SwitchingirrigationtechnologiesDoes switching from rainguns to booms, sprinklers ortrickle save water, energy and money – fact or fiction?

Why switch?

Increasing water scarcity and rising energy prices are forcinggrowers to re-assess their irrigation practices. Rainguns arestill the dominant irrigation method in the UK but theyare reputed to waste water and energy. So will they still bearound in 20 years from now? Should growers start thinkingabout switching to more 'efficient' technologies?

Rainguns, booms, sprinklers, and trickle – the facts

There is growing pressure from the government, the regulatory agenciesand supermarkets to use available water resources more wisely.Because rainguns apply over 75% of all water used for irrigation thesesystems are in the spotlight. In catchments where water resources areover-abstracted the ‘drivers for change’ are even more acute.

What’s wrong with hose-reel rainguns?

It depends. Rainguns are the most commonirrigation system used in England and Wales. Themajority of growers say they are robust, versatile,labour efficient and fit in well into modern highlymechanised farming. Similar machines are usedfor similar reasons across much of northernEurope and north eastern United States.Nevertheless rainguns have always had areputation for wasting water and energy.

Most farmers refute claims about water wastage.Water costs too much to waste – up to £0.40/m3

for direct abstraction and over £0.80/m3 whenirrigating using reservoir stored water. Recentwater audits on well managed potato farms usingrainguns showed wastage was less than 10% ofwater applied – much lower than seen elsewhereinternationally. If machines are set at the rightpressure and used in moderate wind speeds withappropriate lane spacings, they can apply wateruniformly and efficiently.

How do you decide whether it is worthwhile toswitch technology? There are many issues toconsider – your future irrigation plans, thetechnology options available, their capabilities, andthe costs and benefits.

Switching irrigation technologies02

Rising energyand water costs

Driversfor

Change

Rising labourcosts

Supermarketpressures forenvironmentalsustainability

Crop and soil damage

Less wateravailable for

irrigation

Changingcroppingpatterns

03Switching irrigation technologies

What will it cost?Irrigation costs = capital costs + recurrent costsDo not fall into the trap of looking only at thefixed or `capital' costs of infrastructure andirrigation equipment. The recurrent costs ofoperating and maintaining systems can besignificant now that energy and labour costs arerising faster than interest rates. These costs cangreatly influence your choice of irrigation system.

You cannot just simply add the capital andrecurrent costs together. You must first amortisethe capital costs over the useful life of theequipment to give you an ‘equivalent annual’cost – it is a bit like working out the annualcosts of a mortgage. You can then add thisdirectly to the annual recurrent cost to obtainthe total annual irrigation cost.

Comparing costs

In order to compare the costs of alternativesystems for your farm, do the sums for eachsystem to see which one will give you the leastannual irrigation cost. Beware of comparingirrigation costs between different farms. They willall have different requirements – different cropwater needs; how and where water is sourcedand delivered; the need for a reservoir; and thesize, location, and topography of the irrigatedarea. These will impact on system costs indifferent ways.

Comparing ‘infield’ costs – the cost of equipmentin the field beyond the field hydrant – is easier todo but again make sure you compare like-with-like. For example, the ‘in-field’ cost of a fullyautomated trickle irrigation for potatoes, includingfiltration, fertiliser injector, remote control anddisposable lateral tapes installed in each ridge, isbetween £2,000-3,000 per ha.

Thin-wall disposable tape costs between £0.03-0.05 per m, so the cost of replacing the tapeseach year is between £330-500 per ha. Thissystem does not commit you to a long terminvestment in trickle. But you will have theadditional cost of tape disposal at the end of the season.

The more robust re-usable tapes with pressurecompensating emitters cost between £0.08-0.10per m which means a capital investment for thetape of about £1,000 per ha. However, pressurecompensating emitters mean that laterals can belonger which reduces mainline and control costs,and the tape, if carefully retrieved, can last threeseasons and more. Tape retrieval costs between£40-50 per ha.

If you wish to try out trickle irrigation withoutmaking a long term capital investment then onealternative is to hire the equipment. The typical

annual hire costs for a fully automated tricklesystem for potatoes is about £1,200 per ha.

Whichever trickle system you choose, you willneed labour to install it. Although the system isautomated it requires a higher degree ofmanagement input.

By contrast, a typical capital cost for a hose-reelfitted with a raingun is about £1,000 per ha. Butrainguns are labour and energy intensive whencompared to trickle. They operate at much higherpressures and require labour and tractors tomove them around the field. The typical energycost of applying water on potatoes through ahosereel and raingun is currently £0.36 per m3

compared with only £0.06 per m3 for trickle. Thisdemonstrates just how important it is to includerecurrent costs and not just rely on capital costswhen you are comparing systems.

Recurrent costs are also quite sensitive to theweather – in wet years the demand for irrigationwill be less so some of the recurrent costs will belower. However, because of the sensitivity ofirrigation costs to rising energy prices, it doesmean that the total annual costs for trickle arenow becoming much more comparable tooverhead irrigation particularly for growing highquality salad, potatoes and vegetables.

Management matters moreMore sophisticated irrigation systems and scheduling tools do notnecessarily lead to better irrigation performance. The key factors are yourmanagement skills and experience and your ability to use equipment andtools effectively.

Changing attitudes

The latest Defra irrigation survey for England andWales in 2005 showed that hose-reels fitted withrainguns accounted for 67% of the total irrigatedarea. Nearly 20% is now irrigated with booms, andstatic or hand-move sprinklers and trickle eachaccount for 5%. Industry estimates suggest thatmore growers are switching from rainguns,particularly on high value crops where better

application uniformity and reductions in soilsplash, and crop damage are priorities.

So which method is best?

There is no easy answer – it is ‘horses for courses’.Each method has its own advantages anddisadvantages depending on the crop, soil type,water source, and farm management requirements.

It is important to do the sums and work out whichsystem is best for you bearing in mind both yourcurrent and future needs. Water and energyconservation will undoubtedly become moreimportant and you will need to account for theparticular irrigation needs of UK farming – typicallyquite short irrigation seasons, small amounts (depths)of water applied, and the need for portable systemsthat allow for annual crop rotations around the farm.

Switching irrigation technologies04

Trickle

Trickle is often called the irrigation of the future – accurate, energyefficient, easily automated and producing high yielding, qualityproduce. Its potential to save water is particularly attractive whenwater is scarce or expensive. But what are the drawbacks?

For many growers, trickle irrigation potentially offers the technological advance that could givethem the higher yields and quality that their buyers demand, whilst providing the water savingsand environmental benefits that the government seeks.

Trickle is well established in the soft fruit, orchard fruit, salads, and glasshouse sectors. But is itsuited to the majority of field-scale irrigated crops such as vegetables and potatoes? And howdo the claims for trickle stand up in practice?

Trickle – the basics

Trickle irrigation (sometimes called drip) is a systemof small diameter plastic pipes with speciallydesigned emitters that enable farmers to applysmall quantities of water (2-10 litres/hr) to crops atfrequent intervals (1-3 days). This is quite differentfrom raingun and sprinkler irrigation systems whichare typically used to apply much larger depths ofwater (usually 15-25 mm) every 7-10 days.

Only part of the soil profile around the plant rootsis wetted and so frequent irrigation is needed tomake sure the plants are well supplied with water.This direct connection between the irrigationsystem and the plant and the fact that fertiliser canbe added to the water brings the potentialadvantages of water saving and improved yieldsand crop quality. Low operating pressures (typically1-2 bar) mean lower energy costs and automationmeans savings in labour costs.

Like other methods, trickle is not without itsproblems. Not least of these is emitter blockagefrom dirty water, chemical precipitates such ascalcium and iron, and algae and bacterial slimes.These are preventable with good filtration,chemical injection treatments and goodin-field management.

Trickle irrigation is adaptable to a wide range ofagroclimates, soils, and crops. It is ideal forperennial orchards and soft fruit but it isincreasingly used for seasonal crops such as field-scale vegetables and salad crops. It is now used inmany countries where water is scarce, where soilconditions and water quality are poor, and labouris scarce or expensive.

Scheduling trickle

Farmers are used to seeing irrigation water and sohave a good ‘picture’ of what is going on. But withtrickle you cannot see the water and so you mustrely on instruments for information – flow meters,timers and pressure gauges to monitor waterapplications; and soil moisture probes to monitorwater movement and wetting. It requires a morescientific approach to irrigation management.

Trickle and abstraction licensing

Water abstraction for trickle irrigation is not licensedat present but this is changing. It is incorporated inthe Water Act (2003) but it is not expected to beimplemented before April 2009. By 1st April 2010all abstractors using trickle irrigation will have toapply for an abstraction licence. The EnvironmentAgency will then determine the application by 2015.It is expected that abstractions legally operating

before the introduction of the new regulations willbe allowed to continue until the licence applicationis determined.

Trickle uses less water?

True – but savings are marginal. Remember thatcrops need a certain amount of water to grow andthis is determined by the crop and the evaporatingconditions, not by the irrigation method. Potentialwater savings come from reducing water lossesnormally associated with rainguns and sprinklers –spray evaporation, wind drift, over-irrigation tocompensate for poor uniformity, and evaporationfrom foliage and soil. The agronomic demand forwater remains the same irrespective of theirrigation method.

Trickle is often called the irrigation of the future – accurate, energyefficient, easily automated and producing high yielding, qualityproduce. Its potential to save water is particularly attractive whenwater is scarce or expensive. But what are the drawbacks?

05Switching irrigation technologies

Trickle increases production?

True – but be clear why this is so. Make sureyou are comparing like-with-like. Is trickle beingcompared to raingun/sprinklers or to a rain-fedcrop? Was more water applied with tricklebecause the system is easier to use? Was thefertiliser more effective because it was applied withthe irrigation water?

Trickle improves crop quality?

True – but it does require additionalmanagement skill. Most trickle systems are fullyautomated and include fertigation. So there ispotential for a high degree of control over bothwater and nutrient applications. This can lead tohigh quality and timely produced crops.

Trickle uses less energy?

True – trickle systems operate at much lowerpressures than rainguns and sprinklers and so theywill need to change your pump to get the best

require less energy. To take advantage of this youefficiency at the lower pressures and flow rates.

Trickle is more expensive?

True – but it depends on which costs you arelooking at. ‘In-field’ capital costs are much higherthan for rainguns but recurrent costs are often muchlower, particularly as energy prices rise. So you needto look at both the capital and recurrent costs to geta true picture.

What the farmers say

Most farmers who have switched to trickle grow highquality premium grade produce to meet supermarketrequirements rather than to save water. Farmers say that some water saving is possible but it is not significant.

Trickle wetting patterns can be difficult to establish innewly formed ridges and beds because the soil maynot be compact enough. So some farmers useoverhead irrigation initially to wet up the soil profile.

Trickle irrigation is perceived as an environmentallyfriendly irrigation method and this has marketing advantages.

Case Study – Trickle ‘adds value’ to pre-pack potatoes

David Matthews

When it comes to growing potatoesusing trickle, David Matthews, of G&DMatthews Ltd, West Pinchbeck,Lincolnshire leads the way. He grows140 ha of Maris Piper and Marfona forthe top end of the pre-pack market.He is clear about the quality benefitsthat trickle delivers, but warns, that itis how he manages the system that isthe key to his success.

Over the past 8 years, David hasmastered the use of trickle irrigation onpotatoes, without any previousexperience of overhead irrigation. “In thelate 1990s we were convinced tricklewas the way forward. We could see thebenefits for scab control and skin finishthat localised irrigation could offer”reflects David who manages thebusiness with his son James.

Their irrigation system uses disposabletape which is laid 50 mm below eachridge about two weeks after planting.The silty soils are prone to capping andso this approach means that irrigationcan continue under the cap to controlsoil moisture and prevent scab duringtuber initiation. This would be difficult todo with an overhead sprinkler system.

Irrigation is scheduled using anEnviroscan on 15 ha blocks. “Wenormally irrigate on a 1-3 day interval,and have the capacity to irrigate theentire area in 24 hours if needed. If itrains, we can delay the next irrigationwithout worrying about keeping up withcrop water demand. We also use thesystem to apply fertiliser and nutrients withthe irrigation water. We continually trial newideas to get the best quality potatoes”.

David is well aware of future changes inabstraction licensing. “Trickle is currentlyan unlicensed activity, but we carefullyaudit our water use and make annualreturns to the Environment Agency. It isimportant that we demonstrate efficientuse of water both to our customers andto the regulator”.

Although trickle irrigation works for DavidMatthews, he acknowledges that it is nota panacea for all. The capital investmentis high but the yield and quality dividendscan be significant – “Irrigating potatoeswith trickle is like giving them a steakdinner every night” says David.

Disposable or re-usable tapes?

Some growers replace lateral tapes every yearwhilst others invest in more robust tapes thatcan be used for several years. Re-usable tapemay be more economic but needs carefulretrieving and slows down harvest. Reusing it indifferent shaped fields as you rotate crops canalso introduce additional installation problems.Disposable tape is more straightforward toinstall and use. But you will have the additionalcost of disposal. So carefully examine the prosand cons of each approach before decidingwhich is the best option for you.

Switching irrigation technologies06

Booms and sprinklers

For some growers a switch to trickle is one step too far and sothey are choosing booms or solid-set sprinklers. This is a morefamiliar approach to irrigation particularly when growers like to‘see’ water when they irrigate.

Industry and government surveys confirm a strong underlying growth in the use of booms.When field topography limits the use of booms, solid-set sprinklers are a good alternative. Both seem ideal for field-scale horticulture – but what do growers think about them?

Case Study – Booms offer precision watering for salads

Will Forbes

Applying light, frequent waterapplications with a high degree ofuniformity is critical for growing saladcrops. Will Forbes Farm Manager atJB Shropshire and Sons explains whythey switched technologies and nowrely extensively on booms to grow arange of high value crops on fragile,exposed soils.

JB Shropshire and Sons, based atSoham, Cambridgeshire are one of thelargest salad producers in the countrywith 1200 ha of lettuce, iceberg, littlegem, endive, and celery on light fenlandsilts. In the early 1990s they irrigated withrainguns but the large water dropletscaused soil splash and ‘head rot’ in thecrop, and wind drift on exposed fields led

to non-uniform crop development.Shropshire’s decided to switch tobooms, in order to overcome theseproblems. Today the farm uses 28 hose-reels fitted with booms that can stripsfrom 36-72m wide to accommodate arange of different planting regimes andfield sizes.

“Our clients demanded a better productwith consistent quality, particularlyuniformity of head”, reflects Will Forbes.“We needed to apply much smaller, morefrequent water applications to helplettuce transplants develop their rootsand maintain vigour during their shortgrowing season. It was all about gettingmore precise water application. We alsorecognised that we needed to combine

improvements in application withimprovements in our understanding ofcrop water requirements and any risksassociated with water quality, as most ofour crops are not processed. We nowuse an irrigation scheduling service tomatch water applications to waterdemand, and we regularly monitor waterquality to assess microbiological risksnear harvest.

Will does warn that growers must notforget about the “carwash effect” – onsome soils the high instantaneousapplication rates under booms cancause problems of soil erosion and run-off. So the application rate must not exceed the soils infiltration rate.

Booms – the basics

Mobile systems, such as booms, can apply waterprecisely, particularly when the sprinklers are sprayingwater directly onto the crop canopy, avoidingproblems associated with wind drift. Energyrequirements are lower because pumping pressuresare only 3-4 bar – less than half the pressurerequirement of a raingun. A typical modern boomcomprises a set of fixed spray nozzles located on agantry mounted on a 4-wheel chassis and connectedto a hose-reel. Improvements in design in recentyears have made them more popular among field-scale vegetable and salad growers – reduced energyneeds, good application uniformity, and fine sprays

that minimise soil splash onto delicate crops. Theycan be single-handedly set up and maneuvered andcan irrigate 35-72m wide strips – equivalent to alane width for a raingun – and are well suited tolarge, flat rectangular fields.

Booms are less suited to uneven topography andirregular shaped fields. Application rates are highand so care is needed to avoid runoff on lowinfiltration rate soils.

The cost of replacing a raingun with a modern boomirrigating a 72m wide strip would be an additional£10,000-12,000. This would increase in-field capitalcosts by approximately £40-50/ha/yr.

07Switching irrigation technologies

Case Study – Sprinklers deliver high quality carrots

Ross Howard

Ross Howard, of RE Howard andSons, a family agribusiness in Ranby,Notts, says that solid-set sprinklersare one of the best ways to irrigatehis specialist pre-pack babyChantenay carrots – rainguns werenot the answer.

Ross farms 1,600 ha on light undulatingsandy soils and relies extensively onirrigation to produce high qualityhorticultural crops, including potatoes,onions and carrots. “Baby Chanteneycarrots represent 50% of our businessand at certain growth stages the crop isvery water sensitive and demands afinely tuned approach to scheduling. Wetry to match theory with practice, bymonitoring daily rainfall and croptranspiration (ET) across the farm using aweather station and network of ETgages.This gives us a good idea of the water

balance on a field by field basis. Butaccurate scheduling is of little usewithout accurate water application”,reflects Ross.

"Rainguns could no longer meet our tightirrigation specifications for crop quality –and so we switched to solid-set sprinklersystems that would deliver much higherapplication uniformity with lower operatingcosts. The system comprises twin-nozzlerotary impact sprinklers on an 16m x 15mgrid with laterals up to 300m long. Lowoperating pressure (3 bar) keeps energycosts down and as the system is laiddown for the season, labour requirementsare low".

In 2006, in-field uniformity tests showedthat the coefficient of uniformity (CU)was 77% and the distribution uniformity(DU), which emphasises areas that get

least water, was 67%. Both values are“good” when compared againstreference international data for thesetypes of sprinklers.

Although the capital costs were morethan the equivalent hose-reel raingunsystem, the biggest driver was thepotential loss of income from notmeeting supermarket qualityspecifications. This was a risk too greatto take. “When you invest in the rightirrigation equipment you must at all costshit the premium market” says Ross.

However, Ross warns that there is atemptation to stretch sprinkler spacing toreduce costs. “Care needs to be taken toavoid large spacings on sensitive cropsgrown in locations where the prevailingwind could distort the overlaps andreduce uniformity”.

Sprinklers – the basics

Solid-set systems using rotary sprinklers areanother option that is increasing in popularity.Portable rotary sprinklers systems were firstdeveloped in the USA in the 1930s but solid-setsystems that are laid down for the life of the cropare now preferred as they significantly reducelabour requirements. Originally used on morepermanent crops such as orchard fruit they arenow being used on seasonal field vegetables andsalad crops as an alternative to rainguns. Likebooms they operate at pressures of 2-3 bar. Moresophisticated electronic control systems, such asthose used for sports turf irrigation using remotecontrolled switching of solenoid valves, enablethese systems to apply water more frequently, witha greater degree of flexibility and precision.

Times are changing

In the past sprinklers were not thought of as ‘hightech’ water application systems nor was precisionimportant provided a reasonable level of uniformitywas achieved and productivity increased to justifythe additional cost of irrigation. But times havechanged. Irrigation is no longer a marginal activity. Itis now part of a sophisticated production system.Improved irrigation scheduling – when to irrigate andhow much to apply – using sophisticated equipmentto measure and monitor soil moisture is nowbecoming standard industry best practice. Butprecise scheduling also demands precise waterapplications. Sprinklers and sprinkler systems arenow available to meet these requirements – bothmobile systems and solid-set.

FertigationApplying liquid fertiliser with irrigation water is common place with trickleirrigation but some growers are now using the technique with solid-setsprinklers as well. This can increase the efficiency of fertiliser use andreduce the costs of traditional broadcast methods.

Designed & produced by Visualidentity.co.uk Printed by Taylor Bloxham Leicester who have achieved the environmental

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This publication was funded by Natural England. The project was undertaken byCranfield University in association with RTCS Ltd.

The authors of this publication – Jerry Knox and Keith Weatherhead (CranfieldUniversity) and Melvyn Kay (RTCS Ltd) wish to make it clear that the content andviews expressed are those of the authors and do not necessarily represent theviews or policies of Natural England. The Natural England project manager wasSarah Fraser (sarah.fraser@naturalengland.org.uk).

The authors acknowledge the assistance of Adrian Colwill (Briggs Irrigation),Anthony Hopkins (Wroot Water Systems) and Julian Gruzelier (Revaho) for theirspecialist expertise, and to David Matthews (G&D Matthews, Lincs), Will Forbes(JB Shropshire, Cambs) and Ross Howard (RE Howard, Ranby, Notts) forproviding information for the case studies. For supplying selected photos we wishto thank William Stephens and Briggs Irrigation.

Note: This booklet is for information purposes only. Always seek independentprofessional advice when planning irrigation developments.

Further information:

Copies of this booklet can also be downloaded from the UK Irrigation Associationwebsite www.ukia.org

Booklet produced by:

Jerry Knox

T: 01234 758365E: j.knox@cranfield.ac.ukW: www.cranfield.ac.uk/sas/staff/

knoxj.htm

Melvyn Kay

T: 01427 717627E: m.kay@ukia.orgW: www.ukia.org

Keith Weatherhead

T: 01234 758368E: k.weatherhead@cranfield.ac.ukW: www.cranfield.ac.uk/sas/staff/

weatherheadk.htm

Natural England

East Midlands RegionCeres House, 2 Searby RoadLincoln LN2 4DT

T: 01522 561470www.naturalengland.org.uk

Centre for Water Science

Cranfield UniversityCranfieldBedfordshire MK43 0AL

T: 01234 758365www.cranfield.ac.uk

UK Irrigation Association

c/o Moorland House10 Hayway, Rushden Northants NN10 6AG

T: 01427 717627www.ukia.org

Environment Agency

Rio House, Waterside DriveAztec West, Almondsbury Bristol BS32 4UD

T: 08708 506506www.environment-agency.gov.uk

National Farmers Union

East Midlands RegionAgriculture House, North GateUppingham, Rutland LE15 9NX

T: 01572 824255www.nfuonline.com

CLA

Eastern RegionAspen Grove Farm, Assington GreenSudbury, Suffolk CO10 8LY

T: 01284 789201www.cla.org.uk

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