December, 2002
Issue No: 3

U F/IFA S Nutrie nt Manage me nt

Education Core Group

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Institute of Fod and Agricultural Sciences

Back ground

Federal, state and regional agencies are working
towards formulating regulations for agricultural
operations to reduce nonpoint nutrient source
pollution for water quality protection. Several of our
IFAS faculty are currently involved with these
agencies for developing Interim BMPs for various
commodities. In all cases these efforts are
interdisciplinary requiring frequent interaction among
the UF/IFAS faculty statewide. Several of us feel the
need for a stronger coordination among IFAS faculty
in responding to these needs. The creation and
successful functioning of the proposed Nutrient
Management Core Group will enhance the credibility
of UF/IFAS faculty and educational resources and
create a nodal point for liaison with all the agencies
and public that are interested in the issue. Several
land grant institutions have formed similar core
groups or self-directed teams and have developed
educational material. We will interact with these
institutions to benefit from their expertise and
experience.

In February of 2001, this group coordinated the
FDEP319 Prioritization meeting in Gainesville. This
meeting was attended by state agencies and water
management districts, growers, many commodity
organizations and IFAS faculty and administration.
All comments from this meeting were compiled in an
electronic newsletter and distributed to all
participants throughout the state.

Training for Cor pre h e nsi\e Nutrient
Manage m ent Phnning for Th ird FIrty Vendors
Susan Curry, Soil & Water Science Department

Principal investigators for this project are Rao
Mylavarapu, Randall Brown, and Roger Nordstedt. The
goal of this project is to provide training for members of
approved third party organizations and others desiring to

be trained in one or more of the first three of six
elements described in the USDA-NRCS
Comprehensive Nutrient Management Planning
Technical Guidance. Specifically, the two elements
in which participants will receive training are Nutrient
Management and Land Treatment Practices.
Trainees will have the opportunity to become
Certified Specialists in these two areas. Also,
educational programs dealing with the rationale,
concepts, and particulars of nutrient management will
be targeted to farmers and ranchers, agency officials,
decision-makers, and other citizens who need to
become knowledgeable in nutrient management
problems and solutions in Florida.
A CD was developed which included the reference
materials suggested by speakers, the presentations
and a draft excel spreadsheet for the Florida
Phosphorus Index.
Two Nutrient & Pest Management Module 7 Florida
Practicum Training Courses were delivered in June at
the USDA Service Center in Okeechobee and in
November at the Suwannee County Water
Management District. These courses were intended
for those seeking certification to complete
Comprehensive Nutrient Management Plans
(Nutrient Management & Land Treatment Practice
Elements), Conservation Plans, Nutrient
Management Plans, and/or Pest Management Plans.
This course was provided at no charge to candidates
who are actively seeking certification. Prior to taking
this course the participants should have successfully
completed "Introduction to Water Quality", and
"Nutrient & Pest Management Modules 1 6"
courses offered by the USDA Natural Resources
Conservation Service. These self paced courses are
located on-line at: http://www.nedc.nrcs.usda.gov/.
Our first courses had over 60 participants.
Presenters for the course included Rao Mylavarapu
(IFAS), Randy Brown (IFAS), Roger Nordstedt

Training Continued page 19

Nutrient Managem ent for Tropica IFiruits and Vegetab d s in South Fbrida
Yuncong Li, Tropical Research and Education Center, Homestead

A soil and water science faculty member,
Yuncong Li and his collaborators conducted
various experiments on nutrient
management for tropical fruits, winter
vegetables and ornamental crops at Tropical
Research and Education Center located in
Homestead. In this article, we present brief
summary of two of their research projects to
illustrate their contribution in south Florida:

1. Optimizing fertilizer practice to
improve lychee flowering: Lychee (Litchi
chinensis Sonn.) is gaining popularity in
American markets and is becoming a high
value crop in south Florida. However,
unreliable flowering and yield seriously
impact on lychee production. Flowering
normally follows cold or drought stress.
Under warm weather, high rainfall and
excessive nutrients cause unreliable
flowering and fruit set. Although growers
have no control over the weather, they can
optimize flowering by managing the
vegetative vigor of trees. When excessively
watered and fertilized, lychee trees grow
vigorously and produce vegetative flushes
every two or three months. The lack of
maturity of late vegetative flushes in the late
fall or early winter prevents flowering in
January and February. Vegetative flushes
in late fall can be prevented by restricting
nitrogen in summer. Thus, through proper
nitrogen fertilizing, growers can achieve
abundant flowering. Our results
demonstrated that the timing and rate of
nitrogen fertilizer significantly affected soil

and leaf nitrogen status. High nitrogen
concentrations in the leaves were
associated with vegetative flushing and
reduced flowering and yield.

2. Phosphorus nutrition management in
calcareous soils. Calcareous soils induce
an array of nutritional problem for crops and
phosphorus (P) is one of them. Application
of P fertilizer is important for vegetable
production on calcareous soils. However,
most growers apply too much P fertilizer for
their crops. Over-fertilization leads to
unnecessarily high production costs, may
decrease yield and quality and poses a risk
to the environment. In order to understand
P chemistry and to make fertilizer
recommendation for calcareous soils in
south Florida, several laboratory and field
experiments have been conducted. Soils
from many farming fields were saturated
with P and excessive P applied as fertilizer
often precipitate and become less available
to crops (Fig. 1). Apatite was formed in
calcareous soils which were applied a large
amount of P fertilizer over years (Fig 2).
Field experiments conducted in Miami-Dade
County showed that phosphorous
fertilization increased AB-DTPA extractable
P in the soil but did not affect the
concentration of leaf P, yield and quality of
crops (tomato and potato). For additional
information on these experiments contact
Yuncong Li (Yunlimail.ifas.ufl.edu).

Yuncong Li and Rao Mylavarapu
discuss a tomato field experiment
in Homestead.

Fig. 2. Apatite formed in 3 calcareous
soils which were farmed for many years

Fig. 1. Freundlich and Langmuir P
sorption isotherms and P precipitation
of a calcareous soil.

Lych ee tree

Lycnee rower

Lych ee fruit

Fioritizing Citrus Nutrie nt Manage m e nt De cision
Thomas Obreza, Soil and Water Science Department

Citrus nutrient management is comprised of four
components that cycle through a production season:
Monitoring (visual observations of tree performance
and checking leaf and soil analysis results); Program
Development (deciding what nutrient sources to use,
the rate, timing and frequency at which nutrients will be
applied, and where the nutrients will be placed);
Application (methods used to apply fertilizers); and
Evaluation (determining whether the desired crop
response was achieved).
Ideally, a citrus nutrient management plan will provide
maximum yield and fruit quality while minimizing the
potential for water quality impairment. Nutrient
management becomes a complex subject when
considering all factors that can affect program
development and fertilizer application. In the current
economy, citrus grove managers must prioritize their
activities because they are being asked to accomplish
more tasks than ever before with fewer people, reduced
resources, and less time. When faced with a multitude of
decisions to make, how does a manager decide where
to place the most emphasis?

Citrus tree sensitivity to shortages or excesses of
individual nutrients differs depending on the nutrient. For
example, manganese deficiency does not affect
production nearly as much as nitrogen deficiency.
Similarly, an excess of boron affects fruit quality more
than an excess of magnesium. In the 1960s, researchers
at the CREC in Lake Alfred grew pineapple orange trees
on a previously non-fertilized deep central Florida sandy
soil and omitted single essential nutrients from the
fertilizer program (the N omission treatment was not zero
N, but half of the full N rate). They found that citrus yield
was most sensitive to omission of N, K, and P, and least
sensitive to omission of the micronutrients. It took 7
years for omission of micronutrients to show negative
effects.

When experimenting with mature flatwoods citrus trees
that were well fertilized in their non-bearing years, we
showed that good water management alone provided
about 30 to 40% of maximum yield. When we added
sufficient amounts of N and K fertilizer to good water
management, production reached or surpassed 90% of
its maximum. Thus, the remaining 10% or less of a
grove's yield potential was attributed to the combined
effect of the remaining 11 essential elements. It is
important to recognize that the groves where we
conducted N and K experiments had lime, P, and
micronutrient fertilizers applied to them when the trees
were young.

If citrus is most sensitive to water, N, and K, then

FLORIDA CITRUS INTEGRATED NUTRIENT MANAGEMENT

nutrient management decisions should concentrate on
improving their management before considering other
factors. For example, if a grove is micro irrigated, how
uniform is the water distribution from sprinkler to
sprinkler? Are there any plugged emitters? If a grove
manager chooses to fertigate a significant portion of
the N and K (a recommended BMP), it is important to
check the irrigation system uniformity. If the system
tests below 80%, corrective action should be
implemented to even out the nutrient distribution.

What about N and K20 fertilizer rates? In our research,
we have obtained maximum yield in flatwoods citrus
groves using N rates within the currently recommended
range of 160 to 240 Ibs N per acre per year. When we
used coated, controlled-release fertilizers, rates could
be lowered because nutrient use efficiency increased.
Our current work with P and K fertilizer rates suggests
that K influences citrus yield on the same order of
magnitude as N. However, citrus is not very sensitive
to P fertilization on a flatwoods soil, especially if P has
accumulated in the soil from previous fertilizer
applications.

In summary, when prioritizing nutrient management
decisions, grove managers should recognize the
relative sensitivity of citrus to various nutritional factors
in their groves, and concentrate on improving the most
sensitive ones first.

Nutrie nt Manage m e nt and W ate r Q ua ity in South w e st Fbrida
Rosa M. Muchovej, Southwest Florida Research & Education Center, Immokalee

Application of Biosolids to Bahiagrass Pasture in
Southwest Florida: Impact of grazing on forage, soil,
and water quality.
Grasses, when utilized as feedstuffs for livestock, are
particularly attractive targets for waste utilization
because they are typically under-fertilized. Additionally,
the use of livestock as an intermediate consumer of
crops subjected to organic waste application will
attenuate potentially toxic trace element effects to
humans. Proper timing of pasture applications will also
reduce the amount of biosolids adhering to the forage
and allows possible pathogens to die-off before grazing
or harvesting. Late winter or early spring application will
usually reduce potential harmful effects of biosolids.
There are currently over 12 million acres of grassland in
Florida that require fertilizer, of which 5 million are
planted with bahiagrass (Paspalum notatum Flugge).
Most of the grasslands show signs of N and Fe
deficiencies. Adequate fertilization practices are an
essential part of pasture grasses management and N is
frequently the most limiting nutrient for production.

Previous work with biosolids has shown that biosolids
are capable of supplying as much N to bahiagrass as
commercial fertilizers without impairment of forage or
soil quality. Determination of an environmentally safe
rate of biosolids for application to bahiagrass pastures
(for hay and grazing) on Southwest Florida mineral soils
will contribute to lower fertilizer inputs, improved forage
quality and quantity, and improved soil conditions.

Water quality degradation by nitrate, phosphorus, and
trace metals is of special concern worldwide. In the state
of Florida the concerns are even greater due to the
predominance of extremely sandy soils, abundant
rainfall (high intensity), frequently shallow ground water
tables and heavy reliance on ground water as a
domestic and municipal drinking water source.

The overall objective of this project is to incorporate
production agriculture into a municipal biosolids
management program that combines forage and cattle
production designed to reduce dependence on
commercial fertilizers, improve profitability, maintain or
improve environmental quality, and educate the public
concerning the benefits of biosolids. Specific objectives
are: 1) to determine the rate of municipal biosolids
application required to obtain optimum yield and quality
of bahiagrass under no-grazing and under a grazing
rotational system; 2) to evaluate potential environmental
impacts of biosolids applications to pastures in Florida,
on water quality of shallow ground water aquifers; and
on runoff water; collected in the fields; 3) to determine
the extent of trace metal accumulation in the soil profile
and plant availability of heavy metals from biosolids
application to pasture grasses; and 4) to compare the

biosolids with commercial fertilizer as a source of N and
a supplier of other essential nutrients.

The 3-yr study was set up in a commercial ranch in
Hendry Co., Fl, on established bahiagrass pastures
growing mostly on Immokalee fine sand in South Florida
to determine the release mineralizationn) of nutrients,
especially N, and plant uptake of nutrients and metals
from biosolids and to evaluate impacts of biosolids on
water and soil quality. The biosolids originated from
municipal wastewater treatment facilities and had been
process-stabilized to a "B" classification. Varying rates of
biosolids (ranging from 0 to 20 tons/acre), depending on
previous analyses of the materials employed, were
applied. Rates of biosolids were determined based on
total N content of the material and the highest rate tested
should provide up to 320 Ib N/acre. This rate is up to 3
times greater than recommended N rates for grazed
bahiagrass pastures. Commercial N fertilizer at the rate
of 80 Ibs N/acre (IFAS recommendation for medium
forage production), in the form of NH4NO3, is being used
as a check to determine the rate of biosolids which will
provide that quantity of N to the plants. Treatments were
applied to bahiagrass pastures in the spring, year 2001,
because that is when the supply of biosolids is high and
animals are not intensively grazing (decrease direct
ingestion of potentially harmful trace metals).

For the grazed plots treated with biosolids, three
treatments (0, 80, and 320 IbN/a) were randomly
assigned to 20 field-scale plots, of at least 2 acres in
size, with 5 replications of each treatment. Beef cattle
(cow/calf) rotationally graze (1 week on, 3 weeks off) the
study site from May to October of each year at a
stocking rate based on the carrying capacity associated
with forage produced. Data will be analyzed using
repeated measures analysis with continuous variables
fitted to polynomial models.

Soil samples are also collected periodically, especially
following rain events, at 6-inch increments to a depth of
Continued page 5

Continued from page 4
18 inches, during the growing season. These samples
are analyzed for NH4, NO3, and for all major (S, P, K,
Ca, and Mg) and micronutrients (Fe, Mn, Cu, Zn, and B)
as well as selected trace metals (Pb, Cd, Ni).

The treatment plots were sized, located and oriented to
attempt to avoid cross-contamination of ground water
beneath the plots. A shallow (24 inch depth) and deeper
(48 inch depth) ground water well was installed in each
of the 40 experimental plots. A runoff sampler was also
installed at the soil surface level in each experimental
plot. The water is analyzed for the elements determined
in the soil samples.
Ground water and surface "sheet flow" water was
sampled every 35 days following the application of
biosolids to bahiagrass pasture. There are two separate
sub-studies conducted at the same time: (A) small plots
(10' x 20') ungrazed study and (B) larger plots (2 acre)
grazed study. Each study includes the same treatments
with 5 replications. The treatments are 80 Ibs. N/ac as
ammonium nitrate, 160 Ibs. N/ac as biosolids, 320 Ibs.
N/ac as biosolids, and 0 Ibs. N/ac as a check. Each of
the two studies contains 20 plots, for a total of 40
sampling plots. The treatments were applied to specific
plots in May 2001. Each plot will receive the same
treatment in the spring of the next two following years.
The May 2001 application marked the beginning of this
3-year experiment. The 40 sampling plots are visited for
water sampling every 35 days since May 2001.
At the low end or corner of each plot a permanent GKY
First-Flush Sampler1 was installed for trapping surface
"sheet flow" water after a significant rain event. One
week prior to the scheduled water-sampling week, the 5-
L sample container inside the First-Flush Sampler is
cleaned and rinsed with R. O. water. If significant, but
not flooding, rainfall occurred prior to or during the water-
sampling week, the collected surface "sheet flow" is
recorded.
In the center of each plot, two permanent ground water
collection wells were installed (24" and 48" depth). Water
table height is recorded. Chain of custody records are
kept one each sample.
Each water sample collected was tested in the field for
pH, temperature and electrical conductivity.
Each water sample collected from the field and each QA
standards, spikes, and blanks is tested for the following:
TKN digestion and N analyses; NO3-N, NH4-N
analyses; Ortho P Colorimetric P analyses; Dissolved
total P digestion and P analyses; Total P digestion
and P analyses; Metal analyses K, Ca, Mg, Zn, Mn,
Cu, Fe, Al, B, Ba, Cd, Mo, Ni, Pb, Na, and Cr.
Data from the first year (2001-treatment year) have been
collected and are now being analyzed. A second
application was performed in May 2002 and the same
methodology used in 2001 is being followed.

The results of this project will help determine the
optimum application rate of biosolids for pastures based
on forage production and quality, ground water quality,
surface flow water quality, and concentrations of trace
metals in soil and plant tissue. Information gleaned from
this project will assist government agencies in
conservation and land use planning as it relates to the
application of biosolids.

Nitrogen fertilization of sugarcane on a mineral soil
The response (yield and tissue composition) of
sugarcane variety CP781628 to three N rates (150, 250,
and 350 Ib N/acre), in 4 split applications is being
evaluated on mineral soil for plant cane and two
subsequent ratoon crops. The experimental design is a
completely randomized block, with 4 replications.

The study was initiated in July 1999, with field
preparation. The 12 plots (50 ft x80 ft) were planted to
sugarcane variety CP781628 in Dec. 1999, when the
first split application was done. Subsequent N
applications were done in April, June and August, of
each year. Stalk counts are done in November. Yields
(tonnage and sucrose) were determined for the plant
cane in January 2001. Complete cane removal was
accomplished in February. Soil was sampled from the 0-
6 and 6-12 in depth in the end of February and treatment
application on the first ratoon crop started in March.

Ground water wells were installed in every plot and
samples were collected monthly, if water was present in
the wells, from March until December of each year. In
the winter months the water table remains extremely
low. Water samples are analyzed for pH, temperature,
conductivity, NH4-N, and NO3-N. Leaf tissue and soil
samples (from 0-6 and 6-12 in) are collected
approximately every 4 weeks post treatment application.
Leaf tissue is analyzed for N, P, K, Ca, Mg, Zn, Mn, Cu,
Fe, B, and Na and soil is tested for P, K, Ca, Mg, Zn,
Mn, Cu, Al, Na, Fe, pH, CI-, NH4-N, NO3-N and organic
matter. First stubble sugarcane yields (tonnage and
sucrose) were determined in January 2002 and total
crop removal was completed by mid-January. The same
Continued page 6

Continued from page 5
experimental procedures are being employed in 2002,
for the second stubble crop. The sugarcane should be
harvested by January 2003 and all data collection will be
completed shortly thereafter. Preliminary results have
been presented to growers at growers' meetings and
advisory committee meetings. Growers may be able to
reduce current N fertilizer applications on sugarcane
produced on mineral soils.

Agro-Ecosystem Indicators of Sustainability as
Affected by Cattle Density in Ranch Management
Systems This project, known as the "Buck Island
Research Project" is a cooperative effort between UF-
IFAS, the Archbold Biological Station, the South Florida
Management District, and USDA. The project is
investigating the effects of variable cow-calf stocking
rates on water, forage, and soil quality, as well as
microbial communities, nematodes, and birds. Forty-
(summer) and 80- (winter) acre experimental pastures
were built and flumes were installed for collection of
water samples and monitoring of water quality.

Forages Sub-project: To study the effect of cattle
stocking rate on seasonal forage biomass production,
quality, and utilization in summer and winter pastures.
The specific objectives are: 1) to measure seasonal
forage production from summer and winter pastures
relative to the stocking rate treatments; 2) to quantify the
crude protein and phosphorus concentrations present in
the forage during the grazed and non-grazed periods.
The study includes two pasture systems: winter range
and summer improved pastures. In the winter pastures,
the stocking rates are 0, 2.3 (high), 4.0 (medium), and
5.3 (low) acres per cow. In the summer pastures,
stocking rates are 0, 1.4 (high), 2.5 (medium), and 3.3
(low) acres per cow. The cattle were placed in the winter
pastures in January 2001, were temporarily moved to
summer pastures in February due to water problems,
and returned to the winter pastures in March. Summer
pastures were fertilized in April, and the cattle were
moved to the summer pastures in May, where they
remained until October, when the calves were separated
from the cows. In November, the cattle were moved to
the winter pastures.

Forage samples were collected within summer and

winter pastures from a grazing exclosure cage,
representing ungrazed forage accumulation, and from an
area in proximity to the cage (paired plot), representing
the standing forage after grazing. For the summer
pastures, forage was sampled monthly (June-September)
while cattle were grazing and then every other month
when cattle were grazing the winter range. Forage
sampling in the winter pastures occurred every three
months, regardless of cattle presence. All forage is
clipped at ground level, weighed, and then a sub sample
is dried in a forced air oven to determine percent dry
matter and for forage analysis. Each sample is ground
and analyzed for crude protein, digestibility, and
phosphorus at the Forage Nutrition Laboratory at the
University of Florida. Botanical composition is recorded for
each pasture at each sampling period.

Results obtained thus far indicate that stocking rate
effects on forage production and quality were minimal for
both pasturing systems. For all stocking rate treatments,
percent forage utilization averaged about 30-40% in the
summer pastures and 20-30% for the winter pastures.
Higher utilization levels were expected, given that the high
stocking rates for both pasture systems were above
industry levels where ranchers expect much higher
utilization (50% or higher) of the available forage. This
information does indicate that forage availability should
not be a problem for cattlemen who graze pastures at
stocking rates used in this experiment. Forage production
levels for both summer and winter pastures approached
levels that ranchers achieve. In some months there was a
trend toward lower forage yield with increasing stocking
rate, but this trend was not consistent. Forage quality was
independent of stocking rate. In some months higher
forage quality was observed from the grazed areas
compared to the non-grazed areas. Crude protein levels
approached expected levels, but IVOMD seemed lower
than expected. Phosphorus levels were higher in the
bahiagrass compared to the forage from the winter
pastures. This is probably due to past fertilization of the
summer pastures and subsequently higher soil levels.
With the stocking rates evaluated in this study, forage
production was adequate to support long-term beef
production. Forage quality levels were seasonal, and
supplementation would be needed at certain times of the
year. The data generated from this project provide
information regarding stocking rate effects on forage
biomass, composition, and quality to be used by ranchers
and various agencies to implement better management
practices for Florida's beef cattle industry.

Stocking rates have been found to have no effect on
nutrient loads or concentrations. Summer pastures have
higher nutrient loads than winter pastures and nutrient
concentrations appear to be more stable in the summer
pastures but are variable in the winter pastures due to
annual runoff volume fluctuations. More details can be
obtained at the following web-site:
htto://www.aaen ufl.ed u/~maerc/

Update on Im proved NutrientManagem ent practices for Leath er af Fern

Robert H. Stamps, Mid-Florida Research & Education Center, Apopka

Leatherleaf fern is the predominant
cultivated cut foliage (florists' green) crop
produced in the United States and Florida
accounts for 97% of that production. This
shallow-rooted herbaceous perennial is
grown under shade on highly permeable
soils. The high leaching potential of these
soils places ground water at risk of nitrate
nitrogen contamination. Furthermore,
commercial fertilization practices consist
mainly of applying water-soluble nutrients
using solid-set overhead irrigation systems.
Due to these factors, research and
extension efforts have been conducted for
many years to develop management
practices designed to reduce the potential
for groundwater contamination and to
educate the growers about this potential
problem.

As many of you may be aware, components
of the research effort have included
literature reviews, grower survey, lysimeter
studies, field studies at new and established
ferneries, and other experiments looking at
specific nutritional needs of the crop. The
grower survey was used to characterize the
leatherleaf fern industry by collecting
respondent, fernery, irrigation system,
management practices and financial
information. The economic aspects were
important because only economically
feasible solutions were practical.

Research using gravimetric lysimeters and
micrometeorological monitoring equipment
were conducted in an established fernery.
These studies measured crop water use and
effects of fertilization and irrigation
scheduling setpoints on nitrogen
ammoniacall, NOx, total Kjeldahl) leaching.

Replicated experiments using liquid and
controlled-release fertilizers were carried out
at a field shadehouse research facility in the
heart of the fern production area. That
facility was open to the industry to come and
look at the treatment effects. At that site,
nitrogen concentrations in the root and
vadose zones, as well as in the surficial
aquifer, were monitored.

Additional field studies were conducted at
two commercial ferneries one that was

just being planted and one that had been in
production for years. Nitrogen
concentrations at the top of the surficial
aquifer were monitored at these sites.

Experiments that utilized leatherleaf fern
growing in containers were conducted to
assess the effects of specific nitrogen
sources and micronutrients on leatherleaf
fern fronds. The market demands that
fronds be dark green and have good vase
life characteristics.

Currently, we are in the process of
determining whether or not the
recommended nutrient and irrigation
management practices work under
commercial conditions. We are monitoring
groundwater nitrate nitrogen levels with five
multi-level samplers at six commercial sites
in three counties.

In all these projects, efforts were made to
point out that the data collection efforts were
for research purposes, not regulatory ones.
In addition, frond yield and quality (color and
vase life) were also regularly determined so
that any adverse effects on the crop would
be detected.

Throughout this process, extension
programming has been an important
component. Activities have included "town"
meetings, newsletter articles, field days,
presentations, workshops, personal letter
writing and on-farm visits.

A hollow-stem auger
was used to install the
multilevel samplers.

Multilevel samplers and piezometric
wells have been installed in six
commercial ferneries.

A NutrientManagem entPhn Support(NUMA FS) system for Fbrida crops
J.M.S. Scholberg, H. W. Beck, S. Grunwald, T. Shatar, and T. A. Obreza, Agronomy/Soil & Water Science

In Florida, the majority of drinking water wells that
exceed Maximum Contaminant Levels (MCL) values for
nitrate-N are located near agricultural production areas.
Most Florida soils have poor water and nutrient holding
capacities and are prone to nutrient losses due to
leaching and/or runoff. Current advances in computer
technology provide scientist with unique opportunities to
develop decision support systems (DSS) that will allow
farmers to take full advantage from advances in
information technologies to improve the efficiency of
their production system.

Historically, fertility research focused on maximizing
yield, but such an approach is no longer adequate to
address current environmental concerns. The lack of
information on root interception capacity of Florida
cropping systems is somewhat surprising since in many
cases root systems are the most effective defense
mechanism by which nitrogen contamination of the
groundwater can be prevented. Fertilizer
recommendations for most Florida crops, including
citrus, forages, and vegetable crops are based on a
limited number of rate studies, and are standardized
over large production areas and/or management
systems. Such approach will provide some general
information on overall crop nutrient requirements, but it
will not allow us to improve our understanding of the
dynamic processes that control non-point source
pollution associated with agriculture. Neither will it allow
farmers and producers to take advantage of the capacity
of root system to intercept nutrients before they become
a threat to the environment. Although scientists have
developed models that assess nitrogen uptake and
leaching for agricultural production systems, the
complexity and scope of most of these models confines
their application to academic end-users.

Previous work in citrus allowed the development of a
"temperature N uptake sum" concept. Using this
approach soil temperature effects on N uptake rates can
be accounted for, and universally applicable uptake
functions, similar to the degree day concept used in IPM,
can be developed. Such functions will define the crop's
effectiveness to remove nitrogen from the soil solution
based on soil temperature and initial soil nitrogen
concentrations. The longer nitrogen is kept within the
root zone via appropriate irrigation management
practices, the greater the uptake efficiency will be. A
better understanding of crop nitrogen uptake dynamics
will allow growers and farmers to improve nitrogen
uptake efficiency, and thereby reduce fertilizer cost and
the impact of agriculture on environmental quality.

Use of current computer technology will allow
development of decision support systems (DSS) that are

specifically designed as a management tool for growers.
An example of an existing DSS in Florida is the Decision
Information Systems for Citrus (DISC). This system
includes functional modules to assist growers with
application of agrochemicals and also include record
keeping tools. We aim to extend this work and to take
full advantage of current advances in computer
technology to link scientific and site-specific information
via user-friendly Nutrient Management Plan Support
(NUMAPS) System. This NUMAPS system will provide
optimal nutrient, irrigation and/or other crop
management recommendations for a number of Florida
crops including citrus, tomato and forages. Dynamic
computer modules will be developed to calculate site-
specific fertilizer recommendations based on diagnostic
soil samples and plant tissue values, target yields,
production practices, soil characteristics, and weather
conditions These modules will form the building blocks
and will be integrated into a versatile and grower-tested
decision support system which will facilitate more
efficient transfer of scientific information to the
agricultural producers. Florida Automated Weather
Network (FAWN) data will be combined with a state-wide
digital soil database to provide default values for weather
and soil information, for specific production units and will
be used to assess soil water storage capacity, crop
nutrient and water uptake, nutrient leaching, and runoff.
Site-specific soil information such as depth to confining
layers, soil water holding capacity, and drainage features
along with information from on-farm weather stations,
and/or soil water monitoring devices can be used to
complement and/or refine this information. In this
manner we aim to provide growers with a powerful
nutrient and irrigation management tool.

However, except for citrus, critical information required
for development of such system is greatly lacking.
Additional work will thus be required to develop generic
irrigation management tools, nitrogen uptake, and
nitrogen management modules to provide a scientific
basis required for development of the NUMAPS system.
A team of UF scientists initiated the development of the
NUMAPS system for citrus during the spring of 2002.
Members of this team will implement a series of
greenhouse and field studies to develop comprehensive
information pertaining to root growth, N uptake and
accumulation patterns for other Florida crops at selected
locations throughout the state. This information will be
used for ongoing development and validation of the
NUMAPS system.
Acknowledgement This work is being funded by Florida
Department of Environmental Protection (FDEP) and the
Florida Department of Agriculture and Consumer
Services

BestManagem entFractice s t Reduce Nutrient
Loadings in Surface Runoff from A gricu btra I Land
Z. L. He, D. V. Calvert, P. J. Stoffella, and Y. C. Li
Indian River Research and Education Center, Fort Pierce

Water quality throughout south Florida has been a
major concern for many years. Best management
practices (BMPs) have been proposed to improve
water quality in the surface runoff from the agricultural
land and to restore degraded water systems in the
Indian River area. A field study was initiated in 2000 to
investigate effects of the BMPs on nitrogen (N) and
phosphorus (P) loadings in surface runoff and fruit
yield and quality of citrus. The BMPs implemented
included replacement of 100 % dry application of water
soluble granular blend fertilizer (conventional practice)
with 50 % fertigation and 50 % dry application. Surface
runoff samples were collected using a portable
autosampler that was installed in the field. The BMPs
tended to reduce N and P concentrations in surface
runoff. The differences in N and P loadings were not
significant between the BMPs and conventional
practices because of great variation in discharge rates
affected by field conditions. There was no significant
difference in fruit yield between fertigation plus dry
application and dry application alone. The BMPs
(fertigation) may have beneficial effects on fruit quality,
depending on types of soil and size of the crop.

Autosamper is Instailed in cirus grove to monitor nunert loads
In surMce Toff frm cms eld

Study on Soi ICh em ica I Fope rties and th eir Spectra
Ch aracts ristics in Fbrida
W. S. Lee, J. F. Sanchez, R. S. Mylavarapu, J. S. Choe
Agricultural & Biological Engineering/Soil & Water Science

A study was conducted to develop fundamental
relationship between soil properties from 4
representative soil orders in Florida and their spectral
characteristics. The ultimate goal of this work is to
develop a real-time soil property sensor for use in
effective farm management. A total of 270 samples
were collected from the three representative soil
orders (Alfisol, Entisol, and Ultisol), and were used for
analysis. Soil samples were obtained from 0-15.2 cm
depth at 15 sampling locations in 3 replications.
Reflectance of the soil samples was measured in the
range of 400-2498 nm and the corresponding nutrient
content (P, K, Ca, and Mg) along with pH, and soil
organic matter content were measured for each of the
samples. Partial least square analysis was used to
build prediction models with a calibration data set of
randomly chosen 180 samples. The remaining 90
samples were used to validate the models. The
prediction models for measured soil chemical
properties for 3 soil orders yielded R2 values of
0.24~0.88. This result could further be used toward
development of soil nutrient sensor for site-specific
crop management.

Deve bpmentof t e Green Industries BestManagem entFractices
L.E. Trenholm, Environmental Horticulture Department

According to recent estimates, there are
approximately 4 million acres of home lawns in the
state of Florida at this time. Of this, roughly 1
million acres are maintained by a professional
lawn care service. Due to the high visibility of this
industry and increased concerns about the fate of
nutrients and pesticides applied to residential
lawns, the home lawn care industry has often
been targeted as a primary source of nitrate and
or phosphate pollution of ground or surface
waters. Because of this perception, a number of
municipalities have developed localized legislation
to regulate the lawn care industry, often without
any scientific guidance.

In response to these recurring issues, the Green
Industries Best Management Practices (BMP's)
have recently been developed. Participants
involved in this process included representatives
from industry, the Department of Environmental
Protection, Water Management Districts, and
IFAS. Regular meetings of the steering committee
began in the summer of 2000, where a loose,
generalized outline for the content was adopted
from the Professional Lawn Care Association of
America BMP document.

Four committees were established to develop the
content for the manual: Irrigation, Fertility, Other
Cultural Practices, and Pesticide Safety.
Information was included on establishment of turf
and landscape areas as well as established turf
and landscape areas. Although the basic objective
of the manual was preservation of Florida's ground
and surface waters, general maintenance regimes
were included to the extent that they were an
integral component of turf and landscape
management. Committees met as needed to
develop their modules and the steering committee
met every other month to review information.
While the thrust of the content is general material,
specific recommendations for irrigation and fertility
rates can be found in the manual.

One difference in the Green Industries BMPs from
some other commodity groups is the absence of
rule typically found in other commodities BMPs.
Since the applicator in this case is generally not
the landowner, no formal rule can be applied;
however, the manual still carries the endorsement
of DEP and implies proper procedure. Since the
entire development process was largely industry-
driven, it is apparent that concerns throughout

industry for conforming to these BMPs is high and,
hopefully, compliance will be high as well.

Some specific recommendations:
When applying water-soluble nitrogen
sources, only apply up to 0.5 Ibs of N 1000 ft2

Slow release, or fertilizers containing at least
30% slow release nitrogen, may be applied at
rates of up to 1 Ib N 1000 ft2.

Higher fertilizer rates may be used to help turf
recover from injury or during turf
establishment.

Do not fertilize if heavy rains are forecast
within 48 hours.

Irrigate to replace water as needed by turf. In
most cases, this will be -3/4 in. of water per
irrigation at each application. Application
frequencies will vary depending upon location
in state, soil type, time of year, grass species,
and effects of microenvironment.

Some general recommendations:
Fertilizer spills should be swept up rather than
hosed down.

Grass clippings can be left on the lawn, where
they will not contribute to thatch, but can
provide a source of recyclable nutrients.

When fertilizing near water bodies, deflector
shields should be used. If shields are not
used, increase the distance of fertilized areas.

The next component of the Green Industries BMP
development is to design a training manual to
actually provide training for up to 15,000 lawn care
and landscape workers over a 2 year period. This
basically explains to them how to use the manual
properly and how it will affect how they do
business. A series of train-the-trainer In Service
Workshops have been scheduled beginning in Jan
2003. After completing the workshop, agents will
then conduct their own training programs over a 2
year period.

Long-Term Tesdtng ofFbssib i Fertl Izaldon and Irrigalton BM R for W aterm e bns Grown in North Fbrida
Eric Simonne, Michael Dukes, Robert Hochmuth, George Hochmuth, David Studstill and Wayne Davis
Horticultural Sciences and Agricultural & Biological Engineering

With approximately 142,000 ha, the vegetable industry in
Florida has an estimated annual value of $1.2 billion.
Together with tomato (40,000 acre, $500 million), bell
pepper (20,000 acre, $300 million), and strawberry
(7,000 acre, $160 million), watermelon (45,000 acre, $45
million) is an economically important vegetable crop for
Florida These crops are intensively grown with
plasticulture (raised beds, polyethylene mulch, and drip
irrigation).

Increased environmental concerns supported by reports
of high nitrate levels in springs and streams throughout
Florida, have resulted in the passage of the Surface
Water Improvement and Management (SWIM) Act of
1987 (chapters 373.451-373.4595 of Florida statutes) by
the Florida legislature. Together with the provisions of
the Federal Clean Water Quality Act of 1977 (public law
No. 95-217), the SWIM Act created a program which
focused on preservation and/or restoration of the state's
water bodies through the development and
implementation of Best Management Practices (BMPs).
BMPs are irrigation and fertilization practices designed
to produce economical marketable crop yields while
minimizing the environmental impact of crop production.

This new round of legislation was not welcomed by the
vegetable industry in Florida. Growers, who already did
not believe that economical yields could be produced
with the fertilization recommendations of the Institute of
Food and Agricultural Sciences (IFAS), requested
reliable data documenting the impact of current
production practices on water quality. Growers also
question the relevance of using the EPA drinking water
standard (10 ppm NO3-N) as the threshold for discharge
monitoring, because the fate of nitrates below the root
zone are unknown, and no one drinks water just below
the root zone of vegetables. Because limited information
was available to document the joint effect of current
IFAS fertilization and irrigation recommendations on
watermelon yields and their impact on nitrate leaching
on a sandy soil, a large-scale field project was
conducted between 1998 and 2002. The objectives of
this project were to (1) determine whether commercial
yields of watermelon could be produced when IFAS
recommendations are followed, and (2) document the
impact of these recommendations on nitrate levels below
the root zone of watermelon.

The field was located at the North Florida Research and
Education Center Suwannee Valley, near Live Oak, FL
where the soil is a Lakeland fine sand. Except where
otherwise mentioned, cultural practices were similar for
1998, 2000, 2001 and 2002. Crop sequence was a
spring watermelon, followed by a fall double crop. Each

year, a rye cover crop was grown from October to
February. Five-week-old watermelon transplants were
established at a within-row spacing of 3 ft, onto beds
spaced 7.5-ft apart. This created a plant stand of 1,900
plants/acre). Selected varieties were >Royal Sweet: in
1998 and 2000, and >Mardi Gras= in 2000 and 2001.
High-density, black polyethylene mulch and drip tape (24
gal/100ft/hr; 12-in emitter spacing) were used as
typically done in commercial fields in North Florida.
Transplanting dates were 26 Mar. 1998, 21 Mar. 2000,
27 Mar. 2001 and 26 Mar. 2002.

Current IFAS irrigation and fertilization recommendations
for watermelon production in Florida were followed.
Based on soil test results, fertilization recommendations
were 150-0-150 (N-P205-K20). Fertilization consisted
of a preplant application of 50 Ibs/acre of nitrogen (N)
and potassium (K20), and of weekly injections of liquid
8-0-8 at daily rates ranging from 1 to 2.5 Ibs/acre/day of
N and K20 that provided the remaining N and K. In
1998, 2000 and 2002, the preplant fertilizer source was
either 13-4-13 (>inorganic=) or chicken manure (1.5-2-2,
>organic-). In 2001, the only source of fertilizer was 13-4-
13. Irrigation was applied once a day for one to three
hours so as to maintain soil water tension (SWT) in the
6-to-12 inch zone between 8 cb (field capacity) and 15
cb. SWT was measured with tensiometers. Watermelons
were harvested twice when they reached commercial
maturity on 29 May and 9 June, 1998, 1 and 6 June,
2000, 7 and 20 June, 2001, and 23 May and 7 June,
2002. Each year, soluble solid levels were determined
on eight representative watermelons from each plot from
the first harvest using a hand-held refractometer.
Soluble solid levels are an indication of sweetness.
Watermelon with soluble solids below 10oBrix do not
taste sweet.

Nitrate levels in ground water were determined every
three weeks at the 4-ft depth with suction lysimeters
(one per plot) and at the 20-ft depth with four shallow
wells located at the edges of the field. An additional
control well was placed approximately 1,500 ft up-grade
from the field in a non-fertilized area under natural
vegetation. Suction cup lysimeters consisted of a
porous ceramic tip connected to an air-tight buried
chamber that was accessible through two sealed tubes.
Lysimeter operation consisted of two steps. First, a soil-
water sample was collected by creating a vacuum inside
the chamber with a hand-held pump. Water moved from
the soil into the chamber through the porous cup
because of the difference in pressures. Then, 24 hours
later, samples were retrieved by placing a collection
Continued page 12

Continued from page 11
bottle at the end of one tube, and by blowing air into the
other one. All suction cup lysimeters were placed at the
center of one of the plastic-mulched beds. Lysimeter
and well samples were refrigerated, acidified and
promptly delivered to the University of Florida Analytical
Research Laboratory in Gainesville, where NO3-N levels
were determined using EPA method 353.2.

Each year, the whole 4-acre field was planted. The
experimental design was a randomized complete block
design in 1998 and 2000. Single replications were used
in 2001 and 2002. Large plots were used in 2001 and
2002 to reduce border effects and the lysimeter-to-
lysimeter variability. For each year, plots for data
collection consisted of four adjacent, 300-ft long rows.
Data were collected on six plots in 1998 and 2000, and 8
plots in 2001 and 2002. Each year, yields were
compared to typical yields found in commercial fields.
The average watermelon yield in Florida was 35,000
Ibs/acre in 2000, but this state average includes
watermelons grown on bare-ground as well as those
produced with plasticulture. However, watermelon
growers who use plasticulture consider one truck load
per acre a commercial yield. Lysimeter data were
compared to the 10 ppm NO3-N drinking standard value
because no other value is available for comparison.

During the 4 years of this test, the warm and dry weather
conditions were representative of Spring conditions in
North Florida. Planting dates (between 21 and 27 Mar.)
and harvests completed between 58 and 72 days after

transplanting (DAT; DAT were 64, 72, 73 and 58 in
1998, 2000, 2001, and 2002, respectively) were
representative of watermelon production fields in the
area. Watermelon marketable yields ranged between
43,680 and 72,128 Ibs/acre between 1998 and 2002
(Table 1). Watermelon fruit size ranged between 18 and
21 Ibs/melon, which is close to the 18 to 20 Ibs range
commonly found for allsweet watermelon varieties like
>Royal Sweet: or>Mardi Gras: when grown commercially.
Sweetness ranged between 8.5 and 11.3 Brix.
Although size in 1998 and sweetness in 2000 were
marginal, watermelon yields with IFAS recommendations
were overall very similar to those from commercial fields.
No significant yield differences were found between the
two preplant-fertilizer treatments, although yields tended
to be higher when chicken manure was used (Table 1).
This supports the common practice that chicken manure
is a suitable substitute for pre-plant inorganic fertilizer in
watermelon production. This also suggests that soil
water holding capacity and/or soil organic matter content
are unlikely to be modified in a practical way at the
chicken-manure rates used. Our rate (approximately 2
tons/acre) was based only on nitrogen content and
calculated to supply 50 Ibs of available N. Increasing
chicken manure application rates as an attempt to
increase soil water holding capacity and/or organic
matter content will likely result in over fertilization
(especially in phosphorus) and high salt levels (due to
nitrate) early in the season.

Continued page 13

Table 1. Watermelon marketable yields between 1998 and 2002 and grown on a sandy soil using IFAS
fertilization and irrigation recommendations
Year Pre-plant Mean Individual Soluble Yield and fruit size
fertilizer watermelon fruit weight solids at comparable to those from
source yieldz (Ibs/acre) (Ib/fruit) harvest commercial watermelon
(Brix) fields?x

1998 Inorganic 43,680 a 17 n/a Almost (87%)

Organic 55,418 a 18 n/a Yes (110%)

2000 Inorganic 55,605 a 20 8.5 Yes (110%)

Organic 72,128 a 20 8.5 Yes (143%)

2001 Inorganic 46,340 18 11.0 Yes (92%)
+/-4,144y

2002 Inorganic 53,813 a 19 10.7 Yes (107%)

Organic 57,562 a 18 11.3 Yes (114%)
z Mean yields followed by different letters are significantly different
Y Standard deviation of the mean
x Based on achieving 90% of a reference commercial yield of 50,400 Ibs/acre (100%) and individual fruit weight of 10 to 20 Ibs

Continued from page 12

SWT tension at the 6-to-12 inch depth tended to remain
within the recommended 8-15 cb range. As observed in
2001 and 2002 (Fig. 1), SWT was greater than this
range for several days (between 49 and 55 DAT in 2001,
and 37 and 57 DAT in 2002), when weather demand
increased crop water use as day length increased. At
the same time, watermelon plants were rapidly growing
and fruit development increased crop water use.
Watermelon growers who have sandy soils and use drip
irrigation often report a brief period of water stress
shortly after fruit set especially when no rainfall occurs
during that period. These results illustrate the
importance of daily monitoring of SWT in order to avoid
water stress or excessive water application. These
results also support the need for split irrigations during
fruit enlargement. Our yields and SWT results
emphasize the importance of managing irrigation and
fertilization together in order to obtain highest yields.

Nitrate levels in the lysimeters showed variations and
ranged between 0 and 160 ppm NO3-N (Fig. 2). On most
sampling dates, they were above the 10 ppm NO3-N
EPA drinking water standard. When the field was
covered with a rye cover crop from November to
February, lysimeter nitrate levels ranged between 5 and
20 ppm NO3-N. These levels tended to increase during
the watermelon crop. Highest NO3-N values observed
during the watermelon crops were 7, 90, 78 and 90 ppm
NO3-N in 1998, 2000, 2001 and 2002, respectively.
Highest values for each year tended to occur during the
fall, several months after watermelon harvest. In 1998,
2000 and 2002, no significant differences were found
between the two fertilizer treatments. On most sampling
dates, lysimeter nitrate levels tended to be numerically
lower when chicken manure was used, but these
differences were not significant due to high variability in
the measurements. Nitrate levels in the control well
remained at 0 during the whole experiment, while those
in the wells around the field remained between 0 and 20
ppm NO3-N. These results suggest that when IFAS
recommendations are followed, the range in nitrate
levels below watermelon fields was reduced at the 20-ft
depth as compared to the 4-ft depth. Further reduction
may occur at greater depths. These results support
growers doubts about the relevance of applying this EPA
drinking water standard to shallow ground water.
Moreover, expecting nitrate levels to remain below 10
ppm NO3-N would be sufficient to maintain water quality,
but, it is not necessary. Year-round fluctuations in
nitrate levels also suggest that peak discharge may not
occur during the watermelon crop. Hence, abandoning a
field after harvest may increase nitrate discharge.
Double cropping (planting a second cash crop on the
same plastic) or planting a cover crop immediately after
discing will help trap residual nitrate in the soil, thereby
reducing the potential risk for further discharge.

Date
$ 15

Fig. 1. Soil water tension at the 15-cm and 30-cm depths
below watermelon grown in 2001 and 2002 with IFAS
fertilization and irrigation recommendations.

TT
-.3

Date
Fig. 2. Effect of fertilizer sources (inorganic and chicken
manure) on nitrate (N03-N) levels (1 mg/L = 1 ppm)

In conclusion, economical yields of watermelon
were produced three years out of four when IFAS
fertilization and irrigation recommendations were
followed. Yields during the fourth year (1998) were
marginal. Nitrate levels fluctuated between 0 and 160
ppm NO3-N at the 4-ft depth, but only between 0 and 20
mg/L NO3-N at the 20-ft depth. Since reducing fertilizer
applications is likely to reduce yield, efforts to reduce
nitrate leaching may focus on splitting irrigation,
increasing fertigation frequency (daily instead of weekly),
and year-round field management.

A'

Best Managem ent Factices for Irrigalton and Fe rl Izalton of Fbrida Citrus in F-tw oods Soi I
Calvert D. V. and Z. L. He, Indian River Research and Education Center, Fort Pierce

There has been increasing concern over nutrient loss
from agricultural practices, which may contribute to the
accelerated contamination of groundwater and surface
waters. This concern is greater in sandy soils, which
have minimal nutrient retention capacity. This research
began in October of 1993, with funding from the St.
Johns River Water Management District and the South
Florida Water Management District. The first phase of
the three years project was completed in September
1996. A comprehensive report on the first phase of the
project was submitted to the Districts with a copy to the
Department of Agriculture and Consumer Service
(DACS). DACS-Nitrate Bill funding for the second three
years phase of this project began in October 1996. This
project was approved to extend for another two years
from 1999 to 2001, as approved by the Nitrate-bill
Funding committee.

The objectives of this research are: (i) to evaluate the
effects of varying rates of N application either as dry
soluble fertilizer, liquid source through fertigation or as
controlled-release fertilizer on tree growth, leaf nutritional
response, fruit yield, and fruit and juice quality
parameters; and ii) to develop an optimal irrigation
schedule and rate of N program for improving water and N
use efficiency for production of high quality grapefruit in the
Indian River area.

The field experiment was conducted in a commercial
grove with 26-year-old white Marsh grapefruit trees on
sour orange rootstock on the east coast of Florida, Hobe
Sound, Martin County. The experiment occupied an area
of approximately 20 acres. The major soil type in this
block is Riviera fine sand. Because of replanting of the
grove (removal of the old trees, re-bedding and planting
of young seedlings), an action taken by the grower,
monitoring of water table and soil moisture was forced to
be discontinued.

Nutrient Management for High ydeld
and Quality or Citrus

The experiment included four N rates: 0, 56, 112, and
168 kg ha-1 yr1. The ratio of N:P:K in the fertilizer was
1:0.2:1, accordingly varying N rates also resulted in 0,
10, 20, and 30 kg P ha' yr1 and 0, 56, 112, and 168 kg
K ha1 yr'. The fertilizer was applied as either dry
granular water soluble form (DWS, with N and P derived
from ammonium nitrate and triple superphosphate, while
K was from muriate of potash and sulfate of potassium
and magnesium) or fertigation (FRT, liquid fertilizer with
N, K, Mg, and S from potassium nitrate, magnesium
nitrate, ammonium nitrate and ammonium sulfate and P
from phosphoric acid). Each plot consisted of 5 uniform
trees planted at a 6 x 6 m spacing (269 trees ha1) with 4
replications. The trees were irrigated using an under
tree microirrigation system with one emitter (37.8 liters
per hr) per tree and the irrigation was scheduled by
reading tensiometers at 15 and 30 cm depth (under the
tree along the dripline), using setpoint of 10 cbars during
January to June (dry season) and 15 cbars July to
December (rain season), respectively. These setpoints
were equivalent to 20 and 40% depletion of available
moisture. The annual amount of fertilizer was applied
using a mechanical spreader in 3 equally divided doses
(February, May and October) for the DWS, and in 15
equally divided doses (3,3,3,2,2,2 applications in
February, March, April, May, September, October,
respectively) for the fertigation treatment.

The concentrations of NO3-N, PO4-P, and Kwere
measured in soil solution sampled using suction
lysimeters installed above (120 cm) and below (180 cm)
the hardpan. Six-month old spring flush leaves were
sampled for mineral analysis in July every year. Twenty
leaves per tree were collected from non-fruiting
branches around the tree from each of the middle three
trees within a plot. Fruit sampling began in October and
was continued at 8-week intervals until late May next
year. The fruit were analyzed for fruit weight, juice
Continued page 15

Continued from page 14
weight per box, juice percentage, soluble solids (Ib/box),
and Brix and acid content. Fruit were harvested on April
17, 2001 and the yields were recorded.

The concentrations of N03-N and P04-P in soil solution
at both 120 and 180 cm depths increased with
increasing fertilizer rates. Fertigation tended to enhance
leaching of N03-N and P04-P, as compared with dry
soluble granular application. The concentrations of
N03-N and P04-P in soil solution were much higher at
the 120 cm depth than at the 180 cm depth. The
average concentrations of N03-N in soil solution at both
the 120 and 180 cm depths over three years were well
below 10 mg L1, the maximum contaminant level, even
at the highest rate of fertilizer application. Solution P04-
P concentrations at the 120 cm depth averaged 0.25 to
0.70 mg L1 over three years for plots receiving various
amounts of fertilizer and may constitute a P source for
surface waters, as soil solution above this depth is likely
to seep into water furrows through lateral movement and
be discharged into drainage water. The results indicate
that best management practices in this sandy soil region
should be also directed to minimizing the leaching of
P04-P in addition to N03-N.
There was a close correlation between leaf N
concentrations and N rates (r= 0.93* to 0.98**). Fruit
yield was related quadratically to N rates and leaf N
concentrations. At 90% of maximum yield, leaf N
concentrations were 22 to 23 g kg-1. Fruit quality
parameters such as Brix, juice, and solids were
positively correlated with leaf N concentrations, whereas
fruit size and Brix/acid ratios tended to be negatively
related with leaf N concentrations or N rates. However,
fruit sizes or OBrix/acid ratios were acceptable for fresh
marketing or processing at leaf N concentrations of 22-
23 g kg 1. Therefore, this leaf N concentration of 22-23 g
kg 1 can be considered the optimal concentration
guideline for fertilization of grapefruit.
Autoumnpler i installed orn vegetable farm lo monitor P Ioed in
surface runoff __

achingn ( tal in

Soi IAmendm e nttD Reduce R osphorus
Leach ing in a Sandy Soi I
Z. L. He, D. V. Calvert, P. J. Stoffella, and Y. C. Li
Indian River Research and Education Center,
Fort Pierce

Leaching of phosphorus (P) in sandy soils has been
considered as a nonpoint source of P that affects
surface water quality. Column leaching studies were
conducted to evaluate effects of soil amendments on P
leaching in a sandy soil. The soil was a Riviera fine
sand (loamy, siliceous, hyperthermic, Arenic
Glossaqualf) from a commercial citrus grove in Florida.
The soil amendments were: (1) cellulose (organic
carbon; C), (2) clinoptilolite zeolite (CZ), (3) lime
(CaCO3), (4) gypsum (CaSO4), (5) Recmax (a
commercial product made from slag out from steel
manufacture), and (6) C plus CZ. The application rate
was 15 g kg-1 for all the additives. For low P soil (14
mg kg-1 Olsen-P), addition of cellulose was most
effective, reducing leachate P concentration from 1.2
mg L1 to below 0.3 mg L1 in the first volume of
leaching and from 0.9 mg L1 to <0.1 mg L1 in the
6th volume of leaching. The cumulative amount of P
leached by the six volumes of leaching decreased
among the different amendments in the order of
control, zeolite > gypsum > cellulose + zeolite >
Recmax, lime > cellulose. For high P soil (amended
with 100 mg P kg-1 soil), Recmax was the most
effective, which reduced leachate P from >60 mg L1
to below 0.5 mg L1 in the first volume of leaching,
followed by cellulose and lime amendment.

Research and Extension work in 1h e nutrients anagementand water qua ity area in the EAA.
Samira Daroub, Everglades Research & Education Center, Belle Glade

The Everglades Agricultural Area (EAA) comprises
700,000 acres of highly productive land south and
downstream of Lake Okeechobee. The soils in the EAA
are organic soil and the majority of the land is in
sugarcane production. Other crops include rice, sod,
sweet corn, lettuce and other vegetables. The University
of Florida/ Institute of Food and Agricultural Sciences
(UF/IFAS) Best Management Practices (BMP) research
and education projects to reduce phosphorus (P) load
from the EAA started in 1986. Results from this work
resulted in a number of BMPs that effectively reduced P
loads coming off the EAA. Some of these BMPs included
banding fertilizer for vegetable crops at reduced rates,
and using proper fertilizer handling and application
methods for all crops. A combination of improved
drainage uniformity and a reduction in drainage pumping
also yielded significant reductions in P loads for all
crops. Mandatory BMP implementation for the EAA
stared in January 1995. A list of BMP options adopted by
the South Florida Water Management District (SFWMD)
is in the enclosed table.

Our current research and extension efforts are multi
faceted. One important objective of the project has been
to improve the implementation and to assess the efficacy
of the implemented BMPs. Seven farms, that have
different BMPs implemented, are included in this project
where extensive array of monitoring instruments were
installed to each site to track changes in P
concentrations, and drainage water discharge. The farm
level reductions appear to be reflected in basin-level
monitoring data produced by the SFWMD. Hydrologically
adjusted farm-level load reductions, expressed as the
SFWMD adjusted unit area load (AUAL), averaged 54.9
% for the project sites (7-year average referenced to
WY93-94). The EAA basin-level AUALs decreased by
approximately 41.4% and total P concentrations by
7.9%.

Another equally important area of our research includes
development of management strategies to address
particulate phosphorus (PP) source and transport
mechanisms. Farm-level studies showed that P attached
to particulate matter in drainage water samples accounts
for up to 60% of total P leaving the farm. The majority of
PP in the EAA is sourced from in-stream biological
growth rather than soil erosion. The sediment that
contributes to PP export is recently deposited biological
material such as settled plankton, filamentous algae, and
macrophyte detritus. These materials can be readily
suspended under the turbulent conditions that exit at the
pump start up. This highly mobile material causes a high

concentration of suspended solids during the early
periods of pump events. High velocity in the canal is the
single most important factor in PP transport. Some
BMPs recommended include the removal of biomass
accumulated and transport it well away from the canal.
In addition, it is recommended to evaluate pumping
strategies and revise them to reduce velocity spikes.

Extension effort involves BMP training workshops for
growers, which are tailored for individual growers. A
half- day sessions for BMP training cover the different
soil, fertilizer, PP and hydraulic BMPS. The BMP training
is part of the permit requirement issued by the SFWMD
and needs to be done annually. It is an important venue
we have to share our most recent research results with
the growers and farm managers. We have three EDIS
publications regarding PP in various stages of review
and publication. We also have started an on-farm BMP
demonstration program at EREC. The research station
at Belle Glade has been divided into BMP and non-BMP
plots to show the effects of implementing PP BMPs.

Table 3 Best Management Practices Summary and "BMP Equivalent" Points

BMP PTS DESCRIPTION
WATER DETENTION water table management by controlling levels in canals,
% Inch Detained 5 field ditches, soil profile, fallow fields, aquatic cover crop
1 Inch Detained 10 fields, prolonged crop flood;
measured on a per event basis rainfall vs runoff
FERTILIZER uniform and controlled boundary fertilizer application (e.g.
APPLICATION CONTROL 2 V direct application to plant roots by banding or side-dressing;
pneumatic controlled-edge application such as AIRMAX)
FERTILIZER
CONTENT CONTROLS
Fertilizer Spill 2 formal spill prevention protocols (handling and transfer)
Prevention side-throw broadcast spreading near ditch banks
Soil Testing 5 avoid excess application by determining P levels needed
Plant Tissue Analysis 2 2 avoid excess application by determining P levels needed
apply small P portions at various times dunng the growing
Split P Application 5 season vs. entire application at beginning to prevent excess
P from washing into canals (rarely used on cane in EAA)
Slow Release P avoid flushing excess P from soil by using specially treated
Fertilizer 5 fertilizer which breaks down slowly thus releasing P to the
plant over time (rarely used in EAA)
SEDINTCNTR S EACH SEDIMENT CONTROL MUST BE CONSISTENTLY
DIMENT CONTROLS IMPLEMENTED OVER THE ENTIRE ACREAGE
Sleveling fields cover crops
Any 2 2 ditch bank berm raised culvert bottoms
sediment sump in canal veg on ditch banks
Any 4 5 strong canal cleaning program other BMP
field ditch drainage sump
Any 6 10 slow field ditch drainage near pumps
sump upstream of drainage pump intake
OTHER reduce cattle waste nutrients in surface water runoff by "hot
Pasture Management 5 spot" fencing, provide watering holes, low cattle density,
shade, pasture rotation, feed & supplement rotation, etc.
Improved Infrastructure 5 uniform drainage by increased on-farm control structures
Urban Xenscape 5 lower runoff & P by using plants that require less of each
Det. Pond Littoral Zone 5 vegetative filtering area for property stormwater runoff
Other BMP Proposed TBD proposed by permitted and accepted by SFWMD

Ecobgica Ij Enhanced Storm w ate r/lrrigaton Reuse Fbnd
Mark Clark, Soil & Water Science Department

Water consumption, pollutant runoff, and stormwater
flood control are among numerous environmental
concerns that often seem in conflict with maintaining
profitability of a company. Yet sustaining natural
resources and the economy will require that these
objectives not be mutually exclusive. A project started
by University of Florida students in spring 2000 may
show that in at least one instance, implementation of
environmentally sound practices have proven mutually
beneficial to both environmental resources and a
company mission.

Figure 1. View of San Felasco Nursery (1999) looking
south. Blue arrows indicate direction of runoff. Note
location of pre-enlargement pond in foreground.

The initial catalyst of the project came with the desire by
San Felasco Nurseries to develop water based cold
protection for their more sensitive nursery stock during
the winter months. This cold protection was not feasible
at the time due to limited groundwater pumping capacity.
In addition, limited groundwater pumping rates required
8 hrs to completely irrigate all of the nursery stock at
night. These limitations could have been solved by
drilling a larger well and adding pumping capacity, but
instead an alternative was implemented. It was decided
that increasing the capture rate of rainfall and irrigation
runoff from the fields and reusing it may be sufficient to
supply the needed water for cold protection while
significantly reducing the demand on groundwater. In
addition, although not presently required to mitigate for
changes in stormwater runoff resulting from landuse
changes, increased runoff rates due to roadways,
ground covers, buildings and greenhouses have resulted
in a significant increase in rainwater runoff that could be
temporarily intercepted and used for irrigation before it
evaporated or infiltrated into the ground. Implementation
of this system required establishment of a large storage
pond to receive runoff. Ecological Engineering design of

this pond provided some additional opportunities to
address water quality and ancillary ecological benefits.

San Felasco Nursery's north site, which is approximately
75 acres in size, is located in northwest Alachua County.
The nursery has become one of the biggest wholesale
nurseries in North Central Florida and is recognized as
experts in the growing of herbaceous perennials but also
carry a wide variety of woody containerized plants. The
facility has 60 acres of nearly impervious surface
composed of, 45 acres of ground cloth underlain by
plastic, 8 acres of shade houses, 2 acres of green
houses/cold frames, 2 acres of retractable roof green
houses, and a net work of roads throughout the property.
The property rest's on the south slope of a concave
landscape with surface runoff collecting in a depression
at the north edge of the property with no surface runoff
from the site (Figure 1).

Sizing the runoff reuse pond was conducted by
estimating runoff volumes using runoff coefficients
established for various landuse surfaces and
irrigation/rainfall conditions. Runoff estimated for nightly
irrigation events were upward of 55% (165,000
gallons/irrigation night) and 65% for all surfaces during
rainfall events in excess of 0.25 inches (1.3 million
gallons for a 1 inch storm event). Thus although
intermittent, a conservative runoff capture potential of 64
million gallons per year could be expected assuming 52
inches annual rainfall, 180 days at maximum irrigation
effort and 40% loss of volume in the pond to evaporation
and infiltration. Although timing of rainfall events will not
completely meet irrigation demand, thus requiring some
ground water pumping, capture volume is approximately
the same as irrigation requirements in 1999 (62.8 million
gallons). This would be significant water conservation
onto itself; however, additional benefits with respect to
nutrient management are implied in this water reuse
system and with an ecologically enhanced pond design.

By recirculating a significant portion of the surface runoff
from irrigation and stormwater, the previously "open"
nutrient and pollutant cycle is now partially closed.
Nutrients originally leached from the planting containers
that would have been carried to the pond and eventually
groundwater, are now made available again to the plant
and total water volume moving through the nursery is
reduced, decreasing infiltration and runoff that might
pose a threat to groundwater. To increase storage
capacity, and thereby water for reuse, additional storage
was required in the natural depression of the landscape
at the San Felasco site. A rainfall runoff model was
developed to determine the approximate storage
Continued page 18

Continued from page 17 .
capacity needed for a given rainfall event. It was A
decided that a total storage volume of 6 million gallons
would be used, a compromise between stormwater
runoff mitigation and land allocated to the pond system.
This volume relates to the 5 year 6 hr storm event or a
4.5 inch rainfall. Storage requirement could have been
met by a simple excavation with steep slopes and ,
rectangular design; however, modifying the design
provided an opportunity for additional benefits. The
enhanced design included the addition of a small (1.5

Figure 3. Red Maple (Acer rubrum) and Bald
Cypress (Taxodium ascendens) among two varieties
of Iris (Iris virginica) and needle rush (Juncus
effuses) as a more natural presentation of these
species to customers visiting the Nursery.

pumping system on line. It is anticipated that these
pumps will be installed in the next few months and
icnn r....., quantitative evaluation for successes and limitations of
l .c o this project can be made.

nI,~tur Acknowledgements: The spring 2000 student design
'" team consisted of Kerry McWalter, Shannon Ludwig,
.7 John Kasbar and Melanie Craig. Alan Shapiro, owner of
San Felasco Nurseries was instrumental in this project
Figure 2 Design of irrigation reuse pond with and he is thanked for his financial support of the project,
integrated wetland treatment system. willingness to open up his business to our research, and

acre) wetland and forebays for sedimentation (Figure 2).
This design allows for 60 % of irrigation water and 50%
of the stormwater to flow through the wetland prior to
entering the pond. Sediment carried by the runoff water This newsletter was created to disseminate
is mostly deposited within the wetland and forebays prior information on current projects in the
to discharge to the pond and significant nitrate Nutrient Management area. If you would
reductions occur within the wetland complex. Direct like to submit an article for inclusion in a
groundwater infiltration of nitrate through the wetland
and pond soil/sediment is negligible due to anaerobic future newsletter please contact:
conditions causing denitrification of nitrate-nitrogen
species if present. Additional ancillary benefits of the Susan Curry
wetland include a rich and growing vegetative species PO Box 110290
diversity (57 species initially planted), the wetlands are Soil & Water Science
also being developed so that specimens of various University of Florida
wetland plants can be shown to customers in a more Gainesville, FL 32611
natural setting (Figure 3), and wildlife utilize the wetland (352) 392-1805
and pond as evidenced by tracks and sightings reported scurry@ufl.edu
by employee's of the nursery.

Only limited quantification of the projects benefits have
been made to date due to a delay in putting the reuse

Enrich m entand Re ase Fte ntia lof
F osph orus and H e ay Meta in A ggregate
Fractions of Sandy Soi 4
Z. L. He, D.V. Calvert, P. J. Stoffella, and Y. C. Li
Indian River Research and Education Center,
Fort Pierce

Minimal information is known on the enrichment and
release potential of P and heavy metals in aggregate
fractions of sandy soils. To obtain a better
understanding of this subject, five aggregate-size
fractions, ranged from 1.00-0.50 to < 0.053mm, were
separated from seven Florida sandy soils by dry
sieving. Each aggregate fraction was characterized by
phosphate sorption, sequential fractionation of P, total,
water and Mehlich III extractable concentrations of P
and heavy metals. Aggregates in all the sandy soils
were dominated by the 0.5-0.25 mm and 0.25-0.125
mm fractions, both, on average, accounting for 80.6 %
of the whole soil. Chemical analyses indicated that
elemental enrichment (particularly heavy metals)
increased with decreasing aggregate sizes. As surface
area / volume ratios increase with decreasing
aggregate size, increasing enrichment with decreasing
aggregate size may be an indication of surface
enrichment of these elements on clay minerals. The
higher percentages of water-extractable and Mehlich
Ill-extractable P and heavy metals were found in both
the 0.50-0.25 mm and 0.25-0.125 mm aggregate
fractions, suggesting that P and heavy metals in these
two fractions had higher release potential. Phosphorus
adsorption maximum of the <0.053 mm fractions in all
the sandy soils were higher than other larger size
fractions, and the differences in P adsorption capacity
for various fractions could be explained by the
differences in Al, Ca and Fe contents among the
different fractions. The sequential fractionation of P
suggested that 1.00-0.50 mm fraction contained larger
percentage of Ca-bound P, whereas the 0.50-0.25
mm, 0.25-0.125 mm and 0.125-0.053 mm fractions
had higher ratios of labile P forms (H20-P and
NaHCO3-P), and therefore, a greater P release
potential. Results from P release dynamics in water
from various aggregate fractions suggest that P
release from smaller aggregate fractions is faster than
from larger aggregate fractions because of larger
amounts of water soluble P enriched in the smaller
aggregate fractions.

Training for Comprehensive Nutrient Management
Planning Continued from page 1

(IFAS), Gerald Kidder (IFAS), Jerry Sartain (IFAS),
Vince Seibold (Florida Department of Environmental
Protection), Tom Obreza (IFAS), Greg Hendricks
(NRCS), Steve Boetger (NRCS), Nga Watts(NRCS),
Justin Jones (IFAS) and Susan Curry (IFAS). These
presentations were well received by the participants. All
participants rated the program good or excellent. The
participants liked the mixture of science, theory and
practice.
Field visits to local dairies were conducted and Nutrient
Management Plans for these dairies will be developed
by each student. The data collected included soil survey
information, field inventories and land uses, identification
of sensitive areas, cropping history and rotations, and
current practices and land treatments. There was also
discussion of the waste management system, bio-
security, and conservation practices. The assessment
and calculations involved in determining the phosphorus
index (P-index) were explained. Other topics of
discussion were land treatment practices to reduce risks,
current manure and fertilizer applications, and irrigation
methods. Participants successfully completing this
course with an 80% or higher on the post-test must
submit two Nutrient Management Plans to NRCS for
approval. At this time they will be certified for Nutrient
Management.
The next planned course will take place in Okeechobee
in mid-May, 2003.

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