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Part 652Irrigation Guide

Farm Distribution ComponentsChapter 7

7–31(210-vi-NEH, September 1997)

Chapter 7 Farm DistributionComponents

Contents:

7–i

652.0700 General 7–1

652.0701 Pipelines 7–2

(a) Typical pipe installation and materials for irrigation systems ................ 7–2

(b) Specific applications .................................................................................... 7–3

653.0702 Open ditches 7–4

(a) Unlined ditches ............................................................................................. 7–4

(b) Lined ditches ................................................................................................. 7–4

(c) Seepage losses ............................................................................................... 7–5

652.0703 Water control structures 7–6

(a) Related structures for open ditches ........................................................... 7–6

(b) Related structures for gravity pipelines ..................................................... 7–8

(c) Related structures for pumped pipelines ................................................... 7–8

652.0704 Water measurement 7–9

(a) Planning and design considerations ........................................................... 7–9

652.0705 Irrigation runoff, tailwater recovery and reuse 7–11

(a) Planning and design considerations ......................................................... 7–11

652.0706 Irrigation system automation 7–15

(a) Planning and design considerations for automation .............................. 7–15

652.0707 Pumping plants 7–17

652.0708 Drainage systems 7–18

(a) Precipitation runoff .................................................................................... 7–18

(b) Irrigation runoff (tailwater) ....................................................................... 7–19

(c) Subsurface drainage ................................................................................... 7–19

(d) Environmental factors ................................................................................ 7–20

652.0709 Chemigation 7–21

(a) Advantages................................................................................................... 7–21

(b) Disadvantages ............................................................................................. 7–21

(c) Planning and design considerations ......................................................... 7–22

652.0710 State supplement 7–29



7–32 (210-vi-NEH, September 1997)7–ii

Tables Table 7–1 Expected recovery from runoff 7–13

Table 7–2 Tailwater pit sizing for intermittent pumpback facility 7–14

Table 7–3 Overall efficiencies obtainable by using tailwater 7–14

recovery and reuse facility

Table 7–4 Liquid fertilizers (solutions) for sprinkler application 7–27

Table 7–5 Dry fertilizers for sprinkler application 7–28

Table 7–6 Comparison of typical analysis of clear 7–28

suspension-type liquid fertilizers

Figures Figure 7–1 Irrigation water distribution system layout for several 7–1

fields and various irrigation methods and systems

Figure 7–2 Typical tailwater collection and reuse facility for 7–11

quick-cycling pump and reservoir

Figure 7–3 Gravity flow from storage tank 7–23

Figure 7–4 Injection on suction side of pump 7–23

Figure 7–5 Venturi principle of injection 7–23

Figure 7–6 Pitot tube injection 7–23

Figure 7–7 Pressure metering pump injection 7–24

Figure 7–8 Backflow prevention device using check valve with 7–25

vacuum relief and low pressure drain

Figure 7–9 Safety devices for injection of chemicals into 7–26

pressurized irrigation systems using electric power

Figure 7–10 Safety devices for injection of chemicals into 7–26

pressurized irrigation systems using internal

combustion engine power




Chapter 7 Farm Distribution Components

652.0700 General

Irrigation water should be made available to each partof the farm irrigation system at a rate and elevation orpressure that permits proper operation of irrigationapplication devices or facilities. Irrigation watershould be conveyed as economically, efficiently, andsafely as possible without excessive losses or erosion.Water should be delivered to the plant at a suitablequality for the planned purpose. All components of afarm irrigation water delivery system must be sized tofurnish adequate irrigation water to meet planned cropuse or scheduled delivery from an irrigation district. If

water is delivered on a rotation or turn basis, thesystem must be large enough to allow delivery ofwater in the time allowed. Plans should provide forfuture needs and expansion. Figure 7–1 displays atypical multifield delivery system for various irrigationmethods and systems.

Sizing a system to meet peak (or planned) period cropwater use requires careful consideration of manyalternatives and compromises. They involve ditch andpipe size, pump size, labor considerations, capitalinvestment, operating costs, available water capacityof soils, crop rotations, plant stress risk levels, andoverall management of the farm enterprise. Providingwater, along with good water management, to meet

Figure 7–1 Irrigation water distribution system layout for several fields and various irrigation methods and systems

Lateral canal

Concrete canalconveyance eff. 90%

PipelineField 280 acresside-roll

Field 3120 acrescenter pivot

Field 660 acresborder

Field 7100 acresfurrow

Pipeline



Earth canalconveyance eff. 80%

Field 1100 acresfurrow irrigated

Earth ditchconveyance eff. 70%

Field 8320 acreslateral move

Concrete canalconveyanceeff. 90%

Concrete canalconveyanceeff. 95%

Earth ditchconveyance eff. 80%



7–2 (210-vi-NEH, September 1997)

crop needs 80 percent or even 50 percent of the timecan be more economical than providing full irrigationfor all conditions. This is especially true in humid andsemihumid areas where a substantial part of plantwater need is provided by rainfall.

Farm distribution components (facilities) include allnecessary appurtenances, such as water control struc-tures, slide gates, trash racks, screening devices, watermeasuring devices, flow control valves, air releasevalves, vacuum relief valves, pressure regulating orrelief valves, controllable flow turnouts and drains,plus other components necessary for the long-termoperation and maintenance of the system. All facilitiesshould be located so they interfere as little as possiblewith farming operations. Components of the distribu-tion system should be readily accessible for operationand maintenance. An operation and maintenance planshould be provided as part of the system plan ordesign.

Water delivery should be adaptable to meet specificcrop water needs for each irrigation system used.Basic components of distribution systems includepipelines, unlined and lined open ditches, water con-trol structures, water measurement devices, tailwaterrecovery and reuse facilities, system automation,pumping plants, surface drainage systems, and chemi-cal storage, injection and transport facilities.

Design criteria, procedures, friction loss tables andcharts, and design examples are provided in manyNatural Resources Conservation Service (NRCS)references. These references include National Engi-neering Handbook (NEH) Part 634 (Section 3), Hy-draulics; NEH Part 623 (Section 15), Irrigation; Na-tional Engineering Field Handbook, Chapters 3, Hy-draulics, and 15, Irrigation; and several design notesand technical releases. Many programmable calculatorand computer programs are also available to assist inthe design of pipelines, open ditches, and pumpingplants. References, tools, and programs most com-monly used are included in 652.0710, State Supple-ment, and in Chapter 15, Resource Planning andEvaluation Tools and Worksheets.

652.0701 Pipelines

Pipeline delivery systems can be pumped or gravityflow and consist of buried pipe, surface installed pipe,or both. A buried pipe can extend from a water sourceto the farm and to individual fields with surface pipeused for distribution within the field. Buried pipe canalso extend into fields as a field main (or submain) andhave risers and valves appropriately spaced to deliverwater to surface ditches, portable water conveyancepipelines, gated pipe, or sprinkler laterals.

(a) Typical pipe installation andmaterials for irrigation sys-tems

(1) Culverts

Culverts are generally short pipe sections wherepartial pipe flow conditions exist.Typical use includes:

• Equipment crossings in open channels (canals,laterals, ditches)

• Water control structures with flow control gateinstallation

• Water measuring

Materials are generally galvanized steel or aluminumcorrugated pipe; PVC plastic pipe; corrugated PE(regular or smooth bore) plastic pipe; and reinforcedor nonreinforced concrete pipe.

(2) Gravity pipelines

Generally gravity pressure pipelines are longer pipesections where full pipe flow, partial pipe flow, or acombination of both conditions exist. They rely onelevation drop to provide sufficient hydraulic gradientfor flow to occur. Gravity pipelines are used to trans-port water in a conveyance or distribution system, orfrom a source to point of use, as buried or surface,permanent or portable pipes. Typical use includes:

• Water conveyance pipelines to reduce seepageand evaporation losses, prevent erosion, orprovide control of water delivery.

• Inverted siphons to replace flumes or to crosslow areas including gullies.

• Gated pipe to distribute water into furrows.• Pipelines to provide gravity pressure for sprin-

kler or micro irrigation systems.




Materials are generally plastic, welded steel, galva-nized steel, reinforced or nonreinforced concrete,reinforced fiber glass, or aluminum.

(3) Pumped pressure pipelines

Pumped pressure pipelines can be buried or surfaceinstalled. Generally longer sections are used where fullpipe flow conditions exist and shorter sections wherewater is pumped from a source (pond, canal, stream,well) to an open ditch that is close by. A pump is usedto provide adequate pressure head to overcome eleva-tion and pipe and fitting friction losses. Pipelines canbe permanent or portable. They are used to transportwater in a conveyance and distribution system or fromsource to point of use. Typical use includes:

• Pipe within a pumping plant system that liftswater from source to open ditch or field.

• Conveyance and distribution system.• Pipelines to contain pressurized flows for use in

sprinkler and micro irrigation systems.

Materials are generally welded steel, galvanized steel,aluminum, or plastic.

(b) Specific applications

Gated pipe is a surface portable pipe (generally PVC oraluminum) used to distribute controlled flows tofurrows at very low pressure head (< 1 to 2 lb/in2).Disposable, thin wall (7 or 10 mil), lay-flat PE pipe isalso available. Its use is generally limited to 1 or 2years. With the pipeline filled with water, a handpunch mounted on a handle, approximately 2 feetlong, is moved in an arc to create holes (or gates) ateach furrow. Hole sizes are selected to dischargepredetermined amounts of water at each furrow,based on head available in the pipeline. Pipelinegrades can be established where only two or threehole sizes are necessary in a quarter-mile pipeline.Maximum head (pressure) in lay-flat PE pipe must beless than 10 feet (4 psi).

Gated pipe can be used in place of an open head ditchat the upper end of a field. It is also well suited to usein place of an intermediate temporary head ditch onfields too long to be irrigated in one length of run.Socks or other devices attached to each gate help toreduce exit velocities; thereby minimizing erosion atthe head of furrows. The degree the gates are openedaccurately regulates water flow to each furrow. Where

water source to the gated pipe is from open ditches,screening for debris removal may be necessary toprevent plugging of gate openings. Gated pipe is usedin cablegation and surge systems. Once gated pipe isinstalled at the head of the fields for the duration ofthe irrigation season and the gates are adjusted, addi-tional labor is rarely necessary.

The most common problem with gated pipe is havingexcess pressure head. Excess pressure head acceler-ates pipeline leakage at the joints and furrow erosionimmediately downstream of gates. Easy to installdevices are available to reduce pressure head. Thesecan be installed inside the pipe as controllable lowhead gates or outside the pipe as flow-through standsor boxes.

When disposable PE pipe is used, the pipeline is laidout, filled with water, and predetermined sized holespunched for each irrigated furrow. When reinforcedPVC lay-flat pipe is used, adjustable gates can beinserted in the holes. Typically two or more hole sizesare required across the field to deliver a design flowrate to each furrow (or border strip). Very low pres-sure head is used in the pipelines, thus friction lossand elevation differences become critical.




653.0702 Open ditches

Open ditches are typically open channels of geometriccross sections used to carry irrigation water to itspoint of use. These ditches should be of adequate sizeand installed on nonerosive grades. Small, inadequateditches that do not have proper water control struc-tures and maintenance probably are the source ofmore trouble and consume more time in operating asurface irrigation system than any other cause.

Open channels that carry irrigation water from asource to one or more farms are typically referred toas canals and laterals; and are generally permanentinstallations. Field or farm ditches convey and distrib-ute water from the source of supply (canals, laterals,wells) to a field(s) within a farm. Most are permanentinstallations except where they are used within a longfield to shorten length of runs, where excessive sedi-ment is in irrigation water, or where crop rotationsrequire differing field layouts. In these cases they areinstalled at planting time and removed before orfollowing harvest.

Head ditches are used to distribute water across thehigh end of a field for surface irrigation, typicallyperpendicular to the direction of irrigation. Theyprovide water for all surface irrigation systems includ-ing basin, border, furrow, corrugations, contour ditch,and contour levee. The water surface in head ditchesshould be high enough above the field surface toallow design discharge from outlet devices under allconditions. Outlets installed too high can cause soilerosion, which in turn requires correction.

Outlet devices may be siphon tubes, notches or cut-outs, gated ports or pipes (spiles), or gated structures.Notches or cutouts require less head to operate thansiphon tubes; however, variation in flow caused bywater surface elevation change can be greater. Siphontubes require at least 4 to 6 inches head differencebetween the water level in the ditch and field, with 8to 10 inches recommended. If possible, head ditchesshould be nearly level so that water can be checkedfor maximum distances, thus requiring fewer checkdams and less labor. Good workable grades are 0.05to 0.2 foot per 100 feet.

Field ditches work best and require less maintenancewhen constructed in medium to fine textured soils.Seepage is typically low, and banks are more stableand are easier to build and maintain. Vegetation andburrowing animals can cause problems with any soil.Open ditches take up valuable space and can hinderfarm operations. Maintenance requirements are muchhigher than those for pipelines.

Open ditches, laterals, and canals can provide goodhabitat for a variety of wildlife. Keeping ditches clearof vegetation requires less overall maintenance, butlimits wildlife cover and food. Herbicides are some-times not friendly to wildlife and their food supply.Well vegetated ditchbanks can help prevent soilerosion and at the same time be good habitat forseveral varieties of upland game birds.

(a) Unlined ditches

Seepage is generally not a problem in medium to finetextured soils; however, erosion and downstreamsediment deposition can occur if soils are erosive. Incoarse textured soils, seepage can be a big problem.Delivery and field ditches are generally installed andcleaned with a V-ditcher mounted on or pulled by afarm tractor. Larger ditches can be constructed andmaintained using backhoe type equipment or smallfront-end loaders.

Water measuring and control using unlined ditches isless convenient and sometimes difficult. Portableplastic or canvas dams are generally used to raise thewater elevation for diversion onto a field. Typicallyportable plastic or canvas dams have a useful life of 1year.

(b) Lined ditches

Seepage, erosion and bank stabilization problems inmedium to coarse textured soils can be controlledwith ditch linings. The lining material used depends onclimate (temperature extremes, freezing and frostheave potential), soil conditions, on-farm livestock,local area wildlife, such as deer, installation cost, andmaintenance. Improved water control on the down-stream end of head ditches can be reason enough toinstall ditch lining material.




Ditch lining materials include compacted soil, highexpanding colloidal clay (bentonite), hand formednonreinforced or reinforced concrete, slip formednonreinforced concrete, pneumatic applied concretemortar (gunnite), cold spray-applied membrane, andflexible membranes of plastic, elastomeric, or butylrubber. Flexible membranes should be protected fromphysical damage and ultraviolet light by covering withaggregate or soil. Flexible membranes with concreteor aggregate protection can be installed underwater ifthe water velocity is less than 5 feet per second.

The suitability, limitations, and general installationrequirements of lined ditches are described in moredetail in NEH, Part 623 (Section 15), Chapter 3, Plan-ning Irrigation Systems. Design criteria, installationrequirements, and material specifications for the mostcommon linings are detailed in the National Handbookof Conservation Practices and other references.

(c) Seepage losses

Methods used to determine conveyance efficiency andestimate seepage losses from open ditches include:

• Measuring inflow and outflow in specific reachesusing existing or portable measuring devices,such as weirs, flumes, or current meters.

• Using controlled ponding and measuring the rateof water level drop.

• Using seepage meters, such as a portable con-stant-head permeameter.

• Estimating losses based on characteristics of thebase material.

Controlled ponding is one of the most accurate meth-ods, but must be done during a non-operation period.It requires installation of small dams to isolate thestudy area. Ponding must begin above the normalwater surface elevation and continue below the nor-mal elevation of operation. At the normal water sur-face, the volume of water lost (usually cubic feet) canbe converted to a rate per hour (or minute) per squarefoot of wetted ditch perimeter.

Accuracy of the inflow-outflow method depends onaccuracy of flow measuring devices and is generallylimited to longer reaches. However, seepage can bemeasured during operation periods.

Estimating seepage losses in the delivery system isdescribed in more detail in NEH, Part 623 (Section 15),Chapter 2, Irrigation Water Requirements. A range ofexpected seepage losses, depending on the base mate-rial in the ditch, lateral or canal, is provided. The rangeis dependent on the amount of fines in the soil.




652.0703 Water controlstructures

Water control structures are an integral part of thefarm distribution system. These structures are typi-cally constructed to help assure proper delivery anddistribution of water supply, to prevent erosion, and tokeep water losses to a minimum. Adequate watercontrol structures also reduce labor. They includewater measuring devices, an essential part of efficientwater application and use. The type of structures andmaterials adaptable are dependent on climate, siteconditions, water delivery system, irrigation systemused, and cost of installation and maintenance. Watercontrol structures are described in more detail inNEH, Part 623 (Section 15), Chapter 3, Planning FarmIrrigation Systems; National Engineering Field Hand-book, Chapter 15; and National Handbook of Conser-vation Practices, FOTG (Section 4).

(a) Related structures for openditches

Where open ditches are used to deliver water to sprin-kler, surface, or subirrigation systems, structures aretypically needed to screen and remove trash anddebris, settle and remove sediment, measure flow,divide water, control grade for erosion protection atgated flow turnouts and ports, for spill and overflow,ditch checks, and pipeline inlets and outlets. Sometype of structure may be needed to carry water acrossdepressions or drains and under roadways or otherobstructions. Flumes, inverted siphons (sag pipes),and culverts are the most commonly used structuresfor these purposes.

(1) Flumes

Flumes are channels constructed from metal, wood,concrete, or plastic. They are used to:

• Control water through a short channel reach; i.e.,water measuring flume ditch check.

• Transport water across landscape depressions.• Transport water across high seepage or unstable

areas.

Flumes can be supported directly on earth or by aconcrete, metal, or wood substructure. Flume capacityis usually determined by the flow capacity of the ditch.The foundation and substructure are designed tosupport full flume conditions even though normal flowrates are less. Flume channels can be any shape, butare typically rectangular, half round, or full diameterpipe. Hydraulically, all operate as open channels.Properly designed welded steel and corrugated metalpipe can be used to span short distances instead ofproviding a continuous substructure.

(2) Siphons

Siphons are used to carry water over low rises on thelandscape or other obstructions. For flow to occur thenet hydraulic gradient must be positive, includingentrance head, pipeline friction, and outlet headlosses. Maximum allowable rise is determined bylocation of the site above mean sea level. In all practi-cality, elevation differences should be no more than 5to 10 feet, with both ends of the siphon either coveredby water or controlled with a valve.

A vacuum pump can be used to prime the siphon andexhaust accumulated air during operation, thus main-taining siphon capacity. Air must be exhausted, butnot allowed to enter the conduit. Siphon design watervelocities should be 2 to 3 feet per second.

Slow velocities can be a problem in siphons. Negativepressures cause dissolved air to release and collect atthe high point of the siphon. The increased size of theair bubble causes reduction in flow by reducing theeffective cross section area of the pipe. Ultimately, thesiphon may cease operation. High velocities help carrydissolved air on through the siphon or at least give lessresidence time in the negative pressure zone. Multipleindividually controlled pipelines that are small indiameter may be desirable rather than one largerpipeline. Operating as few pipelines in the group aspossible is suggested where flows are low. This helpsmaintain higher pipeline velocities.

Available alternatives to using a siphon should beseriously considered because construction require-ments are high and continuous high maintenance isrequired. If energy is available, high volume propelleror axial flow pumps are generally preferred.




(3) Inverted siphons

Inverted siphons (sometimes called sag pipes) areclosed conduits used to carry water across depres-sions in the landscape. They can be installed on mul-tiple foundations above the ground surface or can beburied. Inverted siphons can also be used to crossunder roadways, pipelines, and other obstructions. Forflow to occur the net hydraulic gradient must bepositive, including entrance head, pipeline friction,and outlet head losses. To prevent freezing damage incold climates, drainage of the conduit during wintermonths should be considered. Inverted siphons differfrom flumes in that some part of the siphon operatesunder a pressure head.

(4) Culverts

Culverts are conduits installed at or slightly belowditch grade and are commonly used to carry waterunder farm roads or field access points. They aretypically corrugated metal pipe (CMP), welded steelpipe, concrete pipe, or plastic pipe. Either full orpartial pipe flow conditions occur, depending ondesign and installation. To increase flow area at shal-low depths, a larger circular pipe installed below grademay be more desirable than a pipe of elliptical (pipearch) cross section or multiple pipes on grade. Wherepipeline velocities are greater than 2 feet per second,the full pipe diameter can be considered as the effec-tive hydraulic cross section. Where pipeline velocitiesare less than 2 feet per second, or to be more conser-vative, assume the below grade portion of the pipe issilted full.

(5) Grade control structures

Where the ditch grade is such that the design flowwould result in an erosive velocity, some protectivestructure, such as a chute spillway, drop spillway, orpipe drop (or canal lining), is necessary. These struc-tures control velocity in the ditch by dropping thewater abruptly from a higher elevation to a lowerelevation in a short protected distance. They can alsoserve as a ditch crossing (if designed as such) or watermeasuring device. With grades exceeding 2 to 3 per-cent, such alternatives as a pipeline or lined ditchshould be considered. In all cases unstable flows(including hydraulic jumps) must occur within thestructure.

(6) Distribution structures and devices

Distribution control structures are necessary for easyand accurate division of irrigation water to fields on afarm or to various parts of a field. These structuresmay consist of:

• Division boxes to direct flow of water to two ormore pipelines or ditches.

• Check structures that raise the elevation of thewater surface upstream so that water can bediverted from the ditch onto a field.

• Turnout structures to divert part or all the irriga-tion stream to a selected part of the irrigatedarea.

Each water division structure should provide flowmeasurement on every outlet. Calibrated flow crosssections or standard water measuring weirs andflumes can be used. Little cost increase is incurredwhere the measuring device is designed and installedas a part of the initial structure.

Various devices are used for controlling and discharg-ing water into each furrow, basin, or border. For basinand border systems, outlet control devices are gener-ally either flashboard structures, gated structures,short gated pipe, or large diameter siphon tubes.Where large flows are used, erosion protection at thestructure outlet is generally needed. Where watervelocities within the structure are appropriate toprevent sedimentation, outlets can be installed belowfield grade. Excess energy is absorbed as water raiseswith the structure (apron or pipeline).

For furrow systems, near equal flow should be deliv-ered to each furrow. The most commonly used outletsare siphon tubes or gated spiles or pipe. To changeflow, only the slides on gates need to be adjusted orthe water level can be raised or lowered at the up-stream or downstream end of the siphon tube. Flowrate in siphon tubes results from head (elevation)difference in upstream and downstream water levels.Where the outlet end of a siphon tube is above thewater surface in the furrow, the pipe centerline eleva-tion of the tube outlet becomes the downstream waterlevel. Two smaller diameter siphon tubes are fre-quently used for each furrow. This allows one to beremoved to cutback or reduce flow in a furrow wherethe advance rate is excessive (such as wheel com-pacted or hard furrows).




Cutback flows can also be achieved by raising theoutlet end of the siphon tube (generally by inundatinga larger part of the siphon tube), thereby reducing theavailable head on the tube. However, the irrigationhead or ditch flow must be reduced, the additionalwater must be bypassed, or additional siphon tubesmust be set. When additional tubes are set, a newirrigation set start time and end time are established.They then need to be cut back, and the extra waterreset, and so forth.

(b) Related structures for gravitypipelines

Where gravity flow pipelines are used to distributewater to surface or subsurface irrigation systems or tohelp pressurize sprinkler irrigation systems, structuresare typically needed for:

• Trash and debris removal, and perhaps waterscreening (or filtering)

• Pipeline inlet and outlet• Flow measurement• Miscellaneous valves, such as flow control, air

release, vacuum relief, pressure regulation, andsurge control

• Head control for gated pipe, cablegation, andsurge systems

• Drains

(c) Related structures for pumpedpipelines

Where pumped pipelines are used to distribute waterto surface, sprinkler, micro, and subirrigation systems,structures are typically needed for pumping plantinlets (including trash and debris removal), waterscreening (filtering), flow measurement, drains, surgeblocks, and valves, such as pressure regulation, airrelease, vacuum relief, and flow control.

Standard drawings for water control structures

should be used whenever and wherever possible.

Materials used in water control structures includecast in place concrete, concrete or cinder blockmasonry, grouted rock riprap, steel (painted, galva-nized, glass coated), aluminum, treated or nontreatedwood, and plastic. Nonstructural concrete or cinderblock masonry structures can be installed withoutmortar if every hole is filled with mortar and a #3 (3/8inch) reinforcing bar is used to help maintain verticalalignment. Horizontal reinforcement (i.e., K web) withmortar, is provided every 16 to 24 inches of height. Anextended reinforced concrete structure floor providesfootings (foundation) for stacked blocks. Numberthree or larger reinforcing bars extend out of thefoundation into the first two or three layers of blocks.For aesthetics, exposed areas can be plastered withmortar.

Durability, installation and maintenance costs, aesthet-ics and environmental compatibility, ease of use, farmlabor skills, and availability of materials are all neces-sary considerations for designing these related struc-tures. Many standard drawings are available for watercontrol structures. See section 652.0710, State supple-ment, for standard drawings and design procedures.




652.0704 Water measure-ment

A method of measuring water flow onto a field is animportant part of every irrigation system. As the demandfor water and energy increases, the need for moreefficient use of water increases. Water measurement isessential for equitable distribution of the water supplyand for efficient use on the farm. Knowing how much

water is applied is essential for proper irrigation watermanagement. Flow measurement has other uses; forexample, they can indicate when a pump impeller isbecoming worn and inefficient or when well dischargebecomes reduced. Flow changes can also indicateclogged screens or partly closed or plugged valves.Water rights and use requirements increasingly specifythat measuring devices be installed.

The most common methods of water measurementand the equipment or structures are described ingreater detail in NEH, Part 623 (section 15), Chapter 9,Measurement of Irrigation Water; the ASAE publica-tion Flow Measuring Flumes for Open Channel Sys-tems written by Bos, Replogle, Clemmens in 1991; andthe U.S. Bureau of Reclamation’s interagency 1997publication of the Water Measurement Manual. USDANRCS and Agricultural Research Service providedinput to this publication to make it state-of-art in flowmeasurement. Publication is late 1997.

Common measuring devices are further described

in chapter 9 of this guide. Units of flow rate andflow volume commonly used are cubic feet per second(ft3/sec), gallons per minute (gal/min), gallons per hour(gal/hr), million gallons per day, acre-inches per day,acre-feet per day, miners inches, head of water, acresof water, feet of water, shares, acre feet, acre inches,and inches of water. Head or depth units commonlyused are feet, tenths and hundredths of feet; andinches and tenths of inches.

Irrigation consultants must acquaint themselves withterms and flow units used locally and must be able toconvert to units commonly used in tables, graphs,charts, and computer programs. Many ARS, commer-cial, and university computer programs used for de-sign of irrigation system components can use eitherEnglish or metric units.

(a) Planning and designconsiderations

To accurately measure water, water measurementdevices must be installed according to requirementsspecific to that device. In addition, they must be oper-ated under the conditions for which they are designed.Maintenance must be performed as with any other partof an irrigation system. Re-calibration of some devicesmay be necessary to assure long-term continuingaccuracy.

Many types of devices can be used for flow measure-ment. The best suited device depends on accuracydesired, ease of use, durability, availability, mainte-nance required, hydraulic characteristics, ease ofconstruction, and installation cost. In some areas stateand local requirements dictate. The following methodsor devices each have their own flow equation or cali-bration process.

(1) Open ditch flow

Volumetric—Flow measurements are made by mea-suring time required to fill a known volume.

Submerged orifices—Sharp edged orifices of vari-ous shapes and sizes can be used. Head differential ofwater surface upstream and downstream causes flowthrough the orifice. Flow is calculated using standardorifice flow equations. The orifice flow “Coefficient”for many types of orifices has been determined experi-mentally.

Weirs—Sharp crested (Cipolletti, 90° V-notch, rectan-gular) and broad crested (Replogle). Flow depth(head) is measured upstream of crest. Crest width(opening width) can be either standard to fit previ-ously prepared tables or measured, and flow is calcu-lated using standard equations. Sharp crested weirsmust meet criteria for the specific type (typically 1/8inch). Tables are readily available for standard crestwidths. Head loss across sharp crested weirs is high,often several inches or feet. Where installation andoperation meet standard, accuracy can be within 5percent of actual.

The broad crested weir (sometimes called a Replogleflume) is the easiest to install of any weir or flume andcan accurately measure water with as little as 1 inch ofhead loss. There is only one critical surface and it islevel in all directions. However, a short section of




lined ditch or flume is required (plus or minus 10 ft).With a stilling well, accuracy can be within 2 percentof actual. Well designed and constructed shaft gaugesare typically within 5 percent of actual. Only one flowmeasurement depth is required.

Flumes (Parshall, WSC, cutthroat, or V-notch)—

Head is measured, crest width is standard or measur-able, and flow is calculated using standard equations.Tables are readily available for standard widths. Mea-surement is fairly accurate at near submerged flowcondition; however, measurement of flow depth bothupstream and downstream of the control section isrequired. Accuracy can be within 5 percent of actual.Because of the numerous critical surfaces, theseflumes can be difficult to construct. Since flow mea-suring accuracy is no better (and often worse) theseflumes are no longer recommended. The Replogleflume should be used.

Current meter—Actual flow velocity at variouspoints and depths (typically .6 or .2 and .8) within theflow cross-section is measured. Flow is calculatedbased on

Q A V=

Repeated measurements are typically taken at eachmeasuring location. Technique and practice are impor-tant to keep accuracy within 10 percent of actual.

Velocity head rod (jump stick)—Rise in watersurface elevation is measured when a standard rod isplaced in the water flow path with the narrow side andthen the flat side facing upstream. The difference inwater surface level represents velocity head. Velocity(V) is calculated from:

V g h= ( )21

2

Flow is then calculated using Q=AV, wherein A is theflow area represented by each velocity and segmentsare accumulated to present the total flow.

Float method—Surface flow velocity and flow cross-section are measured, then flow rate is calculatedusing:

Q C A V=

where:C = coefficient of discharge calibrated for site

conditions, typically 0.80 to 0.95

Rated sections—A staff gage is provided to indicateflow depths. Velocity at various depths is measuredusing a current meter. Flow is calculated using Q = AV.A depth versus flow rate curve is developed for eachspecific cross section; thereafter, only flow depth ismeasured. Accuracy depends on technique and consis-tency of the technician taking readings.

(2) Pipe flow

Flow meters (propeller, impeller)—Flow metersare volumetrically calibrated at the factory for variouspipe diameters. Accuracy can be within 5 percent ofactual if meter is well maintained and calibratedperiodically. Annual maintenance is required. Debrisand moss collect quite easily on the point and shaft ofthe impeller causing malfunction. Therefore, somedegree of screening for debris and moss removal maybe necessary.

Differential head meters—These meters includepitot tube, shunt flow meters, and low head venturimeters. Pressure differential across an obstruction ismeasured, thus providing velocity head. Flow is calcu-lated using Q = AV. Coefficients provide for improvedaccuracy.

Orifice plates—Pressure head upstream and down-stream of an orifice of known cross section is mea-sured. Flow is calculated using Q = AV. Coefficientsprovide for improved accuracy.

Ultrasonic meters—These meters measure changesin sound transmission across the diameter of the pipecaused by the flowing liquid. They are generally highcost and are most often used only in permanent instal-lations. Some types work well only with turbid water(doppler). Others (transit time) work best in cleanwater. Portable sonic meters are available, but requirea high degree of technology to operate them satisfacto-rily on different pipe diameters and materials. Fre-quent calibration can be required.




652.0705 Irrigation run-off, tailwater recovery andreuse

Tailwater recovery and reuse (pumpback) facilitiescollect irrigation runoff and return it to the same,adjacent, or lower fields for irrigation use. Such facili-ties can be classified according to the method ofhandling runoff or tailwater. If the water is returned toa field lying at a higher elevation, it is referred to as areturn-flow or pumpback facility. If the water is ap-plied to adjacent or lower-lying field, it is termedsequence use. In all cases runoff is temporarily storeduntil sufficient volume has accumulated to optimizeapplication efficiency on each succeeding irrigationset.

Components consist of tailwater ditches to collect therunoff, drainageways, waterways, or pipelines toconvey water to a central collection area, a sump orreservoir for water storage, a pump and power unit,and a pipeline or ditch to convey water for redistribu-tion. Under certain conditions where gravity flow canbe used, neither a pump nor pipeline is necessary.

(a) Planning and design consider-ations

(1) Storage

A tailwater collection, storage, and return flow facilitymust provide for temporary storage of a given amountof water. It includes the required pumping equipmentand pipeline or ditch to deliver water at the appropri-ate rate to the application system. A sequence systemshould have storage, a pump, and only enough pipe toconvey water to the head ditch of the next adjacent ordownslope field. It may be possible to plan the facilityso there is enough elevation difference between fieldsto apply runoff water to a lower field by gravity with-out pumping. Only the lowest field(s) requirepumpback or have tailwater runoff.

Recovery facilities may also be classified according towhether or not they accumulate and store runoffwater. Facilities storing precipitation and irrigationrunoff water are referred to as reservoir systems.Reservoirs can be located either at the lower end of

the field or at the upper end. Facilities that return therunoff water for direct irrigation require the leaststorage capacity. They have automatically cycledpumping and are termed cycling-sump facilities.

One or more types of recovery systems may be appli-cable to a given farm. A sump is used where land valueis high, water cannot be retained in a reservoir, orwater ponding is undesirable. Dugouts or reservoirsare more common and most easily adapted to storageand planned recovery of irrigation tailwater. Hydrauli-cally, only tailwater runoff from one irrigation setneeds to be stored. Storing water from a maximum oftwo irrigation sets improves management flexibility.Figure 7–2 displays a typical plan for tailwater recov-ery facility involving a pumpback system.

Cycling-sump facilities require more intensive watermanagement. When cycling begins, the furrow ad-vance phase should begin, otherwise additional fur-rows must be started. One option is to reduce theincoming water supply by the amount equivalent to thereturn rate being added.

Reservoir facilities tend to increase irrigation effi-ciency while decreasing management intensity require-ment. Reservoir tailwater reuse facilities collect

Figure 7–2 Typical tailwater collection and reuse facilityfor quick-cycling pump and reservoir

Inlet Collector ditch

Regulatingreservoir

Watersupply

Headditch

Sump &pump

Returnpipeline




enough water to use as an independent supply or as asupplement to the original supply. Thus they have themost flexibility. The reservoir size depends on whethercollected water is handled as an independent supplyand, if not, on the rate water is pumped for reuse.

Tailwater reuse reservoirs should be at least 8 feetdeep, preferably 10 feet deep, to discourage growth ofaquatic weeds. For weed control, side slopes of 2 or2.5 feet horizontal to 1 foot vertical are recommended.Some soils require flatter slopes to maintain stability.A centrally located ramp with a slope of five to one(5:1) or flatter should be provided for wildlife, eitheras access or for exiting after accidentally falling in.The reservoir should remain nearly full when not inuse to help assure a positive hydraulic gradient forreservoir sealing. At least 2 feet of water depth shouldremain in the reservoir to provide pump intake sub-mergence, protect the reservoir bottom seal, andprovide water for wildlife. Tailwater inflow must enterthe reservoir at or near the pump intake. Most sus-pended sediments return to the upper end of the fieldinstead of settling in the reservoir.

(2) Pumps

Cycling-sump facilities consist of a sump and pumplarge enough to handle the expected rate of runoff.The sump is generally a vertical concrete or steelconduit with a concrete bottom. The conduit is about 6to 10 feet deep when placed on end. Pump operation iscontrolled automatically by a float-operated or elec-trode-actuated switch. Some storage can be providedin the collecting ditch or pipeline upstream of thesump.

The size, capacity, location, and selection of equip-ment for these facilities are functions of the selectedirrigation system, topography, layout of the field andthe water users irrigation management and desires.

Many different low head pumps are used with tailwa-ter reuse facilities. Pumps include single stage turbine,horizontal centrifugal (permanent or tractor driven),submerged vertical centrifugal, and propeller or axialflow pumps. Pumping heads are generally low, conse-quently energy requirements are low (5 to 10 hp), evenfor reasonably high flow rates. Tractor driven pumpsare typically overpowered.

Caution should be used when selecting pump andpower unit size. For example, in a cycling-sump facil-ity the lowest continuous pumping rate that will main-tain the design flow rate should be used. For reservoirtype facilities where water is delivered from a tailwa-ter sump directly to the head ditch, it is better to pumpat a high rate for the first part of an irrigation set (todecrease irrigation advance time). Pumping efficien-cies can be in the range of 20 to 75 percent, dependingupon the type and size of pump selected, the powerunit used, and pump inlet and outlet conditions. Somedegree of screening at the pump inlet is generallyrequired. In all cases, irrigation water managementshould optimize use of water, labor, and energy.

(3) Sizing for runoff

Runoff (RO) flows must be measured or estimated toproperly size tailwater reuse sumps, reservoirs, andpumping facilities. Table 7–1 displays expected recov-ery in gallons per minute based on irrigation head orinflow and expected runoff. Expected recovery andreturn to the head of the irrigation system is based on65 percent of the runoff. Seepage, evaporation, over-flow, and miscellaneous losses occur in a recovery,storage, and pumpback system. An irrigation systemevaluation should be used to determine runoff. Anexample of a tailwater recovery and pumpback facilityfollows:

Furrow flow analysis gives runoff RO = 35%Irrigation head (inflow) Qi = 1,000 gpmExpected recovery at peak runoff Qr = 228 gpm

Use this recovery flow to size transport and storagefacilities. In addition, capacity should be provided tohandle concurrent peak runoff events from bothprecipitation and tailwater, unexpected interruption ofpower, and other uncertainties. Where a reservoir,recovery pit, or dugout is used, it should have thecapacity to store the runoff from one complete irriga-tion set. Pump capacity will be dependent on themethod or schedule of reuse planned. Table 7–2 pro-vides data for sizing tailwater reservoirs and sumpsbased on desired pump peak flow and desired set time.Overall irrigation efficiencies obtainable by usingtailwater recovery facilities are listed in table 7–3.

Where irrigation tailwater cannot enter at or near thepump, a small collection basin installed at the inlet tothe storage reservoir is more desirable than allowingsediment to collect in the reservoir. The basin can be




cleaned easily with available farm machinery, while alarge pit requires cleaning with contractor-sized equip-ment. Either way, sediment storage must be provided.Generally when an irrigation water user sees howmuch sediment accumulates, erosion reduction mea-sures are taken. They readily relate to costs involvedin removal.

Examples of determining recovery volume and storagecapacity for tailwater recovery and reuse systemsusing tables 7–1 and 7–2 follow:

Given: Inflow = 1,000 gpm @ 12 hour set timeOutflow = 40 %

Table 7–1 Expected recovery from runoff 1/

Inflow - - - - - - - - - - - - - - - - - - - - - - - - Estimated runoff, Qr (gpm) - - - - - - - - - - - - - - - - - - - - - - - - -Qi (gpm) 20% 25% 30% 35% 40% 45% 50%

150 20 24 29 34 39 44 49200 26 33 39 46 52 59 65300 39 49 59 68 78 88 98400 52 65 78 91 104 117 130500 65 81 98 114 130 146 163

600 78 98 117 137 156 175 195700 91 114 137 159 182 205 228800 104 130 156 182 208 234 260900 117 146 176 205 234 263 2931,000 130 163 195 228 260 293 325

1,200 156 195 234 273 312 351 3901,400 182 228 273 319 364 410 4551,600 208 260 312 364 416 468 5201,800 234 293 351 410 468 527 5852,000 260 325 390 455 520 585 650

2,200 286 358 429 501 572 644 7152,400 312 390 468 546 624 702 7802,600 338 423 508 592 676 671 8452,800 364 455 546 637 728 819 9103,000 390 488 585 683 780 878 975

1/ Note: Estimated runoff is that amount of water that normally runs off the end of the furrows orborders. This flow rate can be arrived at by field measurement or from judgment based on soil orfield intake characteristics, inflow rates, field slope, length of run, method of irrigation, and irrigator’sability. Irrigation inflow is the amount of irrigation water (or head) used for the irrigation set.

Solution: From table 7–1:Recovery = 260 gpm.This would be the expected flow for acontinuously operating pumpback facility.

Given: Inflow = 1,000 gpm @ 12 hour set timeDesired pumpback flow 500 gpm @ 12hour set

Solution: From table 7–2:Volume of storage = 2,000 ft3.This would be the expected storageneeded for an intermittent pumpbackfacility.




Table 7–3 Overall efficiencies obtainable by using tailwater recovery and reuse facility

Original % of - - - - - - First reuse - - - - - - - - - - - Second reuse - - - - - - - - - - Third reuse - - - - - - - - - - - Fourth reuse- - - - -applic water % of Effect Accum % of Effect Accum % of Effect Accum % of Effect Accumeffic reused orig use - effect orig use - effect orig use - effect orig use - effect

water % of water % of water % of water % of% used orig % used orig % used orig % used orig %

60 40 16 9.6 69.6 2.6 1.5 71.1 1.1 0.7 71.8 0.2 0.1 71.960 24 14.4 74.4 5.8 3.5 77.9 1.4 0.8 78.7 0.4 0.2 78.980 32 19.2 79.2 10.2 6.1 85.3 3.3 2.0 87.3 1.0 0.6 87.9

50 40 20 10.0 60.0 4.0 2.0 62.0 0.8 0.4 62.4 0.2 0.1 62.560 30 15.0 65.0 9.0 4.5 69.5 2.7 1.4 70.9 0.8 0.4 71.380 40 20.0 70.0 16.0 8.0 78.0 6.4 3.2 81.2 2.6 1.3 82.5

40 40 24 9.6 49.6 5.8 2.3 52.9 1.4 0.6 53.5 0.3 0.1 53.660 36 14.4 54.4 13.0 5.2 59.6 4.7 1.9 61.5 1.7 0.7 62.280 48 19.2 59.2 23.0 9.2 68.4 11.0 4.4 72.8 5.3 2.1 74.9

30 40 28 8.4 38.4 7.8 2.4 40.8 2.2 0.7 41.5 0.6 0.2 41.760 42 12.6 42.6 17.8 5.3 49.9 7.5 2.3 52.2 3.1 0.9 53.180 56 16.8 46.8 31.4 9.4 56.2 17.6 5.3 61.5 9.8 3.0 64.5

20 40 32 6.4 26.4 10.2 2.1 28.5 3.2 0.7 29.2 1.0 0.2 29.460 48 9.6 29.6 23.0 4.6 34.2 11.0 2.2 36.4 5.3 1.1 37.580 64 12.8 32.8 41.0 8.2 41.0 26.2 5.3 46.3 17.5 3.5 49.8

Table 7–2 Tailwater pit sizing for intermittentpumpback facility 1/

Pumpback - - - - - - - - - - - - - - - Length of set - - - - - - - - - - - - - -flow (gpm) 6-hour 8-hour 12-hour 24 hour

- - - - - - - - - - - - - - - ft3 - - - - - - - - - - - - - - -

100 200 267 400 800200 400 533 800 1,600300 600 800 1,200 2,400400 800 1,067 1,600 3,200500 1,000 1,333 2,000 4,000600 1,200 1,600 2,400 4,800700 1,400 1,867 2,800 5,600800 1,600 2,133 3,200 6,400900 1,800 2,400 3,600 7,2001,000 2,000 2,667 4,000 8,0001,100 2,200 2,933 4,400 8,800

1/

This includes a 10 percent safety factor.




652.0706 Irrigationsystem automation

Automated irrigation systems reduce labor, energy,and water input while maintaining or increasing irriga-tion efficiency. Automation is the use of mechanicalgates, valves, structures, controllers, and other devicesto automatically divert water into an operating irriga-tion system to satisfy the water requirement of agrowing crop.

Research and development by ARS, state experimentStations, and industry have produced successfulstructures, controls, computer software, and otherdevices to automatically control irrigation water.However, automated irrigation (with the exception ofmicro and solid set sprinkler) use is limited. Newtechnology, including automation, is adopted onlywhen the irrigation water user views the real (orperceived) risk as being equal to or less than thecurrent procedure being used. Commercially producedsystems and components are currently available.

The increasing cost of power for pumping and irriga-tion labor is increasing water users’ interest in ways ofreducing costs. Automation of surface and sprinklersystems is one consideration. Many irrigators whoconsider switching from surface irrigation to sprinklerirrigation have continued with surface methods toreduce or eliminate pumping costs. All irrigationsystems that apply water by surface, sprinkler, subsur-face, and micro irrigation methods can presently beautomated to some degree. A high potential exists toincrease irrigation efficiencies through improvedirrigation water management using existing irrigationsystems. Reduced labor and increased production areadded benefits.

(a) Planning and design consider-ations for automation

Automated irrigation systems and their associatedcomponents are classified as either automatic orsemiautomatic.

(1) Automatic systems

Fully automated irrigation systems normally operatewithout operator attention except for calibration,periodic inspections, and routine maintenance. Theirrigator determines when or how long to irrigate andthen turns water into the system and starts pro-grammed controllers to initiate the automated func-tions.

Fully automated systems typically use either soilmoisture sensors or computer processed climatic datato activate electric or pneumatic controlled switchesand valves. Soil moisture sensors send a signal to acentral controller when soil water has been depletedto predetermined levels. Daily climatic data can alsobe used to signal a controller to apply irrigations.NRCS SCHEDULER is a field proven irrigation sched-uling software usable nationwide. It can be used withfully automatic, semiautomatic, and manually oper-ated surface, sprinkle, micro, and subsurface irrigationsystems.

Once irrigation has been started, water is diverted intothe farm distribution system and irrigation is com-pleted without operator intervention. Irrigation dura-tion can be controlled by programmed timers, soilmoisture sensors, or surface water sensors. Fullyautomated systems require a water supply availableessentially on demand, such as from irrigation districtcanals, private wells or reservoirs.

(2) Semiautomatic systems

Semiautomatic systems and controls require attentionduring each irrigation and are usually simpler and lesscostly than automatic systems. Most semiautomatedsystems use mechanical or electronic timers to acti-vate control structures at predetermined times. Theirrigator generally determines the beginning time andduration, then manually resets or returns the devicesto their original position. Some devices can be movedfrom one location to another before the next irriga-tion. Parts of a given system may be automatic, whileother parts are semiautomatic or manually operated.Often automation of one irrigation set change (duringthe night or offsite working hours) has nearly the samebenefits as a fully automated system and at consider-ably less cost and risk.




(3) Communications

Most automated and some semiautomated systemcomponents can be remotely controlled by centrallylocated controllers. Such systems require communica-tion between the controller and system componentslocated in the field. Communication may be by directinterconnecting electrical wires, hydraulic or pneu-matic conduits, radio or infrared telemetry, or a com-bination of these. Spurious signals and interference issometimes a problem when telemetry is used.

(4) Surface irrigation system automation

Technology is available to automate most surfaceirrigation systems; however, automation use is limited.New technology adoption by a user must have a real orperceived risk equal to or less than the method orsystem currently in use. If an irrigator cannot sleepuntil he or she personally checks to see if a valve orgate changed during the night, automation is of nobenefit.

Level basin and level furrow surface irrigation systemsare perhaps the easiest to automate. Where irrigationinflows are known application volume can be con-trolled by time. With graded furrow and graded bordersurface irrigation systems, succeeding irrigation setchanges can be initiated by the presence of free wateron the soil surface at a predetermined location downthe field.

Drop-open or drop-close gates in a short flume or linedditch can be used to control water surface elevationand location in open ditches. Gravity plus the pressureof water in the ditch operates each gate. Typically,irrigation water discharge from a supply ditch onto afield is controlled by water surface elevation in theditch and the number of openings onto the field.Ditches must be installed on a predetermined gradeand elevation so that water will be applied uniformlyto borders or to the correct number of furrows at aproper design rate. Set time is provided to allow a fullor planned irrigation to occur.

Simple electronic or windup timers can control gateoperation. A 12 volt battery (or 120 volt AC) with asolenoid can move a slide bolt initiating gate move-ment. Some batteries are kept charged by solar panels.Both drop-open and drop-close gates are actuated andsealed by the energy from water moving in the supplyditch. With drop-open gates irrigation progressesdownstream. Drop-close gates require that irrigation

proceed upstream. A 12 volt battery (or 120 volt AC)can be used (either directly or to power a pump) forelectric, hydraulic, and pneumatic opening and closingmotors and cylinders. Each irrigation head can besemiautomatic with two gate opening (closing) assem-blies. While the second assembly is operating, the firstor previous assembly is moved ahead and adjusted forthe next irrigation set.

Gates, ports, spiles, notches, or longitudinal overflowweirs can direct water onto a field. Adequate erosioncontrol is always a consideration.

Gated pipe systems, including surge and cablegation,can be automated using electric or wind-up timercontrolled valves to initiate the irrigation cycle. Thereafter, the surge or cablegation controller operates theirrigation set. Some field cross slope or fall in thegated pipeline is necessary. ARS Publication 21,Cablegation Systems for Irrigation: Description, De-sign, Installation and Performance (ARS 1985), shouldbe referenced for cablegation design. NRCS publica-tion Surge Flow Irrigation Field Guide (USDA 1986),should be referenced for surge design.

(5) Sprinkler and micro irrigation systems

Several methods of automating sprinkler and microirrigation systems are available. Center pivot manufac-turers presently have fully automatic devices includingmonitoring of climate for determining crop ET, soilmoisture monitoring, and system on-off controllers, allcontrolled with an onboard computer. Automaticsystems are available with fully automatic controllersincluding moisture sensors or time clock operation forsolid set sprinkler, micro, and greenhouse irrigationsystems.

Periodic move irrigation systems, such as side roll andhandmove systems, generally are not automated.However, a simple form of automation is timer con-trolled lateral shutdown and turn-on. With two lateralsthe dry lateral can be moved at a time more conve-nient to the irrigator. This allows the irrigator to havesome flexibility when water is changed. Although notnecessary, this method works best when water isavailable on demand.




652.0707 Pumping plants

As power and equipment costs increase, designing andmaintaining efficient pumping plants becomes moreimportant. Designing an efficient, cost effective pumprequires close attention to detail and a knowledge ofbasic hydraulic principles of pump design. The de-signer must consider the pump, delivery system, andirrigation system as a whole. An annual economicanalysis may be needed to determine the least costlyalternative. See chapter 11 of this guide for economicanalysis procedures.

Every commercially manufactured pump has a knownand published relationship between head (pressure)and volume (capacity) produced. This relationship isgenerally plotted as a curve called the pump character-istic curve, pump performance curve, or pump head-capacity curve. Multiple curves are used to showcharacteristics of different impeller diameters andimpeller rotation speeds used in the same size andmodel pump. Pump characteristic curves are availablefrom pump dealers and manufacturers free of chargeto designers and pump owners. Every pumping plantevaluation should include a review of the pump char-acteristic curves for the pumps being used. Pumpspecific characteristic curves are essential for design-ing or evaluating pumps operating in series or parallel.

Variables contributing to the head-capacity relation-ship include:

• Pump make, model number, and discharge size• Impeller type, diameter, and speed of rotation• Number of impellers (or pumps) operating in

series• Net input energy required (usually expressed in

brake horsepower)• Net positive suction head (in feet)• Impeller efficiency

Net Positive Suction Head (NPSH) is the elevationwater can be raised at sea level by the suction side of aspecific pump impeller. Unless the pump is self prim-ing, the pump impeller must first be filled with water.If the allowable NPSH for a specific pump is exceeded,the pump will lose prime.

Every pump installation has an optimum operatingefficiency. The designer should strive to select pumpoperation at or near that efficiency. It is very unlikelythat a used (or even new) pump at a bargain price canbe obtained that fully meets the system needs withoutfirst checking the specific Head-Capacity Curve forthat specific make, model, and size of pump. Horse-

power alone is an inadequate specification for

selecting a pump. Flow capacity (Q) and Total Dy-namic Head (TDH) are required for pump selection. Athigh elevations an adjustment factor for elevation maybe needed. Manufacturers use different factors toconvert brake horsepower to recommended motor orengine horsepower of the drive unit.

Detailed examples of pump design are in NEH, Part623 (Section 15), Chapter 8, Irrigation Pumping Plants,and NEH, Part 624 (Section 16), Chapter 7, DrainagePumping. In addition, pump manufacturers’ catalogsand computer programs have information and designassistance on pump design and pump head-capacitycharacteristics. Chapter 15 of this guide gives informa-tion on interpreting pump characteristic curves, andchapter 11 has information about cost analysis forirrigation systems.




652.0708 Drainage systems

Purposes of agricultural drainage of irrigated land areto control and manage soil moisture in the crop rootzone, provide for improved soil conditions, and im-prove plant root development. Soil used for growingturf, landscaping, and agricultural crops must havefree drainage. In some cases soils are naturally welldrained; however, many soils need installed surfaceand subsurface drainage systems to provide propersoil moisture management flexibility. The greater themanagement flexibility, the greater the potential forproper water and nutrient management. Thus, toimprove water quality, management flexibility mustimprove. Where water tables are in or near the plantroot zone, water table control is an essential compo-nent of irrigation water management.

Capacity of drainage improvements must be based onan analysis of the area irrigated, the anticipated irriga-tion application efficiency, and the proportion ofrunoff and deep percolation anticipated as runoff.

Subsurface drainage installation on irrigated land isnot a substitute for proper irrigation water manage-ment. However, adequate drainage of the crop rootzone is essential for long-term production. Only whengood irrigation water management is practiced shouldsubsurface drainage installation be considered as anadditional water management practice. Also, subsur-face drainage is a part of, not a substitute for, propersalinity, sodicity, nutrient, and pesticide management.

Irrigation with saline or sodic water can inhibit cropgrowth and degrade the soil resource. See chapters 2and 13 of this guide for information on irrigation waterand soil salinity or sodicity. Good water managementalong with properly designed and managed subsurfacedrainage systems can help maintain a level of salinityor sodicity in the plant root zone that allows sustainedagricultural production.

Provisions to remove excess precipitation and soilseepage water promptly and safely from irrigated landmust be maintained as part of farm irrigation watermanagement. Without proper water removal, soil,water, plant and animal resources can be degraded. Insome cases discontinuation of improperly managedirrigation may be the only possible alternative.

Properly installed subsurface drainage systems can beused successfully in water short areas as a supplemen-tal source of irrigation water, if it is of reasonablygood quality. The water may be used on the field thatwas drained or on other crops in a different field.

Increasing the plant root zone (available soil-waterstorage) is a recommended water conservation prac-tice. In high saline or sodic areas, subsurface drainagewater may be used on salt-tolerant crops that arespecifically grown to dispose of drainage water. Spe-cial disposal methods, such as use of the effluent forirrigation of agroforestry plots, for constructed wet-lands, or in evaporation ponds, may be necessary forpoor quality water that cannot be disposed of in publicwater bodies. Caution must be exercised, however, toknow if toxic elements are in the drainage effluentand, if so, the concentration. Because ponded waterattracts waterfowl, any negative impacts on wildlifeneed to be known and avoided.

In high water table soils, subsurface drainage im-proves soil condition and the potential plant root zonedepth for most crops. This increased soil volumeincreases plant-water availability when precipitation isless than adequate, and improves plant nutrient avail-ability. Improved soil condition increases soil micro-organism activity, thus less fertilizer is generallyneeded, plus the potential for leaching of nutrientsbelow the plant root zone is decreased.

Laws, regulations, and public perception may increas-ingly limit new subsurface drainage developments andmethods used to dispose of drainage water. Mostdrainage issues will involve maintaining or rehabilitat-ing existing drainage systems. The irrigation/drainageplanning technician must be thoroughly familiar withlocal laws and regulations governing drainage.

(a) Precipitation runoff

High volume storm water runoff should be safelystored, diverted around, or carried through the irriga-tion system to protect the land, irrigation system, andcrop. This may require special erosion control mea-sures or modifications in the design or layout of anirrigation system.




Standard NRCS procedures, as illustrated in theEngineering Field Handbook, are available to deter-mine the volume and rate of runoff from precipitation.Runoff from precipitation can leave the land throughnatural watercourses or constructed ditches andchannels. Tailwater or wastewater ditches are gener-ally needed at the lower end of irrigation runs tocollect runoff from rainfall and irrigation. Stormrunoff peaks generally govern capacity requirements.Where storage and tailwater recovery facilities areprovided for irrigation, storm runoff containing alarge sediment volume should bypass or be trappedbefore entering the storage reservoir to prevent rapidloss of storage capacity.

(b) Irrigation runoff (tailwater)

Surface irrigation systems cannot place 100 percent ofapplied water in the plant root zone. However, levelbasin, border, and furrow surface irrigation systemsoperated with good water management includingplanned deficit irrigation in all or part of the field canapproach 100 percent water use. Using tailwater reuseon surface irrigation systems along with good watermanagement practices can be efficient. Planned irriga-tion deficit in all or part of the field, surge, cutback,blocked ends and tailwater reuse are techniques ormodifications that, when properly used, can improveirrigation uniformity while reducing field or farmrunoff.

To make a near uniform application of water with agraded surface irrigation system without using someof the above techniques or modifications, some irriga-tion runoff must result, typically 30 to 50 percent.Often runoff water is reduced or eliminated by reduc-ing inflow streams or blocking the ends of furrows andborders. This practice without an appropriate changein water management and system layout often tradesrunoff water for deep percolation (nonuniformity),which cannot be seen.

Theoretically, sprinkle irrigation systems should nothave runoff. In reality, even with proper water and soilmanagement, local translocation, and perhaps somefield runoff can occur because of the variable conditionsincluding soils, topography, and crop interference. Iffield runoff is anticipated, runoff facilities and manage-ment must be a part of every irrigation system plan.

Tailwater from irrigation must be recovered and reused,or it must be disposed of without damage to down-stream lands and water supplies.

(c) Subsurface drainage

Excess percolation of precipitation and irrigationwater and nearly impermeable soil layers can causehigh water tables. High water tables can restrict croproot development and promote saline or sodic soilconditions. Seepage from upslope areas, canals, reser-voirs, and sumps may also waterlog adjacentdownslope lands. Excess water that enters the soilprofile often percolates below the crop root zone.Unless the underlying material is sufficiently perme-able to allow continued flow, a water table can formand encroach into the potential plant root zone. Thewater table must be held below the crop root zone toprovide aerobic soil conditions for plant root develop-ment and function.

Subsurface drains are normally designed to control thewater table at least 4 feet below the ground surface.Significant quantities of water can be provided from awater table for plant use. Desirable depth to watertable is somewhat dependent on soil type. See infor-mation on upflux rate in Chapter 6, Subirrigation.Subsurface drainage systems may consist of intercep-tor drains, relief drains, or pumped drains. Subsurfacedrains may also be needed to reduce or eliminate toxicmaterials from moving to deeper aquifers that containhigh quality water.

Design of subsurface drains should be according toprocedures for arid land as described in NEH, Part 624(Section 16), Drainage of Agricultural Lands, chapters4 and 5. Chapter 7 of this guide provides informationon pumped drainage.

(1) Interceptor drains

Interceptor drains are used in sloping areas that have ahigh water table gradient. They are generally orientedperpendicular to the direction of ground water flow.Subsurface drains are commonly used because thedrain must be located according to soil and groundwater conditions, which may not correspond to fieldboundaries, fences, or property lines.




(2) Relief drains

Relief drains are generally used in level to gentlysloping areas that have a low water table gradient(slow water movement through the soil). These drainsgenerally are planned as a series of parallel drainconduits in a grid or herringbone pattern in whicheach lateral is connected to a submain or main thatleads to an open channel or sump pump.

(3) Pumped drains

Pumped drains are used when soils are underlain byporous sand or gravel with aquifers that can be low-ered by pumping or where insufficient fall exists for agravity outlet. Detailed subsurface and ground waterstudies are required to determine the feasibility oflowering the water table by pumping, on a largeenough area to be economical.

Pumped drains are also used where a layering of thegroundwater table is for a short period of time, i.e.,during harvest for improved soil trafficability, in theearly part of the growing season for plant establish-ment, and following periods of excess precipitation.

(d) Environmental factors

Drainage planning requires careful consideration ofenvironmental factors including wetlands, wildlifehabitat, and water quality. An environmental assess-ment of impacts on soil, water, air, plant, and animalresources is important when dealing with drainage.Drainage related environmental issues and laws arecomplex and subject to varying interpretation, whichcomplicates planning. It frequently takes considerableeffort to resolve or to even determine the status ofthese issues.

(1) Wetlands

A wetland classification determination is necessarywhere wetland conditions are suspected or evident.Wetlands created by irrigation water seepage or runoffmust be considered under current laws. It may benecessary to mitigate irrigation caused wetlands ifsystem improvements in adjacent areas dry up irriga-tion induced wetlands.

Surface and subsurface drainage can have beneficialwetland effects. Discharges of drainage water can beused to create or enhance wetland areas. Quality ofdrainage discharges is an important consideration forthe creation or enhancement of wetlands used bywildlife.

(2) Water quality

National and State laws require that drains discharginginto State watercourses meet certain water qualitystandards. Currently irrigation runoff is classified as anonpoint source. As such, discharge permits are notrequired. However, if a downstream water user files acomplaint, water quality restrictions may be placed ondischarges from irrigated land. Permits are requiredfor discharges from point sources, such as feedlots,and can be required for subsurface drain outlets.




652.0709 Chemigation

Chemigation is the application of chemicals via anirrigation application system. Included are fertilizers,soil amendments (gypsum or sulfur), herbicides,insecticides, fungicides, nematicides. Specific forms ofchemigation are sometimes called fertigation,herbigation, or insectigation; however the most com-monly used term that covers everything is chemiga-tion.

Chemigation is accomplished by injecting the chemicalinto a flowing water supply. Most chemigation isapplied by sprinkler systems (linear or center pivots)or micro systems. Soil amendments are typicallyapplied in surface systems. Unless uniformity is high,applying agricultural chemicals through irrigationsystems is not recommended. Always follow instruc-tions on the chemical label to determine suitability andmethodology of chemigation.

Properly managed chemigation requires injectingchemicals into the water in carefully measuredamounts. Care must be taken to prevent backflow ofchemically laden water into any water source.Backflow prevention devices are required wherechemicals are injected into any pressurized irrigationsystem. Distribution of water on the field must beuniform, carefully managed, and controlled. Thisrequires the proper equipment and careful attention todetail. Water quality laws are strict concerning han-dling of chemicals applied through irrigation systems.Only chemicals labeled for chemigation (usuallysprinkler system) application should be used.

(a) Advantages

The advantages of using chemigation include:• Cost of chemigation versus aerial or ground

application can be less.• A chemical can be applied when it is needed

without waiting for the proper weather condi-tions the supplier or labor availability. The proce-dure can reduce total labor.

• Application can be more uniform than by othermethods under certain conditions.

• With soil incorporated herbicides, the appropri-ate amount of water can be applied to incorpo-rate the herbicide to the depth desired and toactivate it immediately.

• Soil compaction is reduced because it is notnecessary to pass field equipment over the fieldto apply chemicals.

• Mechanical damage to crops is less than withmechanical surface application methods.

• The hazards to operators are fewer.• Less fertilizer may be required, particularly under

micro irrigation.• Losses from wind drift can be reduced or elimi-

nated depending on the method of irrigation.This can reduce one cause of chemical loss andpollution.

• Chemigation techniques are compatible with no-till soil management systems.

(b) Disadvantages

The disadvantages of using chemigation are:• Some chemicals are corrosive to irrigation equip-

ment, especially immediately downstream of theinjection point. In most cases the chemicals arediluted further downstream to the point thatcorrosion is not a serious problem. Injectionequipment must be designed to handle concen-trated chemicals.

• Combining chemicals can be dangerous andexpensive if not done with full knowledge of thepotential, sometimes violent, reactions. Chemi-cals can also produce precipitates, which canclog equipment, or produce toxic vapors.

• Losses because of volatilization can occur,particularly under sprinkler irrigation.

• Chemicals that can be used successfully underchemigation are limited. Many chemicals areeither not registered for chemigation applicationor are specifically prohibited from being used.

• Excess water application or rainfall duringchemigation can cause the loss of chemicals ormake them ineffective through deep percolationor runoff. Lost chemicals can contribute to waterpollution.

• Special injection equipment and irrigation systemsafety equipment are required. This adds to theexpense of the operation.




• A potential hazard to water supplies is alwayspresent particularly with pesticides and herbi-cides.

• Much is still not known about the best and safestways to handle chemigation. The technique isrelatively new.

• A high degree of management and irrigationuniformity are required.

(c) Planning and designconsiderations

The following information is intended to give NRCSpersonnel a general understanding of chemigation onpressure type systems. Detailed design of such sys-tems must be done by a qualified engineering firm orby those involved in the sale and servicing of equip-ment.

(1) Chemical injection equipment

Chemical compounds to be applied through injectionequipment must be in one of the following forms:

• Miscible or emulsible liquid• Soluble, dry powder (crystal)• Insoluble, wettable, dispersible powder.

Some equipment is manufactured for specific material(i.e., type of chemical, chemical concentration, viscos-ity), so the appropriate types of chemicals and equip-ment should be chosen. The equipment must haveadequate capacity. The common methods of injectingchemicals are illustrated in figures 7–3 to 7–8. Pumpscan be powered by electric drives, engine drives, orwater motors. Equipment can be categorized by theway the inflow rate of the chemical is controlled. Thefour categories are gravity flow, educator, meteringpump, and proportioner system.

(i) Gravity flow from chemical storage tanks

(fig. 7–3)—This is the crudest category of chemicalinjection. Control of injection rate is accomplished byadjusting a valve that approximately regulates chemi-cal flow into the irrigation water. Chemical flow iseither into the suction end of a pump or into an opengravity flow system. This type injection is generallyused in surface systems, particularly to add soil addi-tives, such as sulfur compounds. It requires carefuloperator attention.

(ii) Educator—This is the simplest way of introduc-ing chemicals into the system. Methods used for thiscategory are:

• Injection on suction side of pump (fig. 7–4)• Venturi principle injection (fig. 7–5)• Pitot tube injection (fig. 7–6)

The chemical injection rate is approximately propor-tional to water flow. The method requires some oper-ating attention. It can handle liquids and water solubleor dry material. The educator equipment should beused where water flow is nearly constant.




Figure 7–6 Pitot tube injection

��

Backflow preventiondevice

Pressurizedsupply tank

Screen

Discharge

Pitot tube unit

Tosprinklers

Controlvalves

Checkvalve

Figure 7–3 Gravity flow from storage tank

��

Supply tank

Screen

Ditch

Outlet pipeControl valve

Figure 7–4 Injection on suction side of pump 1/

��

Supply tank

Screen

Controlvalves Backflow prevention valve

Backflowpreventionvalve

Tosprinklers

Centrifugalpump

Suction pipe

Foot valve

Dis

char

ge

1/ Note: Check local regulations before using this method ofchemical injection.

Figure 7–5 Venturi principle of injection

��

Backflow preventionvalve

Backflowpreventionvalve

Pressurizedsupply tank

Screen

Discharge

Venturi unit

Tosprinklers

Controlvalves




(2) Safety equipment

Technology is available to make the safety aspects ofchemigation acceptable. However, any time mechani-cal devices are being used there is always the possibil-ity of failure, malfunction, or accidents. Successful andsafe chemigation requires safety devices be installedon the chemigation system. These devices are de-signed to eliminate three possible pollution problems:

• Backflow of undiluted chemicals to the nursetanks or water source

• Spill of chemicals on the surface• Backflow of water mixed with chemicals from

the irrigation system.

American Society of Agricultural Engineering Stan-dard ASAE EP409 covers safety standards for chemi-gation equipment and operation. Bulletins, such as No.1717, Safety and Calibration Requirements for Chemi-gation, from Oklahoma State University, CooperativeExtension Service, are readily available through mostCooperative Extension Service offices.

The Environmental Protection Agency provides strin-gent requirements for safety equipment and proce-dures when applying certain agricultural chemicalsthrough pressurized irrigation systems. Chemicalsapproved for chemigation have specific verbatimstatements on the label. They include:

• The system must contain a functional checkvalve, vacuum relief valve, and low pressuredrain appropriately located on the irrigationpipeline to prevent water source contamination.

• The pesticide injection pipeline must contain afunctional, automatic, quick-closing check valveto prevent flow of fluid back toward the injectionpump.

• The pesticide injection pipeline must also con-tain a functional, normally closed, solenoid-operated valve located on the intake side of theinjection pump and connected to the systeminterlock to prevent fluid from being withdrawnfrom the supply tank when the irrigation systemis either automatically or manually shut down.

• The system must contain functional interlockingcontrols to automatically shut off the pesticideinjection pump when the water pump motor/engine stops.

(iii) Metering pump (fig. 7–7)—This methodaccurately meters the chemical into the irrigationwater at a predetermined rate. The chemical inflowrate is constant with respect to time and allows theoperator to make changes in the application rate. Itshould be used where the rate of water flow is nearlyconstant. The method of injection used is the injectionpump. It can only inject liquids.

(iv) Proportioner system—This method of injec-tion accurately proportions chemicals to irrigationwater flow. It consists of a sensor that determines thewater flow rate, a chemical flow control module, andan injector pump that injects the chemical. This cat-egory of injection equipment should be used where theirrigation flow rate varies. It is automatic and requireslittle operator attention.

Figure 7–7 Pressure metering pump injection

��

Backflow prevention valve

Backflow prevention valve

Motor driveninjector pump

Supply tank

Screen

Tosprinklers

Controlvalve




• The irrigation line or water pump must include afunctional pressure switch which will stop thewater pump motor when the water pressuredecreases to the point where pesticide distribu-tion is adversely affected.

• Systems must use a metering pump, such as apositive displacement injection pump (i.e., adiaphragm pump) effectively designed andconstructed of materials that are compatiblewith pesticides and capable of being fitted with asystem interlock.

• Do not apply pesticides when wind speed favorsdrift beyond the area intended for treatment.

Safety devices are described in the following para-graphs.

Interlock—This connects the irrigation pumping plantand the chemical injection pump. If the irrigationpump stops (line pressure drops), the injection pumpstops.

Low pressure drain—An automatic low pressuredrain should be placed on the bottom of the irrigationpipeline. If the mainline check valve leaks, the solutionwill drain away from, rather than flow into the watersource.

Backflow prevention valve—Used to keep water or amixture of water and chemical from draining or si-phoning back into the water source (fig. 7–8).

Figure 7–8 Backflow prevention device using checkvalve with vacuum relief and low pressuredrain

From chemical tank

Toirrigation

system

Solenoid valve

Coupler

Flow

Injectionpump

Checkvalve

Injection portwith check valve

Gatevalve

Vacuum breakerand inspectionport

Pressuregauge

From watersupply

Lowpressuredrain

87

54

8 94

2

Inspection port—Located between the pump dis-charge and the mainline check valve, the port allowsfor a visual inspection to determine if the check valveleaks. The vacuum relief valve connection can serve asan inspection port.

Chemical injection line check valve—This devicestops flow of water from the irrigation system into thechemical supply tank and, if the opening pressure islarge enough, can prevent gravity flow from the chemi-cal supply tank into the irrigation pipeline following anunexpected shutdown (figs. 7–9 and 7–10).

Chemical suction line strainer—The strainer isnecessary to prevent clogging or fouling of the injec-tion pump, check valve, or other equipment.

Solenoid valve—Additional protection can be pro-vided by installation of a normally closed solenoidvalve so that it is electrically interlocked with theengine or motor driving the injection pump. The valveprovides a positive shutoff on the chemical injectionline. If any portion of the downstream irrigation sys-tem is lower than the chemical tank, the solenoid valvecan prevent the chemical from being siphoned out ofthe tank.

Chemical resistant hose clamps and fittings—Allcomponents that are in contact with the chemical orchemical mixture, from the strainer to the point ofinjection on the irrigation pipeline, should be made ofchemically resistant materials.

Check valve—Used in a pipeline to allow flow in onedirection only.




Figure 7–10 Safety devices for injection of chemicals into pressurized irrigation systemsusing internal combustion engine power


Irrigation pumpIrrigation pipe line

Suction line

Suction linestrainer

Solenoidvalve

Chemicaltank

Pressure switch

Discharge line

Check valve Pump

Vacuumbreaker

Drainpoint

3

1

5 9

8

7

8

4

2

6

��

Figure 7–9 Safety devices for injection of chemicals into pressurized irrigation systems using electric power


Electric motorand pump

Electricallyinterlockedcontrolpanels

Irrigation pipe line

Suction line

Suction linestrainer

Solenoidvalve Chemical

tank

Pressure switch

Discharge line

Check valveMotor

Pump

Vacuumbreaker

Drainpoint

3

1

5 9

87

8

1

4

2

6




(3) Fertilizer application

The great variety of fertilizer products available allowseveral choices to be considered in selecting a fertil-izer for a particular situation. The three categories offertilizers used are clear liquid, dry, and suspensionliquid.

Clear liquid fertilizers—These materials are flowableproducts containing nutrients in solution. This makesthem convenient to handle with pump injectors, ven-turi-tubes, and gravity flow from gravity storage tanks.Liquid fertilizers contain a single nutrient or combina-tions of nitrogen (N), phosphate (P), and potash (K).The most common liquid fertilizers used are listed intable 7–4.

Dry fertilizers—A wide variety of soluble dry fertiliz-ers is used for injection into irrigation systems. Thedry fertilizer may be dissolved by mixing with waterin a separate open tank and then injected into theirrigation stream, or they can be placed in a pressur-ized container through which is bypassed a portion ofthe sprinkler stream. In the later case the bypassedstream continuously dissolves the solid fertilizer untilit has been applied. Typical dry fertilizers are shownin table 7–5.

Suspension liquid fertilizers—Suspension liquidfertilizers produce higher analysis grades than cleargrades given the same ratio of N, P, and K. Table 7–6shows a comparison of typical analysis of clear andsuspension liquid fertilizers. The suspension mixturescontain 110 to 133 percent more plant nutrients thancorresponding clear liquids. Because of their highernutrient content, suspensions generally are manufac-tured, handled, and applied at less cost than clearliquids. Another advantage is that they can hold largequantities of micronutrients.

Table 7–4 Liquid fertilizers (solutions) for sprinkler application 1/

Solution product Total Avail Water Total Approximate pounds of productnitro phos soluble sulfur for 1 pound of nutrient

acid potash% N % P % K % S N P K S

Ammonium nitrate 20 5Ammonium phosphate 8 24 12 4Potassium ammonium phosphate 15 15 10 7 7 10(N-P-K liquid mixes) 10 10 10 10 10 10

15 8 4 7 12.5 25Urea (low biuret) 23 4.4Urea - ammonium nitrate 32 3.1Phosphoric acid 52 – 54 1.8 – 1.9Calcium ammonium nitrate 17 6

1/ Source: National Fertilizer Development Center, Tennessee Valley Authority, Muscle Shoals, Alabama, 1965.




Table 7–5 Dry fertilizers for sprinkler application 1/

Dry product Total Avail Water Total Approximate pounds of product fornitro phos soluble sulfur 1 pound of nutrient

acid potash% N % P2O4 % K2O % S N P2O4 K2O S

Ammonium nitrate 33.5 3Calcium ammonium nitrate 26 4(Mono) ammonium phosphate 11 48 2.6 9 2 40Ammonium phosphate sulfate 13 39 7 8 2.5 14Ammonium phosphate sulfate 16 20 15.4 6 5 7

Ammonium phosphate nitrate 24 20 4 5Ammonium phosphate nitrate 27 14 4 7Diammonium phosphate 21 53 5 2

Ammonium chloride 25 4Ammonium sulfate 20-21 24 5 4Calcium nitrate 15.5 6Sodium nitrate 16 6Potassium nitrate 13 44 8 2.3Urea 45-46 2.2

Double or treble super phosphate 42-46 10 2.3 10Potassium chloride 60-62 1.7Potassium sulfate 50-53 18 2 5.5Sulfate potash magnesia 26 15 4 7Nitrate soda potash 15 14 7 7

1/ Source: National Fertilizer Development Center, Tennessee Valley Authority, Muscle Shoals, Alabama, 1965.

Table 7–6 Comparison of typical analysis of clearsuspension-type liquid fertilizers 1/

Ratio GradeN-P-K clear Suspension

3:1:0 24-8-0 27-9-02:1:0 22-11-0 26-13-01:1:0 19-19-0 21-21-01:2:2 8-8-8 15-15-151:3:1 5-10-10 10-20-201:3:2 5-15-10 9-27-181:3:3 3-9-9 7-21-21

1/ Source: National Fertilizer Development Center, TennesseeValley Authority, Muscle Shoals, Alabama, 1965.




(i) Herbicide application—A few herbicides areapplied by sprinkler systems. Most treatments involvecombinations of herbicides in suspension. Only herbi-cides registered for application with irrigation watercan be used. Most application is done with soil appliedherbicides before crop germination. Applying irriga-tion water at low enough rates to use foliage typeherbicides is difficult.

(ii) Pesticide application—Application of pesti-cides by sprinkler systems is limited. Only pesticidesfor grasshoppers and corn borers are registered forapplication by irrigation. Water application must beless than 0.5 inch per hour.

(iii) Other planning and management consider-

ations—When irrigators apply chemicals through anirrigation system, consideration needs to be given totravel time to the field area being irrigated. The time ittakes for a chemical to travel from the point of injec-tion (usually at the pump) to the area being irrigatedmust be known to calculate when to close the valve orshut down the pump, thus being assured that all thechemical is applied. Volume of clean water followingchemical application can be reduced.

652.0710 State supplement

nig ch 7 - unimore

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