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Proc. Fla. State Hort. Soc. 112:172-176. 1999.
FERTILIZER MANAGEMENT SURVEY FOR TROPICAL FRUIT CROPS IN SOUTH FLORIDA
Yuncong Li and Jonathan Crane
University of Florida
Tropical Research and Education Center
18905 SW 280 Street
Homestead, FL 33031
Brian Boman
University of Florida
Indian River Research and Education Center
2199 South Rock Road
Ft. Pierce, FL 34945
Carlos Balerdi
University of Florida
Miami-Dade County Cooperative Extension Service
18710 SW 288 Street
Homestead, FL 33030
Additional index words. Avocado, lime, mango, carambola,
lychee, longan, mamey sapote, and papaya.
Abstract. Little is known of growers' fertilizer practices for trop
ical fruit crops in south Florida. A survey of avocado, Tahiti'
lime, mango, carambola, lychee, longan, mamey sapote, and
papaya was conducted to obtain background information on
current fertilizer practices including rates, methods of applica
tion, timing, and perceived information needs. The survey was
carried out during the summer and fall of 1998 and the data
compiled and analyzed in 1999. Of the 108 surveys mailed, 53
commercial growers responded. Fertilizer practices varied
widely among commodities and growers. This benchmark in
formation will give us the opportunity to design extension and
research programs to address the needs of these growers.
Introduction
Commercial acreage of tropical fruits in Florida covers
about 13,853 acres and farm level sales are about $103 million
annually. About 85% of the Florida's commercial tropical
fruit acreage is located in Miami-Dade County. Collier and
Lee Counties rank second and third with about 900 and 400
acres, respectively. The industry in south Florida is adjacent
to several natural ecosystems (i.e., Everglades National Park,
Biscayne National Marine Park, and Big Cypress National Pre
serve and overlays the surficial Biscayne Aquifer). These areas
are highly sensitive to agricultural inputs including fertilizers.
The existence of the tropical industry is partly due to the
marine subtropical climate, which is suitable for many tropi
cal fruits. However, only sandy or gravelly soils with low nutri-
Florida Agricultural Experiment Station Journal Series No. N-01780.
Thanks to Ms. Luice King for her assistance in conducting the survey and all
growers who responded the survey. This project was supported in part by a
grant from the Smith-Lever Special Needs Funds, Cooperative State Re
search, Education and Extension Service, USDA.
172
ent and water holding capacities are available in this area.
The unique soil conditions result in widespread problems for
crop production such as microelement deficiencies, low use
efficiency of fertilizers, and potential leaching of nutrients
into the groundwater.
Little is known of the current fertilizer practices for trop
ical fruit crops grown commercially in south Florida. There
fore a survey was conducted to assist in the future design and
implementation of extension and research programs to ad
dress the needs of growers and of the natural environment.
The objectives of the survey were 1) to obtain background
information on current fertilizer practices for selected tropi
cal fruits (i.e., avocado, lime, mango, carambola, lychee, lon
gan, mamey sapote, and papaya) including rates, methods of
application, timing, and perceived information needs, and 2)
to use this benchmark survey information to design and im
plement extension and research programs to address the
needs of the industry and develop or improve precision fertil
izer practices.
Materials and Methods
The survey instrument was written and reviewed during
spring of 1998. Each questionnaire includes 28 questions. A
list of tropical fruit growers was compiled from previous mail
ing lists and industry contacts and the survey was mailed to
108 growers during August 1998. Introductory letters were in
cluded to describe the nature of the survey. Announcements
of the survey were made at local extension meetings. Follow-
up phone calls were made and some surveys were resent dur
ing the intervening 9 months to encourage more participa
tion. Of the 108 surveys sent, 49% (53) usable surveys were
returned and during April and May the results were placed in
a database, compiled and summarized. The low response rate
may have stemmed from concern that the information would
be used by regulatory agencies and because of time con
straints. Because of the large number of growers for each
crop, it was generally difficult to obtain information from the
majority of acreage of any one crop. Despite these problems,
much useful information was obtained.
Results and Discussion
Crops and soils
A total of 959 acres was represented by this survey which
accounts for 6.9% of the total tropical fruit acreage in south
Florida. The size of groves ranged from 0.25 acre to 211 acres
with an average of 18 acres. The major cultivars, rootstocks,
and in-row and between-row spacing for each crop are listed
in Table 1. Tree age ranged from 0.5 to 70 years old.
A large number of lychee and longan trees had been
planted within the last fives. Eighty-seven percent of respon
dents indicate that they grow tropical fruit trees on gravelly
Proc. Fla. State Hort. Soc. 112: 1999.
Table 1. The major cultivars and rootstocks grown by the respondents, and ages and spacing of trees.
Crop
Avocado (7)z
Tahiti' lime (2)
Mango (6)
Carambola (8)
Lychee (26)
Longan (16)
Mameysapote (2)
Banana (5)
Papaya (3)
Cultivars
'Lula', 'Pollock', 'Booth', 'Simmonds',
'Donnie', 'Choquette', and 'Russell' y
Tommy Atkins', 'Keitt', 'Kent', 'Van Dyke',
'Glenn' and 'Stevens'
'Arkin', 'B-10', 'FwangTung', and 'Kary'
'Brewster', Mauritius', 'Emperor' and 'Hak Ip'
'Kohala', 'Dagelman'
'Pantin', 'Magafia', and 'Pace'
—
Rootstock
'Waldin'
—
Turpentine'
'Golden Star'
—
—
—
Age (year)
1-70
1-30
2-48
2-16
0.5-20
0.5-16
1-18
1-10
6-18
Tree spacing (ft)
In-row
15-25
10
15-25
10-15
7.5-25
10-25
20-30
6-12
5-7
Between-row
24-55
10
15-30
12.5-25
12-30
16-30
20-30
12-20
10-22
zNumbers in parentheses indicate the number of respondents for each crop.
Wot reported by respondents.
soil (Rockdale or Rockland). Krome very gravelly loam and
Chekika very gravelly loam are the new scientific names to
represent Rockdale or Rockland. Five lychee and longan
growers indicated their soils are either marl or the complex
of marl and gravelly soils. One grower in Broward County
grows banana, carambola, lychee and papaya on organic soils
and one grower in Palm Beach County has carambola on Riv
iera sand. Fifty-nine percent of growers planted their trees in
trenches, 26% planted without trenches and 15% planted
some crops in trenches and some without trenches in Miami-
Dade County. Almost all the acreage of avocado was trenched
(315.75 acres) and over half of mango groves were trenched.
The percentage of groves trenched is approximately 60% for
carambola, 80% for lychee, 78% for longan, 50% for banana,
40% for mamey sapote, and 10% for papaya.
Soil testing, plant analysis and fertilizer recommendation
In order to determine the most important factors growers
use to make fertilizer decisions, respondents were presented
with a list of eight possible factors and asked to rank each in
their order of importance. Weighted responses were calculat
ed based on ranks and numbers of responses (Fig. 1). Most
growers indicated they base their fertilizer program on the
time of year or environmental factors (crop growth stage,
rainfall, temperature, etc.). Some growers always use the
same amount fertilizer every year. The University of Florida/
IFAS fertilizer recommendations and advice from fertilizer
dealers or consultants are important factors for some grow
ers. Surprisingly, soil testing and tissue analysis were the least
important factors indicated by respondents. However, in
most cases growers are using multiple criteria to determine
their fertilizer program.
Eleven growers indicated they use soil testing, but only
two growers do it once a year and four growers test every 2
years (Fig. 2). Some growers check their soil pH regularly.
Measurement of soil pH is used to guide liming applications
to maintain soil pH for acidic sandy soils outside Miami-Dade
County. The lack of calibrated soil testing and a proper soil
extraction method for the calcareous soils in south Florida is
a problem for growers' utilizing soil tests. However, the Uni
versity of Florida Extension Soil Testing Laboratory will soon
analyze calcareous soils with a new extraction method.
Fifty-one percent of growers surveyed never use leaf tissue
analysis, 15% of respondents take leaf samples several times
per year, 13% do so once a year and 21% do so only when
crop appearance indicates a problem (Fig. 3). Four respon
dents who take an annual leaf tissue test indicated they col
lected leaf samples at same time or month every year and ten
of them do not take the sample at the same time each year.
Growers that used leaf testing also answered a question on
how long they wait to sample leaves after fertilizing. Most
growers collect leaf samples either prior to or 15 days to 6
months after a fertilizer application. Growers surveyed col
lected leaves from a three to eight ft height, collected one to
sixty leaves per sample, and sampled from one to twenty trees
per acre. Eighty-eight percent of respondents separated sam
ples from healthy and non-healthy trees. Sixty-three percent
collected leaves from non-fruiting shoots while 19% each col
lected from fruiting shoots or a mixture of both. Only 50% of
respondents separated leaf samples for each cultivar of a par
ticular fruit crop. Eighty-eight percent of respondents do not
wash their samples before submission for analysis.
About two-third of respondents follow the recommenda
tions provided by the tissue testing laboratory while only 35%
of respondents closely use recommendations based on soil
testing results. Seventy-five percent of respondents send their
300 -T
1. Time of year
2. Environmental factors
3. Always use the same amount
4. IFAS recommendation
5. Advice from fertilizer dealer/consultant
6. Use tissue testing
7.
8. Other
8
Figure 1. Ranking of factors used for determining how much fertilizer to
apply (n = 53).
Proc. Fla. State Hort. Soc. 112:1999. 173
1. Never
2. Once a year
3. Every 2 years
4. Other
1 2 3
Figure 2. Frequency of soil testing (n = 45).
40
30
20
10 -
1. Not helpful/not necessary
2. Don't know how to do it
3. Other
4. Costs too much
5. Takes too long to get results
6. Sampling takes too much time
12 3 4 5
Figure 4. Reasons for not using tissue testing (n = 42).
samples to local analytical laboratories, 12% use the Universi
ty of Florida Soil Testing Laboratory, and 12% use services
provided by fertilizer dealers or grove services. Growers were
also asked why they do not use tissue testing (Fig. 4). The
most common reasons given were: 1) results not helpful or
not necessary (31%); 2) do not know how to do it (17%); 3)
costs too much (17%); 4) takes too long to get results (9%)
and; and 5) sampling takes too much time (9%).
Fertilizer application methods and rates
Nine fertilizer application methods were listed in the sur
vey (Fig. 5). The most common method of fertilizer applica
tion was dry material of major elements (89%), liquid
application as a soil drench or through the irrigation system
(fertigation, 53%), foliar application (49%) and forty-nine
percent of respondents use a combination of these three meth
ods. Thirty-nine percent of the growers use either biosolids or
composts in their groves and 18% use slow-release fertilizers.
In general, for mature trees, two to six applications of
NPK are applied each year and as many as 9 applications for
young trees (Table 2). Application rates vary for different
crops. Nitrogen fertilizer rates ranged from 6 to 288 lb per
acre for young trees and from 5 to 320 lb per acre for mature
trees. Phosphorus fertilizer rates are from 0 to 360 lb P2O5 per
acre and potassium ranged from 0 to 501 lb KgO/acre. The
response to which nitrogen-phosphorus -potassium (NPK) ra
tios are used varied (Table 3).
The Florida Statutes require that all irrigation systems
into which chemicals are injected for agricultural purposes
(fertigation) be equipped with safety devices which will auto
matically prevent the backflow of water and chemicals to the
60 1. Dry fertilizer
2. Fertigation or soil drench
3. Foliar application
4. Combination (liquid + dry)
5. Biosolids
6. Slow-release fertilizer
7. Compost
8. Other
1. Never
2. When crop appearance
indicates a problem
3. Several times per year
4. Once a year
1 2 3
Figure 3. Frequency of tissue testing (n = 47).
174
Figure 5. Types and application methods of fertilizer or soil amendments
(n = 53).
Proc. Fla. State Hort. Soc. 112: 1999.
In general, about a third of those surveyed indicated they ap
ply about the same amount of fertilizer each year. Relatively
few growers utilize soil or leaf tissue analysis as a tool in their
fertilizer program. The most common reasons sited for not
utilizing soil and tissue analysis were that results are not help
ful or not necessary (31%). This may reflect the lack of a lo
cally calibrated soil test and "optimum" leaf tissue levels for
many of tropical fruit crops (i.e., carambola, lychee, longan,
mamey sapote, papaya). Some growers indicated that they do
not know how to take samples (17%) and that it takes too
long for taking samples and receiving results (18%). The cost
of analysis is also a concern of growers (17%). The responses
suggested a need for research on a calibrated soil test for the
major tropical fruit crops and the development of a user-
friendly method for taking proper leaf tissue tests.
The most common application method for NPK is in dry
form. However, the frequency and amount varied greatly
among crops and among growers of a given crop. Foliar appli
cation is the major method for applying most micronutrients
(e.g., Mn, Zn, and B) whereas soil drench or fertigation is the
most common application method for Fe materials. A num
ber of growers reported the use of compost, sludge, or slow
release fertilizer materials. Many growers with fertigation sys
tems were not familiar with the back flow, check valve, and
shut-off equipment indicating a need for extension of rele vant information.
Proc. Fla. State Hort. Soc. 112:176-178. 1999.
PRELIMINARY RESULTS ON THE EFFECTIVENESS OF TWO ORGANOSILICONE
ADJUVANTS PLUS IRON TO CORRECT LEAF IRON CHLOROSIS OF CONTAINERIZED
CARAMBOLA (AVERRHOA CARAMBOLA) TREES
Jeremy Green, Jonathan Crane, Yuncong Li,
Robert Sanford and Osvany Rodriguez
Tropical Research and Education Center
Homestead, FL 33031
Additional index words. Tropical fruit, star fruit, deficiency, sur
factant, wetting agent.
Abstract. Iron deficiency is a common problem in carambola
trees grown in south Florida. Typical symptoms include mild
to severe interveinal chlorosis and premature leaf drop. Cur
rently, the most effective treatment is soil drench applications
of water mixed with ferric ethylenediamine di-(o-hydroxyphe-
nylacetate (EDDHA) chelated iron sources. However, EDDHA
chelates are expensive and time consuming to apply. Foliar
applications of two organosilicone wetting agents, Silwet L-
77® and Kinetic Non-ionic Surfactant® at 0.025% and 0.1%
concentration, respectively, plus EDDHA or ferrous sulfate
heptahydrate at four concentrations (0%, 0.025%, 0.05%, 0.1%)
were tested for their effectiveness at reducing leaf iron defi
ciency symptoms of six-year-old containerized 'Arkin' caram
bola trees. Leaf chlorosis severity was rated for each tree prior
to and at 10,17, and 34 days after application. In general, chlo
rosis ratings were inconsistent among treatments. Water plus
EDDHA iron at the 0.025% and 0.05% rates resulted in signifi cantly less chlorosis than Kinetic and Silwet plus iron. There
was no significant difference among treatment at the 0.1% rate
of iron. No practical differences were found among adjuvant
and iron treatments.
Iron deficiency is a common problem for carambola trees
grown on the calcareous, high pH soils in Miami-Dade Coun
ty, Florida. Typical leaf symptoms include mild to severe inter-
Florida Agricultural Experiment Station Journal Series No. N-01792. This
project was partially funded by the Carambola Research Committee.
veinal chlorosis and premature leaf drop. If the iron
deficiency is severe, new leaves are stunted and may appear
bleached. Previous research with citrus and avocado trees
growing in calcareous soils has demonstrated that ferrous sul
fate and many chelated formulations are inconsistent or inef
fective in preventing or correcting iron deficiency (Young,
1969; Malo, 1966; Malo, 1965; Leonard and Calvert, 1971).
Currently, the most effective treatment to correct and prevent
iron deficiency on Tahiti' lime, avocado, mango, and caram
bola trees is applications of ferric ethylenediamine di-(o-hy-
droxyphenylacetate (EDDHA) chelated iron sources as a soil
drench. However, EDDHA iron is expensive and, depending
upon the equipment and technology available to the produc
er, time consuming to apply.
The efficacy of foliarly applied iron compounds mixed
with numerous surfactants has been tested for their ability to
correct or prevent iron deficiency in citrus, French prune,
and mango (Neumann and Prinz, 1974; Horesh and Levey,
1981; Weinbaum and Neumann, 1977; Kadman and Gazit,
1984). In general, organosilicate surfactants plus iron per
formed best. Preliminary testing of foliarly applied EDDHA
chelates and iron sulfates with or without surfactants on car
ambola have not been consistently effective nor long lasting.
Furthermore, the use of foliarly applied organosilicone sur
factants has been observed to be phytotoxic and cause leaf
drop in carambola.
Organosilicates are one type of surfactant that has dem
onstrated superior leaf wetting and leaf stomatal penetration
characteristics (Neumann and Prinz, 1974; Stevens, 1994).
They are widely used as adjuvants for herbicides and pesti
cides (Stevens, 1994; Jansen, 1973). The major drawback of
the organosilicates is their potential to be phytotoxic and/or
their ability to greatly increase the amount and rapidity of tar
get material (e.g., iron) that may enter leaves; which may
cause a phytotoxic reaction.
176 Proc. Fla. State Hort. Soc. 112: 1999.