• TABLE OF CONTENTS
HIDE
 Historic note
 Front Cover
 Front Matter
 Table of Contents
 Efficiency definitions
 Irrigation efficiencies
 Crop water use efficiency
 Irrigations water use efficien...
 Factors affecting irrigation...
 Gravity flow irrigation system...
 Potential irrigation system application...
 Reference
 Tables
 Back Cover














Group Title: Bulletin - University of Florida. Florida Cooperative Extension Service ; no. 247
Title: Efficiencies of Florida agricultural irrigation systems
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF90000450/00001
 Material Information
Title: Efficiencies of Florida agricultural irrigation systems
Series Title: Bulletin
Physical Description: 11 p. : ; 28 cm.
Language: English
Creator: Smajstrla, A. G ( Allen George )
Florida Cooperative Extension Service
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville Fla
Publication Date: [1991]
 Subjects
Subject: Irrigation efficiency -- Florida   ( lcsh )
Irrigation engineering -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 9).
Statement of Responsibility: A.G. Smajstrla ... et al.
General Note: Title from cover.
General Note: "5/91."
Funding: Bulletin (Florida Cooperative Extension Service)
 Record Information
Bibliographic ID: UF90000450
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 001753224
oclc - 26898554
notis - AJG6187

Table of Contents
    Historic note
        Historic note
    Front Cover
        Front Cover
    Front Matter
        Front Matter
    Table of Contents
        Table of Contents
    Efficiency definitions
        Page 1
    Irrigation efficiencies
        Page 2
        Page 3
    Crop water use efficiency
        Page 4
    Irrigations water use efficiency
        Page 4
    Factors affecting irrigation efficiencies
        Page 4
        Page 5
        Page 6
    Gravity flow irrigation systems
        Page 7
    Potential irrigation system application efficiencies
        Page 8
    Reference
        Page 9
    Tables
        Page 10
        Page 11
    Back Cover
        Page 12
Full Text





HISTORIC NOTE


The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
(EDIS)

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida






5/91 Bulletin 247


Efficiencies of Florida

agricultural

irrigation systems


A.G. Smajstrla, B.J. Boman, G.A. Clark, D.Z. Haman,
D.S. Harrison, F.T. Izuno, D.J. Pitts and F.S. Zazueta








Central Science
Library
SEP 8 1992

University of Florida




Florida Cooperative Extension Service
Institute of Food and Agricultural Sciences
University of Florida
John T. Woeste, dean


-I I-


l/, /91
3@ q 5/91


Bulletin 247











































































A. G. Smajstria, professor, Agric. Eng. Dept. Gainesville; B. J. Boman, associate professor, AREC. Ft. Pierce; G. A. Clark, assistant
professor, Gulf Coast REC., Bradenton; D. Z. Haman, associate professor and D. S. Harrison, professor emeritus, Agric. Eng. Dept.,
Gainesville; F. T. Izuno, associate professor, Everglades REC., Belle Glade; D. J. Pitts, assistant professor, Southwest FL REC.,
Immokalee; and F. S. Zazueta, associate professor, Agric. Eng. Dept. Gainesville, IFAS University of Florida.








Contents
Introduction ........................................................................---.......................... .................
Efficiency definitions .............................................................................................................................................1
Irrigation efficiencies ................................................................................................................................... 2
Irrigation system components ........................................................................................................ 2
Irrigation systems or projects ................................................................................. .................. ............ 3
Crop water use efficiency ................................................................... ...............................
Irrigation water use efficiency .... ............................................................................................................... 4
Factors affecting Irrigation efficiencies .................... .................................................................................. 4
Pressurized irrigation systems ................................................................................................................ 4
Sprinkler Irrigation systems................................................................................................................ 5
Microirrigaton systems .......................................................................................... .......................... 6
Gravity flow Irrigation systems ....................................................................................................
Subirrigation (seepage) systems ........................................................................... .............. ....7
Surface (flood) irrigation systems ................................ ........................... ............................... 8
Potential irrigation system application efficiencies ................................................................ ........................
References ...................................................................................................................... ............. 9
Table 1. Pressurized irrigation system application efficiencies, Ea (%).................................. .... 10
Table 2. Gravity flow irrigation system application efficiencies, Ea (%)......................................... ....... 11









Introduction
Irrigation efficiency is a measure of (1) the
effectiveness of an irrigation system in delivering
water to a crop, or (2) the effectiveness of irrigation
in increasing crop yields. From definition (1),
irrigation efficiency may be expressed as the ratio
of the volume of water used or available for use in
crop production to the volume pumped or delivered
for use. From definition (2), irrigation efficiency
may be expressed as the ratio of crop yield or
increase in yield over nonirrigated production to
the volume of irrigation water used. Irrigation
efficiencies thus provide a basis for the comparison
of irrigation systems from the standpoint of water
beneficially used (or conversely, water wasted) and
from the standpoint of yield per unit of water used.
No irrigation system will apply water without
some waste or losses because the cost to prevent all
losses is prohibitive. Thus, some water losses are
expected and accepted in proper irrigation system
design, installation, and management. However,
excessive waste may be caused by poor irrigation
system design, improper installation, poor manage-
ment, and equipment failures. Waste may occur as
nonuniform water applications, excessive applica-
tions, evaporation or wind drift during application,
surface runoff or subsurface (lateral) flow from the
irrigated area, canal seepage, percolation below the
root zone, evaporation from the irrigation distribu-
tion system, leakage from defective pipe connec-
tions, or other losses.
It is not possible to apply the exact amount of
irrigation water required with perfect uniformity
because of variations in soil properties, variations
in irrigation system components, pressure losses in
systems due to friction and elevation changes, or
other causes. When the correct average amount of
water is applied, nonuniform water applications
waste water due to excess applications in some
areas while crop yields may be reduced due to
inadequate applications in other areas.
Water may be lost due to evaporation or wind
drift during application, especially for sprinkler
and spray types of irrigation systems. However,
evaporation during sprinkling cools the crop
canopy, thus it reduces transpiration and partially
compensates for evaporation losses.
Surface runoff, subsurface flow from the irri-
gated area, canal seepage, percolation below the
crop root zone, and evaporation from a water
distribution system during application will reduce
irrigation efficiencies. Conversely, recovery and


reuse of surface runoff and subsurface water will
increase irrigation efficiencies.
Irrigation efficiencies vary with the type of
irrigation system and with many other factors such
as soil, crop, and climate characteristics, as well as
with the level of maintenance and management of
the irrigation system. The type of irrigation system
used and the intended level of irrigation efficiency
will partially depend on the availability and value
of water for irrigation. Thus, economic factors will
influence the irrigation efficiency sought or ob-
tained in a specific production system. Estimates of
irrigation efficiencies are required by consultants
and system designers and managers so that irriga-
tion systems can be properly designed and effec-
tively managed to meet the objectives of an indi-
vidual production system.
Estimates of irrigation efficiencies are also
needed by water management personnel so that
water needs can be estimated for management of
the state's water resources.
Commonly used definitions of irrigation efficien-
cies, factors affecting irrigation efficiencies, and
typical values for well-designed and well-managed
Florida field-scale irrigation systems are presented
in this publication.

Efficiency definitions
There are many meaningful definitions of
efficiency which relate to irrigation and crop water
use. In general, the term "irrigation efficiency"
refers to the ratio of the volume of water delivered
by an irrigation system to the volume that is input
to the system. Irrigation efficiencies can be defined
for components of irrigation systems, for entire
field or farm-scale irrigation systems, as well as for
multi-farm or regional irrigation projects.
The term "crop water use efficiency" nor-
mally refers to the ratio of crop yield to the volume
of water used to produce the crop. The term "irri-
gation water use efficiency" normally refers to
either (a) the volume of water beneficially used
relative to the volume delivered from an irrigation
system, or (b) the increase in crop yield over
nonirrigated yields relative to the volume of water
applied by an irrigation system.
Because of the many efficiency definitions that
are used, it is necessary that efficiency terms be
clearly defined for each specific application. The
following paragraphs present commonly used
efficiency definitions.









Irrigation efficiencies

Irrigation system components
Reservoir storage efficiency (E,). Reservoir
storage efficiency is the ratio of the volume of
irrigation water available from an irrigation
reservoir to the volume of water delivered to the
reservoir. This ratio is normally less than 1.0
because of seepage, evaporation, and transpiration
losses.
In Florida, seepage losses to underlying soil
formations and water tables occur through the
sides and bottoms of earth structures. In high
water table (flatwoods) locations, seepage may
occur from the surrounding water table to a reser-
voir, adding water to the reservoir. In locations
where water tables are deep, such as areas of
northwest Florida where reservoirs are constructed
to collect runoff water for future irrigation, seepage
will cause losses from reservoirs.
The amount of seepage loss will strongly depend
on the properties of the materials from which the
reservoir is constructed. Seepage losses may be
reduced by lining reservoirs with impermeable soils
(typically clays) or manmade liners such as plastic
sheets. Metal, plastic, or fiberglass tanks may be
used as reservoirs to eliminate seepage losses, but
the cost of tanks is often prohibitive for the volumes
of water required for irrigation.
Evaporation losses from reservoirs occur when-
ever the water surface is exposed to the atmo-
sphere. Evaporation losses can be eliminated by
covering the water surfaces, but this is not practi-
cal except for tanks or small reservoirs. Evapora-
tion losses from field scale reservoirs can be re-
duced by designing reservoirs with smaller surface
areas and greater depths. Deep reservoirs have
less surface area than shallow reservoirs that store
the same volume. Because evaporation is a surface
process, less water will be evaporated from deeper
reservoirs because less will be exposed to the
atmosphere. Shallow water areas also heat up and
evaporate at higher rates than deep areas.
Transpiration losses from a reservoir occur as a
result of vegetative growth in and around the
reservoir. These losses can be reduced by prevent-
ing or minimizing growth in and near the reservoir.
Vegetative growth along the shoreline can be
reduced by minimizing shallow water areas. Some
vegetation, especially grasses, will normally be
required to stabilize the soil embankments and
prevent sediment transport into reservoirs.


Reservoir losses and Es for Florida reservoirs
vary widely, primarily due to the variable nature of
seepage losses. In general, Florida reservoirs
which are not recharged by seepage from a high
water table should be designed to hold at least
twice the anticipated water requirement for irriga-
tion (Es = 0.50). However, site specific conditions
may result in Es values that vary considerably
from 0.50.
Water conveyance efficiency (Ec). Water
conveyance efficiency is the ratio of the volume of
water delivered for irrigation to the volume of
water placed in the conveyance system. This ratio
is normally less than 1.0 for open channel convey-
ance systems, but it may be approximately 1.0 for
pipeline conveyance systems.
Losses from open channel conveyance systems
occur due to seepage, evaporation, and transpira-
tion. These losses can be reduced by using lined
channels and controlling vegetative growth. Some
evaporation losses will be unavoidable. Open
channels are used in south Florida where existing
high water tables and restrictive soil layers mini-
mize seepage losses. However, even under these
conditions, Ec is very site-specific and must be
determined by measurements taken at the site or
estimated by persons experienced with these
systems.
Pipelines are extensively used in Florida because
large seepage losses occur from unlined channels
constructed in deep sandy soils and because pres-
surized irrigation systems are extensively used.
Seepage and other losses are avoided in pressurized
irrigation systems because leakage is minimal from
well-designed and well-managed pipelines.
Irrigation application efficiency (E1). Irriga-
tion application efficiency is the ratio of the volume
of irrigation water stored in the root zone and
available for crop use evapotranspirationn) to the
volume delivered from the irrigation system. This
ratio is always less than 1.0 because of losses due to
evaporation, wind drift, deep percolation, lateral
seepage (interflow) and runoff which may occur
during irrigation.
Application efficiencies are also affected by those
cultural practices that affect water storage in the
crop root zone. For example, Ea is reduced by the
use of plastic mulches which shed water from the
production bed of sprinkler-irrigated vegetable crop
production systems, by nonuniform wetting of
hydrophobic soils (soils which are resistant to
wetting), and by crop root zones limited by








containers in sprinkler irrigated container nursery
production systems. The effects of site-specific
factors such as these need to be evaluated to
accurately determine application efficiencies of
individual systems.
Application efficiencies are also affected by
irrigation system management practices. Because
it is not possible to measure and apply the exact
amount of water required in the crop root zone at
precisely the time that available soil water is
depleted, excess water applications will sometimes
occur. As a result, Ea will be reduced.
Typical and expected ranges of application
efficiencies of Florida irrigation systems are dis-
cussed in detail in later sections of this publication.

Irrigation systems or projects
Overall (irrigation system, project or farm)
irrigation efficiency (Eo). Overall irrigation
efficiency is calculated by multiplying the efficien-
cies of the components. For a system which in-
cludes reservoir storage, water conveyance, and
water application, the overall irrigation efficiency is
defined as
Eo = (Es) x (Ec) x (Ea) (1)
where all terms are as previously defined. Thus,
the overall irrigation efficiency for an irrigation
system which is using water from an open reservoir
with a 60% (0.60) storage efficiency, conveying it
using an open channel from which 1/5 is lost in
transit (0.80 or 80% conveyance efficiency), and
which is using the flood method of water applica-
tion, which is 50% (0.50) efficient, would be
Eo = 0.60 x 0.80 x 0.50 = 0.24 or 24%
A system with this overall irrigation efficiency
would need a reservoir that is designed to collect
over 4 times the crop irrigation requirement
because only 24% of the water collected in the
reservoir would be effectively used.
As another example, if a grower has an irrigation
system that pumps water from the Floridan aquifer
rather than storing it (E. = 1.00), conveys the water
in a pipeline without leaks (E. = 1.00), and applies
it with a drip type of microirrigation system which
has an application efficiency of 85% (Ea = 0.85),
then the overall irrigation efficiency of this system
would be
E = 1.00 x 1.00 x 0.85 = 0.85 or 85%
This system would only need to pump 18% (1.0/
0.85 = 1.18 or 118%) more water than the crop


irrigation requirement because losses did not occur
in storage or conveyance, and the application
efficiency was high.
Effective irrigation efficiency (E,). Effective
irrigation efficiency is the overall irrigation effi-
ciency corrected for water which (1) is reused, or (2)
is restored to the water source without a reduction
in water quality. Tailwater recovery systems allow
runoff from an irrigated field to be recycled or used
on another field. These systems increase Ee above
Eo. A citrus crown flood system, where water is
drained from one block but used to irrigated the
next block, is an example of a Florida production
system where E is greater than E.. Other ex-
amples include those watercress production sys-
tems where water is continuously recycled, seepage
irrigation systems where tailwater is recycled from
drainage ditches or ponds, and other systems such
as sprinkler-irrigated strawberry and ornamental
fern production systems where surface runoff or
subsurface drainage is routed into ponds for reuse.
If seepage from open channels flows into the field
being subirrigated, this flow will not be lost from
the irrigation system. Thus, Ee will be greater than
Eo.
If irrigation water moves from the crop root zone
due to lateral flow or deep percolation, its quality
may be degraded by salts and other production
associated chemicals. If this water cannot be
intercepted for reuse in the same production
system, then it is considered to be lost, reducing E
and Eo. Thus, lateral flow and deep percolation will
reduce irrigation efficiencies unless interceptor
drains or ditches are installed to recover this water
for reuse.
The effective irrigation efficiency is defined as
Ee = Eo + (FR) x (1.0 E,) (2)
where FR is the fraction of the water lost that is
recovered. Some of the water that leaves an irri-
gated field due to runoff, seepage, or deep percola-
tion might be recovered in some cases. Losses due
to evaporation, wind drift, and transpiration cannot
be recovered.
If, for example, an irrigator pumps from the
Floridan aquifer (E. = 1.00), conveys water in a
pipeline (Ec = 1.00) and seepage irrigates potatoes
and cabbage (E. = 0.50) near Hastings, the overall
irrigation efficiency would be
E = 1.00 x 1.00 x 0.50 = 0.50 or 50%








If this grower installs a system to recycle runoff
water and is thus able to recover 40% (FR = 0.40) of
the water which was being lost from the field (that
is, approximately 40% of the water being lost was
due to runoff), the effective irrigation efficiency
(from Equation 2) would be
E. = 0.50 + 0.40 x (1.00 0.50) = 0.70 or 70%
Thus, the irrigation efficiency would be increased
from 50% to 70% by recycling water which was
previously being lost to runoff.

Crop water use efficiency
Crop water use efficiency is defined as the ratio
of the mass of marketable yield or biomass pro-
duced per unit of water used. For this definition,
crop water use efficiency has units of production
unit per water volume unit. Units typically used
are tons/acre-inch, pounds/acre-inch, or bushels/
acre-inch in English units and kilograms/cubic
meter in metric units.
This definition is not a true efficiency because it
does not express a dimensionless ratio. It does,
however, have the advantage of comparing both
yield and water used, thus it is often used in
economic comparisons of alternative crops.

Irrigation water use efficiency
There is no general agreement on a single
definition of irrigation water use efficiency (En). Eu
can be defined in two different ways.
1. E can be defined as the ratio of the volume of
water beneficially used to the volume delivered
from the irrigation system. Water that is benefi-
cially used includes that which is applied for
leaching of salts from the crop root zone, crop
cooling, freeze protection, and other such uses, in
addition to that stored in the crop root zone for
evapotranspiration.
This definition of Eu is a true efficiency; that is, it
is dimensionless and it expresses the ratio of two
volumes of water. This ratio expresses the fraction
of each unit of water delivered that is beneficially
used.
As an example, excess water beyond that which
can be stored in the crop root zone may be required
to leach salts from the crop root zone if poor quality
water is being used for irrigation. Since this would
be a beneficial use, the irrigation water use effi-
ciency would remain high, although the irrigation
application efficiency would be reduced because all


of the water applied was not stored in the crop root
zone.
2. E can also be defined as the ratio of the
increase in production of the marketable crop
component to the volume of water applied by
irrigation for irrigated as compared to nonirrigated
production.
E, = (Y, Yo) / V (3)
where Y1 = mass of marketable crop produced
with irrigation,
Y = mass of marketable crop produced
without irrigation,
V. = volume of irrigation water applied.
Although this definition of E is not a true
efficiency, it has the advantage of expressing the
increase in production from irrigation for economic
evaluations of the profitability of proposed irriga-
tion projects. It is not meaningful if the crop
cannot be produced without irrigation.
Because both of these definitions of irrigation
water use efficiency are sometimes used, it is
always necessary to clearly define E. and to give its
units when this efficiency term is used.

Factors affecting irrigation
efficiencies

Pressurized irrigation systems
Pressurized irrigation systems include sprinkler
and micro- irrigation systems. Pressure is required
for proper operation of the sprinklers and
microirrigation emitters. These systems use
pipelines to distribute water throughout the sys-
tem.
Because networks of pressurized pipelines rather
than soil hydraulic properties are used to distribute
water, the field-scale uniformity of water applica-
tion (and the associated irrigation application
efficiency) is more strongly dependent on the
hydraulic properties of the pipe network designed
than site-specific soil hydraulic properties. Thus,
application efficiencies of well-designed and well-
managed pressurized irrigation systems are much
less variable than application efficiencies of gravity
flow irrigation systems, which depend heavily on
soil hydraulic characteristics.








If this grower installs a system to recycle runoff
water and is thus able to recover 40% (FR = 0.40) of
the water which was being lost from the field (that
is, approximately 40% of the water being lost was
due to runoff), the effective irrigation efficiency
(from Equation 2) would be
E. = 0.50 + 0.40 x (1.00 0.50) = 0.70 or 70%
Thus, the irrigation efficiency would be increased
from 50% to 70% by recycling water which was
previously being lost to runoff.

Crop water use efficiency
Crop water use efficiency is defined as the ratio
of the mass of marketable yield or biomass pro-
duced per unit of water used. For this definition,
crop water use efficiency has units of production
unit per water volume unit. Units typically used
are tons/acre-inch, pounds/acre-inch, or bushels/
acre-inch in English units and kilograms/cubic
meter in metric units.
This definition is not a true efficiency because it
does not express a dimensionless ratio. It does,
however, have the advantage of comparing both
yield and water used, thus it is often used in
economic comparisons of alternative crops.

Irrigation water use efficiency
There is no general agreement on a single
definition of irrigation water use efficiency (En). Eu
can be defined in two different ways.
1. E can be defined as the ratio of the volume of
water beneficially used to the volume delivered
from the irrigation system. Water that is benefi-
cially used includes that which is applied for
leaching of salts from the crop root zone, crop
cooling, freeze protection, and other such uses, in
addition to that stored in the crop root zone for
evapotranspiration.
This definition of Eu is a true efficiency; that is, it
is dimensionless and it expresses the ratio of two
volumes of water. This ratio expresses the fraction
of each unit of water delivered that is beneficially
used.
As an example, excess water beyond that which
can be stored in the crop root zone may be required
to leach salts from the crop root zone if poor quality
water is being used for irrigation. Since this would
be a beneficial use, the irrigation water use effi-
ciency would remain high, although the irrigation
application efficiency would be reduced because all


of the water applied was not stored in the crop root
zone.
2. E can also be defined as the ratio of the
increase in production of the marketable crop
component to the volume of water applied by
irrigation for irrigated as compared to nonirrigated
production.
E, = (Y, Yo) / V (3)
where Y1 = mass of marketable crop produced
with irrigation,
Y = mass of marketable crop produced
without irrigation,
V. = volume of irrigation water applied.
Although this definition of E is not a true
efficiency, it has the advantage of expressing the
increase in production from irrigation for economic
evaluations of the profitability of proposed irriga-
tion projects. It is not meaningful if the crop
cannot be produced without irrigation.
Because both of these definitions of irrigation
water use efficiency are sometimes used, it is
always necessary to clearly define E. and to give its
units when this efficiency term is used.

Factors affecting irrigation
efficiencies

Pressurized irrigation systems
Pressurized irrigation systems include sprinkler
and micro- irrigation systems. Pressure is required
for proper operation of the sprinklers and
microirrigation emitters. These systems use
pipelines to distribute water throughout the sys-
tem.
Because networks of pressurized pipelines rather
than soil hydraulic properties are used to distribute
water, the field-scale uniformity of water applica-
tion (and the associated irrigation application
efficiency) is more strongly dependent on the
hydraulic properties of the pipe network designed
than site-specific soil hydraulic properties. Thus,
application efficiencies of well-designed and well-
managed pressurized irrigation systems are much
less variable than application efficiencies of gravity
flow irrigation systems, which depend heavily on
soil hydraulic characteristics.








If this grower installs a system to recycle runoff
water and is thus able to recover 40% (FR = 0.40) of
the water which was being lost from the field (that
is, approximately 40% of the water being lost was
due to runoff), the effective irrigation efficiency
(from Equation 2) would be
E. = 0.50 + 0.40 x (1.00 0.50) = 0.70 or 70%
Thus, the irrigation efficiency would be increased
from 50% to 70% by recycling water which was
previously being lost to runoff.

Crop water use efficiency
Crop water use efficiency is defined as the ratio
of the mass of marketable yield or biomass pro-
duced per unit of water used. For this definition,
crop water use efficiency has units of production
unit per water volume unit. Units typically used
are tons/acre-inch, pounds/acre-inch, or bushels/
acre-inch in English units and kilograms/cubic
meter in metric units.
This definition is not a true efficiency because it
does not express a dimensionless ratio. It does,
however, have the advantage of comparing both
yield and water used, thus it is often used in
economic comparisons of alternative crops.

Irrigation water use efficiency
There is no general agreement on a single
definition of irrigation water use efficiency (En). Eu
can be defined in two different ways.
1. E can be defined as the ratio of the volume of
water beneficially used to the volume delivered
from the irrigation system. Water that is benefi-
cially used includes that which is applied for
leaching of salts from the crop root zone, crop
cooling, freeze protection, and other such uses, in
addition to that stored in the crop root zone for
evapotranspiration.
This definition of Eu is a true efficiency; that is, it
is dimensionless and it expresses the ratio of two
volumes of water. This ratio expresses the fraction
of each unit of water delivered that is beneficially
used.
As an example, excess water beyond that which
can be stored in the crop root zone may be required
to leach salts from the crop root zone if poor quality
water is being used for irrigation. Since this would
be a beneficial use, the irrigation water use effi-
ciency would remain high, although the irrigation
application efficiency would be reduced because all


of the water applied was not stored in the crop root
zone.
2. E can also be defined as the ratio of the
increase in production of the marketable crop
component to the volume of water applied by
irrigation for irrigated as compared to nonirrigated
production.
E, = (Y, Yo) / V (3)
where Y1 = mass of marketable crop produced
with irrigation,
Y = mass of marketable crop produced
without irrigation,
V. = volume of irrigation water applied.
Although this definition of E is not a true
efficiency, it has the advantage of expressing the
increase in production from irrigation for economic
evaluations of the profitability of proposed irriga-
tion projects. It is not meaningful if the crop
cannot be produced without irrigation.
Because both of these definitions of irrigation
water use efficiency are sometimes used, it is
always necessary to clearly define E. and to give its
units when this efficiency term is used.

Factors affecting irrigation
efficiencies

Pressurized irrigation systems
Pressurized irrigation systems include sprinkler
and micro- irrigation systems. Pressure is required
for proper operation of the sprinklers and
microirrigation emitters. These systems use
pipelines to distribute water throughout the sys-
tem.
Because networks of pressurized pipelines rather
than soil hydraulic properties are used to distribute
water, the field-scale uniformity of water applica-
tion (and the associated irrigation application
efficiency) is more strongly dependent on the
hydraulic properties of the pipe network designed
than site-specific soil hydraulic properties. Thus,
application efficiencies of well-designed and well-
managed pressurized irrigation systems are much
less variable than application efficiencies of gravity
flow irrigation systems, which depend heavily on
soil hydraulic characteristics.









Sprinkler irrigation systems
During water applications, sprinkler irrigation
systems lose water due to evaporation and wind
drift. More water is lost during windy conditions
than calm conditions. More is also lost during high
evaporative demand periods (hot, dry days) than
during low demand periods (cool, cloudy, humid
days). Thus, sprinkler irrigation systems usually
apply water more efficiently at night (and early
mornings and late evenings) than during the day.
Whether growers can benefit from night-time
irrigation depends on characteristics of their
production systems. For example, some crops may
suffer from increased disease due to night-time
irrigation, others may require irrigations more
frequently than once per day or may require cooling
by irrigation during peak water use periods of the
day.
More water is lost by sprinklers that discharge
water at high angles, over great distances, and at
great heights above the ground surface because of
greater opportunity time for evaporation. In addi-
tion, greater water losses occur from systems which
discharge a greater proportion of small droplet
sizes because small droplets are more readily
carried by wind and they expose more surface area
to the atmosphere for evaporation.
Some water is lost by interception on vegetative,
soil, mulch, and other surfaces during irrigation.
However, much of this intercepted water is not lost
- rather it compensates for a portion of the plant
transpiration by evaporating directly from the
plant canopy and other surfaces, thus cooling the
canopy. Application efficiencies will be reduced if
water falls between widely spaced plants or outside
the crop root zone, as in the cases of container
nurseries or young citrus production systems, or
water which is shed away from the crop root zone
as in the case of plastic mulched bed production
systems.
Sprinkler irrigation application efficiencies are
reduced by nonuniform water application.
Nonuniform application causes some areas to be
over-irrigated (and lose water and nutrients to deep
percolation) while other areas are under-irrigated
(reducing crop yields). Thus, system design affects
application efficiency. Nonuniform water applica-
tion occurs when sprinklers are not properly
selected nor properly matched to the sprinkler
spacing and operating pressure used.
Nonuniformity also occurs if pressure losses within
the irrigation system are excessive (due either to


friction losses or elevation changes). Other causes
of nonuniformity such as clogged nozzles or en-
larged nozzles from abrasion by pumping sand also
reduce application efficiencies.
It is not possible to apply water with perfect
uniformity because of friction losses, elevation
changes, manufacturing variation in components,
and other factors. Also, achieving greater uniformi-
ties generally increases irrigation system cost
because of the need for larger pipe sizes, pressure
compensating emitters, or other considerations.
State or national standards should be followed to
achieve acceptable uniformities in irrigation system
design. These standards balance the cost of wasted
water and chemicals agfied through irrigation
systems against the irrigation system cost to
achieve high uniformities.
Solid set sprinkler systems. Properly de-
signed solid set systems have sprinklers perma-
nently installed at spacings that result in optimum
uniformity. However, wind, incorrect operating
pressure, and component wear or failure can still
distort application patterns and reduce uniformity
and application efficiency.
Sprinkler water application patterns must
overlap sufficiently (typically about 50%) to apply
water uniformly. Because of this need for overlap,
nonuniformity occurs at the edges of fields where
overlap is not possible. This effect is less signifi-
cant for large fields and fields shaped so that the
perimeter is minimized with respect to the total
land area. Thus, large square or rectangular fields
are less affected by this problem than small odd-
shaped fields. Part-circle sprinklers can be used at
the edges of fields to improve uniformity, but they
are more mechanically complicated and more
expensive than full-circle sprinklers. Because of
their mechanical complexities, part-circle sprin-
klers fail more frequently under field conditions.
Thus part-circle sprinklers are not commonly used
in large scale field irrigation systems.
Gun sprinkler systems. Gun sprinklers are
large sprinklers that discharge high flow rates at
high pressures. Because water is sprayed over
greater distances, at greater heights, and at greater
velocities, greater amounts of water are typically
lost to wind drift and evaporation than from solid
set systems.
Portable guns irrigate circular land areas. They
are moved from location to location, usually with
some overlap of the previously irrigated area.
Because of nonuniform water applications where








patterns overlap, and because of the greater wind
drift and evaporation losses, portable guns typically
have lower application efficiencies than solid set
systems.
Traveling guns are self-propelled. They move
slowly across the field, irrigating rectangular strips
of land. This continual motion compensates for
nonuniformity in the application pattern in the
direction of travel, resulting in greater uniformity
in the direction of travel than between the irrigated
strips. Because of insufficient overlap at startup
and at the end of a length of run, water is applied
more efficiently for long lengths of run than for
short run lengths. Traveling guns typically have
greater application efficiencies than portable guns
because of the greater uniformity that occurs in the
direction of travel.
Center pivot and lateral move systems.
Center pivot and lateral move irrigation systems
are self-propelled multiple sprinkler systems which
are designed for a specific location. Overlap of
sprinkler patterns and uniformity of water applica-
tion are generally not problems except at field
boundaries. Large changes in elevation which
affect system pressures, or large changes in soil
properties which affect infiltration rates and soil
water storage may also lower water application
efficiency and uniformity. Center pivot or lateral
move systems which use gun sprinklers on the ends
of the laterals to expand the irrigated area will
have lower overall application efficiencies because
of the greater water losses from the guns.
In recent years, center pivot and lateral move
systems have been developed which operate at low
pressure and apply water either with controlled
droplet sizes or by dripping near the surface so that
application efficiencies are high, even under moder-
ately windy conditions. These systems are gener-
ally limited in application to soils with high infil-
tration rates such as typical Florida sandy soils.
These systems may have application efficiencies
equal to or better than those of solid set irrigation
systems.
Periodic move lateral systems. Periodic
move lateral systems include hand-move or por-
table, end-tow, side-move, and side-roll systems.
Each of these four types of systems functions
similarly from the standpoint of water application
each consists of a lateral pipe with sprinklers
located along its length. The different classifica-
tions refer to the way that the sprinkler laterals are
moved.


Hand-move or portable sprinkler systems are
moved manually between irrigations by disassem-
bling sections of aluminum lateral pipe and carry-
ing them to the next location. End-tow systems are
typically skid-mounted, and they are moved by
towing them from the end of the lateral with a
tractor. Side-move and side-roll systems are
laterals mounted on wheels. Between irrigations,
these systems are manually or automatically rolled
in a lateral direction to the new location.
Periodic move lateral systems are designed to
apply water uniformly along the laterals.
Nonuniform applications and lower application
efficiencies occur when the laterals are not properly
positioned between settings. Nonuniformity also
occurs at the ends of the laterals where sprinkler
overlap is not adequate. Thus, long laterals may
apply water more uniformly and efficiently than
short laterals if field slope and soil properties do
not affect applications.

Microirrigation systems
Microirrigation systems are low pressure sys-
tems which distribute water through low flow rate
emitters. Water is discharged near or within the
root zone of the crop being irrigated. These sys-
tems include drip, line source, spray,
microsprinkler, bubbler, and other similar types of
systems.
Application efficiencies ofmicroirrigation sys-
tems are typically high. Because these systems
distribute water near or directly into the crop root
zone, water losses due to wind drift and evapora-
tion are typically small. Wind drift and evapora-
tion losses can be high if spray or microsprinkler
systems are operated under windy conditions on
hot, dry days. Thus management to avoid these
losses is important to achieving high application
efficiencies with these systems.
Primary losses in efficiency of micro systems
occur from nonuniform water applications due to
pressure losses from friction or elevation changes,
or management problems such as over-irrigation or
clogged emitters. As with other types of irrigation
systems, design standards (resulting from economic
considerations) require that water applications
from micro systems be made at less than perfect
uniformities, and this results in application effi-
ciencies that are less than 100%.
Drip and line source systems. Drip irrigation
systems apply water in individual drops or small
streams from individual drip emitters on, near, or









below the soil surface. Line source systems apply
water from closely spaced orifices or by continuous
seepage along the lateral pipe length. Application
rates are typically in the range of 0.25-4 gph per
emitter or 0.3-2.0 gpm per 100 ft of lateral length.
The soil surface wetted is only that within 1-2 ft of
the water source for typical Florida sandy soils.
Wind does not affect these systems. Evaporation
losses are also typically small because of the
limited surface area wetted and the rapid surface
drying and mulching of sandy soils.
Application efficiencies of drip and line source
systems are primarily dependent on hydraulics of
design of these systems and on their maintenance
and management. However, soil hydraulic proper-
ties influence water conveyance from drip emitters,
thus also affecting application efficiencies, espe-
cially for young annual plants with immature root
systems. Thus, system design, especially number
of emitters per plant and the placement of emitters
with respect to the plant root zone, influence
application efficiencies. Application efficiencies are
slightly greater for subsurface placement of emit-
ters because the reduced wetting of the soil surface
reduces soil evaporation losses.
Spray systems. Spray irrigation systems use
low flow rate emitters to distribute water within a
few feet around the emitter. By far the most
common application in Florida is that of under-tree
microirrigation systems for citrus. With these
systems, water is typically applied at rates of 10-20
gallons per hour (gph) over a radius of 8-18 ft, from
one emitter per tree. The popularity of these
systems results from their ability to distribute
water in a lateral direction and over a significant
fraction of the crop root zone and to provide a
measure of freeze protection as compared to drip
systems.
Because water is sprayed in very small droplets,
some evaporation and wind drift losses may occur.
Wind distortion of spray patterns may also occur.
Thus, application efficiencies of these systems are
typically less than those of drip or line source types
ofmicroirrigation systems, but Ea can be consider-
ably less if these systems are operated on hot, dry,
windy days.
Bubbler systems. Bubbler irrigation systems
apply water into individual containers or basins
around trees or other plants. Flow rates are higher
than drip systems and thus clogging problems are
avoided. 'In Florida, these systems are primarily
used in nursery and landscaping applications
because typical sandy soils limit large scale field


applications. Bubbler system application efficien-
cies depend on the hydraulics of design, system
management, and the effectiveness of the contain-
ers or basins in retaining water for use by the
plant.

Gravity flow irrigation systems
Gravity flow irrigation systems include
subirrigation (seepage) and surface irrigation
systems. These systems distribute water by flow
through the soil profile or over the soil surface.
Because water is distributed by gravity flow, the
uniformity of water application (and the associated
irrigation application efficiency) is strongly depen-
dent on the soil topography and hydraulic proper-
ties. Growers typically use precision land grading
practices to minimize the effects of topography.
However, soil characteristics are not readily
changed, and losses of irrigation water due to
lateral flow is highly dependent on the soil water
status on surrounding land areas at the time that
irrigation is practiced. As a result of these site-
specific factors, water application efficiencies of
gravity irrigation systems may vary widely in space
and time, and they are very site-specific.

Subirrigation (seepage) systems
Subirrigation or seepage irrigation systems
irrigate by water table management. A water table
is established above an existing water table or
above a restrictive soil layer by pumping water into
open ditches or underground conduits. Not all of
the water pumped is available for crop use -
depending on the depth to the natural water table,
large quantities may be required to build and
maintain the water table, and this reduces the
application efficiency. Other losses occur due to
deep percolation below the crop root zone and to
subsurface lateral flow to surrounding areas. The
magnitudes of losses by both of these mechanisms
are site- and time-specific as they depend on the
permeability of restrictive soil layers and the
management practices occurring in surrounding
fields. Thus, irrigation application efficiencies for
these types of systems can vary widely, depending
upon site-specific conditions.
Two types of seepage irrigation systems, classi-
fied by method of water application, are used in
Florida. Surface ditch systems use field ditches
which are called water furrows or lateral ditches.
Subsurface systems use underground pipes or mole
drains to control water tables. The underground








pipes are slotted plastic pipes that are typically
used for subsurface drainage.
Florida's humid climate requires drainage on
high water table soils, and field slope is necessary
for surface drainage. Surface runoff normally
occurs from surface ditch systems because of field
slope. Runoff reduces irrigation application effi-
ciencies unless this water is recycled.
The use of subsurface irrigation systems allows
water to be applied and water tables to be con-
trolled without surface runoff. However, in many
areas of the state, water quality problems prohibit
the use of underground pipes because of clogging.
Water distribution from seepage irrigation
systems occurs below the soil surface. Therefore,
wind and other climatic factors do not affect the
uniformity of water application. Also, evaporation
losses from both surface ditch systems and under-
ground pipes are about equal because the soil
surface is wet and evaporation occurs at near
potential rates with both systems.
Conveyance efficiencies are affected by the
system design. In open ditch systems, water is
conveyed from the pump or other water source to
the lateral ditches in open ditches. In semi-closed
systems, water is conveyed by pipe from the water
source to a header or manifold pipe which individu-
ally distributes water to the open field ditches.
Conveyance losses of open ditch systems depend
on the hydraulic properties of the soil in which the
ditch is constructed, the height of surrounding
water tables, and the location of the water source
with respect to the irrigated field. Losses may be
very significant when water is conveyed long
distances through nonirrigated areas. Conversely,
conveyance losses may be negligible if the water
source is a well in the center of the field being
irrigated and seepage from the ditch flows into the
field being irrigated. Conveyance losses are
avoided in semi-closed systems where the water is
contained in a pipeline.

Surface (flood) irrigation systems
Surface irrigation systems are those in which
water is distributed by flow across the soil surface
due to either soil slope or slope of the water surface.
Two types of systems exist. In the first, water
tables are not established rather, the soil hy-
draulic properties restrict water movement through
the soil to low rates. These soil properties allow
water to be distributed across the surface before
significant deep percolation losses occur. This type


of system is thus limited to "heavy" soils with low
hydraulic conductivities such as loams, clay loams,
and clays. This type of system is not used in
Florida because the typical Florida agricultural soil
is sandy with high hydraulic conductivity. The
heavier Florida soils are generally not irrigated for
agricultural purposes because their high water-
holding capacities can store much of the large
annual rainfall.
A second type of surface irrigation system is
flood irrigation. Two types of flood irrigation
systems, crown flood (for citrus production) and
continuous (paddy) flood (for rice production) are
used in Florida. Flood irrigation is practiced only
on flatwoods soils with shallow restrictive soil
layers or high natural water tables.
Crown flood systems. Crown flood systems
are used to irrigate citrus in some areas of Florida.
This is practiced only on bedded citrus groves on
flatwoods soils. With this system, water furrows
are filled with enough water to cause the water
level to rise to the tree trunks (crowns) on the beds.
Water is left in the water furrows for a few hours
up to 2 days so that it can move into the soil beds.
The field ditches are then drained.
Application efficiencies of crown flood systems
greatly depend on the soil hydraulic characteristics,
permeability of restrictive layers, water table
levels, and the characteristics of surrounding land
areas. Application efficiencies are significantly
increased if the excess irrigation water drained
from the citrus groves is reused. If drainage water
is reused, the application efficiency has been
observed to be high (75%), while if the excess water
is lost, then the application efficiency has been
observed to be low (25%).
Continuous flood (paddy) systems. Rice
production systems are continuously flooded. This
irrigation practice involves establishing and main-
taining a water table above the soil surface. Again,
as for subirrigation and crown flood irrigation
systems, site-specific characteristics strongly
impact irrigation application efficiencies. The
value of Ea will vary as a function of the soil
hydraulic characteristics and water table charac-
teristics of surrounding land areas.

Potential irrigation system
application efficiencies
Potential irrigation system application efficien-
cies are application efficiencies that can be
achieved with well-designed and well-managed








irrigation systems. Potential application efficien-
cies must be known by irrigation system designers,
managers, and water management personnel.
Designers need to estimate how much water is lost
in transmission, storage, and application, so that
pumping systems and water supply systems can be
adequately selected for specific applications.
Irrigation system managers need to develop water
budgets and irrigation schedules, both of which are
partially based on the efficiency of water applica-
tions. Water management personnel need to know
application efficiencies as one of the factors re-
quired to determine the proper amounts of water to
be permitted for irrigation systems.
Irrigation system application efficiencies can
vary widely, depending upon how well a system is
designed and managed. Application efficiencies also
vary with other factors, including stage of crop
development, time of year, and climatic conditions.
However, average seasonal application efficiencies
of well-designed systems that are scheduled to
maintain adequate soil moisture levels to meet crop
water requirements for evapotranspiration (ET)
will be much less variable. The application efficien-
cies listed in Tables 1 and 2 are believed by the
authors of this publication to be reasonable values
to be used for typical Florida conditions when
irrigations are scheduled to meet crop water
requirements for (ET). The values given are
seasonal values which represent average produc-
tion conditions throughout the growing season.
Application efficiencies will be reduced from the
values given in Tables 1 and 2 if irrigation systems
are operated to apply water for purposes other than
maintaining adequate soil moisture for crop ET. As
examples, application efficiencies will be reduced if
water is applied for leaching of salts, freeze protec-
tion, establishment of young plants, crop cooling, or
other beneficial uses. These water uses are reason-
able and necessary for crop production, however,
they are not all required for all production systems.
Thus, irrigation water requirements for beneficial
uses other than maintaining adequate soil moisture
for crop ET must be determined on a case-by-case
basis.


Because uniformity of water application of
gravity irrigation systems is strongly influenced by
soil hydraulic properties, application efficiencies of
gravity flow irrigation systems range much more
widely than those of pressurized irrigation systems.
Average values are not estimated in Table 2 be-
cause gravity flow system application efficiencies
are very site-specific.

References
ASAE. 1990. ASAE Standards for Soil and
Water Resource Management. ASAE Standards
1990. American Society of Agricultural Engineers.
St. Joseph, MI. 659 pages.
ASCE. 1987. ASCE Manual on Selection of
Irrigation Methods for Agriculture. In Review.
American Society of Civil Engineers. New York. 68
pages.
Israelsen, O.W. and V.E. Hansen. 1962. Irriga-
tion Principles and Practices. John Wiley and
Sons, Inc. New York. 447 pages.
Jensen, M.E. (Ed.). 1980. Design and Operation
of Farm Irrigation Systems. ASAE Monograph No.
3. American Society of Agricultural Engineers. St.
Joseph, MI. 829 pages.
Merriam, J.L. and J. Keller. 1978. Farm irriga-
tion system evaluation: A guide for management.
Utah State Univ., Logan Utah. 271 pages.
Pair, C.H. (Ed.-in-Chief). 1983. Irrigation. The
Irrigation Association. Silver Spring, MD. 686
pages.
Schwab, G.O., R.K Frevert, T.W. Edminster, and
KK Barnes. 1981. Soil and Water Conservation
Engineering. 3rd Edition. John Wiley and Sons.
New York. 525 pages.
SCS. 1982. Florida Irrigation Guide. USDA,
Soil Conservation Service. Gainesville, FL.
SCS. 1987. Farm Irrigation Rating Method.
Engineering Technical Note FL-17. USDA, Soil
Conservation Service. Gainesville, FL.








Table 1. Pressurized Irrigation system application efficiencies, Ea (%) 2

Sprinkler irrigation systems
System type Range Average
Solid set systems 70 80 75
For container nurseries 15 50 20
Guns
Portable guns 60 70 65
Traveling guns 65 75 70
Center pivot and
Lateral move systems 70 85 75
Periodic move laterals 65 75 70
Hand-move or portable laterals
End-tow systems
Side-roll systems
Side-move systems
Microirrigation systems
Drip or line source systems
Surface 70 90 85
Subsurface 70 90 85
Spray systems 70 85 80
Bubbler systems 70 85 80


2 Average seasonal irrigation system application efficiencies for well-designed Florida irrigation systems that are scheduled to
maintain adequate soil moisture levels to meet crop water requirements for evapotranspiration (ET). Individual Irrigation application
efficiencies will vary more widely as a function of stage of crop development, time of year, climatic conditions and other factors.
Application efficiencies will be reduced from these values when water in addition to that required for crop ET Is applied for leaching
of salts, establishment of young plants, freeze protection, crop cooling, or other beneficial uses.









Table 2. Gravity flow Irrigation system application efficiencies, E (%)


Subirrigation (seepage) systems
System type Range
Open field ditch systems
Open ditch conveyance systems
Flow through 20 70
Tailwater recycle 30 80
Semi-closed conveyance systems
Flow through 30 70
Tailwater recycle 40 80
Subsurface conduit systems 40 80
Surface (flood) systems
Crown flood systems 25 75
Continuous flood (paddy) systems 25 75


3 Average seasonal irrigation system application efficiencies for well-designed and well-managed gravity flow irrigation systems In
Florida. Average values are not estimated because application efficiencies are site-specific and range widely for gravity flow
systems. Individual irrigation application efficiencies will vary more widely as a function of stage of crop development, time of year,
climatic conditions and other factors. Application efficiencies will be reduced from these values when irrigation water is applied for
other beneficial uses such as freeze protection.



















































































COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTITUTE OFFFOODANDAGRICULTURAL SCIENCES, John T. Woeste,
director, in cooperation with the United States Department of Agriculture, publishes this information to further the purpose of the May 8 and June
30,1914 Acts of Congress; and is authorized to provide research, educational information and other services only to individuals and institutions that
function without regard to race, color, sex, age, handicap or national origin. Single copies of extension publications (excluding 4-H and youth
publications) are available free to Florida residents from county extension offices. Information on bulk rates or copies for out-of-state purchasers
is available from C.M. Hinton, Publications Distribution Center, IFAS Building 664, Universityof Florida, Gainesville, Florida32611. Before publicizing
this publication, editors should contact this address to determine availability. Printed 6/91.




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