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^ UNIVERSITY OF
3-2 A Gulf Coast Research and Education Center
I L-"FLOR ID A I 5007 60th Street East, Bradenton,FL 34203
Bradenton GCREC ResearcheI~t lfAI-1"t 8
Institute of Food and Agricultural Sciences November 1993 I *' -
MAY 2 0 1994
CONSIDERATIONS OF ALTERNATIVE IRRIGATION PRACTICES
FOR CALADIUM TUBER PRODUCTION university of Florida
B. K. Harbaugh, G. A. Clark, A. J. Overman and J. P. Gilreath'
The importance of irrigation practices for production of caladiums cannot be
overstated. Yet, little information is available regarding optimum water
application amounts or alternatives to subirrigation. The relative importance
of water in tuber development can be illustrated by comparing reported tuber
yield improvements attributed to various production components. For example, a
40% increase in tuber weights (yield) was due to fertilizer alteration (3), 37%
due to fumigation (5), and 30% due to use of tissue cultured seed stock (4).
However, an increase in tuber weight as great as 500% was attributed to
irrigation and water management (6). This latter experiment was performed in a
fiberglass greenhouse with potted plants irrigated to the water holding capacity
of the medium once, twice or three times per week. Plants showed no visible
signs of wilt for any of the irrigation schedules. Bringing the medium to field
capacity three times per week resulted in a 500% increase in tuber weight with
a 150% increase in seasonal water application compared to water used with one
irrigation per week. Two irrigations per week resulted in only a 20% increase
in applied water compared with one irrigation per week, yet tuber weights were
100% greater from the extra water.
In 1989, a research project was initiated to determine the effects of applying
different daily amounts of water for production of field grown caladium tubers.
That research was also designed to evaluate drip irrigation as a component of a
conservative water management system for an alternative to subirrigation.
Sprouting of tuber seed pieces under drip irrigation was extremely variable and
slow. Subsequent plant growth was also very poor even though water was applied
at amounts of evapotranspiration and above. After elimination of as many
potential causal factors as we could measure (such as fertilization, pH, disease
incidence, and nematodes), variation in soil temperature was investigated.
Measured soil temperatures were extremely high under the plastic mulch with drip
irrigation (often 110 OF or above, unpublished data). In subsequent experiments,
potted tubers exposed to temperatures in this range took longer to sprout and
growth was reduced in comparison to plants forced at 79 OF (2). Tubers exposed
to 118 OF for three days failed to sprout.
The objectives of this experiment were to evaluate effects of mulched-raised-bed
or unmulched-flat-bed culture in combination with drip or overhead irrigation on
caladium tuber production in fine sandy soil.
'Professor, (Environmental Horticulturist), Associate Professor, (Extension Water
Management Specialist), Emeritus Professor, (Nematologist), Associate Professor,
Materials and Methods
The experiment was designed as a randomized complete block (5 blocks) with six
mulch-irrigation treatment combinations. The treatments were: 1) mulch-drip
irrigation; 2) mulch-overhead irrigation; 3) mulch-overhead/drip; 4) no mulch-
drip irrigation; 5) no mulch-overhead irrigation; 6) no mulch-overhead/drip
On March 15, 1990, the test area was broadcast fumigated with methyl bromide
67%/chloropicrin 33% at 350 Ib/acre. The soil was an EauGallie fine sand.
Mulched plots were raised beds formed 8 inches high and 24 inches wide covered
with white/black laminated polyethylene film (1.25 mil). Flat ground beds were
used for treatment plots without plastic mulch.
Drip irrigation was applied with 10 mil high flow T-tape (0.5 gpm/100 ft at 10
psi) and emitters every 12 inches. Overhead irrigation was with micro-
sprinklers (26 gph at 20 psi) spaced at 6 ft on 24-inch risers. The overhead/
drip irrigation treatment was used to apply water overhead until seed pieces had
sprouted and the plants provided shade for the soil surface. Initial water
applications were daily from 0700 HR to 0800 HR for drip treatments, and on
Monday, Wednesday, and Friday.0800 HR to 0900 HR for overhead irrigation. Water
delivered to the drip plots (24-inch wide x 15-ft long) was used to wet the soil
to a 12-inch radius and applied approximately 0.1 inch per day. In mid May,
overhead plots received daily irrigation for 60 minutes in two.30 minute cycles
at 0800 and 1300 HR resulting in approximately 0.1 inch per day. This schedule
continued until canopy coverage in late June when the overhead schedule ceased
on the overhead/drip plots and the drip schedule was added. Plots which only
received overhead irrigation remained on the same 0800, 1300 HR schedule.
One-inch diameter seed pieces of the cultivar Candidum were planted April 3.
Seed pieces were planted 2 inches deep, 4 inches apart down the row, 6 inches
apart across the bed, and with 4 rows in a 6 foot plot. The drip tube was in the
bed center so that the center two rows of seed pieces were planted 3 inches from
the drip tube and the outer two rows 9 inches from the drip tube. Three-foot
buffer plots of Carolyn Whorton and Candidum Junior cultivars were planted 1 foot
from each end of 'Candidum' plots for a total experimental plot length of 14
feet. All plots were sprayed with Surflan herbicide (2 lb a.i./A) three times
at approximately monthly intervals beginning in April.
Osmocote 18-6-12 resin-coated controlled release fertilizer (8-9 month release
at 70 OF) was incorporated in the top inch of the bed at 300 lIbs N per planted
acre (calculated as bed width x bed length). Tissue samples were taken on July
23 and September 28 to determine the need for additional N-P-K. On July 31 and
August 16, a rate of 25 Ibs N and 50 Lbs K per planted acre was applied with 4
gallons of water per plot from a solution of'KNO3 and NH4NO3.
Soil temperatures at a 2-inch depth were recorded on a weekly basis at
approximately 1500 HR. Soil temperatures were measured from the outside row (9
inches from the drip tube) and inside row (3 inches from the drip tube).
Tubers were dug on January 2, 1991. They were cured for 2 weeks in open trays
in a glass greenhouse with minimum night temperatures of 600F. Cured tubers were
then weighed and graded into commercial sizes: No. 3 = < 1 inch diam; No. 2 = 1
to 1.5 inches; No. 1 = 1.5 to 2.5 inches; Jumbo = 2.5 to 3.5 inches; Mammoth =
3.5 to 4.5 inches. A production index (PI) was used to reflect crop value: PI
= n No. 3 + 1.5n No.2 + 3n No.1 + 6n Jumbo + 9n Mammoth, where n = number of
tubers in each grade.
On May 20, the number of sprouted tubers in the unmulched-drip plots was 15 in
comparison to 42 to 48 for all other treatment plots (Table 1). Sprouting in the
unmulched-drip plots was similar to the poor sprouting observed in the test the
previous year (unpublished data) with mulched-drip production practices. While
there are many factors which could contribute to the differences between seasons,
the fact that seed pieces were planted a month earlier in this test appeared to
aid sprouting in mulched-drip plots, probably due to cooler temperatures in April
of 1990 compared to May of 1989.
Total number of tubers dug (Table 1) was similar for all treatments indicating
seed pieces eventually sprouted even in the unmulched plots. However, the weight
of harvested tubers and the production index were much lower for unmulched-drip
plots compared to other treatments. There was a general trend for increased
numbers of jumbo and mammoth tubers in mulched plots compared to unmulched plots,
with the exception of similar numbers of jumbo tubers in overhead-unmulched
plots. The production of larger sized tubers resulted in an increased production
index as their value is significantly greater than the smaller sized tubers.
Foliar tissue levels of nitrogen from July 23 samples were 4.2% for plants in
mulched-drip and mulched-overhead plots, 3.6% for unmulched-overhead, and 3.0%
for unmulched-drip. The sufficiency range for foliar N in caladium is 3.1 to
4.1% (1). Since the soil temperatures were averaging high enough to cause
premature release of nutrients from the controlled release fertilizer (8-9 month
release at 700F), and since plants in unmulched-overhead plots had foliar tissue
levels below the sufficiency range, two applications of soluble fertilizer were
applied (see Material and Methods). This resulted in all treatments falling
within the N sufficiency range by the September sampling date (Table 2), except
the mulch-overhead was slightly above at 4.2% N. Phosphorus and potassium were
also within established sufficiency range of 0.37 to 0.68 P and 2.3 to 4.1 K
(1). Thus availability of N-P-K was sufficient for all mulch-irrigation
treatments and plant nutrient availability should not have significantly
contributed to differences in yield.
Overhead irrigation had the greatest effect on reducing soil temperature in
unmulched-overhead plots (Table 3). Afternoon soil temperatures ranged from 910F
to 930F for both middle and outside rows for the first three months of the
experiment (April through June) in unmulched-overhead plots. Monthly soil
temperatures for the outside rows of drip irrigated plots were 96 to 102 OF for
these same months. In general, as the crop canopy covered the area, soil
temperatures decreased 5 to 100F in July. Only in the unmulched-drip plots did
the soil temperature in the outside row remain high (970F as late as September)
due to slow sprouting and resulting late canopy development.
General Conclusions to Date
Whenever a component of a production system is changed, it affects other
components of the production system. When the component is water amount or
irrigation system, many facets of the production system are impacted. Water
amount and irrigation system may have direct, indirect and interactive effects
on almost all other production inputs. While direct effects are often the
primary concern of new production concepts, these preliminary investigations into
alternatives to subirrigation practices demonstrated the importance of indirect
and interactive effects. For example, because subirrigated fields have higher
overall water contents than drip irrigated fields, thermal conductivities are
greater and dissipation of excess heat is greater than in relatively drier
fields. The result is that soil temperatures may be raised 100F or more in drip
irrigated beds with plastic mulch in comparison to soil temperatures in
General conclusions and areas for further investigation from these preliminary
studies include: 1. Limitations of drip irrigation include uneven distribution
of water in the bed and increased (potentially damaging) soil temperature; 2.
Early planting dates and relatively large seed pieces improve sprouting and early
canopy development, decreasing effects of increased soil temperatures with
plastic mulch; 3. Overhead irrigation provided excellent irrigation for
caladiums. Thus, a fixed or traveling overhead system may be practical for
caladium tuber production since these irrigation systems can be efficient (water
conserving compared to subirrigation) if nozzles are placed close to the ground
with an unmulched system; 4. Weed control on sand with three applications of
Surflan herbicide was excellent and indicates use of herbicides has the potential
to replace the weed control provided by plastic mulch; 5. Current soil
fumigation procedures impact water conservation plans because 2.0 to 2.5 inches
of water is commonly necessary during field preparation for successful
fumigation, (this quantity must be included in water budgets); 6. Additional
research with drip irrigation systems would be necessary before recommendations
of improved management practices could be developed. Research to date indicates
drip irrigation may not be the best alternative to subirrigation due to economic
considerations, effects on the total production system, and specific crop
1. Harbaugh, B. K. 1987. Foliar tissue analysis standards for nitrogen,
phosphorus and potassium in Caladium x hortulanum Birdsey. Acta
2. Harbaugh, B. K. and M. R. Evans. 1994. Growth inhibition of caladium by
high temperature. HortScience (In Press).
3. Harbaugh, B. K. and A. J. Overman. 1983. Evaluation of fertilizer types
and rates on Caladium x hortulanum Birdsey 'Candidum' tuber production in
muck and sandy soil management systems. Proc. Fla. State Hort. Soc.
4. Harbaugh, B. K., G. J. Wilfret, and A. J. Overman. 1988. Tissue cultured
stock history and hot water treatment affect caladium tuber production on
sandy soils. Proc. Fla. State Hort. Soc. 101:305-307.
5. Overman, A. J. and B. K. Harbaugh. 1982. Effect of tuber source and
fumigation on caladium tuber production in two soil management systems.
Proc. Fla. State Hort. Soc. 95:175-178.
6. Overman, A. J. and B. K. Harbaugh. 1988. Relationship of caladium tuber
size to water use in production. Proc. Fla. State Hort. Soc. 101:311-312.
Table 1. Influence of mulched or unmulched culture in combination with overhead (OH) or drip irrigation on
sprouting, harvest tuber weights, tuber grades, and production index.z
Number Weight Total
sprouted of tubers tubers Number of Tubers by Grade Production
Treatment May 20y (oz.) (no.) No. 3 No. 2 No. 1 Jumbo Mammoth Index
Mulched-Drip 48 192 129 12 28 60 24 5 428
Mulched-OH 48 187 133 12 30 65 22 4 417
Mulched-OH/Drip 45 180 130 15 31 61 21 2 388
Unmulched-Drip 15 125 133 18 41 65 9 0 372
Unmulched-OH 42 160 136 18 31 70 16 1 380
Unmulched-OH/Drip 48 160 136 13 36 74 13 0 368
LSD (d=0.05) 10 29 NS 5 8 2 6 3 50
ZProduction Index = n No. 3 + 1.5 n No. 2 + 3 n No. 1 + 6 n Jumbo + 9 n Mammoth, where n = number of tubers
in each grade.
YThere were 76 seed pieces planted on April 3.
Table 2. Foliar tissue levels September 28 for nitrogen, phosphorus, and
potassium affected by mulched or unmulched culture in combination
with drip or overhead (OH) irrigation.
Nitrogen Phosphorus Potassium
Treatment (%) (%) (%)
Mulched-Drip 4.1 0.47 2.7
Mulched-OH 4.2 0.46 2.6
Mulched-OH/Drip 4.1 0.47 2.8
Unmulched-Drip 4.0 0.50 2.9
Unmulched-OH 3.7 0.45 2.7
Unmulched-OH/Drip 4.1 0.56 2.9
LSD (a = 0.05) 0.2 0.05 NS
Table 3. Average monthly soil temperature for outside (9 inches from drip tube) or inside (3 inches from
drip tube) rows of caladiums grown with mulched or unmulched culture in combination with drip or
overhead (OH) irrigation.
April May June July August September October
Treatment Out In Out In Out In Out In Out In Out In Out In
Mulched-Drip 102 94 101 95 98 92 91 89 86 86 88 87 83 80
Mulched-OH 98 91 98 96 97 93 90 86 84 83 85 84 79 77
Unmulched-Drip 96 99 100 101 100 98 95 88 95 86 97 87 86 79
Unmulched-OH 92 94 92 93 93 91 90 87 86 84 87 85 83 80
ZSoil temperatures recorded at 3 pm at a 2 inch depth once per week.