A Vegetable Crops Extension Publication University of Florida
Vegetarian 02-03 Institute of Food and Agricultural Sciences
March 2002 Cooperative Extension Service
(Note: Anyone is free to use the information in this newsletter. Whenever possible, please give credit to the authors.
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I Print Version
* Development of Controlled Release Fertilizer Program for Potato Production
6 Iron Deficiency and Iron Fertilizer Management of Vegetables Grown on Calcareous Soils
* Flooding in Agricultural Fields in South Florida Hydrological Aspects
* Herbs in the Florida Garden
List of Extension Vegetable Crops Specialists
Commercial Vegetable Marketing In-service Training. May 20-21. To be held at the Mid-Florida REC-Apopka. For
more information, contact Fritz Roka at 941-658-3400 or fmro(@gnv.ifas.ufl.edu.
FACTS 2002 Florida Agricultural Conference & Trade Show. May 22, 23. Lakeland Center.
Florida State Horticulture Society Annual Meeting. June 2-4. Marco Island.
Development of Controlled Release
Fertilizer Program for Potato Production
The St. Johns River has been identified by the state of Florida as a priority water body in need of restoration under the
auspices of the Surface Water Improvement and Management Act implemented by the Florida legislature in 1987.
Personnel from the St. Johns River Water Management District (SJRWMD), University of Florida, multiple state government
agencies, and the North Florida Grower's Exchange have developed "Best Management Practices" (BMP) for potato
production in the Tri-County (St. Johns, Putnam, and Flagler Counties) Agricultural Area (TCAA). The purpose of BMP
implementation is to reduce the potential nitrate run-off from approximately 20,000 acres of land in potato production in the
St. Johns River watershed. The SJRWMD manages the BMP program through the TCAA Water Quality Protection Cost
Share Program. The program was developed to provide potato growers in the TCAA with an economic incentive to
voluntarily implement verified BMPs that may incur a greater cost and/or risk by area growers.
The average amount of nitrogen applied to potato acreage in the TCAA is 255 Ib N/A. This rate is falls between a high of
350 Ib N/A on some chip potato acreage to a low of 175 Ib N/A on fresh market potato acreage. The IFAS recommended
nitrogen rate (200 Ib N/A) has been adopted as the BMP nitrogen rate for the TCAA. Grower opinion is that the BMP
nitrogen rate is not sufficient to maintain historical potato yields during all years. In production years with heavy rainfall,
nitrogen can be leached from potato beds making it unavailable to the potato plant. Provisions have been made in the BMP
program to allow for additional nitrogen fertilization during seasons with leaching rains (30 Ib N/A). However, depending on
when leaching rains occur, growers are concerned that they may not be able to side-dress the crop during the critical bulking
period resulting in reduced yields.
Fertilizer technology currently exists, if developed for the region, which could provide a long-term solution to the problem of
nitrate leaching on sandy soils and the need for supplemental nitrogen applications during the season. Controlled release
fertilizer (CRF) technology could overcome the concerns of both growers and regulatory agencies by supplying nutrients to
the crop while reducing the potential for off-site movement of nutrients. Relatively recent improvements with formulation
and prill coating technology have made it possible to release nutrients based on soil temperature independent of soil
moisture. This insures that even under heavy rainfall, nutrients will be left in the prill for release later in the season.
Two challenges need to be overcome before a CRF can be used in commercial potato production. First, a product needs to
be identified or developed that releases nutrients at a rate required by the potato plant. That is, the product should produce
a potato crop with yields and quality characteristics equal to or better than conventional soluble fertilizers. Secondly, the
cost of CRF products needs to fit the economics of potato production. Cost of CRFs for growers will ultimately be
determined by the rate of material used, pricing by the manufacturer based on large scale production (economics of scale),
and whether CRFs are adopted as a reimbursable BMP in the SJRWMD Cost Share Program.
Initial research on CRFs conducted by IFAS personnel at the Hastings REC has had a two fold approach. First, CRFs have
been evaluated for their ability to produce a marketable potato crop compared to conventional soluble fertilizers. Second,
nutrient release curves for nitrogen, phosphorus, and potassium have been constructed for multiple CRFs and soluble
fertilizers under field conditions.
The research has demonstrated to this point that CRFs can be used successfully for potato production. Tuber production
and quality using CRFs have been equal to or greater than soluble fertilizers at equal nitrogen rates (Table 1). Initial results
have verified that approximately 50 Ib/A of nitrogen can be saved by using a CRF in a dry season instead of a conventional
CRF without a loss in quality or yield. Nitrogen savings would be greater in wet years when supplemental nitrogen is applied
to replace leached nitrogen from soluble fertilizers. All fertilizers in studies to this point have been incorporated at planting
and the crops produced using standard practices common to seepage irrigated production in the Hastings area.
Initial in-field nutrient release studies have demonstrated that under heavy leaching conditions, CRFs leach much less
nitrate than conventional ammonium nitrate. Two CRFs have been identified which have release curves that compliment
the nutrient uptake of the potato plant.
Three projects are currently underway this season to further evaluate the influence of CRFs in potato production. CRFs
from four companies are being evaluated in potato production and release curve studies. Also, the influence of leaching
irrigation events on potato production and nitrate movement is being evaluated in plots fertilized with either conventional or
controlled release fertilizers. In addition, two large-scale, on-farm studies are being conducted comparing potato production
using CRFs to the grower's standard fertilizer practices in the Hastings area.
Development of a successful controlled release fertilizer program for potato production will be a "win-win" situation for
growers and regulatory agencies. Florida's farmers will be able to continue to farm with the knowledge that Florida's natural
resources are protected.
Table 1. Yield, marketable yield, percentage of yield by grade, and specific gravity of potato tubers from plants
grown with alternative fertilizer programs at the Hastings REC in 2001.
AN + Urea3
AN + Urea
AN + Urea
PCU + PSCU
PCU + PSCU
Size Distribution By Class (%)2
1 2 3
10 68 22
6 56 36
3 36 52
4 40 43
0.0001 0.0001 0.0001 0.0005
1Marketable Yield: size classes 2 to 4.
2Size Classes: 1 < 1 7/8"; 2 = 1 7/8 to 2.5"; 3 = 2.5 to 3.25"; 4 = 3.25 to 4"; 5 = > 4" diameter.
3AN = ammonium nitrate.
4pCU = poly coated urea; PSCU = poly sulfur coated urea.
5PCU, PSCU, Osmocote 11-11-11 and Osmocote 15-9-12 are proprietary products of the Scotts Company,
6Means separated within columns by Waller-Duncan's k-ratio t test.
(Chad Hutchinson and Eric Simonne Vegetarian 02-03)
Iron Deficiency and Iron Fertilizer Management
of Vegetables Grown on Calcareous Soils
Calcareous soils usually contain from 3% to 94% calcium carbonate (CaCO 3). The pH values of calcareous soils are greater
than 7, and commonly in the range of 7.4-8.4. Iron chlorosis is the most frequent nutritional disorder encountered in crops
grown on calcareous soils. Inorganic forms of Fe in calcareous soils are largely or almost totally unavailable for plant
uptake. High concentrations of bicarbonate in the soil solution can prevent Fe uptake by the plant, as well as its transport
within the plant.
Iron is an essential nutrient for plant growth, which includes the formation of chlorophyll. When the amount of iron available
to plants is not enough for normal growth, plant leaves become pale green, yellow or white, particularly between the veins.
The symptoms begin with young leaves first. Severely affected plants fail to flower or set fruits and may even die from lack
of iron. Iron deficient plants are more susceptible to wind damage during windy winters in south Florida. The visual
symptoms are often clear for plants grown on calcareous soils, but they can be confused with other deficiencies such as
magnesium, manganese, zinc or boron. Tissue analysis will be helpful to confirm iron deficiency.
There are many approaches to deal with iron deficiency of vegetable crops. Most vegetable crops commonly grown on
calcareous soils in Florida have been selected for good adaptation to high pH soils. Thus, vegetable crops generally do not
suffer from Fe deficiency. Some iron-efficient crops release organic acids from their roots to neutralize the bicarbonate and
to mobilize soil Fe. Other iron-efficient crops possess high Fe-reductase activity, or other superior physiological and
biochemical characteristics. However, many new crops and varieties are introduced in to south Florida and many of them
are native to acid soils and iron-inefficient. It is important to test these new crops on a small scale before a large acreage
Growers often ask whether they should use soil acidulents such as elemental sulfur (S), sulfuric acid, triosulfate salts, etc.
to acidify the calcareous soil. To date, no research data have been generated to establish a beneficial effect of applications
of any acidic products on calcareous soils in Florida.
Both soil and foliage application of inorganic sources of Fe such as ferrous sulfate (FeSO 4) or ferric sulfate [Fe2(SO4)3], are
ineffective and should not be used on calcareous soils with high concentrations of calcium carbonate such as soils in
Many chelated iron are available in various formulations. The most popular synthetic organically chelated forms of Fe
include Fe-EDTA, Fe-HEDTA, Fe-DTPA, and Fe-EDDHA. These chelated irons can be used as foliar fertilizer and often
mixed with other micronutrients in a fertilizer product. Foliar application of iron fertilizer cannot effectively correct severe
iron deficiency. Fe-EDDHA is only an effective source if iron is applied through soil for calcareous soils. Soil drench (water
plus iron) or fertigation (through the microirrigation system) are more effective and responses of plants to iron fertilizer are
much more rapid.
Other factors may also cause iron deficiency and iron fertilizer may not be needed. Extreme high or low temperatures can
affect Fe uptake by plants and cause chlorotic symptoms. Plants will grow normal after the weather condition changes.
Over-watering, poor drainage or high water tables also stress plants and affect iron nutrition in soils and plants. Root
diseases such as Fusarium and Rhizoctonia are often associated with wet soils and cause iron deficiency. Poor drainage is
quite common in south Florida. Growing crops on raised beds probably will avoid root diseases.
(Yuncong Li Vegetarian 02-03)
Flooding in Agricultural Fields
in South Florida Hydrological Aspects
There is a great deal of concern among members of the agricultural community in south Florida about the potential impact of
regional water management decisions on crop production. The primary concern is the potential for crops to be flooded as a
result of elevated canal levels. Currently, regional water management decisions in south Florida are generally based on
large-scale hydrological (2 x 2 mile) grids or larger. These regional scales are generally too large to make predictions at the
field (farm)-scale level.
In Miami-Dade County, the hydrological and soil conditions are unique and currently not well understood. This can result in
the inability to predict accurately the effects on individual fields of different canal management scenarios adopted at the
regional level. Work has been initiated by Rafael Muioz-Carpena, Bruce Schaffer and others at the Tropical Research and
Education Center (TREC) of the University of Florida Institute of Food and Agricultural Sciences (IFAS), and colleagues at
the U.S. Department of Agriculture, to gather more detailed information about the interaction between the canal and field
hydrological conditions. This work requires quantification of the small-scale variability of the hydrological properties of the
soil and aquifer and their effects on soil and ground water flow and water table depth changes. The effort will lead to
development and testing of new (and existing) smaller scale hydrological models that will allow the prediction of flooding
events in individual fields (or specific areas within a field) in response to a given canal management scenario. Water quality
issues (nutrients and pesticides) linked to these dynamic conditions are also being researched both at the surface water
(canal) and groundwater. A challenging problem under study is how the canals and the shallow Byscane aquifer in this area
interact and exchange chemicals at the field scale.
A critical issue that needs to be resolved for south Miami-Dade County is the lack of detailed information on surface
elevations for the agricultural area. This is extremely important for successful development and application of field-scale
models for predicting flooding in agricultural fields as a response to canal levels under specific water management
Plant Responses to Flooding
Hydrological conditions need to be linked to plant responses to minimize the potential effects of high water levels on crop
production. Work has been underway by researchers at IFAS and other institutions to determine the effects of flooding on
crops and to identify, develop, and recommend flood tolerant crops for areas that may be affected by elevated water tables
in the future.
Flooding is the major risk to fresh vegetable production in south Florida especially in the south Dade area. Although most
soils are normally well drained, low-lying areas are often prone to flooding during periods of high rainfall. In Miami-Dade
County, agriculture loss estimates from flooding as a result of rainfall (13.9") in December 2000 were 13 million dollars. In
October 1999, vegetable crop losses due to Hurricane Irene were estimated to be about 77 million dollars with nearly 19,000
acres of agricultural production damaged by floods. A project is currently being conducted to develop effective management
techniques to prevent or reduce flooding damage to vegetable crops. Yuncong Li at TREC and Stewart Reed at the USDA
in Miami are currently studying flood tolerance of vegetable crops and developing effective management techniques to
prevent or reduce flooding damage to these crops.
Jorge Peha of TREC has been working on testing woody ornamental crops for flood tolerance in the "Frog Pond" area
adjacent to Everglades National Park. He has found that some native ornamental species [ Conocarpus spp., Quercus
virginiana, Sabal palmetto] can survive flooding very well and even require fewer pesticides under flooded conditions
compared to non-flooded conditions. Plants have been grown under "organic" and "chemical" systems. Those plants grown
with minimum to no insecticides and herbicides have similar market quality to those grown with the use of agrichemicals
(agrichemicals). An economic analysis for both systems will be done at the end of the study to provide growers with
alternative systems for growing native plants under conditions in the Florida Everglades.
Tropical Fruit Crops
For the past 15 years, Bruce Schaffer and others at the TREC have been studying flood-tolerance mechanisms of tropical
fruit crops and trying to develop flood-tolerant rootstocks. Much of this work is published, but some of the highlights are
1. Scions of commercial Annona trees such as 'Gefner' atemoya have been successfully grafted (with the help of Gary Zill
of Zill's High Performance Plants Nursery) on rootstocks of the non-commercial species Annona glabra (pond apple),
which is native to the Florida Everglades. The commercial crops grafted on their traditional Annona squamosa
rootstocks can only survive about 3 days of continuous flooding, whereas plants grafted on Annona glabra rootstocks
have survived and grew for up to 17 months in continuously flooded conditions. These Annona cultivars are currently
being evaluating for horticultural and fruit quality characteristics and in the future they will be field tested in
conjunction with Jorge Peia on his flood-prone experimental site in the "Frog Pond" near the Everglades National
2. For avocado, it has been determined that a strong synergistic effect exists between Phytophthora root rot (PRR) (caused
by Phytophthora cinnamomi) and flooding. The disease generally does not cause mortality under non-flooded
conditions. By preventing Phytophthora infection, one can greatly improve flood-tolerance of avocado trees. Flood
tolerance of avocado was improved by preventing Phytophthora infection with the use fungicides applied to the soil or
injected directly into the tree. However, this approach is impractical since fungicides are expensive and growers do
not want to apply them if they are not sure that their fields will be flooded. The best solution for improved avocado
flood tolerance is Phytophthora-resistant rootstocks; however, there are no truly resistant rootstocks (some cultivars
are said to have resistance, but this is only because the roots outgrow the pathogen). Although the avocado tree has
little or no resistance to PRR, other Persea species in the subgenus Eriodaphne are highly resistant to the disease.
Unfortunately, these related species are sexually and graft-incompatible with avocado. A promising but long-term
solution is the work being done in Richard Litz's laboratory at UF TREC. Through somatic hybridization and other
genetic manipulation approaches, artificial hybrids between avocado and the PRR resistant species are being
synthesized. One of the PRR resistant species is Persea borbonia, which is native to the Florida Everglades.
Plants that develop in-vitro from fused protoplasts of resistant species and avocado are still in the test tube stage
and first need to be acclimated to pots, than the field tested for horticultural performance. Developing flood-tolerant
avocado through molecular techniques is very promising, but a long-range goal.
3. Work with carambola trees has indicated that short-term flooding (a couple of days) actually can stimulate flowering of
carambola, whereas longer-term flooding can harm the plants. Trees will recover from flooding stress after the water
recedes, unless the flooding goes too long (several weeks) or there are repeated flooding cycles for a few days each.
4. Anatomical and morphological features that confer flood-tolerance to some mango trees, have been identified by Bruce
Schaffer and colleagues at TREC. These features have been utilized as markers for screening and selection of
flood-tolerant rootstocks. The mangoes that are grown in south Florida are of the monoembryonic type and do not
come "true to type" from seed, unlike polyembryonic mangoes. Thus, in order to assess the genetic diversity within
mango germplasm for flooding tolerance, it is essential to develop clonal material of monoembryonic mango
accessions to successfully screen and select for flood tolerance. This work has been tried in Richard Litz's lab using
tissue culture techniques. The study was successful in the laboratory, but long-term survival following transplantation
from test tubes to the field is a problem.
The Bottom Line
Several conclusions can be made concerning flooding in agricultural fields in South Florida:
A better understanding of the hydrological system by experimental fieldwork is critical for developing and testing
much needed field-scale models. These small-scale tools could then be linked to more general regional models
currently in use to assess the effects of different canal management scenarios on the field in the south Florida
agricultural area. Initial work by researchers at TREC and the USDA is under way in this direction, but will need
sustained funding by the water and soil management institutions in the area.
Detailed surface elevation data are critically needed for accurate predictions of flooding at the field (farm)-scale.
Public and private institutions in the area should join efforts to obtain this information for the agricultural land in South
Research has been conducted to understand crop responses to flooding and identify or develop flood-tolerant crops
and rootstocks. There are some promising results with native woody ornamentals. For tropical fruit crops, we may
soon be successful in developing flood-tolerant rootstocks for Annona, but whether it is economical is uncertain.
There also may be other horticultural problems associated with this new material so it is being tested. Flood-tolerant
rootstocks for some tropical fruit species (i.e., avocado) can be developed using molecular and tissue culture
techniques, as a long range, environmentally sensitive solution to the problem and to overcome the current reliance
upon agrichemicals for disease control.
(B. Schaffer and R. Muioz-Carpena- Vegetarian 02-03)
Herbs in the Florida Garden
12" seed heads
cloves 6" bulb
root division 24" rhizome
seed/seedlings 12" root
seed/cuttings 12" leaves
seed/cuttings 12" leaves
seed/plants 12" leaves
seed/cuttings 12" leaves
cuttings/division 12" leaves
division 24" leaves
seed 12" leaves
seed/cuttings 24" leaves
seed/cuttings 18" leaves
seed 12" leaves
cuttings/division 12" leaves
(Stephens Vegetarian 02-03)
Extension Vegetable Crops Specialists
Daniel J. Cantliffe
Professor and Chairman
Timothy E. Crocker
Professor, deciduous fruits and nuts,
Assistant Professor, strawberry
Mark A. Ritenour
Assistant Professor, postharvest
Ronald W. Rice
Assistant Professor, nutrition
Steven A. Sargent
Assistant Professor, vegetable
Elizabeth M. Lamb
Assistant Professor, production
Assistant Professor, soils
Donald N. Maynard
Stephen M. Olson
Professor, small farms
Assistant Professor and editor, vegetable
William M. Stall
Professor, weed control
James M. Stephens (retired)
Professor, vegetable gardening
Charles S. Vavrina
James M. White (retired)
Associate Professor, organic farming
University of Florida
Institute of Food and Agricultural Sciences
Horticultural Sciences Department
Florida Cooperative Extension Service
North Florida Research and Education Center Suwannee Valley
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