Title: Trickle irrigation scheduling for Florida citrus
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 Material Information
Title: Trickle irrigation scheduling for Florida citrus
Alternate Title: Bulletin 208 ; Florida Cooperative Extension Service
Physical Description: Book
Language: English
Creator: Smajstrla, Allen G.
Harrison, Dalton S.
Zazueta, Fedro S.
Parsons, Larry R.
Stone, Kenneth C.
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Publication Date: 1987
Copyright Date: 1987
 Record Information
Bibliographic ID: UF00026383
Volume ID: VID00001
Source Institution: University of Florida
Holding Location: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aab7821 - LTQF
aer4744 - LTUF
17717153 - OCLC
000095243 - AlephBibNum

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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






26' Bulletin 208


Trickle Irrigation Scheduling

for Florida Citrus


Allen G. Smajstrla, Dalton S. Harrison,
Fedro S. Zazueta, Larry R. Parsons, and Kenneth C. Stone


RAINFALL
CANOPY
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OCT 2 3 1987
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ROOT SOIL WATER STORAGE \ \
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OCT 231987

Un ve, .ty of Florda
Florida Cooperative tmE x Cs i / Intitnte of Food and Agricultural Sciences
University of Florida, Gainesville / John T. Woeste, Dean for Extension









Trickle Irrigation Scheduling

for Florida Citrus


Allen G. Smajstrla, Dalton S. Harrison,
Fedro S. Zazueta, Larry R. Parsons, and Kenneth C. Stone





























A.G. Smajstrla is Associate Professor, D.S. Harrison is Professor Emeritus,
F.S. Zazueta is Assistant Professor, Agricultural Engineering Department,
Gainesville. L.R. Parsons is Associate Professor, Citrus Research and Educa-
tion Center, Lake Alfred and K.C. Stone is Graduate Research Assistant,
Agricultural Engineering Department, Gainesville, IFAS, University of Florida.













































































































h.








Table of Contents


List of Tables . . . . . . . . . . . . iv

List of Figures . . . . . . . . . . . iv

Introduction . . . . . . . . . . . . 1
1. Citrus Water Use .................. 2
2. Average Daily Evapotranspiration (ET) Rates for Citrus 3
3. Soil Water Storage in the Effective Root Zone . .. 4
4. Allowable Water Depletion Effect on Irrigation Depth 5
5. Water to Apply per Emitter at Each Irrigation . .. 5
6. Irrigation Frequency . .. . . . . .. 6
7. Irrigation Time per Application . . . . . 8

Rainfall Effects on Trickle Irrigation Schedules . . . 9
8. Tree Canopy Areas ................ 10
9. Relative Area Occupied by Tree Canopy . . .. 10
10. Irrigated Zone Soil Water Content . . . ... 11
11. Non-Irrigated Root Zone Soil Water Content . . 11
12. Antecedent Soil Water Content . . . .... 12
13. Potential Rainfall Storage in Effective Root Zone . 12
14. Effective Rainfall ................. 12
15. Rainfall Stored Under the Tree Canopy . . .. 13
16. Days to Delay Irrigation Following Rainfall ..... 14

Discussion . . . . . . . . . . . . . 14
Example Problems ................... 16

Sum m ary . . . . . . . . . . . .. . 16

Appendix A . . . . . . . . . . . . 36

Appendix B .. . . ........ . ...... .38
Example 1. Drip Irrigation Scheduling . . ... 38
Example 2. Spray-Jet Irrigation Scheduling . . .. 41

Appendix C . . . . . . . . . . . . 44








List of Tables


Table 1. Florida citrus evapotranspiration (ET). . . ... 18
Table 2. Average daily evapotranspiration (ET) rates for citrus
at various tree densities. . . . . . .. 19
Table 3. Soil water storage in soil depth irrigated. . . 20
Table 4. Depth of water to be applied at each irrigation,
considering allowable water depletion. . . ... 21
Table 5. Volume of water to be applied at each irrigation by
each emitter (gallons). . . . . . . ... 22
Table 6. Irrigation frequency, days between scheduled
irrigations. . . .... . . . . .. .. 23
Table 7. Irrigation time per application (hours). . . ... 24
Table 8a. Tree canopy area or emitter wetted area based on
tree canopy diameters or emitter wetted diameters. 25
Table 8b. Tree canopy area based on tree spacing and canopy
width. . . . . . . . . .. ... . 26
Table 9. Relative area occupied by tree canopy. ... 27
Table 10. Irrigated zone correction factor. . . . ... 28
Table 11. Non-irrigated root zone correction factor. ... 29
Table 12. Antecedent soil water content correction factor. 30
Table 13. Potential rainfall storage in soil depth irrigated
(inches). . . .. . . . . . . . . 31
Table 14. Effective rainfall, rainfall stored in the soil depth
irrigated. . . . . . . . . . 32
Table 15. Readily available effective rainfall, effective rainfall
stored under and near tree canopy. . . .. 33
Table 16. Days to delay irrigation following rainfall. ... 34








List of Figures


Figure 1. Components of citrus water balance and other
definitions ................... 18
Figure 2. Average daily ET rate in gallons per tree based
on tree density and the average daily ET rate
in inches. . . . . . . . . .. 19
Figure 3. Soil water storage in the effective root zone
based on the effective root zone depth and the
soil water-holding capacity. . . . . ... 20
Figure 4. Irrigation depth per application based on soil
water storage in the root zone and allowable
soil water depletion. . . . . . . ... 21
Figure 5. Irrigation volume per emitter at each irrigation
based on emitter wetted diameter and depth of
water to be applied. . . . . . . .. 22
Figure 6. Irrigation frequency based on the volume of
water applied per tree at each irrigation and
the average daily ET rate per tree. . . .. 23
Figure 7. Irrigation time (duration) per application based
on volume applied per emitter at each
application and the emitter flow rate. . . ... 24
Figure 8a. Tree canopy area or emitter wetted area based
on the tree canopy diameter or the emitter
wetted diameter. . . . . . . . .. 25
Figure 8b. Tree canopy area based on the tree spacing
along the row and the average tree canopy,
width..... ............... ... 26
Figure 9. Relative tree canopy area based on the average
canopy area per tree and the number of trees
per acre. . . .. . .... . . . . 27
Figure 10. Irrigated zone correction factor based on the
time after irrigation until rain occurred and the
scheduled irrigation frequency. . . . ... 28
Figure 11. Non-irrigated root zone correction factor based
on the average canopy area per tree and the
total emitter wetted area per tree. . . .. 29








Figure 12. Antecedent soil water content correction factor
based on the irrigated zone correction factor
and the non-irrigated root zone correction
factor.. . . . . . . . . . .. 30
Figure 13. Potentional rainfall storage in the tree root
zone based on the soil water storage in the
root zone and the antecedent soil water
content ...................... 31
Figure 14. Effective rainfall based on actual rainfall and
the potential soil water storage in the effective
root zone. . . . . . . . . . 32
Figure 15. Readily available effective rainfall based on
total effective rainfall and the relative area
occupied by the tree canopy. . . . . ... 33
Figure 16. Days to delay irrigation following rainfall based
on the average daily ET rate and the readily
available effective rainfall. . . . . ... 34







Introduction


Irrigation scheduling is a procedure for determining (1) when to
irrigate, and (2) how much water to apply. Irrigation scheduling is
complicated by the fact that irrigation timing and the amount of
water to apply are not independent of each other, the climate, or
the characteristics of the crop. The decision concerning when and
how much to irrigate will depend upon how much water was last
applied, when it was applied, and the rate of its use since it was
applied. Further complications exist in that irrigation decisions are
also affected by rainfall and by irrigation system limitations.
This publication presents a method of scheduling trickle irrigation
applications for citrus in Florida. The objective of this method is
to maintain a favorable soil water status in the tree root zone so
that water is always available. The method is based on a water
balance of the tree effective root zone with water use by citrus
based on normal Florida climatic conditions. Figure 1 shows the
components of the water balance and defines some of the other
terminology used in this procedure.
The irrigation scheduling method presented here requires that the
individual irrigator make inputs to a series of 16 tables or figures
concerning grove characteristics, soil properties, irrigation system
characteristics, rainfall, and management decisions in order to
optimize irrigation scheduling for an individual grove.
Both tables and figures are presented to allow the user to not
only obtain the accuracy associated with tables of data, but also to
see the graphs to aid in interpolation. The figures also allow the
user to determine the relative effects of errors in inputs. The
information presented in this bulletin can be used for flatwoods
(high water table soils) or ridge (deep sandy soils) soil conditions.
It can be used when scheduling irrigations for either drip or
spray-jet emitters and for any number of emitters per tree. Tables
1 through 7 and the corresponding figures 1 through 7 can be used
to determine a monthly irrigation schedule assuming that rain does
not occur. Because rainfall occurs frequently in Florida, tables 8
through 16 and figures 1 through 16 allow an irrigator to determine
the period of time that a scheduled irrigation should be delayed
following rainfall. Because of the large number of tables and
figures presented, the following sections of this bulletin are
consecutively numbered with the corresponding table and figure
numbers.
This bulletin was written to be sufficiently general to be
applicable to all irrigation system, soil, and crop conditions in the
state; therefore, 16 tables and corresponding graphs were required.







The authors do not expect that the average Florida irrigator will
use all of the tables and figures on a day-by-day basis to schedule
irrigations. Rather, this bulletin should be used to develop
irrigation schedules for site-specific conditions. The first seven
tables and figures will be used only once for a specific grove and
irrigation system. They will be used to develop monthly irrigation
schedules which can be programmed on irrigation timers/controllers.
Those schedules will remain in effect as long as rain does not
occur.
The last nine tables and figures will be used more often to
develop a table of delay times for specific sites and months when
rainfall occurs. This site-specific table will be used on a
day-by-day basis to reset the irrigation controller following a
rainfall.

1. Citrus Water Use

Water is used by citrus by evaporation from the soil surface and
transpiration from leaves. For practical purposes, these processes
are not separable, so the term evapotranspiration (ET) is used to
describe both evaporation and transpiration which occur simul-
taneously
Evapotranspiration depends very heavily on climatic conditions.
On hot, dry days, climatic demand will be great, and if water is
available to the trees, evapotranspiration rates will also be great.
Conversely, on cool, mild days, evapotranspiration rates will be
small.
Monthly climatic conditions do not vary a great deal from year
to year. Therefore, ET for future months can be predicted based
upon ET rates observed in the past. ET data for Florida ridge
citrus are summarized in the IFAS Water Resources Council fact
sheet WRC-4, "Water Requirements for Citrus." These data are used
in the irrigation scheduling method described in this bulletin and
are presented in Table 1.
Table 1 also presents ET data for flatwoods citrus. Those data
were compiled in the IFAS Agricultural Engineering Extension
Report 83-10, "Evapotranspiration and Net Irrigation Requirements
for Crops in South and Central Florida." They are data from the
IFAS and USDA SWAP research project, Ft. Pierce.
Table 1 presents the best estimates currently available for citrus
ET in Florida. Data are presented as monthly values, average daily
values, and as annual totals. Annual totals were 47.6 inches for
the ridge citrus and 44.6 inches for the flatwoods citrus.
Differences presumably reflect climatic differences such as cloud








cover and cultural differences which occur between the ridge and
flatwoods areas.
Monthly ET values given in Table 1 are the expected average
amounts of water that citrus would use during those months for
long-term average (normal) climatic conditions. They range from
small values during the winter months to large values in late spring
and early summer. Average daily ET values are the monthly values
divided by the number of days per month.
Actual daily ET rates for well-irrigated citrus may be greater (or
less) than the monthly average values on any given day. This will
occur whenever actual climatic demand is greater (or less) than the
average. Also, since seasonal climatic changes are gradual rather
than abrupt, average daily values may overpredict the actual ET
values during the early parts of the spring months. Likewise, they
may underpredict during the later parts of the months as the next
warmer month is approached. The reverse will occur in the fall as
the succeeding months become progressively cooler. The irrigation
system manager may wish to take this into consideration as
irrigations are scheduled. Also, the actual ET will be greater or
less than the monthly average during an unseasonably warm or cool
day, respectively. The system manager can correct for this differ-
ence by adjusting the actual daily ET as appropriate.

2. Average Daily Evapotranspiration (ET) Rates for Citrus

The average daily ET rate in gallons per tree per day must be
known to properly schedule citrus trickle irrigation systems. This
rate can be calculated using the average daily ET rate in inches
from Table 1, and from a knowledge of the number of trees per
acre. Because ET is an energy-based process, water will be
evaporated and transpired only in amounts sufficient to satisfy
climatic demand. Under normal climatic conditions if a near-com-
plete tree canopy exists, that is, if at least 60% to 70% of the
ground surface is covered by the canopy, then ET will occur at
approximately the rates given in Table 1. This condition is
typically met when there are at least 70 mature trees per acre.
If there are very few trees per acre, or if the trees are
immature such that less than 60% of the ground is shaded by the
canopy, then a trickle-irrigated grove will normally use less water
than the values given in Table 1. The exact value will depend
upon the amount of canopy cover which exists, although it is not
linearly related to canopy cover.
The average daily ET rate in gallons/tree/day can be read from
Table 2 or Figure 2 for inputs of average daily ET in inches and








from the number of trees per acre. From Table 2, if the average
daily ET is 0.10 inches and there are 70 trees per acre, then each
tree will use 39 gallons per day. If the tree density is 140 trees
per acre, then each tree will use only 19 gallons per day.
The trees' rate of water use will respond to the climatic demand.
The water use on an area basis will be roughly equivalent to the
amount of energy available to evaporate water over that area. For
a given canopy coverage, if there are few trees per acre to provide
the ET to meet the climatic demand, then the water use rate per
tree will be large. For the same canopy coverage, if there are
many trees per acre, then each will transpire fewer gallons to meet
the climatic demand.



3. Soil Water Storage in the Effective Root Zone

If irrigation is to be effective, water applied must be stored in
the root zone so that it is available for use by the tree. Water
applied beyond the effective root zone will not be used by the
trees. Thus, the depth to be applied should never move below the
effective root zone. Rather, it should remain in the upper portion
of the root zone where most of the roots actively involved in
water uptake are located. For trickle irrigation of ridge citrus,
this zone should be defined as the upper 1.5- 3 ft of the root
zone. For flatwoods citrus where root zones are limited to 1-1.5 ft,
because of high water tables or soil restrictive layers, this should
be the zone irrigated. Major emphasis should be placed on the
upper portions of the root zone where most of the roots actively
involved in water uptake are located.
The volume of water stored in the soil also depends upon the
soil's water-holding capacity. In general, finer-textured soils have
greater water-holding capacities than coarse-textured soils. These
data for specific soil series can be obtained from local soil survey
reports or from the Soil Conservation Service State Irrigation
Guide. They may need to be refined for a specific field site by
observing the soil depth wetted after an initially dry soil is
irrigated with a known depth of water. Then the soil water-
holding capacity can be determined from Table 3.
From Table 3 or Figure 3, if the soil depth irrigated was 2.0 ft
and the soil water-holding capacity was 0.6 inches per foot of soil,
the soil water storage in the irrigated depth would be 1.2 inches.
Likewise if the water-holding capacity was 1.0 inch per foot, the
soil water storage would be 2.0 inches.








4. Allowable Water Depletion Effect on Irrigation Depth

All water stored in the soil is not equally available to citrus
trees. As water is extracted from the soil, each succeeding
increment becomes more difficult to extract. This occurs because
the most readily available water is used by the tree first. The
remaining water is held more tightly in smaller soil pores thus
making it more difficult for the tree to extract it. A point is
reached where the tree cannot extract water at a rate sufficient to
meet climatic demands, and water stress occurs. To keep the tree
from undergoing stress as it attempts to extract all of the soil's
water, irrigations must be scheduled before all of the readily
available water is depleted. For citrus, irrigations are typically
scheduled when 1/3-2/3 of the soil's waterholding capacity has been
depleted. That is, when the allowable depletion is in the range of
33% to 67%.
The actual water depletion used for a specific irrigation depends
upon the tree's sensitivity to water stress at various stages of
growth. If a given growth stage is very sensitive to water stress,
then the allowable depletion should be small. If the tree is not
very sensitive to water stress at a given stage, then the allowable
depletion may be larger. For citrus irrigation, allowable water
depletions of 33% (1/3) are recommended for irrigation during
spring months when flowering and fruit-set occur. Irrigations at
50% (1/2) to 67% (2/3) depletions are often used for less sensitive
growth periods.
From Table 4 or Figure 4, the depth of water to be applied at
each irrigation can be determined from the soil water storage in
the effective root zone and from the allowable depletion. For a
soil water storage of 1.0 inch and a 50% allowable depletion, the
depth to apply at each irrigation would be 0.50 inches. For a soil
water storage of 0.75 inches and a 33% allowable water depletion,
the depth to apply would be 0.25 inches.

5. Water to Apply per Emitter at Each Irrigation

The volume of water to be applied per emitter at each irrigation
depends upon the depth of water that can be stored in the
effective root zone and the portion of the root zone that is wetted
by an emitter. Because trickle irrigation systems normally do not
irrigate the entire tree root zone, the actual volume of the root
zone being irrigated must be determined. This can easily be done
by observing the size of the wetted pattern created as an emitter
operates.








The diameter of the wetted pattern under a trickle emitter should
be determined by field measurement. It can be measured at the
soil surface or by digging a few inches below the surface. In the
typical Florida sandy soils, the wetted zone expands slightly just
below the soil surface. It then essentially moves downward,
forming a "cylinder" of wetted soil (Fig. 1). The cylinder shape is
more pronounced in sandier soils where gravity forces predominate
as water moves in the soil. A bulb shape is more common in
finer-textured soils where soil capillary forces are relatively greater
than in sandy soils.
From Table 5 or Figure 5, for a depth of water to be applied per
irrigation of 0.5 inches (obtained from Table 4) and a
field-measured wetted diameter of 3.0 ft (typical of a drip emitter
on Florida's sandy soils), the volume of water to be applied per
emitter would be 2.2 gal. For a depth of application of 0.75 inches
and a 12.0 ft wetted diameter (typical of a spray-jet emitter), the
volume of water to be applied per emitter would be about 53 gal.
These examples illustrate that a much greater proportion of a
tree root zone would be irrigated with a spray-jet emitter as
compared to a point source drip emitter on Florida's sandy soils.
Research data for the ridge soils indicate that yields were greatest
when at least 50% to 70% of the root zones under the tree canopies
were irrigated.


6. Irrigation Frequency

Irrigation frequency depends upon both the amount of water
being applied at each irrigation and the rate at which it is being
used by ET. Table 6 or Figure 6 allows irrigation frequency to be
read for these inputs. The average daily ET rate to be used is
that read from Table 2. The volume of water to be applied per
tree at each irrigation is obtained by multiplying the volume of
water to be applied per emitter (from Table 5) by the number of
emitters per tree.
For example, if the amount of water to be applied using one
spray-jet emitter per tree is 100 gal (from Table 5), and if the
average ET rate per tree (from Table 2) is 25 gal/day, then the
irrigation frequency is 4.0 days from Table 6.
If the volume of water to be applied per emitter from Table 5 is
10 gal/ emitter, and there are 4 emitters per tree, then the volume
of water to be applied per tree is 40 gal at each irrigation. This
value (40 gal) would then be used in Table 6 to determine the
irrigation frequency.








If the volume of water to be applied per tree at each irrigation
is small, such as only 15 gal for example, and the average daily ET
rate per tree is larger, such as 30 gal/tree/day, then the irrigation
frequency is 0.5 days. This means that, because of the limited
volume of the root zone wetted, all of the tree's daily water
requirements cannot be supplied with one irrigation per day.
Rather, irrigations must be scheduled twice per day (1/0.5 = 2.0),
allowing time for the tree to extract water from the wetted area
between irrigations.
If the number representing irrigation frequency is very small, this
indicates that several irrigations must be scheduled per day. With
such a system, it may not be possible to provide all of the tree's
daily ET requirements. There may not be sufficient opportunity for
the tree to uptake all of its water needs between irrigations
because of the limited portion of the root zone wetted. To assure
that the tree will be able to make best use of the water applied, a
large fraction of the root zone beneath the tree canopy (at least
50%) should be wetted at each irrigation. If less than 50% of the
root zone is irrigated, water stress may occur during extended
droughts despite frequent irrigations.
It is desirable that the irrigation frequency from Table 6 be an
integer (whole number) of days, if possible. This is because it is
much easier to manage an irrigation system if irrigations are to be
scheduled every 5 days rather than every 5.4 days, for example.
To achieve this and yet still apply the proper amount of water at
each irrigation, the following procedure should be used: (1) round
the irrigation frequency to the nearest whole number of days; (2)
recalculate the volume of water to be applied per tree at each
irrigation by multiplying the whole-number irrigation frequency
and the average daily ET rate per tree; (3) divide the new volume
of water to be applied per tree at each irrigation by the number of
emitters per tree to determine the new volume of water to be
applied per emitter at each irrigation.
As an example of the above procedure, assume that at the
desired allowable water depletion the irrigation frequency of a
spray-jet system is 5.4 days. Assume also that there are two
spray-jets per tree, and the ET rate is 30 gallons per day. Then
the amount to apply per irrigation would be 203 gallons, assuming
an 80% irrigation efficiency. If we desire to irrigate every 5 days
rather than every 5.4 days, the amount of water to be applied
would be 150/0.8 = 188 gallons per irrigation or 94 gallons per
emitter.
The above procedure for obtaining an integer number of days
between irrigations should only have the effect of changing the








allowable depletion percentage in Table 5 slightly. To be conser-
vative in the roundoff procedure, the irrigation frequency should
always be rounded down to the nearest integer number. This will
provide for more frequent irrigations and will maintain a more
desirable soil water content for citrus growth.


7. Irrigation Time per Application

The irrigation time per application depends upon the emitter flow
rate, the volume of water to be applied per emitter at each
application, and the irrigation system application efficiency. The
emitter flow rate can be obtained from the manufacturer's
specifications and a knowledge of the average operating pressure
for the emitter being used. Alternatively, it could be obtained by
field measurement. The volume of water to be applied per emitter
at each application can be obtained from Table 5 either directly or
as adjusted to achieve a whole number of days between irrigations
as discussed in the previous section.
The irrigation application efficiency reflects the fact that some
of the water is lost in application. Some evaporates or is lost to
wind drift. Also, because of the nature of trickle irrigation system
design, water application is not perfectly uniform. Therefore, the
system must be operated longer to assure that those portions of
the grove which receive the least amount of water are adequately
irrigated.
For trickle irrigation of citrus, an application efficiency of 80%
has been assumed to adequately represent Florida climatic
conditions and irrigation system design criteria. In Table 7 and
Figure 7, irrigation times per application have been calculated
including the assumed 80% efficiency.
From Table 7 or Figure 7, for a spray-jet flow rate of 20
gal/hour and a volume of water to be applied per emitter of 60 gal,
the application time for each irrigation would be 3.8 hours. For a
drip emitter flow rate of 1 gal/ hour and a volume of water to be
applied per emitter of 4 gal, the application time for each
irrigation would be 5.0 hours.
The irrigation time per application is the final piece of
information required to schedule trickle systems for citrus
irrigation in Florida in the absence of rainfall. As long as rain
does not occur, the previously-determined irrigation frequencies
and durations of water applications can be set on an irrigation
timer-controller at the beginning of each month, and the system
can operate automatically for that month.








Rainfall, however, seriously complicates irrigation scheduling in
Florida. Tables 1 through 7 allow citrus irrigation schedules to be
determined in the absence of rainfall. Tables 8 through 16 allow
the irrigator to determine how long irrigations should be delayed
after rainfall has occurred.

Rainfall Effects on Trickle Irrigation Schedules

The effect of rainfall on trickle irrigation scheduling is obviously
that of alleviating the need for or delaying irrigations. The
question to be answered is, "How long should trickle irrigation be
delayed following a given amount of rain?" The answer depends
upon the rate of water use and the mechanism of water uptake by
trickle-irrigated citrus in a humid region.
Florida citrus trees take up a portion of their ET requirements
from the soil in those regions where roots occur but which are
outside of the trickle-irrigated zone. Roots remain active in this
region because of rainfalls which periodically resupply the soil
water in this region. Therefore, following a rainfall when water is
readily available throughout the tree root zone, water will be taken
up throughout the entire root zone. As water is used and less
becomes available in the non-irrigated zone, the tree will uptake an
increasingly larger portion of its ET from the irrigated zone.
The previously-described mechanism of water uptake demon-
strates that a tree will have a larger volume of water available to
it following a rainfall than following trickle irrigation in which the
same depth of water is applied because of the greater volume of
the root zone wetted. This is especially important if the trickle
system irrigates only a small portion of the tree root zone. It
further demonstrates that the rate of water use from the irrigated
zone will be less following a rainfall than following an irrigation.
Again, the reason is that the tree will satisfy some of its
requirements by extracting water from outside of the irrigated
zone, thus proportionally less of the water will be extracted from
the irrigated zone.
Unfortunately, at this time citrus research results have not yet
indicated the exact proportions of water extractions from the
irrigated and non-irrigated zones following rainfall. Therefore, the
following sections of this bulletin are based on our best estimates
of that process at this time. They should be used as guides for
specific applications, realizing that refinements may need to be
made as field experience is obtained.
In the following discussion, it was assumed that water extractions
beneath and near tree canopies take place at the same rates both







within and outside of the irrigated zone immediately following
rainfall. It was further assumed that water depletions take place
preferentially beneath the tree canopy and near the tree drip line
where most of the roots are located. Water stored in the alleys
between tree rows and distant from the trees was assumed to be
less available for use by the trees because fewer roots occur in
those areas. Irrigations would then be scheduled whenever the
water capacity in the effective root zone beneath and near the tree
canopy has been depleted to the desired available water level.


8. Tree Canopy Areas

The tree canopy areas must be estimated in order to calculate
the delay time following rainfall. The tree canopy area is that
area beneath the tree within the drip line. Table 8a or Figure 8a
gives tree canopy areas for trees spaced so that their canopies are
not touching and therefore are approximately circular in shape. In
that case, the canopy areas are calculated from the measured tree
canopy diameter. From Table 8a, for example, a young tree with a
canopy diameter of only 12 ft would have a canopy area of 113 ft2.
A mature tree with a canopy diameter of 18 ft would have a
canopy area of 254 ft2.
If trees are closely spaced along rows, then their canopies touch
and their areas are better described as rectangles. Table 8b or
Figure 8b allows canopy areas to be estimated for that condition.
Both tree spacing along the row and the average width of the
canopy are required for this calculation. From Table 8b, for
example, if the tree spacing along the row is 15 ft and the canopy
width is 22 ft, the canopy area per tree would be 330 ft2.

9. Relative Area Occupied by Tree Canopy

The relative land area covered by the tree canopy is defined as
the ratio of the land area covered by the tree canopy to the
average land area occupied by each tree. The average area
occupied by each tree is determined from the number of trees per
acre. The relative land area covered by the tree canopy is
required to determine the amount of rainfall stored beneath or near
the tree canopy and immediately available to the tree.
From Table 9 or Figure 9, if the average canopy area of each
tree is 200 ft2, and there are 120 trees per acre, then the relative
canopy area is 0.61. That is, about 61% of the land surface is
shaded by the tree canopies. If the average canopy area is 325 ft2








and there are 100 trees per acre, then approximately 82% of the
land surface is shaded by the tree canopies.

10. Irrigated Zone Soil Water Content

The antecedent soil water content is water stored in the soil at
the time that rainfall occurs. If rain occurs just before the next
scheduled irrigation, then the rainfall will be most effective. That
is, more of it will be stored in the soil because the soil was
initially drier. Conversely, if the soil is wet when rain occurs, the
rainfall will be less effective. More of it will run off or be lost to
deep percolation.
In most cases, trickle systems do not irrigate the entire area
beneath and near the tree canopy. Rather, there exists both an
irrigated and a non-irrigated zone which may have greatly different
soil water contents when rainfall occurs. For this procedure, it is
necessary to separately account for the irrigated and non-irrigated
zone water contents.
Table 10 or Figure 10 can be used to obtain an antecedent soil
water content correction factor for the irrigated zone. This
correction factor depends upon the irrigation frequency and the
time after irrigation that rainfall occurred. The water use in the
irrigated zone is assumed to occur linearly. For example, if the
irrigation frequency is 3 days and rain occurred after 1 day, the
correction factor from Table 10 would be 1/3 = 0.33. If two days
elapsed before rainfall, the correction factor would be 2/3 = 0.67.
This factor is an indication of the relative amount of soil water
storage capacity remaining for rainfall following a recent irrigation.


11. Non-Irrigated Root Zone Soil Water Content

A correction factor for the soil water storage capacity in the
non-irrigated portion of the tree root zone under and near the tree
canopy can be obtained from Table 11 or Figure 11. The
correction factor depends upon the average canopy area per tree
and the emitter wetted area per tree. For example, if the average
canopy area per tree is 250 ft2 and the emitters which irrigate that
tree cover 50 ft2, the correction factor for the non-irrigated zone
would be 0.80. If the tree canopy area is 350 ft2 and the irrigated
area beneath the canopy is 200 ft2, the correction factor would be
0.43. This correction factor is an indication of the relative
proportion of the tree root zone which is not irrigated, and
therefore, available for soil water storage when rainfall occurs.








12. Antecedent Soil Water Content


For citrus irrigation, the antecedent soil water content is water
which is stored in the tree root zone at the time that rain occurs.
Rainfall will be less effective if the soil is already wet when rain
occurs.
From Table 12 or Figure 12, the antecedent soil water content
correction factor can be determined from the previously determined
irrigated zone correction factor (Table 10) and the non-irrigated
root zone correction factor (Table 11). For example, if the
irrigated zone correction factor is 0.4 and the non-irrigated root
zone correction factor is 0.2, the antecedent soil water content
correction factor would be 0.52. If the irrigated zone correction
factor is 0.8 and the non-irrigated root zone correction factor is
0.5, then the antecedent soil water content correction factor would
be 0.9. These factors are an index of the amount of water that
can be stored in the tree root zone when rain occurs.

13. Potential Rainfall Storage in Effective Root Zone

The potential (maximum possible) rainfall storage in the effective
root zone can be determined from Table 13 or Figure 13. It
depends upon the soil water storage in the effective root zone for
the soil water depletion allowed (from Table 4) and the amount of
water already in stor age (antecedent soil water content).
From Table 13, if the potential soil water storage in the
effective root zone is 1.0 inch and the antecedent soil water
content correction factor is 0.5, then the potential rainfall storage
in the effective root zone would be 0.5 inches. If the potential
soil water storage is 0.75 inches and the correction factor is 0.8,
then the potential rainfall storage would be 0.60 inches.

14. Effective Rainfall

Effective rainfall is that which is stored in the root zone and
available for crop use to satisfy ET demands. All rainfall is not
effective because some is lost due to runoff, deep percolation, or
interception by the crop canopy.
In Florida, because of the very sandy soils on which citrus is
typically produced, a relatively small amount of rainfall is lost to
runoff. More is lost to deep percolation below the tree root zone
because of the relatively low water-holding capacity of the sandy
soils. With each rainfall, a small constant amount is lost due to
interception by the tree canopies. Interception losses are not very








large because some of the water is not truly lost, but rather it
compensates for some of the water which would normally be lost to
ET. Water on the leaves evaporates, cooling them and thus reduc-
ing some of the ET demand while the leaves remain wet.
From Table 14 or Figure 14, effective rainfall can be estimated
for specific rainfall and soil conditions. In this bulletin, inter-
ception losses were assumed to be 0.1 inch per rainfall. That is,
rainfalls of 0.1 inch or less were assumed to be ineffective in
delaying the need for irrigation.
From Table 14, if the potential soil water storage in the
effective root zone is 1.5 inches, and 0.5 inches of rain occurs, the
effective rain is 0.4 inches. That is, all of the rain is assumed to
be stored in the tree root zone except for 0.1 inch interception
loss.
If the potential soil water storage in the tree effective root zone
is 1.0 inch and a rain of 1.75 inches occurs, then the effective
rainfall would be only 1.0 inch. That is the maximum amount that
the soil could store, and this rainfall would refill that storage
capacity. The remainder would be lost to interception, deep perco-
lation, and perhaps runoff.



15. Rainfall Stored Under the Tree Canopy

Following rainfall or irrigation, citrus trees use water near the
soil surface and under the tree canopy first. They use that water
which is near at hand and easiest to obtain before that which is
more distant or deeper in the soil. In this analysis, the number of
days to delay irrigations following rainfall is based upon the
rainfall stored under and near the canopy only (tree canopy area
plus 10% in the area near the tree drip line). This is a conser-
vative estimate in that it does not require that all of the water in
the areas between trees be consumed before irrigations are
re-initiated.
From Table 15 or Figure 15, the rainfall depth stored under and
near the tree canopy (the readily available effective rainfall) can
be determined from the relative area occupied by the tree canopy
and the effective rainfall. If, for example, the relative area occu-
pied by the tree canopy is 0.6 and the effective rainfall is 0.5
inches, then the rainfall depth under the tree canopy and most
available for the tree's use would be 0.3 inches. If the relative
tree canopy area is 0.8 and the effective rainfall is 1.4 inches, then
the readily available effective rainfall would be 1.12 inches.








16. Days to Delay Irrigation Following Rainfall


From Table 16 or Figure 16, the number of days to delay irri-
gation following a rainfall can be calculated. The number of days
to delay is based upon the average daily ET rate (the rate at which
the trees are using water) and on the rainfall stored in the soil
and readily available to the trees (the readily available effective
rainfall from Table 15). The average daily ET rate is the value
from Table 1 for the appropriate month. For example, if the
readily available effective rainfall from Table 15 is 0.40 inches,
and the average daily ET rate for the month is 0.10 inches/ day,
then the irrigation schedule should be delayed four days. If the
readily available effective rainfall is 0.3 inches and the average ET
rate is 0.15 inches/ day, then the irrigation schedule should be
delayed two days.
It is important to note that the delay time obtained from Table
16 is based only on rainfall additions to the soil water storage. It
is, therefore, a period of time to delay irrigations which is in
addition to the existing irrigation schedule. For example, if ir-
rigations are scheduled at a frequency of three days, and rain
occurs two days after the last irrigation, the next irrigation should
be scheduled in one day (3-2) plus the delay time calculated from
Table 16. If the delay time obtained from Table 16 was four days,
then the next irrigation should be scheduled five days (1 + 4) after
the rainfall.

Discussion

The methods and procedures presented in this bulletin allow an
irrigator to schedule water applications for citrus production using
a trickle system in Florida. This bulletin can be used for flatwoods
or ridge soil conditions. It can be used for systems equipped with
either drip or spray-jet emitters, and for any number of emitters
per tree as long as the irrigation system can supply all of the
tree's water requirements if necessary. Mature trees with only one
or two drip emitters per tree may not meet this qualification if
they cannot prevent a tree from wilting during drought.
Tables 1 through 7 can be used to determine a monthly irrigation
schedule assuming that rain does not occur. In that case, the
schedule can be set on an irrigation timer-controller to permit
automatic operation.
In Florida, rainfall occurs frequently. Therefore, Tables 8 through
16 allow an irrigator to calculate the period of time that an irriga-
tion schedule should be delayed following rainfall.








The irrigation scheduling method presented in this bulletin was
based upon maintaining a water balance in the effective root zone
of the citrus trees being irrigated. Water stored in the root zone
was calculated based on the root zone depth and the soil
water-holding capacity. Extractions from the water stored were
obtained from long-term average ET data. Irrigations were then
scheduled whenever water in the root zone was depleted to a
predetermined critical level.
The water balance method of irrigation scheduling presented here
requires that the irrigator describe his specific conditions in order
to develop an irrigation schedule. The information required
includes a description of the trees, specifically the number per acre
and the tree canopy area (area beneath the drip line). The
irrigator must also provide a description of the soil, specifically the
soil water-holding capacity and soil depth to be irrigated (effective
root zone). Certain irrigation system characteristics must be
known, specifically the number of emitters per tree, emitter flow
rate, and the soil wetted diameter resulting from each emitter.
The irrigator must measure rainfall depths and timing with respect
to the irrigation schedule. Finally, the irrigator must make a
management decision concerning the allowable soil water depletions
between irrigations. All of these factors are then integrated to
provide an irrigation schedule specific for that set of conditions.
Because of the number of inputs which must be made and the
possibility of errors associated with each, the water balance
approach to irrigation scheduling does not allieviate the need for
field observations on a day-by-day basis and adjustments to the
irrigation schedule based on those observations. For example, the
long-term average ET rates presented in Table 1 may not be
representative of a given time period because of unseasonably hot
(or cool) weather. Also, the soil water-holding capacity of a
specific site may be different than it was originally assumed to be.
Likewise, estimates of effective rainfall may need to be refined by
field observation.
Adjustments can be made in the irrigation schedule based on field
observations. An excellent tool for field observation is a tensio-
ometer located in the wetted pattern of the trickle emitters.
Tensiometers located in the emitter wetted pattern will indicate if
the soil becomes too dry or remains too wet between irrigations.
The irrigation schedule can then be adjusted accordingly.
When tensiometers are located in the wetted soil zone created by
trickle emitters, they will accurately track both wetting and drying
cycles. They will not require frequent service unless the soil
becomes very dry. Because the soil remains moist in the trickle








wetted pattern, a tensiometer will be relatively troublefree when
located in this zone. It is also a relatively low-cost instrument.
When used to verify irrigation schedules as previously described,
large numbers of tensiometers are not required. Rather, a
relatively few can be used to check critical areas of the grove.
Tensiometers can be moved from site to site as necessary to check
specific locations.
To check the soil water depletion with depth in the effective
root zone, at least two tensiometers should be used per location.
One should be located near the soil surface where most of the
roots are located (6-12 inches below the soil surface). The second
should be located nearer the bottom of the effective root zone that
will be irrigated (24-36 inches below the soil surface). It is
important to concentrate both water applications and observations
in the upper portions of the effective root zone where most of the
roots actively involved in water uptake are located.
The methods and procedures for trickle irrigation scheduling as
presented in this bulletin are based on fundamental physical laws,
research data, and our best current estimates of the processes of
water use by citrus trees. Refinements will be made as improved
research data become available. Currently, this bulletin can be
used to accurately schedule irrigations for Florida citrus if the
required data inputs are accurately made. The irrigation schedules
derived using this bulletin can and should be refined for specific
locations by field observations.


Example Problems

Example problems are shown in Appendix B to illustrate the use
of the irrigation scheduling procedure presented in this bulletin.
Examples are given for both drip and spray-jet trickle irrigation
systems following a standard 16-step format. A blank irrigation
scheduling worksheet following the same format is given in
Appendix C.


Summary

Trickle irrigation scheduling for citrus production in Florida was
discussed. A method was presented which allows individual
irrigators to schedule irrigations based upon their specific soil,
grove and irrigation system characteristics, management decisions,







and upon long-term average citrus evapotranspiration (ET)
requirements. A method was also presented to allow the effects of
rainfall on the irrigation schedule to be determined. Example
irrigation scheduling problems were presented, and an irrigation
scheduling worksheet was included for individual use.








TABLE 1. FLORIDA CITRUS EVAPOTRANSPIRATION (ET).
............................................................................
MONTH RIDGE CITRUS FLATWOODS CITRUS **
MONTHLY ET AVERAGE DAILY MONTHLY ET AVERAGE DAILY
(INCHES) ET (INCHES) (INCHES) ET (INCHES)
JAN 2.1 0.07 2.1 0.07
FEB 2.3 0.08 2.6 0.09
MAR 3.1 0.10 3.6 0.12
APR 3.9 0.13 4.5 0.15
MAY 5.0 0.16 5.3 0.17
JUN 5.6 0.18 4.4 0.15
JUL 5.9 0.19 4.9 0.16
AUG 5.7 0.18 4.8 0.15
SEP 4.9 0.16 4.0 0.13
OCT 4.0 0.13 3.6 0.12
NOV 2.8 0.09 2.7 0.09
DEC 2.3 0.07 2.1 0.07

TOTAL 47.6 44.6

Ridge Soils are deep sandy soils. Data are from IFAS water resources fact
sheet WRC-4, "WATER REQUIREMENTS FOR CITRUS."
**Flatwoods soils are shallow, high water table soils. Data are from the
swap research project, Ft. Pierce, reported in the Ag. Eng. Ext. Report 83-10,
EVAPOTRANSPIRATIONN AND NET IRRIGATION REQUIREMENTS FOR CROPS IN SOUTH AND
CENTRAL FLORIDA."


RAINFALL

CANOPY
DIAMETER T EVAPOTRANSPIRATION



1' < : *:
I- *, ,
IRRIGATION '-,
SPO ET ORIP

-'-' /IRRIGATED RR -$'/ '// ROOT DEPTH
ZONE IRRIGATED

/,d / o Y / / \ \ \ ,,
ROOT ) SOIL WATER STORAGE
ZONE


DEEP PERCOLATION


Figure 1. Components of citrus water balance and other definitions.







TALE 2. AVERAGE DAILY EVAPOTRANSPIRATION (ET) RATES
FOR CITRUS AT VARIOUS TREE DENSITIES.
...........................................................
AVERAGE
DAILY ET TREE DENSITY (NUMBER OF TREES/ACRE)
(INCHES)
(FROM TABLE 1) -------------------------------------------
70 80 90 100 110 120 130 140
...............................................................
AVERAGE DAILY ET RATE (GALLONS/TREE/DAY)

.05 19 17 15 14 12 11 10 10
.06 23 20 18 16 15 14 13 12
.07 27 24 21 19 17 16 15 14
.08 31 27 24 22 20 18 17 16
.09 35 31 27 24 22 20 19 17


39 34
43 37
47 41
50 44
54 48

58 51
62 54
66 58
70 61
74 64


30 27 25 23 21
33 30 27 25 23
36 33 30 27 25
39 35 32 29 27
42 38 35 32 29

45 41 37 34 31
48 43 39 36 33
51 46 42 38 36
54 49 44 41 38
57 52 47 43 40


.20 78 68 60 54 49 45 42 39
.21 81 71 63 57 52 48 44 41
.22 85 75 66 60 54 50 46 43
.23 89 78 69 62 57 52 48 45
.24 93 81 72 65 59 54 50 47


AVERAGE DAILY ET RATE


0 I I
70 80 90 100 110 120 130 14n
TREE DENSITY (NUMBER OF TREES/ACRE)

Figure 2. Average daily ET rate In gallons per tree based on tree
density and the average daily ET rate in inches.


o
0
w





60

Lii

W
4 80
-2
0
J
o eo




, 20
cr
W
2>











TABLE 3. SOIL WATER STORAGE IN SOIL DEPTH IRRIGATED.
..................................................................
SOIL SOIL DEPTH TO BE IRRIGATED, FT
WATER-HOLDING
CAPACITY ---------------------------- ---------
(INCHES WATER/ 1.0 1.5 2.0 2.5 3.0
FT SOIL)
..................................................................

SOIL WATER STORAGE (INCHES)
-....----..-------------------------------------
0.4 0.40 0.60 0.80 1.00 1.20
0.5 0.50 0.75 1.00 1.25 1.50
0.6 0.60 0.90 1.20 1.50 1.80

0.7 0.70 1.05 1.40 1.75 2.10
0.8 0.80 1.20 1.60 2.00 2.40
0.9 0.90 1.35 1.80 2.25 2.70

1.0 1.00 1.50 2.00 2.50 3.00
1.1 1.10 1.65 2.20 2.75 3.30
1.2 1.20 1.80 2.40 3.00 3.60

1.3 1.30 1.95 2.60 3.25 3.90
1.4 1.40 2.10 2.80 3.50 4.20
1.5 1.50 2.25 3 00 3.75 4.50
.-_. ..............................................................


0.0 -
0.0


SOIL WATER STORAGE


0.5 1.0 1.5 20
EFFECTIVE ROOT ZONE (FT)


2.5 30


Figure 3. Soil water storage in the effective root zone based on the
effective root zone depth and the soil water-holding capacity.


2.5




S2.0


Z

W
z


3 1.5










0 0.5
In
U1








TABLE 4. DEPTH OF WATER TO BE APPLIED AT EACH IRRIGATION,
CONSIDERING ALLOWABLE WATER DEPLETION.
........................................................................
SOIL WATER
STORAGE IN ALLOWABLE DEPLETION (%)
SOIL DEPTH
IRRIGATED
(INCHES) ------------- -------------------..........
(FROM TABLE 3) 30 33 40 50 60 67 70
----------------------------------------................................
DEPTH OF WATER TO BE APPLIED PER IRRIGATION (INCHES)
------------------------------------------------------
0.40 0.12 0.13 0.16 0.20 0.24 0.27 0.23
0.50 0.15 0.16 0.20 0.25 0.30 0.33 0.35
0.60 0.18 0.20 0.24 0.30 0.36 0.40 0.42


0.70
0.80
0.90

1.00
1.10
1.20

1.30
1.40
1.50

1.75
2.00
2.25


0.21 0.23 0.28 0.35 0.42 0.47 0.49
0.24 0.26 0.32 0.40 0.48 0.54 0.56
0.27 0.30 0.36 0.45 0.54 0.60 0.63

0.30 0.33 0.40 0.50 0.60 0.67 0.70
0.33 0.36 0.44 0.55 0.66 0.74 0.77
0.36 0.40 0.48 0.60 0.72 0.80 0.84

0.39 0.43 0.52 0.65 0.78 0.87 0.91
0.42 0.46 0.56 0.70 0.84 0.94 0.98
0.45 0.49 0.60 0.75 0.90 1.00 1.05

0.52 0.58 0.70 0.83 1.05 1.17 1.22
0.60 0.66 0.80 1.00 1.20 1.34 1.40
0.67 0.74 0.90 1.13 1.35 1.51 1.57


2.50 0.75 0.82 1.00 1.25 1.50 1.67 1.75
2.75 0.82 0.91 1.10 1.38 1.65 1.84 1.92
3.00 0.90 0.99 1.20 1.50 1.80 2.01 2.10
........................................................................


125 -
(n
W IRRIGATION DEPTH

e\ /
S/ / \
Z 100 A*




0.
0 .5 /


a_





z o ALLOWABLE DEPLETIONS





0.0
DO 0.5 10 1.5 20 2.5 30

SOIL WATER STORAGE IN ROOT ZONE (INCHES)

Figure 4. Irrigation depth per application based on soil water storage
in the root zone and allowable soil water depletion.









TABLE 5. VOLUME OF WATER TO BE APPLIED AT EACH IRRIGATION
BY EACH EMITTER (GALLONS).
--------------------------------------...................................
EMITTER DEPTH OF WATER TO BE APPLIED AT EACH IRRIGATION (INCHES)
WETTED (FROM TABLE 4)
DIAMETER --------------------------------------------
(FT) 0.25 0.50 0.75 1.00 1.50 2.00 2.50
VOLUME OF WATER PER IRRIGATION PER EMITTER (GALLONS)----------------------------------------
VOLUME OF WATER PER IRRIGATION PER EMITTER (GALLONS)
-----------------------------------------------------------


3.0 4.5 6.0 9.0 12.0 15.0
3.9 5.9 7.8 11.7 15.6 19.6
5.0 7.4 9.9 14.9 19.8 24.8
6.1 9.2 12.2 18.3 24.5 30.6

8.8 13.2 17.6 26.4 35.2 44.0
12.0 18.0 24.0 35.9 47.9 59.9
15.6 23.5 31.3 46.9 62.6 78.2
19.8 29.7 39.6 59.4 79.2 99.0


10.0 12.2 24.5 36.7 48.9 73.4
12.0 17.6 35.2 52.8 70.4 105.6
14.0 24.0 47.9 71.9 95.9 143.9
16.0 31.3 62.6 93.9 125.2 187.8


97.8
140.8
191.7
250.4


122.3
176.1
239.6
313.0


18.0 39.6 79.2 118.8 158.5 237.7 316.9 396.1
20.0 48.9 97.8 146.7 195.6 293.4 391.2 489.1


IRRIGATION VOLUME


100


z
0





w
60




F 40




20


DEPTH OF WATER TO
SBE APPLIED (INCHES)


EMITTER WETTED DIAMETER (FT)

Figure 5. Irrigation volume per emitter at each irrigation based on
emitter wetted diameter and depth of water to be applied.









TABLE 6. IRRIGATION FREQUENCY, OAYS BETWEEN SCHEDULED IRRIGATIONS.
...................................................................................
VOLUME OF
WATER TO BE AVERAGE DAILY ET RATE PER TREE (GALLONS/TREE/DAY)
APPLIED PER (FROM TABLE 2)
TREE AT EACH
IRRIGATION ---------------------------------------------------
(GALLONS/TREE) 5 10 15 20 25 30 35 40 50 60
...................................................................................
IRRIGATION FREQUENCY (DAYS)

5 1.0 0.5 0.3 0.3 0.2 0.2 0.1 0.1 0.1 0.1
10 2.0 1.0 0.7 0.5 0.4 0.3 0.3 0.3 0.2 0.2
15 3.0 1.5 1.0 0.8 0.6 0.5 0.4 0.4 0.3 0.3
20 4.0 2.C 1.3 1.0 0.8 0.7 0.6 0.5 0.4 0.3

30 6.0 3.0 2.0 1.5 1.2 1.0 0.9 0.8 0.6 0.5
40 8.0 4.0 2.7 2.0 1.6 1.3 1.1 1.0 0.8 0.7
50 10.0 5.0 3.3 2.5 2.0 1.7 1.4 1.3 1.0 0.8
60 12.0 6.0 4.0 3.0 2.4 2.0 1.7 1.5 1.2 1.0

70 14.0 7.0 4.7 3.5 2.8 2.3 2.0 1.8 1.4 1.2
80 ---- 8.0 5.3 4.0 3.2 2.1 2.3 2.0 1.6 1.3
90 ---- 9.0 6.0 4.5 3.6 3.0 2.6 2.3 1.8 1.5
100 ---- 10.0 6.7 5.0 4.0 3.3 2.9 2.5 2.0 1.7

200 ---- 20.0 13.3 10.0 8.0 6.7 5.7 5.0 4.0 3.3
300 ---- ---- 20.0 15.0 12.0 10.0 8.6 7.5 6.0 5.0
400 ---- ---- ---- 20.0 16.0 13.3 11.4 10.0 8.0 6.7
500 ---- ---- ---- ---- 20. 1.7 14.3 12.5 10.0 8.3
---------------------------------------------------------- --------------


IRRIGATION FREQUENCY
10




SAVE DAILY FT
S(GAL/TREE/DAY)




6-


IJ

Z4
O0










0 20 40 60 80 100 120

VOLUME PER TREE AT EACH IRRIGATION (GAL)

Figure 6. Irrigation frequency based on the volume of water applied per
tree at each irrigation and the average daily ET rate per tree.








TABLE 7. IRRIGATION TIME PER APPLICATION (HOURS).
---------------------------------------------------------------
VOLUME OF
WATER PER
EMITTER PER EMITTER FLOUR RATE (GALLONS/HOUR)
APPLICATION
(GALLONS) ----------------------------------------
(FROM TABLE 5) 0.5 1.0 1.5 2.0 3.0 5.0 10.0 15.0 20.0 25.0 30.0

IRRIGATION TIME PER APPLICATION (HOURS) *


2.5 1.3
5.0 2.5
10.0 5.0
15.0 7.5


0.8 0.6 0.4
1.7 1.3 0.8
3.3 2.5 1.7
5.0 3.8 2.5


8 20.0 10.0 6.7 5.0 3.3 2.0 1.0 0.7 0.5 0.4 0.3
10 --- 12 5 8.3 6.3 4.2 2.5 1.3 0.8 0.6 0.5 0.4
15 --- 18.8 12.5 9.4 6.3 3.8 1.9 1.3 0.9 0.8 0.6
20 ---- --- 16.7 12.5 8.3 5.0 2.5 1.7 1.3 1.0 0.8

30 ---- ---- ---- 18.8 12.5 7.5 3.8 2.5 1.9 1.5 1.3
40 --- ---- ---- --- 16.7 10.0 5.0 3.3 2.5 2.0 1.7
50 ---- ---- ---- --- 20.8 12.5 6.3 4.2 3.1 2.5 2.1
60 -- ---- ---- ---- ---- 15.0 7.5 5.0 3.8 3.0 2.5

70 ---- -- ---- ---- ---- 17.5 8.8 5.8 4.4 3.5 2.9
80 .-- --------- --- ---- 20.0 10.0 6.7 5.0 4.0 3.3
90 --- --- --- -- ---- 22.5 11.3 7.5 5.6 4.5 3.8
100 ---- ------ --- ---- ---- 12.5 8.3 6.3 5.0 4.2

200 ---- ----.- ---- ---- ---- ---- 16.7 12.5 10.0 8.3
300 -------- ---- ---- ---- ---- ---- ---- 18.8 15.0 12.5
400 ---. -- -- .-- .--. -- .------- ---- 20.0 16.7
500 --- -- -- --- ---- -- ---- ....... --- ---- 20.8
500-----------------------------------------------------------------------208 -
ASSUMES AN 801 APPLICATION EFFICIENCY.


IRRIGATION TIME PER APPLICATION


0 10 20 30 40 50 60

VOLUME PER EMITTER AT EACH IRRIGATION

Figure 7. Irrigation time (duration) per application based on volume
applied per emitter at each application and the emitter flow rate.


-----------------------------


-----------------------------------------










TABLE 8A. TREE CANOPY AREA OR EMITTER WETTED AREA BASED ON
TREE CANOPY DIAMETERS OR EMITTER WETTED DIAMETERS.

TREE CANOPY DIAMETER OR TREE CANOPY AREA OR
EMITTER WETTED DIAMETER EMITTER WETTED AREA
(FT) (SQ FT)


18 254
20 314
22 380
24 452


TREE CANOPY AREA AND
EMITTER WETTED AREA


0 4 8 12 16 20
TREE CANOPY DIAMETER OR EMITTER WETTED DIAMETER (FT)

Figure 8a. Tree canopy area or emitter wetted area based on the tree
canopy diameter or the emitter wetted diameter.


<250


W
0
t- 200

W

I-
t: 150
w

0
4
w 100


0-
0
Z 50
U
W
W
cr
I-









TABLE 88. TREE CANOPY AREA BASED ON TREE SPACING AND CANOPY WIDTH.

TREE SPACING AVERAGE CANOPY WIDTH (FT)
ALONG ROW ----------------------------------------
(FT) 12 14 16 18 20 22 24 25

TREE CANOPY AREA (SQ FT)

10 12' 140 160 180 200 220 240 260
12 144 168 192 216 240 264 288 312
14 169 196 224 252 280 308 336 364


192 224 256 288 320 352 384 416
216 252 288 324 360 396 432 468
240 280 320 360 400 440 480 520
264 308 352 396 440 484 528 572


24 288 336 384 432 480 528 576 624
26 312 364 416 468 520 572 624 676
28 336 392 448 504 560 616 672 728
30 360 420 480 540 600 660 720 780


TREE CANOPY AREA


* AVE. CANOPY WIDTH (FT)


10 14 18 22 26 30

TREE SPACING ALONG ROW (FT)

Figure 8b. Tree canopy area based on the tree spacing along the row and
the average tree canopy width.


500




400

N
LL.

S300
W
a:


0
Z 200


u
W
I-







TABLE 9. RELATIVE AREA OCCUPIED BY TREE CANOPY.
..............................................................................
AVERAGE CANOPY
AREA PER TREE TREE DENSITY (NUMBER OF TREES / ACRE)
(FROM TABLE 8A OR 88) ------------------------------------------------------
(SQ FT) 70 80 90 100 110 120 130 140
..............................................................................
RELATIVE AREA OCCUPIED BY TREE CANOPY
----------------------------------------------------------
50 0.09 0.10 0.11 0.13 0.14 0.15 0.16 0.13
75 0.13 0.15 0.17 0.19 0.21 0.23 0.25 0.27
80 0.14 0.16 0.18 0.20 0.22 0.24 0.26 0.28
90 0.16 0.18 0.20 0.23 0.25 0.27 0.30 0.32
100 0.18 0.20 0.23 0.25 0.28 0.30 0.33 0.35
125 0.22 0.25 0.28 0.32 0.35 0.38 0.41 0.44
150 0.27 0.30 0.34 0.38 0.42 0.45 0.49 0.53
175 0.31 0.35 0.40 0.44 0.49 0.53 0.57 0.62
200 0.35 0.40 0.45 0.51 0.56 0.61 0.66 0.71
225 0.40 0.45 0.51 0.57 0.62 0.68 0.74 0.80
250 0.44 0.51 0.57 0.63 0.69 0.76 0.82 0.88
275 0.49 0.56 0.62 0.69 0.76 0.83 0.90 0.97
300 0.53 0.61 0.68 0.76 0.83 0.91 0.93 ---
325 0.57 0.66 0.74 0.82 0.90 0.98 --
350 0.62 0.71 0.80 0.88 0.97 --
400 0.71 0.81 0.91 --- --- -- -- --
450 0.80 0.91 -- -- --- ---
500 0.88 -- -- --- -- -- --


RELATIVE TREE CANOPY AREA


* NUMBER OF TREES / ACRE


0 100 200 300 400 500

AVERAGE CANOPY AREA PER TREE (FT2)

Figure 9. Relative tree canopy area based on the average canopy area
per tree and the number of trees per acre.


w
Q:
0.6
>-
Oa
0
z
u
0.4
0d

>

S0.









TABLE 10. IRRIGATED ZONE CORRECTION FACTOR.
.......................................................................
IRRIGATION TIME AFTER IRRIGATION UNTIL RAINFALL OCCURRED (DAYS)
FREQUENCY ---------------------------------------------
(DAYS) 1 2 3 4 6 8 10 12

IRRIGATED ZONE CORRECTION FACTOR*

1 1.00 -- -- -- --
2 0.50 1.00 -- -- --- --
3 0.33 0.67 1.00 -- -- -- -- --
4 0.25 0.50 0.75 1.00 --- --- ---
5 0.20 0.40 0.60 0.80 -- -- -- --
6 0.17 0 33 0.50 0.67 1.00 --- ---
7 0.14 0.29 0.43 0.57 0.8 -- -- ---
8 0.13 0.25 0.38 0.50 0.75 1.00 -- --
9 0.11 0.22 0.33 0.44 0.67 0.89 ---
10 0.10 0.20 0.30 0.40 0.60 0.80 1.00 ---
12 0.08 0.17 0.25 0.33 0.50 0.67 0.83 1.00
14 0.07 0.14 0.21 0.29 0.43 0.57 0.71 0.86


IRRIGATED ZONE CORRECTION FACTOR


* IRRIGATION FREQUENCY (DAYS)


0 2 4 6 8 10 12

TIME AFTER IRRIGATION UNTIL RAIN OCCURRED (DAYS)

Figure 10. Irrigated zone correction factor based on the time after
irrigation until rain occurred and the scheduled Irrigation
frequency.


W 0.8
O
I-
0

Z
O

z
o 0.6


a:
O
o 0.4
Z



W 0.2
r-

a:
a,









TABLE 11. NON-IRRIGATED ROOT ZONE CORRECTION FACTOR.
..........................................................................
AVERAGE CANOPY
AREA PER TREE EMITTER WETTED AREA PER TREE (SQ FT)
(FROM TABLE 8A
OR TABLE 8B) -----------------------------------------------
(SQ FT) 5 10 20 50 100 200 300 400
..........................................................................
NON-IRRIGATED ZONE CORRECTION FACTOR
-----------------------------------------------------------
50 0.90 0.80 0.60 0.00 0.00 0.00 0.00 0.00
75 0.93 0.87 0.73 0.33 0.00 0.00 0.00 0.00
100 0.95 0.90 0.80 0.50 0.00 0.00 0.00 0.00
125 0.96 0.92 0.84 0.60 0.20 0.00 0.00 0.00

150 0.97 0.93 0.87 0.67 0.33 0.00 0.00 0.00
175 0.97 0.94 0.89 0.71 0.43 0.00 0.00 0.00
200 0.97 0.95 0.90 0.75 0.50 0.00 0.00 0.00
225 0.98 0.96 0.91 0.78 0.56 0.11 0.00 0.00

250 0.98 0.96 0.92 0.80 0.60 0.20 0.00 0.00
275 0.98 0.96 0.93 0.82 0.64 0.27 0.00 0.00
300 0.98 0.97 0.93 0.83 0.67 0.33 0.00 0.00
325 0.98 0.97 0.94 0.85 0.69 0.38 0.08 0.00

350 0.99 0.97 0.94 0.86 0.71 0.43 0.14 0.00
400 0.99 0.97 0.95 0.88 0.75 0.50 0.25 0.00
450 0.99 0.98 0.96 0.89 0.78 0.56 0.33 0.11
500 0.99 0.98 0.96 0.90 0.80 0.60 0 40 0.20
..........................................................................



NON-IRRIGATED ROOT ZONE CORRECTION FACTOR

10


EMITTER WETTED AREA
O PER TREE(FT2)
U-
08 -
Z
0 100

U
a. 06 -
O
L) 200

O
S04


>- 300


02





0 100 200 300 400 500

AVERAGE CANOPY AREA PER TREE (FT2)


Figure 11. Non-irrigated root zone correction factor based on the
average canopy area per tree and the total emitter wetted area per
tree.










TABLE 12. ANTECEDENT SOIL WATER CONTENT CORRECTION FACTOR.
-------- -----------.---------------------------------------------------------
IRRIGATED ZONE NON-IRRIGATED ROOT ZONE CORRECTION FACTOR
CORRECTION (FROM TABLE 11)
FACTOR -----------........................................
(FROM TABLE 10) 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
---------------------------------------------------------------

0.0 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00
0.1 0.10 0.19 0.28 0.37 0.46 0.55 0.64 0.73 0.82 0.91 1.00
0.2 0.20 0.28 0.36 0.44 0.52 0.60 0.68 0.76 0.84 0.92 1.00

0.3 0.30 0.37 0.44 0.51 0.58 0.65 0.72 0.79 0.86 0.93 1.00
0.4 0.40 0.46 0.52 0.58 0.64 0.70 0.76 0.82 0.88 0.94 1.00
0.5 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00

0.6 0.60 0.64 0.68 0 72 0.76 0.80 0.84 0.88 0.92 0.96 1.00
0.7 0.70 0.73 0.76 0.79 0.82 0.85 0.88 0.91 0.94 0.37 1.00
0.8 0.80 0.82 0.84 0.86 0.88 0.90 0.92 0.94 0.96 0.98 1.00

0.9 0.90 0.91 0.92 0.93 0.94 0.95 0.96 0.97 0.98 0.99 1.00
1.0 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00 1.00




0
ANTECEDENT SOIL WATER CONTENT CORRECTION FACTORS
,

*- NON- IRRIGATED ROOT ZONE
CORRECTION FACTOR


0.2 0.4 0.6 08
IRRIGATED ZONE CORRECTION FACTOR


Figure 12. Antecedent soil water content correction factor based on the
irrigated zone correction factor and the non-irrigated root zone
correction factor.











TABLE 13. POTENTIAL RAINFALL STORAGE IN SOIL DEPTH IRRIGATED (INCHES).
....................................................................................
SOIL WATER
STORAGE IN ANTECEDENT SOIL WATER CONTENT CORRECTION FACTOR
SOIL DEPTH (FROM TABLE 12)
IRRIGATED
(INCHES) ----------------------------------------.----------
(FR(O TABLE 4) 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
....................................................................................
POTENTIAL RAIN STORAGE IN ROOT ZONE (INCHES)
......................................................................
0.25 0.02 0.05 0.07 0.10 0.13 0.15 0.17 0.20 0.22 0.25
0.50 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50
0.75 0.07 0.15 0.22 0.30 0.38 0.45 0.52 0.60 0.67 0.75
1.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00

1.25 0.12 0.25 0.37 0.50 0.63 0.75 0.87 1.00 1.12 1.25
1.50 0.15 0.30 0.45 0.60 0.75 0.90 1.05 1.20 1.35 1.50
1.75 0.17 0.35 0.52 0.70 0.88 1.05 1.22 1.40 1.57 1.75
2.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00

2.25 0.22 0.45 0.67 0.90 1.13 1.35 1.57 1.80 2.02 2.25
2.50 0.25 0 50 0 75 1.00 1.25 1.50 1.75 2.00 2.25 2.50
2.75 0.27 0.55 0.82 1.10 1.38 1.65 1.92 2.20 2.47 2.75
3.00 0.30 0.60 0.90 1.20 1.50 1.80 2.10 2.40 2.70 3.00
....................................................................................


POTENTIAL RAIN STORAGE IN TREE ROOT ZONE


* ANTECEDENT SOIL WATER
CONTENT CORRECTION FACTOR


SOIL WATER STORAGE IN EFFECTIVE ROOT ZONE (INCHES)



Figure 13. Potentional rainfall storage in the tree root zone based on
the soil water storage in the root zone and the antecedent soil water
content.







TABLE 14. EFFECTIVE RAINFALL, RAINFALL STORED IN THE SOIL DEPTH IRRIGATED.

POTENTIAL SOIL WATER STORAGE IN SOIL DEPTH IRRIGATED
RAINFALL (INCHES) (FROM TABLE 13)
---------------------------------------------------------
(INCHES) 0.50 0.75 1.00 1.25 1.50 2.00 2.50 3.00

EFFECTIVE RAINFALL (INCHES)
-----------------------------------------------------------


0.10 0.00 0.00
0.20 0.10 0.10
0.30 0.20 0.20
0.40 0.30 0.30

0.50 0.40 0.40
0.60 0.50 0.50
0.70 0.50 0.60
0.80 0.50 0.70

0.90 0.50 0.75
1.00 0.50 0.75
1.25 0.50 0.75
1.50 0.50 0.75

1.75 0.50 0.75
2.00 0.50 0.75
2.25 0.50 0.75
2.50 0.50 0.75


2.75
3.00
3.50
> 3.50


0.50 0.75
0.50 0.75
0.50 0.75
0.50 0.75


0.00 0.00
0.10 0.10
0.20 0.20
0.30 0.30

0.40 0.40
0.50 0.50
0.60 0.60
0.70 0.70

0.80 0.80
0.90 0.90
1.00 1.15
1.00 1.25

1.00 1.25
1.00 1.25
1.00 1.25
1.00 1.25

1.00 1.25
1.00 1.25
1.00 1.25
1.00 1.25


0.00 0.00
0.10 0.10
0.20 0.20
0.30 0.30

0.40 0.40
0.50 0.50
0.60 0.60
0.70 0.70

0.80 0.80
0.90 0.90
1.15 1.15
1.40 1.40

1.50 1.65
1.50 1.90
1.50 2.00
1.50 2.00

1.50 2.00
1.50 2.00
1.50 2.00
1.50 2.00


0.00 0.00
0.10 0.10
0.20 0.20
0.30 0.30

0.40 0.40
0.50 0.50
0.60 0.60
0.70 0.70

0.80 0.80
0.90 0.90
1.15 1.15
1.40 1.40

1.65 1.65
1.90 1.90
2.15 2.15
2.40 2.40

2.50 2.65
2.50 2.90
2.50 3.00
2.50 3.00


EFFECTIVE RAINFALL


POTENTIAL SOIL WATER STORAGE
IN EFFECTIVE ROOT ZONE


S 1.5
RAINFALL (INCHES)


Figure 14. Effective rainfall based on actual rainfall and the
potential soil water storage in the effective root zone.


2.5




cn 2.0
w
U




z


4 1.0
w .
L_
t-
u
U.
Id
W 0.5


0.0-
00










TABLE 15. READILY AVAILABLE EFFECTIVE RAINFALL, EFFECTIVE
RAINFALL STORED UNDER AND NEAR TREE CANOPY.
----------------------------------------................................
EFFECTIVE RELATIVE AREA OCCUPIED BY TREE CANOPY
RAINFALL (FROM TABLE 9)
(INCHES) --------------------------------------------
(FROM TABLE 14) 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0
-----------------------------------.---------...........................
READILY AVAILABLE EFFECTIVE RAINFALL (INCHES)
--------------------------------------------------------
0.1 0.03 0.04 0.05 0.06 0.07 0.08 0.09 0.10
0.2 0.06 0.08 0.10 0.12 0.14 0.16 0.18 0.20
0.3 0.09 0.12 0.15 0.18 0.21 0.24 0.27 0.30
0.4 0.12 0.16 0.20 0.24 0.28 0.32 0.36 0.40
0.5 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50
0.6 0.18 0.24 0.30 0.36 0.42 0.48 0.54 0.60
0.7 0.21 0.28 0.35 0.42 0.49 0.56 0.63 0.70
0.8 0.24 0.32 0.40 0.48 0.56 0.64 0.72 0.80
0.9 0.27 0.36 0.45 0.54 0.63 0.72 0.81 0.90
1.0 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00
1.2 0.36 0.48 0.60 0.72 0.84 0.96 1.08 1.20
1.4 0.42 0.56 0.70 0.84 0.98 1.12 1.26 1.40
1.6 0.48 0.64 0.80 0.96 1.12 1.28 1.44 1.60
1.8 0.54 0.72 0.90 1.08 1.26 1.44 1.62 1.80
2.0 0.60 0.80 1.00 1.20 1.40 1.60 1.80 2.00
2.5 0.75 1.00 1.25 1.50 1.75 2.00 2.25 ---
3.0 0.90 1.20 1.50 1.80 2.10 --- --- --
..................------------------------------------------------------


READILY AVAILABLE EFFECTIVE RAINFALL


_J
-J

Z 2.0


W



LLLJ
U
WZ

m 1.0



-J
05


RELATIVE AREA OCCUPIED
BY TREE CANOPY


EFFECTIVE RAINFALL (INCHES)


Figure 15. Readily available effective rainfall based on total
effective rainfall and the relative area occupied by the tree canopy.







TABLE 16. DAYS TO DELAY IRRIGATION FOLLOWING RAINFALL.
------- ----------------------- --------------------------------------------
AVERAGE DAILY READILY AVAILABLE EFFECTIVE RAINFALL (INCHES)
ET RATE (FROM TABLE 15)
(INCHES/DAY) -------------.---.----... --. ......................... .....
(FROM TABLE 1) .1 .2 .3 .4 .5 .6 .7 .8 .9 1.0 1.2 1.4 1.6 1.8 2.0
--------------------------------------------------------------------------------
DAYS TO DELAY IRRIGATION
---------------------------------------------------------------------
0.05 2 4 6 8 10 12 14 16 18 20 -
0.06 2 3 5 7 8 10 12 13 15 17 20
0.07 1 3 4 6 7 9 10 11 13 14 1 20 -
0.08 1 2 4 5 6 7 9 10 11 13 15 17 20 --
0.09 I 2 3 4 6 7 8 9 10 11 13 16 18 20 --

0.10 1 2 3 4 5 6 7 8 9 10 12 14 16 18 20
0.11 1 2 3 4 5 5 6 7 8 9 11 13 15 16 18
0.12 1 2 2 3 4 5 6 7 8 8 10 12 13 15 17
0.13 1 2 2 3 4 5 5 6 7 8 9 11 12 14 15
0.14 1 1 2 3 4 4 5 6 6 7 9 10 11 13 14

0.15 1 1 2 3 3 4 5 5 6 7 8 9 11 12 13
0.16 1 1 2 2 3 4 4 5 6 6 7 9 10 11 13
0.17 1 1 2 2 3 4 4 5 5 6 7 8 9 11 12
0.18 1 1 2 2 3 3 4 4 5 6 7 8 9 10 11
0.19 1 1 2 2 3 3 4 4 5 5 6 7 8 9 11

0.20 1 1 1 2 3 3 3 4 5 5 6 7 8 9 10
0.21 0 1 1 2 2 3 3 4 4 5 6 7 8 9 10
0.22 0 1 1 2 2 3 3 4 4 5 5 6 7 8 9
0.23 0 1 1 2 2 3 3 3 4 4 5 6 7 8 9
0.24 0 1 1 2 2 2 3 3 4 4 5 6 7 8 8
...........................................................................................


DAYS TO DELAY IRRIGATION FOLLOWING RAINFALL


2.0






o
-1.0
(06
cr

064

-j

S0.2 4
0




2

READILY AVAILABLE
EFFECTIVE RAINFALL

0 I I I I I
0.0 0.05 0.10 0.15 0.20 0.25
AVERAGE DAILY ET RATE (INCHES/DAY)

Figure 16. Days to delay irrigation following rainfall based on the
average daily ET rate and the readily available effective rainfall.

















Appendices


Appendix A . . . . . . . . . . . . 36

Appendix B . . . . . . . . . . . . 38
Example 1. Drip Irrigation Scheduling . . . ... 38
Example 2. Trickle Irrigation Scheduling . . ... 41


Appendix C . . . . . . . . . . . . 44







APPENDIX A


The equations used to develop the Tables and Figures In this bulletin are presented in this Appendix.
Equation numbers correspond to the Table and Figure numbers in this bulletin.

1. Table 1 contains citrus evapotranspiration data from IFAS Water Resources Council Fact Sheet WRC-4,
"Water Requirements for Citrus," and from Ag. Eng. Extension Report 83-10, "Evapotranspiration and Net
Irrigation Requirements for Crops in South and Central Florida."


2. Average Daily ET Rate Average Daily ET
Per Tree (gal/tree/day) = 27,154 gal/ac-in Rate (inches/day)


Tree Density
(No. trees/acre)


3. Soil Water Storage In Soil Soil Depth to be Soil Mater Holding Capacity
Depth Irrigated (inches) Irrigated (ft) (inches water/ft soil)


4. Depth of Water to be applied Allowable Water
at Each Irrigation (inches) Depletion (%)


Soil Water Storage in Soil /100.0
Depth Irrigated (inches)


5. Volume of Water to be Applied 0623 3.14 Wetted Dia.2 Depth of Water to be Applied
at Each Irrigation by Each Emitter (gal) 4 at Each Irrigation (inches)


6. Irrigation Frequency (days) Volume of Water to be Applied per
Tree at Each Irrigation (gal/tree)


7. Irrigation Time per Volume of Water to be Applied per Emitter Flow Rate
Application (hours) Emitter at Each Irrigation (gal) / (gal/hour)


Average Daily ET Rate per tree
(gal/tree/day)


/ o.no


8a. Tree Canopy or Emitter Wette Area 0.785 Tree Canopy Dia.2 or Emtter etted Dia.2
Based on Canopy Diameter (ft) 0.785 Tree Canopy a.2 or Emitter Wetted D







8b. Spaee Canop p Aea Baedton r Tree Spacing (ft) Canopy Width (ft)
Spacing and Canopy Width (ft')


9. Relative Area Occupied 1.1 Average Canopy Area
by Tree Canopy per Tree (ft2)


10. Irrigated Zone
Correction Factor


No. of Trees 43,560 ft2
per Acre acre


Time After Irrigation Until Ir n F y
Rain Occurred (days) / Irrigation Frequency (days)


11. Non-Irrigated Root Zone min
Correction Factor


Emitter Wetted Area
Tree Canopy Area


1.0 -

0.0


12. Antecedent Soil Water Content Non-Irrigated Zone +
Correction Factor Correction Factor


1.0 Non-Irrigated Zone Irrigated Zone
Correction Factor Correction Factor


13. Potential Rainfall Storage in Antecedent Soil Water Soil Water Storage in Soil
Soil Depth Irrigated (inches) Content Correction Factor Depth Irrigated (inches)



14. Effective Rainfall (Inches) max Potential Soil Water Storage in Soil Depth Irrigated (inches)(
active Rainfall 0.1 inch interception losses

15. Readily Available Effective Relative Area Occupied Effective Rainfall (inches)
Rainfall (inches) by Tree Canopy

16. Days to Delay Irrigation Readily Available Average Daily ET
Following Rainfall Effective Rainfall (inches) Rate (inches/day)









APPENDIX B


Example 1. Drip Irrigation Scheduling


Irrigation Scheduling Worksheet
Information Required


Climatic Information:
Month of Year: April
Geographical Location (Ridge or Flatwoods Areas): Ridge


Tree Information:
Tree density: 100 trees/acre


Tree Canopy Diameter:
Tree Spacing Along Row: 15 ft
-- ft or Average Canopy Width: 18 ft


Soils Information:
Soil Water-Holding Capacity:


0.7 inches of water/ft of soil


Irrigation System Information:
Emitter Wetted Diameter: 3.0 ft
Number of Emitters/Tree: 4
Emitter Flow Rate: 1.0 gal/hr


System Management Information:
Root Depth to be Irrigated: 3.0 ft
Allowable Soil Water Depletion: 50 %






Scheduling Calculations


Calculation step numbers correspond to Table and Figure numbers in
this bulletin.

1. Average daily ET rate = 0.13 inches/day, for (month)
April and location = Ridge .


2. Average daily ET rate = 35
0.13 inches/day (from Step 1) and


gallons/tree/day, for ET rate
100 trees/acre.









3. Soil water storage in soil depth irrigated = 2.1 inches, for
0.7 inches of water/ft of soil and 3.0 ft irrigated depth.


4. Depth of water to be applied at each irrigation = 1.05 inches
for 2.1 inches of soil water storage in soil depth irrigated (from
Step 3) and 50 % allowable soil water depletion.

5. Volume of water to be applied at each irrigation by each emitter =
4.6 gallons, for 3.0 ft emitter wetted diameter and 1.05
inches depth of water applied per emitter per irrigation (from Step
4).


6. Irrigation frequency = 0.53 days, for 18.4 gallons/tree to be
applied per irrigation (4.6 gallons from Step 5 multiplied by 4 emit-
ters/tree) and 35 gallons/tree/day average daily ET rate (from
Step 2).


Adjust to even Increment of days = 0.5 days for 17.5 gal/tree and 35
gal/tree/day ET rate. This is 4.4 gal/emitter.


7. Irrigation time per application = 5.5 hours*, for 4.4 gallons of
water per emitter per application (from Step 5 or as adjusted in step
6) and 1.0 gal/hr emitter flow rate.
*This assumes an 80% application efficiency.


Comments: Note that this system should be operated twice per day (every
0.5 days) allowing for water depletions between irrigations. If very
frequent irrigations do not permit water depletions (based on field ob-
servations) between irrigations, then this irrigation system will not be
able to supply all of the tree's water requirements because an insuffi-
cient volume of the tree's root zone is being irrigated. To solve this,
more emitters or spray-jets should be used to irrigate a larger fraction
of the tree's root zone.





Rainfall Information Required

To calculate delay times following rainfall, the following addition-
al information is required about each rainfall:

Rainfall depth: 2.00 inches
Days after last irrigation until rain occurred: 1 days


8. (a) Tree canopy area = --- ft2, for --- ft canopy diameter









8. (b) Tree canopy area = 270 ft2, for 15 ft tree spacing along
row and 18 ft average canopy width.

9. Relative area occupied by tree canopy 0.68 for 270 ft2
average canopy area per tree (from Step 8) and 100 trees per
acre.

10. Irrigated zone correction factor = 1.00 for 1.0 days irriga-
tion frequency (from Step 6) and 1.0 days after irrigation until
rainfall occurred.

11. Non-irrigated root zone correction factor = 0.90 for 270 ft2
average canopy area per tree (from Step 8) and 28* ft2 emitter
wetted area per tree (from Table 8a multiplied by the number of
emitters per tree).
*From 4 emitters per tree and 7 sq.ft. per emitter for this example.

12. Antecedent soil water content correction factor = 1.00 for 1.00
irrigated zone correction factor (from Step 10) and 0.90 non-
irrigated root zone correction factor (from Step 11).

13. Potential rainfall storage in soil depth irrigated = 1.05 inches,
for 1.05 inches soil water storage in the soil depth irrigated
(from Step 4) and 1.00 antecedent soil water content correction
factor (from Step 12).

14. Effective rainfall = 1.05 inches, for 2.00 inches of rainfall
and 1.05 inches of potential soil water storage in the soil depth
irrigated (from Step 13).

15. Readily available effective rainfall = 0.71 inches, from 1.05
inches effective rainfall (from Step 14) and 0.68 relative area
occupied by the tree canopy (from Step 9).

16. Days to delay irrigation following rainfall = 5.5 days, for 0.13
inches/day average daily ET rate (from Step 1) and 0.71 inches
readily available effective rainfall (from Step 15).

Adjust to even multiple of normal irrigation schedule = 5.5 days.

Comments: Note that irrigation can be delayed for 5.5 days because the
entire area under the tree canopy was wet by the rain, whereas irriga-
tions were required twice daily because of the limited fraction of the
tree root zone irrigated by only 4 1-gal/hr drip emitters.









Example 2. Spray-Jet Irrigation Scheduling


Irrigation Scheduling Worksheet
Information Required


Climatic Information:
Month of Year: April
Geographical Location (Ridge or Flatwoods Areas): Ridge


Tree Information:
Tree density: 100 trees/acre
Tree Canopy Diameter:
Tree Spacing Along Row: 15 ft
--- ft or
Average Canopy Width: 18 ft

Soils Information:
Soil Water-Holding Capacity: 0.7 inches of water/ft of soil

Irrigation System Information:
Emitter Wetted Diameter: 12.0 ft
Number of Emitters/Tree: 1
Emitter Flow Rate: 15.0 gal/hr

System Management Information:
Root Depth to be Irrigated: 3.0 ft
Allowable Soil Water Depletion: 50 %



Scheduling Calculations

Calculation step numbers correspond to Table and Figure numbers in
this bulletin.

1. Average daily ET rate = 0.13 inches/day, for (month) April and
location = Ridge .


2. Average daily ET rate = 35 gallons/tree/day, for ET rate = 0.13
inches/day (from Step 1) and 100 trees/acre.


3. Soil water storage in soil depth irrigated = 2.10 inches,
for 0.7 inches of water/ft of soil and 3.0 ft irrigated depth.


4. Depth of water to be applied at each irrigation = 1.05 inches, for
2.1 inches of soil water storage in soil depth irrigated (from Step
3) and 50 % allowable soil water depletion.









5. Volume of water to be applied at each irrigation by each emitter =
74 gallons, for 12.0 ft emitter wetted diameter and 1.05
inches depth of water applied per emitter per irrigation (from Step
4).

6. Irrigation frequency = 2.1 days, for 74 gallons/tree to be
applied per irrigation (from Step 5 multiplied by the number of
(emitters/ tree) and 35 gallons/tree/day average daily ET rate
(from Step 2).


Adjust to even number of days = 2.0 for 70 gal/tree and 35
gal/tree/day ET rate. This is 70 gal/emitter.


7. Irrigation time per application = 5.8 hours*, for 70 gallons of
water per emitter per application (from Step 5) and 15.0 gal/hr
emitter flow rate.
*This assumes an 80% application efficiency.


Comments: Note that the irrigation frequency has been reduced by a
factor of 4 for spray-jet emitters (every other day) as compared to the
twice-per-day frequency required for the drip emitters in Example 1.
This results because the 1 spray-jet emitter per tree covers 4 times the
tree root zone as compared to the 4 drip emitters in Example 1.




Rainfall Information Required

To calculate delay times following rainfall, the following addition-
al information is required about each rainfall:

Rainfall depth: 2.00 inches
Days after last irrigation until rain occurred: 1
days


8.(a) Tree canopy area = -- ft2, for --- ft canopy diameter

or


8. (b.) Tree canopy area = 270 ft2, for 15 ft tree spacing
along row and 18 ft average canopy width.

9. Relative area occupied by tree canopy = 0.68 for 270 ft2
average canopy area per tree (from Step 8) and 100 trees per
acre.









10. Irrigated zone correction factor = 0.50 for 2 days irriga-
tion frequency (from Step 6) and 1 days after irrigation until
rainfall occurred.


11. Non-irrigated root zone correction factor = 0.58 for 270 ft2
average canopy area per tree (from Step 8) and 113 ft2 emitter
wetted area per tree (from Table 8a multiplied by the number of
emitters per tree).


12. Antecedent soil water content correction factor = 0.79 for 0.50
irrigated zone correction factor (from Step 10) and 0.58 non-
irrigated root zone correction factor (from Step 11).


13. Potential rainfall storage in soil depth irrigated = 0.83 inches,
for 1.05 inches soil water storage in the soil depth irrigated
(from Step 4) and 0.79 antecedent soil water content correction
factor (from Step 12).


14. Effective rainfall = 0.83 inches, for 2.00 inches of rainfall
and 0.83 inches of potential soil water storage in the soil depth
irrigated (from Step 13).


15. Readily available effective rainfall = 0.45 inches, from 0.83
inches effective rainfall (from Step 14) and 0.68 relative area
occupied by the tree canopy (from Step 9).


16. Days to delay irrigation following rainfall = 3.4* days, for 0.13
inches/day average daily ET rate (from Step 1) and 0.45 inches
readily available effective rainfall (from Step 15).


*Adjust to even multiple of normal irrigation schedule or whole
number of days = 3.0 days.


Comments: Note that the next irrigation would be scheduled in 4 days (3
from step 16 plus the 1 day remaining in the normal irrigation schedule,
from step 10).









APPENDIX C


Irrigation Scheduling Worksheet
Information Required



Climatic Information:
Month of Year:
Geographical Location (Ridge or Flatwoods
Areas):


Tree Information:
Tree density: trees/acre
Tree Spacing Along Row: ft
Tree Canopy Diameter: ft or
Average Canopy Width: ft


Soils Information:
Soil Water-Holding Capacity: inches of water/ft of soil

Irrigation System Information:
Emitter Wetted Diameter: ft
Number of Emitters/Tree:
Emitter Flow Rate: gal/hr

System Management Information:
Root Depth to be Irrigated: ft
Allowable Soil Water Depletion: %







Scheduling Calculations

Calculation step numbers correspond to Table and Figure numbers in
this bulletin.

1. Average daily ET rate = inches/day, for (month) and
location =

2. Average daily ET rate = gallons/tree/day, for ET rate
= inches/day (from Step 1) and trees/acre.

3. Soil water storage in soil depth Irrigated = inches,
for inches of water/ft of soil and ft irrigated depth.










4. Depth of water to be applied at each irrigation = inches,
for nches of soil water storage in soil depth irrigated (from
Step 3) and %, allowable soil water depletion.


5. Volume of water to be applied at each irrigation by each emitter
= __ __ gallons, for ft emitter wetted diameter and
inches depth of water applied per emitter per irrigation (from Step
4).

6. Irrigation frequency = _days, for ___ gallons/tree to be
applied per irrigation (from Step 5 multiplied by the number of
emitters/tree) and gallons/tree/day average daily ET rate
(from Step 2).


Adjust to even number of days = days for gal/tree and
gal/tree/day ET rate. This is gal/emitter.

7. Irrigation time per application = hours*, for gallons of
water per emitter per application (from Step 5) and gal/hr
emitter flow rate.
*This assumes an 80% application efficiency.








Rainfall Information Required

To calculate delay times following rainfall, the following addition-
al information is required about each rainfall:

Rainfall depth: ____ inches
Days after last irrigation until rain occurred:
days.

8.(a) Tree canopy area = ft2, for ft canopy diameter.

or

8.(b) Tree canopy area = __ ft2, for ft tree spacing along
row and ft average canopy width.

9. Relative area occupied by tree canopy = for _ft2
average canopy area per tree (from Step 8) and trees per
acre.










10. Irrigated zone correction factor = __, for days
irrigation frequency (from Step 6) and days after irrigation
until rainfall occurred.

11. Non-irrigated root zone correction factor = for ft2
average canopy area per tree (from Step 8) and ft2 emitter
wetted area per tree (from Table 8a multiplied by the number of
emitters per tree).

12. Antecedent soil water content correction factor = for
irrigated zone correction factor (from Step 10) and non-
irrigated root zone correction factor (from Step 11).


13. Potential rainfall storage in soil depth irrigated = ___ inches,
for inches soil water storage in the soil depth irrigated
(from Step 4) and antecedent soil water content correction
factor (from Step 12).

14. Effective rainfall = inches, for inches of rainfall
and inches of potential soil water storage in the soil depth
irrigated (from Step 13).

15. Readily available effective rainfall = inches,
from inches effective rainfall (from Step 14)
and relative area occupied by the tree canopy (from Step
9).

16. Days to delay irrigation following rainfall = _days, for_
inches/day average daily ET rate (from Step 1) and inches
readily available effective rainfall (from Step 15).

Adjust to even multiple of normal irrigation schedule or nearest
whole number of days = days.

Comments: Note that the next irrigation would be scheduled in days
(from step 16 plus the days remaining in the normal irrigation sche-
dule, from step 10). This is days total.





















































This publication was promulgated at a cost of $2,092.05, or 95
cents per copy, to assist Florida growers in scheduling trickle
irrigation in citrus groves. 9-2.2M-87


COOPERATIVE EXTENSION SERVICE, UNIVERSITY OF FLORIDA, INSTITUTE
OF FOOD AND AGRICULTURAL SCIENCES, K.R. Tefertiller, director, in coopera-
tion 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,
Gainesville, Florida 32611. Before publicizing this publication, editors should contact this address to
determine availability.




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