Krome Section

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.