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Iu of FLORIDA
Institute of Food and Agricultural Sciences
Gulf Coast Research and Education Center
5007 60th Street East, Bradetoa, FL 34203
Brdentos GCREC Research Report BRA 1996.4
A PRELIMINARY SDY STUDY ON TIMING PHOSPHORUS
FERTILIZATION FOR CALADIUM TUBER PRODUCTION
Brent K. Harbaugh and David A. DeVg rston Sc ierc
JUN 19 1996
University of Florida
Bradenton GCREC Research Report BRA1996-4
A Preliminary Study on Timing Phosphorus Fertilization
for Caladium Tuber Production
Brent K. Harbaugh'
Gulf Coast Research and Education Center
University of Florida, IFAS
S 5007 60th Street East
Bradenton, FL 34203
David A. DeVoll2
Highlands County-District IV
County Extension Office
4509W George Blvd
Sebring, FL 33872
Phosphorus is considered one of the most important macronutrients essential for plant growth.
Phosphorus is involved in energy transport systems and the movement of sugars from chloroplasts
to other parts of the cell or plant. It is a component of DNA and RNA, the carriers of genetic
information in each cell. Phospholipids play a vital role in cell membranes. It is no wonder then that
phosphorus is one of the key components of almost all fertilizer formulations used in the production
of caladium tubers.
The normal range for foliar tissue levels of phosphorus in ornamental plants is from 0.3 to 0.8% on
a dry weight basis. In caladiums, the optimal foliar phosphorus concentration is about 0.5%.
Deficiency symptoms are not particularly obvious with caladiums as decreased plant height and
overall plant size are generally the only symptoms expressed. In other plants, a red or purplish
coloration is a sign of phosphorus deficiency. The coloration is caused by the build up of sugars and
accumulation of pigments caused by the lack of phosphorus needed for movement of sugars within
the cell. With caladiums, unless nonstressed plants are growing close to deficient plants, phosphorus
deficiency will not be detected until the deficiency is so serious that an obvious severe plant stunting
is easily seen. Thus, caladium growers have relied upon soil tests and use of fertilizers with a low
percentage of phosphorus to insure yields are not reduced before symptoms are expressed.
2Extension Horticulture Agent I.
Acknowledgement: Appreciation is extended to Happiness Farms, Inc., and to Bates Sons &
Daughters for their support of this project.
Phosphorus can be a potential pollutant as phosphorus from runoff of agricultural crops can cause
eutrophication of lakes. The agricultural community has responded to this threat by reducing the use
of phosphorus in fertilizers and developing best management practices that insure cropping
procedures and fertilization practices do not endanger lakes. Caladium growers have reduced the use
of phosphorus over the years to insure that they would not contribute phosphorus to the canal-lake
system in their production area. If phosphorus is to be applied at very low rates, it will be important
to apply it when the plant response will be the greatest. The purpose of this preliminary study was
to determine if application date of phosphorus fertilizer during the normal production cycle would
affect caladium tuber production.
Materials and Methods
Two similar experiments were conducted with plants either grown under a 30% shade cloth or in a
fan-and-pad cooled glass greenhouse. 'Candidum' caladium tubers were cut to 2.5 cm (1 inch) size
and planted into 15 cm diameter (6 inch) pots filled with muck soil (sedge-peat) from a caladium field
in the Lake Placid area. Tubers were planted on 22 May and pots were placed on a capillary mat.
Subirrigation was used to irrigate plants in both experiments so that leaching of nutrients would not
be caused by irrigation practice. Thus, only plants grown in the shade structure were subject to
leaching from rainfall.
Each pot received one application of 0.25 g (0.009 oz) per pot of single superphosphate on either
19 May, 21 June, 21 July, 21 August, 20 September, or 20 October. This rate was to simulate the
amount of phosphorus available to plants in a production field with one application of a 10-5-15
fertilizer at 449 kg per ha (400 lbs per acre) and 232 cm2 (36 inches2) per plant. On 22 June and
21 July each pot received 100 ml (3.4 oz) of a solution containing 0.1 g (.0036 oz)of nitrogen and
0.13 g (.0046 oz) of potassium from calcium nitrate and potassium nitrate. This was to simulate the
nitrogen and potassium from two applications of a 10-0-15 fertilizer applied at 449 kg per ha (400
Ibs per acre).
There were six treatments (phosphorus application dates) with ten single plant replications arranged
in a randomized block design. Tubers were harvested on 22 November (shade structure) or 25
November (greenhouse structure), washed, allowed to dry for two weeks, and then weighed.
Results and Discussion
Tubers produced in the greenhouse were approximately 1.5 times heavier than tubers grown in the
shade house (Figure 1). However, the effect of phosphorus application date on tuber weight was
similar regardless of production environment. There was a significant (P < 0.05)quadratic relationship
for the effect of fertilization date on tuber weight for caladiums produced in both the shadehouse
(estimated response = 76 + 11.9x 1.7x2) and greenhouse (estimated response = 104 + 21.7x 3.1
x2 ). These trends indicated that tuber production would be greatest if phosphorus was applied
around the first week of August.
Studies on other crops grown in colder climates have shown that the greatest response to phosphorus
was with pre-plant or very early applications. This was perhaps due to the fact that in colder climates
root growth is slow initially and thus uptake of phosphorus is limited. Caladiums are grown as a
subtropical crop and root growth is not limited by low temperatures at sprouting. The initial water
soluble P20s for this soil was 34 kg per ha (30 lbs per acre), and with the high temperatures during
sprouting, this phosphorus would have been available early in the crop. Caladium tubers have about
0.5% phosphorus (dry weight) which could benefit early growth since pieces of tubers are used as
"seed". However, new tubers expand rapidly from late September through October and the plants
may require the highest amount of phosphorus at this time.
While this study was done in pots rather than under field conditions, these results indicate a field
study would be warranted since there was about a 10% (shadehouse) or 20% (greenhouse) increase
in tuber weights when phosphorus was applied in August rather than May. It is interesting to note
that 125 cm (49.2 inches) .of rainfall occurred during this test. Leaching of some of the nutrients
from the soil would have been expected with plants grown in the shadehouse, but no leaching
occurred with plants produced in the greenhouse. Although further studies are needed to verify the
poor growth in the shade structure was due to loss of nutrients, plants in the shade structure showed
signs of nutrient deficiency while greenhouse plants did not. One might hypothesize then that
phosphorous application date would affect tuber growth similarly under field conditions in "wet"
years and "dry" years. Until this hypothesis is tested, results from this preliminary study indicate
phosphorus application date significantly influences tuber yields and further investigations are needed
to develop best management practices for phosphorus fertilization of caladiums.
P Application Date
P Application Date
Figure 1. Influence of phosphorus application date on weight of 'Candidum' caladium tubers
harvested on 22 November (shadehouse) or 25 November (greenhouse). Each 15 cm (6-in
pot) received one application of 0.25g (0.009 oz) of single superphosphate on the dates
The Gulf Coast Research and Education Center
The Gulf Coast Research and Education Center is
a unit of the Institute of Food and Agricultural Sci-
ences, University of Florida. The Research Center
originated in the fall of 1925 as the Tomato
Disease Laboratory with the primary objective of
developing control procedures for an epidemic out-
break of nailhead spot of tomato. Research was ex-
panded in subsequent years to include study of sev-
eral other tomato diseases.
In 1937, new research facilities were established
in the town of Manatee, and the Center scope was
enlarged to include horticultural, entomological, and
soil science studies of several vegetable crops. The
ornamental program was a natural addition to the
Center's responsibilities because of the emerging in-
dustry in the area in the early 1940's.
The Center's current location was established in
1965 where a comprehensive research and extension
program on vegetable crops and ornamental plants is
conducted. Three state tension specialists posi-
tions, 16 state research scientists, and two grant
supported scientists from various disciplines of
training participate in all phases of vegetable and
ornamental horticultural programs. This interdisci-
plinary team approach, combining several research
disciplines and a wide range of industry and faculty
contacts, often is more productive than could be ac-
complished with limited investments in independent
The Center's primary mission is to develop new
and expand existing knowledge and technology, and
to disseminate new scientific knowledge in Florida, so
that agriculture remains efficient and economically
The secondary mission of the Center is to assist
the Cooperative Extension Service, IFAS campus
departments, in which Center faculty hold appropri-
ate liaison appointments, and other research centers
in extension, educational training, and cooperative
research programs for the benefit of Florida's pro-
ducers, students, and citizens.
SProgram areas of emphasis include: (1) genetics,
breeding, and variety development and evaluation;
(2) biological, chemical, and mechanical pest manage-
ment in entomology, plant pathology, nematology,
bacteriology, virology, and weed science; (3) produc-
tion efficiency, culture, management, and counteract-
ing environmental stress; (4) water management and
natural resource protection; (5) post-harvest physiol-
ogy, harvesting, handling and food quality of horti-
cultural crops; (6) technical support and assistance to
the Florida Cooperative Extension Service; and (7)
advancement of fundamental knowledge ofdisciplines
represented by faculty and (8) directing graduate
student training and teaching special undergraduate
Q The Institute of Food and Agricultural Sciences,
University of Florida.
Q A statewide organization dedicated to teaching,
research and extension.
Q Faculty located in Gainesville and at 13 research
and education centers, 67 county extension
offices and four demonstration units throughout
Q A partnership in food and agriculture, and natural
and renewable resource research and education,
'funded by state, federal and local government,
and by gifts and grants from individuals, founda-
tions, government and industry.
Q An organization whose mission is:
Educating students in the food, agricultural,
and related sciences and natural resources.
Strengthening Florida's diverse food and
agricultural industry and its environment
Enhancing for all Floridians, the application
of research and knowledge to improve the
quality of life statewide through IFAS exten-