NFREC, Quincy Research Report 90-17
Irrigation Use by Mulched
Staked Tomatoes in North Florida
F. M. Rhoactdss 2
~~ ^, o. ,, ^ '"0
Florida Agricultural Experiment Stations
Institute of Food and Agricultural Sciences
University of Florida, Gainesville
Irrigation Use by Mulched
Staked Tomatoes in North Florida
F. M. Rhoads
Water management districts in Florida are encouraging crop
producers to use water for irrigation more efficiently because of
increased demand on the water supply by a rapidly increasing
population. More efficient water use (i.e. greater crop production
per unit of water used) makes water available to more users and
reduces nutrient leaching and pesticide movement in soil profiles.
Irrigation use permits are required in order for tomato growers and
other irrigation users to withdraw water from wells and streams.
Permits for irrigation use are based on both a maximum daily use
rate and seasonal total amount. Therefore, the purpose of water
use permits is two fold, first to conserve water and second to
protect the environment.
This report was written to provide tomato growers with a
source of data on which to base requests for irrigation use
permits. Tomato growers need to be assured that adequate water use
is permitted to produce a profitable yield while water management
officials are concerned about conservation in order for everyone to
have water. Irrigation use and tomato fruit yields are reported
for three experiments covering a wide range of environmental
conditions. Seasonal irrigation use was calculated for a 120-day
growing season, therefore, actual irrigation use will vary with
length of growing season. The purpose of this report is not to
establish a daily water use rate or seasonal amount of irrigation
to be permitted for tomato production, but to provide some unbiased
data that should be helpful to water management officials and
tomato growers in negotiating irrigation use permits.
METHODS AND MATERIALS
Experiment #1: Field plots were transplanted with tomato
plants of the Walter cultivar on 19 March during a relatively dry
growing season. Plant rows (six feet apart) were located on beds
three feet wide covered with black plastic mulch. Spacing between
plants was two feet with wood stakes driven into the ground between
plants with twine attached to prevent plants from falling over. A
fumigant was applied just before the plastic mulch to control
pests. Soil type was Tifton loamy fine sand (fine, loamy,
siliceous, thermic, Plinthic Kandiudult).
There were three irrigation treatments: sprinkler (SI),
automatic drip (ADI), and manual drip (MDI). All treatments were
scheduled for irrigation with tensiometers (one per plot) placed
six inches from plants with the sensor at the six-inch depth.
Therefore, plant demand for water determined the amount of
irrigation used in each treatment. Irrigation was turned on for
each treatment when the reading reached 20 centibars (cb). One bar
is equal to 14.5 lbs/square-inch of negative pressure or suction;
20 cb = 0.2 bar or 2.9 Ibs/square-inch of suction. Treatments SI
and MDI were irrigated with one-inch and 0.2 inches of irrigation
at each application, respectively. Treatment ADI had a switching
tensiometer connected to a solenoid that turned the irrigation on
above 20 cb and off below 20 cb. A municipal type water meter was
used to measure the amount of irrigation applied. Meter accuracy
was checked with standard volumetric containers. Via-flow (a white
porous plastic) drip tubing was used in treatments ADI and MDI.
Sprinkler irrigated (SI) plots had dykes constructed between rows
to prevent runoff from the four small radius sprinklers in each
One-thousand lbs/acre of a 3-14-4 mixture was incorporated
into plant beds of all treatments to supply 30 lbs/acre N, 60
lbs/acre P, and 30 lbs/acre K (N = nitrogen, P = phosphorus, and K
= potassium). A 19-0-24 mixture (1100 lbs/acre) was applied to
supply 200 lbs/acre N and 200 lbs/acre K. The 19-0-24 was applied
in bands six inches from the plant row on each side of the bed to
treatment SI. One band of 19-0-24 was applied to treatment ADI
between the drip tube and plants to evaluate the influence of high
fertilizer salt concentration on tomato yield. In treatment MDI,
the 19-0-24 was dissolved in water, filtered and injected into the
drip tubing at weekly intervals to supply 20% of the total during
the first seven weeks of growth and the remainder between 8 and 13
Tomatoes were hand-harvested at two or three day intervals, a
total of ten times. Yield is reported in tons/acre of pink and
mature green fruit of marketable sizes.
Experiment #2: Tomato plants of the Sunny cultivar were
transplanted in field plots on 8 April in a year with higher
rainfall than for experiment #1. Soil type was Orangeburg loamy
fine sand (fine, loamy, siliceous, thermic, Typic Kandiudults).
Fertilizer and pest control chemicals were applied uniformly to all
plots. Row width was six feet and distance between plants was 20
inches. Plots were mulched and staked as in experiment #1.
Two frequencies and four rates of drip irrigation were
compared in a factorial arrangement. Daily irrigation was compared
with irrigation applied Monday, Wednesday, and Friday (MWF) for a
given amount of water per week. The four irrigation rates were 25,
50, 75, and 100% of 0.2 inches d'1 from 8 April to 15 May and 0.3
inches d'1 from 16 May to 15 July. An automatic timing system
turned irrigation on and off for individual treatments. Emitter
(12 inch spacing) flow rates from twin wall drip tubing
manufacturer's specifications were used to calculate the time
required to apply each irrigation rate.
Rainfall and evaporation data for Exp-1 and Exp-2 were
obtained from weather records maintained by the National Oceanic
and Atmospheric Administration (NOAA).
Mature green and pink fruit were harvested on each of the
following dates: 23 and 29 June and 7 and 15 July. Yields are
reported as marketable fruit in tons per acre.
Experiment #3: Plywood boxes 36 x 20 x 18 inches (L x D x W)
containing 6 inches of topsoil over 12 inches of subsoil were used
to grow plants of the Sunny tomato cultivar under a transparent
rain shelter. The soil, Greenville loamy fine sand clayeyy,
kaolinitic, thermic, Rhodic Kandiudults), was packed approximately
to field bulk density. Fertilizer materials and chemicals for pest
control were applied uniformly to all treatments.
Water was applied through drip tubing underneath black plastic
mulch. One treatment received 0.24 inches of irrigation when
tensiometer readings were >20 cb (tensiometers were placed 6 inches
from plants with sensors 6 inches deep). Use of tensiometers allow
irrigation to be applied in accord with plant demand. Other
treatments consisted of two rates of irrigation with each applied
at two irrigation frequencies. Irrigation rates were 0.03 (rate-l)
and 0.06 (rate-2) inches per day from 0 to 7 weeks and 0.06 (rate-
1) and 0.12 (rate-2) inches per day from 8 to 12 weeks after
planting. Frequencies were daily and Monday, Wednesday, and Friday
(MWF) for each rate.
Fruit was harvested on 16 and 27 June and ripe fruit, green
fruit and total fruit weights were determined.
Statistical evaluation of data: The experimental design was
a randomized complete block with four replications for all
experiments except Exp. #1 which had three replications.
Regression analysis procedures were used to evaluate yield response
to amount of irrigation. Analysis of variance procedures and
orthogonal contrasts were employed to make appropriate comparisons
between individual treatments (Steel and Torrie, 1960).
RESULTS AND DISCUSSION
Rainfall during the growing season for Exp-1 was below normal
(Fig. 1). Total rainfall for April, May and June was 4.92 inches
or 0.06 inches per day seasonal average for Exp-1. Growing season
rainfall for Exp-2 was above normal in March and June, and below
normal in April, May and July. Only 0.35 inches of rainfall
occurred in April and average daily rainfall for May was 0.1 inches
per day. Total rainfall for June was 8.34 inches. Normal rainfall
amounts for March, April, May, June, and July are 5.23, 4.89, 4.28,
5.22, and 6.90, respectively (Davis and Mickelson, 1969). There-
fore, the normal average daily rainfall during the growing season
of spring planted tomatoes in Gadsden County is 0.17 inches per
day. However, rainfall in individual years can vary widely from
the norm as shown in Figure 1. Tomato plants in Exp-3 were grown
under a transparent rain shelter in order to provide a better
estimate of actual water use by tomato plants.
Rainfall (Inches/day) Rainfall (inches/day)
0.8 2x. Exp. 21
E Exp. #2 V Exp. #2
0.2 i | I I 0 I |
Ap-4 17 19 23 24My-8 9 11 12 14 16 1 17 19 21 22 27 29 31 Jn-26 7 13 14 15 1 177 0 1 20 21 22232426 2 27Jy-13 4 5 7 8 10 11
Day of Month Day of Month
Figure 1. Rainfall for exp. #1 and exp. #2 from 1 April to 15
Tensiometer scheduling provides irrigation at approximately
the rate of plant use. Manual and automatic drip irrigation
treatments used about the same amount of irrigation (Fig. 2). This
was expected and verifies the effectiveness of the switching
tensiometer. Total irrigation for the drip system was about 10
inches compared with almost 39 inches for the sprinkler system.
The sprinkler system, with no runnoff allowed, was only about 25%
as effective as drip irrigation in supplying water to tomato
plants. Plastic mulch sheds most of the irrigation from sprinklers
and movement of water from the middles to plants is not very
efficient. Rainfall would be less than 25% efficient if runoff
occurred. Estimated total water use (98 days) for drip irrigated
tomatoes was 13 inches based on rainfall being 25% as effective as
drip irrigation. Average daily irrigation use with sprinklers was
0.23 inches/day between 19 March and 2 May and 0.53 inches/day
between 2 May and 29 June. Drip irrigation used 0.03 inches/day
between 19 March and 2 May and 0.17 inches/day between 2 May and 24
June. Estimated drip irrigation use in Exp-1 for 120 days is 14.2
inches. Maximum daily irrigation was 1.0 inch for sprinklers and
0.23 inches for drip.
Accumulative Irrigation Use (Inches)
80 -ES Manual Drip
E Automatic Drip
Mr-19 Ap-lO My-2 My-20 Jn-7 Jn-24
Figure 2. Accumulative irrigation use by treatments in exp. #1.
Total irrigation ranged from 6.5 to 25.9 inches in Exp-2 (Fig.
3). Rainfall was ignored in the irrigation schedule for this
experiment, however, estimated available water from rainfall in
June was 2.09 inches (0.25 x 8.34). Therefore, total available
water in June from maximum irrigation plus rainfall was 11.09
inches or 0.37 inches/day average. Estimated total average daily
water use during June for tomatoes in Exp-2 at 25, 50, and 75% of
maximum irrigation was 0.15, 0.22, and 0.29 inches/day,
Accumulative Irrigation Use (Inches)
% of Maximum Irrig.
20 -ES so
Ap-8 Ap-26 My-16 Jn-15 Jy-15
Figure 3. Accumulative irrigation use by treatments in exp. #2.
Tensiometer scheduled irrigation and a maximum irrigation rate
of 0.12 inches/day received similar amounts of total irrigation in
Exp-3 (Fig. 4). This was not surprising since average daily
irrigation between 22 May and 29 June for tensiometer scheduled
irrigation was 0.126 inches/day. Tensiometer scheduled irrigation
under a shelter reflects total water demand of tomato plants.
Estimated irrigation use for a 120-day growing period from
tensiometer scheduled irrigation in Exp-3 is 13.8 inches.
Calculations are based on irrigation with 0.06 inches/day for the
first 37 days of growth and 0.14 inches/day for the last 83 days.
The close agreement between Exp-1 and Exp-3 on estimated seasonal
irrigation use confirms that a 120-day tomato crop can be produced
with about 15 inches of drip irrigation in a dry year. The amount
used will vary with length of growing season.
10 Accumulative Irrigation Use (Inches)
E o.0o-0.00 Inohal/day
E 0.06-0.12 Inches/day
Ap-4 Ap-17 My-1 My-11 My-22 Jn-5 Jn-19 Jn-29
Figure 4. Accumulative irrigation use by treatments in exp. #3.
The relationship between amount of irrigation and total
marketable yield was linear for tomatoes irrigated daily in Exp-2
(Fig. 5). However, regression analysis showed no significant
response of total marketable tomato yield to irrigation applied on
Monday, Wednesday, and Friday of each week. The equation, Y = 16.1
+ 0.125W (r = 0.597, P < 0.01), describes predicted total yield
response to daily irrigation, where Y = tons/acre and W = % of
maximum irrigation. Predicted yield without irrigation was 16.1
tons/acre or 1.15 tons/acre-inch of rainfall during the growing
season. Daily irrigation yield was greater than MWF irrigation
yield at 75% of maximum irrigation (P < 0.05) using a single-
Total Yield (Tons/Acre)
25 Irrig. Applied Dally
Irrig. Applied MWF
6.5 13 19.4 26.9
Total Irrigation Use (Inches)
Figure 5. Total yield by irrigation treatments in exp. #2.
Response of tomatoes in Exp-2 to irrigation was not
significant for harvests 1, 2, and 4 but was strongly expressed in
the third harvest (Fig. 6). The MWF irrigation schedule produced
a positive linear response to irrigation amount at the third
harvest, Y = 6.59 + 0.0402W, r2 = 0.218, P < 0.10), while the daily
irrigation schedule produced a quadratic response (Y = 0.75 +
0.256W-0.00144W2, r2 = 0.629, P < 0.01). Daily irrigation was more
effective than MWF irrigation in Exp-2.
12- irrig. Applied Dally
10- Irrig. Applied MWF
6.5 13 19.4 25.9
Total Irrigation Use (Inches)
Figure 6. Yield of third harvest by irrigation treatments in exp.
Yield of tomatoes was related to maximum daily irrigation use
(Fig. 7). Maximum yield occurred in each experiment at about 0.25
inches/day maximum irrigation use and higher irrigation rates did
not increase yield.
-Exp. #l Exp. #2 EExp. #8
1 .23 .08 .15 .23 .3 .06 .12 .24
Maximum Daily Irr. Use (inches/Day)
Ratio of yield to irrigation use was highest in Exp-1 with
drip irrigation and lowest with sprinkler irrigation (Fig. 8).
Higher rainfall in Exp-2 caused the ratio to drop rapidly as
irrigation use increased. Actual irrigation efficiency for Exp-2
was 0.48 tons/acre-inch. The ratio of yield to irrigation use was
nearly constant in Exp-3 because irrigation was the only source of
water for plant growth. About 2.5 tons of tomatoes/acre-inch of
irrigation were produced in Exp-3; this is similar to values in
Exp-1 after accounting for rainfall effects. Therefore, 15 inches
of effective drip irrigation would produce about 38 tons of
Yield:Irrigation Use Ratio (Tons/Ac-in)
I Exp. #1 E Exp. #2 E Exp. #3
38.76 10.32 26.9 19.43 12.96 6.48 8.98 7.83 4.02
Total Irrigation (Inches)
Figure 8. Ratio of yield:irrigation use versus total irrigation
for all experiments.
Maximum drip irrigation use by mulched tomatoes was 0.3
inches/day, however, maximum yield was produced with a maximum use
of about 0.25 inches/day. Maximum sprinkler irrigation use was
about 1.0 inch/day. Rainfall and sprinkler irrigation were about
25% or less as effective as drip irrigation for mulched tomatoes.
Maximum yields of tomatoes were obtained with total drip irrigation
use of 15 to 20 inches for a 120-day growing season. Average daily
pan evaporation for Exp-l, which was conducted during a dry year,
was 0.17 inches for the first 50 days of growth and 0.25 inches for
the last 70 days or a season total of 26 inches.
Dr. S. M. Olson supplied plants and equipment for seed bed
preparation for Experiment-2. Audley Manning assisted in
collecting data from all experiments. Mike Bundy assisted with
experiments two and three. Special thanks to Jan Smith for typing
1 Davis, D. R., and J. E. Mickelson. 1969. A climatological
summary for the North Florida Experiment Station, Quincy.
Univ. of Fla. IFAS. Mimeo Report NFS 69-1.
2 Steel, R. G. D., and J. H. Torrie. 1960. Principles and
procedures of statistics. McGraw-Hill, New York.
Conversion of inches of irrigation to gallons per acre
(7260 feet of row).
inches gal/acre inches gal/acre inches gal/acre
0.01 271 0.1 2713 1.0 27127
0.02 543 0.2 5425 2.0 54254
0.03 814 0.3 8138 3.0 81381
0.04 1085 0.4 10851 4.0 108508
0.05 1356 0.5 13564 5.0 135635
0.06 1628 0.6 16276 6.0 162762
0.07 1899 0.7 18989 7.0 189889
0.08 2170 0.8 21702 8.0 217016
0.09 2441 0.9 24414 9.0 244143