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Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
Chapter 2 part 1 sprinkler
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Chapter 2 part 1 sprinkler

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IRRIGATION WATER MANAGEMENT AS PER GTU SYLLEBUS CHAPTER 2 PART 1 SPRINKLER IRRIGATION SYSTEM..

IRRIGATION WATER MANAGEMENT AS PER GTU SYLLEBUS CHAPTER 2 PART 1 SPRINKLER IRRIGATION SYSTEM..

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  • 1. IRRIGATION WATER MANAGEMENT Page 1 IRRIGATION WATER MANAGEMENT AS PER GTU SYLLEBUS B.E. VIII CIVIL 11/14/2012 DARSHAN INSTITUTE OF ENGINEERING & TECHNOLOGY ASST. PROF. V.H.KHOKHANIl
  • 2. IRRIGATION WATER MANAGEMENT Page 2 CHAPTER NO 2 SUBSURFACE IRRIGATION METHODS PART 1 SPRINKLER IRRIGATION SYSTEMS- 1.4 Role of remote sensing and GIS 1. Identifying lanuse land cover pattern.  Remote sensing & GIS technologies can make a significant contribution in collecting land use data, particularly preparing accurate land cover map .  Such a map then permit better understanding of land utilization aspect i.e. cropping pattern, fallow lands, waste land and surface water bodies.  The use of multitemporal data helps in detecting the changes in land cover and also monitoring these changes at regular interval. The remotely sensed data can also help in detecting changes in land cover and also in monitoring these changes at regular interval.  The remotely sensed data helps in detecting the changes in land cover and also in monitoring these changes at regular interval. 2. Identifying nutrient deficiency -  The remotely sensed data can also help in identifying nutrient deficiency, disease, water deficiency, weed infection, insect damage, hail damage, wind damage. Such a problem within a field can be identified remotely before it can be identified visually.  Timely detection of pests and diseases as well as assessment of crop condition are other processes where remote sensing can play a important role. The condition assessment is carried out utilizing the multiband satellite data by dividing the area of interest into geographically referenced grid cells of appropriate size.  The stressed plants in a field can be identified by establishing their spectral signature and that of healthy plants. The spectral signature of stressed plants appears altered as compared to that of healthy plants. 3. Identifying water depth for crop -  If a crop gets an insufficient water supply from the soil, the surface temperature of the crop will increase and this increase can be detected by measuring the radiance in the thermal region of electromagnetic spectrum. 4. Identifying cropping pattern -  A crop type can be identified in a remote sensing image by its
  • 3. IRRIGATION WATER MANAGEMENT Page 3 spectral response pattern and by the image texture.  The remote sensing data, if suitably complemented with ground truth and sample surveys can provide a valuable input in acreage and yield estimation of major crops.  Crop acreage estimation is an area which requires a quantitative use of subtle differences in spectral data. Thus digital image processing for acreage estimation consists of - o Identifying the representative sites of various crops on the image based on ground observations. o Generating signatures for different representative training sites. o Classifying the image using the training statistics. 5. Yield of crop -  Yield estimation is influenced by such factors as crop genotype, soil characteristics, and cultural practices and weeds, pests and diseases. The effects of all these are manifested in the growth of crop.  The remotely sensed data can provide the parameters directly related to yield and other biometric parameters, which may be utilized as the input parameters to a yield model. 6. Identifying methods of irrigation –  Remotely sensed data and GIS data provides basic information related to type of land and its hydraulic conductivity which can be used for deciding methods of irrigation. 7. Canal operation –  Water release days can be predicted by soil moisture relationship provided by GIS data.  Quantity of water also can be identified by the land cover map. 2.1 Adaptability OR Favourable situations of subsurface irrigation  Existence of a high water table or an impervious subsoil above which an artificial water table can be created,  Highly permeable root zone soil with reasonably uniform texture permitting good lateral and upward movement of water,  Irrigation water is scarce and costly, and  Soil should not have any salinity problem. It must be ensured that no water is lost by deep percolation. The artificial water table is created at a depth of 30 to 120 cm depending on crops
  • 4. IRRIGATION WATER MANAGEMENT Page 4 to be grown, nature of soil capillarity and the depth of the impervious soil layer.  Uniform topographic conditions and moderate slopes favour sub irrigation.  In places where sprinkler irrigation may become expensive, sub irrigation is adopted.  Sub irrigation is made by constructing a series of ditches or trenches 60 to 100 cm deep and 30 cm wide, the two sides of which are made vertical. Ditches are spaced 15 to 30 m apart depending on soil types and lateral movement of water in soils.  Various types of crops, particularly with shallow root system are well adapted to sub irrigation. Crops like wheat, jowar, bajra, potato, beet, peas and fodder can be irrigated by sub irrigation.  Sometimes, sub irrigation is made to high priced vegetable crops by installing a perforated pipe distribution system below the soil surface but within the crop zone. This is often termed the artificial sub irrigation.  A good quality water supply must be available throughout the growing season and outlet drainage is provided, particularly in high rainfall areas. 2.2 Advantages and limitations Advantages  Soil water can be maintained at a suitable tension favourable for good plant growth and high yields,  Evaporation loss from soil surface is held at minimum resulting in saving of water,  Labour cost of water application is very low and  Supply ditches may serve as drainage ditches in humid areas  It can be used for soils having a low water holding capacity and a high infiltration rate where surface method cannot be adopted and the sprinkler irrigation is expensive. Limitations  Presence of a high water table or impervious subsoil is a prerequisite for adopting this method,  Good quality water must be available,  There are chances of saline and alkali conditions being developed by upward movement of salts with the water and  Soils should have a good hydraulic conductivity for upward movement of water.  The method is practiced to a limited extent in India for growing vegetable crops around Dal Lake in Kashmir and coconut in Kuttanad area in Kerala.
  • 5. IRRIGATION WATER MANAGEMENT Page 5 2.3 2.3.1 2.3.2 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 the 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 of 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 distribution 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 a rate less than the intake rate of soils so that there occurs no run-off. Measured quantity of water is applied to meet the soil water depletion. Adaptability of sprinkler system Sprinkler irrigation may be used for many crops and on all types of soil on lands of widely different topography and slopes. However, it finds its best useto irrigate  Sandy soils and soils with high infiltration rates,  Shallow soils that do not allow proper land levelling required for surface irrigation methods,  Areas with steep slopes having erosion hazards  For growing high priced crops and  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 be 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  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. Advantages and disadvantages of sprinkler irrigation  Water use is economized as losses by deep percolation can be
  • 6. IRRIGATION WATER MANAGEMENT Page 6 2.3.3 totally avoided,  Small and frequent applications of water can be made,  Water-application efficiency is usually very high  There is very little waste of land for laying out the system,  Measured amount of water can be applied,  Land levelling is not necessary,  It can be adopted even in undulating topography,  It is adopted where water is scarce and high priced  Soil water can be easily maintained at a favourable tension for optimum growth and yield,  Application of fertilizers, pesticides and herbicides can be easily made along with irrigation water  Crops can be saved from frost damage,  Uniform application of water can be made in highly porous soils  High yields or good quality fruits and vegetables are obtained. Limitations are  High capital investment is involved in its installation,  Operating cost of sprinkler is higher  Technical personnel for its operations and maintenance are required,  Clean water is needed to avoid clogging of nozzles,  Mechanical difficulties are expected,  Areas with hot winds are unsuitable,  It is not adopted in places where plenty of cheap water is available as surface methods are more useful and less costly and  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 Types of nozzle systems or Portability of systems perforations in pipelines, and Nozzle line sprinkler system Permanent sprinkler system
  • 7. IRRIGATION WATER MANAGEMENT Page 7 Rotary head system, Semi-permanent sprinkler Fixed-head sprinkler system, Solid-set sprinkler system Propeller type sprinkler system, Semi portable System Perforated pipe system. Portable sprinkler system. A. Types of nozzle systems or perforations in pipelines, 1. 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 90°. Water is sprayed at a pressure of two to three atmospheres at right angles to the pipe line and at an angle of 45° to the horizontal plane. The pipe line is rotated through 90° to cover with water spray 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. 2. 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 pipelines at uniform intervals along the length of pipes. There may be a single nozzle or double nozzles on a riser pipe. Laterals are usually laid on the 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 advantages  Water is prayed at a slow rate using nozzles with large openings,  It is favourable for soils of low infiltration rates  Water containing some amount of fine silt and debris may be sprayed since the clogging of nozzles is less frequent. 3. 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 irrigating seedlings in nurseries. 4. Propeller type sprinkler system The system includes a number of sprinklers 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 super structure propels slowly and sprays a wide area. The whole structure can be wheeled to new positions through pathways in the field. Water is conveyed to the sprinkler pipeline by a rubber hose either directly from the
  • 8. IRRIGATION WATER MANAGEMENT Page 8 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. 5. 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 a strip of 6 to 15 m wide is usually covered with a pipeline. The water application rate 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 plant does not exceed 60 cm. Water should be clean to prevent clogging of perforations. B. Sprinkler Irrigation Systems according to Portability A sprinkler system usually includes nozzles, risers, lateral distribution pipes, mainline pipes, a filter unit, a fertilizer tank with assemblies and a pumping plant. The system may be installed permanently for an area or it may be portable for use in different fields. There are five classes according to portability. 1. Permanent system A sprinkler system is said to be permanent when the components especially the pumping unit with its water source, mains, submains and laterals are stationary. Mains, sub mains, and laterals are usually buried in the soil. Sprinklers with risers also remain in the same position. However, availability of quick coupling risers with sprinklers makes it possible t6 move the sprinklers along the lateral lines and it then reduces the number of sprinklers. Such a system is costly but automation of the system is possible along with water measuring devices. The main advantage is that it greatly reduces the labour Cost and the trouble of shifting the various components during irrigation. 2. Solid-set system A solid-set system has enough laterals requiring no movement during irrigation. The laterals are set in the field i^, the beginning of the crop season and they remain there till the end of the season. The system is employed for crops requiring short and frequent irrigation. 3. Semi-permanent system The system consists of buried mains and submains and a fixed
  • 9. IRRIGATION WATER MANAGEMENT Page 9 2.3.4 2.3.5 2.3.6 pumping plant and water source. Laterals and risers with sprinklers are portable. The system Is used for irrigating orchards, permanent pastures and also general crops. It requires comparatively a lower capital investment than the permanent system, as one or a few laterals may suffice to cover a wide area with extended mainline. However, it needs shifting of laterals while irrigating a field. 4. Semi-portable system When the pumping plant with its water source remains fixed and mains, submains, laterals and sprinklers with risers are portable, the system is referred to as semi-portable system. It facilitates irrigation to different fields with different crop rotations requiring frequent change of position of the lines. The propeller type sprinkler system is semi-portable when its pumping unit and water source remain fixed. 5. Portable system This system has portable pipelines, sprinklers and even the pumping plant. It is designed for easy movement in fields or installation in different pumping sites to facilitate irrigation of crops in rotation with other crops irrigated by surface methods. A larger area with minimum capital cost on pipelines and sprinklers can be irrigated. However, the operation involves more skilled personnel and labour. Portable sprinkler system has proved beneficial in areas with high water table and in soils with high infiltration rates requiring frequent light irrigations. Besides, this system is useful for sprinkler irrigations occasionally for protection against frost or freezing temperatures and for humidity control. The propeller type sprinkler system may come under this category. Efficiency of Sprinkler Irrigation Sprinkler irrigation is more efficient than the surface irrigation. A comparative efficiency of sprinkler, check basin, furrow and skip furrow methods of irrigation in cotton crop at Madurai is presented. 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 evapotranspiration from a just sprinkled crop does not exceed the normal evapotranspiration rate. The water application efficiency is high and it is about 85 to 90 per cent. % Factors affecting on Selecting Sprinkler System
  • 10. IRRIGATION WATER MANAGEMENT Page 10 2.3.7  Water requirement of the crop,  Capacity of the system to apply water equal or less than intake rate of the soil,  The system with maximum water application efficiency  Cost efficiency from the point of crop production economics,  Nature of land topography that can not be properly graded owing to the subsoil being exposed,  Soil texture, particularly the soils of very porous nature,  Comparative superiority of the system over other methods of irrigation in saving water,  Cost and adequacy of the available water. The sprinkler system capacity should be in conformity with the water requirement of the crop. Design of sprinkler irrigation – Steps are as follow – 1. Inventory of Resources and Conditions. A. Map of the area. It is essential that a map of the area concerned is prepared and drawn to scale with sufficient accuracy to show all dimensions so that lengths of main and laterals can be scaled there from. It should be a contour map or, at least, should show all relevant elevations with respect to water source, pump location, and critical elevations in the fields to be irrigated. The elevation map provides information about pressure developed for pump. B. Water supply—source, availability and dependability.- The quantity available should also meet the seasonal and annual requirements of the crops and the area to be irrigated. The water should be chemically suitable for irrigating the crops and soils of the area. It should not have any corrosive effect on the equipment. The water should be relatively clean and free of suspended impurities so that the sprinkler lines and nozzles are not clogged. C. Climatic conditions. - The consumptive use of a crop depends upon the climatic parameters such as temperature, radiation intensity, humidity and wind velocity. Sprinkler system is designed for the daily peak rate of consumptive use of the crops irrigated by it. A peak demand in the range of 2 to 10 mm depth per day is equivalent to a continuous flow of 0.23 to 1.16 litres/second/hectare.
  • 11. IRRIGATION WATER MANAGEMENT Page 11 D. Depth of irrigation-. The depth of irrigation is calculated on the basis of available moisture holding capacity of the soil in its different layers and the soil moisture extraction pattern of the crop in its root zone depth. Depth of water to be applied for irrigation E. Irrigation interval.- From the point of view of sprinkler design, the irrigation interval is the length of time allowable between successive irrigations during the peak consumptive use of the crop. It is interesting to note that the irrigation interval can also be varied by altering the hours of set. For instance, a system designed to supply 100 mm with 20-hour sets at 20-day intervals can also apply 50 mm with 10-hour sets at 10-day intervals. Such practices are common during the early stages of crop growth when the root system has not been fully developed. Number of days after which an irrigation must be applied F. Water application rate-. The rate of water application by sprinklers is limited by the infiltration capacity of the soil. Application at rates in excess of the infiltration capacity of the soil results in runoff, with accompanying poor distribution of water, loss of water and soil erosion. G. Sprinkler spacing.- To achieve uniform sprinkling of water, it is necessary to overlap the area of influence of the sprinklers. The overlap increases with the increase in wind velocity. H. Power source.- The source of power to operate the pump is to be known in advance. Electric power is most convenient when the pump is stationary. Electric pumping sets are cheaper in initial cost and maintenance cost. Portable diesel pumping sets are the most suitable and practical for fully portable sprinkler systems. 2. Types of Systems and Layout.- Type of sprinkler determined, based on pressure limitations, application rates, cover conditions, crop requirements, and availability of labour, the next step is to determine the location of the pumping unit, the orientation of mains and laterals,
  • 12. IRRIGATION WATER MANAGEMENT Page 12 sprinkler spacing, operating pressure, and nozzle sizes that will most nearly provide the optimum water-application rate with the greatest degree of uniformity of distribution. A. Location and nature of water supply. –  The layout of the mains will depend on the location of the well. It is advantageous if the pump for the well designed to lift the water and provide necessary pressure to overcome the friction loss in the pipelines and to operate the sprinklers.  Sometimes it may be necessary to adopt a sprinkler irrigation system with an already laid underground pipeline water distributuion system or field channels.  In case of underground pipelines a portable pumping set can be used with the suction attached to the hydrants mounted on the pipe outlet  In case of field channels running , the channel can be run down the centre of the field the laterals will then be only half as long so that smaller length laterals could be used, but the channel may interfere with tillage operations and may result in some reduction in the net area cropped.  Another alternative is to have a permanent pumping plant at the source and distribute the water in buried pressure pipelines. These pipelines will usually run down the centre of the field so that the outlets offer little hindrance to tillage and other farm operations. B. Orientation of laterals.-  To obtain a reasonable degree of uniformity in the discharge of each sprinkler, the mains should be located in the general direction of the steepest slope, with the laterals at right angles  If the lateral slopes upgrade appreciably, it is difficult to design for a reasonable length. If it slopes downgrade, the length can be longer than usual, but rarely does the slope remain uniform for each setting.  A main located along the middle of a field, a given lateral will normally be moved to successive positions up one side and then down the other. (a) Length of Main pipe, = (b) Frictional loss for assumed diameter of pipe,
  • 13. IRRIGATION WATER MANAGEMENT Page 13 Where, hm = fractional loss in metre Lm = length of main pipe Q = discharge lit/sec dm = Assumed diameter of pipe, cm f = frictional coefficient (c) Length of lateral pipe, m (d) Diameter of lateral pipe Where, d; = diameter of Lateral pipe, cm f = coefficient of friction q = discharge of one sprinkler =Total discharge(Q)/Nos of sprinkler ha = operating pressure in terms of height or head of wat (1 kg/cm2 = 10 m of water) 1/R = value for Nos of sprinklers from standard Table, (for 13 sprinklers value of 1/R = 3068) S = spacing of sprinkler, metre.  C. The number of possible arrangements  The arrangement selected should provide for a minimal investment in irrigation pipe, have low labour requirement.  The choice will depend to a large extent upon the types and capacities of the sprinklers and their operating pressures. D. Sprinkler Selection and Spacing.-  The actual selection of the sprinkler is based largely upon design information furnished by the manufacturers of the equipment.  The choice depends mainly on the diameter of coverage required, pressure available and sprinkler discharge.  The best combination of sprinkler spacing and lateral moves, suiting the application rate for the soil and wind conditions should be selected.  The required discharge of an individual sprinkler by the following formula: in which, Q = required discharge of individual sprinkler,
  • 14. IRRIGATION WATER MANAGEMENT Page 14 litres/second i. Sj = spacing of sprinklers along the laterals, metres ii. Sm = spacing of laterals along the main, metres iii. I = optimum application rate, cm/hr. E. Height of sprinkler riser pipes.  Sprinklers are located at maximum height of the crop.  To avoid excessive turbulence in the riser pipes the minimum height of riser is 30 cm when the riser pipe is of 2.5 cm diameter and 15 cm when it is of 1.8 to 2 cm diameter. 4. Capacity of Sprinkler Systems.-  The required capacity of a sprinkler system depends on the size of the area to be irrigated (design area), the gross depth of water applied in each irrigation, and the net operating time allowed to apply water to this depth.  The capacity of the system may be calculated by the formula: in which, Q = discharge capacity of the pump, litres/sec A = area to be irrigated, hectares d = net depth of water application, cm F = number of days allowed for the completion of one irrigation H = number of actual operating hours per day E = water application efficiency, per cent.  In equation it may be noted that F and H are of major importance in that they have a direct bearing on the capital investment per hectare required for equipment.  From the formula it is clear that the greater the product of these two factors (operating time) the smaller is the system capacity (and thereby the cost) for a given area. 6. Hydraulic Design of Sprinkler Systems.  The hydraulic design of sprinklers is aimed at obtaining a uniform irrigation coverage, the desired rate of application, the break-up of sprinkler drops necessary to Minimize structural deterioration of the soil surface, the efficiency desired to reduce the energy requirement in operating the system and to maximize area of coverage.  The main hydraulic principles involved in a sprinkler system design are given below. A. Discharge of sprinkler nozzle. The discharge of a sprinkler nozzle
  • 15. IRRIGATION WATER MANAGEMENT Page 15 In which, q = nozzle discharge, m3/sec a = cross-sectional area of nozzle or orifice, m2 h = pressure head at the nozzle, metres g = acceleration due to gravity, m/sec2 C = coefficient of discharge which is a function of friction and contraction losses (the coefficient of good nozzles should be 0.95 to 0.96) B. Water spread of sprinkler.- The area covered by a rotating head sprinkler may be estimated in which, R = radius of wetted area covered by the sprinkler, metres d = diameter of nozzle, metres h = pressure head at the nozzle, metres. Maximum coverage is attained when the jet emerges from the sprinkler at an angle of 30° to 32° above the horizontal. Most rotating sprinklers are standardized at 30°. C. Break-up of jet.- Some break-up of the jet of water is necessary to attain uniformity of coverage and to minimize the presence of excessively large drops. The larger drops lose less velocity and travel farther.  They also strike the soil surface at a higher velocity, with more energy to cause structural deterioration of the soil surface. There is need for some compromise among distance of throw, uniformity of coverage, and effect on the soil surface.  There is a natural tendency of jets to break-up because of air resistance, and the break-up increases with pressure. The break-up is usually increased by having slots in the nozzle or by a pin impinging on the jet.  Slow rotation sprinklers, which make about 0.67 to 1 rpm for small sprinklers and 0.25 to 0.5 rpm for large sprinklers, provide good coverage. in which, Pd= index for jet break-up h = pressure head at nozzle, metres q = sprinkler discharge, litres/sec  It has been noticed if Pd is greater than 2, the condition of drop size is good; if 4, the condition of drop size is best; and if greater
  • 16. IRRIGATION WATER MANAGEMENT Page 16 than 4, pressure is being wasted. D. Rate of application.- The average rate of application, often called "precipitation intensity", for a single sprinkler may be estimated by the following formula: In which, = water application rate cm/hour. Q = rate of discharge of sprinkler litre/ sec A = Wetted area of sprinkler m2. 2.3.8 Components of sprinkler irrigation system The components of portable sprinkler system are shown through fig .3. A sprinkler system usually consists of the following components 1. A pump unit 2. Tubings- main/submains and laterals 3. Couplers 4. Sprinker head
  • 17. IRRIGATION WATER MANAGEMENT Page 17 5. Other accessories such as valves, bends, plugs and risers. 1. Pumping Unit:  The pressure forces the water through sprinklers or through perforations or nozzles in pipelines and then forms a spray.  Centrifugal pump is used when the distance from the pump inlet to the water surface is less than eight meters.  For pumping water from deep wells or more than eight meters, a turbine pump is suggested.  The driving unit may be either an electric motor or an internal combustion engine. (ii) 2. Tubings: Mains/submains and laterals:  The tubings consist of mainline, submanins and laterals.  Main line conveys water from the source and distributes it to the submains.  The submains convey water to the laterals which in turn supply water to the sprinklers. Aluminum or PVC pipes are generally used for portable systems, while steel pipes are usually used for center-pivot laterals.  Asbestos, cement, PVC and wrapped steel are usually used for buried laterals and main lines. 3. Couplers: Couplers are used for connecting two pipes and uncoupling quickly and easily. Essentially a coupler should provide ,  a reuse and flexible connection  not leak at the joint  be simple and easy to couple and uncouple  be light, non-corrosive, durable. 4. Sprinkler Head:  Sprinkler head distribute water uniformly over the field without runoff or excessive loss due to deep percolation.  Different types of sprinklers are available. They are either rotating or fixed type.  The rotating type can be adapted for a wide range of application rates and spacing. They are effective with pressure of about 10 to 70 m head at the sprinkler.Pressures ranging from 16 to 40 m head are considered the most practical for most farmers.  Fixed head sprinklers are commonly used to irrigate small lawns and gardens. They release more water per unit area than rotating sprinklers. Hence fixed head sprinklers are adaptable for soils with high intake rate. 5. Fittings and accessories: The following are some of the
  • 18. IRRIGATION WATER MANAGEMENT Page 18 important fittings and accessories used in sprinkler system.  Water meters: It is used to measure the volume of water delivered. This is necessary to operate the system to give the required quantity of water.  Flange, couplings and nipple used for proper connection to the pump, suction and delivery.  Pressure gauge: It is necessary to know whether the sprinkler system is working with desired pressure to ensure application uniformity.  Bend, tees, reducers, elbows, hydrants, butterfly valve and plugs.  Fertilizer applicator: Soluble chemical fertilizers can be injected into the sprinkler system and applied to the crop. The equipment for fertilizer application is relatively cheap and simple and can be fabricated locally. The fertilizer applicator consists of a sealed fertilizer tank with necessary tubings and connections. A venturi injector can be arranged in the main line, which creates the differential pressure suction and allows the fertilizer solution to flow in the main water line. 2.3.9 General outline of design of sprinkler irrigation – Step 1 consists Data required for sprinkler irrigation system – 1. Name of crop 2. Depth of irrigation to be applied 3. Peak water requirement 4. Maximum infiltration rate of soil 5. Characteristics of water source such as its location from field, type, 6. Discharge capacity etc. 7. Area to be covered 8. Type of topography 9. Irrigation Efficiency 10. Operating hours of pump 11. Efficiency of pump 12. Water level for pumping 13. Shifting of a whole system per day Step-2 : Calculate discharge capacity : (a) Number of days after which an irrigation must be applied
  • 19. IRRIGATION WATER MANAGEMENT Page 19 (b) Depth of water to be applied for irrigation (c) Discharge in lit/sec. where Q = discharge capacity of the pump, l/s A = area to be irrigated, ha H = actual operating hours of the pump/day, and D = depth of water application I = optimum application rate. Step-3 : Design of Main and lateral pipes (e) Length of Main pipe, = (f) Frictional loss for assumed diameter of pipe, Where, hm = fractional loss in metre Lm = length of main pipe Q = discharge lit/sec dm = Assumed diameter of pipe, cm f = frictional coefficient (g) Length of lateral pipe, m (h) Diameter of lateral pipe Where, d; = diameter of Lateral pipe, cm f = coefficient of friction q = discharge of one sprinkler =Total discharge(Q)/Nos of sprinkler ha = operating pressure in terms of height or head of wat (1 kg/cm2 = 10 m of water) 1/R = value for Nos of sprinklers from standard Table, (for 13 sprinklers value of 1/R = 3068) S = spacing of sprinkler, metre.
  • 20. IRRIGATION WATER MANAGEMENT Page 20 Step-4 : Lateral spacing :  According to condition of shifting of system, spacing of lateral determine. If each lateral is shifted twice a day then numbers of day required for irrigation for assumed spacing of lateral = width of field / assumed spacing  Out of two or three trial of assumed spacing in metre, the spacing which is most economical is selected. (Trial should be done for 12 m, 15 m or 18 m) Step-5 : Head loss in the lateral : From standard table, for size of lateral pipe head loss (frictional 1$ is determine. Step-6 : H.P. requirement for pumping : Where Q = Total discharge E = efficiency of pump H = Lift of water to be pumped, it includes frictional losses of main pipe, lateral pipe, miscellaneous loss etc. 2.3.10 Moisture distribution pattern and uniformity of coverage The basic objectives of sprinkler irrigation is to simulate rainfall and to apply uniformly a calculated depth of water at a predetermined application rate . The irrigation efficiency of sprinklers will depend upon the degree of uniformity of water application. The water spray distribution characteristics of sprinklers and their spacing regulate the uniformity of water application. The spray distribution characteristics of sprinklers heads are typical and change with nozzle size and operating pressure. With lower pressure the drops are larger and water from nozzle falls in a ring away from sprinkler. With higher pressure the water from the nozzle breaks up into very fine drops and falls close to sprinkler.wind also distorts the application pattern. The higher the wind velocity, greater the distortion and this factor should be considered when selecting the sprinkler spacing under windy conditions. The distribution pattern from sprinklers operating under favorable conditions of pressure and wind is given in figure. In this distribution pattern the depth of water applied surrounding the sprinkler decreases as the distance from the sprinkler increases. The absorption of water in the same pattern because the rate of water
  • 21. IRRIGATION WATER MANAGEMENT Page 21 application at any point under the sprinkler coverage is lower than the infiltration rate of the soil. To obtain uniformity of water application the wetted circles of the adjacent sprinklers should be overlapping so as to add water to areas of the adjoining sprinklers. The aggregate depth of distribution obtained by overlapping thus becomes nearly uniform as in figure
  • 22. IRRIGATION WATER MANAGEMENT Page 22 2.3.11 OPERATION AND MAINTENANCE OF SPRINKLER IRRIGATION  Proper design of a sprinkler system does not in itself ensure success. It should be ensured that the prime mover and the pump are in alignment, particularly in the case of tractor-driven pumps.  For these the drive shaft and the pump shaft should lie at nearly the same height to prevent too great an angle on the universal shaft. Service and installation procedures of the pump and power unit should be strictly observed.  While laying the main and lateral pipes, always begin laying at the pump. This necessarily gives the correct connection of all quick coupling pipes.  While joining couplings, it is ensured that both the couplings and the rubber seal rings are clean. In starting the sprinkler system, the motor or engine is started with the valves closed. The pump must attain the pressure stated on type-plate, or otherwise there is a fault in the suction line. After the pump reaches the regulation pressure, the delivery valve is opened slowly.  Similarly, the delivery valve is closed after stopping the power unit. The pipes and sprinkler-lines are shifted as required after stopping. Dismantling of the installation takes lace in the reverse order to the assembly described above. Maintenance of the sprinkler irrigation A sprinkler system, like any other farm equipment, needs
  • 23. IRRIGATION WATER MANAGEMENT Page 23 maintenance to keep it operating at peak efficiency. Parts of the system subject to wear are the rotating sprinkler heads, the pumping set, the couplers and the pipeline. General principles regarding the maintenance of the pipes and fittings and sprinkler heads are given below: 1. Pipes and Fittings.- The pipes and fittings require virtually no maintenance but attention must be given to the following procedures:  Occasionally clean any dirt or sand out of the groove in the coupler in which the rubber sealing ring fits. Any accumulation of dirt or sand will affect the performance of the rubber sealing ring.  Keep all nuts and bolts tight.  Do not lay pipes on new damp concrete or on piles of fertilizer. Do not lay fertilizer sacks on the pipe.  The pipes are automatically emptied and ready to be moved. When the pump is first started and before the pressure has built up in the system the seals may give a little leakage. With full pressure in the system the couplers and fittings will be effectively leak-free.  If, however, there is a leakage, check the following: There is no accumulation of dirt or sand in the groove in the coupler in which the sealing ring fits. Clean out any dirt or sand and refit the sealing ring. The end of the pipe going inside the coupler is smooth, clean and not distorted. In the case of fittings such as bends, tees and reducers ensure that the fitting has been properly connected into the coupler. 2. Sprinkler heads.- The sprinkler heads should be given the following attention:  When moving the sprinkler lines, make sure that the sprinklers are not damaged or pushed into the soil.  Do not apply oil, grease or any lubricant to the sprinklers. They are water lubricated and using oil, grease or any other lubricant may stop working.  Sprinklers usually have a sealed bearing and at the bottom of the bearing there are washer. Usually it is the washers that wear and not the more expensive metal parts. Check the washers for wear once a season or every six months—this is especially important where water is sandy. Replace the washers if worn.  After several season's operation the swing arm spring may
  • 24. IRRIGATION WATER MANAGEMENT Page 24 need tightening. This is done by pulling out the spring end at the top and rebending it. This will increase the spring tension.  In general, check all equipment at the end of season and make any repairs and adjustments and order the spare parts immediately so that the equipment is in perfect condition to start in the season. Storage. The following points are to be observed while storing the sprinkler equipment during the off season.  Remove the sprinklers and store in a cool and dry place.  Remove the rubber sealing rings from the couplers and fittings and store them in a cool, dark place.  The pipes can be stored outdoors in which case they should be placed in racks with one end higher than the other. Do not store pipes along with fertilizers.  Disconnect the suction and delivery pipe work from the pump and pour in a small quantity of medium grade oil. Rotate the pump for a few minutes. Blank off the suction and delivery branches. This will prevent the pump from rusting. Grease the shaft.  Protect the electric motor from the ingress of dust, dampness and rodents. Troubleshooting - The following are the general guidelines to identify and remove the common troubles in the sprinkler systems: 1. Pump does not prime or develop pressure -  Check that the suction lift is within the limits. If not get the pump closer to the water body.  Check the suction pipeline and all connections for air leaks. All connections and flanges should be air tight.  Check that the strainer on the foot valve is not blocked.  Check that the flap in the foot valve is free to open fully.  Check the pump gland(s) for air leaks. If air leaks are suspected tighten the gland(s) gently, if necessary repack the gland(s) using a thick grease to seal the gland satisfactorily.  Check that the gate valve on the delivery pipe is fully closed during priming and opens fully when pump is running.  Check that the direction of rotation of the pump is correct. 2. Sprinklers do not turn.  Check pressure.  Check that the nozzle is not blocked. Preferably unscrew the nozzle or use a small soft piece of wood to clear the blockage.
  • 25. IRRIGATION WATER MANAGEMENT Page 25 Example 2.1 Design a sprinkler irrigation system for a square, 10- hectare field to irrigate the entire area within 10 days period. Not more than 16 hours per day are available for moving the pipe and sprinkling. The required depth of irrigation is 5 cm and the water application rate is not to exceed 0.75 cm/hr. A 30 m deep well located in the centre of the field will provide the following discharge- drawdown relationship 12.5 lit./sec at 15 m and 15.8 lit. /sec at 20 m. Do not use a piece of wire or metal as this may damage the nozzle.  Check that the sprinkler bearing is quite free and smooth. During operation, the sprinkler can usually be pushed down towards the riser pipes so that the water pressure flushes out the bearing. If the bearing is still stiff dismantle and then clean it. Do not use oil, grease or any lubricant.  Check the condition of washers at the bottom of the bearing and replace them if worn or damaged.  Check that the swing arm moves freely and that the spoon which moves into the water stream is not bent by comparing it with a sprinkler which is operating correctly. If it is bent then very carefully bend it back into position.  Adjust the swing arm spring tension. Usually it should not be necessary to pull up the spring by more than about 6 mm. 3. Leakage from coupler or fittings.-  The sealing rings in the couplers and fittings are usually designed to drain the water from the pipes when the pressure is turned off. This ensures that the pipes are automatically emptied and ready to be moved.  When the pump is first started and before the pressure has built up in the system, the seals may give a little leakage. With full pressure in the system the couplers and fittings will be effectively leak-free. If, however, there is a leakage, check the following:  There is no accumulation of dirt or sand in the groove in the coupler in which the sealing ring fits. Clean out any dirt or sand and refit the sealing ring.  The end of the pipe going inside the coupler is smooth, clean and not distorted.  In the case of fittings such as bends, tees and reducers ensure that the fitting has been properly connected into the coupler.
  • 26. IRRIGATION WATER MANAGEMENT Page 26 Design the system for an average pressure of 3 kg/cm2 at the sprinkler nozzle. The highest point in the field is 1.25 m above the well site and 1 m risers are needed for the sprinklers, Assuming a pump efficiency of 60 per cent and supposing that the engine will furnish 70 per cent of its rated output for continuous operation, determine the rated output for a water cooled internal combustion
  • 27. IRRIGATION WATER MANAGEMENT Page 27 Example 2.2 Determine the required capacity of a sprinkler system to apply water at the rate of 1.25 cm/hr. Two 186 metres long sprinkler lines are required. Sixteen sprinklers are spaced at 12 metre intervals on each line. The spacing between lines is 18 metres. Solution: System capacity = total discharge of all sprinklers = 0.75 x 32 = 24 litres/sec. Example 2.3 Allowing 1 hour for moving each 186 metre sprinkler line described in Example 2.1 how many hours would be required to apply a 5 cm irrigation to a square 16-hectare field? How many days are required assuming 10-hour days? Solution: Irrigation time to apply 5 cm irrigation at the rate of 1.25 cm/hour= = 4 hours Time required for moving the lateral = 1 hour Total time per setting = 4 + 1 = 5 hours Area of field = 16 x 10,000 = 1,60,000 Length of field = = 400 m The entire length of 400 m is covered by the two 186 m laterals. The number of moves required= 400/18 =22.2 say 22 moves Total time required for irrigation = 22 x 5 = 110 hours = 110/10 = 11 days.
  • 28. IRRIGATION WATER MANAGEMENT Page 28 Example 2.4 Determine the system capacity for a sprinkler irrigation system to irrigate 16 hectares of maize crop. Design moisture use rate is 5 mm per day. Moisture replaced in soil at each irrigation is 6 cm. Irrigation efficiency is 70 per cent. Irrigation period is 10 days in a 12- day interval. The system is to be operated for 20 hours per day. Solution: Given: A = 16, F = 10, H = 20, d = 6 System capacity = 9.4 liters / second Example 2.5 Determine the size of sprinklers, laterals, pump and power unit for the sprinkler system layout with the following conditions: Hn = 35.3 m, Hj = 0.5 m, Hm = 2.2 m, Hs = 3.5 m, I = 1.25 cm / hr, maximum length of main = 60 m, Sj= 15 m, Sm = 20 m and allowable variation in pressure in the lateral is 20 per cent. Solution: 1. Determine the sprinkler and the lateral capacities: Area of sprinkler nozzle,
  • 29. IRRIGATION WATER MANAGEMENT Page 29 = 0.45 x 10-4 m2 Diameter of sprinkler nozzle,d = 0.75 cm 2. Select 7.5 cm diameter lateral (assumed) 3. Select 10 cm diameter main(assumed) 4. Pump size – = 35.5 + 0.5 + 2.2 + 3.5 = 43.0 m
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  • 35. IRRIGATION WATER MANAGEMENT Page 35 2.4 APPLICATION OF FERTILIZERS AND CHEMICALS THROUGH PRESSURISED IRRIGATION SYSTEMS 2.4.1 Applied chemicals and fertilizers =  Pressurised irrigation systems (both sprinkler and drip) provide a convenient means of supplying nutrient materials to the crop.  The term fertigation is often used for the method of fertilizer application through pressurized irrigation systems. Besides fertilizers, other than chemical products can also be applied through pressurized irrigation systems for the following purposes: (1) for improving the chemical properties of water (e.g., lowering the pH) or of the soil (2) for controlling certain crop diseases (insecticides, nematicide, systemic fungicides); (3) cleaning the irrigation equipment network and removing from it calcareous deposits or disinfecting it in order to prevent clogging resulting from the proliferation of certain micro-organisms.  Most water soluble fertilizers and liquid fertilizers can be applied efficiently to almost any crop through irrigation water, at any time of the growing season. The reason why fertigation has become the 'state of art' in vegetable cultivation is that nutrients can be applied in the correct dosage at the time appropriate for the specific stage of plant growth.  The fertilizers most commonly used are nitrogen, phosphorus and potassium (N, P and K). Micronutrients are to be applied when they are deficient in the crop root zone. Nitrogen application.  Nitrogen, the plant nutrient most commonly deficient for crop production, is often applied in pressurized irrigation systems.  Nitrate nitrogen can be applied separately or in mixture with such compounds as ammonium sulphate, urea, calcium ammonium nitrate, and, ammonium nitrate. Calcium nitrate can also be used when bicarbonates are low.  Anhydrous ammonia, aqua ammonia and ammonium phosphate in most instances cause clogging problems.  Nitrogen source selection should be based on its possible reactions with the irrigation water and the soil Phosphorus application.  Phosphorus has not generally been recommended for application with irrigation water because of its tendency to cause clogging and its limited movement in soil.  If irrigation water is high in calcium and magnesium, precipitate of insoluble calcium and magnesium phosphate may result .  The application of phosphoric acid along with short pulses of sulphuric acid keeps the water pH low in drip irrigation system and solves the precipitation or clogging problems.  The ortho-phosphoric acid lowered the pH of irrigation water enough to minimize clogging problems from phosphate precipitation over 3 and 24 days irrigation period.  The most common phosphate fertilizers are triple super-phosphate, mono- ammonium phosphate, diammonium phosphate and ammonium polyphosphate.
  • 36. IRRIGATION WATER MANAGEMENT Page 36  The ammonium phosphate is also a good source of nitrogen. Mono-ammonium phosphate and ammonium polyphosphate, either alone or with some added potassium, makes excellent starter fertilizers because of their high P to N ratios, high water-solubility, and low in free ammonia.  Di-ammonium phosphate (DAP) is not recommended as a starter material. However, many starter fertilizers contain DAP. Thus, it is critical that the starter is accurately placed and high rates are avoided.  Hence, the common practice is to apply the phosphorus separately and not through the irrigation system. Potassium application.  There are no problems associated with potassium application through micro irrigation systems.  Most potassium fertilizers are water soluble and quick acting such as potassium chloride or muriate of potash, potassium sulphate, potassium magnesium sulphate, also known as sulphate of potash magnesia.  The K ions are adsorbed in the soil and thus remain available, and largely protected against leaching.  However, split application is advisable where higher leaching losses may be expected. Some immobilization into clay lattice layers reduces availability but strong fixation into completely unavailable forms is limited to a few special soil types.  All types of fully-water soluble granular and liquid fertilizers are suitable for fertigation. However, for higher yield and quality, chloride-free fertilizers such as Multi-K (potassium nitrate), Mono Ammonium Phosphate and Mono Potassium Phosphate are preferable.  Soluble dry fertilizers containing N, P and K in different combinations are also available in the market.  Liquid fertilizers with varying N, P and K contents are also available but these are more expensive. Mostly, Nitrogen (N). Potassium or both are injected.  But phosphorus does not move in soil. Commercially prepared liquid fertilizer for fertigation are also good. These are combinations of N and K.  Water temperature is an important factor for determining solubility. The solubility of most fertilizer decreases with decreasing temperatures.  Fertilizer compounds differ greatly in their solubility in water. These differences are usually unimportant for application in the solid form. Micronutrients application.  Manganese copper, etc., may be applied as soluble salts through the irrigation system.  These should each be injected separately and apart from other fertilizer and chemicals to avoid chemical interaction and precipitation in emitters. Through drip irrigation requires careful metering.  Figure 12 .32 illustrates application diagram of fertilizers and chemicals.
  • 37. IRRIGATION WATER MANAGEMENT Page 37 2.4.2 Frequency of fertilizer application –  Fertilizers can be injected into the irrigation system at various frequencies once a day or once every two days or once a week.  The frequency depends on system design irrigation scheduling, soil type, nutrient requirements of the crop and the farmer's preference it is also important to monitor the application of water as fertilizer application is linked to water application.  In any case it is extremely important that the nutrients applied in any irrigation are not subject to leaching either during the same irrigation or during subsequent irrigation.  When applying the fertilizer through the sprinkler system, it is desirable to operate the system long enough to wet the soil and the plant foliage.  The fertilizer is than injected through the system in a solution of 1 kg of fertilizer to about 30 kg of water and timed in such a way as to complete the injection in about 30 minutes  After this, the system is worked for 20 to 30 minutes toflush it from any toxic effects of the fertilizer solution on the sprinkler tubings. 2.4.3 Computation of the quantity of fertilizer to be applied.  To determine the quantity of fertilizer to be injected into the system for each setting, the area irrigated in each setting of the lateral line is obtained by multiplying the length of the lateral coverage and the move of the lateral.  The quantity of fertilizer to be injected is calculated for this area according to the recommended rate of fertilizer application in kilograms per hectare, using the following formula:  WHERE, WF = amount of fertilizer per setting, kg DS = distance between sprinklers, metres
  • 38. IRRIGATION WATER MANAGEMENT Page 38 DE = distance between laterals, metres NS = number of sprinklers, and WF = recommended fertilizer dose, kg/ha Example 2.8. A lateral has 12 sprinklers spaced14 m apart. The laterals are spaced 20 metres on the main line. Determine the amount of fertilizer to be applied to each setting when the recommended fertilizer doze is 80 kg/ha. solution: Ds = 14 m, De = 20 m, Ns=12 and Wf = 80 kg/ha 2.4.4 Equipments and Methods for Fertilizer Injection -  Fertilizers can be injected into pressurised irrigation system by selecting a wide variety of available pumps, valves, fertilizer tanks, venturies and aspirators.  Fertilizers may be injected into sprinkler/drip irrigation system by a differential pressure system, venturi injector or by pumping under pressure into the pipeline.  The commonly used components of the equipment to apply fertilizers in pressurized irrigation systems, in addition to the irrigation system, include a fertilizer tank, fertilizer dissolver, fertilizer injection device, a filter, a pressure gauge, check valves, and a pressure regulator. 1. Fertilizer tank. The fertilizer tank is used for mixing the fertilizer. The fertilizer tank should have a sufficiently large capacity to contain the entire fertilizer solution required for the cropped area for any application. It should be made from materials that withstand corrosivity of the fertilizers. Large, low cost tanks constructed from epoxy-coated metal, plastic or fiberglass are useful when injection pumps are used. For a pressure differential injection system the high pressure rated chemical tank should have enough capacity for a complete irrigation application. 2. Fertilizer dissolver. Fertilizer dissolver is a device that can be used for preparation of fertilizer solution. After filling the tank with water, the pump injects the water into an inner strainer that contains the dry fertilizers. The water gradually dissolves the fertilizer into a solution by circulating the solution within the dissolver. 3. Fertilizer Injection Devices. Pressurized irrigation methods require fertilizer injector for injection of fertilizers, into the irrigation water. The following are the two basic concepts on the basis of which fertilizer injectors are designed: (a) Proportional concept is characterized by constant concentration of the fertilizer solution in irrigation water throughout the irrigation duration. Fertilizer injection devices such as venturi pump and fertilizer injection pump operate on this principle. It enables the delivery of constant concentration during the entire irrigation duration. (b) Quantitative or non-proportional concept is characterized by change in the concentration of fertilizers in irrigation water. The concentration of fertilizer decreases gradually with the irrigation duration. Fertilizer tanks work on this
  • 39. IRRIGATION WATER MANAGEMENT Page 39 principle. The total amount of fertilizers applied in both the cases should be equal since the requirement of nutrients of the plants is independent of the injection device and method of fertilization. (i) Fertilizer injection through a volute centrifugal pump. Fertilizer is introduced into the system from the suction side of the pump through a pipe and regulated by a valve (Fig. 12.34). Another pipe is connected from the discharge side of the pump to the fertilizer container for the required water supply in the tank. This system is relatively simpler, but pump impellers must made of corrosion resistant material.fig 12.34 shows volute centrifugal pump. (ii) Fertilizer injection pump system, In this method a pump is used to draw the fertilizer stock solution from the storage tank and inject it under pressure into the irrigation stream. The injection rate can be set to create a desirable mixing ratio. The fertilizer solution is normally pumped from unpressurised storage tank.fig 12.35 shows typical layout of pump. (iii) Pressure differential injection Pressure differential (PD) units are another method of injecting fertilizer into drip irrigation systems. The PD unit takes advantage of the system's pressure-head differences. Valves, venturi, elbows, or pipe friction can develop
  • 40. IRRIGATION WATER MANAGEMENT Page 40 pressure differences. The main advantage of the PD applicators is the absence of moving parts. They are simple in operation and require no electric, gasoline, or water-powered pumps and the rate of application is not constant and changes continuously with time; thus, a uniform concentration of a nutrient cannot be maintained. (iv) Venturi injection system. The venturi injection system consists of a converging section, a throat and a diverging section (Fig. 12.37). In a pressurized irrigation system using filters, the venturi unit is located between the sand filter and the screen filter. The venturi creates the differential pressure (about 20% from one side of device to the other) and allows the fertilizer solution to flow in the main water line. The main advantages of the venturi system are the simplicity in operation, low cost and good control over the fertilizer concentration. The disadvantages are heavy power loss, the relatively low discharge rate, difficulty in precise regulation of flow and the need to operate the system at fully capacity prior to injecting the fertilizer solution.
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