Efficiency in Irrigation (RMI 1990)

EFFICIENCY IN IRRIGATION: A Source book and Information Guide

By June Weintraub

ROCKY MOUNTAIN INSTITUTE May 1990

1739 SNOWMASS C REEK R·OAD. SNOWMASS. C OLORADO 81654 · 9199

( 303) 927 - 3 8 5 1, 927 - 31 2 8

CONTENTS

IN1RODUCITON .................................. ~ ...............•.............. ................. 1

'WATER m AGRICULTURE ..................•..........•. : .................................... 3

Efficiency in Irrigation ...................................................... ............. 4

~URFACE METIIODS .......•................... .-................................................. 6

Increasing efficiency of smface systems ........ ; .... ~ ................................. 8 .

SPRINKLER· SYSTEMS ..... ~ .... · ............................... ··········~·············· .... .-... 10

·· Increasing efficiency of sprinkler systems .......... · .. ." ...................... : ......... 10

TRICKLE SYSTEMS .................... ~ ........................................................ 12

Types of Trickle Systems .................... .' ................. , .............. ; ............ 12

SOIL WATER .................... .......................... ; .................................... ... 13

Soil Moisture· Monitoring .... ·: ........................................................... 13

Crop WaterUse ............. ...................... ~ ........................................ 14

Climate Factors ......... ............................................................... .. .. 15

LAND PREPARATION ME1HODS ...................... ..... ...................... , ....... .. 16

CONCLUSION ....... ............. .. ............ ........... .. .... ......... .. .... .. .... ' ........... .. 17

REFERENCES ..................................... ...... ................ ............... .. ... .. ... 18

RESOURCES .: ..................................................... ............... .. .... ....... ... 20

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INTRODUCTION

This document is concerned with the conservation of water through its efficient use in irrigation. This is just one aspect of a sustainable agricultural system which we need to pursue. The ideals of sustainable agriculture encompass a variety of principles all revolving around the efficient use of resources in ways that do not disrupt our quality of life or environment A sustainable agriculture uses inputs -- water, energy, land, and labor -- wisely, and seeks to mitigate some of the social and environmental problems created by conventional agricultural practices.

Conventional, high-input agricultural practices have contributed to environmental degradation the world over. Over-tillage and over-irrigation have eroded soil. More and more chemical fertilizers must be produced and applied to decreasingly fertile land. Farms that only grow one crop, or monocultures, have provided abundant food and habitat for persistent pests; the increasing use of chemical pesticides has contaminated the food chain and our water supplies. Overuse of water has led to resource depletion and loss of quality.

Some conventional agricultural systems are more efficient than otherS-in their resqurce use. Nonetheless, most agricwture relies heavily on non-renewable resources. This depe_ndency has its own adverse impacts. In particular, the use of fossil fuels in large-scale ~g contributes to air pollution and global wfilming. Fossil fuels are commonly used in all phases of farming: ~o .manufacture, transport, and apply fertilizers and pesticides; to prepart; land, harvest crops, and transport them to markets; and to pump and distribute water. Water, too, is a non-renewable resource. fn the Higli Plains of the United States, fossil groundwater supplies have been exploited to the point where the future of irrigated farining is threatened.

Many analyses of the sustainability of a farming system are limited to an economic realm. While a profitable farming system may be economically sustainable, it may still have unquantified costs. Some of these expenses may include: supporting and restoring the rural economies which have been displaced by huge farms; excess energy inputs related to food processing and distribution; and the cost to mitigate the environmental consequences of inefficient, non-sustainable farming processes. Unless the incidental costs of our food production system are defined, its economic sustainability can not be properly assessed.

These "hldden" inputs of conventional agriculture are often ignored. Thomas Edens (1985) writes " ... the notion of one farmer supporting a multitude of consumers is erroneous. It would be more accurate to say that for every seventy people fed, one farmer, four tractors, thousands of dollars of capital, three hundred semi-vans, 82,000 miles of concrete highway, two people in processing and marketing, etc., are employed .. ". Agriculture is a complex system. Its impacts are far reaching and can not be alleviated by simply changing one or two farming practices

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A sustainable agriculture seeks to avoid the myriad costs and problems associated with

conventional agriculture. Numerous definitions of sustainable agriculture exist. Wendell

.Berry has called sustainable agriculture one that "does not deplete soils or people."

(Jackson et al 1984.) Marty Strange of the Center for Rural Affairs in Nebraska wrote

••nie objective of an agriculture that is sustainable must be to nourish a renewable pool of

human land stewards who earn a healthy living by farming well." (Jackson et al, 1984.)

The International Alliance for Sustainable Agriculture has this definition: · "A sustainable ·

agriculture is ecologically sound, econoriiically viable, socially just and humane .. " (Gips,

1990.)

Philosophically, the goals of sustainable agriculture make sense, butwhat does sustainable

agriculture mean in real terms? Environmentally, socially, and economically s<>und fanning

techniques exist which can in effect replace conventional agricultural techniques without . . .

adversely affecting our food supply. The National Research Council, in its report

confmning the viability of sustainable agriculture, defines "alternative agriculture" in these

concrete terms:

Alternative agriculture is any system of food or fiber production

tlutt systematically pursues the following goals: • More thorough incorporation of natural processes. such as

nutrient cycles~ nitrogen fixation, and pest-predator relationships into the agricultural production process;

• Reduction iti ·the use of off-farm inputs with . the greatest

potential to harm the environment or the health of farmers and consumers; .

• Greater productive use of the biological and genetic

potential of plant and animal species; • Improvement of the match between cropping patterns and

the productive potential and physical limitations of

agricultural lands to ensure long-term sustainability of current production levels;· and

• Profitable and efficient production with emphasis on

improved farm management and conservation of soil,

water, energy, and biologica.J. resources. (NRC, 1989.)

There are many ways to improve the sustainability of our agricultural ·system. This

document focuses on just one way that growers can reduce their use of some resources,

namely water and the energy used to move it


WATER IN AGRICULTURE

Irrigated agriculture dates back several thousand years. Native Americans used irrigation to support their populations as early as 100 B.C., (USDI, 1979) and irrigation in Mesopotamia can be traced back to 500 B.C. (Postel, 1989.) Although irrigation· technqlogy has developed over the centuries, some ''primitive" irrigation techniques are still in use today. These low-technology methods may be as appropriate and efficient as more modern, highly technical irrigation schemes. For instance, when properly managed, the diversion of water through rock lined canals can achieve efficiencies similar to some sprinkler systems.

The global community has realized enormous benefits from irrigatioµ. The use of irrigation to supplement rainfall has allowed otherwise inarat?le lands to be pro~uctive. The resulting increase in global food stores has made possible population growth, which would be severely curtailed if we were dependent only on naturally available moisture to provide food and fiber.· In fact, the growth of irrigated lands has closely paralleled the growth of the world popu~ation. (Jensen, 1983.) ·

While irrigation has made possible the increase in food production and accompanying increases in the output of certain sectors of the economy, it has not been without negative impacts. The excessive use of energy to withdraw water from deep underground wells, the depletion of streamflows and resulting reductions in wildlife habitat and recreational use areas, and decreases in water quality and soil fertility are some of the· widespread problems which have accompanied the growth of irrigated agriculture. (USDI, 1979.)

Many of these problems may be alleviated through increases in the efficiency of irrigation, yet all must be considered in the context of the larger issues mentioned previously. Efficiency in irrigation is just one· step toward resolution of the problems within our global agricultural system .. Efficiency in irrigation may be an expensive investment, and most fanners base dedsions on short-term economic efficiency, rather than water or energy efficiency. Many water-efficient techniques are more energy intensive than the ones they replace, and some are more labor intensive. (Whittlesey, 1986.)

The long term costs of inefficiency probably exceed any expense incurred in upgrading an irrigation syste~ The real value of an efficient irrigation scheme can not be determined unless the costs of decreasing environmental quality, reductions in arable land, losses of soil and depletion of water are factored in. It is the farmer who has to increase his input of nutrients when soil losses due to over-irrigation deplete the land's fertility. It is the farmer who has to drill deeper and deeper wells and pump longer distances to supply crops with water from diminishing groundwater sources. Thus, it is the farmer who suffers the hidden costs of inefficient irrigation. It is therefore to the irrigator' s advantage to switch to a water-efficient irrigation system. Improving efficiency is not li~ted to redesigning the

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entire irrigation system. Careful water-management and upgraded land-preparation techniques are also effective ways to enhance water efficiency.

Efficiency in Irrigation

In order to evaluate the efficiency of an irrigation technique, one must have a clear understanding of what is meant by efficiency. Using the con~ept of consumptive and nonconsumptive use; efficiency can be defined in .a Ii.umber of ways.

Consumptive uses are those in which the use of water makes it unavailable to others. For most inigation, water is withdrawn at one point and used and returned at another distant point downstream. H the distance between withdrawal and return. is significant, interim users are denied the use of that water. Such water has been consumptively used. Ti:anspiration by the crop and the loss of water through evaporation also fall into this class. Additionally, water which is returned to a point near whereit was withdrawn but is of diminished quality may be considered to have been consumptively used. A nonconsumptive use is any in. which water is returned at or near the point of withdrawal without having experienced any decrease in quality;

. Conveyance efficiency refers to the ratio of water delivered. to a ~rop versus that diverted from the source~ Water losses during conveyance are often non-consumptive. Seepage from ditehes, leakage from distribution pipes, and pump losses .are .all. ways in whi~h water may be lost on its way to an irrigated field This lost water is returned to the aquifer or swface water source without any loss of quality. In some applications, conveyance losses are evaporative, and thus consumptive. Enhancing c.onveyance .. efficiency always decreases the irrigators costs to procur~ and move the water, however such improvements may not increase actual availability of water for other uses.

Application efficiency refers to ·the amount of water available to the crop, versus the amount actually applied to the field Most-losses during application are consumptive. When applied water moves deep into the soil profile or runs off the field it is no longer . u~eful for crop growth. While this excess water may return. to a point near where it was withdrawn, it usually is of decreased quality, and contains dissolved salts, fertilizers, or pesticides. Evaporative losses during application are also common and generally not recoverable. Reducing deep percolation, runoff, and evaporation by increasing application efficiency makes previously inaccessible water available to downstream users.

Uniformity of application is a related concept which can affect the application efficiency. If water is applied evenly to all points in a field, the likelihood of overwatering one part while underwatering another is decreased. This results in a decrease in deep percolation and runoff on the one hand, and of crop water stress on the other. An ideal irrigation system Will have a high unifonnity of application and a high application efficiency.

Finally, economic efficiency is the ratio of financial output to financial input as relates to application of irrigation water. Financial output includes the gmss income produced by sale of the crop; financial input must take into account water and pumping costs, application

ROCKY MOUNTAIN INS'ITI'UTE EFFICIENCY IN IRRIGATION PAGE 5

costs, labor inputs, land preparation for irrigation, the annualized cost of the hardware involved in the irrigation system. and the aforementioned costs of inefficiency. (Jensen, 1983; Whittlesey, 1986.)

Crop type, soil moisture holding capacity, climatic factors, labor, energy, and water availability are all factors which come into play when an irrigator selects and analyzes an irrigation system. There is no one perfect irrigation system. The following sections describe the three main types of traditional irrigation methods: surface, sprinkler, and subsurface. The discussions briefly explain the mode of operation of each irrigation type followed by descriptions of specific ways that the efficiency of ihe irrigation system may be improved. Sections on soil moisture management techniques and land preparation methods are also included. Finally the references and resources sections contain bibliographies and highlights of available information on specific topics. ·

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SURF ACE ·METHODS *

Surface methods are the most prevalent of all irrigation types, both in the U.S. and

throughout the world. In 1984, more than 126,000 American farms irrigated 27.4 million

acres, approximately half of all irrigated cropland. (Bajwa, et al, 1987.) . In surface

irrigation systems, soil wetting is achieved by overland flow. Water is released at the high

end of a field and travelS either in channels or as shallow overland flow. As the water ·

moves, it percolates into the soil where it is then stored in the pore spaces in the root zone.

Excess water will either move down below the root zone as deep percolation or will run off

the land surface. The rate at which the water moves down the field and into the soil ·

depends on four basic factors -- the rate of water application, the slope of the land, the

resistance of the soil to the. flow, and· the infiltration characteristics of the soil. Each of

these factors can be controlled to varying extents, in tum affecting the efficiency of the

system.

Surface techniques can be adapted to a variety of terrains and generally have lower capital

costs than other irrigation methods, however labor requirements are typically higher.

Whµe furrows can be constructed along the contours of steeply sloped land; some land

may require levelling to make it suitable for a selected surface technique. In fact, land

preparation is generally the major cost associated with surface techniques. Most surface

methods ·require some land preparation, and some are inore suited to particular soils and

cliniates. Runoff and erosion may be problems on steep slopes or in areas where inflow

rates are too high for the terrain; thtis proper design is vital to ensure efficiency . .

It is difficult to categorize surface methods, as countless variations are in use today. The

table on the next page sUIIIIIIBiizes five basic types of surface techniques, their mode of

operation, and certain applicable design constraints.

*This section is based on Jensen, 1983; CAST, 1988; and Solomon, 1988. ~


SURFACE IRRIGATION TYPES

SURFAC~ METHOD TYPE AND MODE APPLICABLE OPTIMAL SLOPES OTHER INFO OF APPLICATION CROPS . AND SOIL TYPES

ditch sod forming 0.5% - 4% erosive high labor to achieve a series of ditches run along contour lines crops or any soils; good efficiency, as approximate! y 25 meters to 100 meters apart; crop on non- up to 15% for other irrigations must be in water flows over the downslope bank of an erosive soils soils; short frequent sets; upper ditch, over cultivated land and into the any soil but those no land preparation next pickup ditch with high infiltration cost

rates basin most crops · level land; low labor; water is released at one or more points into a low infiltration rates . high leveling cost level area and ponded until infiltration border non-ctiltivated <0.5.%; okay for up low labor water is released at the upper end of a graded close-growing to 4% slopesµ non- requirements; area and flows down overland as a sheet, crops; sod forming crops land must be graded infiltrating the soil as it travels orchards and best for moderate

vineyards infiltration rates contour levee paddy rice or <0.5% levees must be water is introduced at a levee on an upper pastureland soils of medium to reconstructed after contour line and floods the irrigated area at a fine texture with criltivation specified depth for a specified time, after . gqod waterholding which excess water is draine<;l at the lower capacity levee; vertical distance between contours (and thus levees) is typically aoout 60mm or 3in. furrow best for row grades up to 4% low labor;· water is applied in channels spaced about 1 crops but may medium to usually low capital meter apart and runs downslope through the be used for moderately fine cost channels, infiltrating the soil as it moves most crops textured soils with .

except rice relatively high water holding capacity

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Increasing efficiency of surface systems

Given that a surface system has been appropriately designed and maintained, a certain degree of application efficiency may be assumed. Certain innovative technologies are available tliat can be applied to a surface system without extensive modification of an existing system. Additionally, proper water-management methods . (described elsewhere) can enhance efficiency.

The two efficiency-increasing methods described below are most easily adapte.d to furrow type irrigation systems that use gated pipes for water delivery. A gated pipe is a delivery pipe with a series of openings located at intervals. Each opening, or gate, is located at the high end of each furrow. In regular operation, water travels the length of the delivery pipe ·and is released simultaneously into all furrows through the·gat:es. By modifying the rate of water release, uniformity of application can be increased, and efficiencies enhanced.

Cablegation is one such methoo of controlling water delivery to furrows from gated pipes. Rather than releasing water through all gates at once, inigation water moves behind a plug as it travels downslope through the gated delivery pipe. At the)ow end of the water

. stream, water pressure is greatest and therefore water flows most heatly out of the gates · located right nexf to the plug .. As the plug moves past a gate, pressure gradually decreas.es until finally the water level in the ·pipe is below ·that of the gate and water flow to the furrow served by that gate ceases.

This method can reduce labor, rap.off and pumping costs along with lowered water use. Water inflow to each furrow is gradually decre8sed-as the wetting front moves down the furrow length. Thus deep infiltration is less of a problem and efficiencies as high as 95% can be realized if tailwater, or runoff, is recovered and reilsed. (USDA I SCS, 1985; and USDA I ARS, 1985.) ,

~urge irrigation works on the principle .that the infiltration chara~tetjsti.cs of the soil are changed after the soil has been wetted. Surge irrigation results in more uniform water

application, so less water is lost to deep percolation. .

Surge is best adapted to furrow systems. Instead of covering all furrows completely with water in one long time period, water is r~leased into-the furrows in several short sets. The first release wets the near or upper end of those furrows in the "on" set; water flow is then cut off from that set and the surge valve. directs flow to an alternate set of furrows. ·During the "off' period, water infiltrates each furrow over the area of coverage. As a result, clay . .

particles swell, the top layer of the soil consolidates, and sediments are deposited, thereby· reducing the surface roughness and the soil resistance to flow. In subsequent ''on" .

periods, the water moves more quickly over the already wetted portion, reducing the ti.me

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period over which water is available for infiltration in the previously wetted area. By alternating "on" and "off'' sets, the entire length of the furrow is wetted. Surge irrigation sets require the same or less time than is needed for irrigation by continuous flow, and less water is lost to deep infiltration. '

Where gated pipes have already been installed, the only new equipment needed are surge valves and controllers. Initial investment costs are relatively low andwater savings necessary to justify the investment are easily achieved. As with any irrigation system, ·proper management can have extensive effects on efficiency. (Henggeler et al, 1986; Broner, 1988; and Stringham, 1988.)

Land leveling can improve efficiencies in surface irtigation systems by as much as 20%~ The use of lasers insures precision in a leveling operation and is a simple, cost-effective way ofimproving water distribution uniformity. (Blair, 1989; and University of California, 1987.)

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SPRINKLER SYSTEMS

Jn 1984, approximately 104,000 farms sprinkler-irrigated more than 16.8 million acres, almost one-third of all irrigated land (Bajwa, et al, 1987 .) Sprinkler systems are widely popular because they are adaptable to a variety of teirains and are easily automated. In sprinkler Systems, nozzles are attached to one or more main water delivery pipes, or laterals. The laterals may be permanently situated in a field, or they may be mobile. The three basic. types of sprinkler systems are categorized by their mobility.

In solid set systems, sprinkler heads are attached. at inter\i'als to a series of pipes, or laterals, which are lain across a field.. No movement of these laterals occurs in solid set irrigation. Solid set systems are installed either bek>w or above the ground surface. Some solid set systems are permanently installed underground, with only the sprinkler heads and risers above ground Others are situated on the· ground surface and removed at the end of

· the growing season.

As the name suggests, periodic move systems are moved to accomplish field coverage. Sprinkler heads are mounted on one or more laterals, which are moved either manually or mechanically after each irrigation set The sys~m remains stationary while the sprillklers are in operation.

Continuous move systems are constantly traveling across a field. Commonly used continuous move sprinklers are center pivot, side roll, and tr:aveling types. ~enter pivot sprinklers are supplied water at a fixed point to a single lateral ann which moves continuously around the pivot. This is the irrigation scheme that creates the circular fields often seen in aerial photos of agricultural areas. Side roll sprinklers are those in which the lateral arm moves across the field Several Side roll sprinklers niay be set up in one field, allowing total field coverage in a shorter time period. Traveling gun sprinklers are another type of continuous move system, in which a sprinkler nozzle attached to a flexible hose is mechanically moved by a motor driven or water powered cable reeL Traveling sprinklers can be designed to automatically irrigate a rectangular strip as long as one half mile. (Jensen, 1983; Council on Agricultural Science and Technology, 1988; and New, 1986.)

Increasing ,efficiency of sprinkler systems

Traditional sprinkler systems can be particularly wasteful. First, water evaporates as it moves through the air. Second, much of the irrigation water ends up on the crop canopy, where it cannot be used by the crops. Third, sprinkler systems are usually supplied by pumps. If the pumps are inefficient, substantial amounts of energy are used. Also, water droplets can disturb the soil matrix as they hit the surface, thus exacerbating erosion problems. (Center for Rural Affairs, 1988; and Ley, 1988.)

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· The costs of inefficiency in sprinkler systems are borne by the grower. Water waste and energy overuse are expensive. Erosion can mean loss of fertility which the farmer has to replace with outside inputs. Technological retrofits and improved management techniques can enhance sprinkler system efficiency and increase profits over the long term. .

. Low Energy Precision Application, LEPA, heads, attached to center pivot or side roll laterals, address several problems growers encounter with traditiortal sprinklers. These pressure regulated nozzles apply water 8 to 18 inches from the ground surface, thus decreasing the water exposure to eVa.porative forces and wind drift and reducing the force at which the droplets hit the ground. This reduces erosion and runoff losses as well a.s problems caused by foliage wetting. LEP A reduces water losses from about 20% to 25%

to just 2% .or 3%. Reduced pumping expense and improved crop yields generally pay for the additional cost of fitting a center pivot with LEP A nozzles. (Fipps and New, 1990.)

' .

. Timing of irrigations is an especially effective way of improving efficiency in sprinkler applications. By applying water at night or in the early mommg, evaporative losses are greatly reduced. Because some electric companies charge higher rates for daytime and early evening use, additional savings can be realized simply by operating electricity driven machinery during off peak hours. (Kincaid and Busch, 1985.)

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TRICKLE SYSTEMS

Trickle irrigation is any type in which distribution lines are laid oil or under the ground _and where water is applied at or below the ground swface at low pressure. Trickle systems are inherently efficient~ Because water is applied directly at the root zone, evaporative losses and runoff are reduced; water use can be 25% less than sprinkler systems, and 50% less than furrow systems._. The high cost of installation of trickle systems makes them cost effective only for high value crops.

A number of advantages are realized with trickle systems. The decreased water use reduces pumping costs. Weed problems are dinrinished because water i~ applied only to the crop and not ~o extraneous· areas where it is available for wCed growth. Disease and insect problems are alleviated because foliage is not wetted.

While trickle irrigation systems are ·generally easy to automate, proper management is vital to ensure proper operation . . Because the balance between water applied and water used is so even in subsurface systems, there is less storage in the root zc>ne. irrigations must be scheduled properly to prevent water stress. F'tlters are generally necessary to prevent clogging in the emitters,· and drip lines must be checked to insure that water is being delivered at each point. (Jensen; 1983; and Carkner and Ley, 1987.)

Types of Trickle Systems

Drip irrigation systems apply water at discrete points near the ground surface. Small drip tubes are distributed along the length of a pipe, and water is.released through these tubes at a slow, consistent rate. Drip systeqis work best when irrigations occur at short ir!tervals throughout the day. Timers can be used .to regulate the length of irrigation sets. Soil moisture monitors can be connected to timers to automatically initiate irrigations when moisture levels fall to a predetermined level. (Wilson et al, 1984; and Ross, 1985.)

Subsurface soaker hoses are constructed of recycled tires, tire scraps, or other manufactured material that has microscopic pores throughout its total swface area The irrigation pipe is buried under the ground swface, and water is fed in at low pressure. When the surrounding soil dries out, capillary forces draw water out of the pipe through the tiny pores. Thus, when the pipe fills with water, irrigation occurs continuously as needed. These irrigation systems are most used in twf and home garden applications. However, they may be appropriate in certain larger scale o~rations.

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SOIL ·WATER

Regardless of the type of irrigation system fanners use, they can realize significant water savings through precise evaluation of crop water needs.

Overwatering crops is a common mistake which produces a number of undesirable results. Soil erosion is especially prevalent in surface systems used on steep slopes. Erosion reduces land fertility and value; growers supplement nutrients lost to erosion with purchased inputs, thus increasing their real costs . . In areas where ·the soil is underlain by an impermeable soil layer, excess watering causes the groundwater table to rise, th~ root zone is deprived of oxygen, and crops wilt or die. In such cases,· salts build in the soil, causing further. crop growth problems. Even jf the. salini.zed water is removed, it must be treated to make it sl,litable ·for other uses. Salinization may also occur under conditions wheri. too little water is applied. The grower must achieve a balance in irrigation, applying enough waterto leach the salts from the soil, but not so much that waterlogging or runoff becomes a problem. (Jensen, 1983.)

Other results of unnecessary water use include: exacerbation of weed growth; depletion of groundwater supplies; increased energy costs for pumping more water; and other related costs due to unnecessary use of water~ such as the expense of purchased water. (Blair, 1989.)

Many irrigators water on. a strict schedule, regardless of actual crop water neaj.s. Yet water use can be curtailed substantially if available moisture is monitOred and water applied only as necessary. There are a number of ways to measure soil moisture, track climatic factors, and estimate crop water Use. Cooperative extension services will be able to provide detailed information on the usage and prices for some of the following equipment (Duke, 1987.) ..

Soil Moisture Monitoring

By keeping track of how much moisture is in the soil, irrigators can determine how much water is available to· their crops and how much is being used or lost, and thus better determine when an irrigation may be required. Soil moistUre may be measured directly, which results in an actual measure of the amount of water m a sample. Indirect methods use measurements of electrical resistance or water tension· and relate· them to soil moisture. In order to get a good idea of moisture content, measurements should be taken at a number of different spots throughout the field, at varying distances from the irrigation source, and at varying depths in the soil profile. (Broner, 1989; Sweeten and Henggeler, 1988; and Rhoads and Yonts, 1984.)

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Hand probes or soil augurs are the simplest direct way of determining soil moisture,

These tools remove soil samples from the ground and the farmer estimates soil moisture by

sight and feel Experienced irrigators become familiar with their particular soils and can

achieve satisfactory estimates of soil moisture content by using this method.

Gravimetric methods provide a direct measurement of soil moisture in a sample.

Samples are weighed right after removal from the ground 1llld again after drying in an oven.

The weight fost during drying is the weight of the water in the sample. Irrigators can

determine the percent of water in a sample by comparing dry weight to wet weight. While

any oven, including a microwave, niay be used to dewater the soil sample, a precise scale

should be used to measure the weight difference. The price of the scale is therefore the

greatest expense incurred in this method. (Duke, 1987.)

Tensiometers measure water content indllectly. Water moves through the porous

cefamic tip of a closed tube buried in the soil. The water will move to establish equilibrium

with the surrounding soil as the profile loses and gains moisture. A vacuum guage

measures the change in water content of the tube as the waterleaves and reenters the tube

through the porous tip. (Ross et al, 1984.)

Resistance blocks, commonly made of gypsum, are ariother ind4"ect measurement of

soil moisture. These porous blocks are buried at various locations and depths in the soil

profile. As the surrounding soil gains and loses water. so ·does the resistance block; as the

tension within the blocks changes due to varying moisture content, so does the electrical

resistance. (Richardson and Mueller-Beilschmidt, 1988.)

Crop Water Use

Soil moisture changes under irrigation; water percolates down through the soil profile,

evaporates from the surface, and is used by the crop. A number of simple methods can

estimate crop water use.

Evaporation pans gain water during rainfall and irrigations, and lose water by

_evaporation. The rate at which water is lost from an evaporation pan is analogous to the

rate at which water is lost from the soil profile by evapotranspiration. However, because

high winds and dry air can increase evaporation from a pan, this method is not well suited

to arid or semiarid areas. (Duke, 1987; and Crandall and Middleton, 1975.)

Atmometers supply water from a calibrated container to a porous surface upon which

evaporation occurs. The change in volume in the container is related to the crop

evapotranspiration rate. The evaporative surface can be-of various textures and colors, thus

mimicking the leaf surface and making this method more adaptable for dry climates. (Law'

1988.)

Infrared thermometers measure the temperature of the leaf surf ace. As transpiration

decreases, the temperature of the leaf will rise. Changing leaf temperatures are early

,_


indicators of the onset of water stress. Using this information, growers can apply water at precisely the time when it is needed by the crop. Though infrared thermometers may be too expensive for some uses, they supply a precise indication of the crop's need for an irrigation. Their cost may be justified fot larger farms, high value crops, or where water and energy costs are excessive. (Duke, 1987 .)

Climate Factors

Water balances determine water deposits resulting from rainfall and irrigations, and water withdrawals due to crop water use. Water use data is based on solar radiation, humidity, winds, and temperature. When the water balance drops· below a certain level, an irrigation is indicated. Computer software programs are widely available that allow · growers to input site specific data and schedule irrigations based on actual water needs. (Yonts and Klocke, 1985.)

Climate information services are proVide4 by a number.of regional and local organizations. Most local newspapers in agricultural areas publish evapotranspiration data

. which can be adapted to various crops and locations. Additionally, some cooperative extension services and state and local Water resources agencies provicfu. climatic data, water use information, and water balance computations for growers. (Graser, 1988.)

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LAND PREPARATION METHODS

Careful land surface preparation can enhance soil moisture retention. Dikes and ponds hold water that would otherwise be lost to runoff or deep percolation. Simple modification of a field surface makes the best use of available water, whether it is from rainfall or from irrigation. These methods may apply best where surface irrigation is used, however they are also applicable to row crops irrigated in any manner. ·

Furrow diking is a method of land preparation in which runoff is collected after rainfall and held in small~ diked ponds in each fmrow. Diking equipment is readily available and can· attach to traditional farm equipment (Coburn and Alexander, 1986; and Wistrand, 1984.)

Runoff farming or rainwater harvesting is similar to furrow diking in that it tries to make the most use of available water. Precipitation is directed by retaining walls to catchments where it is stored for use when natural moisture or irrigation water is not available.

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CONCLUS·ION

Approximately 70% of the world's water use is for agriculture. (Postel, 1989.) Increasing efficiency in irrigation would reduce water pollution, save energy, and preserve our precious water resources. Water saved on the fann becomes available for other uses, be they agricultural, recreational, industrial, or residential. Unfortunately. resource preservation is often not reason enough to give up the insurance that excess water application provides.· No farmer wants to risk crop loss due to water stress. For this reason, many states now offer other incentives to fanners who save water. Some farmers are granted the rightto sell the water that they save. Some electric compames offer discounts to agricultural· users who operate their irrigation equipment during off-peak hours, such as the early morning when water loss to evaporation is l~ss prevalent. Most agricultural states provide rree,.readily accessible information and consulting to fanners who are looking for ways to save water.

This· document has outlined some of the most popular ways of saving water on farms. The resources noted in the following sections will help people who are ini~rested in learning more about efficient irrigation techniques. The list is by no· means cOinprehensive, some of the most straightforward irrigation guides and water-related periodicals are listed; names · and addresses of organizations and institutions that cond~ctresemch or provide infc>rmation on sustainable agriculture and water use are also included. ·

Deciding between irrigation methods always involves trade-offs. Irrigators have to choose between irrigation techniques that require v3rying initial and continuing costs. However, expenses iticurred are for more than just equipment and labor. · Energy use, water use, and the on- and off-farm consequences of resource overuse all have a price tag. · When all the real costs of wasting water on the farm are added up, it becomes clear that water efficiency in irrigation is profitable, and that water is not such cheap insurance, after all.

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REFERENCES Bajwa. Rajinder S .• William M. Crosswhite, and John E. Hostetler. 1987. Agricultural Irrigation and Water Supply. USDA I ERS. Washington D.C.

Blair, Leslie. 1989. Saving Energy in Irrigation. New Mexico Energy. Minerals and Natural Resoui'ces Department University of New Mexico. Las Cruces.

Broner, Israel. 1989. '1rrigation Scheduling." Service in Action. Colorado State University Cooperative Extension. Fort Collins'.

Broner, Israel L 1988. "Surge Irrigation Guide." Colorado State University Cooperative

. Extension. Fort Collins Colorado.

Carkner, Richard W. and Thomas W. Ley. 1987. "An Economic and Engiiieering Comparison of Replacing Overhead with Trickle Irrigation in Red Raspberries." Washington State University Cooperative Extension. Pullman.

Center for Rural Affairs. 1988. "Beneath the Wheels of Fortune: The Economic and Environmental Impacts of Center Pivot Irrigation Development on Antelope County, Nebraska.'.' Walthill Nebraska. .

Coburn, A. Edwin and U.U. Alexander. 1986. ''Furrow Diking in Texas." Texas Agricultural Extension Service. College Station Texas.

Council for Agricultural Science and Technology. 1988. Effective Use of Water in Irrigated Agriculture. Ames Iowa

Crandall, P.C .• and J.E. Middleton. 1975. "Scheduling the Irrigation of StrawberrieS' from Pan Evaporation." College of Agriculture Research Center. Washington State University.

Dllke, Harold R. editor. 1987. Scheduling Irrigations: A Guide for Improved!rrigation Water Management Through Proper Tiniing and Amount ·of Water Application. High Plains Technical Coordinating Committee. Fort Collins Colorado.

Edens, Thomas C., Cynthia Fridgen, and Susan L. Battenfield, editors. 1985. Sustainable Agriculture and Integrated F armmg Systems: 1984 Conference Proceedings; Michigan State University Press. East Lansing. ·

Fipps, Guy, and L. Leon New. 1990. ''LEPA Conversion and Management" Proceedings of the Southern Texas Irrigation Conference, January 11, 1990. Texas Agricultural Extension Service. Pearsall Texas.

Gips, Terry. 1990. "Sustainable Agriculture Defined." New Alchemy Quarterly. Winter 1989-90, No. 38. East Falmouth MA.

Graser, Jerry. 1988. "Water Management Services." The Washingtonirrigator. Issue 6. Spokane.

Henggeler; Joseph C.,_John M Sweeten, and c. Wayne Keese. 1986. "Surge Flow Irrigation." Texas Agricultural Extension Service. College Station Texas.

Jackson. Wes, Wendell Berry, and Bruce Colman, editors. 1984. Meeting the Expectations of the Land. North Point Press. San Francisco.

Jensen, M.E.· editor. 1983. Design and Operation of Farm Irrigation Systems. American Society of Agricultural Engineers. St Joseph Michigan.

Katz, David. 1984. "Sustainable Agriculture: . Basic Guidelines for Future Farming." In Context, Winter, 1984, No. 8. Sequim WA.

Kincaid, D.C. and J.R. Busch. 1985. "A Comparison of Low Pressure Center Pivot Irrigation Systems."Irrigation Energy Efficiency Series. Bonneville Power Admmistration I U.S. Department of Energy.

Law, Rodrigo A. P. and Israel Israeli. 1988. "Evaluation of Atmometer Performance as a Tool for Irrigation Scheduling." Presented at the Meeting of the American Society of Agricultural Engineers, December 13-16, 1988. Chicago.

ROCKY MOUNTAIN INSTITlITE

Ley, Thomas W. 1988. "Set-Move and Pennaneht Sprinkle Irrigation Systems." Drought Advisory. Washington State University Cooperative Extension. Pullman.

. National Research Council. 1989. Alternative Agriculture. National Academy of Sciences. Washington D.C.

New, L. Leoti. 1986. "Center Pivot Irrigation Systems." Texas Agriculutural Extension Service. College Station. ·

O'Mara, Gerald T. editor. 1988. Efficiency in Irrigation: The Conjunctive Use of Slllface and Groundwater Resources. The International Bank for Reconstruction and Development/ The World bank. Washington D.C. ·

Postel, Sandra. 1989. "Water for Agriculture: Facing the Limits." Worldwatch Paper 93. Washington D.C. ·

Rhoads, F.M. and C.C. Yonts.1984. "Irrigation Scheduling for Corn ""-Why and How." National Corn Handbook." Cooperative Extension Service, Purdue University. West Lafayette Indiana

Richardson, Gail, and Peter Mueller-BeiJschmidt 1988. Winning With Water: Soil Moisture Monitoring/or Efficient Irrigation. INFORM, Inc. New York.

Ross, D.S., R.A. Parsons, and H.E. Carpenter. 1985. "Trickle Irrigation in the Eastern United States." Northeast Regional Agricultural Engineering SerVice.

Ross, David S., Herbert L. Brodie, and Lewis E. Carr.1984. "Tensiometers for Irrigation Management." Agricultural Engeineering Facts. University of Maryland Agricultural Engineering Department. College Park. ·

Solomon, Kenneth H. 1988. "Irrigation System Selection." Irrigation Notes. California Agricultural Technology Institute/ Center for Irrigation Technology. Fresno California.

Stringham, Glen E., ed. 1988. Surge Flow Irrigation. Utah Agricultural Experiment Station. Logan Utah.

EFFICIENCY IN IRRIGATION PAGE 19

Sweeten, iohn M. and Joseph C. Henggeler. 1988. "Soil Moisture Monitoring." Texas Agricultural Extension Service. College Station Texas .

USDNARS. 1985. Minutes of Annual Cablegation Workshop. Snake River Conservation Research Center. Kimberly Idaho.

USDNSCS. 1985. "Cablegation: An Automated Furrow Irrigation System." Lincoln Nebraska.

·United States Department of the Interior I USDA /EPA. 1979. Irrigation Water Use and Management. United States Government Printing Office. Washington D.C.

University of California, Division of Agriculture and NatUral Resources. 1987. Irrigation Water Use in the Central Valley of California. Department of Water Resources.

Whittlesey, Nonnan K .. editor. 1986. Energy and Water Management in Western Irrigated Agriculture. Westview Press. Boulder CO.

Wilson, Paul, Harry Ayer, and Gary Snider. 1984. "Drip Irrigation for Cotton: Implications for Farm Profits." USDA I ERS. Government Printing Office. Washington D.C.

Wistrand, Glen L. 1984. Furrow Dike Water Conservation Practices in the Texas High Plains. USDA/ERS. Washington DC.

Yonts, C. Dean and Norman L. Klocke. 1985. "Irrigation Scheduling Using Crop Water Use Data." NebGuide. Cooperative Extension Service Institute of Agriculture and Natural Resources. Uni\rersity of Nebraska. Lincoln.

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RESOURCES

Books on Irrigation

Design and Operation of Farm Irrigation Systems ME. Jensen, editor American Society of Agricultural Engineers St. Joseph Michigan 49085 ·

This technical manuscript is a com:Prehensive look at all aspects of large scale irrigation system design. Chapters include: the mechanics of water in the soil; water supply and drainage considerations; delivery, pumps. and distribiltion system design; specific design considerations; system efficiency evaluation; and ifrigation water manag~enl

Effective. Use of Water in Irrigated Agriculture Council for Agricultural Science and Technology 137 Lynn Avenue Ames Iowa 50010-7120

A less technica1 overview of irrigation systems and design considerations. This 63 page book includes chapters on irrigation development, economics, water sources, system mat)agement, conservation concept:S, and sample ~ign calculations.

Efficiency in Irrigation: The Conjunctive Use of Surface and Groundwater Resources. Gerald T. O'Mara The International. Bank for Reconstruction and Development/ The World Ban1c 1818 H Street, NW Washington D.C. 20433

An analytical cliscussion of efficiency in irrigation. this collection of papers describes theoretical issue8 facing irrigated agi:iculture, includes case studie8 where both groUlld- and surface waters are used for irrigation. and explains analytical methods and applications.

"Irrigation System Selection" Kenneth H. Solomon California Agricultural Technology Institute / Center for Irrigation Technology California State University Fresn9 California 93740-0018

A simple to read pamphlet describing capabilities and limitations, labor and energy considerations, and economic factors for surface, sprinkler, and subsurface irrigation systems.

Periodicals on Irrigation

Water Conservation News California Department of Water Resources P.O. Box 942836 Sacramento CA 94236-0001 · This quarterly publication provides "the latest information on .urban and agricltural water conservation develapments and activities."

The Divining Rod New Mexico Water Resources Research Institute Box 30001 /Dept. 3167 Las Cruces NM 88003-0001 505-646-1813 This quarterly publication describes water resources and irrigation-oriented research and demonstration projects ongoing in New Mexico . ..

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.. ROCKY MOUNTAIN INSTITUTE

Agricultural Water Management Journal Information Center 655 Avenue of the Amerk:as New York NY 10010 212-989-5800 This journal is published eight times yearly and is .. concerned with the publication of scientific papers of international significance to the management of agricultural water."


Irrigation Engineering American Society of Agricultural Engineers 2950 Niles Road SL Joseph MI 49085-9659 Published at least twice per year, this selection of technical articles deScribes recent research on irrigation technology.

For More Information on I~rigation

State Cooperative Extension Services are excellent resoµrces for ge~ral and technical infonnation for farmers and non farmers. Extension Services are usually listed under County Government in the phone book.

University of California Division of Agriculture and Natural Resources Agricultural Publications Catalog 6701 San Pablo A venue Oakland California 94608-1239· · ·

Te~as Department of Agriculture P.O. Box 12847 Austin Texas 78711 Texas has a comprehensive publications list covering aspects of irrigation and agriculture for regional and national applications.

A number of federally operated institutions also provide information on· sustainable agriculture and irrigation applications:

The United- States Department of Agriculture administ~rs the Soil Conservation Serv~ce (SCS) and the Agricultural Stabilization and Conserva~ion Service (ASCS). The SCS and ASCS can be useful resources for people seeking region-specific information on irrigation agriculture. Offices are located in many cities in every state, and can be found in the U.S. Government listings in the phone book.

Appropriate ·Technology Transfer for Rural Are~ (ATTRA) in Memphis Tennessee provides infonnation on sustainable agriculture at a toll-free number: 800-346-9140.

ROCKY MOUNTAIN INSTirUTE EFFICIENCY IN IRRIGATION PAGE 22

Weather Information

The California Irrigation Management Information System (CIMIS) P.O. Box 942836 Sacramento California 94236-0001 CIMIS provides evapotranspiration data to irrigators throughout California. The office also organiz.es irrigation workshops and provides extensive information serviees to growers.

The Washington Energy Extension Service has a computer water management program available free of charge which explains how to use moisture monitoring equipment and helps users compute a water balance and determine when to irrigate. Contact The Washington Irrigator West 808 Spokane Falls Boulevard Room 627 Spokane Washington 99201 So<J-624-4180

Washington State University also has a program that allows users to input site-specific data to predict crop water use and schedule irrigations. The program entitled "Washington Irrigation Forecaster" is available for a fee. by calling 509-335-2811.

.. ROCKY MOUNTAIN INSTITUI'E EFFICIENCY IN IRRIGATION PAGE 23

Periodicals Concerned With Sustainable Agriculture

Choices 2708 Oak Farms Road Herndon Virginia 22071 202-786-1899 "Choices is published quarterly by the American Agricultural Economics Association for people who want to be informed about food, farm, and resource issues -- and the policies that affect them."

Missouri Farm Route 1, Box 237 Clark Missouri 65243 314-687-3525 This periodical is published six times per year and is ••dedicated to preserving and promoting small fanning and rural living."

The New Farm 222 Main Street Emmaus Pennsylvania 18098 215-967-5171 Published seven times per year, "The New Farm is dedicated to putting people, profit and biological penhanence back into fanning by giving farmers the information they need to take charge of their farms and their futures."

Sustainable Agriculture Organizations

Alternative Energy Resources Organization 44 North Last Chance Gulch, #9 Helena Montana 59601 406-443-7272 AERO Sun Times is the newsletter of this "nonprofit, open membership educational group promoting sustainability ·or energy resources, agriculture and community-based economic development" ·

The Center for Rural Affairs P.O~ Box405 Walthill Nebraska 68067 The Center publishes a monthly newsletter primarily addressing economic issues facing the farming community in Nebraska, and including monthly "Special Reports" on issues of general· concern to those iriterested in sustainable agriculture in the nation.

Institute for Alternative Agriculture, Inc. 9200 Edmonston Road Greenbelt Maryland 20770 301-441-8777 Information on issues of eoncern to· organic farmers, agricultural researchers, and other interested persons is synopsized in Altternative Agriculture News, the monthly publication of this nonprofit research and education organization. New resources, national conferences, news analyses, and employment opportunities are highlighted

International Alliance for Sustainable Agriculture 1701 University Avenue SE Minneapolis Minnesota 55414 MANNA is the newsletter of this organization that is working to "develop ecologically sound, economically viable, socially just, and humane agricultural systems around the world."

ROCKY MOUNf AIN INSTifUTE

The Land Institute 2440 East Waterwell Road Salina Kansas 67401 A research report and The Land Report explain the work of The Land Institute, which promotes· sustainable agriculture and good stewardship of ihe earth. The Land is pioneering research into the development of a sustainable agriculture ~ on the model of the prairie.

Land Stewardship Project 14758 Ostlund Trail North Marine Minnesota 5504 7 612-433-2770 The Land Stewardship Letter is the Newsletter of this "non-profit education program worlcing for the development of a saund stewardship ethic toward our nation's farmland and for public policy changes that will lead to the development of a sustainable agricultural system." This organiz.ation has sustainable agriculture projects for small farmers in Minnesota and has an extensive publications list.


The ·New Alchemy Institute 237 Hatchville Road East Falmouth Massachusetts 02536 508-564-6301 New Alchemy Institute publishes a quarterly newsletter and has a number of publication on alternative and sustainable agriculture. Research is conducted in biological control, cover crops, aquaculture, alternative shelters, and interconnected biological systems.

Rodale Research Center R.D. 1 Box 323 Kutztown Pennsylvania 19530 215-683-6383 Research is conducted on alternative crops, pest control, and cropping systems; comparisons between organic and conventional farming practices are doCumented

Organizations With General Publications About Sustainable Agriculture

Resoqrces for the Future 1616 P Street, NW Washington DC 20036 202-328-5000

Institute for Food and Deve~opment Policy 145 Ninth Street San Francisco California 94108 415-864-8555

Natural Resources Defense Council 122 East 42nd Street New York NY 10168 212-949-0049

Worldwatch Institute 1776 Massachusetts Avenue, NW Washington DC 20036

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Bibliographies and ·sourcebooks about Sustainable Agriculture

AgAccess P.O. Box 2008 Davis CA 95617 916-756-7177

Island Press Box7 Covelo CA 95428 800-828-1302

Winrock International Agribookstore 1611 North Kent Street Arlington Virginia 22209-2134 703-525-9455

AGRICOLA U.S. Department of Agriculture National Agricultural Library Public Services Division Room 111 Beltsville Maryland 20705 301-344-3755 AGRJC'OLA is the National Agricultural Library data base. Bibliographies on all agricultural subjects can _be produced.

Efficiency in Irrigation (RMI 1990)

Documents

Transcript of Efficiency in Irrigation (RMI 1990)