• TABLE OF CONTENTS
HIDE
 Copyright
 Front Cover
 Authors
 List of figures
 Tensiometer for soil moisture measurement...
 Tensiometer components
 Principle of operation
 Units of measurement
 Range of operation
 Site selection
 Installation
 Field service
 Irrigation scheduling
 Automated tensiometers
 Summary
 Back Cover






Group Title: Florida Cooperative Extension Service circular 487
Title: Tensiometers for soil moisture measurement and irrigation scheduling
CITATION PAGE IMAGE ZOOMABLE PAGE TEXT
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00049264/00001
 Material Information
Title: Tensiometers for soil moisture measurement and irrigation scheduling
Series Title: Circular Florida Cooperative Extension Service
Physical Description: 15 p. : ill. ; 23 cm.
Language: English
Creator: Smajstrla, A. G ( Allen George )
Harrison, D. S ( Dalton Sidney ), 1920-
Duran, Frank X
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville
Publication Date: 1981?
 Subjects
Subject: Soil moisture -- Measurement   ( lcsh )
Irrigation   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: Allen G. Smajstrla, Dalton S. Harrison, and Frank X. Duran.
General Note: Cover title.
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Bibliographic ID: UF00049264
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: oclc - 08853167

Table of Contents
    Copyright
        Copyright
    Front Cover
        Page 1
        Page 2
    Authors
        Page 3
    List of figures
        Page 3
    Tensiometer for soil moisture measurement and irrigation scheduling
        Page 4
    Tensiometer components
        Page 4
    Principle of operation
        Page 4
        Page 5
    Units of measurement
        Page 6
    Range of operation
        Page 7
    Site selection
        Page 7
    Installation
        Page 8
        Page 9
        Page 10
    Field service
        Page 11
    Irrigation scheduling
        Page 12
        Page 13
    Automated tensiometers
        Page 14
    Summary
        Page 15
    Back Cover
        Page 16
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





/ Central Science
Library
JUN 0 8 1987 Circular 487
University of Florida

Tensiometers for Soil

Moisture Measurement
and
Irrigation Scheduling


Allen G. Smajstrla, Dalton S. Harrison, and Frank X. Duran



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


-1 8-








Authors


Allen G. Smajstrla is Assistant Professor, water management
specialist, Dalton S. Harrison is Professor, water management
specialist, and Frank X. Duran is a student assistant, Agricultural
Engineering Department, IFAS, University of Florida, Gainesville,
FL 32611.


List of Figures

Figure 1. Tensiometer components. 5
Figure 2. Typical vacuum gauge dial face with gradations
in centibars. 6
Figure 3. Tensiometer placement for row crop production systems. 7
Figure 4. Tensiometer placement for tree crop production systems. 7
Figure 5. Filling a tensiometer using a plastic squeeze bottle
and a small diameter flexible tube.
Figure 6. Using a vacuum hand pump to extract air from a
tensiometer to test for leaks before installing, and
to service the instrument in the field. 9
Figure 7. Installation procedure for heavy soils, using a
commercially available soil coring tool. 10
Figure 8. A properly placed tensiometer in the field. 10
Figure 9. Refilling the tensiometer in the field to remove
air bubbles. 12
Figure 10. Soil water capacity function for Lake Fine sand. 13
Figure 11. Irrigation scheduling and durations as controlled by
tensiometers at two depths. 13
Figure 12. Wiring diagram for automatic irrigation control. 14








Authors


Allen G. Smajstrla is Assistant Professor, water management
specialist, Dalton S. Harrison is Professor, water management
specialist, and Frank X. Duran is a student assistant, Agricultural
Engineering Department, IFAS, University of Florida, Gainesville,
FL 32611.


List of Figures

Figure 1. Tensiometer components. 5
Figure 2. Typical vacuum gauge dial face with gradations
in centibars. 6
Figure 3. Tensiometer placement for row crop production systems. 7
Figure 4. Tensiometer placement for tree crop production systems. 7
Figure 5. Filling a tensiometer using a plastic squeeze bottle
and a small diameter flexible tube.
Figure 6. Using a vacuum hand pump to extract air from a
tensiometer to test for leaks before installing, and
to service the instrument in the field. 9
Figure 7. Installation procedure for heavy soils, using a
commercially available soil coring tool. 10
Figure 8. A properly placed tensiometer in the field. 10
Figure 9. Refilling the tensiometer in the field to remove
air bubbles. 12
Figure 10. Soil water capacity function for Lake Fine sand. 13
Figure 11. Irrigation scheduling and durations as controlled by
tensiometers at two depths. 13
Figure 12. Wiring diagram for automatic irrigation control. 14







Tensiometers
for
Soil Moisture Measurement and Irrigation Scheduling
The tensiometer is an instrument which is used to measure the
energy status (or potential) of soil water. That measurement is a
very useful one because it is directly related to the ability of plants
to extract water from soil. Irrigators often use tensiometers for ir-
rigation scheduling because they provide direct measurement of soil
moisture status, are easily managed, and they are inexpensive. In
addition, tensiometers can be automated to control irrigation water
applications when the soil water potential decreases to a predeter-
mined critical value.

Tensiometer Components
A tensiometer consists of a porous cup, connected through a rigid
body tube to a vacuum gauge, with all components filled with water.
The porous cup is normally constructed of ceramic because of its
structural strength as well as permeability to water flow. The body
tube is normally transparent so that the status of water within the
tensiometer can readily be observed. A Bourdon tube vacuum gauge
is commonly used for water potential measurements, although a
water manometer or mercury manometer also can be used. Figure 1
illustrates the components of one model of commercially available
tensiometer using the vacuum gauge.
Tensiometer cost is a function of the instrument's length, or the
depth at which it will be installed. In general, prices range from
about $25 each for the 6 inch size to about $35 for the 6 foot size.
Tensiometers are manufactured by several companies and are
available at most irrigation supply businesses.

Principle of Operation
The tensiometer is placed in the field with porous ceramic cup
firmly in contact with the soil. The porous ceramic allows water to
move through it in response to soil water potential. A partial
vacuum is created as water moves from the sealed tensiometer tube.
The vacuum causes a reading on the vacuum gauge which is a direct
indication of the attractive forces between the water and soil par-
ticles. It is therefore, also an indication of the energy that would
need to be exerted by the plant to extract water from the soil.
Because the porous ceramic cup is permeable to both water and
dissolved salts, tensiometers do not record the water potential due
to dissolved salts osmoticc potential). The actual total potential that
plants would need to overcome to extract from soils includes







Tensiometers
for
Soil Moisture Measurement and Irrigation Scheduling
The tensiometer is an instrument which is used to measure the
energy status (or potential) of soil water. That measurement is a
very useful one because it is directly related to the ability of plants
to extract water from soil. Irrigators often use tensiometers for ir-
rigation scheduling because they provide direct measurement of soil
moisture status, are easily managed, and they are inexpensive. In
addition, tensiometers can be automated to control irrigation water
applications when the soil water potential decreases to a predeter-
mined critical value.

Tensiometer Components
A tensiometer consists of a porous cup, connected through a rigid
body tube to a vacuum gauge, with all components filled with water.
The porous cup is normally constructed of ceramic because of its
structural strength as well as permeability to water flow. The body
tube is normally transparent so that the status of water within the
tensiometer can readily be observed. A Bourdon tube vacuum gauge
is commonly used for water potential measurements, although a
water manometer or mercury manometer also can be used. Figure 1
illustrates the components of one model of commercially available
tensiometer using the vacuum gauge.
Tensiometer cost is a function of the instrument's length, or the
depth at which it will be installed. In general, prices range from
about $25 each for the 6 inch size to about $35 for the 6 foot size.
Tensiometers are manufactured by several companies and are
available at most irrigation supply businesses.

Principle of Operation
The tensiometer is placed in the field with porous ceramic cup
firmly in contact with the soil. The porous ceramic allows water to
move through it in response to soil water potential. A partial
vacuum is created as water moves from the sealed tensiometer tube.
The vacuum causes a reading on the vacuum gauge which is a direct
indication of the attractive forces between the water and soil par-
ticles. It is therefore, also an indication of the energy that would
need to be exerted by the plant to extract water from the soil.
Because the porous ceramic cup is permeable to both water and
dissolved salts, tensiometers do not record the water potential due
to dissolved salts osmoticc potential). The actual total potential that
plants would need to overcome to extract from soils includes







Tensiometers
for
Soil Moisture Measurement and Irrigation Scheduling
The tensiometer is an instrument which is used to measure the
energy status (or potential) of soil water. That measurement is a
very useful one because it is directly related to the ability of plants
to extract water from soil. Irrigators often use tensiometers for ir-
rigation scheduling because they provide direct measurement of soil
moisture status, are easily managed, and they are inexpensive. In
addition, tensiometers can be automated to control irrigation water
applications when the soil water potential decreases to a predeter-
mined critical value.

Tensiometer Components
A tensiometer consists of a porous cup, connected through a rigid
body tube to a vacuum gauge, with all components filled with water.
The porous cup is normally constructed of ceramic because of its
structural strength as well as permeability to water flow. The body
tube is normally transparent so that the status of water within the
tensiometer can readily be observed. A Bourdon tube vacuum gauge
is commonly used for water potential measurements, although a
water manometer or mercury manometer also can be used. Figure 1
illustrates the components of one model of commercially available
tensiometer using the vacuum gauge.
Tensiometer cost is a function of the instrument's length, or the
depth at which it will be installed. In general, prices range from
about $25 each for the 6 inch size to about $35 for the 6 foot size.
Tensiometers are manufactured by several companies and are
available at most irrigation supply businesses.

Principle of Operation
The tensiometer is placed in the field with porous ceramic cup
firmly in contact with the soil. The porous ceramic allows water to
move through it in response to soil water potential. A partial
vacuum is created as water moves from the sealed tensiometer tube.
The vacuum causes a reading on the vacuum gauge which is a direct
indication of the attractive forces between the water and soil par-
ticles. It is therefore, also an indication of the energy that would
need to be exerted by the plant to extract water from the soil.
Because the porous ceramic cup is permeable to both water and
dissolved salts, tensiometers do not record the water potential due
to dissolved salts osmoticc potential). The actual total potential that
plants would need to overcome to extract from soils includes











(-4: Sric-a


Service cap

0 ring seal


-Depth label

Port for
vacuum gauge


Plastic gauge
dial cover






- Vacuum dial gauge







Plastic body tube

Ceramin porous cup


Figure 1. Tensiometer components.








osmotic potentials. If soils are saline, or if poor quality irrigation
water is being used, the osmotic potential will be a large portion of
the total potential. In that case, osmotic potential should also be
recorded, using appropriate instrumentation.
As the soil dries, water potential decreses (tension increases) and
the tensiometer vacuum gauge reading increases. Conversely, an in-
crease in soil water content (as by irrigation or rainfall) decreases
tension and lowers the vacuum gauge reading. The tensiometer con-
tinuously records fluctuations in soil water potential if air is not
allowed into the system. If the soil becomes extremely dry, air
enters the system due to cavitation of the water column in the tube
and the instrument ceases to function. When a significant amount
of air enters the instrument, it must be refilled with water before it
will operate again.

Units of Measurement
The tensiometer measures water potential or tension. Water
potential is commonly measured in units of bars (and centibars) or
centimeters of water. One bar is approximately equal to one at-
mosphere (14.6 lb/in2) of pressure. One bar is also equal to 1,013 cm
of water.
Because water is held by capillary forces within unsaturated soil
pore spaces, its potential is negative, indicating that work must be
done to extract water from the soil. A water potential reading of 0
indicates that the soil is saturated, and plant roots may suffer from
lack of oxygen. As the soil dries, water becomes less available and
water potential becomes more negative. The negative sign is usually
omitted for convenience when soil water potentials are referenced.
The negative sign will be omitted in this paper.
Figure 2 illustrates the dial face of a typical tensiometer vacuum
gauge. Divisions are in units of centibars (cb), with a range of
0-100 cb.


40 vacuum gauge dial face with graduations in centibars.
30
20
100






Figure 2. Typical vacuum gauge dial face with graduations in centibars.








Range of Operation
Because of its method of operation, a tensiometer operates in the
water potential range of 0 to 85 cb. Above this tension the column of
water in the plexiglass tube will form water vapor bubbles
cavitatee), and the instrument will cease to function. This range
represents only a small fraction of the entire water potential range
that is normally considered to be available for the plant growth.
Plants are normally able to survive to water potentials of 15 bars.
However, plant growth and productivity ceases well before the per-
manent wilting point of 15 bars.
Research has shown that to optimize production, irrigation
should be scheduled when water potentials reach 70 cb in medium
textured soils, and when water potentials reach the range of 20 to 30
cb in sandy soils. These ranges are dependent upon crop suscep-
tibility and soil hydraulic properties. All of these values are well
within the range of application of the tensiometer. Therefore, the
tensiometer is a very useful instrument for irrigation management
on soils of these types.

Site Selection
Tensiometers will measure water potential in only a small volume
of soil immediately surrounding the ceramic cup. Therefore, the
ceramic cup should be placed in the active root zone of the crop for
which irrigations are being scheduled. Depending upon crop type,
two or more tensiometers may be required at a measurement site.
Figures 3 and 4 illustrate proper depths of installation for row crops
and tree crops. respectively.


Figure 3. Tensiometer placement for Figure 4. Tensiometer placement for
row crop production systems. tree crop production systems.








Range of Operation
Because of its method of operation, a tensiometer operates in the
water potential range of 0 to 85 cb. Above this tension the column of
water in the plexiglass tube will form water vapor bubbles
cavitatee), and the instrument will cease to function. This range
represents only a small fraction of the entire water potential range
that is normally considered to be available for the plant growth.
Plants are normally able to survive to water potentials of 15 bars.
However, plant growth and productivity ceases well before the per-
manent wilting point of 15 bars.
Research has shown that to optimize production, irrigation
should be scheduled when water potentials reach 70 cb in medium
textured soils, and when water potentials reach the range of 20 to 30
cb in sandy soils. These ranges are dependent upon crop suscep-
tibility and soil hydraulic properties. All of these values are well
within the range of application of the tensiometer. Therefore, the
tensiometer is a very useful instrument for irrigation management
on soils of these types.

Site Selection
Tensiometers will measure water potential in only a small volume
of soil immediately surrounding the ceramic cup. Therefore, the
ceramic cup should be placed in the active root zone of the crop for
which irrigations are being scheduled. Depending upon crop type,
two or more tensiometers may be required at a measurement site.
Figures 3 and 4 illustrate proper depths of installation for row crops
and tree crops. respectively.


Figure 3. Tensiometer placement for Figure 4. Tensiometer placement for
row crop production systems. tree crop production systems.








Because of differences in soil characteristics, several sites may be
required to adequately assess the water status of large areas. In
general, one set of tensiometers for each five acres of crop area is
considered to be desirable. For more valuable or more sensitive
crops, more tensiometers would be required. For uniform soil types
fewer tensiometers may be adequate.
The sites selected for installation should be representative of the
surrounding field conditions. Low, wet areas or high, dry areas
should be avoided if they are not representative of average soil con-
ditions. Tensiometers should be placed within the plant canopy in
positions such that the instruments are not shielded from water nor
such that abnormally large amounts of precipitation are directed to
the instrument sites.
Placement of tensiometers with depth is critical. For very shallow
rooted (less than 1 ft) crops such as some vegetables, only one ten-
siometer may be required with depth. It should be centered in the
crop root zone, but at least 4-6 inches below the surface. In no case
should any portion of the ceramic cup be exposed to the atmosphere.
For crops with moderate root zones such as most field crops. two
tensiometers should be used at each measurement site. The
shallower one should be placed in the zone of maximum root concen-
tration. This is normally at about one-third of the active rooting
depth. In shallow-rooted tree crops, depths of 12 and 24 inches are
often used. For deep rooting crops with active root depths of more
than 4 feet, it is desirable to have tensiometers installed at three
depths. Other depth combinations may be used where appropriate.

Installation
The tensiometer can be a useful instrument for irrigation schedul-
ing only if it is properly installed. In general, proper installation re-
quires that the instruments be in good hydraulic contact with the
surrounding soil so that water can move into and away from them
as efficiently as possible. In addition, the tensiometers should be
properly located in the field as discussed in the section on site selec-
tion.
Before field installation, each tensiometer should be tested to
assure that it is operating properly. Each should be filled with clean
water and allowed to stand in a vertical position or allowed to stand
in a container of water for at least 15 minutes so that the ceramic
tip will saturate. A plastic squeeze bottle and small diameter plastic
tube can be used to fill the tensiometer from the bottom to help
eliminate air bubbles (Figure 5). When its tip is thoroughly wetted,
the tensiometer can be refilled and capped. The tensiometer will not
be serviceable immediately because there will be air bubbles in the









vacuum gauge. A small hand vacuum pump (Figure 6), obtainable
from tensiometer manufacturers can be used to remove the air bub-
bles. Air bubbles can also be removed by allowing the capped ten-
siometer to stand with the ceramic cup exposed to the atmosphere.
Water will evaporate from the ceramic, creating a vacuum which
will allow the air bubbles to be expelled from the vacuum gauge.
This technique may take several hours and require several replica-
tions before all of the air is removed, therefore the vacuum pump
technique is recommended.


Figure 5. Filling a tensiometer using a plastic squeeze bottle and a small diameter flexi-
ble tube.




Vacuum
hand pump


Figure 6. Using a vacuum hand pump to extract air from a tensiometer, (a) To test for
leaks before installing, and (b) To service the instrument in the field.









Tensiometers are installed in previously cored holes in the field.
Manufacturers sell coring tools of the proper dimensions for ten-
siometer installation. In sandy soils, the access holes can be cored
by hand, while on heavier soils it may be necessary to use a hammer
to aid the installation (Figure 7). The tensiometer is pushed into the
access hole to the proper depth. In this position, the vacuum gauge
will be located 2-3 inches above the soil surface. The soil around the
tensiometer should be tamped at the surface to seal the instrument
from air contact with the ceramic cup and to prevent surface water
from running down around the tube (Figure 8).


Soil coring tool


Tamp soil


Figure 8. A properly placed tensiometer
in the field.


If commercially available coring tools are not available, a length
of standard water pipe or other tubing of the proper diameter can be
used with acceptable results. It is critical, regardless of the installa-
tion method used, that the ceramic cup be in intimate contact with
soil in order for the tensiometer to function properly.
If a rock or other impediment is encountered, the tensiometer
should be moved to an adjacent location to avoid possible damage
when it is placed in the cored hole. The tensiometer should not be
driven into place with a hammer or other object. Although adequate
for normal use, the mechanical strength of the ceramic cup is not
adequate to allow it to be hammered into place.


Figure 7. Installation procedure for
heavy soils, using a commer-
cially available soil coring tool.








In very loose, cultivated soils, such as frequently encountered in
commercial row crop production, it is possible to push the ten-
siometer into place without coring a hole. This method of installa-
tion is acceptable when applicable. Again, the surface soil must be
firmly packed around the instrument after installation.
For shallow depths, a hole can be dug with a spade to accept the
tensiometer. Again, the soil should be firmly packed around the ten-
siometer after it is set into place.
After installation, several hours may be required before the ten-
siometer reads the correct soil water potential value. This is because
of the disturbance to the soil caused by the installation procedure,
and because of the need for water to move through the walls of
ceramic cup before equilibrium is reached. The correct reading will
be reached more quickly in moist soils than in dry soils. After this
initial equilibrium period, the tensiometer will accurately indicate
the soil water potential, and it will closely follow changes in water
potential as they occur in the soil.
Tensiometers are delicate instruments and should be protected
from harm both before and after installation. They should be han-
dled carefully and protected from impact by equipment or animals
in the field. Also, freezing conditions will damage tensiometers.
They should not be left filled with water under freezing conditions.


Field Service

To operate properly, tensiometers must be serviced in the field
periodically. This is because with normal use, air is extracted from
water under tension. The air becomes trapped within the ten-
siometer and reduces response time progressively until the instru-
ment fails to operate.
If the soil in which the tensiometer has been installed is moist, soil
tensions will be low, and very little air will accumulate. If, however,
the tensiometer is installed in drier soils, with water potentials in
the range of 40 to 60 centibars, air will accumulate more quickly.
The body tube should be inspected for accumulated air each time
the tensiometer is read. If more than /2 inch of air has accumulated
beneath the service cap, the cap should be removed, and the tube
refilled with water as shown in Figure 9. In wet soils, the ten-
siometer will probably need to be serviced approximately every 2
weeks. In dry soils, servicing will need to be more frequent, perhaps
as often as every time the tensiometer data is collected.











Accumulated air


Figure 9. Refilling the tensiometer in the field to remove air bubbles.


Irrigation Scheduling
Tensiometer measurements are useful in helping to decide when
to irrigate because they give a continuous indication of soil water
status, but they do not indicate how much water should be applied.
The decision to irrigate is made when the average of all appropriate
tensiometer readings exceeds a given critical value. To optimize pro-
duction, the critical value is approximately 30 cb for sandy soils and
approximately 70 cb for medium textured soils. The critical values
are specific for different soil types and may also be functions of
stage of crop growth. Normally lower values are used, resulting in
irrigations being scheduled more frequently at critical stages of
growth. The critical values are also functions of economic considera-
tions, with higher values set if the irrigated commodity sale prices
drop or if the cost of irrigation increases.
A tensiometer indicates only when irrigation should be scheduled,
and not how much water should be applied. To determine the
amount of water to be applied, a moisture characteristic curve
specific for the irrigated soil must be used. Figure 10 is a moisture
characteristic curve for Lake Fine Sand, a typical deep sandy soil of
central' Florida. The depth of irrigation water to be applied should
be adequate to restore only the root zone to field capacity. Ex-
cessive water will be lost to deep percolation below the crop root













Lake fine sand
water capacity


0 10 20 30 00
Volumetric water content (%)

Figure 10. Soil water capacity function for lake fine sand.


1 10 20 1 10 20 30


May


June


Date


Figure 11. Irrigation scheduling and
depths.


durations as controlled by tensiometers at two


o-
CD
S30


O
0.


0
10

U,







zone carrying nutrients with it. In addition, there is some research
evidence to indicate that water applications should be less than that
required to restore the soil moisture to field capacity so that some
storage space would be available for rainfall which might occur.
Figure 11 illustrates the tensiometer data and irrigations sched-
uled by the tensiometer method. In this illustration, timing and
amount of irrigation were controlled with tensiometers at two
depths. When the major root zone (12 inch) depth became as dry as
desired, small irrigations were scheduled to rewet the 12 inch zone,
but not the 24 inch depth which was still sufficiently wet. When,
eventually, the 24 inch zone also reached the desired degree of
dryness, a larger irrigation was scheduled to rewet the entire soil
profile.

Automated Tensiometers
A major advantage of tensiometers is that they can be in-
strumented to provide automatic control of irrigation systems. The
modification required to allow a tensiometer to be used as an irriga-
tion controller is very simple. The vacuum gauge is equipped with a
magnetic pick-up switch so that, when a desired (and preset) water
potential is obtained, the switch closes, starting the irrigation

Time
clock .. ..


Circuit
breaker


-t v nelay uro I


Power
120 v


Solenoid
valve


Figure 12. Wiring diagram for automatic irrigation control.








pump. The pump operates for a preset period of time, lowering the
tensiometer reading, after which the tensiometer is again monitored
until the critical water potential is again obtained. A schematic of
such an automatically controlled irrigation system is shown in
Figure 12.

Summary
Tensiometers are useful instruments for measurements of soil
water status and irrigation scheduling. The tensiometer measures
soil water potential, which is a measure of the energy required for
plants to extract water from the soil. When used with a water
characteristic curve, tensiometers can be used to indicate both the
timing and amount of required irrigations.
Tensiometers are delicate instruments and must be properly
handled and installed to assure that they will produce reliable
results. When properly installed and maintained they will produce
continuous records of soil water potential. In addition, tensiometers
are easily modified to create automatically controlled irrigation
systems.




















































This publication was promulgated at a cost of $189.46, or 18.9
cents per copy, to inform irrigator of the proper use of ten-
siometers and their capabilities for soil moisture measurement
and irrigation scheduling. 7-1MI-85



COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLOR-
IDA, INSTITUTE OF FOOD AND AGRICULTURAL SCIENCES,
K. R. Tefertlller, 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 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, University of Florida,
Galnesvllle, Florida 32611. Before publicizing this publication, editors should contact
this address to determine availability.




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