Chapter 11: Sprinkle Irrigation - NRCS Irrigation ToolBox Home Page

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Chapter 11 Sprinkle Irrigation Adaptability Sprinkle irrigation is the application of water in the form of a spray formed from the flow of water under pressure through small orifices or nozzles. The pressure is usually obtained by pumping, although it may be obtained by gravity if the water source is high enough above the area irrigated. Sprinkle irrigation systems can be divided into two general categories. In periodic-move and fixed systems the sprinklers remain at a fixed position while irrigating, whereas in continuous-move systems the sprinklers operate while moving in either a circular or a straight path. The periodic-move systems include hand-move and wheel-line laterals, hose-fed sprinkler grid, perforated pipe, orchard sprinklers, and gun sprinklers. The dominant continuous-move systems are centerpivot and traveling sprinklers. With carefully designed periodic-move and fixed systems, water can be applied uniformly at a rate based on the intake rate of the soil, thereby preventing runoff and consequent damage to land and to crops. Continuous move systems can have even higher uniformity of application than periodic-move and fixed systems, and the travel speed can be adjusted to apply light watering that reduces or elimi- Sprinkle irrigation is suitable for most crops. It is also adaptable to nearly all irrigable soils since sprinklers are available in a wide range of discharge capacities. For periodic-move systems with proper spacing, water may be applied at any selected rate above 0.15 inch per hour (iph). On extremely finetextured soils with low intake rates, particular care is required in the selection of proper nozzle size, operating pressure, and sprinkler spacing to apply water uniformly at low rates. Periodic-move systems are well suited for irrigation in areas where the crop-soil-climate situation does not require irrigations more often than every 5 to 7 days. Light, frequent irrigations are required on soils with low water holding capacities and shallow-rooted crops. For such applications, fixed or continuously moving systems are more adaptable; however, where soil permeability is low, some of the continuously moving systems, such as the centerpivot and traveling gun, may cause runoff problems. In addition to being adaptable to all irrigation frequencies, fixed systems can also be designed and operated for frost and freeze protection, blossom delay, and crop cooling. The flexibility of present-day sprinkle equipment, and its efficient control of water application make the method's usefulness on most topographic conditions subject only to limitations imposed by land use capability and economics.
Advantages Some of the most important advantages of the sprinkle method are: 1, Small, continuous streams of water can be used effectively, 2. Runoff and erosion can be eliminated, 3. Problem soils with intermixed textures and profiles can be properly irrigated. 4. Shallow soils that cannot be graded without detrimental results can be irrigated without grading. 5. Steep and rolling topography can be easily irrigated. 6. Light, frequent waterings can be efficiently applied. 7. Crops germinated with sprinkler irrigation may later be surface irrigated with deeper applications. 8. Labor is used for only a short period daily in each field. 9. Mechanization and automation are practical to reduce labor. 10. Fixed systems can eliminate field labor dur. ing the irrigation season. 11. Unskilled labor can be used because decisions are made by the manager rather than by the irriga tor. 12. Weather extremes can be modified by increasing humidity, cooling crops, and alleviating freezing by use of special designs. 13. Plans for intermittent irrigation to supplement erratic or deficient rahfall, or to start early grain or pasture can be made with assurance of adequate water. 14. Salts can be effectively leached from the soil. 15. High application efficiency can be achieved by a properly designed and operated system. Disadvantages Important disadvantages of sprinkle irrigation are: 1. High initial costs must be depreciated. For simple systems these costs, based on 1980 prices, range from $75 to $150 per acre; for mechanized and self-propelled systems, from $200 to $300; and for semi and fully automated fixed systems from $500 to $1,000. 2. Cost of pressure development, unless water is delivered to the farm under adequate pressure, is about $0.20 per acre-ft, of water for each pound per square inch (psi) of pressure, based on $0.751gal for diesel or $O.OGIKWH for electricity. 3. Large flows intermittently delivered are not economical without a reservoir, and even a minor fluctuation in rate causes difficulties. 4, Sprinklers are not well adapted to soils having an intake rate of less than 0.15 inches per hour (iph). 5. Windy and excessively dry locations appreciably lower sprinkler irrigation efficiency. 6. Field shapes, other than rectangular, are not convenient to irrigate especially with mechanized sprinkle systems. 7. Cultural operations must be meshed with the irrigation cycle. 8. Surface irrigation methods an suitable soils and slopes have higher potential irrigation efficiency. 9. Water supply must be capable of being cut off at odd hours when the soil moisture deficiency is satisfied. 10. Careful managemmt must be exercised to obtain the high potential efficiency of the method. 11. Systems must be designed by a competent specialist with full consideration for efficient irrigation, economics of pipe sizes and operation, and convenience of labor. 12. When used in overhead sprinklers, irrigation water that has high concentrations of bicarbonates may affect the quality of fruit. 13. Saline water may cause problems because salt may be absorbed by the leaves of some crops. Sprinkle irrigation can be adapted to most climatic conditions where irrigated agriculture is feasible. Extremely high temperatures and wind velocities, however, present problems in some areas, especially where irrigation water contains large amounts of dissolved salts. Crops such as grapes, citrus, and most tree crops are sensitive to relatively low concentrations of sodium and chloride and, under low humidity conditions, may absorb toxic amounts of these salts from sprinkle-applied water falling on the leaves. Because water evaporates between rotations of the sprinklers, salts concentrate more during this alternate wetting and drying cycle than if sprayed continuously. Plants may be damaged when these salts are absorbed. Toxicity shows as a leaf burn (necrosis) on the outer leaf-edge and can be confirmed by leaf analysis. Such injury sometimes occurs when the sodium concentration in the irrigation wa-
Page 1 and 2: United States Department of Agricul
Page 3: Application intensity .............
Page 7 and 8: End-Tow Lateral An end-tow lateral
Page 9 and 10: Figure 11-4.-Solid-set sprinkler la
Page 11 and 12: or for dual cropping, it is practic
Page 13 and 14: Planning Concepts A complete farm s
Page 15 and 16: I. Crop (Type) (a) Root depth (ft)
Page 17 and 18: Sample calculation 11-1,-Computing
Page 19 and 20: 11-rfi Such systems are capable of
Page 21 and 22: Table 11-2. Effective crop root dep
Page 23 and 24: Impact sprinklers produce a circula
Page 25 and 26: n n = mean depth of observations (i
Page 27 and 28: 11-24 I. Increases of 20 to 40 perc
Page 29 and 30: plants is similar for all systems.
Page 31 and 32: 1. At the lower side of the specifi
Page 33 and 34: diameter based on average wind spee
Page 35 and 36: LATERAL SET A L 50 FEET LATERAL SET
Page 37 and 38: such as forage crops, According to
Page 39 and 40: Table 11-10.-A guide to recommended
Page 41 and 42: Table 1 l-12.-A guide to recommende
Page 43 and 44: I. Crop (type) (a) Root depth (ft)
Page 45 and 46: F F I k% TabIe 11-13.-Nozzie discha
Page 47 and 48: 1‘ HOSE-LINE ’ A-Fully portable
Page 49 and 50: A-Layout on moderate, unifbrm Slope
Page 51 and 52: such cases, lines are laid on the c
Page 53 and 54: .I* en factor (F) based on the numb
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Figure Il-33.-lateral laid downhill
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This is obviously outside the 20 pe
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Table 11-17.-Typical as % 3 -. " 3
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Table 11-19a.-Friction-loas J value
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one of selecting mainline pipe size
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ft; for D3 and Dz, friction loss in
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The standard capital recovery facto
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Step 4.-The WHP savings needed to o
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1. Economic method-Selection of the
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Table Il-24.-Comparison of total an
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ial, and then determine the total a
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Table 11-28.-Values of resistance c
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can be solved very simply from equa
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sure is representative of the entir
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turer at the given pressure. This o
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Table 11-30.-Typical discharges and
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This allows for a 1-hr set time, 20
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ftlmin. The required sprinkler disc
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R *= maximum radius irrigated when
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sprinkler pattern. High instantaneo
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Where soil sealing and infiltration
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Thus, to compute the (Hfk, with two
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And the net depth of application as
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Machine Selection Ultimately the ty
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Span I Container Span Position Weig
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Sample calculation 11-20.-Using fie
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Span Container span No. Position We
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4. Increasing system pressure and r
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Figure 11-60.-A method for adding f
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Table Il-35.-Steps for estimating f
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Frost Control Operation For complet
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Installation and Operation of Sprin
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T actual operating time (hrlday) t
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