Water Conservation Through Irrigation Technology

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Utah State University

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U.S. Government Documents (Utah RegionalDepository)

11-1-1989

Water Conservation rough IrrigationTechnology

Donald H. Negri

John J. Hanchar

United States Department of Agriculture, Economic Research Service

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Recommended CitationNegri, Donald H.; Hanchar, John J.; and United States Department of Agriculture, Economic Research Service, "Water Conservationrough Irrigation Technology" (1989).All U.S. Government Documents (Utah Regional Depository). Paper 119.hp://digitalcommons.usu.edu/govdocs/119
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: .' .:': Technology Agriculture ResourcesUnited StatesDepartment ofAgriculture Water Conservation Through:EconomicResearchService

Irrigation TechnologyAgricultureInformationBulletinNumber 576November 1989

Donald H. NegriJohn J. Hanchar

In this report .. lmproved irrigation technology andadvanced farm management practices offer anopportunity for agriculture to use water more efficiently. Farmers may install new equipment, suchas drip irrigation systems, or adopt advanced watermanagement practices to conserve water withoutsacrificing crop yields. While farmers' decision toadopt water-saving irrigation technology respondsto the cost of water, physical properties of the landsuch as topography or soil texture dominate thechoice of irrigation technology.Irrigated agriculture surely faces a future of increased water scarcity and higher water prices.Although the demand for water from irrigation andindustrial uses leveled off in the 1980's, continuedgrowth in urban water use and awareness of environmental and recreational values of water pointtoward sustained demand growth. Water supplydevelopment is not keeping pace with expandingdemand, creating fierce competition for existingsupplies. Improved irrigation technology and re-lated developments in water management on thefarm offer an opportunity for agriculture to alleviatewater scarcity and more efficiently allocate water.Increased water supplies from surface or groundwater sources are not the solution for meetingwater scarcity that they were in the past. Today,dwindling opportunities to develop new surfacesupplies, large Government budget deficits, andincreasing concern for environmental and recreationvalues make large-scale water projects such asdams and reservoirs unlikely. Concurrently, groundwater users in many areas are facing decliningground water tables, reduced well yields, and higher energy costs.In the absence of supply expansion, growing competition for water must be resolved through more

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efficient allocation and conservation. Agriculture isa logical target for water conservation and reallocation since it consumes over 80 percent of theNation's water resources.A question of considerable importance to poliCY-makers concerns how farmers will adjust productionto conserve water in response to less water andhigher water prices. The response may take avariety of forms: farmers may adopt more efficientirrigation technology, convert irrigated land to dryland farming, shift to crops that use less water,apply less water per acre for a given technologyand crop, or retire land from production. Irrigatorsoften responded to water scarcity in the past byadopting improved water-saving technology. Inresponse to increases in the price of water, irrigators will most likely again look to technology asa viable method of conserving water.

I' REPRODUCED BY:.s, Department of Commerce .... -

National Technicallntolmation Serv:ce ISpringfield, Virginia 22161 II-___ _________ J


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Agriculture Faces CompetHion for Water" \ 'e

Agriculture competes with households, Industries,' and other Interests fo r limited waterresources, many of which were developed with Government support. .Beginning in the late 1800's, Government policiesand legal tenets governing water rights encouragedwater supply develo'pment, particularly in the ari,d

West. These policies promoted the exploitation ofrivers, streams, and ground water aquifers for irrigated agricuhure, and fostered the successful settlement of arid and semiarid western lands.Today, irrigated agriculture consumes the largestportion of the Nation's water resources. Waterconsumption occurs when water is evaporated,transpired, incorporated into products or crops,consumed by humans or livestock, or otherwiseremoved from the water environment. Total freshwater consumptive use in the United States wasestimated at 103 million acre-feet during 1985 withirrigation accounting for approximately 83 percent ofthe total (fig. 1). (One acre-foot is the amountofwater needed to cover an acre of land to a depthof 1 foot, and is equal to 325,850 gallons.)In return, irrigated agricuhure contributes ,a substantial amount to the total value of agricultural products sold. Irrigated lands account for 13 percentof the Nation's harvested cropland acres, and contribute about 30 percent to the value of croplandproduction (fig. 2, table 1).Government Played a Key Role In DevelopingWater SuppliesWater storage and conveyance facilities that 'werefinanced and constructed by the Federal Government ,provide irrigation water to about one-fourth ofthe irrigated acreage in the West. Since 1902 theBureau of Reclamation has constructed an irrigationinfrastructure of 355 water-storage reservoirs, 254diversion dams, and thousands of miles of transportation canals, pipelines, tunnels, and laterals. Inmany cases, 'these facilities provided-and stillprovide-water to municipal, industrial, and agricultural users at prices below cost.Competition. fo r Water Resources Is GrowingThe demands placed on, the Nation's water resources by competing uses are increasing and thetrend is expected to continue. Water withdrawaloccurs when water is removed ,from the ground ordiverted from a surface source for use. Some ofthe water withdrawn is returned to the stream.Water consumption implies that the water is not'available for reuse. Water demands for traditional2

uses (for example, a g r i c u h u n ~ , energy, domestic,and industrial) are expected to increase as population grows, even though withdrawals declinedslightly from 1980 to 1985.Competition may also originate from two relativelynew sources of water demand. First, growingawareness of environmental and recreational' consequences of water diversions has increased thevalue of water remaining in rivers and streams. Ofparticular importance is the 9rowing recognition thatwater has value for water-qu.ality improvement, fishpropagation, and recreation when left instream: 'A second source of water competition currentlyarising from outstanding Indian claims to reservedwater rights. When Indian rElservations were cre-'ated, the Federal Government implicitly establishedIndian water rights. The armunt of water as so- 'ciated with the rights, if sustained, is uncertain butpotentially large.In many cases, increasing dElmands from traditionalsources and new sources of demand conflict withexisting appropriations a m o n ~ J agriculture, urban;industrial, or hydroelectriC USI3S. 'Era of Water Supply Expal1lslon Has EndedIn the past, the development of abundant sourcesof supplies resolved competing demands for scarcewater resources and relieved pressure to adoptmore efficient allocation mechanisms. Abundantwater supplies and subsidized prices from manyGovernment water projects stimulated consumptionand discouraged efficient use!. In the era of abun-'dant supply, efficient water allocatiOn was not ahigh priority. That era has nJn its course.Three significant revisions in Federal water policytestify that the era of large-scale surface water 'supply development has endl3d. First, Congresshas authorized only one new water project in thelast 12 years. Second, the mission of the Bureauof Reclamation has recently changed from water ,development to water management. The Bu're'au ofReclamation will devote fewer resources to thedevelopment of new water SlJpplies and more resources to the efficient management and use ofexisting water supplies.1 Third, the Federal

, u.s. Dept. of the Interior, Bureau of Reclamation, Assess-ment '87: A New Direction for the j9ureau of Redamation,1987.


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Government is expanding protection of rivers andstreams from all forms of development. At thebeginning of 1988, 7,700 miles of rivers andstreams had been protected from developmentunder the Wild and Scenic Rivers Act of 1968.Ground water constitutes the second major sourceof water supply, comprising 30 percent of totalfreshwater use from all sources. But the availa-bility of ground water is also shrinking in manyareas as water tables and well yields fall. Theaverage annual rates of ground water decline in 11States, identified as problem areas range from one-half to 4 feet. Declining ground water tables, high-er energy costs, and increasing ground water con-tamination have diminished the availability andincreased the cost of ground water.Efficient Allocation and Conservation CanAlleviate Water ScarcityIn the absence of supply expansion, efforts toresolve increasing competition for water resourcesmust stress conservation and efficient allocationamong competing uses. Agriculture ,is a likelytarget of efforts to more efficiently allocate water,since it is, the largest consumer.With water supply development unlikely, higherwater prices and less water for irrigated agricultureare inevitable. Although the mechanisms for moreefficient water allocation are still evolving, waterconservation through more efficient water use isthe leading candidate for alleviating water scarcity.More efficient irrigation technology and new water ,management practices have the potential to con-serve water with little or no loss in agricultural 'production.

~ r e 2Importance of Irrigation to U ; s ~ ,agriculture, % of 'harvesledcropla'nd irrigated

Rice' 100.0Land in orchards 73.6Irish potaloes 67.6 IVegetables 63.6 ISugarcane 54.7 ISugar beets 51.61 ,Dry beans 4 2 . ~ ICotton 36.1 IPeanuts for nuts 29.0 IHay 1 4 . 8DBarley 1 4 . 6DCorn for silage 14.0 DCorn for grain 13.6 DGrain sorghum 13.3 DWheat for grain 7.0 DSoybeans 4.7 D1987 dala. SOUIll.: CensU8 01 AglcLdture,

Table 1-Acreage and value of Irrigatedagriculture, 1982

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Irrigation Technology and Management Practices Can Save WaterIrrigators can choose better technology and Improve their methods of using wate'r toconserve scarce water supplies without sacrificing crop yields.

Water-conserving irrigation technology and watermanagement practices are playing an increasinglyimportant role in reducing both energy costs andwater use. Not all of the water applied to the fieldis available for use by the plant, since some fraction is lost to evaporation, deep percolation, orrunoff. Irrigation technology and managementpractices-by substituting more capital, labor, andmanagement skills for water-reduce water lossthrough increased application efficiency with liHie orno loss in yields. However, the efficiency of anapplication system depends not only on the attributes of the irrigation system but also on thephysical characteristics of the farm such as soiltexture, topography, and weather.Irrigation Technology That Conserves WaterWater distribution systems available to earlyirrigators were limited to gravity flow systems suchas simple stream diversions, flooding, and ditchand siphon systems. Gravity flow systems use theforce of gravity to distribute water across thesurface of the field. Water is supplied to the upperend of a field by a ditch or pipe and then appliedto the field through a siphon tube or gate.Since water percolates down below the root zoneas it flows across the field, excess water must beapplied to the upper end of the field to ensure thatsufficient water reaches the lower end of the field.Guaranteeing a fully irrigated field often requiresthat water be allowed to run off the tail end of thefield. Furrow irrigation, where water flows over thesoil only in shallow channels between the croprows, can reduce water lost to deep percolation.Sprinkler SystemsAs economic conditions changed and technologyimproved, water-saving sprinkler irrigation systemsbecame more attractive alternatives. Most sprinklerirrigation technologies save water relative to gravityflow systems by distributing water evenly on thefield, reducing percolation below the root zone andeliminating runoff. Sprinkler systems spray wateronto the field through nozzles attached to a network of pressurized pipes.Examples of some early sprinkler systems includesolid set, hand move, and side roll. A major advancement in sprinkler irrigation technology was thecenter pivot irrigation system.

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Primarily in response to increased costs of; water ..and a greater interest in water conservation,irrigators recently have begun adopting advancedirrigation systems. These improved technologiescan achieve exceptionally high application efficien- .cies. Examples of advancelj sprinkler systemsinclude drip irrigation, low-pressure sprinklers, andlow-energy precision application (LEPA). (Illustra- .tions and descriptions are on pages 6-7) ..Improved Gravity Systems:Economic conditions have also spawned improved gravity irrigation technologiel) such as surge flow orcablegation. These technol()gies can significantlyimprove application efficienciies by contrOlling runoffand reducing deep percolatii:m.Surge flow and cablegation techniques modifygated pipe furrow irrigation systems so that thetiming and quantity of flow from the gates of thepipeline are more efficiently controlled. Theirrigator qm thus apply w a t e ~ r more uniformlyacross the field.Water Management Practlc:es ThatConserve WaterTechnological advances in irrigation efficiency havealso occurred in water manclgement. Water management practices can signilricantly reduce water . .use for a given irrigation system. Managementpractices typically involve more labor and watermanagement skills. Sophistiicated management :practices applied to gravity-irrigated fields can .....achieve efficiencies comparalble to sprinkler systems. Management practices include precision fieldleveling, furrow diking, limited irrigation-dryland .farming, computer-aided irrigation scheduling, andreusing field runoff (tailwater).Deficit irrigation saves water through reduced waterapplication rates for a given cropping pattern andirrigation technology. Deficit irrigation is the practice of stressing crops and k)wering crop yield withreduced water application rales. Maximizing netreturn may dictate lower application rates, forfeitinghigher yields in exchange for lower water use. Inmany cases, water can be reduced considerablywithout significantly reducing crop yield. Carefultiming of water application and efficient applicationminimize yield losses.


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Technology and Management ImproveIrrigation EfficiencyGreater irrigation efficiencies associated with improved irrigation technology and advanced watermanagement practices allow fanners to meet thewater needs of the plant while applying less water.Water use efficiency is a measure used to compare irrigation systems. It measures the amount ofwater used for plant growth as a percentage oftotal water applied.Numerous experimental and empirical studies haveshown that sprinkler technology reduces water usecompared with gravity flow systems. Water useefficiencies range from 35 to 85 percent for gravityand 50 to 85 percent for sprinkler systems (table2). For LEPAirrigation systems, for example, ofthe total water applied, 80-90 percent is used forplant growth. The rest runs off the field, evaporates, or percolates below the plant's roots. Actualirrigation efficiency depends on the physical textureof the field including soil texture, topography, andclimate. Drip irrigation and LEPA systems canachieve effiCiencies ranging from 80 to 90 percent.Tailwater reuse pits, by recirculating field runoff,can produce water savings from 10 to 30 percentover conventional gravity depending on topographyand soil characteristics.

Table 2-Water use efficiencies of IrrigationsystemsSystem

Gravity: .FloodFurrow'Improved gravity'Sprinklers:Big gunCenter pivorSide rollSolid setHand moveLow Energy PrecisionA p p l i ~ a t i o n (LEPA)

Drip-trickle

Field efficiency

Percent35-5055-7075-85

50-6570-8565-8065-8055-65

, Includes tailwater recovery, precision land leveling, andsurge flow systems.2 Includes h i g h ~ and low-pressure center pivot., - ~ - - - - - - - - - - - - ~ Of the total amount 01 waterapplied, 80-90 percent isused lot plant growth. Therest runs oH, evaporates, orpercolates below the plant'sroots.

Irrigators Are Adopting New TechnologyFigures 3 and 4 show the increase in water-savingirrigation technologies in use. Although drip ortrickle systems cover a relatively small number ofacres, use of this very efficient method more thandoubled between 1979 and 1984. Thus far thesesystems are typically used on tree crops, ongrapes, and in nurseries.

FIgure 3Trends In use of Irrigation systemsMillion acres1

SprinklerCenter pivot ~ : ~ W & r r 1 @ Mechanical move ~ : g ~ wrrraHand move 3.71.92__Solid set and permanent 1 iiiGravityGated pipe 8 .408.36

[2j1979.1984

Ditch with siphon tubes 1 9 ~ ~ F 1 W ' l C Flooding l a : ~ ~ ~ M OtherDrip-trickle . 3 2 ~ .88Subirrigation . 2 4 ~ .62

0 2 4 6 8 10 12V ConlerrrB10U8 United States.Source: 1979 and 1984 Farm IIl1d RlIl1ch ntgatlon 5uT\/8Y.

F"lQUre 4ExpanSion of drip-trickle Irrigation in 17Western States, 1974-86Million acres0.60.50.40.30.2

0.1o1974 76 78 80 82 84

1416

86

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Main Features of Irrigation Systems and PracticesSprinkler SystemsSolid Set is a stationary s p r i r i k l e r ~ s y s t e m o f t e n used in orchards. Supply pipelines are fixed, usually below the surface, and sprinkler nozzles areelevated above the surface. .Hand Move is a portable sprinkler system in whichthe irrigator moves the supply pipelines in sectionsfrom one position to the next.Side Roll is a portable sprinkler system in whichthe pipeline acts as an axle for a series of largediameter wheels. An engine mounted in the centerof the pipeline moves the system across the field.Center Pivot is a seH-propelled sprinkler system inwhich the pipeline is suspenped above the field ona row of mobile towers. Water is pumped into thepipe at the center of the field, and the towers ro-tate slowly around the pivot point. Sprinkler nozzles mounted on the pipeline distribute water underpressure to the field as the pipeline rotates. Thisbasic system has been adapted to both high (45 to100pounds per square inch) and low (15 to 45pounds per square inch) pressure systems.

i .LEPA (Low Energy Precision Application) is anadaptation of the center. pivot system that usestubes extending down from the pipeline to applywater at low pressure below the plant canopy.Emitting the water close to the ground cuts waterloss from evaporation and wind and increasesapplication uniformity.Drip or Trickle Irrigation uses small-diameter tubesplaced above or below the field's surface near theplant's root zone. Water emitters in the tubesdispense water directly to the root zone, precludingrunoff or deep percolation and minimizing evapora-tion. ... .

Side roll6

Low-pressure center pivot

LEPA

Drip-trickle


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Gravity SystemsDitch with Siphon Tubes supplies water by siphoning water .from the irrigation ditch to the field.-Gated Pipe supplies water through a series ofopenings in a supply pipe. This system has beenimproved to allow irrigators more control overtiming 'and quantity of water flows.Surge Flow delivers water to the furrow in timedreleases. After a surge the soil forms a water sealpermitting the next surge of water to travel furtherdown the furrow. This technique significantly reduces the time needed for irrigation water to bedistributed the full length of the field, reducing deeppercolation and results in higher water applicationefficiency.Cab/egationdelivers water to furrows automaticallyand sequentially using a plug attached to a cableinsideJhe supply pipe. f The water savings is basedon the same principle as surge flow.Water Management PracticesPrecision Fie/d Leveling (also called laser leveling)grades a field so there is little variation in fieldcontour. Precise leveling promotes uniform waterapplication across the field.Limited Irrigation-Dry/and Farming irrigates only theupper end of the field leaving the lower end of thefield solely dependent on rainfall. This techniqueminimizes or eliminates field runoff and reducesdeep percolation and evaporative losses./rrig"ation Scheduling monitors soil moisture andclimate to' precisely regulate water applications.'Monitoring soil moisture involves preCision instru.ments (such as tensiometers, gypsum blocks, and'neutron probes) which accurately measure themoisture available for plant growth. The operatordelivers water to the field during critical cropgrowth stages in precise quantities.Furrow Diking places dikes in the furrows to capture additional rainfall.Tai/waterBeuse captures field runoff in pits dug inlOW-lying areas of the farm and recirculates thewater to the-top of the field. Rising water costshave made tailwater reuse a popular conservationmeasure; ,"

Ditch with siphon tubes

Gated pipe

Furrow diking

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Many Factors Affect Producers' 'Choice of Irrigation TechnologyWhile the decision to adopt water-saving Irrigation technology responds to the COlin ofwater, physical properties of the land such as topography or soli texture dominatE! thechoice of Irrigation technology.Physical properties of the irrigated land and economic principles together determine the most profitable irrigation system for the farm. This sectionreports on selected resuns of a study relating thechoice of irrigation system or management practiceto the physical and economic characteristics of thefarm.Physical characteristics of the farm, like climate,soil texture, or land topography, restrict the technology options available to the farm operator.Gravity systems, for example, require flat topography so that irrigation water can flow evenly overthe field. In some cases, physical characteristicsmay dictate a particular technology. Steep slopesare not suited to gravity irrigation without costlymodification.Even where the physical characteristics do notpreclude irrigation technology or management options, they may still favor one alternative over an- .other. Hot and windy regions, for example, favorgravity irrigation because a large share of watersprayed into the air through sprinklers evaporates.Of course, economics also plays an important rolein irrigation technology choice. Higher water costsor water scarcity encourage more efficient use ofwater on the farm. Indeed, farmers facing highwater costs may adopt more efficient irrigationtechnology than their low-cost counterparts. Al-though more efficient water application systemsreduce water use and associated costs over time,the system itself can represent a substantial investment over traditional gravity irrigation. A centerpivot system irrigating 130 acres can cost $60,000or more. Advanced water management practices,on the other hand, do not require large capitalinvestments but often require more labor and ex-pertise than high-technology equipment.The study examined to what extent choosing moreadvanced technology, such as sprinkler irrigation ortailwater reuse pits, depends on the cost of water,the price of labor, climate, land topography, soilcharacteristics, and farm size. The analysis considered two broad categories of irrigation technology, sprinkler and gravity irrigation, but did notdistinguish between various types of systems withinthe two categories. For those irrigators who selected gravity systems, the choice of adopting tailwaterreuse pits was also examined.8

A separate analysis examinel:! whether irrigatorsimplemented deficit irrigation techniques.Research Shows Multiple Factors AffectIrrigation Cholc.e .The resuns indicate that both physical characteristics of the land and economics play an importantrole in choosing an irrigation system. The probability that producers will adopt water-saving technOl-ogy responds to the cost of water, but only marginally. For example, in 1984 the' average cost ofpumping an acre-foot of ground water was $15.78.The analysis suggests that a 10-percent increase inprice to $17.34 would produce a 0.3-percent i n ~ ' : crease in acreage irrigated b ~ f sprinkler.If the resuns are applied to the 45 million irrigatedacres in the United States, this translates into156,000 additional acres converted to sprinklerirrigation. If water costs incroase an average of $5to $20.77, an increase of almost one-third, thennearly 600,000 acres would c:onvert to sprinklerirrigation. Assuming that sprinklers save 15 percent more water than gravity irrigation, the totalwater savings would amount to 156,000 a c r e - h ~ e t , or enough water to serve a city of almost 1 millionfor 1 year.Analysis of irrigation technol09Y choice on the farmindicates that physical characteristics of the farm'dominate the decision. Soil characteristics including slope, texture, and quality, and, to a lesser ..extent, climate and labor costs have significanteffects on the technology choice. Specifically, theresearch shows: Irrigators who farm soils with low water-holdingcapacity are more likely to adopt sprinkler systems. Porous soils or steep slopes are unsuitable for gravity because! deep percolation or .

inadequate coverage inhibit efficient water ap-plication. Farmers in regions with high rainfall are morelikely to adopt sprinkler systems. Irrigation inthese regions is primarily supplemental.Sprinkler irrigation, by providing greater controlover the water quantity applied, can prevent' cropdamage and inefficient watE!r use which mightresuH from an unexpected rainfall following aheavy irrigation.


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Farmers in hot or windy regions are more likelyto adopt gravity since a large fraction of waterapplied with sprinkler systems evaporates underthese climate conditions. Since gravity irrigation systems tend to be morelabor-intensive than sprinkler, high labor costsinduce a shift to laborsaving sprinkler irrigation.Tal/water ReuseFor gravity irrigators an analysis of factors thatdetermine the adoption of tailwater recirculationreveals results similar to those obtained for sprinkler irrigation choice. Onfarm physical characteristics have the greatest impact on the selection probabilities. Selected results show: Tailwater reuse is an effective water-savingpractice only on soils with high water-holding

c a p a ~ i t y since high water intake ratesassociated with sandy or porous SOils limit waterrunoff. . Where soils have high salt content, irrigatorsavoid recirculating runoff water to prevent furthersalt concentration. Compared with sprinkler adoption, water cost ismore effective in inducing gravity irrigators toadopt water-saving recirculation practices. More rainfall reduces the effectiveness and then'eed for tailwater reuse because less irrigationwater is applied and conservation is less essen

tial.Deficit IrrigationDeficit irrigation is the practice of reducing waterapplication rates with consequent lower yields. .This management practice trades high yields forlower water costs to maximize net returns ratherthan yields.The effects of water prices, weather, soil conditions, and farm characteristics on water applied peracre for various crops were statistically analyzed.Results provide little evidence that farmers engagein deficit irrigation of crops in response to higherwater prices. Statistical measures indicate thatonce farmers decide to irrigate a crop with a particular technology, they do not reduce water appliedper acre in response to high water prices. Rather,they appear to maximize crop yield, Instead ofdeficit irrigating, farmers adjust other components ofwater demand. For example, farmers may choosea more efficient irrigation technology or change thecrop planted to one that uses less water.

How Do Farmers Respond to theCost of Water?Price Elasticity for Water

Higher water prices will reduce agriculturalwater use, but by how much? Several studiesof agricultural water demand place the priceelasticity of demand in the range of -0.15 to-0.25. Thus, a1 O ~ p e r c e n t increase in theprice of water would produce a 1.5- to 2.5-percent reduction in the water demand.While the response is inelastic, at currentwater withdrawal levels the correspondingwater savings range from 2.3 to 3.8 millionacre-feet per year, enough water to servebetween 12 and 19 million people per year.Moreover, price elasticities are apt to increaseas more technological substitutes are introduced and awareness of new water-savingmanagement practices grows.

The results were different for pastureland. Farmerswith expensive water forfeit yields on pastureland,As pumping costs increase, farmers tend to applyless water to pasture and accept the lower production associated with the lower water use. Thereason is that irrigated pasture tends to be amarginal use of water. As water becomes moreexpensive, irrigators would be expected to allocatewater away from marginal uses, such as pasture.Although water application rates for most cropswere insensitive to water price, application rates formany crops were quite sensitive to the physicalcharacteristics of the farm.Rainfall reduces the amount of irrigation waterrequired to meet the water needs of crops.Farmers tend to apply less water per acre as theamount of rainfall increases.Soil conditions influence water use for severalcrops. Farmers tend to apply less water per acreto sorghum, wheat, barley, hay, and pasture grownon clay soils compared with loam soils. Clay soilshave a higher water-holding capacity than loams.Crops with deep and profuse root systems (forexample, small grains, grain sorghum, and alfalfahay) are able to exploit the increased soil moisturelevels present in clay soils. Therefore, the waterneeds of crops grown on clay soils relative toloams may be met by a lower level of waterapplied.

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Irrigated Land in Farms: 19821 Dol = 10.000 Acres

United Slale.Tolal49.002,433U 5 L)epanment 01 Commerce

Bureau 01 the Census

Contact Don Negri or John Hostetler, (202-786-1410), Economic Research Service, U.S. DelPartmentof Agriculture, Room 534, 1301 New York Avenue, NW., Washington, DC, 20005-4788.

Technology Agriculture ResourcesThis ongoing series of bulletins includes lively, up-to-the-minute analysis of significant issues affecting technology,agriculture, and resources. To order another copy of this report, just dial 1-800-999-6779. Toll frE!e.Ask for Water Conservation ThrouQh Irrigation Technology (AIB-576).The first report in the series, International Technology Transfer in Agriculture (AIB-571). is also available. Forfurther information on this series, contact John Reilly (202-786-1448), Economic Research Servicl9, U.S. Department of Agriculture, Room 524, 1301 New York Avenue, NW., Washington, DC, 20005-4788.

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