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Group Title: GCREC Bradenton research report - University of Florida Gulf Coast Research and Education Center ; BRA1991-26
Title: Application volumes and wetting patterns for scheduling drip irrigation in Florida vegetable production
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Permanent Link: http://ufdc.ufl.edu/UF00065252/00001
 Material Information
Title: Application volumes and wetting patterns for scheduling drip irrigation in Florida vegetable production
Series Title: GCREC Bradenton research report
Physical Description: 22 p. : ill. ; 28 cm
Language: English
Creator: Clark, Gary A
Smajstrla, A. G ( Allen George )
Gulf Coast Research and Education Center (Bradenton, Fla.)
Publisher: Gulf Coast Research and Education Center, IFAS, University of Florida
Place of Publication: Bradenton Fla.
Publication Date: 1991
 Subjects
Subject: Microirrigation -- Florida   ( lcsh )
Irrigation -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
 Notes
Statement of Responsibility: by Gary A. Clark and Allen G. Smajstrla.
General Note: Cover title.
General Note: "December, 1991."
Funding: Bradenton GCREC research report ;
 Record Information
Bibliographic ID: UF00065252
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: oclc - 64024716

Table of Contents
    Historic note
        Historic note
    Front Cover
        Front cover
    Main
        Page 1
        Page 2
        Page 3
        Page 4
        Page 5
        Page 6
        Page 7
        Page 8
        Page 9
        Page 10
        Page 11
        Page 12
        Page 13
        Page 14
        Page 15
        Page 16
        Page 17
        Page 18
        Page 19
        Page 20
        Page 21
        Page 22
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











GULF COAST RESEARCH AND EDUCATION CENTER

g WATER MANAGEMENT SERIES











Institute of Food and Agricultural Sciences, University of Florida


GCREC Bradenton Research Report


December 1991


BRA-1991-26



Application Volumes and Wetting Patterns

for Scheduling Drip Irrigation

in Florida Vegetable Production

by

Gary A. Clark and Allen! G. Smajstrlia


fi







Application Volumes and Wetting Patterns


for Scheduling Drip Irrigation in Florida Vegetable Production


Gary A. Clark and Allen G. Smajstrlal



INTRODUCTION

Drip irrigation offers many advantages as a method of water
application. Water is applied to the root zone of the plant at
discrete locations through emitters which are either embedded
into, embossed onto, or attached directly to plastic tubing.
This water application method reduces the potential for foliar
diseases compared to overhead application systems and increases
water application efficiency. In addition, liquid fertilizer may
be injected and applied as needed to provide prescription water
and fertilizer applications in response to plant needs, even
under plastic mulch. Drip irrigation is particularly beneficial
on sandy soils which have low water-holding capacities and low
cation exchange capacities. However, without proper system
management, drip irrigation can waste water and nutrients or can
reduce yields.

Proper use of drip irrigation requires that system designers
and managers know the soil hydraulic characteristics, plant
growth and water use characteristics, and evaporative demand.
Irrigation schedules must be developed considering these factors
and must conform to existing irrigation system and cultural
constraints. Because excessive water applications leach plant
nutrients out of the crop root zone, the water management program
must be coordinated with the fertilizer management program. This
bulletin disscusses those aspects of drip irrigation scheduling
specifically related to the soil and drip tube characteristics
that affect water placement, distribution, and availablility to
the plant.


SOIL PROPERTIES


Soil properties play an important role in irrigation
scheduling and plant water management. As much as 30% to 40% of
the soil volume is pore space, which is filled with water at



1 Associate Professor of Agricultural Engineering, Extension
Irrigation Specialist, University of Florida, Gulf Coast Research
and Education Center, Bradenton, FL; and Professor of
Agricultural Engineering, University of Florida, Agricultural
Engineering Department, Gainesville, FL.







saturation. However, because a soil has a wide range of pore
sizes and water drains quickly from large pores, following
saturation drainage occurs to the "field capacity" (FC) level of
the soil. Plant extraction of water from the soil occurs until
the remaining water is held so tightly that it is unavailable to
the plant and the wilting point (WP) of the soil occurs.

The "available water-holding capacity" (AWHC) of the soil is
defined as the difference between WP and FC (see Fig. 1). Soil
water content for a typical Florida sandy soil may be 34%, 14%,
and 8% by volume for the saturation, field capacity, and wilting
point levels, respectively. The AWHC of this soil would be (14%
- 8%) 6% by volume. Available water-holding capacity in typical
Florida soils ranges from 3% to 8% in sands to 10% to 15% in
sandy loam and sandy clay loam soils. Soils with greater
proportions of clay, silt or organic matter will have even higher
water holding capacities.

The volume of water available to the crop depends on the
distribution of plant roots and the water holding characteristics
of the soil. Irrigations are generally scheduled when an
allowable fraction of the available water above WP has been
depleted so that potential crop stress is avoided. Typical
levels of allowable depletion may range from 30% of the available
water for sensitive crops to 70% for drought tolerant crops with
50% sometimes used as an average. Therefore, in the previous
example of available water, irrigations would be scheduled when
the water content of the soil drops to 10% to 12% rather than
allowing the water content to drop all the way to the wilting
point of 8%.

Drip irrigation systems deliver water from drip emitters in
slow drips at discrete locations along the irrigation tubing (see
Fig. 2). Drip emitters are located at regular intervals such as
8, 12, or 16 inches. Therefore, when drip irrigation tubes or
emitters are used, only portions of the field are wetted by the
irrigation system. Because drip irrigation relies on the soil
capillarity to convey water from the emitter location to the crop
root zone, short run times may apply the desired volume of water,
but the applied water may not be positioned in a location
available to the root system. This is common during the early
stages of plant development with immature root systems.
Therefore, during early crop development, irrigations must be run
long enough to ensure that the applied water is available to the
crop.

Soil capillarity is related to the size of the pore spaces
between the soil particles and is an important factor in water
movement from drip emitters. While large capillaries will
transmit water more rapidly than smaller capillaries, the smaller
capillaries will provide greater lateral distribution of water
from the emitter. Sandy soils have relatively large capillaries
in comparison to clay or loam soils.







Horizontal water distribution from point source drip
emitters is by soil capillarity while vertical movement is
influenced by both capillarity and gravity. Therefore, water
distribution from drip emitters is also affected by the
irrigation run time. In general, water and chemicals applied
through the irrigation system will be in greater concentrations
near the drip emitters. Figure 3 show an example of the
progression of the wetting front from a drip emitter located on a
sandy soil. After 20 min of run time, the wetting front had
progressed 4 inches from the drip emitter. Thus, as previously
discussed, sufficient run time may need to be scheduled in order
to move the applied water laterally into the root zone of
immature plant systems. After roots grow into the areas wetted
by the drip emitters, schedules can be adjusted accordingly.

Sandy soils generally have poor water distribution
characteristics with maximum lateral water distributions ranging
from 8 to 12 inches from the emitter. This will depend on how
long the system is operated and initial moisture conditions.
Pulsing the water application with a series of on/off cycles may
affect lateral movement of water on some soil types, but
generally not on very sandy soils. On heavy, fine textured (loam
or clay) soils, drip application rates may exceed the
infiltration rate of the soil, resulting in ponding or runoff of
applied water. In general, on sandy soils, closely spaced
emitters will result in greater uniformity of moisture
distribution within the soil profile. Individual soils should be
tested to determine their lateral wetting capabilities to aid in
selecting an emitter spacing and in irrigation scheduling. Field
instruments, such as tensiometers or other moisture measurement
devices, should be used to check actual soil wetting patterns and
water distributions from irrigation schedules.

Run time per irrigation cycle is also important. The total
run time required per day can be divided into 2 or 3 cycles per
day depending on the dripper, soil, plant, and irrigation system
constraints. Multiple, short duration cycles (e.g. 15 min/cycle)
will minimize deep percolation of applied water (Fig. 4A), but
may also confine the lateral distribution of water near the
dripper and may not be long enough for liquid fertilizer
injections. As dripper spacing increases, complete distribution
of applied water between drippers will be reduced (Fig. 4B)
unless greater run times are used (Fig. 4C), which could
potentially leach nutrients away from the plant root zone.


VOLUME OF AVAILABLE WATER

The volume of water available to a drip irrigated plant will
depend upon water distributions from the drip emitters, the soil
water-holding properties, and the size of the root zone. Water







distributions will be: 1) hemispheres for short duration run
times with wide spacings (Fig 5.); 2) vertical cylinders for long
run times with wide spacings (Fig. 6); 3) horizontal half-
cylinders for closely spaced emitters and short run times (Fig.
7); or 4) rectangular blocks for closely spaced emitters with
long run times (Fig. 8). Distribution patterns 1 and 2 would be
expected for widely spaced emitters or short run times per
irrigation. Each plant may have one or more emitters, but the
distribution patterns may not overlap. Patterns 3 and 4 would be
common for vegetable or other row crop drip systems with closely
spaced emitters.

The volume of available water that is stored in each of
these distribution patterns must be known by the irrigation
manager in order to develop irrigation schedules and to manage
the irrigation system throughout the crop production season.
Tables 1 through 4 provide the volume of available water for each
of these patterns based upon the dimensions of the wetted areas
and the available water-holding capacity of the soil.

For example, consider a vegetable drip irrigation system on
a sandy soil with an available water-holding capacity of 5% and
emitters spaced 24 inches apart. The system is operated to
irrigate no deeper than 12 inches and also provides 12 inches of
lateral wetting from the dripper providing a wetted pattern
similar to the hemispheres in Fig. 5. Using Table 1, the
available water in the wetted pattern would be 78 gallons per 100
drippers. If each p.ant was located next to a dripper, then each
plant would have about 0.78 gallons of water available from that
wetting pattern. If the system were operated for a longer period
of time such that the lateral wetting did not increase but the
wetted depth approached 2 feet, the distribution pattern may
approach the cylinder shape shown in Fig. 6. Using Table 2C, the
available water would become 235 gallons per 100 drippers or 2.35
gallons per plant.

Now assume that the emitter spacing is changed to 8 inches,
the wetted depth remains at 12 inches, and the wetting pattern
approaches the half cylinder shown in Fig. 7. Using Table 3, the
available water would be 59 gallons per 100 feet. If plants were
spaced 24 inches apart, a 100 ft length of bed would contain 50
plants, and each plant would have 1.18 gallons of available
water. It is important to remember that these examples assume
that the roots are distributed within the wetted soil volumes and
that the plant has full access to the applied water.


EVAPORATIVE DEMAND AND VOLUMETRIC WATER USE


Estimates of potential evapotranspiration obtained from
calculations using measured weather data, measured pan







evaporation, or from historical data bases is reported in units
of depth (inches) of water use over the irrigated area. This
unit is appropriate for scheduling irrigations with an overhead
irrigation system that also applies water in inches. However,
drip systems apply water in volume units such as gallons per 100
feet of row or gallons per plant. Therefore, it would also be
convenient to know the crop water requirements in gallons per
plant or per 100 feet of row. Tables 5 or 6 can be used to
convert from inches of crop water requirement or water
application depth to volume units. Table 5 converts from inches
of depth to gallons per 100 feet of plant row based upon plant
bed spacing. Table 6 converts from inches of depth to gallons
per 100 plants and is based upon the plant population in number
of plants per acre.

For example, from Table 5 a drip irrigated tomato crop on
beds spaced on 6 foot centers with a crop water use of 0.15
inches per day would require a volume (V) of water of 56 gal/100
feet of row per day. Thus, if the field had 50,000 ft of row,
then 28000 gallons of water would be required each day.

Drip systems are normally 80% to 90% efficient with the
actual efficiency dependent upon system design, operation, and
cultural arrangement. Therefore, it is important to remember
that additional water is required to compensate for losses due to
system inefficiency. If, in the above example, water was applied
daily at 85% efficiency, then [28000/0.85] 32,941 gallons should
be pumped each day.



DRIP TUBING DISCHARGE


Drip irrigation tubing discharges water from small emission
points or orifices. The water discharge rate is an important
consideration for scheduling and management purposes. In many
drip emitters, the water discharge varies with operating pressure
and tubing flow rates are provided as either gallons per hour
(gph) per emitter or gallons per minute, gpm per 100 feet of tube
length, at a certain operating pressure. Common discharge rates
range from 0.2 to 2.0 gph per emitter or from 0.3 to 0.5 gpm/100
feet of lateral.

Choice of emitter spacing should be based on plant spacing,
expected root distribution, and soil hydraulic characteristics.
For example, a 12 inch emitter spacing would be appropriate for
strawberry plants spaced 12 inches apart on a sandy soil. While
a wider spacing such as 16.or 18 inches may be used, irrigation
run times must be long enough to move water at least 9 inches
from the emitter for plants between emitters. The applied water
will move downward at least 9 inches which could be lower than







the effective root zone on young plants. This also may result in
leaching of plant nutrients at the emitter locations.

The tubing discharge per emitter can be converted to tubing
discharge per unit of length (ft) or per acre which is useful for
irrigation system design and scheduling purposes. The following
equation can be used to convert emitter discharge rates in
gallons per hour (gph) per emitter to gallons per minute (gpm)
per 100 feet of tubing length.


Qgpm(100) = (20)(Qem)/Se

Where Qgpm(100) = the tubing water discharge rate
(gpm per 100 feet of pipe),

Qem = the emitter water discharge rate
(gph/emitter), and

Se = the emitter spacing along the drip
tube (inches).



For example, a drip tube with an emitter discharge rate of 0.3
gph and an emitter spacing of 9 inches would have a corresponding
tubing discharge of '20 x 0.3)/9 = 0.67 gpm/100 ft.










SUMMARY


Scheduling of irrigations for drip irrigated crop production
in Florida is a dynamic process requiring constant attention.
Topics to consider include soil and plant characteristics,
evaporative demand and crop water requirements, scheduling
methods, drip tube characteristics, and irrigation system
characteristics. Proper irrigation scheduling must incorporate
the application characteristics of the system with the
requirements of the crop and the water holding characteristics of
the soil to achieve an operable and effective system. The steps
to follow are: (1) Determine the water requirements of the crop
in units which are consistent with drip irrigation such as
gallons/100 feet of lateral, gallons per acre, or gallons per
irrigated block; (2) Determine the water-holding characteristics
of the soil in the same units as the crop water requirements; (3)
Recognize the limitations of the crop root zone and of the water
application capabilities of the irrigation system; (4) Develop a
water budget to maintain soil water storage with the allowable
depletion level for the crop by considering the crop water
demands, the storage amounts, and rainfall; (5) Finally field
checks of soil moisture levels using tensiometers or other soil
moisture measurement devices should be used to adjust irrigation
schedules to conform to actual field conditions.








RELATED PUBLICATIONS


Clark, G. A., C. D. Stanley, and A. G. Smajstrla. 1988. Micro-
irrigation on mulched bed systems: Components, system capacities,
and management. Fla. Coop. Ext. Ser. Bul. 245, Univ. of Fla.,
Gainesville.

Jones, J. W., L. H. Allen, S. F. Shih, J. S. Rogers, L. C.
Hammond, A. G. Smajstrla, and J. D. Martsolf. 1984. Estimated and
measured evapotranspiration for Florida climate, crops, and
soils. Fla. Coop. Ext. Ser. Tech. Bul. 840, Univ. of Fla.,
Gainesville.

Pitts, D. J., D. Z. Haman, and A. G. Smajstrla. 1990. Causes and
prevention of emitter plugging in micro irrigation systems. Fla.
Coop. Ext. Ser. Bul. 258, Univ. of Fla., Gainesville.

Smajstrla, A. G., D. S. Harrison, and F. X. Duran. 1984.
Tensiometers for soil moisture measurement and irrigation
scheduling. Fla. Coop. Ext. Ser. Tech. Cir. 487, Univ. of Fla.,
Gainesville.

Smajstrla, A. G., B. J. Boman, G. A. Clark, D. Z. Haman, D. S.
Harrison, F. T; Izuno, and F. S. Zazueta. 1988. Efficiencies of
Florida agricultural irrigation systems. Fla. Coop. Ext. Ser.
Bul. 247, Univ. of Fia., Gainesville.

Smajstrla, A. G., B. J. Boman, G. A. Clark, D. Z. Haman, F. T.
Izuno, and F. S. Zazueta. 1988. Basic irrigation scheduling in
Florida. Fla. Coop. Ext. Ser. Bul. 249, Univ. of Fla.,
Gainesville.

Smajstrla, A. G., F. S. Zazueta, G. A. Clark, and D. J. Pitts.
1989. Irrigation scheduling with evaporation pans. Fla. Coop.
Ext. Ser. Bul. 254, Univ. of Fla., Gainesville.

Zazueta, F. S., A. G. Smajstrla, and D. Z. Haman. 1987.
Evapotranspiration estimation utilities. Fla. Coop. Ext. Ser.
Cir. 744, Computer Series, Univ. of Fla., Gainesville.







Figure 1.


Figure 2.


Figure 3.


Figure 4.




Figure 5.


Figure 6.


Figure 7.



Figure 8.


Water-holding capacity and available water example for
a typical Florida sandy soil.

Wetting patterns on a raised, vegetable production soil
bed using drip irrigation.

Wetting front characteristics from a single dripper on
a sandy soil.

Wetting patterns for different emitter spacings and run
times (A) close emitter spacing, short run time; (B)
wide emitter spacing, short run time; and (C) wide
emitter spacing, long run time.

Hemisphere water distribution pattern from individual
drip emitters operated for short run times.

Vertical cylinder water distribution patterns from
individual drip emitters operated for long run times.

Horizontal half-cyliner water distribution pattern from
closely spaced drip emitters or line-source drip tubing
operated for short run times.

Rectangular block water distribution pattern from
closely spaced drip emitters or line-source drip tubing
operated for long run times.








Table 1.


Volume of available water stored in the hemisphere
distribution pattern shown in Fig. 5 and based upon the
available water-holding capacity of the soil and the
wetted radius from the dripper (in gallons per 100
drippers).


Available Wetted Radius (inches)
Water (%) 3 6 9 12 15 18


Gallons of available water per 100 drippers

3 0.7 6 20 47 92 159
4 1.0 8 26 63 123 212
5 1.2 10 33 78 153 265
6 1.5 12 40 94 184 318
7 1.7 14 46 110 214 371
8 2.0 16 53 125 245 423
9 2.2 18 60 141 276 476
10 2.5 20 66 157 306 529
11 2.7 22 73 173 337 582
12 2.9 24 79 188 368 635
13 3.2 25 86 204 398 688
14 3.4 27 93 220 429 741
15 3.7 29 99 235 459 794








Table 2A.


Volume of available water stored in the cylindrical
distribution pattern of Fig. 6 and based upon the
available water-holding capacity of the soil, the
wetted radius from the dripper, and: A) a 1 foot depth
of wetting; B) a 1.5 foot depth of wetting; C) a 2 foot
depth of wetting; and D) a 3 foot depth of wetting (in
gallons per 100 drippers).


2A) 1 foot depth of wetting


Available Wetted Radius (inches)
Water (%) 6 9 12 15 18


Gallons of available water per 100 drippers

3 18 40 71 110 159
4 24 53 94 147 212
5 29 66 118 184 265
6 35 79 141 221 318
7 41 93 165 257 371
8 47 106 188 294 424
9 53 119 212 331 476
10 59 132 235 368 529
11 65 146 259 404 582
12 71 159 282 441 635
13 76 172 306 478 688
14 82 185 329 515 741
15 88 199 353 552 794








2B) 1.5 foot depth of wetting.


Available Wetted Radius (inches)
Water (%) 6 9 12 15 18


Gallons of available water per 100 drippers

3 26 60 106 166 238
4 35 79 141 221 318
5 44 99 177 276 397
6 53 119 212 331 477
7 62 139 247 386 556
8 71 159 283 442 636
9 79 179 318 497 715
10 88 199 353 552 795
11 97 219 389 607 874
12 106 238 424 662 954
13 115 258 459 718 1033
14 124 278 495 773 1113
15 132 298 530 828 1192



2C) 2 foot depth of wetting.



Available Wetted Radius (inches)
Water (%) 6 9 12 15 18


Gallons of available water per 100 drippers

3 35 79 141 221 318
4 47 106 188 294 424
5 59 132 235 368 529
6 71 159 282 441 635
7 82 185 329 515 741
8 94 212 376 588 847
9 106 238 424 662 953
10 118 265 471 735 1059
11 129 291 518 809 1165
12 141 318 565 882 1271
13 153 344 612 956 1377
14 165 371 659 1029 1482
15 176 397 706 1103 1588








2D) 3 foot depth of wetting.


Available Wetted Radius (inches)
Water (%) 6 9 12 15 18


Gallons of available water per 100 drippers

3 53 119 212 331 477
4 71 159 283 442 636
5 88 199 353 552 795
6 106 238 424 662 954
7 124 278 495 773 1113
8 141 318 565 883 1272
9 159 358 636 994 1431
10 177 397 707 1104 1590
11 194 437 777 1214 1749
12 212 477 848 1325 1908
13 230 517 919 1435 2067
14 247 556 989 1546 2226
15 265 596 1060 1656 2385








Table 3. Volume of available water stored in the half cylinder
distribution pattern shown in Fig. 7 and based upon the
available water-holding capacity of the soil and the
wetted radius from the dripper (in gallons per 100 feet
of row length).



Available Wetted Radius (inches)
Water (%) 3 6 9 12 15 18


Gallons of available water per 100 feet of length


35
47
59
71
82
94
106
118
129
141
153
165
176


55
74
92
110
129
147
165
184
202
221
239
257
276


79
106
132
159
185
212
238
265
291
318
344
371
397







Table 4A. Volume of available water stored in the rectangular
distribution pattern shown in Fig. 8 and based upon the
available water-holding capacity of the soil, the
wetted radius from the dripper, and: A) a 1 foot depth
of wetting; B) a 1.5 foot depth of wetting; C) a 2 foot
depth of wetting; and D) a 3 foot depth of wetting (in
gallons per 100 feet of row length).

4A) 1 foot depth of wetting



Available Wetted Radius (inches)
Water (%) 6 9 12 15 18


Gallons of available water per 100 feet of length

3 22 34 45 56 67
4 30 45 60 75 90
5 37 56 75 94 112
6 45 67 90 112 135
7 52 79 105 131 157
8 60 90 120 150 180
9 67 101 135 168 202
10 75 112 150 187 225
11 82 124 165 206 247
12 90 135 180 225 270
13 97 146 195 243 292
14 105 157 210 262 314
15 112 168 225 281 337








4B) 1.5 foot depth of wetting


Available Wetted Radius (inches)
Water (%) 6 9 12 15 18


Gallons of available water per 100 feet of length


34
45
56
67
79
90
101
112
124
135
146
157
168


51
67
84
101
118
135
152
168
185
202
219
236
253


67
90
112
135
157
180
202
225
247
270
292
314
337


84
112
140
168
197
225
253
281
309
337
365
393
421


101
135
168
202
236
270
303
337
371
404
438
472
505


4C) 2 foot depth of wetting


Available Wetted Radius (inches)
Water (%) 6 9 12 15 18


Gallons of available water per 100 feet of length


45
60
75
90
105
120
135
150
165
180
195
210
225


67
90
112
135
157
180
202
225
247
270
292
314
337


90
120
150
180
210
240
270
300
329
359
389
419
449


112
150
187
225
262
300
337
374
412
449
487
524
562


135
180
225
270
314
359
404
449
494
539
584
629
674








4D) 3 foot depth of wetting


Available Wetted Radius (inches)
Water (%) 6 9 12 15 18


Gallons of available water per 100 feet of length


67
90
112
135
157
180
202
225
247
270
292
314
337


101
135
168
202
236
270
303
337
371
404
438
472
505


135
180
225
270
314
359
404
449
494
539
584
629
674


168
225
281
337
393
449
505
562
618
674
730
786
842


202
270
337
404
472
539
607
674
741
809
876
943
1011








Table 5. Conversion from depth of crop water use or application
to volume in gallons per 100 feet of bed length for
different plant bed spacings.


Bed Spacing Crop Water Use or Application Depth
(feet) (inches)
0.05 0.10 0.15 0.20 0.25 0.30


(Gallons per 100 feet of bed length)

3 9 19 28 37 47 56
4 13 25 37 50 62 75
5 16 31 47 62 78 93
6 19 37 56 74 93 112
7 22 44 65 87 109 131
8 25 50 75 100 125 150
9 28 56 84 112 140 168
10 31 62 93 125 156 187


Table 6.


Conversion from depth of crop water use or application
to volume in gallons per 100 plants for different plant
population levels in number of plants per acre.


Plant Crop Water Use or Application Depth
Population (inches)
(No./acre) 0.05 0.10 0.15 0.20 0.25 0.30


(Gallons per 100 plants)

100 1358 2715 4073 5430 6788 8146
150 905 1810 2715 3620 4525 5430
200 679 1358 2036 2715 3394 4073
300 453 905 1358 1810 2263 2715
400 339 679 1018 1358 1697 2036
600 226 453 679 905 1131 1358
800 170 339 509 679 849 1018
1000 136 272 407 543 679 815
1500 91 181 272 362 453 543
2000 68 136 204 272 339 407
3000 45 91 136 181 226 272
4000 34 68 102 136 170 204
5000 27 54 81 109 136 163






WATER HOLDING CAPACITY

AND AVAILABLE WATER




"Sandy Soil"
Dry Saturated
Soil WP FC Soil


I-
Pore 0%
Volume 1B
Unavailable
Water


Available
Water (AW)


-I I---
8% 14%
SAvailable
Water


= FC WP


AW = 14% 8%

AW = 6%

AW = 0.72 in/ft



Figure 1. Water-holding capacity and available water example for
a typical Florida sandy soil.


Figure 2. Wetting patterns on a raised, vegetable production soil
bed using drip irrigation.


--I
34%
Drainage
Occurs


I


I


'''
i. -,~
,. .:~











DRIPPER


12 In 8 in 4 in 4 in 8 In 12 in i


4 i ---------- -- ----.-- ----
20 min
8 in --- --------- ----- -------- ---------- --
40 min
12 in --- ----- -""- ----------- ---------

WETTING FRONT 60 min






Figure 3. Wetting front characteristics from a single dripper on
a sandy soil.




Row Direction --- -

A Close spacing; Short run time
Dripper



Wetted Perimeter
B Distant spacing; Short run time





C Distant spacing; Long run time








Figure 4. Wetting patterns for different emitter spacings and run
times (A) close emitter spacing, short run time; (B)
wide emitter spacing, short run time; and (C) wide
emitter spacing, long run time.



















Figure 5. Hemisphere water distribution pattern from individual
drip emitters operated for short run times.


Wetted
Radius


Depth

4


Figure 6. Vertical cylinder water distribution patterns from
individual drip emitters operated for long run times.


C~I





























Figure 7. Horizontal half-cyliner water distribution pattern from
closely spaced drip emitters or line-source drip tubing
operated for short run times.


Raised Soil Bed


i.


Figure 8. Rectangular block water distribution pattern from
closely spaced drip emitters or line-source drip tubing
operated for long run times.




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