per hour). Most crops excepting rice and jute can be sprinkler irrigated. The flexibility of sprinkler equipment and efficient control of its application make this method adaptable to most of the topographic conditions.
However, extremely high temperature and wind velocity markedly reduce the uniformity of water distribution and irrigation efficiency. This I system of irrigation is especially useful to the soils that have steep slopes or irregular topography and soils which are too shallow to level.
Advantages:
(i) This technique enables judicious utilization of even small water flows and permits efficient irrigation of undulated lands, and soils with shallow depths.
(ii) It saves 10 to 16% land that is used in construction of channels and ridges in other methods.
(iii) Highly permeable as well as relatively less permeable soils can be easily irrigated by sprinkler method without any risk of run-off and erosion, inundation and seepage losses.
(iv) Fertilizers, pesticides and wedicides can be applied along with water spray, thus, saving extra labour.
Disadvantages:
(i) High initial cost of equipment.
(ii) Operating costs are generally higher than irrigation by surface methods.
(iii) Winds disturb the sprinkler pattern giving uneven distribution of the irrigation water.
(iv) Sprinkling with water containing an appreciable amount of salts may result in bum or death of the plants.
(v) Under certain climatic conditions diseases may be encouraged. The problem of fruit rotting in tomato and strawberry gets aggravated especially in moist soil condition.
4. Essay on the Localized Irrigation:
(a) Drip Irrigation:
As the name signifies, drip irrigation, also termed as trickle irrigation, involves the slow application of water to the root zone of a crop. The method was initiated in Israel and is now being tried in other countries. In this method, water can be used very economically, since loss due to deep percolation and surface evaporation are reduced to the minimum. This method, therefore, is highly suitable to arid regions and orchard crops.
The successful raising of orchards even on saline soils has been made possible by the drip system of irrigation. The system can also be used for applying fertilizers in solutions. In this system, water is applied more frequently, close to the stems of plants through suitably spaced drippers (emitters) attached to plastic or metallic pipes spread above or below soils along crop rows.
The pipes are hooked to source of water supply through a storage tank or pressure device which provides necessary hydraulic head or pressure for movement of water to the drippers. A pumping unit creates a pressure of about 2.5 kg/sq cm. In this case only a part of soil in the vicinity of plant roots is wetted and kept close to field capacity.
The amount of water dripping from nozzles can be regulated as desired by varying the pressure at the nozzles and the size of the orifice of the nozzles. The initial high cost of the equipment and its maintenance are the major limitations in this system. It may, however, work out to be cheaper than the sprinkler system especially for the orchards and other widely spaced crops.
(b) Earthen Pot Irrigation:
This method has been recently developed by the Haryana Agriculture University, Hissar. It is very cheap and convenient method and can be easily adopted. In this method, first a pit (60 cm deep and 90 cm wide) is dug out and the earthen pot is embedded up to the neck level and then it is filled with water. The water is absorbed by the soil through capillary action. One pot is sufficient to moisten one square meter area. Care should be taken to cover the pot by lid and supply water from time to time. The pots may be replaced by new ones after two or three seasons.
This system is especially useful for irrigating vegetable crops ego cucurbitaceous crops grown in sandy loam or sandy soils.
Advantages:
(i) It is the most suitable method for vegetable and orchard crops where plants are widely spaced.
(ii) It can be used in sandy and undulating lands.
(iii) Saline water can be freely used because salts are deposited at the bottom of the pot.
(iv) High water use efficiency.
(v) A simple and comparatively cheap method.
(c) Double Walled Pot “Jaltripti”:
It is a useful irrigation device for the desert, developed by the Central Arid Zone Research Institute (CAZRI), Regional Station, Bikaner. It reduces the frequency and total amount of water needed and ensures a regulated constant supply of moisture to tree plants for survival and better growth.
This device consists of a double walled earthen pot called “Jaltripti” (water satisfaction). The diameter of the outer pot is kept, approximately 25 cm at the top and at base it is 18 cm. The diameter; of inner pot is 15 cm on top and 12 cm at base. The height is kept 30 cm. (Since it is prepared on potter’s wheel, approximate dimensions have been given.
Moreover, some variations in the measurement may occur. The dimensions of the inner pot have been kept slightly bigger than the size of the polythene bags (25 cm long measuring 10 cm across) used for raising plants in nursery. Both the pots are joined together at the base and the basal portion of inner pots is kept almost open. The external side of the outer pot is made impervious with the f help of paint, cement or coaltar.
The “Jaltripti” functions on two simple principles:
(i) Soil moisture tension and plant roots create a suction force which draws moisture towards it from the neighboring high moisture zone.
(ii) Earthen pots have many micro-pores in their wall which do not allow water to flow freely but allow its seepage in the direction where suction develops.
At the place where planting has to be done, the device is fixed in the soil in such a way that the brim of the outer pot is above soil surface. A tree sapling along with a soil ball is transplanted in the inner pot. The water is filled in the space between two pots and the circular surface of water is caused by a polythene sheet to avoid direct evaporation of water.
The paint on the external surface of the pot prevents outward movement of water through seepage. But the suction force created by the inner pot allows for the seepage of water steadily in that direction and keeps the soil sufficiently moist for the growth of the plants. Water is filled weekly or fortnightly depending upon the season and size of the pot. The device has been named ‘Jaltripti’.
Advantages:
(i) Economy of water (80 to 90 per cent).
(ii) It saves more water than drip and sprinkler system.
(iii) Low irrigation frequency.
(iv) Labour saving.
(v) No loss through percolation, evaporation and seepage.
(vi) Regulated supply of moisture. Moisture is always available at field capacity.
(vii) Promising in stabilization of sand dune.
(d) Tueboponics:
Tueboponics is a fairly recent development in the field of irrigation. This technique has been developed in Israel and practiced in the desert areas of that country in order to convert it into green lush forests.
In tueboponics, water is provided to plants/trees through injections. The needle is inserted into the plant stem and water is delivered into the phloem. The needle and injection used for this purpose are of special shape and design prepared only for this purpose.
In India, this technique has not yet arrived but it may prove very useful in Indian reserves where water is very scarce. Its use in crop plants seems to be impracticable. It is a very simple device.