The manner in which water is applied to the land is commonly referred to as method of irrigation. These methods are adopted to apply irrigation water to the crop depending on the landscape, amount of water and equipment available, the crop and method of cultivation of crop. The main aim of these methods is to store water in the effective root zone uniformly and in maximum quantity ensuring minimum water loss and to get optimum yield. Various methods of irrigation are: 1. Surface method 2. Sub-surface method 3. Sprinkler method .
Drip method Surface method In the surface system, water flows by gravity either through furrows basins or borders. In this type, water loss by conveyance and deep percolation is heavy and the efficiency of irrigation is only 40 to 50% at field level. Efficiency can be improved by lining the canal and by proper leveling of the field. Sub-surface method The method is suitable for specific types of soils. Evaporation and other losses are reduced considerably since water is applied below the surface through porous pipes. Sprinkler method
Water is applied in the form of rain. Water is conveyed through pipes and sprayed though sprinklers. This method is most suited for steep sloppy and sandy soils. Drip irrigation Drip irrigation is adopted in water scarce areas for conserving water. In this method, water is applied in drops around the root zone through a pipeline with appropriate drippers. The common methods of irrigation are indicated schematically as follows: Whatever be the method of irrigation, it is necessary to design the system for the most efficient use of water by the crop.
Surface method of irrigation Surface irrigation (gravity irrigation) is the most ancient method of irrigation and this method still holds good for more then 95 per cent of the irrigated area in the world. It can be defined as the process of introducing a stream of water at the head of a field and allowing gravity and hydrostatic pressure to spread the flow over the surface throughout the field. To move forward, the flowing water must have a downward slope in the direction of flow.
This is, generally, provided by running water over a sloping land surface, but in the irrigation of level land, the water must build its own slope (from deepest at entry to near zero depth at advancing front). The soil surface thus serves the dual role of water conveyance and distribution. As it conveys the water, it controls the spreading pattern and hence the opportunity time for water to infiltrate. Spatial and temporal variability in infiltrability of the soil translates into non uniformity of water distribution into the root zone.
Field area nearest to the water inlet receives the greatest opportunity time and hence the greatest depth of infiltration, whereas the down field farthest from inlet receives least. This non—uniformity is most pronounced in coarse (sandy) soils, in which the infiltration rate is so high that much of the water entering the field infiltrates near the inlet and relatively little water remain for farther reaches of the field. On the other hand, fine textured soil (clayey) exhibit low infiltrability leading to significant flow of applied water to the lower sections of field, while higher section (near the inlet) remains insufficiently watered.
The distribution of water is obviously affected by the slope and length of run. Major components of a typical surface irrigation system and the idealized distribution of water in an almost level border are illustrated in (Fig. 5. 2). Water application efficiency is usually higher on fine textured (clayey) soils than on coarse textured (sandy) soils because of their lower infiltration rates and more water retention per unit depth within the root zone. However, clayey soils are more prone to excessive wetness, compaction and impeded aeration. Land leveling and smoothing are essential operations for successful surface irrigation.
On regularly sloping lands, graded long furrows and borders can significantly reduce leveling cost. Surface systems have advantages over others. 1. Initial capital investment for a surface irrigation system is usually lower than for sprinkler or drip systems, 2. Surface irrigation systems have relatively low energy requirements in routine operations, 3. Certain fruits and vegetables which can be damaged by sprinkling because of leaf scorch from salt residue of sprinkled water can be safely irrigated by surface systems, 4. Surface systems can avoid wind drift and canopy interception losses common in sprinkler irrigation, and 5.
Most important advantage of surface irrigation is its mechanical simplicity and easy adaptation to small land holdings. 6. Principal disadvantages of surface irrigation systems are their low application efficiencies, waste of water, water table raise, water logging and salinization Wild Flooding This is the primitive and least controlled of all surface irrigation systems. Water is delivered to the upper part of the plot and allowed to spread over the land in accordance with the natural topography. Distribution of water is highly uneven.
Consequently, part of the area becomes water logged, while ther part remains &y leading to eventual pattern of crop growth. Controlled Flooding Land is leveled or graded and subdivided by means of channels and ridges. Water is guided to each of the subdivisions. Depending on the manner in which the land is divided, controlled flooding methods are named differently (Fig 5. 3). Basin Basins are small level plots surrounded by low earth dikes, also called checks, within which water can be impounded to irrigate a single tree or a few trees in an orchard. This method is also referred as basin flooding and check—basin irrigation.
Water, is retained in the basin at a relatively uniform depth until the net application has had opportunity to be taken into to soil. This method is ideal for soils with moderate to slow intake rates and moderated to high available water holding capacities. On sloppy lands, basin irrigation can be carried out in conjunction with terracing. Check basin Check irrigation involves application of water to nearly level areas of limited or pre—determined size at a rate sufficiently in excess of intake rate of the soil to rapidly cover the area. This method is also known as check flooding, level border and flat bed irrigation.
Water is retained in place by small dikes on the contour and surrounding the individual area or strips. It is used to irrigate a wide variety of crops like wheat, finger millet, groundnut, pulses, etc. Border—strip Border (strip) irrigation involves division of field into strips between parallel dikes or ridges and each strip is irrigated separately (Fig. 5. 2). The border strips (graded border) should have little (not more than 0. 5%) or no cross slope, but should have some grade in the direction of irrigation, thus distinguishing from check method of irrigation which have little or no rade.
The entering water moves down the slope as an advance wave and infiltrates the soil as it moves. During advancing phase, the upslope part of strip, being closer to the source and having longer period of ponding, naturally infiltrates more water than the down slope section (Fig 5. 2 B). At the termination of supply, however, the water moving over the surface recedes down slope and augments the supply to the lower section, thus tending to equalize the initially non-uniform infiltration. Average depth of water application can be computed with the equation.
Important field characteristics to be considered in the design are infiltrability of soil and slope. The design variables are width and length of strips and the input discharge. Border irrigation is suitable for a variety of close growing and row crops. Furrow Irrigation Method In furrow irrigation, water is applied in small streams between the rows of crops, grown on ridges or furrow sides (Fig 5. 4). The size and shape of the furrows depend upon the soil, crop spacing and the equipment used for furrow forming. Water is applied in small stream into the furrow.
It infiltrates into the soil and spreads laterally to wet the area between the furrows. The size of the furrow streams usually varies from 0. 5 to 2. 5 us. The purpose of the optimum stream size is to wet the entire furrow length uniformly as quickly as possible without causing soil erosion. This method of irrigation is generally used to irrigate row crops and vegetables. It is most suited for soils having infiltration rate of 0. 5 and 2. 5 cm per hour. Water use efficiency is high and the furrows also function as drains. It is possible to irrigate alternate furrows in times of water scarcity.
Furrow method is not recommended for very light soils with high infiltration capacity as water is wasted on the upper end of the furrow due to deep percolation. Alternative furrow irrigation In this method, a particular set of furrows is irrigated during any one run of irrigation. During the next run, the left over furrows is irrigated. The interval of irrigation is normally shortened compared to the conventional furrow method. Skip furrow irrigation This method is best suited to heavy soils like clay and barns. Alternate furrows are skipped and converted to ridges of wide bed.
To avoid crop congestion, the furrow width can be widened compared to the original width. Both alternate and skip furrow irrigation methods are recommended during the period of water scarcity for crops like cotton. Flow rates needed for adequate water distribution in a furrow depends on the length and cross section of the furrow and on the infiltrability and retentively of the soil. The maximum non-erosive flow can b. estimated with the equation Average depth of water application can be computed by the equation Furrow length varies from about 20 to 300 m or even more.
Effective furrow widths range from 20 to 60 cm with between furrow ridge spacing of 60—120 cm. Ridge should raise about 30—60 cm high above furrow bottoms, Furrow inflow rates are limited to the range of 2 to 15 m3 hr’ per furrow to overcome the problems of overtopping and scouring. Slopes along the furrow may range from 0. 2 to 2. 0% but may be as high as 5. 0 per cent occasionally. Fine grained soils and densely compacted ridges increases the distance of lateral sorption but decreases its rate. Application of water to completely wet the soil ridges often leads to wastage of water by over irrigation.
Coarse soils exhibit high rate of downward infiltration beneath the furrow, but very little lateral sorption into the ridges. Hence, they require very closely spaced furrows or may be completely unsuitable for furrow irrigation. Surge irrigation Surge irrigation is a modified furrow method. In furrow irrigation, large stream sizes are used for fast advance of water along furrows. High infiltration rate in first quarter of the furrow at start of irrigation decline to a steady value To reduce runoff, cut—back methods are used for gradual reduction in inflow to much the changing soil infiltration rate.
Surge irrigation provides the opportunity to automate this procedure. It is the intermittent application of water under gravity flow resulting in a series of ‘on’ and ‘off’ of constant or variable time spans. Large intermittent flows rather than a continuous one are used with two sets of furrows and gated pipes laid out in a ‘Tee’ configuration. Water is switched alternatively from one set of furrows to the other by a valve and automatic time controller until the irrigation is completed. The cycle time (irrigation period plus rest period) can be varied from 30 minutes to several hours.
Large surge flows encourage rapid advance along the furrows and cutbacks are achieved either by reducing the cycle time cr by switching to continuous flow, once water reaches the end of furrows by running all the gated pipe outlets at half the surge distance (50% cutback). It is an effective method for achieving faster advance of water down the furrows compared to continuous application: Total volume of water required to complete advance phase is less. Frequent light irrigations can be given at initial crop growth stage when rooting depths are shallow and infiltration rates are high to reduce deep percolation losses.
Cablegation Cablegation is another development of gated pipe approach •to simplify management of furrow irrigation. A plug controlled by a cable moves slowly along a pipeline laid on a carefully prepared gradient (0. 001 to 0. 01%) at the head of the field. Outlets in the pipe, which feed water to individual furrows, are opened by passage of the plug. As the pressure behind the plug is highest, those outlets near the plug have the highest discharge. As the distance from the plug increases, so the pressure and hence the flow decreases, producing a cutback effect.
Speed of the plug can be chosen to control the furrow stream sizes required to match infiltration rate and reduce runoff. Low labor requirement, simplicity and high degree of uniformity with reduced runoff can make this system more popular. Corrugation This method can be placed between border and furrow irrigation methods. It is a partial flooding method, as water may not cover the entire field surface. Corrugations are V—shaped or U—shaped channels of about 10 cm deep, 40—75 cm spaced apart. The slope should be just enough not to permit soil erosion.
Corrugations are usually made after the crops sown and a simple implement called ‘corrugator’ is used for this purpose. This method is recommended for medium of soils and close growing crops. Pitcher irrigation This method is also known as porous cup irrigation method. This consists of embedding earthen cups of 500 ml capacity by the side of the seedling. The cups are initially filled with water up to the brim. Subsequently water is added to the cups at 4—5 days interval. This method results in ain1 saving of water as compared to check basin method.
The technique has a promise in arid and semi—arid zone light textured soils where water is very scarce. This technique practically eliminates all losses due to evaporation and deep percolation. Sub-surface irrigation methods Subsurface irrigation, also designated as sub—irrigation, involves irrigation to crops by applying water from beneath the soil surface either by constructing trenches or by installing underground perforated pipelines or tile lines. ‘Water is discharged into trenches and allowed to stand during the whole period of irrigation for lateral and upward movement or water by capillarity to the soil between trenches.
Underground perforated pipes or tiles in which water is forced, trickle out water through perforations in pipes or gaps in between the tiles. Water moves laterally and upward to moist the root zone soil under irrigation. The upper layers of soil remain relatively dry owing to constant evaporation while the lower layers remain moist. Overhead or Sprinkler Irrigation Methods Sprinkler irrigation refers to application of water to crops in form of spray from above the crop like rain. It is also called overhead irrigation as water is allowed to fall as spray from above the crop.
Water under pressure is carried and sprayed into the air above the crop through a system or overhead— perforated pipes, nozzle lines or through nozzles fitted to riser pipes attached to a system of pipes laid on the ground. Nozzles of fixed type or rotating under the pressure of water are set at suitable intervals in the distributions pipes. Water is sprayed through these perforations or nozzles over the crop wetting both the crop and soil. The spraying has a refreshing effect on plants. Water is applied at rate, 1es than the intake rate of soil so that there is no run—off.
Measured quantity of water is applied to meet the soil water depletion. Adaptability of sprinkle system Sprinkler irrigation may be used for many crops and on all type of soil on lands of widely different topography and slopes. However, it finds its best use to irrigate (i) sandy soils and soils with high infiltration rates, (ii) shallow soils that do not allow proper land leveling required for surface irrigation methods, (iii) areas with steep slopes having erosion hazards, (iv) for growing high priced crops and (v) where water is scarce and costly. The sprinkler system is designed according to necessity.
It may be for main irrigations, supplemental irrigations or for protective irrigations. In arid regions, sprinklers may e used to apply the full quantity of water needed by crops grown as the irrigation water is scarce and the sprinkler irrigation ensures a high efficiency of water application (Table 5. 2 and 5. 3). The sprinkler system should be designed to apply sufficient water to meet the crop demands at peak periods of consumptive use when the system is to be used for total irrigation. On other occasions, the system may be of lower capacity to apply only the required amount of water.
In humid areas it may provide supplemental irrigation during the periods of drought. Sprinkler irrigation is also used for protecting crops from being damaged by freezing temperature or frost. Advantage and disadvantages of sprinkler irrigation Sprinkler irrigation has many advantages over the surface irrigation. The principal advantages are that 1. Water use economized as looses by deep percolation can be totally avoided, 2. Small and frequent application of water can be made, 3. Water—application efficiency is usually very high, 4. There is very little waste of land for laying out the system, 5.
Measured amount of water can be applied, 6. Land leveling is not necessary, 7. It can be adopted even un undulating topography, 8. It is adopted where water is scarce and high priced, 9. Soil water can be easily maintained at a favorable tension for optimum growth and yield, 10. application of fertilizers, pesticides and herbicides can be easily made along with irrigation water, 11. crops can be saved from frost damage, 12. uniform application of water can be made in highly porous soils and 13. High yields or good quality fruits and vegetables are obtained.
There are, however, certain disadvantages associated with the method that limits the wide use of sprinklers. Principal limitations are: 1. High capital investment is involved in its installation, 2. Operating cost of sprinkler is higher, 3. Technical personnel for its operations and maintenance are required, 4. Clean water is needed to avoid clogging of nozzles, 5. Mechanical difficulties are expected, 6. Areas with hot winds are unsuitable, 7. It is not adopted in places where plenty of cheap water is available as surface methods are more useful and less costly and 8.
Pipe system laid on the soil surface may interfere with farm operations and movements of implements and animals. Classification of Sprinkler System Sprinkler irrigation system may be classified in two ways depending on i. Types of nozzle systems or perforations in pipelines, and ii. Portability of the systems The former classification includes; i. Nozzle line sprinkler system, ii. Rotary head sprinkler system, iii. Fixed—head sprinkler system, iv. Propeller type sprinkler system, and v. Perforated pipe system The systems according to the latter classification are described as: i. Permanent sprinkler system, i. Semi—permanent sprinkler system, iii. Solid—set sprinkler system and iv.
Semi—portable sprinkler system and v. Portable sprinkler system Types of Sprinkler Irrigation Systems There are five different types of sprinkler—irrigation, which are described in the following paragraphs. Nozzle line sprinkler system It consists of one or more pipes of relatively smaller diameter having a single row of fixed small nozzles spaced at uniform intervals along their entire length. Pipes are supported on rows of posts at a height convenient to spray over crops and can be rotated through 900.
Water is sprayed at a pressure of two to three atmospheres at right angles to the pipeline and at an angle of 450 to the area on both sides and the width of the strip covered varies from 6—to 15 m according to the pressure of water and nozzles used. Rotary head sprinkler system This system consists of nozzles that rotate under pressure of water and spray water in a circular way. Nozzles are fitted on riser pipes attached to lateral nozzle or double nozzles on a riser pipe. Laterals are usually laid on the pipelines at uniform intervals along the length of pipes. There may be a single ground and are spaced at about 15 m intervals.
A working pressure of 1. 4 to 3. 4 atm is used for high—pressure nozzles. The system has certain advantage and they are: i. Water is sprayed at a slow rate using nozzles with large openings, ii. It is favorable for soils of low infiltration rate and iii. Water containing some amount of fine silt and debris may be sprayed since the clogging of nozzles is less frequent. Fixed —head sprinkler system Nozzles in this system remain stationary and spray water in one direction only to which the spray nozzle is directed. The system is used extensively in orchards and nurseries. It has high water application rates.
The spray is usually fine which is helpful for irrigation seeding in nurseries. Propeller type sprinkler system The system includes a number mounted on a horizontal pipeline, which is held above the crop by a horizontal superstructure centrally pivoted over a wheeled platform in a wing—like fashion. Sprinkler pipeline with the superstructure propels slowly and sprays a wide area. The whole structure can be wheeled to new positions through path ways in the field. Water is conveyed to the sprinkler pipeline by a rubber hose either directly from the pumping plant or from the main line.
The rubber hose trails along with the structure just like a giant umbilical cord. The force of water is used for propelling the system. It. does away with laterals and by that reduces the capital investment. The operation is easy and the cost of irrigation is relatively cheap. Perforated pipeline system This system includes lateral pipes perforated at regular intervals in a definite pattern to spray water through these perforations. Pipes are installed in rows at an interval of 6 to 15 m and the working pressure is only from 0. 3 to 1 atm. An overhead tank suffices the need to create the pressure.
Pipes are perforated to spray the area on both sides of a pipe and strip of 6 to 15 m wide is usually covered with a pipeline. The water application is higher which is quite suitable for soils of higher infiltration rates. The system is adapted for irrigating lawns, gardens and small vegetable fields where the height of perforations does not exceed 60 cm. Water should be clean to prevent clogging of perforations. Types of Sprinkler System: on the basis of portability of sprinkler units they are classified as:- Portable and semi-portable types are most commonly used in agriculture.
These systems can be moved manually or mechanically. Efficiency of Sprinkle Irrigation Sprinkler irrigation is more efficient than the surface irrigation. It may be noted that sprinkler irrigation had been far better than all the methods stated herein. Evaporation losses from sprinklers depend on the relative humidity, temperature, wind velocity and fineness of drops that in turn depends on the water pressure and nozzle size. It may be only 2 to 8 per cent of the total sprinkler discharge. Leaf transpiration is greatly reduced due to free water on the leaf surface and high humidity near the leaf surface.
The evapo— transpiration from a just sprinkled crop does not exceed the normal evapo— transpiration rate. The water application efficiency is high and it is about 85 to 90 per cent Principles of Selecting Sprinkler System Choice of a sprinkler system depends on i. Water requirement of the crop, ii. Capacity to the system to apply water equal or less than intake rate of the soil, iii. The system with maximum water application efficiency, iv. Cost efficiency form the point of crop production economics, v. Nature of land topography that can not be properly graded owing to the subsoil being exposed, vi.
Soil texture, particularly the soils of very porous nature, vii. Comparative superiority of the system over other methods of irrigation in saving water, and viii. Cost and adequacy of the available water The sprinkler system capacity should be in conformity with the water requirement of the crop. The irrigation is scheduled to maintain the available soil water regime in 100 to 50 per cent level. When plenty of inexpensive water is available, high efficiency of the system may not be a consideration while high efficiency is wanted in areas of water scarcity and costly water.
The main objective should be to produce more with higher economic return for a given amount of water. Spacing of Sprinklers and Laterals The uniformity of water distribution from sprinklers depends on the pressure of water, wind velocity, rotation of sprinklers, spacing and so on. However, the spacing of sprinklers in a lateral and the spacing of laterals are adjusted considering all these conditions. Generally, a higher amount of water is applied near the sprinkler and the amount decreases gradually with distance from the sprinklers.
Sprinklers are arranged along a lateral not more than 50 per cent of the diameter of the coverage by an individual sprinkler. The distance between successive positions of laterals should not exceed 65 per cent of the diameter of the coverage by an individual sprinkler. It there is a wind of considerable speed, the spacing between sprinklers is further reduced. Formula to Determine Discharge, Spacing, and Spread of Sprinklers and the Capacity of Sprinkler System 1. Sprinkler discharge (i) The discharge from a sprinkler can be estimated by the formula ii)
The required discharge of an individual sprinkler may be estimated by the following formula as, 2. Spread of sprinkler The area converted by a rotating head sprinkler can be estimated from the formula as, Where, R = radius of the wetted area covered by sprinkler, m, 3. Rate of water application or precipitation intensity The rate of water application by an nozzle may be decided by the formula as, 4. Capacity of sprinkler system The capacity of a sprinkler system is decided by the area to be irrigated, depth of water needed per irrigation and time during which water is necessary to be applied. It may be decided by the formula as,
TRICKLE (DRIP) IRRIGATION It can be defined as the process of slow application of water in the form of discrete, continuous drops, tiny stream or miniature sprays through mechanical devices called emitters or applicators located at selected points along water delivery lines. Fertilizers and other chemical amendments can be effectively applied to individual or several plants using trickle irrigation. Trickle system has few characteristics in common with flood or sprinkler irrigation. Water advances in the soil around emitter only after the amount of water applied exceeds the infiltration rate at a point.
Then it advances until the infiltration rate of pounded area equals the emitter flow rate. Typically, a wetted dia of less than 10m, depending upon the soil properties and emitter application rate, will become saturated on the soil surface. Trickle irrigation, like other methods, will not fit every crop, specific site or objective. Presently, trickle system has greatest potential where water is expensive or scarce, soils are sandy, rocky or difficult to level and high value crops are produced. Principal crops under trickle irrigation are avocado, citrus, stone fruits, grapes, strawberry, sugarcane and tomato.
Each irrigation method has possible advantages and limitations with respect to technical, economical and crop production factors. Potential benefits and disadvantages of trickle systems as stated by Bucks et al (1982) are: 1. Advantages 2. Increased beneficial use of available water, 3. Enhanced plant growth and yield, 4. Reduced salinity hazard to plants, 5. Improved fertilizer and other chemical applications, 6. Limited weed growth, 7. Reduced operational labor, 8. Decreased energy requirement, and 9. Improved cultural practices 10. Disadvantages 11.
Persistent maintenance requirements, 2. Salt accumulation near plants, 13. Restricted soil water distribution and plant root development, and 14. Economic and technical limitations A typical drip irrigation system is illustrated in Fig. 5. 6 Water is delivered to the plants via a set of plastic lateral tubes laid along the ground or buried at a depth of 15—30 cm and supplied from a field main. The tubes are usually 10—25 mm in dia, either perforated or fitted with emitters designed to drip water into the soil at rates as close as possible to the mean rate of water consumption by the crop.
The trickling rate, generally, in the range of 1—10 lhr1 per emitter, should not exceed soil intake rate to avoid runoff, if any. The operating water pressure is usually 1—3 atm(15 to 45psi). This pressure is dissipated by friction in flow through the narrow passage or orifices of the emitter such that the water emerges at atmospheric pressure in the form of drops. Commercial emitters are either of the in line type, spliced into the tubes or of the on—line button type, plugged into the tube through a hole punched into the tubing wall. Emitters are recalibrated to discharge at constant rate of 2, 4 or 8 lhr1.
The frequency and duration of each irrigation is controlled by means of manual valve or of a programmable automatic valve assemble. The spacing between lateral rubes is determined by spacing of the crop rows. In recent years, several modifications of drip system have been developed in the continuing effort to improve water use efficiency. Some of these methods are adaptable to the needs of small scale farmers in developing countries. Surface trickle irrigation In this system, the lateral lines are laid on the surface. It is most popular application method, particularly for widely spaced crops.
Advantages of this system include the ease of installing, inspecting and changing and cleaning emitters. However, surface trickle lines interfere with cultural operations. Sub—surface trickle irrigation These systems with lateral lines are buried below soil surface are gaining importance as problems with clogging have been reduced. Advantages of this system include freedom from necessity of anchoring of tubing at the beginning and removing at the end of growing season, little interference with cultural operations and longer economic life. Low—head bubbler irrigation
It is a modification of drip irrigation, designed to reduce the energy requirements by using inexpensive thin walled, corrugated plastic pipes for minimizing pressure requirements, besides obviating the need for filtration altogether (Fig. 5. 6). It is designed to simplify the system and make it less dependent on components, which are likely to deteriorate with use. Bubblers resemble short orifice emitters used for surface trickle, except that discharge rates are higher and range from 1 to 4 lmin1. As the emitter discharge rate normally exceeds the infiltration rate of soil, small basin is usually formed around the trees.
It is particularly suited for irrigating widely spaced fruit crops. Micro—spray irrigation Micro—spray (mini—sprinkler irrigation) is similar in principle to drip systems in which water is applied only to a fraction of the ground surface (Fig 5. 6). However, instead of dripping water from emitters with capillary orifices, micro-sprayer system ejects fine jets that fan out from a series of nozzles. Each nozzle can cover an area of about a square meter, which is larger than individual area wetted by drip emitters.
Another advantage, of micro-spray irrigation over drip system is that the hazard of clogging of emitters is minimized by way of larger nozzle orifices.. Micro-spray irrigation retains potential advantages of drip irrigation. Mechanical—move irrigation These systems expand the bubbler concept to large scale row crops. They utilize liner—move sprinkler lines that have drop structures or tubes to deliver water as a continuously and uniformity of water applications over the field are excellent. Potential advantages of these systems include reduction in clogging problem and less expensive pipe network compared to solid set trickle systems.
Pulse irrigation It has a series of irrigation time cycles with an operating (water discharge) and rest phase (no discharge). Typical operating phases are 5, 10, 15 minhr1. Primary advantage is reduction in clogging problems and disadvantage is the need to develop reliable inexpensive pulse emitters and automatic controllers. Selection of an appropriate irrigation method for any combination of physical, agronomic and socio-economic conditions involves complex and sometimes conflicting considerations.
The decision of what irrigation system to adopt is still a matter of judgment, based on one’s evaluation of relative importance of the factors involved. The advent of relatively inexpensive water application system has apparently removed some of the economic constraints to the widespread adoption of scientific innovations. New irrigation methods when properly applied can raise yields, while minimizing waste, reducing drainage requirements and promoting the integration with essential inputs.