c*i"ta 
 
 
 sion of Agri 
 
 c i e n c e 
 
 UNIVERSITY OF CALIFORNIA 
 
 SPRINKLER 
 IRRIGATION 
 
 VERNE H. SCOTT 
 
 CALIFORNIA AGRICULTURAL 
 Experiment Station 
 Extension Service 
 
 CIRCULAR 456 
 
SPRINKLER IRRIGATION 
 
 ,-,,, ■,-■ 
 
 is sometimes the only method of applying 
 water that can be used successfully. On some 
 farms it has replaced the furrow or flood 
 method of irrigation. On others, surface 
 methods may be more satisfactory. 
 
 Each farm has its own particular set of condi- 
 tions, its own particular problems. The general 
 advantages and limitations of sprinkler systems 
 must be thought of in relation to the conditions 
 of soil, terrain, crops, and total operation of your 
 own farm. You will find a discussion of the condi- 
 tions that call for a sprinkler system, plus an anal- 
 ysis of the pros and cons, on pages 4-9 
 
 Sprinkler systems may be stationary, portable, or 
 semiportable. The systems and the various units 
 of which they are composed are described on — 
 
 pages 9-18 
 
 Good design and proper operation are essential 
 
 to successful sprinkler irrigation, as they are to 
 any other method. The points to consider, to- 
 gether with guides for selecting equipment and 
 planning layout, are outlined on. . . .pages 18-36 
 
 Special aspects — the application of fertilizers 
 through the sprinkler system and the problem of 
 corrosion — are discussed on pages 37-40 
 
 Cost is an important factor. Sprinkling is usually 
 expensive, but often it may be cheaper than other 
 methods. The initial investment and annual op- 
 eration costs should be estimated carefully. For 
 guidance in calculating total expenses, see — 
 
 pages 40-43 
 
Ask these questions 
 
 1 What are the advantages and limitations of sprinkling 
 * in relation to your farm? 
 
 O What type of system, what capacity, what method of ^m 
 
 * operation do the conditions on your farm call for? J 
 
 Q What would such a system cost to install, operate, and ^M 
 
 * maintain? J 
 
 M How does the estimated cost of sprinkling compare 
 * with other methods of irrigation? 
 
 C If the cost of sprinkling is greater, do the advantages 
 * justify the increased cost? 
 
 This circular cannot give detailed answers to these questions for every 
 farmer. It does, however, tell how you can arrive at the answers for your 
 own situation. The information contained here will help you in making 
 decisions — first, whether or not to adopt the sprinkler system; second, 
 how to proceed if you do decide on a sprinkler installation. 
 
 This publication replaces Circular 388 
 
 THE AUTHOR: 
 
 Verne H. Scott is Associate Professor of Irrigation and Associate Irrigation Engineer, Experiment 
 Station, Davis. 
 
 OCTOBER, 1956 
 
 [3] 
 
SPRINKLER SYSTEMS— WHEN AND WHY 
 
 A 
 
 satisfactory irrigation system applies 
 water to the soil in the amounts needed 
 to maintain an adequate and constant 
 supply of soil moisture in a major portion 
 of the plants' root zone. It does so at rea- 
 sonable cost, with minimum waste of 
 water, land, power, and labor. 
 
 Sprinkling is the best method of irriga- 
 tion in many cases, though not all. In 
 some situations conditions of soil or ter- 
 rain, or the crops to be grown, may make 
 surface methods more desirable. Since no 
 two farms have the same requirements, it 
 is necessary to consider all the facts for 
 a particular farm to decide which type of 
 irrigation system will be most satis- 
 factory. 
 
 Most sprinkler systems are alike in 
 that they carry the water under pressure 
 through pipe and discharge it through 
 sprinklers, nozzles, or perforations in the 
 pipe. Among sprinkler systems, however, 
 there are a number of variations or 
 adaptations to meet the special require- 
 ments of a particular farm. 
 
 No two farms have exactly the same 
 conditions. Bear in mind that the best 
 
 system for a particular farm is the one 
 that best meets the conditions on that 
 farm. 
 
 Field operation of sprinkler systems 
 has established fairly well their general 
 advantages and limitations. Weigh these 
 carefully before you adopt a system. 
 
 When is a sprinkler 
 system desirable? 
 
 Assuming that there is land available 
 for growing irrigated crops, a sprinkler 
 system may be desirable in any one of 
 the following situations: 
 
 New land is to be developed for irriga- 
 tion. 
 
 The topography is rolling or rough. 
 
 Soil conditions vary. 
 
 The present method of irrigation in- 
 volves certain difficulties and the irriga- 
 tion efficiency is poor. 
 
 The crops to be grown require frequent 
 light irrigations. 
 
 Problems of seed germination have 
 been encountered. 
 
 The flow of water is not large enough 
 to permit efficient irrigation by surface 
 methods. 
 
 Sprinkler systems are often desirable on uneven land 
 
 " ■ ■- ,■■■'■ " ...< '■;■ .-.."' "- , ■.. ■■ . 
 
Other problems may exist, unique to a 
 particular farm, and these may suggest 
 the use of a sprinkler system. 
 
 Sprinkler systems have 
 these advantages . . . 
 
 In general, a sprinkler system can be 
 used satisfactorily under most conditions, 
 provided enough water is applied at 
 proper rates to meet the crop and soil 
 requirements. 
 
 Sprinkling is particularly adapted for 
 use on land with rough, irregular fea- 
 tures. It reduces the cost of, or eliminates, 
 expensive land grading and preparation 
 often needed for surface methods. 
 
 In some areas where excessive land 
 grading can be detrimental, sprinkling 
 has a definite advantage. Furthermore, 
 shallow hardpans, a limited depth of till- 
 able soil, or organic soil types such as 
 peats may restrict, if not completely pre- 
 vent, grading operations. 
 
 Good water control is possible with 
 sprinkling. With proper design and 
 operation, sprinkling achieves nearly uni- 
 form water application even on irregular 
 terrain or under variable soil conditions. 
 In some areas, especially on pervious 
 soils with sand or gravel subsoils, much 
 of the water applied by surface methods 
 may be lost by deep percolation unless 
 the system is carefully designed and 
 operated to minimize such losses. The 
 
 same soils may be sprinkled without ex- 
 cessive waste. 
 
 If the water-holding capacity of the 
 soil is very low, sprinklers can provide 
 the frequent irrigations that are neces- 
 sary at a saving in both water and labor. 
 Similar saving is also possible in situa- 
 tions where the crop needs only a single 
 light irrigation during the year. 
 
 In some areas of high water table, 
 sprinkling has this advantage over sur- 
 face methods — it can apply the proper 
 depth of water to wet the soil without 
 raising the water table. 
 
 In a few places farmers have had diffi- 
 culty in irrigating deep-rooted crops on 
 clay-type soils by flooding because sink- 
 holes develop in the fields. Large cracks 
 occur as the soil dries. During irrigations 
 water enters these cracks, washes away 
 the soil, and enlarges the cracks into siz- 
 able cavities. In addition, they become a 
 hazard to harvesting or cultivating equip- 
 ment. Sprinklers prevent the accumula- 
 tion of large amounts of water on the 
 soil surface and the continued develop- 
 ment of the holes. 
 
 Land slopes are so steep in some parts 
 of California that efficient surface irriga- 
 tion is difficult or virtually impossible, 
 and surface washing causes excessive soil 
 erosion. Sprinkling can prevent soil ero- 
 sion and still provide the required 
 amount of water. The planting of a per- 
 
 Courtesy Ames Company, San Franciscc 
 
 or on widely spaced row crops 
 
 
'' V.'- 
 
 ... in vineyards . . . 
 
 manent cover crop in orchards, combined 
 with the use of sprinklers, helps reduce 
 soil loss. 
 
 Often, only light irrigations are needed 
 to germinate seed. These can usually be 
 applied more efficiently by sprinklers 
 than by furrow irrigation. Lateral move- 
 ment of water from furrows into the seed 
 bed may be limited or nonuniform, re- 
 sulting in poor stands. Sprinklers also 
 help to leach salts from the surface, 
 creating a more favorable environment 
 for seed germination. The exact place- 
 ment of fertilizers in the beds may not be 
 as critical where sprinklers are used as 
 it is with furrow irrigation. 
 
 ... or in orchards. 
 
 Many orchard, field, and vegetable 
 crops have been irrigated successfully by 
 sprinklers. However, experience with 
 some crops under the variety of field 
 conditions that exist is lacking. Certain 
 changes in cultural practices may be 
 necessary when sprinklers are used; in 
 some cases furrows and raised beds are 
 eliminated, thus reducing labor costs. 
 
 On widely spaced row crops sprinklers 
 can provide more uniform application of 
 water over the entire soil area. This is 
 true on soils where lateral movement of 
 moisture from the furrow into the crop 
 row is slow, and the young plants often 
 suffer before enough soil moisture 
 reaches the root zone. 
 
 In the seed production of some row 
 crops and crops with tall stalks, such as 
 corn and pole beans, sprinklers are satis- 
 factory during the early part of the grow- 
 ing season. To start these crops short 
 sprinkler risers are often used, their 
 length being gradually increased as the 
 crop matures. 
 
 Certain advantages have been realized 
 in the irrigation of field crops. For ex- 
 ample, borders or levees used in grow- 
 ing alfalfa can be eliminated. This lowers 
 the land-preparation costs, facilitates har- 
 vesting, and may reduce the hours of 
 mowing and raking operations. 
 
 Irrigation by sprinklers has advan- 
 tages in areas of sandy or shallow soils 
 or where a hilly terrain makes it difficult 
 to secure uniform water application by 
 other methods. 
 
 In orchards, sprinkling eliminates the 
 need of constructing ridges, levees, or 
 furrows between the trees and allows the 
 soil surface to remain smooth throughout 
 the season. The reduction in soil manipu- 
 lation may contribute to better water 
 penetration, reduce the dust problem, 
 and facilitate mechanical harvesting of 
 certain nut crops. 
 
 Insect control is often listed among 
 the advantages of sprinkler systems, al- 
 though little experimental work has been 
 
done from which definite conclusions 
 can be drawn. Many growers report, how- 
 ever, that such pests as aphids, thrips, 
 and red spiders are less troublesome on 
 some crops that are sprinkler irrigated. 
 Under some conditions sprinkling may 
 reduce certain pests, particularly if it is 
 started early in the season. The explana- 
 tion for this is that the environment is 
 probably less favorable for the insects. In 
 general, leaf-feeding insects are not con- 
 trolled, for they crawl under the leaves 
 during the irrigation. Certain insecticides 
 can be applied through a sprinkler sys- 
 tem, providing the material is relatively 
 soluble and noncorrosive. Also, it should 
 be injected into the system near the end 
 of each irrigation set ; othewise it may be 
 washed off. Although a sprinkler system 
 may aid in reducing insects, it should not 
 be considered a substitute for an ade- 
 quate insect control program. 
 
 A sprinkler system can be designed to 
 operate effectively with a small rate of 
 flow. This may be a distinct advantage 
 on a small farm with a limited water sup- 
 ply, for in many places the volume of 
 water from surface supplies or a well is 
 not great enough for other methods of 
 irrigation. 
 
 Sprinkler systems can eliminate many 
 field ditches and so permit the planting 
 of almost the entire acreage. Typical irri- 
 gated farms have from 2 to 5 per cent 
 of the acreage in ditches. Eliminating 
 ditches may in turn lessen the weed prob- 
 lem and allow cultivation in large blocks. 
 Ditch seepage and evaporation are also 
 reduced or eliminated. 
 
 Present-day sprinkler system equip- 
 ment, including the appurtenances, is 
 readily adapted to various field condi- 
 tions. The orientation and arrangement 
 of pipelines and sprinklers can be altered 
 to some extent to meet changing field 
 requirements. Flexibility in operation is 
 an advantage, but each change must be 
 carefully studied, considering all of the 
 factors involved. 
 
 Some liquid or soluble fertilizers can 
 be applied through sprinklers. When they 
 are distributed evenly by a properly de- 
 signed system, certain advantages are 
 realized: (1) the fertilizer is distributed 
 over the entire soil mass; (2) a saving 
 may result from eliminating machine ap- 
 plication and cultivation required to 
 work dry fertilizers into the soil. A fur- 
 ther saving may be accomplished when 
 both irrigation and fertilizer distribution 
 can take place at the same time. How- 
 ever, poor design and operation of the 
 system will result in nonuniform fer- 
 tilizer application. 
 
 There is no general rule regarding the 
 fertilizers that can and those that cannot 
 be applied through sprinklers. Some are 
 corrosive. Others may not dissolve suffi- 
 ciently and clogging may occur, thereby 
 changing the performance of the system. 
 The use of any one fertilizer will depend 
 on its composition, including impurities, 
 and its corrosive action on all the parts 
 of the sprinkler system. Materials and 
 methods for fertilizer application are dis- 
 cussed on pages 37-39. 
 
 The labor involved in assembling and 
 moving a sprinkler system does not re- 
 quire an experienced irrigator. Sprin- 
 kling schedules, once worked out, are 
 generally fixed, and all that is necessary 
 is to move the pipe at the proper time. 
 
 A relatively high efficiency is usually 
 achieved by sprinkler irrigation, but 
 other factors than efficiency often enter 
 into the picture, too. For example, if a 
 field can be irrigated satisfactorily by 
 either the surface method or a sprinkler 
 system, the over-all irrigation efficiencies 
 of both methods may be equal. With the 
 surface method, however, an irrigator 
 often has to be on the job practically all 
 of the time, and he must be a man who 
 has had considerable experience in man- 
 aging and controlling water. 
 
 . . . and these limitations 
 
 All methods of water application 
 should be designed to give as uniform 
 
 [7] 
 
application of water as possible. Local 
 conditions will dictate to a large extent 
 the degree to which this may be achieved. 
 A sprinkler system, when correctly de- 
 signed and operated, can approach fairly 
 uniform distribution, but it still cannot 
 achieve the evenness of rainfall. 
 
 One of the biggest difficulties is wind. 
 A carefully planned distribution pattern 
 can be completely distorted by wind. 
 Parts of the area normally covered and 
 wetted may be dry. In some cases opera- 
 tions have been shut down when wind 
 conditions created serious distortions. 
 Certain measures can be taken to relieve 
 this problem — for example, changes in 
 sprinkler nozzles, in the spacing of 
 laterals and sprinklers, and in arrange- 
 ment. However, changes mean additional 
 equipment and, thus, extra cost. Further- 
 more, the delay involved in making 
 changes may also cause decreases in crop 
 yields, due to lack of water during critical 
 growing periods. Wind conditions should 
 be considered in the original design of 
 the system to minimize this disadvantage. 
 
 More water is lost by evaporation dur- 
 ing sprinkling than with surface flood 
 methods. There are two sources of evapo- 
 ration loss — from the water drops or 
 spray moving through the air, and from 
 the wetted soil and foliage surfaces. The 
 amount lost from the drops and spray is 
 much smaller than that lost from the soil 
 and foliage. The net loss by evaporation 
 will depend on climatic and operating 
 conditions, but it may amount to 5 to 40 
 per cent of the water applied. In some 
 cases sprinkling only at night will help 
 reduce these losses. 
 
 On some soils movement of portable 
 pipe after an irrigation may be a prob- 
 lem. This is true on clay-type soils that 
 drain slowly. It is hard, dirty work to 
 move pipe from one position to another 
 after a heavy application of water, and 
 some puddling of the soil may take place. 
 If the pipe could be left until the soil 
 drained sufficiently, this would not be as 
 
 great a problem. However, additional 
 equipment would be required for lateral 
 sets at other locations, thereby increas- 
 ing the investment in equipment. 
 
 To avoid the muddy soil condition, 
 some operators shut down the system and 
 move the laterals before they have run 
 long enough to wet the soil to the re- 
 quired depth. As a result, frequent light 
 applications are necessary. Often, re- 
 peated sprinklings mean much more mov- 
 ing of pipe, and hence more operation 
 and labor expense. Also, this increases 
 the amount of water lost by evaporation 
 from the soil surface. 
 
 Sprinkling systems cost money. The 
 initial cost, depreciation, maintenance, 
 and repair must be given careful con- 
 sideration. In general, the initial outlay 
 is relatively high, particularly if a large 
 part of the system is permanent or sta- 
 tionary. A portable system reduces the 
 first cost, but there is additional expense 
 for the labor required to move the pipe. 
 Improvements in the materials used in 
 the construction of the systems are in- 
 creasing their useful life, but certain 
 field conditions will cause more rapid 
 deterioration than others. For example, 
 if the source of water contains sand, parts 
 of the sprinklers will wear faster. Sand 
 removal devices and wear-resistant ma- 
 terials, such as stainless steel and nylon, * 
 however, are being used. 
 
 There is little conclusive evidence that 
 sprinkling will either encourage or con- 
 trol plant diseases. Some diseases may 
 occur or spread under the conditions pro- 
 vided by sprinkling because of the rela- 
 tively high humidity that is created in 
 and around the plants. This is particu- 
 larly true in low-growing vegetable crops. 
 Climatic conditions may also contribute 
 to an environment that is favorable for 
 blight, fungi, and rot damage. A farmer 
 should be on the lookout for any out- 
 breaks, and in some cases it may be de- 
 sirable not to operate the system during 
 humid weather. 
 
 [8 
 
The effectiveness of insecticides and 
 fungicides may be reduced, unless a 
 coordinated program of sprinkling, 
 spraying, and dusting for insect and dis- 
 ease control is worked out. Dusting and 
 spraying should follow an irrigation. 
 
 Orchard irrigation by sprinkling pre- 
 sents special problems. Close spacing of 
 trees increases the difficulty of moving 
 the pipe from one setting to the next. 
 When under-tree sprinklers are used, low- 
 hanging branches may interfere with a 
 uniform distribution of water. In a few 
 areas sprinklers are located above the 
 trees. This provides more uniform dis- 
 tribution, but losses due to evaporation 
 and wind interference reduce effective- 
 ness. 
 
 Corrosion of sprinkler systems is a 
 problem in a few isolated areas in Cali- 
 fornia. It may be caused by one of several 
 factors or by a combination of them. The 
 sources of difficulty are, principally, the 
 chemical composition of the water and 
 certain electro-chemical relationships be- 
 tween the soil and the material of the 
 system. In some cases certain preventive 
 measures can be used to control this 
 damage. 
 
 Distribution of fertilizer through 
 sprinkler systems has certain limitations. 
 Not all fertilizers are soluble enough to 
 be injected into a system. They may 
 sometimes cause moving parts to clog, 
 and this means added maintenance and 
 labor costs. Some fertilizers are corro- 
 
 sive. If certain precautions are taken — 
 such as allowing enough time to flush 
 out the system after the fertilizers are 
 injected, or applying protective coatings 
 to the inside of the pipe — damage can be 
 controlled or perhaps eliminated. 
 
 During the period of crop blossom set 
 sprinkling should be watched carefully. 
 The impact of the spray may damage or 
 shatter blossoms. 
 
 Availability of the water supply may 
 create some problems with sprinkling. In 
 many areas of California, water is de- 
 livered to the farmer on a rotation basis 
 by irrigation districts or companies. De- 
 liveries are made at intervals and in rela- 
 tively large quantities. In some cases to 
 use the water when it is delivered would 
 require an excessive amount of sprin- 
 kling equipment. It is generally true that 
 sprinklers are most efficient if they can 
 be operated almost continuously. 
 
 All irrigation methods require work, 
 and sprinkling is no exception. Once a 
 carefully planned and designed system is 
 laid out, it will not operate by itself. 
 Occasionally there may be a power 
 failure, the pump may lose suction, or the 
 sprinklers may clog or fail to operate cor- 
 rectly. Therefore, some supervision and 
 maintenance must be continuing func- 
 tions along with the labor needed to move 
 the pipe. The capabilities and desires of 
 the operator must be considered along 
 with the operational requirements of the 
 system. 
 
 SYSTEMS ARE OF MANY DIFFERENT TYPES 
 
 Although they have certain basic fea- 
 tures in common, sprinkler systems 
 differ widely. They are classified as 
 "portable" when most of the equipment 
 can be moved readily from place to place 
 over the area irrigated; "semi-portable" 
 when only a part of the equipment is 
 moved; "stationary" or "permanent" 
 when all of the equipment is fixed. 
 
 Systems may also be classified accord- 
 ing to their method of distributing the 
 water. This may be by means of rotating 
 sprinklers, fixed sprinkler heads, nozzle 
 lines, or perforated pipeline. 
 
 In California, portable systems using 
 rotating sprinklers outnumber all other 
 agricultural sprinkling systems com- 
 bined. 
 
 [9] 
 
Sprinkling is often called "overhead" 
 irrigation. This is not accurate, how- 
 ever — the water does not always issue 
 from an overhead outlet. One true "over- 
 head" system is the kind that discharges 
 water over orchard treetops from outlets 
 attached to high risers; but even in 
 orchards, some sprinklers (called "under- 
 tree," "low-angle," or "ground") dis- 
 tribute the water near the ground. 
 
 Different types of outlets 
 do different kinds of work 
 
 Rotating sprinklers. The majority 
 of agricultural sprinklers are of the 
 rotating type. A wide range of sizes, with 
 discharge capacities of 1 to more than 
 600 gallons per minute, is available to 
 meet a variety of field conditions. A rela- 
 tively large area is covered by these 
 sprinklers, depending on the pressure, 
 size of nozzle, and speed of rotation. 
 
 There are two general types of rotating 
 sprinklers: The slow revolving, which 
 rotates slowly, and the whirling, which 
 rotates rapidly. The slow-revolving type 
 is the most common. The speed of rota- 
 tion varies but ordinarily is from 1 to 2 
 revolutions per minute. Rotation of the 
 sprinkler is caused by the impact of a 
 lever arm that oscillates in and out of the 
 nozzle jet. The sprinklers used in agri- 
 cultural practice are designed for two — 
 sometimes one — replaceable nozzles. In- 
 terchanging of nozzles provides addi- 
 tional flexibility of operation, as the dis- 
 
 charge rate and diameter of coverage can 
 be altered. The angle of the nozzle varies 
 between 7 and 30 degrees. The low angle 
 is used in orchards or in situations where 
 the spray should be kept close to the 
 ground. 
 
 The operating pressure is important. 
 Most sprinklers will operate satisfactorily 
 over a range of pressures. However, best 
 results are obtained by maintaining pres- 
 sures at or above the minimum recom- 
 mended by the manufacturer for a given 
 size of sprinkler and a given number and 
 size of nozzles. The pressure recom- 
 mended is usually between 25 and 50 
 pounds per square inch at the sprinkler. 
 Larger-capacity sprinklers usually re- 
 quire pressures beyond this range. It 
 should be pointed out that although a 
 greater diameter may be obtained by 
 increasing the pressure, this may not 
 produce desirable results. The shape of 
 the distribution pattern will also be af- 
 fected, and uneven water distribution 
 may result. 
 
 Remember, too, that one sprinkler will 
 not give uniform distribution over the 
 entire area of coverage. To obtain fairly 
 uniform coverage, there should be an 
 overlap from an adjacent sprinkler or 
 sprinklers. A 40 per cent overlap is usu- 
 ally considered desirable with square 
 spacing of sprinklers; however, square 
 spacing is seldom used in agricultural 
 practice except on permanent installa- 
 tions. When rectangular spacing is used, 
 
 A few of the common slow-revolving type of agricultural sprinkler heads. 
 
 [10] 
 
which is most common, best results are 
 obtained by spacing the sprinklers about 
 60 per cent of the wetted diameter one 
 way and from 20 to 60 per cent of the 
 wetted diameter the other way. Under 
 windy conditions (4 miles per hour or 
 more), special planning is necessary, 
 such as closer lateral and sprinkler spac- 
 ing, laterals placed perpendicular to the 
 wind, use of a single nozzle, or higher 
 operating pressures. 
 
 Whirling sprinklers operate at much 
 faster and more constant speeds of rota- 
 tion than the slow revolving. Rotation is 
 caused by the reaction of the jet of water 
 discharging from the nozzle. The nozzles 
 are attached to a rotating arm at an offset 
 angle. However, if both types are oper- 
 ated with similar capacities and under 
 equal pressures, the whirling sprinkler 
 covers about half the diameter of the 
 slow-rotating type. 
 
 Slow-revolving sprinklers have these 
 advantages over the whirling type: (1) 
 they permit the economy of spacing pipe- 
 lines and sprinklers farther apart because 
 of their greater diameter of coverage; 
 (2) slower rates of water application can 
 be obtained, a very desirable feature 
 where soils are not highly porous; (3) 
 slow rotation reduces wear, prolonging 
 the life of the sprinkler. 
 
 Fixed heads. Fixed heads are used 
 mainly for lawns, to some extent in 
 avocado and citrus orchards, and in 
 nurseries. Most of these heads have no 
 moving parts. A few have units that rise 
 vertically out of the fixed-head housing 
 when water is being discharged. One 
 other type has rotating nozzles; this is 
 known as the rotary pop-up sprinkler and 
 is used largely in golf courses and parks. 
 
 Fixed-head sprinklers are designed to 
 operate at pressures of 15 to 40 pounds 
 per square inch. They cover areas 15 to 
 25 feet in diameter with a fine spray 
 fairly evenly distributed. Some overlap is 
 required. Rates of discharge vary from 
 1.5 to 5 gallons per minute. This is 
 
 equivalent to an application rate of 0.7 
 to 3.0 inches per hour, a rate too high 
 for most soils to absorb so that runoff 
 or puddling results. 
 
 Fixed heads are sometimes used on 
 portable under-tree orchard systems on 
 permeable soils. Their cost per unit is 
 low. For other orchard and field uses on 
 less permeable soils, their application is 
 limited. 
 
 Nozzle lines. Nozzle lines are usually 
 stationary. They are relatively expensive, 
 and so they are generally used only for 
 crops yielding a high gross return, such 
 as certain truck crops and small fruits, 
 and for nurseries, greenhouses, lawns, 
 and other special purposes. 
 
 The nozzle lines are, as a rule, parallel 
 lines of pipe, % to 1% inches in diam- 
 eter, each fitted with a row of small brass 
 nozzles spaced 2 to 4 feet apart. The com- 
 mon height is 4 feet above ground, but 
 they may be as high as 7 feet where pas- 
 sage underneath is needed for cultivation. 
 Sometimes the pipe is held up by a sus- 
 pension cable slung from much higher 
 poles set 100 to 200 feet apart. 
 
 Stationary nozzle line for irrigating straw- 
 berries. An oscillating motor at the head of the 
 line slowly rotates the pipe back and forth so 
 as to wet a strip on each side. The nearest jets 
 are different from the others; they come from 
 special nozzles being tested. 
 
 [ii] 
 
1 
 
 Portable perforated line irrigating young alfalfa. This system operates at low pressure. 
 
 To wet a strip on both sides, the pipes 
 are slowly rotated through an angle of 
 about 90 degrees (from about 45 degrees 
 on one side to the same on the other). 
 This can be done either by hand or by a 
 water-operated oscillating motor. The 
 oscillators are usually double-acting pis- 
 ton devices. Being fairly expensive, they 
 are made to do multiple duty. Sometimes 
 they are moved from line to line ; in other 
 cases they operate several parallel lines 
 at one time by means of cables attached 
 to arms on each line. A special union is 
 required to permit the oscillating move- 
 ment needed to give uniform coverage of 
 the area between sprinkler lines. 
 
 Nozzle lines generally operate at pres- 
 sures of 25 to 40 pounds per square inch. 
 At 30 pounds the nozzles in common use 
 can deliver 0.15 to 0.30 gallon per 
 minute. Where the pressure is adequate, 
 the lines are spaced about 50 feet apart. 
 The nozzles, being small, clog easily. 
 Water containing algae or other clogging 
 matter must be screened, and this is done 
 usually at the head of the line. 
 
 Perforated pipe. Lightweight port- 
 able pipe with holes so spaced in its sides 
 as to discharge water at various angles is 
 
 [ 
 
 available. The spacing of the small holes 
 varies, depending on the rate of water to 
 be discharged. This pipe is available in 
 types applying from % to 2 inches per 
 hour or more. Perforated pipe should be 
 used only on soils that will absorb water 
 at relatively high rates. 
 
 This type of system has the advantage 
 of performing at relatively low operating 
 pressure — from a maximum of about 20 
 to as low as 4 or 5 pounds per square 
 inch. 
 
 Distribution of water from a line is 
 fairly uniform. The width of the strip 
 wetted depends on the pressure, varying 
 from approximately 50 feet at 20 pounds 
 per square inch to 20 feet at lower pres- 
 sures. 
 
 Besides applying water at relatively 
 high rates, perforated pipe has other 
 limitations. Since the pipe is laid on the 
 ground, plants may grow so close and 
 high that they impinge on the water jets. 
 It is impossible to regulate or equalize 
 the pressure along the line, as with sprin- 
 kler heads, except possibly by changes in 
 pipe diameter. Therefore, the system 
 operates most efficiently when it is used 
 on level land or on a contour line. 
 
 12] 
 
Perforated plastic pipe or tubing. 
 
 Perforated plastic pipe is still in the ex- 
 perimental stage, particularly for agri- 
 cultural purposes. However, for irri- 
 gating irregularly shaped turf areas or 
 floricultural beds, flexible pipe or tubing 
 offers considerable promise. 
 
 Two basic types are available — a 
 soaker hose and a sprinkler hose. The 
 soaker hose is a single tube that has many 
 small perforations on the bottom or 
 around the entire circumference of the 
 tube. Discharge from the perforations 
 varies with pressure, and considerable 
 variation may occur along a length of 
 hose. The application rate, when com- 
 puted for a narrow wetted strip of 1 foot, 
 is relatively high — in excess of 1 inch 
 per hour. However, since most soils will 
 not absorb water at this high rate, the 
 water floods across the soil surface, wet- 
 ting a strip 2 feet wide or more, depend- 
 ing on the infiltration capacity of the 
 soil. 
 
 The sprinkler-hose type usually con- 
 sists of one to three parallel tubes with 
 perforations only on the top. The extra 
 width gives the unit stability and keeps 
 it from rolling over. The perforations 
 may be punched or burned, and they vary 
 in size and spacing. The burned holes 
 give somewhat better control. 
 
 Water application rates vary for each 
 type of hose and perforation, but in gen- 
 eral they tend to be high. Spacing for 
 the sprinkler hose should be from 10 to 
 15 feet. Observation of the uniformity 
 of spray height from the hose will help 
 in making proper adjustments in length 
 and spacing of the hose. 
 
 Stationary, semiportable, 
 and portable systems 
 
 Stationary systems. Stationary 
 types were once the most popular sprin- 
 kler systems in California farming. Most 
 of the original orchard systems were of 
 this type, with rotating sprinklers 
 mounted on high risers over the trees. 
 
 Today, however, except for special situ- 
 ations, few stationary systems are being 
 installed. 
 
 A few growers of potatoes and 
 specialty crops, who have light sandy 
 soils and irrigate every two or three days, 
 are using a form of a permanent-type 
 system. After planting, portable surface 
 pipelines are placed at proper intervals 
 and left in that position until time for 
 harvest. Increased yields and reduced 
 labor costs help offset the high invest- 
 ment cost, which may be four to six times 
 that of a portable system moved regu- 
 larly. 
 
 A stationary system, once it has been 
 properly installed, with fixed or rotary 
 heads to fit conditions, has certain ad- 
 vantages over a portable system. For ex- 
 ample, it can duplicate a known perform- 
 ance over and over. In addition, it takes 
 less attention and costs less to operate 
 than a portable system, which must be 
 shifted about from place to place. 
 
 On the other hand, its pipelines, which 
 supply water to the risers, interfere with 
 cultivation unless they are buried fairly 
 deep; the risers and their attached sprin- 
 klers may also interfere unless extra 
 precautions have been taken in planning. 
 More important still, the initial invest- 
 ment is quite high, often approaching 
 $1,000 per acre. 
 
 Stationary system with fixed high risers used in 
 sprinkling an orchard. 
 
Semiportable systems. Some sprin- 
 kler systems have stationary pipelines 
 and portable sprinklers. They are espe- 
 cially adaptable for orchards and for the 
 turfs of golf courses and parks. They are 
 less expensive than stationary systems 
 and do not present some of the difficulties 
 of portable systems. 
 
 Frequently, in semiportable systems, 
 the portable sprinklers are of the under- 
 tree type. A satisfactory arrangement 
 used in some foothill areas of the Sacra- 
 mento Valley is a pipeline down every 
 other tree row, with a valve between 
 every second and third tree. To this valve 
 is attached a hose and sprinkler which 
 can be set at four positions between trees. 
 Sometimes high risers are used for over- 
 head irrigation. In another type of semi- 
 portable system a permanent pipeline is 
 placed down every eighth or tenth tree 
 row with an outlet valve between every 
 third and fourth tree. A flexible hose with 
 four or five sprinklers is attached to the 
 valve, permitting irrigation on both sides 
 of the pipeline. 
 
 Portable systems. A portable system 
 usually consists of a main distribution 
 line, which may be portable or perma- 
 nent, and one or more lateral lines of 
 portable, lightweight pipe to which sprin- 
 klers are attached. In a completely 
 portable system all of the pipe and pump 
 would be portable. 
 
 If steel pipe is used as a buried main 
 line, 12-gage metal is recommended, and 
 the pipe should be at least single-dipped 
 in hot asphalt to give reasonable service 
 under average conditions. Steel pipe is 
 connected by couplers, by welding, or by 
 driving tapered ends together. When a 
 driven connection is used, the asphalt 
 coating should be uniformly heated so 
 that it is soft but does not run off the 
 pipe before the joint is driven together. 
 Transite pipe has carefully tapered ends 
 that accommodate a coupling with rubber 
 "0" rings, which slides over the pipe 
 and secures the joint. 
 
 When the pipe is buried, it should be 
 placed deep enough to protect it from 
 heavy loads and cultivating equipment. 
 Normally, soil cover of 18 to 24 inches is 
 desirable. 
 
 Risers with valves need to be placed at 
 intervals along the main pipeline to 
 which the lateral lines are connected. The 
 most convenient spacing is to use the 
 same interval between valves as between 
 laterals. However, since risers and valves 
 are expensive, it is common practice to 
 use one riser for every three lateral set- 
 tings. A length of portable pipe equal to 
 the spacing of the lateral lines is used as 
 a "jumper" connection. 
 
 Portable sprinkler pipe comes in stand- 
 ard lengths of 20, 30, and 40 feet; other 
 lengths can be furnished on order. 
 
 A few of the many types of portable sprinkler pipe couplings 
 
Special aluminum alloys are used in the 
 manufacture of lightweight sprinkler 
 pipe to provide strength and resistance to 
 corrosion. Pipe is manufactured by ex- 
 trusion, drawing, or welding. 
 
 Sections of portable pipe are connected 
 to each other by a quick-operating cou- 
 pling. The type of coupling used is the 
 major difference between the various 
 portable irrigation systems. Most cou- 
 plings permit the operator to couple or 
 uncouple the connections from any loca- 
 tion along the pipe. Some type of foot- 
 ing device is desirable to keep the pipe 
 and coupler from tilting or rolling. 
 
 In general, a coupling contains at least 
 one rubber gasket. The water pressure 
 holds the gasket tightly in place against 
 the pipe, thereby preventing leakage as 
 the flow continues from one pipe to the 
 next. This arrangement provides for a 
 rather loose coupling and for flexibility 
 of the line so that it can follow relatively 
 rough land surfaces. 
 
 To prevent leakage and provide flexi- 
 bility, the gaskets are carefully manufac- 
 tured. Most of those available today are 
 similar in design and constructed of 
 special rubber or plastic. Although 
 plastic gaskets have a more uniform sur- 
 face than rubber, they have the disad- 
 vantage of changing in flexibility with 
 variations in temperature. Cold water or 
 low temperatures may make them brittle. 
 
 Gaskets can be expected to deteriorate 
 and will need to be replaced. Their length 
 of service will depend on local operating 
 conditions. Factors contributing to de- 
 terioration include heat and dirt. When 
 the sprinkler system is not in use and is 
 exposed to the intense summer heat, de- 
 terioration can take place rather rapidly, 
 as the pipe and couplings will absorb a 
 large amount of heat. Each time the pipe 
 is uncoupled, some soil may be picked 
 up on the end of the pipe or in the cou- 
 pling and cause abrasion to the gasket 
 when the pipe is recoupled. Suspended 
 material in the water supply will also tend 
 to cause wear on the gasket. 
 
 The following suggestions will aid in 
 giving longer life to your gaskets: 
 
 1. Eliminate suspended material from 
 the water (this will reduce maintenance 
 and repair of the pump and sprinkler 
 heads, too). 
 
 2. Dust new, sticky gaskets with a fine 
 powder, such as soapstone or talcum. 
 Do not use oil. 
 
 3. Wipe excessive dirt from each gas- 
 ket before reassembling. 
 
 4. Do not leave the sprinkler system 
 in direct sunlight. 
 
 5. Provide cool, dry storage, if pos- 
 sible, for the system when it is not in use. 
 
 6. Remove the gaskets at the end of 
 each season and store them in a barrel of 
 water. 
 
 . . . and on the right, one type of valve-opener elbow. 
 
Other fittings for portable systems may 
 include ells, tees, reducers, plugs, tee- 
 type valves for mainline hydrants, and 
 valve-opener elbows. 
 
 In most systems the couplings contain 
 the outlets to which the sprinkler-head 
 risers are attached; in others, the outlets 
 are attached directly to the pipe. 
 
 The distance portable lateral lines are 
 moved for each setting is usually 40, 50, 
 or 60 feet, depending on the application 
 rate, the time required to cover a field, 
 and wind conditions. After each set the 
 pipe is uncoupled and carried to the next 
 position. The number of men required to 
 move the pipe efficiently depends on the 
 length and weight of the pipe, the height 
 and density of the crop, and the type of 
 soil. The experience and ability of the 
 men will also be a factor. 
 
 Many farmers have constructed low 
 trailers to transport the pipe from field 
 to field. These are constructed with either 
 two or four wheels. 
 
 Axial-move system. In this system 
 the portable lateral line is moved as a 
 unit from one position to another in the 
 direction of the pipeline or axis. This 
 system cuts labor costs, as no uncoupling, 
 carrying, or recoupling of pipe sections 
 by hand is required. 
 
 Two moving methods are possible. In 
 one, skids are attached at each joint, sup- 
 porting the line off the ground. A move 
 is made by attaching a clamp to the end 
 of the line and towing it with a tractor 
 or jeep. This method operates best on a 
 permanent turf or well-established, low- 
 growing cover crop. It should not be 
 used on rough land because abrasion of 
 aluminum pipe will cause rapid wear. 
 
 The other method is to mount the 
 sprinkler pipe on dollies every 30 to 40 
 feet. Each dolly has two wheels parallel 
 to the pipe. A move is made in the same 
 manner as in the previous method. 
 
 A number of mechanical improve- 
 ments are being made in mounting wheels 
 to provide greater flexibility in moving 
 lateral lines. One device includes a uni- 
 
 versal joint and mounting for two rub- 
 ber-mounted, ball-bearing wheels. This 
 permits a great degree of flexibility in 
 turning corners and is designed to keep 
 the riser vertical at all times. The light 
 weight of each flexible unit, coupled with 
 ball-bearing wheels, results in a minimum 
 of resistance when the pipe is moved. 
 
 An even more flexible device has a 
 pair of wheels attached to a dolly in such 
 a way that they can turn through an angle 
 of 45 degrees from a position parallel to 
 the pipe. The pipeline can thus be towed 
 sideways to the next lateral position. 
 
 Lateral-move systems. In another 
 adaptation of a portable system, a wheel 
 is mounted perpendicularly to the pipe at 
 each 30- or 40-foot joint. This combina- 
 tion makes a complete mobile unit that 
 can be moved laterally from one setting 
 to another by a ratchet or by power drive. 
 One man can move as much as a quarter 
 of a mile of lateral pipe at one time. 
 
 The initial cost of wheel-type systems 
 is relatively high, but savings in labor 
 and convenience may justify the invest- 
 ment. It should be pointed out that it is 
 more difficult to move a wheel-type sys- 
 tem from one field to another than a 
 hand-moved system. 
 
 Traveling sprinkler machines. A 
 few growers use traveling sprinkler ma- 
 chines that pump water from a ditch and 
 distribute it through large sprinkler noz- 
 zles mounted on the machine. These 
 machines move continuously along the 
 ditch; most of them are geared to move 
 1 to 5 feet per minute. 
 
 Operating pressures vary from 60 to 
 150 pounds per square inch. One or more 
 sprinklers, each discharging from 200 to 
 800 gallons per minute, are used. In some 
 cases this rate of discharge would be far 
 beyond the soil's capacity to absorb 
 water. The diameter of coverage may be 
 as great as 300 feet. 
 
 For this type of operation an adequate 
 water supply must be available; also sup- 
 ply ditches at required intervals must be 
 constructed and maintained. This limits 
 
 [16] 
 
■ ,-- 
 
 A four-wheeled trailer used for transporting pipe around the field or from one field to 
 another. Pipe may be stored on trailer when not in use. 
 
 
 Above— sled- or skid-type attachment, and 
 right— wheel-dolly attachment. These are used 
 for longitudinal movement of pipes. 
 
 A wheel-mounted, portable sprinkler on a pasture. This type 
 of rig is used for lateral movement of pipe. 
 
 Courtesy Sprinkler Irrigation Assn. 
 
 [17] 
 
the operation to lands where ditches are 
 feasible. Furthermore, each ditch, in- 
 cluding the tractways along each side, 
 removes some land from production. This 
 may amount to 5 or 10 per cent of the 
 field. 
 
 While the labor of moving pipe is 
 removed, pumping costs are greater be- 
 cause of the higher pressures, and main- 
 tenance of the machine and water-supply 
 ditches must also be considered. 
 
 Self-propelled systems. Recently, 
 automatically controlled self-propelled 
 units have been developed. Large wheel 
 towers support the pipe 6 to 7 feet above 
 the ground. The system moves in a circle 
 around a pivot point where water is de- 
 livered into the system. Each tower is 
 driven by a stroke of a hydraulic cylinder 
 which operates on the normal water pres- 
 sure. The size of sprinklers is increased 
 
 toward the end of the line to compensate 
 for the larger area covered. The system 
 can be engineered to turn on or off auto- 
 matically. 
 
 Maintenance and storage 
 
 Regardless of the type of system, an- 
 nual inspection is good practice. Pipe, 
 sprinklers, couplings, gaskets, and any 
 other appurtenances should be carefully 
 examined and any repairs made before 
 each season's operations. Particular at- 
 tention should be paid to the sprinklers, 
 making sure all bearings and bushings 
 are in proper adjustment and that exces- 
 sive sand conditions have not enlarged 
 the nozzle openings. 
 
 Adequate storage for the equipment is 
 recommended. The pipe should be care- 
 fully stacked and stored under a shed at 
 the end of the season. 
 
 DESIGN and OPERATION OF SYSTEMS 
 
 The design of a well-planned sprinkler 
 system calls for a knowledge of engineer- 
 ing and agricultural principles; it cannot 
 be executed by simple rules of thumb. 
 Each area or field presents individual 
 problems that must be analyzed and con- 
 sidered in the design of the system if it is 
 to operate efficiently. 
 
 What conditions must 
 be considered? 
 
 The conditions that will influence the 
 design of a sprinkler system are, in brief: 
 the requirements and limitations of the 
 crop, the nature of the soil, the water 
 supply, the size and shape of the field, 
 arrangement and layout of the system, 
 
 and the cost. Other cultural practices and 
 farm-management problems should also 
 be kept in mind. 
 
 The subcommittee on sprinkler irriga- 
 tion of the American Society of Agri- 
 cultural Engineers has recommended 
 certain minimum requirements of design, 
 which serve as helpful guides. These are, 
 briefly: 
 
 1. The system should meet peak mois- 
 ture requirements of any regularly irri- 
 gated crop and apply a stated amount of 
 water in a specified time. 
 
 2. The application rate should not 
 cause runoff. 
 
 3. The pressure and spacing should be 
 designed to apply water uniformly. 
 
 [18] 
 
THE CROP— ITS REQUIREMENTS AND LIMITATIONS 
 
 Efficient sprinkler irrigation meets peak crop needs and takes care of field 
 application losses. Here are the key points of plant growth in relation to 
 water needs. 
 
 Crop production is the prime con- 
 sideration. Water must be supplied in 
 the amounts necessary to maintain steady 
 and continued crop growth. 
 
 Rooting characteristics 
 
 Among the most important crop fac- 
 tors are the rooting characteristics, which 
 include rooting depth and distribution. 
 These are frequently overlooked, or in 
 many cases not fully understood. 
 
 A guide to the effective rooting depth 
 of certain vegetable, field, and orchard 
 crops is given in table 1. It should be 
 noted that these measurements are for 
 mature crops grown on deep, well- 
 drained soils under average conditions. 
 There are exceptions and variations. 
 
 Irrigation methods vary depending on 
 whether the crop is deep- or shallow- 
 rooted. For example, where all of the soil 
 to the full effective rooting depth is 
 
 TabBe 1. Depths to Which the Roots of Mature Crops Will Exhaust 
 the Available Water Supply When Grown in a Deep, Well- 
 Drained Soil under Average Conditions 
 
 Crop Depth 
 
 feet 
 
 Alfalfa 8 to 12 
 
 Almonds 6 to 9 
 
 Apricots 6 to 9 
 
 Artichokes ± l A 
 
 Asparagus 10 
 
 Beans (bush) * 13^2 
 
 Beans (lima) 4 
 
 Beets (sugar) 5 to 6 
 
 Beets (table) 3 
 
 Broccoli 2 
 
 Cabbage 2 
 
 Cantaloupes 4 to 6 
 
 Carrots 3 
 
 Cauliflower 2 
 
 Celery* 2 
 
 Chard 3 
 
 Cherries 6 to 9 
 
 Citrus 4 to 6 
 
 Corn (sweet) * 3 .to 4 
 
 Corn (field)* 5 to 7 
 
 Cotton 4 
 
 Cucumber 33^ 
 
 Eggplant 3 
 
 Figs 5 
 
 Grain and flax 5 
 
 Grapes 6 to 8 
 
 Crop Depth 
 
 feet 
 
 Hops 6 to 8 
 
 Permanent pasture V/ 2 to 3 
 
 Lettuce* 1 
 
 Melons 5 
 
 Milo 6 
 
 Mustard ZY 2 
 
 Olives 6 to 9 
 
 Onions 1 
 
 Parsnips 4 
 
 Peas Z]4, 
 
 Peaches 6 to 9 
 
 Pears 6 to 9 
 
 Prunes 6 to 9 
 
 Peppers 3 
 
 Potatoes (Irish)* \y 2 
 
 Potatoes (sweet) 4 to 6 
 
 Pumpkins 6 
 
 Radishes \y 2 
 
 Spinach , 2 
 
 Squash (summer) 3 
 
 Sudan grass 6 + 
 
 Tomatoes 6 to 10 
 
 Turnips 3 
 
 Strawberries 2 to 3 
 
 Walnuts 12 to 18 
 
 Watermelons 6 to 8 
 
 Crops known to have sparse or skeleton-type root development during early stages of growth. 
 
 [19] 
 
utilized for storing soil moisture, and the 
 crop is deep-rooted, fewer irrigations are 
 needed, and irrigation efficiency is in- 
 creased. 
 
 The rooting characteristics of annual 
 and perennial plants differ considerably. 
 Perennial crops, such as fruit trees, gen- 
 erally have well-developed root systems 
 that permeate the entire soil depth, gen- 
 erally 4 to 9 feet. Rooting characteristics 
 of annual crops, on the other hand, are 
 quite variable. They have continually en- 
 larging root systems, particularly during 
 the earlier stages of growth. What is at 
 first a skeleton system may develop later 
 into a very complete system. Some have 
 deep roots, others very shallow ones. 
 Some have very sparse or less vigorous 
 root systems than others. Even though 
 a plant may send its roots very deep, they 
 may permeate only a small part of the 
 soil mass. As a result, the plant may wilt 
 or cease to grow even though the soil 
 moisture is generally at a high level 
 throughout that part of the soil mass 
 which is not in contact with the roots. 
 
 Other conditions that may modify root 
 development include the presence of 
 hardpans or any dense, compact layer or 
 layers, a high water table or salt accumu- 
 lation in the soil, or diseases and root 
 insects. 
 
 Another point to consider is that in 
 irrigating some deep-rooted crops, it is 
 not desirable to wait until all of the 
 readily available soil moisture has been 
 depleted in the entire rooting depth. The 
 
 time required to apply water to an entire 
 field should be estimated, and irrigation 
 should be completed before soil moisture 
 is completely lost from any part of the 
 field. 
 
 The amount of readily available mois- 
 ture held by the soil in the effective root- 
 ing depth depends on the soil charac- 
 teristics. This subject is discussed on 
 pages 21-23. 
 
 Water use 
 
 Transpiration. The rate of water use 
 by a crop (transpiration) depends on 
 certain plant characteristics and clima- 
 tological factors. Long hours of sun- 
 light, high temperature, low humidity, 
 and strong winds all tend to increase the 
 rate of water use providing moisture is 
 readily available in the major part of the 
 root zone. 
 
 Changes in the rate of transpiration 
 occur during a growing season. The rate 
 is less for young plants with few leaves or 
 mature plants in poor growth than for 
 those with abundant leaf surfaces and 
 dense stand and in good vigor. It is low 
 early in the season and tapers off in the 
 late summer and fall. In California the 
 peak use of water may occur any time 
 during June, July, or August, or, in some 
 years, even September. Peak use may last 
 only a day, or it may continue for two 
 weeks or more. The capacity of the 
 sprinkler system should be great enough 
 to satisfy the needs of the crop during 
 this peak period. 
 
 Table 2. Estimated Peak Water Use of Crops in Five 
 Geographical Areas of California 
 
 Water use 
 Area (Inches per day) 
 
 Dry desert 0.30 to 0.40 
 
 San Joaquin Valley 0.25 to 0.35 
 
 Sacramento Valley 0.20 to 0.30 
 
 Inland Coastal areas 0.15 to 0.20 
 
 Coastal slopes 0.10 
 
 [20] 
 
Evaporation. Closely associated with 
 the use of water by transpiration is the 
 water evaporated from the soil surface. 
 The same climatic factors that control 
 transpiration also control the rate of 
 evaporation. However, evaporation losses 
 during the growing season are usually 
 much less than the amount used in trans- 
 piration because evaporation takes place 
 only when the soil surface is wet and to 
 a limited depth — 4 to 8 inches, depend- 
 ing on the soil type and the frequency of 
 irrigation. A loss of 0.2 to 0.5 inch fol- 
 lowing each irrigation can be expected. 
 
 The combined use of water in any 
 given time and area by crop transpira- 
 tion and evaporation from the soil sur- 
 face is called the water use of the crop. 
 
 Values of the estimated peak water-use 
 rate for five geographical subdivisions of 
 California are given in table 2. These 
 rates are for mature crops in good grow- 
 ing vigor, completely shading the soil. 
 The absolute rate for a specific crop at 
 any time will depend on the plant char- 
 acteristics and climatic factors discussed 
 above. 
 
 Other water losses. It should be 
 noted that the rates given do not include 
 other losses or factors that determine the 
 field-application efficiency of the system. 
 These include: evaporation from the 
 spray and wetted foliage, deep percola- 
 
 tion, runoff, unavoidable losses, uneven- 
 ness in the distribution pattern, and 
 breakdowns or repairs. These must be 
 considered in determining the peak gross 
 water requirements of the sprinkler 
 system. 
 
 The evaporation loss from the spray 
 and wetted foliage may be appreciable, 
 particularly under conditions of low ap- 
 plication rates, high temperatures, and 
 low humidity. Strong winds also con- 
 tribute to a high loss, for some water may 
 be carried out of the area being sprinkled. 
 
 Evaluation of the loss from the spray 
 is difficult, but experiments indicate it 
 can be as much as 5 per cent of the water 
 discharged by the nozzles. 
 
 The loss from the soil and foliage dur- 
 ing an irrigation may be relatively high 
 because sprinkling wets practically all of 
 the plant foliage and generally more soil 
 surface than surface irrigation does. The 
 extent of these losses depends on the fac- 
 tors already mentioned, but it may 
 amount to 5 to 35 per cent of the water 
 applied. 
 
 The field-application efficiency of well- 
 designed sprinkler systems may vary, on 
 the average, from 50 to 90 per cent. 
 
 A properly designed sprinkler system 
 must, therefore, apply a sufficient depth 
 of water not only to meet the peak water 
 requirements of the crop but also to take 
 care of the field-application losses. 
 
 THE SOIL AND ITS CHARACTERISTICS 
 
 How soil type and structure influence water-application rates. 
 
 Infiltration capacity 
 
 The rate at which water enters the soil 
 is known as the soil's infiltration capac- 
 ity. This rate varies greatly depending on 
 the type and structure of the soil. Sandy 
 soils usually take water faster than loams 
 and clays. Soils that have been compacted 
 or are lacking in good tilth take water 
 slowly. 
 
 The infiltration capacity also varies 
 
 during the time of water application de- 
 pending on soil-moisture conditions. If 
 the soil is dry, the water intake will be 
 relatively high at the beginning of an 
 irrigation. However, the infiltration rate 
 may decrease rapidly during the first few 
 hours of an irrigation and then gradually 
 become constant. 
 
 A sprinkler system should, therefore, 
 be designed to apply water at such a rate 
 
 [21] 
 
that the soil will absorb it throughout the 
 entire sprinkling period without produc- 
 ing surface runoff. The rate of applica- 
 tion should be designed for the slowest 
 intake rate, and water should be applied 
 uniformly to all parts of the field. 
 
 For many clay soils, which have a low 
 infiltration capacity, the application rate 
 should not exceed 0.3 inch per hour. Ap- 
 plication rates up to 0.5 inch per hour 
 can be used on most loam soils, whereas 
 sandy soils may take water in excess of 
 1 inch per hour. 
 
 There are many exceptions to these 
 general rates. The proper application rate 
 for a particular soil type can be deter- 
 mined only by experience. In some cases 
 it may be necessary to make several trial 
 irrigations, varying the operation of the 
 system by changing sprinkler nozzle sizes, 
 line pressure, or lateral spacing, and 
 observing field conditions. Adjustments 
 can then be made to meet as closely as 
 possible the infiltration capacity of the 
 soil. It should be remembered that a 
 change in operation or design to meet 
 one factor must be integrated with the 
 other features of the system to maintain 
 efficient operation. 
 
 In some cases the rate of application 
 may exceed the infiltration capacity be- 
 cause of soil differences within a given 
 field, and water may collect on the sur- 
 face. It may be necessary to provide 
 some surface drainage so that crops 
 growing in low spots in the field will not 
 receive excessive amounts of water. 
 
 Water-holding capacity 
 
 During an irrigation, water enters the 
 soil and fills the pore space between the 
 soil particles. When all of the space is 
 full, the soil is saturated. In general, this 
 is a temporary condition, for once irri- 
 gation is completed some of the water 
 moves downward. In most soils this 
 downward movement practically ceases 
 after one to three days. The moisture re- 
 tained in the wettest portion of the soil is 
 called field capacity. 
 
 The amount of water held at the field 
 capacity depends on the soil texture, 
 structure, uniformity, and depth. It may 
 range from less than 1 inch per foot of 
 depth for a sandy soil to 3 inches or more 
 for some clays. A shallow soil with poor 
 drainage will hold more water per foot of 
 soil when at field capacity than will a 
 deep soil with poor drainage. 
 
 Another important soil-moisture con- 
 dition is the permanent wilting per- 
 centage. This soil condition is reached 
 when the soil particles hold the water so 
 tightly that plant roots are unable to 
 absorb it rapidly enough to supply the 
 needs of the growing plant. Some plants 
 show this condition by a wilting of the 
 leaves. Others may show it by a change 
 in leaf color or by slower growth of the 
 plant or fruit. Still others may not show 
 any visible signs, yet their normal growth 
 functions are essentially stopped until 
 more water is added to the soil. 
 
 The soil-moisture content between the 
 field capacity and the permanent wilting 
 
 
 Table 3. 
 
 Average Readily 
 Various Soil 
 
 Available Moisture for 
 Types* 
 
 Soil type 
 
 
 
 
 Readily available 
 
 moisture (Inches 
 
 per foot) 
 
 Sands 
 
 
 
 
 0.5 -0.75 
 
 Loams .... 
 
 
 
 
 0.75-1.50 
 
 Clays 
 
 
 
 
 1.50-3.00 
 
 
 * These quantities are 
 available water than clays. 
 
 given only as an approximate guide, since 
 
 some sands may hold more readily 
 
 [22] 
 
percentage is known as the readily 
 available moisture. As long as the 
 major part of the root system of any 
 plant is in contact with soil containing 
 readily available moisture, the plant can 
 continue to function normally. The aver- 
 age readily available moisture per foot 
 for the three general soil types is given in 
 table 3. 
 
 A soil tube or auger is invaluable for 
 examining the soil profile to observe con- 
 ditions under which the roots of the crops 
 are growing. With it you can obtain soil 
 samples from various depths to see if the 
 soil moisture has been depleted. It is also 
 handy for determining the depth of soil 
 wetted after an irrigation. 
 
 WATER SUPPLY MUST BE ADEQUATE AND RELIABLE 
 
 Factors to consider are: quantity and reliability, water quality, the water 
 level (if the source is a well), and the location of the source. 
 
 Quantity 
 
 The source of water may be a stream, 
 lake, farm pond or reservoir, an open 
 ditch or canal, or a well. Whatever the 
 source, the reliability and adequacy of 
 the supply is most important. You must 
 be sure of enough water to maintain 
 steady and continuous crop growth for 
 the entire area to be irrigated. 
 
 A continuous flow of water is essential 
 for the most efficient use of a sprinkler 
 system. Full-time use of the system dur- 
 ing the peak of the growing season means 
 a lower initial investment and lower an- 
 nual operating costs. The rate of flow 
 needs to be enough to satisfy the peak 
 water use of the crop and cover field 
 application losses. Sprinkling can use 
 smaller rates of flow more efficiently than 
 other methods. 
 
 Quality 
 
 The quality of the water and the 
 amount of suspended material it contains 
 must also be considered. The water 
 should be analyzed to make sure that it is 
 suitable for irrigation use. Water high in 
 total salts, for example, may be injurious 
 to some plants. Also important are the 
 amounts of chlorides and boron and the 
 ratio of sodium to calcium. 
 
 Silt and debris may cause needless 
 wear on the mechanical parts of the pump 
 and sprinkler heads. Also, debris or moss 
 may clog or plug the nozzles of the sprin- 
 klers, requiring additional labor. 
 
 Whenever water is pumped from a 
 ditch or stream, a screen or strainer is 
 usually provided at the intake. It may be 
 necessary to install a screening and de- 
 silting chamber or sediment trap under 
 some conditions. 1 Water from a well is 
 usually free of debris, but in some cases 
 it may contain sand. 
 
 Location of 
 the water level 
 
 Water-level conditions are important 
 if the source is a well. When a pump is 
 turned on, the water is quickly drawn 
 down from the static to the pumping 
 water level. The amount of drawdown 
 will depend on the water-bearing char- 
 acteristics of the materials supplying 
 water to the well and the amount of water 
 being pumped. Assuming that the speed 
 of the pump is constant, the pumping 
 level in the well may drop with time. This 
 may occur during a day, throughout a 
 season, or from season to season. Reasons 
 for this can be mutual interference of 
 adjacent wells, intensified pumping dur- 
 ing the summer, or a general lowering of 
 water levels within a ground water basin. 
 Should the level be lowered, the capacity 
 of a given pump will be reduced. This 
 may have serious consequences if a 
 sprinkler system is designed to operate 
 
 1 Details of a desilting device may be found in 
 "Desiher in the economy size," by M. W. Hois- 
 veen, in Irrigation Engineering and Mainte- 
 nance 4(2) : 11-12, 26. February, 1954. 
 
 [23 
 
at a given capacity and a reduction takes 
 place because of a drop in the water level. 
 Careful study of the water-level con- 
 ditions is very important if you are think- 
 ing of installing a sprinkler system. A test 
 of the well is invaluable. In making the 
 test, be sure to take into consideration 
 the time of year and make certain that 
 results are interpreted accurately for the 
 lowest possible water-level conditions at 
 other seasons. Once a system is in opera- 
 tion, the water level should be checked 
 frequently — this will help to determine 
 if the proper amounts of water are being 
 applied. 
 
 Proximity of the water 
 source to the field 
 
 The relative location of the water 
 source to the field or fields to be irrigated 
 may dictate the type of sprinkler system 
 to install and the method of operation. 
 In many cases open ditches offer flexi- 
 bility in operation. When topography 
 permits, ditches can be constructed at 
 convenient intervals and locations. In 
 general, most sprinkler systems will be 
 less expensive if the source of water is 
 located at or near the center of the field. 
 
 Existing concrete pipelines can be used 
 to carry the water from a well or canal 
 to the field. Since ordinary concrete irri- 
 gation pipe is not designed to carry water 
 under pressures greater than 8 to 10 
 pounds per square inch, a booster pump 
 must be used to develop the pressure re- 
 quired after the water leaves the concrete 
 pipeline. This pump can be a portable or 
 permanent unit. 
 
 In some foothill areas of California, a 
 water supply can be developed from 
 springs or streams. Often these are high 
 enough to develop the necessary pressure 
 to overcome the pipe friction loss and 
 operate the sprinkler system properly. 
 The pressure lost because of friction will 
 depend on the difference in elevations, 
 length and size of pipeline, and rate of 
 water flow. Most rotating-type sprinkler 
 systems require a pressure of 40 to 60 
 pounds per square inch at the upper end 
 of the main pipeline. This corresponds 
 to an elevation of 90 to 140 feet, which 
 would be the absolute minimum differ- 
 ence in elevation from the point where 
 the water supply is tapped to the sprin- 
 kler system. 
 
 A 60-horsepower motor and centrifugal pump used as a booster unit. Water is pumped 
 from a concrete pipeline into a 10-inch steel main line. 
 
THE PUMPING PLANT IS THE HEART OF THE 
 SPRINKLING SYSTEM 
 
 Pump and power unit should be carefully chosen to make sure they will meet 
 all of the operating conditions. Here is information that will guide you in 
 your selection. 
 
 The pump 
 
 To obtain the most efficient pump for 
 the intended service, choose a well-con- 
 structed, compact pump with good 
 hydraulic characteristics, which, at a 
 given speed, will meet the maximum 
 head-capacity requirements of a properly 
 designed sprinkler system. Naturally, a 
 high operating efficiency is desirable and 
 is usually obtained when the pump is 
 new. However, it should be expected that 
 with use the efficiency will drop, and in 
 some cases the pump motor will become 
 overloaded. Always inspect the individual 
 pump curves before buying. These 
 curves, which the pump vendor can 
 supply, show the relationship between 
 the quantity of water pumped and the 
 operating head, efficiency, and brake 
 horsepower. 
 
 Long hours of continuous operation 
 place a heavy duty on the pumping equip- 
 ment. The lower the operating speed of 
 the pump, the longer will be its life. High- 
 speed pumps (those operating at speeds 
 in excess of 2,000 rpm), although lower 
 in initial cost, may not be the most eco- 
 nomical over a period of years. 
 
 The centrifugal pump is the type most 
 commonly used when water is taken from 
 a ditch or pipeline. The pump should not 
 be located more than 10 to 15 feet above 
 the water level. The biggest disadvantage 
 of this type of pump is that it has to be 
 primed; however, inexpensive devices, 
 such as check valves, can be used to re- 
 duce or eliminate this difficulty. 
 
 In California, small positive displace- 
 ment pumps are often conveniently at- 
 tached to the centrifugal pump. These 
 pumps are hand-operated and quickly 
 take care of the priming problem. 
 
 When a cased well is the source of 
 
 water, or when the suction lift exceeds 20 
 feet, a deep-well turbine pump is used. Its 
 major elements consist of a head-and- 
 drive assembly above ground, from 
 which the column and bowls are sus- 
 pended. Since the pump bowls are sub- 
 merged in water, no priming is necessary. 
 With the proper design, a suitable bowl 
 unit and adequate drive power can be 
 tused to lift the water to the ground sur- 
 face and develop the pressure needed to 
 operate the sprinkler system. 
 
 If a turbine pump is already available 
 and is delivering the required amount of 
 water for a sprinkler system but does not 
 provide the pressure, a centrifugal pump 
 with suitable drive power can be con- 
 nected to the discharge of the turbine, 
 and it will supply the needed additional 
 pressure. 
 
 Power units 
 
 The type of power unit will depend on 
 the speed and horsepower requirements 
 of the pump. Most common in California 
 on stationary pumping plants are electric 
 motors. Their advantages include rela- 
 tively low initial cost, simplicity of op- 
 eration, and practically no repair or 
 maintenance. 
 
 If the source of water is a surface ditch 
 along the side of or through the field and 
 no main-line pipe is used, a portable 
 plant with an internal combustion engine 
 is generally used. In such cases the pump 
 is moved along with the lateral sprinkler 
 lines. Gasoline and diesel oil are the com- 
 mon fuels used in these engines. Popular 
 in California is a power and pump unit 
 mounted on a truck bed or a trailer unit. 
 
 When natural gas is available, it can 
 be used for portable booster pump 
 units. Several quick-coupling natural-gas 
 
 [25] 
 
valves, conveniently located in the field, 
 will permit the portable unit to be moved 
 around the field, pumping the water from 
 a concrete line and discharging it under 
 pressure into a portable main line. 
 
 The tractor type is another adaptation. 
 It utilizes its own power both to operate 
 the pump and to move from one location 
 
 to another. One disadvantage is that this 
 ties up the tractor, which may be needed 
 for other farm operations during the irri- 
 gation season. 
 
 Small air-cooled engines are usually 
 short-lived under the continuous opera- 
 tion required with many sprinkler sys- 
 tems. 
 
 Two types of small positive-displacement pumps used to prime the centrifugal pump. 
 
 Motor and pump unit are sometimes mounted on trailers (below) . 
 
mop "mmmsmmimm^^ >* 
 
 . on a tractor, using tractor as power unit . . . 
 
 ... or sometimes on a truck chassis. 
 
 [27] 
 
THE LAYOUT 
 
 Each field is an individual problem and all possible combinations of layouts 
 should be investigated. 
 
 In general, most sprinkler systems will 
 be cheaper if the source of water is lo- 
 cated at or near the center of the field. In 
 this case, shorter headers and lateral lines 
 are generally feasible. This means smaller 
 pipe can be used, lowering the initial cost 
 of the system. Friction losses will also be 
 lower than when a pump is at the bound- 
 aries of the field. 
 
 The water is supplied to the portable 
 lines from risers and valves located along 
 the pressure line. With two or more lat- 
 erals, the pumping plants can be operated 
 continuously. This arrangement, the most 
 satisfactory from the standpoint of oper- 
 ation, may cost somewhat more than sys- 
 tems using portable plants. This is be- 
 cause a stationary main pressure supply 
 line represents an investment usually 
 greater than the cost of the portable pipe. 
 
 Friction loss in pipes 
 
 As water is conveyed along a sprinkler 
 line, part of the energy or pressure de- 
 veloped at the upper end is lost by fric- 
 tion. The size and kind of pipe you select 
 will depend on the amount of pressure 
 loss due to friction for a given rate of 
 flow, and on the general condition of the 
 inside of the pipe. Calculation of friction 
 loss in lateral lines is complicated in that 
 part of the total water conveyed is dis- 
 charged at each sprinkler. 
 
 In order to maintain reasonably uni- 
 form distribution and discharge from 
 each sprinkler, consistent with economic 
 considerations, certain general rules are 
 suggested : 
 
 1. The friction loss in the main line 
 should not exceed 15 per cent of the pres- 
 sure available at the pump discharge. 
 
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 An arrangement of a portable system operating from a main pressure line with a stationary 
 pumping plant supplied from a well. Jumper lines supplying the laterals permit three settings for 
 each hydrant on the main. Often a single hydrant serves each lateral. Another procedure is to 
 use the portable supply line on one side of the pump, then move it to the other side. 
 
 [28] 
 
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 Single-line arrangement of a portable sprinkler system supplied 
 from a ditch along one side of the field. 
 
 More specifically, pipe sizes may be pumping against additional head when 
 
 selected by economic analysis comparing pipe of smaller diameter is used. Limits 
 
 the fixed annual cost of pipe of different of head loss are established, based on 
 
 sizes with the annual operating cost of local power or fuel cost and the number 
 
 Split-line arrangement of a portable sprinkler system supplied from a ditch running through tht 
 middle of the field. This is more economical than the single-line arrangement shown above. 
 
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 [29 
 
Table 4. Friction Loss in Aluminum Sprinkler System 
 Main Line with Couplers* 
 
 Flow 
 (Gallons per minute) 
 
 Friction Loss 
 Pounds per square inch (psi) per 100 feet of pipe 
 
 Pipe Size (inches) 
 
 10 
 
 10. 
 
 20. 
 
 30. 
 
 40. 
 
 50. 
 
 60. 
 
 70. 
 
 80. 
 
 90. 
 
 100. 
 
 120. 
 
 140. 
 
 160. 
 
 180. 
 
 200. 
 
 220. 
 
 240. 
 
 260. 
 
 280. 
 
 300. 
 
 350. 
 
 400. 
 
 450. 
 
 500. 
 
 550. 
 
 600. 
 
 650. 
 
 700. 
 
 750. 
 
 800. 
 
 850. 
 
 900. 
 
 950 
 
 1,000. 
 
 1,200 
 
 1,400 
 
 1,600 
 
 1,800 
 
 2,000 
 
 0.14 
 0.52 
 1.06 
 1.80 
 2.90 
 3.72 
 4.77 
 
 0.02 
 0.07 
 0.15 
 0.25 
 0.39 
 0.52 
 0.69 
 0.91 
 1.08 
 1.39 
 2.08 
 2.60 
 3.38 
 4.07 
 5.11 
 
 0.13 
 0.17 
 0.22 
 0.27 
 0.35 
 0.52 
 0.64 
 0.85 
 1.00 
 1.30 
 1.52 
 1.77 
 2.12 
 2.51 
 2.86 
 3.68 
 4.42 
 
 0.09 
 0.12 
 0.17 
 0.22 
 0.29 
 0.36 
 0.44 
 0.52 
 0.61 
 0.71 
 0.84 
 0.97 
 1.21 
 1.60 
 1.93 
 2.25 
 2.64 
 3.29 
 3.89 
 4.55 
 
 0.12 
 0.15 
 0.18 
 0.21 
 0.25 
 0.29 
 0.35 
 0.40 
 0.52 
 0.65 
 0.79 
 0.95 
 1.08 
 1.38 
 1.58 
 1.79 
 1.99 
 2.29 
 2.51 
 2.81 
 3.14 
 3.44 
 4.98 
 
 0.18 
 0.25 
 0.31 
 0.37 
 0.43 
 0.52 
 0.64 
 0.73 
 0.82 
 0.93 
 1.04 
 1.17 
 1.32 
 1.45 
 1.60 
 2.34 
 3.16 
 4.02 
 4.76 
 
 0.12 
 0.16 
 0.19 
 0.24 
 0.27 
 0.34 
 0.39 
 0.45 
 0.49 
 0.55 
 0.61 
 0.68 
 0.76 
 0.82 
 1.17 
 1.64 
 2.12 
 2.60 
 3.16 
 
 0.07 
 0.08 
 0.09 
 0.11 
 0.12 
 0.15 
 0.17 
 0.18 
 0.20 
 0.23 
 0.25 
 0.28 
 0.41 
 0.54 
 0.69 
 0.87 
 1.02 
 
 Based on Scobey's friction loss equation using K s = 0.40 
 
 [30] 
 
2. The friction loss in each lateral line 
 should not exceed 20 per cent of the 
 pressure available at the head end of the 
 lateral line. Changes in elevation should 
 be taken into account when figuring fric- 
 tion loss. 
 
 Values for the friction loss in alumi- 
 num irrigation pipe with quick couplers 
 are given in table 4. Table 5 gives values 
 that can serve as a guide for selecting the 
 proper size of lateral pipeline. In this 
 table it is assumed that the friction loss 
 
 Table 5. Guide for Selecting Size of Pipe for 
 Sprinkler Lateral Line* 
 
 Sprinkler 
 discharge 
 
 Maximum number of sprinklers to use on single lateral line with : 
 
 20-foot spacing 
 
 Pipe size 
 3 " 4 " 
 
 30-foot spacing 
 
 Pipe size 
 2" 3" 4" 5' 
 
 40-foot spacing 
 
 Pipe size 
 
 3" 4" 5' 
 
 gpm 
 
 1.0 
 
 1.5 
 
 2.0 
 
 2.5 
 
 3.0 
 
 3.5 
 
 4.0 
 
 4.5 
 
 5.0 
 
 6.0 
 
 7.0 
 
 8.0 
 
 9.0 
 
 10.0 
 
 12.0 
 
 14.0 
 
 16.0 
 
 18.0 
 
 20.0 
 
 22.0 
 
 24.0 
 
 26.0 
 
 28.0 
 
 30.0 
 
 35.0 
 
 40.0 
 
 45.0 
 
 50.0 
 
 36 72 125 280 
 
 27 56 91 156 
 
 23 46 76 114 
 
 21 43 72 105 
 
 19 
 18 
 16 
 15 
 14 
 
 13 
 
 12 
 
 11 
 
 10 
 
 9 
 
 8 
 7 
 7 
 6 
 6 
 
 39 
 37 
 34 
 32 
 31 
 
 27 
 25 
 23 
 22 
 20 
 
 18 
 16 
 15 
 14 
 13 
 
 5 13 
 
 5 12 
 
 5 11 
 
 4 11 
 
 4 11 
 
 4 10 
 
 3 9 
 
 3 8 
 
 3 8 
 
 67 
 62 
 56 
 52 
 50 
 
 46 
 41 
 39 
 37 
 34 
 
 31 
 
 28 
 26 
 24 
 23 
 
 22 
 21 
 20 
 19 
 18 
 
 16 
 15 
 14 
 13 
 
 93 
 88 
 82 
 78 
 74 
 
 66 
 60 
 57 
 54 
 50 
 
 45 
 42 
 39 
 36 
 34 
 
 33 
 31 
 29 
 28 
 27 
 
 25 
 23 
 21 
 20 
 
 31 62 104 200 
 
 24 48 78 120 
 
 21 43 70 97 
 
 18 38 62 90 
 
 16 
 15 
 14 
 13 
 12 
 
 11 
 
 10 
 
 9 
 
 9 
 
 8 
 
 35 
 32 
 29 
 28 
 27 
 
 24 
 21 
 20 
 19 
 18 
 
 7 16 
 
 6 14 
 
 6 13 
 
 5 12 
 
 5 11 
 
 5 11 
 
 4 10 
 
 4 10 
 
 4 9 
 
 4 9 
 
 56 
 53 
 49 
 46 
 
 44 
 
 40 
 36 
 34 
 32 
 30 
 
 27 
 25 
 23 
 21 
 20 
 
 19 
 18 
 17 
 16 
 16 
 
 3 8 14 
 
 3 7 13 
 
 2 7 12 
 
 2 6 11 
 
 84 
 78 
 72 
 68 
 64 
 
 58 
 53 
 50 
 
 47 
 44 
 
 39 
 36 
 34 
 31 
 29 
 
 28 
 27 
 26 
 25 
 24 
 
 21 
 20 
 18 
 17 
 
 28 56 93 160 
 
 21 44 72 106 
 
 18 38 62 88 
 
 16 34 56 82 
 
 15 
 14 
 13 
 12 
 11 
 
 10 
 9 
 8 
 8 
 
 7 
 
 6 
 6 
 5 
 5 
 
 4 
 
 31 
 29 
 27 
 25 
 
 24 
 
 21 
 19 
 18 
 17 
 16 
 
 14 
 13 
 12 
 11 
 10 
 
 4 10 
 
 4 9 
 
 4 9 
 
 3 8 
 
 3 8 
 
 52 
 48 
 44 
 41 
 39 
 
 36 
 33 
 
 31 
 29 
 27 
 
 24 
 22 
 20 
 19 
 18 
 
 17 
 16 
 15 
 
 14 
 14 
 
 3 7 13 
 
 2 7 12 
 
 2 6 11 
 
 1 6 10 
 
 76 
 70 
 64 
 61 
 58 
 
 53 
 
 48 
 45 
 42 
 40 
 
 35 
 32 
 30 
 28 
 26 
 
 25 
 24 
 23 
 22 
 21 
 
 19 
 18 
 17 
 16 
 
 * Based on friction loss in entire lateral line being equal to about 20 per cent of the probable operating 
 pressure. 
 
 [31] 
 
Table 6. The Factors by Which the Friction Loss in a Pipe Without 
 
 Sprinklers Must Be Multiplied to Obtain Loss in a 
 
 Lateral Line with Sprinklers 
 
 Number of 
 Sprinklers 
 
 Factor 
 
 1 
 
 1.0 
 
 2 
 
 0.625 
 
 3 
 
 0.518 
 
 4 
 
 0.469 
 
 5 
 
 0.440 
 
 6 
 
 0.421 
 
 7. . 
 
 0.408 
 
 8. . 
 
 0.398 
 
 9 
 
 0.391 
 
 10 
 
 0.385 
 
 11 
 
 0.380 
 
 12 
 
 0.376 
 
 13 
 
 0.373 
 
 14 
 
 0.370 
 
 15 
 
 0.367 
 
 Number of 
 Sprinklers 
 
 Factor 
 
 16 
 
 0.365 
 
 17 
 
 0.363 
 
 18 
 
 0.361 
 
 19 
 
 . . . 0.360 
 
 20 
 
 0.359 
 
 22 
 
 0.357 
 
 24 
 
 0.355 
 
 26 
 
 0.353 
 
 28 
 
 . 0.351 
 
 30 
 
 . 0.350 
 
 35 
 
 . 0.347 
 
 40 
 
 . 0.345 
 
 50 
 
 0.343 
 
 100 
 
 0.338 
 
 More than 100 0.333 
 
 in the entire lateral line is equal to about 
 20 per cent of the pressure at the head 
 end of the lateral. In table 6 are listed 
 the values by which the friction loss in a 
 pipe without sprinklers must be multi- 
 plied to obtain the loss in a lateral line 
 with sprinklers. 
 
 Although the most economical design 
 of lateral lines would call for a reduction 
 in pipe diameter, since the flow is reduced 
 by discharge from the sprinklers, many 
 farmers prefer to use the same size pipe 
 
 for the entire lateral line. However, where 
 several lateral lines are being operated 
 from a main line, it may be desirable to 
 reduce the size of the main-line pipe to 
 conform to the amount of water being 
 carried. 
 
 Details of the hydraulic design of the 
 system, taking these factors into account, 
 are generally left to a member of the sales 
 company, qualified to provide competent 
 engineering service. 
 
 THE METHOD OF OPERATION 
 
 Operation of the system is generally governed by the limitations of soil- 
 infiltration capacity, soil moisture, depth of rooting, area to be covered, and 
 water supply. 
 
 In situations where greater flexibility 
 is possible, the operation of the system 
 should be designed to fit farm-labor con- 
 ditions. This is particularly important 
 
 when lateral moves must be made entirely 
 by one man. Sprinkler-system operation 
 should be coordinated as well as possible 
 with routine work and other chores. 
 
 [32] 
 
There are two general methods of op- 
 eration. One is to apply water at a high 
 rate and move frequently. The other is to 
 apply water at a relatively low rate and 
 move less often. The first, which is pos- 
 sible only on soils with high infiltration 
 capacities, requires almost continuous 
 labor. This means that on many farms the 
 pipe would have to be moved throughout 
 the night. 
 
 The second method is generally more 
 satisfactory because the laterals can be 
 moved at convenient times of the day. 
 Most popular are sets of 7 hours (three 
 moves per day) or 11 hours (two moves 
 per day), allowing one hour for the 
 move. The twice-a-day move generally ap- 
 plies enough moisture to wet dry soil to 
 the necessary depth for most crops. Sets 
 of 23 hours may be necessary for deep- 
 rooted crops, such as alfalfa, or orchards 
 growing on deep, permeable soils that 
 have low infiltration rates. In these situ- 
 
 Terms of measurement used in this circu- 
 lar, particularly in the example problem, 
 are referred to by the following standard 
 abbreviations: 
 
 ac- acre 
 ac.-in.— acre-inch 
 ac.-ft.— acre-foot 
 cfs— cubic feet per second 
 gpm— gallons per minute 
 hp— horsepower 
 ppm— parts per million 
 psi— pounds per square inch 
 rpm— revolutions per minute 
 
 ations more equipment may be necessary 
 to allow for the longer sets and still cover 
 the area frequently enough. 
 
 Examine carefully all possible layouts 
 for each method of operation to make 
 sure that the maximum efficiency is 
 achieved in both the sprinkler system and 
 other farm operations. 
 
 Any one of the five approximate formulas given below can be conveniently used to 
 compute the depth of water applied to a field: 
 
 cubic feet per second x hours 
 
 acres 
 
 gallons per minute x hours 
 450 x acres 
 
 so. Calif, miner's inches x hours 
 50 x acres 
 
 Calif, statute miner's inches x hours 
 40 x acres 
 
 96.3 x gpm per sprinkler 
 sprinkler spacing x lateral spacing 
 
 acre-inches per acre, or 
 average depth in inches 
 
 [33] 
 
EXAMPLE PROBLEM 
 
 The following step solution can be used as a guide in fitting a sprinkler 
 system to a particular field problem. 
 
 Basic Information 
 
 Crop : Permanent pasture 
 
 Depth of rooting 2 feet (table 1) 
 
 Location : Sacramento Valley 
 
 Peak crop water requirements 0.3 inch per day (table 2) 
 
 Soil : Clay loam 
 
 Readily available water capacity 1.5 inches per foot (table 3) 
 
 Maximum infiltration capacity (estimated) .0.5 inch per hour 
 
 Area : 36.3 acres 
 
 Shape 1200 feet wide x 1320 feet long 
 
 Slope Level 
 
 Water Source Well in the center of the field with a 
 
 discharge capacity of 400 gpm and 
 a pumping water level of 55 feet 
 below the center of the pump dis- 
 charge pipe. 
 
 Irrigation efficiency (estimated) 75 per cent 
 
 The operator wants to move the system twice each day, allowing at least one hour for 
 each move. He is willing to operate 7 days a week. This routine will fit into a well- 
 planned pasture-management program. 
 
 Calculations 
 
 Amount of water available between irrigations. 1.5 inches per foot x 2 feet -3 inches 
 
 Number of days that can elapse before _ . , 
 
 additional water must be added — — — - — — - — = 10 days 
 
 0.3 inch per day 
 
 Depth of water required per irrigation —— — : — — = 4 inches 
 
 H F & 0.75 (irrig. efficiency) 
 
 Total operating time per day 2x11 hours = 22 hours 
 
 Total rate of flow required — - — — = 0.66 cfs 
 
 1 22 x 10 
 
 0.66 x 450 = 297 gpm 
 
 The next step is to determine the lateral and sprinkler spacing. Two general condi- 
 tions must be met: (1) for a given lateral spacing there must be enough laterals to 
 cover the area during the irrigation interval; (2) the lateral and sprinkler spacing 
 must permit a rate of water application not to exceed the maximum allowable for the 
 soil — in this case 0.5 inch per hour. In this problem it will be best to lay a portable 
 
 [34] 
 
main the short way of the field from the pump. It will be — - — = 600 feet long. The 
 laterals will be — - — = 660 feet long. 
 
 Lateral spacing 
 
 Try 40 feet: 
 
 One 660-foot lateral would move 80 feet per day. To cover the entire field would 
 
 2 x 1200 
 require — — — = 30 days. Since the irrigation interval is 10 days, 3 laterals 
 80 
 
 would be required. 
 
 Try 50 feet: 
 
 • One 660-foot lateral would move 100 feet per day. To cover the entire field would 
 
 2 x 1200 
 require — z— — - = 24 days. Since the irrigation interval is 10 days, 3 laterals 
 
 would be required; the field could thus be covered in 8 days. 
 
 Try 60 feet: 
 
 One 660-foot lateral would move 120 feet per day. To cover the entire field 
 
 would require — — - — = 20 days. This spacing with two laterals would meet the 
 
 \-ZAj 
 
 irrigation interval requirement. It would be most satisfactory from the stand- 
 point of less investment in pipe and lower labor cost of moving. If wind condi- 
 tions prevail, shorter spacing is recommended. 
 
 Sprinkler spacing 
 
 If one man is to move the pipe, 30-foot lengths are desirable. With that length and a 
 
 sprinkler for each pipe section, the number of sprinklers per lateral will be -—- — 22. 
 
 With two laterals the total is 44. 
 
 When 44 sprinklers are operating, each will be discharging an average of 
 
 297 gpm 
 44 sprinklers = 6 ' 75 ^ m P er s P" nkler - 
 
 Performance tables of sprinkler manufacturers will give the size and type of a 
 sprinkler with given size nozzles that will discharge this rate at a given operating 
 pressure. The pressure at the last sprinkler on the lateral should be approximately 
 35 psi. 
 
 Application rate 
 
 The application rate for sprinkler and lateral spacing of 30 and 60 feet will be 
 
 96.3x6.75 
 
 — — — 77T— = O.oo inch per hour. 
 30 x 60 r 
 
 If 4 inches is applied during each irrigation at the rate of 0.36 inch per hour, the 
 
 time required per set will be . n/ , . — = : = 11.1 hours, which agrees with 
 
 r 0.36 inch per hour 
 
 the original condition of moving twice a day. 
 
 Main pipeline size. The main line will be 600 feet long. It must be large enough 
 to accommodate the flow of 297 gpm for whatever layout of laterals is used. In the 
 design of the main line it would be well to figure that both laterals might be operat- 
 ing at the extreme end of the main line, which would be the worst condition of opera- 
 
 [35] 
 
tion. Values of the fraction loss per 100 feet for 300 gpm in 4- and 5-inch pipe, taken 
 from table 4, are 2.86 and 0.97 psi respectively. For 600 feet of line the total loss in 
 the 4- and 5-inch lines would be 17.16 and 5.82 psi. If the operating pressure at the 
 pump is assumed to be about 50 psi, the recommended allowable friction loss in the 
 main line would be approximately 7.5 psi. Therefore, the loss in the 5-inch line 
 would be less than the allowable amount, and a 5-inch line would be used. 
 
 This is one way of selecting mainline pipe size. An economic analysis should be 
 made to check this selection. 
 
 Lateral pipeline size. With 30-foot spacing of sprinklers on the laterals there 
 will be 22 sprinklers on each lateral, discharging approximately 6.75 gpm. Table 5 
 shows that for 30-foot spacing, 3-inch pipe will accommodate 21 to 24 sprinklers 
 between 6 and 7 gpm. Therefore, 3-inch lateral lines would be selected. 
 
 To obtain the actual amount of friction loss in the lateral line with sprinklers, a 
 factor can be applied to the friction loss in the same size pipe without sprinklers. 
 Values of this factor are given in table 6. 
 
 In this example the factor for 22 sprinklers is 0.357. This number is then multi- 
 plied by the friction loss obtained from table 4 for the flow of 22 sprinklers : 22 x 6.75 
 gpm = 148.5 gpm in 660 feet of 3-inch line, which is 2.91 psi per 100 feet. The total 
 
 lateral friction loss is, then, 2.91 x ^ **' x 0.357 = 6.85 psi. 
 
 100 ft. ^ 
 
 Horsepower required. The horsepower requirements are determined by the 
 amount of water pumped, the total head or pressure, and the efficiency of the pump. 
 
 In this example the flow required is 297 gpm. The head requirements include 
 the sprinkler pressure, friction loss for the main line laterals, and miscellaneous pipe 
 fittings, and the pumping lift in the well. If the pumping lift for 297 gpm in the well 
 is 52 feet, the total head would be as follows : 
 
 Sprinkler pressure 35.0 psi x 2.31 = 81.0 feet 
 
 Main-line friction loss 5.82 psi x 2.31 = 13.4 feet 
 
 Lateral friction loss 6.85 psi x 2.31 = 15.8 feet 
 
 Miscellaneous friction loss 3.00 psi x 2.31 = 6.9 feet 
 
 Pumping lift 52.0 feet 
 
 Total 169.1 feet 
 
 The theoretical water horsepower would be: 
 
 297 gpm x 169.1 ft. 
 
 h P = p60~ - = 12 - 7 
 
 If a pump efficiency is assumed to be 70 per cent, the brake horsepower required is: 
 
 12 7 
 brake hp = r—~- = 18.15 
 
 This would require a 20-hp electric motor. 
 
 Labor. The labor required to move laterals will depend upon several factors: type 
 of system, frequency of move, number of irrigations per season, spacing of laterals, 
 length of each pipe section, source of water supply, type of pump and drive unit, soil 
 conditions, and type and height of crop. 
 
 Since there are many variables, it is reasonable to expect a wide range of labor 
 requirements. Labor is seldom less than 0.5 man-hour per acre per irrigation, and 
 in some cases it may go as high as 5 man-hours per acre per irrigation. An average 
 figure for hand-moved systems is about l 1 /^ man-hours per acre per irrigation. Gen- 
 erally, orchard requirements are slightly higher, all other things being equal. 
 
 [36] 
 
SPECIAL PROBLEMS 
 
 Fertilizer application 
 
 Some fertilizers can be applied by 
 sprinkler systems, although certain ones 
 present definite problems. Others should 
 not be used in a sprinkler system. In gen- 
 eral, use of the fertilizers depends on two 
 conditions: 1) the compound must be 
 relatively soluble in water or available in 
 liquid form; 2) it should not be corro- 
 sive to the metals of the system, including 
 the pump if the solution passes through 
 the pump. 
 
 In California the fertilizers most com- 
 monly used are compounds containing 
 nitrogen, phosphorus, and occasionally 
 potassium. These compounds are avail- 
 able in different forms — solid, liquid, and 
 gas. Most of the nitrogen and potassium 
 compounds are soluble in water. The 
 commonly used compounds of phospho- 
 rus are only slightly soluble. Those that 
 are soluble enough to apply through 
 sprinklers include phosphoric acid and 
 ammonium phosphate, and these can be 
 corrosive to metals. 
 
 Even though a chemically pure com- 
 pound may dissolve readily, most com- 
 mercial fertilizers contain some impuri- 
 ties. These may reduce solubility or leave 
 residues that may clog the supply lines or 
 sprinklers. The impurities in ammonium 
 sulfate, for example, may amount to 4 to 
 6 per cent and sometimes as much as 10 
 per cent. When this fertilizer is injected 
 into a system, there is also some possi- 
 bility that the concentration of sulfuric 
 acid may be great enough to cause cor- 
 rosion. 
 
 Application of anhydrous ammonia (a 
 compressed gas) and nitrogen solutions 
 containing free ammonia through a 
 sprinkler system is not recommended. 
 Losses by diffusion into the air are ex- 
 cessive. 
 
 Preliminary tests with ammonia salts, 
 such as ammonium, nitrate, sulfate, and 
 
 phosphate, indicate that losses of am- 
 monia due to diffusion can be reduced by 
 applying solutions at as high concentra- 
 tions as possible without causing damage 
 to the crop. 2 For a slightly alkaline wa- 
 ter the initial ammonia concentrations 
 should be 100 ppm or more. The most 
 important factors influencing the loss 
 are : the initial pH, the final pH following 
 injection of the fertilizer, the buffering 
 capacity of the water, and the residual 
 acidity of the fertilizer. Water tempera- 
 ture is less important, although the loss 
 is somewhat smaller at lower water tem- 
 peratures. 
 
 A good procedure to follow in apply- 
 ing fertilizers through a sprinkler system 
 involves three periods of time during 
 each regular set of a lateral. During the 
 first period, water is applied for a long 
 enough time to wet the plant foliage and 
 surface soil thoroughly. This will prevent 
 the concentration of strong fertilizer so- 
 lutions on dry leaves, which may cause 
 injury. 
 
 During the second period the fertilizer 
 is injected into the system. The actual 
 time required will depend on the quan- 
 tity of solution being injected, the length 
 of pipeline, and, in the case of ammonia 
 salts, the maintenance of a high enough 
 concentration of the solution to minimize 
 the evaporation loss. 
 
 The final period is essentially a flush- 
 ing operation. Enough time should re- 
 main at the end of the fertilizer applica- 
 tion period to: 1) rinse the system thor- 
 oughly, and 2) wash the fertilizer solu- 
 tion off the crop foliage. 
 
 These three periods are not of equal 
 length. Actually, in an 11 -hour setting the 
 first two steps may take only about 10 per 
 cent of the total time, but someone must 
 
 2 "Ammonia loss from sprinkler jets," by 
 D. W. Henderson, W. C. Bianchi, and L. D. 
 Doneen in Agricultural Engineering 36(6) : 
 398-399. June, 1955. 
 
 [37] 
 
be present to start the fertilizer solution 
 into the system sometime after the begin- 
 ning of each set. This procedure should, 
 however, help prolong the life of the 
 system. 
 
 Methods of injection. There are sev- 
 eral methods of injecting fertilizer solu- 
 tions into a sprinkler system. A number 
 of devices to aid in this operation are 
 available commercially. 
 
 In one popular and practical method, 
 suitable for a system involving a centrifu- 
 gal pump, the injection is made through 
 
 a line connecting an open supply tank to 
 a fitting on the suction side of the pump 
 (Diagram A). The solution is drawn in 
 by the reduced pressure in this pipe. An- 
 other hose or pipe connection can be 
 made on the discharge side of the pump 
 to facilitate filling the supply tank. 
 
 Occasionally a separate pump unit is 
 used to pump the fertilizer solution from 
 a supply tank into the sprinkler line (Dia- 
 gram B) . This pump must be able to de- 
 liver the solution into the line at greater 
 pressure than that delivered by the irri- 
 gation pump. 
 
 SUPPLY TANK 
 
 I II CONTROL __ 
 (=-' ~*~~VALVES 
 
 II 
 
 CENTRIFUGAL 
 PUMP 
 
 SPRINKLERS 
 
 77777 
 
 SUCTION y4 
 
 J _ PIPE 
 
 AIR TIGHT PRESSURE 
 SUPPLY TANK 
 
 SCREEN r 
 L 
 
 CONTROL __ w 
 VALVES /L 
 
 SUPPLY TANK 
 
 SMALL MOTOR 
 DRIVEN PUMP 
 
 AIR TIGHT PRESSURE 
 SUPPLY TANK 
 
 SCREEN V y// 
 
 111! 
 
 f=~A 
 
 j CONTROL 
 
 JV "*"" valve's" ^ 
 
 Y^T VE 
 
 pJL— 1 — 1 T0 , / l ffl~ 
 
 1 ~-J ^SPRINKLERS / Uli — 
 
 NTURI UNIT-^ >»h\ \ \>>» 
 
 m 
 
 D 
 
 PITOT TUBE UNIT 
 
 'SPRINKLERS 
 
 V \ CHECK 
 VALVE * 
 
 IOTE: A Got* or Butterfly Vol. 
 Is Suitoblt 
 
 Diagrams of the set-up for adding fertilizer in solution to a sprinkler-irrigation system. 
 
 [38] 
 
Other methods make use of differential 
 pressures for circulating water from the 
 sprinkler line through the supply tank 
 and back to the sprinkler line. One such 
 device is a Venturi unit placed in the 
 pipeline (Diagram C), another makes 
 use of Pitot tubes (Diagram D) . 
 
 Whatever method is used, the supply 
 tank must be considered. It should be 
 large enough to hold the proper amount 
 of solution and still permit mixing if 
 necessary. A noncorrosive screen on the 
 outlet to the system is a good idea, as this 
 will prevent large pieces of undissolved 
 fertilizer from being carried into the sys- 
 tem where it may clog a sprinkler. Also, 
 a drain at the bottom to permit rinsing 
 and emptying will help make the tank last 
 longer. When connected to a pressure 
 line, the tank should be designed to with- 
 stand the maximum anticipated operat- 
 ing pressure in the sprinkler line. 
 
 Corrosion of sprinkler systems 
 
 In general, aluminum is an excellent 
 material for use in sprinkler systems be- 
 cause of its resistance to corrosion by 
 many types of water and under most con- 
 ditions. However, in a few scattered areas 
 of California, corrosion of sprinkler sys- 
 tems still presents a problem. In some 
 cases only minor damage has occurred, 
 but in others, pipe and fittings have had 
 to be replaced after one or two seasons' 
 use. 
 
 Corrosion is a very complex phenome- 
 non. In most cases the damage is attrib- 
 uted to electrolytic or galvanic processes. 
 This means that a difference in electrical 
 potential develops between the metal, or 
 metals, of the pipe and its environment. 
 In the case of a sprinkler pipe this differ- 
 ence may occur between dissimilar met- 
 als or between the pipe and the water or 
 soil. As a result, small corrosion cells de- 
 velop on the surface of the pipe, loss of 
 metal occurs, and eventually small holes 
 develop. Another source of corrosion is 
 excess amounts of free carbon dioxide, 
 which is present in some well waters. 
 
 If unusually severe or rapid corrosion 
 occurs or is expected, the manufacturers 
 of aluminum pipe suggest a treatment 
 that will minimize this damage. This in- 
 volves a mechanical and chemical clean- 
 ing to remove all products of corrosion, 
 followed by a protective paint coating. 
 The steps are as follows: 
 
 Thoroughly wire-brush the pipe. This 
 is done with a tapered brush of fine steel 
 wire, slightly larger than the pipe diam- 
 eter, attached to a long-shaft extension, 
 such as half-inch pipe. An electric drill 
 of suitable size is used to rotate the shaft. 
 All loose corrosion products should be 
 removed by blowing or wiping. 
 
 Next, remove the remaining traces of 
 corrosion products by chemical cleaning. 
 This is done by immersing the pipe in an 
 uninhibited phosphoric acid cleaner, 
 such as Oakite 33 or 36, Dexoidine 526, 
 or Kelite Process K. Follow the manufac- 
 turer's recommendations concerning the 
 temperature and time of immersion. For 
 large operations a dipping tank can be 
 constructed by welding together halved 
 sections of 55-gallon oil drums. If no tank 
 is available, one end of the pipe can be 
 plugged and the cleaner poured in the 
 pipe. After cleaning, rinse the pipe thor- 
 oughly with fresh, clean water, and dry 
 it completely. 
 
 The final step is to coat the pipe uni- 
 formly with a good-quality paint. Paints 
 for use on aluminum should not be pig- 
 mented with lead or copper. Some paints 
 that have been used are: Zincilate 300 
 and 410, Aluminum Metal and Masonry, 
 Carbonzite, Zinc Chromate Primer, and 
 Metal Etching Primer. 
 
 The paint can be applied by inclining 
 the pipe at an angle of approximately 10 
 degrees from the horizontal and pouring 
 in enough paint to cover the surface thor- 
 oughly as the pipe is slowly rotated. In- 
 side spray equipment can also be used 
 effectively. Average coverage should be 
 about 500 square feet per gallon of paint. 
 
 In general, initial investment and cost 
 of operation are lowest when a system is 
 
 [39 
 
planned for continuous use and the 
 amount of water applied is just enough 
 to satisfy peak requirements and cover 
 field application losses. But whether a 
 small system, operated more or less con- 
 tinuously, will be more economical than a 
 larger one, operated only a few days for 
 each irrigation, depends primarily upon 
 the conditions on a particular farm. If a 
 
 system requires continuous attention, it 
 may not be economical because the labor 
 cost of operation may be very high. 
 
 A small portable system can sometimes 
 be operated by moving the lines only 
 once or twice a day (morning and eve- 
 ning). This can be a one-man job, leav- 
 ing the farmer free to attend to other 
 farm operations during the day. 
 
 INVESTMENT and OPERATING COSTS 
 
 Figuring annual cost 
 
 After obtaining the initial cost — the 
 investment in equipment and installa- 
 tion — you will want to estimate the total 
 annual cost of sprinkling. This includes 
 fixed and operating costs. Taxes, insur- 
 ance, interest on investment, and depre- 
 ciation are the fixed costs. Operating 
 costs include power, labor, maintenance, 
 and repairs. 
 
 To determine the depreciation, the use- 
 ful life and consequent annual deprecia- 
 tion rate for each item of the system 
 should be figured separately. Other users, 
 manufacturers, or dealers may be able to 
 give you an estimate of the useful life of 
 parts of the equipment. However, a pe- 
 riod of 10 to 15 years is often used as a 
 basis for depreciating the sprinkler sys- 
 tem as a unit. 
 
 The annual costs of operation can be 
 divided into two items: the power cost 
 (including fuel or electricity and lubri- 
 cating oil) and the labor cost for han- 
 dling the system. 
 
 The original investment and annual 
 cost will vary greatly from one system 
 to another even within the same locality. 
 Factors that cause the original investment 
 to vary include: the source and location 
 of the water supply; the size, shape, and 
 arrangement of the area to be sprinkled; 
 and the elaborateness of the system. An- 
 nual costs are influenced by cost of wa- 
 
 ter, fuel charges, crop requirements, 
 number of irrigations, amount of water 
 applied per irrigation, total amount of 
 water applied, and the amount and cost 
 of labor. 
 
 Only a few cost studies on sprinkler 
 systems have been made. The results of 
 some of the more recent studies con- 
 ducted by County Agricultural Extension 
 personnel are presented in table 7. Three 
 examples were selected to represent typi- 
 cal systems of the areas. Included is a 
 breakdown of the original investment 
 and operating costs. In some cases com- 
 plete data were not available. It should 
 be pointed out that from the information 
 obtained it is not possible to tell whether 
 the best designed and operated system is 
 being used in each case. Undoubtedly im- 
 provements could be made in some in- 
 stances. 
 
 Wide variations in the original invest- 
 ment and in the fixed and operating costs 
 will be noted. These reflect the differences 
 in the acres irrigated, the size and type of 
 system, the number of irrigations, and 
 the amount of water applied during each 
 irrigation. For example, compare systems 
 1 and 3 of the Tehama County study. 
 System 1 irrigated 165 acres 26 times, 
 applying 3.3 inches per irrigation. Sys- 
 tem 3 had approximately half this acre- 
 age, irrigated three more times, but ap- 
 plied only 1.5 inches per irrigation. The 
 cost per acre of the two systems was 
 
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 [42] 
 
about the same— $50.90 and $55.60. The 
 costs per acre of power, and particularly 
 of labor, were higher for system 3. As a 
 result, the total annual irrigation cost for 
 system 3 is more than one and one-half 
 times that of system 1. 
 
 Differences such as these are to be ex- 
 
 pected when comparing sprinkler-system 
 costs because each farm has its own par- 
 ticular problems. To do the essential job 
 of maintaining a steady water supply for 
 plant growth involves many factors, and 
 each farmer should consider all of them 
 in determining what his costs will be. 
 
 REFERENCES 
 
 Should I Use Sprinklers for Irrigating Vegetable Crops? 
 P. A. Minges and L. J. Booher. Extension Service Leaflet. 
 
 Adjustable-length Irrigation Pipe Trailer. 
 
 M. O'Brien and L. J. Booher. Extension Service, Farm Irrigation Structures Leaflet. 
 
 Irrigation Pumps, Their Selection and Use. 
 
 C. N. Johnston. Calif. Agr. Exp. Sta. Circular 415. 
 
 In order that the information in our publications may be more intelligible it is sometimes neces- 
 sary to use trade names of products or equipment rather than complicated descriptive or chemical 
 identifications. In so doing it is unavoidable in some cases that similar products which are on the 
 market under other trade names may not be cited. No endorsement of named products is intended 
 nor is criticism implied of similar products which are not mentioned. 
 
 [43] 
 
CONVENIENT EQUIVALENTS 
 
 These equivalents may be used for converting from one unit to another 
 Area : 
 
 lacre =43,560 square feet 
 
 = 66 feet x 660 feet 
 = 33 feet x 1,320 feet 
 Weight: 
 
 1 gallon weighs approximately 8.33 pounds 
 1 cubic foot weighs approximately 62.4 pounds 
 
 Volume: 
 
 1 gallon 
 I cubic foot 
 
 1 acre-inch 
 
 1 acre-foot 
 
 Kates of flow: 
 
 1 cubic foot per second 
 
 1 southern California miner's inch 
 1 California statute miner's inch 
 Volume from rates of flow: 
 
 1 cubic foot per second for 1 hour 
 
 1 cubic foot per second for 12 hours 
 
 450 gallons per minute for 1 hour 
 Pressure and Head : 
 
 1 pound per square inch 
 
 1 foot of water 
 
 1 atmosphere at sea level 
 Work and Power: 
 
 1 horsepower 
 
 1 kilowatt 
 
 -231 cubic inches 
 = 1,728 cubic inches 
 = 7.5 gallons 
 = 3,630 cubic feet 
 = 27,154 gallons 
 = Yi2 acre-foot 
 = 43,560 cubic feet 
 = 325,851 gallons 
 = 12 acre-inches 
 
 = 450 gallons per minute 
 
 = 7.5 gallons per second 
 
 = 50 southern California miner's inches 
 
 = 40 California statute miner's inches 
 
 = 1 acre-inch per hour 
 
 = 2 acre-feet per day (24 hours) 
 
 = 9 gallons per minute 
 
 = ll 1 A gallons per minute 
 
 = 3,600 cubic feet 
 = approximately 1 acre-inch 
 = approximately 1 acre-foot 
 = approximately 1 acre-inch 
 
 = 2.31 feet of water 
 
 = 0.433 pound per square inch 
 
 : 14.7 pounds per square inch 
 
 : 550 foot pounds per second 
 : 33,000 foot pounds per minute 
 
 0.746 kilowatt 
 
 1.34 horsepower 
 
 "--.r^rr^^^^ 
 
 25w-10, , 56(B7722)BEB