Group Title: Research report - Bradenton Agricultural Research & Education Center - GC1977-8
Title: A rationale for the determination of irrigation needs for vegetable crops grown with seep irrigation
Full Citation
Permanent Link: http://ufdc.ufl.edu/UF00067712/00001
 Material Information
Title: A rationale for the determination of irrigation needs for vegetable crops grown with seep irrigation
Series Title: Bradenton AREC research report
Physical Description: 6 leaves : ; 28 cm.
Language: English
Creator: Marlowe, George A ( George Albert ), 1925-
Overman, A. J ( Amegda J )
Agricultural Research & Education Center (Bradenton, Fla.)
Publisher: Agricultural Research & Education Center, IFAS, University of Florida
Place of Publication: Bradenton Fla
Publication Date: 1977
Subject: Vegetables -- Irrigation -- Florida   ( lcsh )
Vegetables -- Water requirements -- Florida   ( lcsh )
Microirrigation -- Florida   ( lcsh )
Genre: government publication (state, provincial, terriorial, dependent)   ( marcgt )
non-fiction   ( marcgt )
Statement of Responsibility: G.A. Marlowe, Jr. and A.J. Overman.
General Note: Caption title.
General Note: "September 1977."
Funding: Florida Historical Agriculture and Rural Life
 Record Information
Bibliographic ID: UF00067712
Volume ID: VID00001
Source Institution: Marston Science Library, George A. Smathers Libraries, University of Florida
Holding Location: Florida Agricultural Experiment Station, Florida Cooperative Extension Service, Florida Department of Agriculture and Consumer Services, and the Engineering and Industrial Experiment Station; Institute for Food and Agricultural Services (IFAS), University of Florida
Rights Management: All rights reserved, Board of Trustees of the University of Florida
Resource Identifier: oclc - 73173948

Table of Contents
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        Page 4
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        Page 6
Full Text


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

site maintained by the Florida
Cooperative Extension Service.

Copyright 2005, Board of Trustees, University
of Florida

Agricultural Research & Education Center
IFAS, University of Florida
Bradenton, Florida

SBradenton AREC Research Report GC1977-8


September 1977


G. A. Marlowe, Jr. and A. J. Overman

A reasonable assessment of the irrigation requirement of vegetable crops depends
largely on five factors:
1. Evapotranspiration (ET)
2. Field Irrigation Efficiency (FIE)
3. Crop Characteristics EC 5 1977
4. Rainfall (amount and distribution)
5. Ground water contribution

These five factors are closely related and an understand feI nerrela-
tionships is important for reasonable and reliable irrigation calculation.

1. Evapotranspiration (ET)

Evapotranspiration figures are the sum of the carefully estimated values of the
amount of water evaporated from the soil and transpired by the crop during a given
period of time. The ET figure is usually expressed in acre inches of water lost by
the soil and crop per season.

The estimated seasonal evapotranspiration figure for a crop is based on long
term climatological records (mainly temperature and hours of sunshine per day) and
a crop growth coefficient (1). Temperatures and hours of sunshine per day are
integral components of the calculation because of their great influence on evapora-
tion and transpiration. The crop growth coefficient is based on the growth rate of
the crop. These coefficients are often expressed as bell shaped, flattened bell
shaped, and S-shaped curves (2). Because the ET is related to the climatological
conditions during a given time period (3), the ET changes drastically with each crop
planting date and its growing season. Tomatoes, for example, planted in southwest
Florida on five different planting dates exhibit five different ET figures:

140 Day Crop

Aug. 1

Sep. 1

Date of planting
Oct. 1

The monthly average evaporation rates from an open pan of water (8 inches deep
by 4 feet in diameter) are as follows for southwest Florida (4):

Month Inches Ionth Inches

Jan 3.3 Jul 5.8
Feb 3.5 Aug 5.3
Mar 5.3 Sep 5.1
Apr 6.2 Oct 4.1
May 6.4 Nov 3.7
Jun 5.2 Dec 2.6

These figures illustrate the extent of seasonal changes in evaporation, one
of the essential portions of ET.

/36 o

Feb. 1

Mar. 1

Evapotranspiration from a crop field rarely exceeds evaporative pan rates.
ET figures vary, as expected, from region to region. Evapotranspiration rates
for field grown beans, sweet corn and tomatoes in the following states provide
the following comparisons: (March 1st date of plantings).

ET (inches)
State Beans Sweet corn Tomatoes

Georgia 9.7 19.8 17.6
Missouri 8.9 13.0 20.4
California 15.9 25.2 26.8
Arizona 13.6 19.6 19.1
Florida 7.0 16.0 19.2

The ET provides only a starting point for the determination of irrigation need.

2. Field Irrigation Efficiency (FIE)

If it were possible to apply the entire ET figure to an acre of crop land
gradually and without loss, then the irrigation requirement would essentially be
the same as the ET. This situation is very unlikely to occur under field growing

Irrigation systems vary greatly in efficiency. The most important factors
influencing efficiency are:

a. Conveyance loss from source to field
b. Percolation during application
c. Run-off during application
d. Evaporation during application
e. Wind displacement during application

a. Conveyance loss

For many years irrigation water was moved from the well-head to the crop field
in open ditches. The great losses due to deep percolation and evaporation have been
reduced significantly in vegetable growing areas by conveying the water from pump to
field in underground pipes. This "semi-closed" system may reduce conveyance loss
to the field to zero, thus reducing total water needs approximately 35% to 50%.

It is also realized that the water conveyed through the field in open ditches
(whether irrigation or drainage) creates a serious loss due to evaporation. The
open ditches may represent between 12-16% of the crop acre and may lose as much as
1300 gallons or .05 ac. in. of water in a 24-hour period.

b. Percolation

It is quite obvious that irrigation ditches between crop rows in sandy soils
lose some effectiveness of delivery because of percolation. Percolation in sandy
soils exhibits a narrow, inverted cone pattern downward, with very little of the
horizontal spread and wide-top pattern characteristic of clay and clay-loam soils.

Some sandy soils percolate water downward so quickly that very.little of the
irrigation stream serves the crop root system. Percolation loss in some sandy
soils may range from 15 to 20% of all the water applied.


c. Run-off

Water that runs off the field is obviously a serious loss to irrigation effi-
ciency. Most growers try to restrict run-off to 10% to 25% or less except in cases
when a deliberate leaching of the crop field is desired.

d. Evaporation

In the seep irrigation system the height of the water table is controlled by
the quantity of water pumped into the field. Vegetable production on sandy soils
with a hard-pan must be grown on raised beds to assist in quick drainage of exces-
sive rainfall.

The water table must be kept high tQ satisfy the poor capillarity of sandy soils
in these raised beds (8-10 in.). The water table is so close to the surface in the
area between beds that evaporation rates approach that of open water. In some vege-
table fields the area between beds may be as much as 50% of the total cropped acre
which may lead to losses in the range of 0.16 acre inches per day.

e. Wind displacement

Wind displacement of water applied by overhead sprinkler systems can cause a
significant loss in efficiency. Thus, most growers restrict their application times
to windless or low-wind periods. Seep and drip irrigation are generally not influ-
enced by wind displacement.

3. Crop Characteristics

a. Time

The planting date, duration of the crop, and climatological conditions in
which the crop is to be grown are important factors in irrigation calculations.
Some vegetable crops are harvested in less than 30 days after planting; whereas,
some may require as much as 180 days for the entire production sequence.

Vegetable growers often produce several crops on the same land within a year
by scheduling crops with different maturity dates. Some typical time requirements
of important Florida vegetables are as follows:

30 days 50 days 65 days 85 days 120 days
or less or less or less or less or more

Radish Leaf lettuce Beans Cabbage Eggplant
Turnips Cucumber Sw. corn Potatoes, I.
Watermelon Pepper

The growing season itself relates to the period of greatest irrigation need,
but irrigation must start well enough in advance to prepare seed beds, allow for
fumigation, etc. There must be enough water to maintain a 10% soil moisture level
in sandy soils for approximately 5 to 6 weeks prior to planting. This pre-planting
moisture need is extremely important and should always be considered in irrigation


b. Plant development

Vegetable crops vary greatly in root system development ieaf display, water
requirement, critical periods of stress, and resistance to drought. A.crop harvested
continually for 6 weeks has a much different water need than one that is sacrificed
at harvest. Vegetables vary also in their tolerance to excess soil moisture. Pota-
toes and vine crops have a relatively high soil oxygen requirement, thus excess water
could reduce the soil oxygen available.

The irrigation regime must be adapted to the unique needs of each to supply
adequate, but not excess, soil moisture at each phase of the growing period.

4. Rainfall

Rainfall, the source of most of Florida's ground and deep water is a rather
unreliable source of direct water for crop production. Florida vegetables are
essentially out-of-season crops, produced at great expense and risk. Florida growers
depend almost entirely on supplemental irrigation as a water source in order to assure
adequate moisture when and where needed.

Irrigation needs should be based on zero rainfall because:

a. Quite often an entire crop season passes without significant rainfall.
b. Even in "normal" rainfall years the distribution may be entirely outside
of the cropping season.

Rainfall is often treated as a gift and a savings of expensive pumping but
excessive rainfall has an opposite effect in that expensive drainage pumping may be

5. Ground Water Contribution

The ground water status of the region surrounding a given crop production area
has a profound bearing on crop irrigation needs. If there is a deficit of ground
water in the region it is obvious that an appreciable upward adjustment must be
made in the irrigation calculation to recharge and offset this shortfall.

6. Overview

An example of a reasonable irrigation calculation for a major vegetable crop
in southwest Florida may be of interest. Let us assume that a grower plans to set
an 80 acre field of tomatoes on August 1 of a given year. The ET figure for this
planting date and the 140 day growing period that follows is 21.3 inches.

The irrigation application for proper field preparation commences at about
the sane time transplants are being produced. The transplants may be grown by the
grower or be produced on contract by a specialized plant grower. Both operations
take from 35-45 days, and are started about the 5th to 10th of July in preparation
for a 10-20 August setting date.


The pan evaporation and estimated ET records for average tomato growing
seasons (assuming zero rainfall) would appear as follows:

Period of


Fall crop
Pan evao. in.

ET in. Date

Spring crop
Pan Evap., in.

Field prep.
Plant prod.*

10 July)
15 July)

5.0 15 Dec.)
20 Dec.)

Field setting 10 Aug.

14.5 (A,S,0)**19.3

10 Feb. 15.0 (F,M,A)** 16.8

First harvest

1 Nov.

Final harvest 10 Dec.


180 days



25.0 in.

1.4 15 May

0.4 10 June 1.7

26.0 in.180 days 27.7 in.

*A tomato transplant production greenhouse operation uses approximately 1.3 acre
inches of water to produce plants for 50 field acres.

**Abbreviation for months of Aug., Sept., Oct., Feb., Mar., and April.

During the peak moisture use period tomatoes use more than 0.3 inch of water
per day, thus accounting for the difference in pan and ET figures during the great-
est growth and fruit sizing period.

These calculations are based on zero rainfall during the cropping season.
These amounts may not reflect actual pumping needs during most seasons because
growers would not irrigate if sufficient rainfall occurred.

The estimates used in this rationale are based on the best information avail-
able at this time. More exact estimates of water needs will be forthcoming through
future research efforts.

1. Blaney, H. F., and H. D. Criddle. 1950. Determining water requirements in
irrigated areas from climatological and irrigation data. U.S.D.A. Soil Conserv.
Service SCS-TP=96.

2. Irrigation Water Requirements. 1970. U.S. Dept. of Agric. Soil Conservation
Division Tec. Release No. 21.

3. Rogers, J. S., and G. A. Marlowe, Jr. 1975. The water needs of Florida vege-
table crops. Univ. of Florida, IFAS-WRC-2.

4. Climatological Data, 1976. Environmental Data Service, National Oceanic and
Atmospheric Administration. Abheville, N. Carolina.

ET in.

4.6 (D-J)


25.6 in.

ODeration ET in. Date

A worksheet example of an irrigation calculation for a fall tomato crop in south-
west Florida could be developed as follows:

Irrigation Calculation Sheet
for a semi-closed irrigation system

Date of planting
Length of preparation time
Length of growing season
Last crop in field
Water source
Soil type

10 Aug. 1977
35-45 days
135 days
Myakka fine sand

Last date field cropped
Irrigation method
Drainage characteristics

Lyle 0. Persicon
Ruskin, Rt. 1
Semi-closed seep
Hard-pan 18 in.
below surface

Step 1. Evapotranspiration (ET) figure for planting date from table:

Step 2. Field Irrigation Efficiency (FIE)
a. Conveyance loss from well to field
b. Percolation during application
c. Run-off during application
d. Evaporation in the field
e. Wind displacement during application

High Efficiency

Low Efficiency

Total Loss in Efficiency % 40

FIE% Total Estimated Efficiency

Step 3. Water needs for field preparation, acre inches High Efficiency Low Efficiency
Situation Situation

ET 5.0
FIE 0.6 = 8.3 acre inches




ET 5.0
FIE 0.35 = 14.3 acre inches

Step 4. Water needs for crop growing period, acre inches

ET 21.3
FIE = .6 = 35.5


ET 21.3
FIE = .35 = 60.9


Step 5. Total water needs, acre inches
Field preparation or plant prod.
Crop growing period
Total, acre inches





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