• TABLE OF CONTENTS
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 Historic note
 Introduction
 Cultural considerations
 Irrigation system components
 System management
 Summary
 Example problems
 Calculations
 References and related publica...














Group Title: Bulletin - University of Florida. Florida Cooperative Extension Service ; no. 245
Title: Microirrigation on mulched bed systems
CITATION THUMBNAILS PAGE IMAGE ZOOMABLE
Full Citation
STANDARD VIEW MARC VIEW
Permanent Link: http://ufdc.ufl.edu/UF00026133/00001
 Material Information
Title: Microirrigation on mulched bed systems components, system capacities, and management
Series Title: Bulletin
Physical Description: 12 p. : ill. ; 28 cm.
Language: English
Creator: Clark, Gary A
Stanley, Craig D
Smajstrla, A. G ( Allen George )
Florida Cooperative Extension Service
Publisher: Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Gainesville
Publication Date: [1993]
Edition: Rev.
 Subjects
Subject: Microirrigation -- Florida   ( lcsh )
Irrigation -- Florida   ( lcsh )
Irrigation engineering   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
bibliography   ( marcgt )
non-fiction   ( marcgt )
 Notes
Bibliography: Includes bibliographical references (p. 11-12).
Statement of Responsibility: Gary A. Clark, Craig D. Stanley, and Allen G. Smajstrla.
General Note: Title from caption.
General Note: "March 1993. First published: March 1988. Revised December 1992."
Funding: Bulletin (Florida Cooperative Extension Service)
 Record Information
Bibliographic ID: UF00026133
Volume ID: VID00001
Source Institution: University of Florida
Rights Management: All rights reserved by the source institution and holding location.
Resource Identifier: aleph - 001820106
oclc - 28154033
notis - AJP4093
 Related Items
Other version: Alternate version (PALMM)
PALMM Version

Table of Contents
    Historic note
        Historic note
    Introduction
        Page 1
    Cultural considerations
        Page 2
    Irrigation system components
        Page 2
        Page 3
        Page 4
        Page 5
    System management
        Page 6
        Page 7
    Summary
        Page 8
    Example problems
        Page 8
        Page 9
    Calculations
        Page 10
    References and related publications
        Page 11
        Page 12
Full Text





HISTORIC NOTE


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

site maintained by the Florida
Cooperative Extension Service.






Copyright 2005, Board of Trustees, University
of Florida







UNIVERSITY OF

S FLORIDA


Bulletin 245
March 1993


Florida Cooperative Extension Service


Microirrigation On Mulched Bed Systems: Components,
System Capacities, And Management'
Gary A. Clark, Craig D. Stanley, and Allen G. Smajstrla2


Microirrigation involves the slow application of
water on, above, or below the soil surface. This
encompasses trickle irrigation including drip, line
source, bubbler, and micro-spray irrigation systems.
Water may be applied in drops, small streams, or
sprays at discrete locations or continuously along the
irrigation tube lateral. Placement of the lateral and
proper scheduling can allow precise application of
water to the active root system of a crop. Therefore
nutrient leaching and deep percolation can be
minimized to increase efficiencies in applying water
and chemical products through the system.

Vegetable production in southwest Florida
typically utilizes plastic mulch on raised beds. The
beds typically are from 6- to 10-inches in height and
24- to 36-inches in width (see Figure 1). The plastic
mulch serves to retain injected fumigants and
nutrients, minimize weed growth, maintain bed shape,
and keeps the lower fruit away from the sandy soil.
This type of bedding practice allows easy adaptation
to microirrigation systems which utilize line-source or
drip-type irrigation laterals. Drip irrigation laterals
can be installed at the same time as the plastic mulch
by modifying the mulch-laying implement to hold a
reel of tubing. Laterals are placed directly under the
mulch. Some tubing manufacturers recommend
burying the tube 1- to 2-inches below the soil surface.
The adjustment to current cultural practices can be
minimal.


Common irrigation practices for vegetable
production in southwest Florida utilize a seepage type
of subirrigation which may or may not be coupled
with a microirrigation system. Most of the soils have
a semi-impermeable spodic layer 18- to 36- inches
below the soil surface. Water is conveyed by open
ditch or pipe to lateral ditches and pumped
continuously, except during rainfall, to maintain a
water table 18- to 24-inches below the soil surface.
Figure 2 shows some bed/ditch arrangements and
typical spacings. Arrangements may range from one
bed between ditches to seven beds between ditches.

Because ditches are used for drainage in addition
to irrigation, the particular bed/ditch combination
required depends on the drainage characteristics of
the soil as well as the infiltration characteristics.
While microirrigation can eliminate the need for
irrigation ditches, some provision for drainage will
still be necessary and bed/ditch combinations may still
be used, depending on drainage requirements. This
publication will discuss the components and capacities
of microirrigation systems for mulched bed systems.


1. This document is Bulletin 245, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.
Publication date: March 1993. First published: March 1988. Revised: December 1992.
2. Gary A. Clark, Associate Professor, Agricultural Engineering and Craig D. Stanley, Associate Professor, Soil Science, Gulf Coast Research and
Education Center, IFAS, 5007-60th Street East, Bradenton, FL, 34203; and Professor, Agricultural Engineering Department; Cooperative
Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville.
The Institute of Food and Agricultural Sciences is an equal opportunity/affirmative action employer authorized to provide research,
educational information and other services only to individuals and institutions that function without regard to race, color, sex, age, handicap,
or national origin. For information on obtaining other extension publications, contact your county Cooperative Extension Service office.
Florida Cooperative Extension Service / Institute of Food and Agricultural Sciences / University of Florida / John T. Woeste, Dean







Microirrigation On Mulched Bed Systems


BED SPACING


DITCH SPACING
BED SPACING
(B) -C PCING






S DITCH SPACING

Figure 2. Bed/ditch cross-sections for (A) single-, (B)
double-, and (C) four-bed arrangements.


CULTURAL CONSIDERATIONS

Because the bed/ditch arrangements can vary as
shown in Figure 2, the linear bed feet of production
per gross acre will vary with each bed/ditch cultural
practice. Therefore it becomes necessary to discuss
production and management practices in terms of
bedded-feet (Bf) or bedded-feet per acre (BfAc).
Table 1 can be used to determine the number of
BfAc in a field based on the ditch spacing and the
number of beds per ditch. The total number of Bf
can be obtained by multiplying BfAc by the number of
gross acres.

The BfAc index can be useful for many
applications such as microirrigation tubing cost per
acre, or for converting fertilizer applications from a
per acre basis to per bed foot or per 100 bed feet.
For example, consider a sixty-acre field farmed on 26
ft ditch centers with 3 beds per ditch. The BfAc from
Table 1 is 5026 ft per acre, therefore the total Bf for
60 acres is 301,560 feet. If a drip lateral which costs
2 cents per foot is used, then the total lateral cost
would be equal to 301,560 ft $0.02/ft or $6,031.
This is a per acre cost of about $100.

IRRIGATION SYSTEM COMPONENTS

The general components of a drip-type
microirrigation system for mulched bed vegetable
production is shown in Figure 3. The basic
components include a pump and motor, a filtration
system, the distribution pipe (i.e. PVC mains,
submains, and manifolds), the drip- or seep-type of
Iot
a4S


lateral pipelines, control valves, pressure regulators,
flow meters, and pressure gauges. Flush valves at the
end of each drip lateral are not necessary but are
recommended to reduce the potential for clogging. If
fertilizers are to be injected then, fertilizer reservoirs,
injection system, and proper backflow prevention
systems are required (see IFAS Extension Bulletin
217, Smajstrla et al., 1991). Automation can be
achieved by adding an irrigation controller and
automatic (solenoid or hydraulic) valves. This can
reduce the labor requirements and possibly increase
the system efficiency. Additional design information
can be found in Howell et al. (1980); Nakayama and
Bucks (1986); Smajstrla (1985); and Smajstrla and
Zazueta (1985).

Pumps And Pumping Requirements

The type of pump required (whether centrifugal
or turbine) depends upon location of the water
source. Centrifugal pumps can be used with surface
water supplies and shallow groundwater supplies (less
than 15 to 20 feet deep). Turbine pumps are used in
deeper wells. These may be submersible with an
electric motor connected directly to the pump in the
well or they may be shaft driven with the power unit
on the ground surface.

Power units may be electrically driven or may use
gasoline, diesel, or natural gas internal combustion
engines. The choice of power unit will depend on
several factors. Pump location will determine if
electrical power is available. Submersible turbine
pumps are run solely by electrical power. Electrical
systems are very adaptable to automatic controllers
and require less maintenance than internal
combustible engines. However these systems are
susceptible to power failures which can happen when
freeze protection is necessary. Therefore internal
combustion engines may become necessary for these
specialty purposes.

The operating pressure of the pump will depend
on the design operating pressure of the drip tube
laterals, the total friction losses in the system (pipe,
filters, valves, meters, regulators, etc.), and the
elevation of the water source with respect to the
irrigation system. If the total irrigation system is to
be divided and operated as several subsystems, then
pressure requirements of the most critical subsystem
should be used to determine the maximum system
pressure. The critical subsystem is defined as the one
which has the greatest flow and/or pressure


Page 2







Microirrigation On Mulched Bed Systems


BED SPACING


DITCH SPACING
BED SPACING
(B) -C PCING






S DITCH SPACING

Figure 2. Bed/ditch cross-sections for (A) single-, (B)
double-, and (C) four-bed arrangements.


CULTURAL CONSIDERATIONS

Because the bed/ditch arrangements can vary as
shown in Figure 2, the linear bed feet of production
per gross acre will vary with each bed/ditch cultural
practice. Therefore it becomes necessary to discuss
production and management practices in terms of
bedded-feet (Bf) or bedded-feet per acre (BfAc).
Table 1 can be used to determine the number of
BfAc in a field based on the ditch spacing and the
number of beds per ditch. The total number of Bf
can be obtained by multiplying BfAc by the number of
gross acres.

The BfAc index can be useful for many
applications such as microirrigation tubing cost per
acre, or for converting fertilizer applications from a
per acre basis to per bed foot or per 100 bed feet.
For example, consider a sixty-acre field farmed on 26
ft ditch centers with 3 beds per ditch. The BfAc from
Table 1 is 5026 ft per acre, therefore the total Bf for
60 acres is 301,560 feet. If a drip lateral which costs
2 cents per foot is used, then the total lateral cost
would be equal to 301,560 ft $0.02/ft or $6,031.
This is a per acre cost of about $100.

IRRIGATION SYSTEM COMPONENTS

The general components of a drip-type
microirrigation system for mulched bed vegetable
production is shown in Figure 3. The basic
components include a pump and motor, a filtration
system, the distribution pipe (i.e. PVC mains,
submains, and manifolds), the drip- or seep-type of
Iot
a4S


lateral pipelines, control valves, pressure regulators,
flow meters, and pressure gauges. Flush valves at the
end of each drip lateral are not necessary but are
recommended to reduce the potential for clogging. If
fertilizers are to be injected then, fertilizer reservoirs,
injection system, and proper backflow prevention
systems are required (see IFAS Extension Bulletin
217, Smajstrla et al., 1991). Automation can be
achieved by adding an irrigation controller and
automatic (solenoid or hydraulic) valves. This can
reduce the labor requirements and possibly increase
the system efficiency. Additional design information
can be found in Howell et al. (1980); Nakayama and
Bucks (1986); Smajstrla (1985); and Smajstrla and
Zazueta (1985).

Pumps And Pumping Requirements

The type of pump required (whether centrifugal
or turbine) depends upon location of the water
source. Centrifugal pumps can be used with surface
water supplies and shallow groundwater supplies (less
than 15 to 20 feet deep). Turbine pumps are used in
deeper wells. These may be submersible with an
electric motor connected directly to the pump in the
well or they may be shaft driven with the power unit
on the ground surface.

Power units may be electrically driven or may use
gasoline, diesel, or natural gas internal combustion
engines. The choice of power unit will depend on
several factors. Pump location will determine if
electrical power is available. Submersible turbine
pumps are run solely by electrical power. Electrical
systems are very adaptable to automatic controllers
and require less maintenance than internal
combustible engines. However these systems are
susceptible to power failures which can happen when
freeze protection is necessary. Therefore internal
combustion engines may become necessary for these
specialty purposes.

The operating pressure of the pump will depend
on the design operating pressure of the drip tube
laterals, the total friction losses in the system (pipe,
filters, valves, meters, regulators, etc.), and the
elevation of the water source with respect to the
irrigation system. If the total irrigation system is to
be divided and operated as several subsystems, then
pressure requirements of the most critical subsystem
should be used to determine the maximum system
pressure. The critical subsystem is defined as the one
which has the greatest flow and/or pressure


Page 2






Microirrigation On Mulched Bed Systems


Table 1. Bed-feet per acre (BfAc) based on ditch spacing and the number of beds per ditch.
Ditch Number of beds per ditch
Spacing --------- ----------------------- -------
(feet) 1 2 3 4 5 6 7
3 14520 -- -
4 10890 -
5 8712 .. -
6 7260 -- -
8 5445 -- ---
10 4356 8712 -
12 3630 7260 -
14 3111 6223 9334 -- -
16 -- 5445 8168 -
18 4840 7260 9680 --- -
20 --- 4356 6534 8712 -- -
22 ---- 5940 7920 9900 -
24 -- -- 5445 7260 9075 -
26 ---- -- 5026 6702 8377 10052 --
28 --- --- -- 6223 7779 9334 ....
30 ---- ---- --- 5808 7260 8712 10164
32 -- ---- ---- 5445 6806 8168 9529
34 .- ---- --- --- 6406 7687 8968
36 --- -- --- 6050 7260 8470
38 --- -- 5732 6879 8024
40 6534 7623
If the field does not contain ditches then substitute the bed spacing for ditch spacing and use the 1 bed per ditch
column to determine the bed-feet per acre.


requirements. This information should be determined
by a qualified irrigation system designer.

The previously described BfAc index can be used
in determining irrigation pump requirements.
Microirrigation drip tubes vary in design with respect
to orifice size and spacing of the orifices.
Furthermore the orifice discharge rate will vary with
operating pressure. Even pressure compensating
emitters will have some variation. Therefore it is
common to refer to drip tube discharges as flow rate
per unit length such as gallons per minute (gpm) per
100 feet of pipe. If the drip tube discharge is
provided in terms of gpm per emitter, the following
formula can be used to obtain gpm per 100 feet.

Qgpm(100) = (Qem*100)/Se (1)

Where


Qgpm(lO0)

Qem
Se


= drip tube flow rate (gpm per 100
feet of pipe),
= emitter discharge (gpm), and
= emitter spacing (feet).


If the emitter discharge is provided in terms of
gallons per hour (GPH), then use the following
formula.


Qgpm(100)-((Qeh6O)*100)/Se


where Qgpm(100) and Se are as previously defined,
and Qeh is the emitter discharge in gallons per hour.

Pump sizing requires a knowledge of the total flow
rate (gpm) that will be pumped at any one time.
Table 2 provides the flow per acre (gpm/acre) for
different combinations of BfAc and drip tube
discharge rate. The total flow necessary for pumping
would be obtained by multiplying the gpm/acre value
from Table 2 by the total number of acres irrigated at


Page 3






Microirrigation On Mulched Bed Systems


Figure 3. Layout of a basic microirrigatiin system.
any one time. For example, if, culturall practices
n,,niL.d of 7000 cbd fk l per acre and a drip line
which provided 0.50 gpm rcpr 10l feet at the system
operating pressure was used, ihcn trh, system would
require 35 pm'n1-t.r: If-.the; irri tiirn s,, inl was
designed to irrigate in 20 acre. blocks, then a. pump
capacity of (20 ae 35 gpmr '.at ?7 '7 .pnlm would be
required.

Filtration

Someo" "rmi l' filtration i,: riecessary with all
microirrigation y.rtem .. PaFriculk tc matter suspended
in thek wti'dr ir"may clog the-tin) orifices -o these
systems. Th& type cI filtr.tir'ln sy tc.m will depend on
the quality and type of water supply (surface or
ground artcr I n well .r. bon the type oFreemitter system
used The csl/oi r the cmiii r brifiee: ai~'flow"Ahi
vary with respect to the manufacturer. Thcr'rd'lr,
some emitters can pass larger particles than others.
The emitter and/oir drip tubing m:inu(.litur~rr's
recommendations for filtration should be followed.
This will gencrAll) be stated iriterms of'a'mesh size
iCich as 200 mesh.

If the water source is a surf.ice supply then media
(~ 'nd) filters should be usidLi to' ri"mme organic
matter such' as algae. Because sand and-: oher
particulates mniaI p.iSS through he media filTir,'ihi-.
stem Thould be f I''ll>o'ed niIh 'a' screen or grooved
disk type offfilt e.. When ground, aler (i.e. pumped
froi~itwells) is used ia ihe water source, -a screen or


grooved disk IlLr system may be adequate. If sand
is being puniped from the well, then a vortex-type
sand separator may be installed in-line before tihe
screen or disk filter. A more-detailed -appraisal-of
filtFation syrstem&s'is--presented b H.mann L al. (1'
and. 1988)

Because pressure is-lost .cr 's the filtcrs, this lbs.
needs to be included in the systemi design. The
manufacturer of the filtration system will supply this
information in their specifications. Because the filters
atr designa8 '6 toll'ccl 'pariiulkies this ss will
increase as the filter begins t ftlog.: Prcssure 'guges
placed on either side of the filtration system can be
used to indlo.tic % hen .leaning is hccc-ssar). Periodic
faniiing will remidV the accumul..ited materials kiid
Sniniminie the associated pressure loss. This dlehning
or flushing may be d6ne manually or automatically.

Flow Meters

All irrigation sitenm should-be equipped,'ithflow
meterss for proper mann:igemtlnt cf the system. Meters
may be rate or volume iidicating-or a combination.
Rates may be obtained firm a vol-ume indicating
mefer by'moni-tbing thevoluine of w ler passed in a
given time period nm.is\ur:d with top, ip\lah Flow
meters may be placed at the pump, at the inlet of
each subsystem, or both. Knowledge of the flow of
the system will allow the irrigation manager td apply
precise volumes of irrigation water and to document
water use for monitoring system consistencies.


Page -4






Microirrigation On Mulched Bed Systems


Table 2. Discharge per gross acre (gpm/acre) based on irrigated bed feet and emitter discharge.

Bed Feet Emitter Discharge (gpm/100 feet)
Per Acre
(BfAc) 0.25 0.30 0.40 0.50 0.75 1.00 1.50
3000 8 9 12 15 23 30 45
3500 9 11 14 18 26 35 53
4000 10 12 16 20 30 40 60
4500 11 14 18 23 34 45 68
5000 13 15 20 25 38 50 75
5500 14 17 22 28 41 55 83
6000 15 18 24 30 45 60 90
6500 16 20 26 33 49 65 98
7000 18 21 28 35 53 70 105
7500 19 23 30 38 56 75 113
8000 20 24 32 40 60 80 120
8500 21 26 34 43 64 85 128
9000 23 27 36 45 68 90 135
9500 24 28 38 48 71 95 143
10000 25 30 40 50 75 100 150
10500 26 31 42 53 79 105 158
11000 28 33 44 55 83 110 165


Furthermore, flow meters coupled with pressure
gauges can be used to monitor the pumping efficiency
as well as line breaks or emitter clogging. If chemical
injection is used, a knowledge of the flow is necessary
for maintaining specific chemical concentration levels
in the water.

Chemical Injection

Because microirrigation systems apply water within
or in close proximity to the root zone of a crop, these
systems are well suited for injection of fertilizers.
Injection equipment is necessary to adapt the
irrigation system for fertigation and a large reservoir
(500 to 1500 gal. capacity) is needed to store the
liquid fertilizer. One type of system utilizes a smaller
reservoir with sufficient size to hold the prescribed
volume of liquid fertilizer for each irrigation cycle. In
this case the larger reservoir is used only as a bulk
storage facility. The chemical (fertilizer) may be
added to the irrigation water by using an adjustable
metering pump or some other injection device such as
a venturi. The injection system may be controlled
manually or automatically. Electronic monitoring of
the injection rate or volume can be combined with
programming of valves or injectors to be shut off after
a prescribed injection volume. It is important to note
that the uniformity of chemical application cannot
exceed the uniformity of water application from the


irrigation system. Therefore, this may be a factor in
determining whether chemigation is practical for a
given system. Additional information may be
obtained from Smajstrla et al. (1986a and 1986b).

Florida law requires that backflow prevention
systems be used on irrigation systems which have
chemical injection systems installed. The level of
prevention will depend on the toxicity of the
chemicals involved. Backflow prevention
requirements, variances, and systems are discussed in
IFAS Bulletin 217 (Smajstrla, et al., 1991). In
addition, county and city ordinances should be
investigated. These local ordinances may be more
stringent than State law requirements.

Pressure Gauges And Regulators

Pressure gauges are necessary to monitor the
system operating characteristics. Decreases or
increases in the system pressure can indicate broken
lines or pipe blockages, respectively. As was
previously discussed, pressure gauges can be used
with filtration systems to indicate clogging of the filter
material.

Regulators are normally required if operating
conditions change from one subset to another, or if
different combinations of subsets will be operated


Page 5






Microirrigation On Mulched Bed Systems


simultaneously. Under these conditions, system
operating characteristics such as the pumping water
level or the number of emitters per irrigation subset
vary. Pressure regulators can be used to provide
constant pressures to the irrigation system, a subset,
an individual lateral line, or any combination of
positions. Location and the number of regulators will
depend on the desired level of system control.

Pipelines

Mainline, submain pipes, and manifolds (see
Figure 3) convey water from the pump to the lateral
line inlets. These pipes may be aluminum, steel, PE,
or PVC. Because plastic pipe is economical, relatively
easy to install, and is noncorrosive to most chemicals
which would be injected into the system, it is the most
common pipe used in permanent systems. If PVC
pipe is used it must be buried or protected from the
sun.

Lateral lines may be a perforated tubing or a solid
tubing with regularly spaced emitters. The spacing of
perforations or emitters can vary from one or two
inches to a couple of feet or more. The spacing
required for a specific application depends on the
ability of water to move laterally away from the
emitter as well as the length of the lateral. Lateral
movement in sands may be in the range of 6- to 12-
inches, whereas lateral movement in heavier loamy or
clayey type soils may be greater than 30-inches.
Greater flow rates are associated with a greater
number of emitters or perforations and will therefore
require shorter lengths of run. Smaller emitter
spacings make the cosequence of random clogging
less severe. Adjacent emitters can provide water to
the area influenced by a clogged emitter if the
distances are not too great. When fertilizers are
injected into the system, smaller emitter spacings
reduce the necessity of nutrients to move larger
distances within the soil.

Flow discharges may be provided in terms of
gallons per hour (gph) per emitter or as a flow per
unit of pipe length, such as gpm per 100 feet or gph
per 100 feet of pipe. Emitter discharge will vary with
operating pressure unless the emitter has pressure
compensating characteristics. Even with pressure
compensation some flow variation will exist.
Therefore pressure regulation and properly designed
mains, submains, manifolds, and laterals are crucial to
the success and uniformity of the system.


Irrigation Controllers

Irrigation systems may be operated by manual,
semi- automatic, or fully automatic methods.
Automation requires a controller of some type. A
simple controller may be used to start and stop a
pump. The level of controller sophistication can
increase by adding options such as valve control
(opening and closing), or chemical injection control.
This may be performed with a clock-type controller or
electronic-type controllers which require programming
and are basically field computers. Costs can range
from less than a hundred dollars to several thousand
dollars. Price will depend on the desired level of
sophistication as well as the number of stations that
can be controlled.

SYSTEM MANAGEMENT

Irrigation Scheduling

Irrigation scheduling involves determining when to
irrigate and how much water to apply. Both of these
decisions will depend on the desired soil moisture
management level, the crop water demand or
evapotranspiration (ET) rate, the water supply in the
root zone available for ET, the water holding
characteristics of the soil,and the system efficiency.
Atmospheric as well as soil condition vary with
geographic location. Therefore variations will exist
between scheduling programs.

Most of the soils in Florida are sandy and have low
water holding capacities (WHC) and low cation
exchange capacities (CEC, the ability of the soil to
hold and exchange nutrients). Because vegetable
crops have shallow root zones, frequent irrigations are
necessary with these soil conditions and nutrients can
easily be leached out of the root zone. Therefore
proper scheduling is very important to good system
management.

One of the first steps in scheduling is to determine
the water storage capacity of the soil. The volume of
water stored by this "reservoir" will depend on the
water holding capacity of the soil, the size of effective
root zone of the crop, and the lateral wetting
distribution of the trickle emitter. The water holding
capacity of the soil refers to the amount of water that
can be held by the soil with only negligable drainage
occurring. This is analogous to the field capacity of
the soil and is expressed as a percent or fraction of
the soil volume. Smajstrla et al. (1985a) provide an


Page 6







Microirrigation On Mulched Bed Systems


extensive listing of textural, conductivity, and available
water capacities of Florida soils.

Table 3 can be used to determine the irrigated soil
volume per 100 linear bed feet of production. The
wetted width represents the lateral distribution of
water from the trickle tube, and the effective root
zone represents the desired depth of irrigation. This
latter parameter will vary with the crop and stage of
production.

Table 3. Soil volume (cubic feet) irrigated per 100
linear bed feet.
Wetted Effective Root Zone
Width (depth to be irrigated, feet)
(feet)
(feet)-------------- ------------ -
0.5 1.0 1.5 2.0 2.5 3.0
.5 25 50 75 100 125 150
1.0 50 100 150 200 250 300
1.5 75 150 225 300 375 450
2.0 100 200 300 400 500 600
2.5 125 250 375 500 625 750
3.0 150 300 450 600 750 900


After determining the irrigated volume of soil,
Tables 4, 5, and 6 can be used to determine the
volume of water required for irrigation. All of the
tables assume a 90% irrigation application efficiency.
Irrigations may be scheduled after only a certain
fraction of the available water in the root zone has
been depleted. Irrigations must never be delayed
until all available water has been depleted, because
this will cause the crop to go into water stress and
reduce yields. Therefore Tables 4, 5, and 6 have been
compiled based on allowable depletions of 1/3, 1/2,
and 2/3 of the available water for crop use. Vegetable
crops are typically irrigated at 1/3 to 1/2 depletion of
available water. By knowing the wetted soil volume
from Table 3 and the soil water-holding capacity, the
volume of water to apply per 100 linear feet of
production can be determined. Most of the sandy
soils of Florida have available water holding capacities
of 4 to 8 percent, however, higher and lower values
exist.

The length of time for the irrigation system to
operate will depend on the volume of water to be
applied and the rate at which it is applied. Table 7
can be used to determine the irrigation application
time. This table provides application times based on
the volume of water to apply (gallons per 100 feet of
bed) and the emitter tubing discharge characteristics


(gpm per 100 feet of tubing). If, for example, a
particular irrigation requires a volume of 60 gallons
per 100 linear bed feet and the microirrigation tubing
discharges 0.4 gpm per 100 linear feet, then 2.5 houts
is required to apply this amount of water. This
irrigation cycle may be scheduled within a single 2.5
hour block or may be divided into two or more
shorter duration periods which would add up to the
required 2.5 hours. The latter management practice
provides some time for soil water redistribution and
extraction, and it will probably reduce deep
percolation with higher flow emitters on very sandy
soils.

Field experience, visual observations, and soil
water monitoring can be used with the
aforementioned procedure to provide an efficient and
effective irrigation management program. A similar
discussion directed toward microirrigation scheduling
of orchard crops (citrus) is given by Smajstrla et al.
(1985b).

Irrigation System Maintenance

All irrigation systems require routine maintenance
in order to continuously provide efficient operation.
A maintenance schedule should include inspection of
the mechanical components as well as the irrigation
lines.

The pump and power unit should be monitored to
insure efficient operation. This can be done by
keeping records of performance and maintenance
actions. Flow rate and pressure delivered by the
pump as well as the energy consumption of the power
unit should be recorded frequently. Records should
be maintained on at least a bi-weekly or monthly
basis. Large deviations from the normal operating
characteristics should be checked by a repair
specialist. Routine maintenance can consist of: (a)
check and lubricate all grease fittings, bearings, and
oil reservoirs; (b) check for excessive noise, vibration,
or leakage and make necessary adjustments; (c)
inspect all electrical connections and check for frayed
wires; and (d) maintain a clean facility. The above list
is not complete but contains items which should be
performed on a regular basis.

Filtration equipment should be continuously
monitored for clogging and cleaned as necessary.
Seals, gaskets, and fittings should be checked for leaks
and adjusted. Control valves and pressure regulators
should be checked for proper operation and flow.
Lubrication may be necessary. Wires and tubes


Page 7







Microirrigation On Mulched Bed Systems


Table 4. Approximate volume of water to apply (gallons) per 100 linear feet of bed for a given wetted soil volume
available water-holding capacity and an allowable depletion of 1/3.

Wetted Soil
Vol. Per Available Water-Holding Capacity
100 ft. (Fraction by Volume)
(cu. ft.) 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16
25 2 3 4 6 7 9 10 11
50 3 6 9 11 14 17 20 23
75 4 9 13 17 21 26 30 34
100 6 11 17 23 29 34 40 46
125 7 14 21 29 36 43 50 57
150 9 17 26 34 43 51 60 69
175 10 20 30 40 50 60 70 80
200 11 23 34 46 57 69 80 91
225 13 26 39 51 64 77 90 103
250 14 29 43 57 71 86 100 114
275 16 31 47 63 79 94 110 126
300 17 34 51 69 86 103 120 137
350 20 40 60 80 100 120 140 160
400 23 46 69 91 114 137 160 183
450 26 51 77 103 129 154 180 206
500 29 57 86 114 143 171 200 229
550 31 63 94 126 157 189 220 251
600 34 69 103 137 171 206 240 274:
700 40 80 120 160 200 240 280 320
800 46 91 137 183 229 274 320 366
900 51 103 154 206 257 309 360 411
An irrigation application efficiency of 90 was assumed


should be
necessary.


checked for damage and repaired as


Generally acid injection, chlorination, or use of a
commercial water treatment chemical will be
necessary to remove chemical precipitates or organic
growths and clean the drip lines and emitters (for
more information, see Ford 1979a, 1979b, 1979c,
1979d, 1979e, and 1979f). Flushing the drip lines
periodically either manually or with automatic flush
valves is a good management practice to remove
settled debris or growths. A routine program of
clogging prevention is better than attempting to clean
up a clogged system.

SUMMARY

The components and operation of microirrigation
systems on plastic-mulched bedded production
systems were discussed. Cultural considerations such
as bed size and bedded feet per acre were defined as


well as system requirements and capacities. The
characteristics of microirrigation systems allow precise
and accurate water application to established crops.
However higher levels of management and
maintenance are required. Tables were presented to
aid the irrigation system manager to determine the
volume of water to apply and the duration of
application based on soil, crop, and irrigation
characteristics. Example problems demonstrating the
use of these tables were discussed.

APPENDIX A
Example Problems

1. Tomatoes are grown on an EauGallie fine sand
with an available water capacity of 0.50 inches per
foot of soil. Drainage ditches are spaced on 24
foot intervals with 3 beds between ditches. The
field encompasses eighteen acres and will be
irrigated in three sets. What is the required pump


Page 8







Microirrigation On Mulched Bed Systems


Table 4. Approximate volume of water to apply (gallons) per 100 linear feet of bed for a given wetted soil volume
available water-holding capacity and an allowable depletion of 1/3.

Wetted Soil
Vol. Per Available Water-Holding Capacity
100 ft. (Fraction by Volume)
(cu. ft.) 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16
25 2 3 4 6 7 9 10 11
50 3 6 9 11 14 17 20 23
75 4 9 13 17 21 26 30 34
100 6 11 17 23 29 34 40 46
125 7 14 21 29 36 43 50 57
150 9 17 26 34 43 51 60 69
175 10 20 30 40 50 60 70 80
200 11 23 34 46 57 69 80 91
225 13 26 39 51 64 77 90 103
250 14 29 43 57 71 86 100 114
275 16 31 47 63 79 94 110 126
300 17 34 51 69 86 103 120 137
350 20 40 60 80 100 120 140 160
400 23 46 69 91 114 137 160 183
450 26 51 77 103 129 154 180 206
500 29 57 86 114 143 171 200 229
550 31 63 94 126 157 189 220 251
600 34 69 103 137 171 206 240 274:
700 40 80 120 160 200 240 280 320
800 46 91 137 183 229 274 320 366
900 51 103 154 206 257 309 360 411
An irrigation application efficiency of 90 was assumed


should be
necessary.


checked for damage and repaired as


Generally acid injection, chlorination, or use of a
commercial water treatment chemical will be
necessary to remove chemical precipitates or organic
growths and clean the drip lines and emitters (for
more information, see Ford 1979a, 1979b, 1979c,
1979d, 1979e, and 1979f). Flushing the drip lines
periodically either manually or with automatic flush
valves is a good management practice to remove
settled debris or growths. A routine program of
clogging prevention is better than attempting to clean
up a clogged system.

SUMMARY

The components and operation of microirrigation
systems on plastic-mulched bedded production
systems were discussed. Cultural considerations such
as bed size and bedded feet per acre were defined as


well as system requirements and capacities. The
characteristics of microirrigation systems allow precise
and accurate water application to established crops.
However higher levels of management and
maintenance are required. Tables were presented to
aid the irrigation system manager to determine the
volume of water to apply and the duration of
application based on soil, crop, and irrigation
characteristics. Example problems demonstrating the
use of these tables were discussed.

APPENDIX A
Example Problems

1. Tomatoes are grown on an EauGallie fine sand
with an available water capacity of 0.50 inches per
foot of soil. Drainage ditches are spaced on 24
foot intervals with 3 beds between ditches. The
field encompasses eighteen acres and will be
irrigated in three sets. What is the required pump


Page 8






RagP


Microirrigation On Mulched Bed Systems


Table 5. Approximate volume of water to apply (gallons) per 100 linear feet of bed for a given wetted soil volume
available water-holding capacity and an allowable depletionqof 1/2l

Wetted Soil
Vol. Per Available.Water-H7olding Capacity
100 ft. : : (Frtio h by Volume)
------------------------------------------------'-------------------------
(Olvft.) .002 :0.04 .06 0.08 ;.io 0.12 0.14 01
25 2 4 .. 7 8 -. 11 - -13 .. i5 7 ...-.... .. ...

50 4 -*9 13 17 ?21 26 30 34
75 6 13 20 26 33 39 45" .82
S100 8 .17 26 .35 43 52 .60 69
125 10 22 -33 43 54 65 -76 .86
150 13 .26 : 9 52 65 78 91 104
175 15 30 46 61 76 91 106 121
200 17 35 52 69 89 104 :121 1.38
25 20 .89 58 78 97 117 136 ..56
250 22 43 65 87 108 130 151 1.73
275 24 48 71 95 119 143 167 190
300 26 52 78 104 -130 156 182 208
350 30 61 91 121 152 182 212 242
400 35 69 104 139 173 208 242 277
450 39 78 117 156 195 234 273 312
500 43 87 130 173 216 260 303 346
-550 48 -95 143 191 238 -286 :.333 .381
600 52 104 .156 208 g60 312 ...364 416
700 61 121 182 242 303 364 424 485
800 69 139 208 277 346 416 485 554
900 78 156 234 312 390 .468 545 623
An irriation applc&n ethfleeny o~ 90% ws assarname
; . .. .. .. .. .. .


capacity if a drip tubing which discharges 0.5 gpm per
100 feet is used?

a. From Table 1 the bed feet per acre (BfAc) is
5445 feet.

b. From Table 2, for an BfAc of 550p ftand an
emitter discharge of 0.5 gpm/100 rtel, the"`
required discharge per gross acre would be
about 28 gpm. Therefore, irrigating 6 acres at
a time requires a pump capacity of (6 acres *
28 gpm/acre =) 168 gpm.

2. Consider the tomato field of example problem 1.
The trickle system can provide a.wetted soil width
of 2.0 feet. Irrigations are to be scheduled when
50% of the available water has been depleted and
a 1.5 foot root zone is to be managed. What is the
required time of operation for this irrigation
system?


a. A wetted width of 2.0 feet and a root zone of
1.5 feet result in an irrigated soil volume of 300
cubic feet per 100 linear feet of bed (Table 3).

/ib Uai-vingg Table 5 f i~th!e.fQ% .depletion levyl :with
a wetted volume of 300 cubic feet per 100 bed
feet and an available water-holding capacity of
50' rid./ft., provides that 52 gallons of wrcer are
,-required per 100 feet of$Bd per irrigation.

c. From Table 7, for a volume of 52 gallons per
100 bed feet and an emitter discharge rate of
0:'--5 'Sgpm/100 feet,. a~ iaippi afion.ir&lf-f.k7 io
J..8 hours is interpolated.

This irrigation period (1.7 to 1.8 hoiui) isrequired
for each of the three sets. However, each set may be
irrigated in two or more cycles. For example in the
above situation each of. the three sets may be
irrigated twice adrcy ( ortinig'and afternonrr) for 0.9
hours eah, time.






Microirrigation On Mulched Bed Systems


Table 6. Approximate volume of water to apply (gallons) per 100 linear feet of bed for a given wetted soil volume
available water-holding capacity and an allowable depletion of 2/3.

Wetted Soil
Vol. per Available Water-Holding Capacity
100 ft. (Fraction by Volume)
(cu. ft.) 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16
25 3 6 9 11 14 17 20 23
50 6 11 17 23 29 34 40 46
75 9 17 26 34 43 51 60 69
100 11 23 34 46 57 69 80 91
125 14 29 43 57 71 86 100 114
150 17 34 51 69 86 103 120 137
175 20 40 60 80 100 120 140 160
200 23 46 69 91 114 137 160 183
225 26 51 77 103 129 154 180 206
250 29 57 86 114 143 171 200 229
275 31 63 94 126 157 189 220 251
300 34 69 103 137 171 206 240 274
350 40 80 120 160 200 240 280 320
400 46 91 137 183 229 274 320 366
450 51 103 154 206 257 309 360 411
500 57 114 171 229 286 343 400 457
550 63 126 189 251 314 377 440 503
600 69 137 206 274 343 411 480 549
700 80 160 240 320 400 480 560 640
800 91 183 274 366 457 549 640 731
900 103 206 309 411 514 617 720 823
An Irrigation application efficiency of 90% was assumed


APPENDIX B
Calculations

1. Calculations of bed feet per acre (BfAc); Table 1:


Bed Feet Per Acre =


43560 (sq. ft./acre) # Beds per Ditch

Ditch spacing (feet)


2. Calculation of discharge per gross acre; Table 2:


Discharge Per Acre (gpm/acre) =


BfAc Emitter Discharge (gpm/100 ft.)


3. Calculation of soil volume; Table 3:


Soil Volume (cu.ft./100 ft.) = Wetted Width (ft.) Root Zone (ft.) 100 ft.


Page 10






Microirrigation On Mulched Bed Systems


Table 7. Irrigation time per application (hours).

Volume of Water
To Apply Emitter Flow Rate (gpm per 100 feet)
(gallons per ---------------------------------------
100 bed ft.) 0.25 0.30 0.40 0.50 0.75 1.00 1.50

2.0 .1 .1**** **** **** **** ****
4.0 .3 .2 .2 .1 **** **** ****
6.0 .4 .3 .3 .2 .1 .1 ****
8.0 .5 .4 .3 .3 .2 .1 ****
10.0 .7 .6 .4 .3 .2 .2 .1
15.0 1.0 .8 .6 .5 .3 .3 .2
20.0 1.3 1.1 .8 .7 .4 .3 .2
30.0 2.0 1.7 1.3 1.0 .7 .5 .3
40.0 2.7 2.2 1.7 1.3 .9 .7 .4
50.0 3.3 2.8 2.1 1.7 1.1 .8 .6
60.0 4.0 3.3 2.5 2.0 1.3 1.0 .7
70.0 4.7 3.9 2.9 2.3 1.6 1.2 .8
80.0 5.3 4.4 3.3 2.7 1.8 1.3 .9
90.0 6.0 5.0 3.8 3.0 2.0 1.5 1.0
100.0 6.7 5.6 4.2 3.3 2.2 1.7 1.1
150.0 10.0 8.3 6.3 5.0 3.3 2.5 1.7
200.0 13.3 11.1 8.3 6.7 4.4 3.3 2.2
300.0 20.0 16.7 12.5 10.0 6.7 5.0 3.3
400.0 **** 22.2 16.7 13.3 8.9 6.7 4.4
600.0 **** **** **** 20.0 13.3 10.0 6.7
800.0 **** **** **** **** 17.8 13.3 8.9
****Irrigation times less than 0.1 hours or greater than 24 hours are not presented.



4. Calculation of the volume of water to be applied per 100 linear feet; Tables 4, 5, and 6:

Soil Volume Water Holding Allowable Depletion
Volume of Water to Apply = 7.48 (cu. ft./100 ft.) Capacity (fraction) (fraction)
Per 100 Feet of bed
Irrigation Efficiency


5. Calculation of Irrigation time; Table 7:


Irrigation Application Time, hours = 60 *



REFERENCES AND RELATED
PUBLICATIONS

Clark, G.A., A.G. Smajstrla, and D.Z. Haman.
Water Hammer in Irrigation Systems. Ci
828. Fla. Coop. Ext. Ser., Univ. of Florida.


Volume of Water to Apply (gal./100 ft.)

Emitter Discharge Rate (gpm/100 ft.)


Clark, G.A., D.N. Maynard, C.D. Stanley, G.J.
Hochmuth, E.A. Hanlon, and D.Z. Haman. 1990.
Irrigation Scheduling and Management of
1989. Microirrigated Tomatoes. Circular 872. Fla.
rcular Coop. Ext. Ser., Univ. of Florida.

Clark, G.A., A.G. Smajstrla, D.Z. Haman, and F.S.
Zazueta. 1990. Injection of Chemicals into


Page 11






Microirrigation On Mulched Bed Systems


Irrigation Systems: Rates, Volumes, and Injection
Periods. Bulletin 250. Fla. Coop. Ext. Ser., Univ.
of Florida.

Clark, G.A. and A.G. Smajstrla. 1992. Treating
Irrigation Systems with Chlorine. Circular 1039.
Fla. Coop. Ext. Ser., Univ. of Florida.

Ford, H.W. 1979a. A Key For Determining The Use
Of Sodium Hypochlorite (Liquid Chlorine) To
Inhibit Iron And Slime Clogging Of Low Pressure
Irrigation Systems In Florida. Lake Alfred
Research Report CS79-3. University of Florida.

Ford, H.W. 1979b. Water Quality Tests For Low
Volume Irrigation. Lake Alfred AREC Research
Report. CS79-6. University of Florida.

Ford, H.W. 1979c. The Use Of Surface Water For
Low Pressure Irrigation Systems. Fruit Crops
Mimeo FC79-1. University of Florida.

Ford, H.W. 1979d. The Present Status Of Research
On Slimes Of Sulfur In Low Pressure Irrigation
Systems And Filters. Fruit Crops Mimeo FC79-2.
University of Florida.

Ford, H.W. 1979e. The Present Status Of Research
On Iron Deposits In Low Pressure Irrigation
Systems. Fruit Crops Mimeo FC79-3. University
of Florida.

Ford, H.W. 1979f. The Use Of Chlorine In Low
Pressure Systems Where Bacterial Slimes Are A
Problem. Fruit Crops Mimeo FC79-5. University
of Florida.

Haman, D.Z., A.G. Smajstrla, and F.S. Zazueta.
1987. Media Filters For Trickle Irrigation In
Florida. Fact Sheet AE-57. Fla. Coop. Ext. Ser.,
Univ. of Florida.

Haman, D.Z., A.G. Smajstrla, and F.S. Zazueta.
1988. Screen Filters In Trickle Irrigation Systems.
Fact Sheet AE-61. Fla. Coop. Ext. Ser., Univ. of
Florida.

Howell, T.A., D.S. Stevenson, F.K. Aljibury, H.M.
Gitlin, I- Pai Wu, A.W. Warrick, and P.A.C. Raats.


1980. Design and Operation of Trickle (Drip)
Systems. In: Design and Operation of Farm Irrigation
Systems (M.E. Jensen ed.). American Society of
Agricultural Engineers. St. Joseph MI.

Nakayama, F.S., and D.A. Bucks. 1986. Trickle
Irrigation for Crop Production; Design, Operation,
and Management. Elsevier Science Publishers.
Amsterdam, The Netherlands.

Smajstrla, A.G. 1985. Design and Management of
Drip Irrigation Systems for Tomatoes.
Agricultural Engineering Extension Mimeo Report
85-13. University of Florida.

Smajstrla, A.G., and F.S. Zazueta. 1985. Design and
Management of Drip Irrigation Systems for
Strawberries. Agricultural Engineering Extension
Mimeo Report 85-14. University of Florida.

Smajslrla. A.G., F.S. Zazueta, and D.Z. Haman.
1985a. Soil Characteristics Affecting Irrigation in
Florida. Agricultural Engineering Extension
Report 85-2 (revised). University of Florida.

Smajstrla, A.G., D.S. Harrison, and G.A. Clark.
1985b. Trickle Irrigation Scheduling 1: Durations
of Water Applications. IFAS Bulletin 204.
University of Florida.

Smajstrla, A.G., D.S. Harrison, W.J. Becker, F.S.
Zazueta, and D.Z. Haman. 1991. Backflow
Prevention Requirements For Florida Irrigation
Systems. IFAS Bulletin 217. University of
Florida.

Smajstrla, A.G., D.Z. Haman, and F.S. Zazueta.
1992. Calibration of Fertilizer Injectors for
Agricultural Irrigation Systems. Circular 1033.
Fla. Coop. Ext. Ser., Univ. of Florida.


Smajstrla, A.G., D.S. Harrison, and
1986b. Chemigation Safety.
Engineering Fact Sheet AE-58.
Florida.


W.J. Becker.
Agricultural
University of


Page 12




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