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Title: Nutrient Management Education core group newsletter
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Permanent Link: http://ufdc.ufl.edu/UF00091329/00002
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Title: Nutrient Management Education core group newsletter
Series Title: Nutrient Management Education core group newsletter
Physical Description: Serial
Language: English
Creator: Soil and Water Science Department, College of Agricultural and Life Sciences, University of Florida
Publisher: Soil and Water Science Department, College of Agricultural and Life Sciences, University of Florida
Place of Publication: Gainesville, Fla.
Publication Date: 2003
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Bibliographic ID: UF00091329
Volume ID: VID00002
Source Institution: University of Florida
Holding Location: University of Florida
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Full Text

December, 2003
Issue No: 4

UF/IFAS Nutrient Management
Education Core Group


Nutrient Management Education Core Group Background

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.

Nutrient Management Research at Tropical Research and Education Center
(TREC), Homestead
Yuncong Li
Program Objectives

Our research program focuses on developing
management practices to improve nutrient use
efficiency, plant nutrition and water quality; nutrient
cycling in calcareous soils; and determining impacts of
agriculture on south Florida's natural ecosystems. The
unique soils, climatic extremes, and diverse commercial
crops have posed great challenges to our program.

Soil P chemistry in farmland and natural
conservation area:
High phosphorus concentrations in the run-off from
farmlands facilitate the displacement of native
vegetation by undesirable vegetation. Everglades
restoration, as well as sustainable crop production,
requires major reductions of phosphorous in runoff,
and this requires in-depth knowledge of phosphorus
biogeochemistry in soils. We conducted a series of
laboratory, greenhouse and field experiments on
phosphorus chemistry and phosphorus fertilizer use
efficiency in calcareous gravelly and marl soils. We
found that most agricultural soils have high
concentrations of phosphorus in forms likely to move
into surface and groundwater even under calcareous
conditions, and that additional applications of
phosphorus fertilizer did not increase phosphorus
availability and crop yield. We developed a simple
one-point isotherm method to predict saturation and
leaching potential of phosphorus in calcareous soils.
We found apatite formed in calcareous soils farmed
for many years.

Calcareous soils in south Florida:
Several hundred commercial crops and diverse native
plant species grow on calcareous gravelly or marl soils
of the south Florida agricultural and Everglades
ecosystems. At the outset information on these
calcareous soils was scant, but in 5 years my research
group determined their physical properties (hydraulic
conductivity, etc.), chemical properties (carbon forms,
phosphorus sorption, etc.), biological properties
(microbial biomass, etc.), and mineralogical properties.
These findings were used to develop our extension
program, teach students, and support others in
conducting agricultural and ecological research in south

FL ... ........

Nutrient management for tropical fruits, winter
vegetables and ornamental crops:
Poor soil conditions create universal problems for
crop production in south area, such as low use
efficiency of fertilizers, microelement deficiencies,
and potential leaching of nutrients into groundwater.
An estimated 60% of vegetable acreage in Dade
County receives fertilizer rates that exceed UF
recommendations. Similar situations exist for tropical
fruit and ornamental crops. Over-fertilization leads to
unnecessarily high production costs, may decrease
yield and quality, and poses a risk to the
environment. On the other hand, micronutrient
deficiencies are common problems for most crops in

Continued page 2


NM Research at TREC Continued
the area due to high soil pH, inadequate fertilizer
applications or use of improper fertilizer formulas.
Moreover, excessive rates of phosphorus may induce
iron chlorosis or other micronutrient deficiencies of
crops grown on rocky soils.

Cover crops:
Cover crops are an integral part of vegetable
production practices in south Florida. We introduced
a legume cover crop, sunn hemp (Crotalaria juncea
L.), which produces up to 12,000 kg dry matter and
fixes up to 300 kg nitrogen per ha. We evaluated
mineralization rates of cover crops and effects of
cover crop residues on soil organic carbon, soil
microbial biomass, soil enzyme activity, and water
holding capacity. We showed that tomato planted
into sunn hemp plots produced more marketable and
extra large fruit. Our findings provide fundamental
information on enhancing the sustainability of
agriculture through use of sunn hemp and other
cover croos.

Soil amendments:
Several projects are conducting to evaluate the
effects of soil amendments (compost, biosolids, fly
ash, zeolite) on crop production, soil fertility and
water quality. We developed a method to quantify
organic carbon in organic waste amended calcareous
soils that overcomes interference of carbonate in
calcareous soils. We modified fractionation methods
for organic carbon and metals, to be better suited for
calcareous soils. We also developed management
practices to utilize biosolids or composts, which
significantly increased soil organic carbon, increased
soil nutrient availability and increased crop yields, but
avoided trace metal accumulation in soils and
nutrient leaching into groundwater. Our studies also
indicated that incorporation of coal ash into biosolids
and yard waste composts significantly improves their
quality. Such use may be made of the 80 million tons
of coal ash from power plants national wide, together
with the 3 million tons of yard waste produced
annually in Florida alone.


Learning to better manage: The Florida drip irrigation school
Eric Simonne, Horticultural Sciences, Gainesville

The Florida Drip Irrigation School (FDIS) is a one-day
educational program that focuses on drip irrigation
maintenance and management for commercial
vegetable growers. In the past, many educational
efforts have sought to teach growers about fertilizer
management, irrigation management, and soil
fumigation separately. With the development of best
management practices (BMPs) and promising
methyl-bromide alternatives that may be injected
through the drip system, the drip system is now the
interface of fertilization, irrigation and fumigation
practices. Hence, an integrated approach to teaching
drip irrigation management is needed. The FDIS goal
is to offer practical, up-to-date management
information on all aspects of drip irrigation.

Since its inception in 2001, the FDIS has been
offered throughout Florida at County Extension
Offices and IFAS Research and Education Centers.
FDIS has brought together Extension personnel,
members of the ag supply industry, state agencies,
and producers. Research and regulatory updates are
taught through combinations of classroom lectures
and hands-on demonstrations in the field (Table 1).
While most popular topics include fertilizer
management, irrigation management, system
maintenance, and visualization of water movement,
each program is tailored to address the specific
needs of the vegetable growers of the area.

Continued page 4

Program location Date Program leaders Topics presented
offered Oral presentations Hands-on field demonstrations

North Florida Research 11/13/01 Bob Hochmuth and Principles of nutrient management Visualization of soil water movements with
and Education Center- Eric Simonne Uses of Cardy meters dye
Suwannee Valley, Drip system maintenance Delivery of chemicals through drip systems
Live Oak Troubleshooting common mistakes in irrigation design Drip system components

Miami-Dade county, 8/12/02 Teresa Olczyk and Scheduling drip irrigation Visualization of soil water movements with
Homestead Eric Simonne Uses of Cardy meters dye
Soil moisture measurement Mobile irrigation lab
Drip system design and maintenance Delivery of chemicals through drip systems
Troubleshooting common mistakes in irrigation design Drip system components
New farm bill Soil moisture measurement

Gulf Coast Research 11/13/02 John Duval and Eric Irrigation scheduling Visualization of soil water movements with
and Education Center Simonne Fertilizer management dye
Dover Regulatory update Soil moisture measurement

North Florida Research 12/04/02 Bob Hochmuth and Role of the Suwannee River Partnership Visualization of soil water movements with
and Education Center- Eric Simonne Drip irrigation in the BMP era dye
Suwannee Valley, Drip tape selection Soil moisture sensors
Live Oak System maintenance Developing a fertilization program
Fumigation with drip irrigation
Indian River Research 3/13/03 Elizabeth Lamb, System design and maintenance Visualization of soil water movements with
and Education Center, Eric Simonne, and Fertilizer management dye
Ft. Pierce Ed Skvarch Cost share programs Chemical updates
Grower's experiences with drip Cardy meters
Water quality conservation System components
System troubleshooting

FACTS X, Lakeland 4/30/03 Eric Simonne Fertilizer management in the BMP era N/A
Fumigation via drip irrigation
Drip system automation
System maintenance

Miami-Dade county, 8/21/03 Teresa Olczyk and Water conservation survey result Visualization of soil water movements with
Homestead Eric Simonne BMP program dye
Flood damage Deliveries of chemicals
Mobile irrigation lab
System maintenance
System components
Common mistakes in irrigation design
EQIP program
System automation

North Florida Research 12/03/03 Bob Hochmuth and Field testing of possible BMPS for watermelon Visualization of soil water movements with
and Education Center- Eric Simonne Pannel discussion: drip irrigation and BMPs dye
Suwannee Valley, Remote control for drip systems Building a BMP plan
Live Oak Maintenance and chlorination

Table 1. Location, date, program leaders and educational content of the Florida Drip Irrigation Schools (2001-2003)

Nutrient Mnt E o P 4 o

Learning to Better Manage Continued

Instructors' background, experience and teaching
styles are also diverse (Table 2). Attendance has
been high and ranged from 23 to 78 (55 average) for
the eight FDIS programs offered between 2001 and

FDIS attendees are provided with supporting
educational materials (EDIS publication, brochures,
and copies of PowerPoint presentations).
Proceedings of the FDIS were published in 2002 by
Citrus & Vegetable Magazine and are available on-
line at
http://www.citrusandvegetable.com/home/2002_OctI r
rigation.html. Electronic copies of Power Point
Presentations are available to IFAS personnel only
at a password-protected section of the North Florida
Research and Education Center-Suwannee Valley
web site accessible at http://nfrec-sv.ifas.ufl.edu.

Together with CEU and CCA credits, FDIS
participants receive a certificate of program
completion. Knowledge increase for each participant

is measured by comparing participants' score
increase in identical pre-training and post training
tests. At the beginning of the day, participants are
asked to answer anonymously and in writing a set of
10 to 20 questions that cover key topics of the
program (pre-training test). Questions are usually
provided by the instructors themselves. Participants
are asked to answer the same questions again after
the training. Based on these test results, knowledge
gain ranged between +17% and +26% and averaged
+21% (Table 2). Overall program ratings at the end
of the day showed consistently that a large majority
(95%) of the participants rated the FDIS as 'excellent'
or 'very good'.

On-coming FDIS programs are regularly
posted on the calendar of events of the 'Vegetarian'
news letter
and the NFREC-SV web site.

z Based on pre-training and post-training test scores

Table 2. Instructors' background, attendance and knowledge gain of the Florida Drip Irrigation School (2001-2003)

Location Date Attendance Knowledge
IFAS- IFAS State Industry gainz
County Specialist agencies representative

NFREC-SV 11/13/01 1 3 0 3 52 +17%

Miami-Dade county 8/12/02 1 4 2 3 78 +20%

GREC-Dover 11/13/02 0 3 1 3 32 +20%

NFREC-SV 12/04/02 1 4 0 2 65 n/a

IRREC 3/13/03 1 4 1 10 35 +22%

FACTS X, Lakeland 4/30/03 1 3 1 1 23 n/a

Miami-Dade county 8/21/03 1 3 1 5 75 +26%

NFREC-SV 12/03/03 1 3 2 3 35 n/a

I Page 5 of 16 Nutrn Mn EI S

Impact of P Fertilizer, Lime, and Gypsum Application on Stargrass
Yield and Quality, and Water Quality
Martin B. Adjei, Jack E. Rechcigl, & Isabella S. Alcordo

Phosphorus (P) is the primary cause of eutrophication or
algae blooms of fresh water bodies or lakes in south
central Florida. Excessive P fertilization on pastures
may contribute to the problem (Sumner et al. 1989).
This is supported by work conducted by Dr. Jack
Rechcigl and his team (Rechcigl et al., 1990; Rechcigl
and Bottcher, 1995), which was funded by the South
Florida Water Management District. That study also
showed that P fertilizer rates on bahiagrass could be
drastically reduced without any adverse effect on
bahiagrass forage yield and quality. In addition, P levels
in surface water runoff were reduced by 33 to 60% as P
fertilizer rates were decreased from 48 to 12 kg P ha-1.
Those studies led the Institute of Food and Agricultural
Sciences (IFAS) of the University of Florida to adopt a
zero P recommendation in 1998 for bahiagrass pastures
grown in Florida south of Orlando.

The recommended P rate for other improved pasture
grasses such as stargrass (Cynodon species) still
ranged from zero P to 40 kg P ha-1 for high and low P
soils, respectively (Kidder et al., 1998). However, as
demonstrated by Rechcigl and Bottcher (1995),
fertilization of pastures even at the optimum P
recommended rates could cause significant elevation of
P levels in surface water runoff. Hence, in addition to
establishing optimum rates of P fertilization for improved
pasture grasses, it became necessary to evaluate the
capacity of soil amendments for tying up fertilizer-
derived P.

Field studies were conducted from 1999 to 2002 at the
Williamson Cattle Company in Okeechobee to: 1) re-
evaluate the existing IFAS recommended P fertilizer
rates for stargrass production and 2) study the
effectiveness of limestone and gypsum for improving the
retention capacity of soils for applied P on stargrass

The experiment was conducted on a stargrass beef
pasture that was grazed rotationally at Williamson Cattle
Company in the Lake Okeechobee Basin. Treatments
were 0, 12.5, 25.0, 50.0 kg P ha-1 from triple super
phosphate applied to 50 x 100 ft plots in the stargrass
pasture every year. The amendments consisted of
calcium carbonate and mined gypsum applied based on
100% CaCO3 at 0, 2, and 4 Mg ha-1 every year only to
plots that received 50 kg P ha-1.

Each treatment was replicated four times in a
randomized complete block design. All plots, including
the control, received one application of 80 Ib K20/A as
KCI and two equal applications of 90 kg N ha-1 as
ammonium nitrate, yearly. Forage was sampled for dry
matter yield, crude protein (CP) content, in vitro organic
matter digestibility (IVOMD) and tissue mineral content
once every 30-35 days. Forage was harvested seven
times in 1999 and six times each in 2000 and 2001. Soil
was sampled before the beginning of the experiment in
March and in August 1999, March 2000, October 2000,
and March 2001 from the surface down to the spodic
layer at 15-cm depth interval, dried and analyzed for
Mehlich 1 extractable nutrients and various P fractions.

Continued page 6

Nut t Mn E o Pg 6 of 1

Continued from page 5

A fully automated weather monitoring network was set
up at the site to measure rainfall, surface runoff volume,
and depth of water table. Earthen berms were used do
divide plots into separate hydrologic units. Water
samples from surface runoff and shallow wells to 0.625
and 1.25 m depths inside plots were collected for quality

Applied Question 1: Did P and liming materials
influence forage yield and quality?
Phosphorus fertilizer did not increase forage yield (Fig.
1), did not improve forage crude protein content (CP)
(Fig. 2) nor IVOMD (Fig. 2) throughout the 3 years.

The soil Ap horizon had an initial pH of 4.4 and there
was an indication that stargrass yield from the control,
which received N and K fertilizer could benefit from
gypsum application only in the first year (Fig. 1) but lime
amendments had no effect on forage CP and IVOMD

Applied Question 2: Did P and liming materials
influence tissue macro and micro nutrients of
stargrass forage?
Phosphorus uptake by forage increased by 0.003% units
for each kg P ha-1 applied to pasture over the three year
period. Fertilizer P also increased Ca uptake by 0.001%
units per kg P ha-1. Neither P nor calcium carbonate
had any effect on tissue K and Mg. Both calcium
carbonate and gypsum had no effect on tissue P even at
the highest liming rate of 4 Mg ha-1 suggesting that the
50 kg P ha-1 that was applied was not tied up but stayed
readily available for plant uptake. Gypsum linearly
increased stargrass tissue Ca at the rate of 0.012% but
reduced tissue Mg by 0.007% at 50 kg P ha-1.
Averaged over three years, fertilizer P showed no effect
on stargrass tissue Cu, Fe, Mn, and Zn. Calcium
carbonate and gypsum also had no effects on stargrass
tissue Cu, Fe and Zn. However, Calcium carbonate
decreased whereas gypsum increased tissue Mn
linearly. The ramification of these complex interactions
on animal nutrition is not very clear, however, most
cattle producers routinely feed mineral mix to provide
adequate P and necessary minerals.

Applied Question 3: Did P and liming materials
influence soil P status?
Phosphorus fractionation indicated a relatively high total P
in the Ap (375-495 ppm), E (28-48 ppm) and Bh (527-825
ppm) horizons of untreated Immokalee fine sand.
Phosphorus fertilization resulted in further build up of soil
P by 0.70 kg P for each kg of applied P ha-1 without any
agronomic benefits but an increased potential for P loss
through runoff.

Applied Question 4: Did P application influence runoff
and groundwater P concentrations on stargrass
The soluble phosphorus (ortho-phosphorus, OP) content
in water samples was typically 85 to 95% of total
phosphorus (TP). In 2001 when sufficient rainfall
occurred, the OP concentrations in shallow wells
increased significantly from less than 1000 to 5000 parts
per billion (ppb), in deep wells from 0 to 1500 ppb, in
surface runoff from 1000 to 1500 ppb as P fertilizer rates
increased from 0 to 50 kg ha-1. (Fig. 3a). Corresponding
increases in TP concentrations to applied P in 2001 were:
in shallow wells from 1000 to 3000 ppb, in deep wells no
effect, and in surface runoff from 800 to 900 ppb (Fig. 3b).
At 50 kg applied P ha-1, increasing rate of gypsum from 0
to 4 Mg ha-1 tied up the P and totally eliminated OP and
TP from deep wells (Fig. 4a and 4b) while increasing rate
of calcium carbonate caused a slight increase of OP in
surface runoff (Fig. 5a) but a 40% decrease in TP
concentration of surface runoff (Fig. 5b).

Phosphorus fertilizer did not increase stargrass forage
yield nor improved forage crude protein or in vitro organic
matter digestion. Although applied P improved forage
tissue P concentration, most cattle producers routinely
feed a balanced mineral mix. Applied P caused a
significant buildup of P in the Ap, E, and Bh horizons,
increased soluble P concentrations in shallow and deep
wells by 400% and 1500%, respectively, and in surface
runoff by 50%. Gypsum was effective in eliminating P
leachate from applied P into deep wells. Although Ca-lime
significantly reduced TP in surface runoff, its long-term
effect is not clear because of equilibrium tendencies.

This study collaborates results from another multi-county
fertilizer study (Adjei et al 2000) to provide strong
evidence that current IFAS P-fertilizer recommendations
for all improved grasses of up to 40 kg P ha-1 could be
further reduced at no cost to forage production. Such cuts
will ultimately result in tremendous savings to ranchers as
well as have beneficial effects on water quality. Since this
study was concluded, the current IFAS P fertilizer
recommendations for stargrass has been modified to 20
kg ha-1.

The authors acknowledge the South Florida Water
Management District for funding the entire project.


Best Management Practices in the Everglades Agricultural Area
Samira Daroub, University of Florida, EREC, Belle Glade, FL

The Everglades Agricultural Area (EAA) is a
280,000 ha of land comprised of organic soils. Farms
in the EAA discharge their water into an extensive
array of canals, which is pumped into the South
Florida Water Management District main canals and
eventually into the Everglades. Land use in the EAA
varies from monocultures of sugarcane and
vegetables to multi-cultures of vegetables, rice, sod
and sugarcane. Best management practices (BMPs)
are in place to reduce total phosphorus (P) loading
out of the EAA.
The objectives of our research and extension
program is to verify BMP effectiveness in the EAA,
and identify sources, mechanisms of transport and
control of particulate P in an effort to reduce total P
loading into the Everglades. Training workshops and
seminars are conducted to improve the wide
implementation of BMPs in the EAA.
Our research has shown that water management and
crop rotation BMPs have the greatest impact on total
P loads and concentrations of farm discharges.
Water management practices that proved most
effective included making internal drainage
improvements to the farm to allow more uniform
drainage. Particulate P transport studies aim to
identify sources and mobility characteristics of
particulate P on EAA farms and to modify
management practices to reduce particulate transport
off the farm. Particulate P accounts for 20 to 70% of
total P exported from EAA farms and is frequently the
cause of spikes in total P loads. A significant fraction
of particulate P in the EAA originates from in-stream
biological growth, rather than from soil erosion. A
major contributing factor to particulate P discharge is
the "Biological Contribution Mechanism" (BCM).
Sediments that contribute significantly to P export
were postulated to be recently deposited biological
material such as settled plankton, filamentous algae,
and macrophyte detritus. The BCM includes bed
sediment erosion as a source of exported particulate

P, and these sediments consists of a heterogeneous
mixture of organic matter in various stages of
decomposition, with various levels of P content, and
variable transport properties.
Management practices that are recommended by
our research to control particulate P in discharges
include practices that reduce the first flush of P and
minimize the occurrence of continued high velocities
in the canals. Aggressive weed control programs in
the main canals are the most productive in reducing
the supply of transportable high P content biomass
and thereby reducing the first flush phenomena.
Relocating sediments upstream from the pump house
is recommended in conjunction with irrigation events.
High velocity flow can cause particulate P to be
mobilized in large amounts. Velocity in farm canals is
the key control parameter for reducing particulate P
export. Recommended velocities in the canal are
relative, in that they must be within the operating
framework of the configuration of the farm. Given
that, velocities should be as low as possible, and
velocity excursions should be avoided. Control of
canal levels is critical in avoiding extreme velocity
The IFAS research projects in the EAA confirm
the effectiveness of existing BMPs as well as provide
direction on areas of future focus. The IFAS
recommendation is that the primary focus should turn
to evaluation of the active biological and chemical
interactions that flourish in the ecosystems south of
the EAA so that relationships between P leaving the
EAA and its eventual downstream points can be
developed. Another key component to the IFAS
research goals is to promote the continued, uniform,
and conscientious implementation and management
of BMPs. This is accomplished through an extension
program consisting of numerous seminars, BMP
training workshops and publications offered to the
EAA community.


NuretMngmn o Pg 8

The Importance of Potassium in a Florida Citrus Nutrition Program
Thomas Obreza, Soil & Water Science, Gainesville

The root zone of most soils used for Florida citrus
production is dominated by quartz sand, with very
little clay and organic matter. These soils are
extremely low in natural fertility and water-holding
capacity. Managing water and nutrients efficiently on
these soils is a challenging task for citrus production

Typically, the nitrogen (N) fertilizer rate applied to
mature citrus ranges between 150 and 250 Ibs/acre.
Potassium (K20) is usually applied at 1.0 to 1.25
times the N rate. While the inefficiency of N fertilizer
is well known, K is usually thought of as an immobile
nutrient in most parts of the world. However, Florida
sands have only a small capacity to hold K against
leaching as evidenced by repeated soil testing. Many
citrus grove soils do not show a substantial increase
in soil test K even after fertilizer has been applied for
many years.

Potassium has numerous functions within the plant,
and citrus fruits remove about 14 Ibs of K per 100
boxes of fruit. Potassium is important in fruit
formation and enhances size, flavor, and color. A
shortage of K can result in lost crop yield and quality.
Moderately low plant K concentrations will cause a
general reduction in growth without visual deficiency
symptoms. The onset of visual deficiency symptoms
means that production has already been seriously

In 1998, funding from the Florida Citrus Producers
Research Advisory Council and the Foundation for
Agronomic Research helped us initiate a K fertilizer
experiment in a young southwest Florida grapefruit
grove. Our objectives were to evaluate the effect of K
fertilization on yield and fresh fruit quality, and to
develop recommendations that will produce qualities
most desired by fresh fruit consumers. We applied
fertilizer rates of 0, 100, 200, or 400 Ibs K20/acre
each year and measured canopy volume, fruit yield,
and fruit quality factors as the trees grew and
produced fruit. We also measured K concentration in
leaves, since citrus response to fertilization is
typically reflected in leaf tissue nutrient
concentrations. We found leaf tissue K of less than
0.5% where no fertilizer was applied, 1.1% with the
100 Ibs/acre rate, 1.3% with the 200 Ibs/acre rate,
and 1.6% with the 400 Ibs/acre rate. (Interpretations
for leaf K concentration are "very low", <0.7%; "low",
0.7 1.1%; "optimum", 1.2 1.7%; "high", 1.8 -
2.3%; and "very high", >2.3%.)

0 100 200 300
Annual K20 rate (Ibs/acre)

Figure 1 Response of grapefruit trees planted on
flatwoods soils to potassium fertilizer.

characterized by a gradual rise to a maximum
followed by a slight decline (Fig. 1). Our data suggest
that maximum tree size and yield will occur when
fertilizer is applied yearly at 200 to 250 Ibs K20/acre.
Visually, trees that received the 200 Ibs/acre rate had
an expanded, branching canopy compared with a
tight, bushy appearance of trees that did not receive
K (Figs. 2 and 3). Fruit was easy to find on trees
receiving K, but finding a grapefruit on the low-K
trees was a difficult task. Interestingly, the low-K
trees did not show any obvious visual leaf symptoms
of K deficiency like necrotic edges or off-green color;
rather, the lack of K was expressed as a compact
canopy and almost no fruit production.

Fig. 2. 4-year-old grapefruit tree grown on a flatwoods
soil with sufficient N fertilizer but no K fertilizer. (Notice
tight, compact tree with no visible fruit.)

The response of grapefruit yield to K was

Continued page 9

A Improved use of root nutrient interception for groundwater protection
Johan Scholberg, UF Agronomy Department, johan@ufl.edu

The relationship between temporal and spatial root
uptake and crop accumulation of N and/or P as
affected by temperature, growth stage, and fertilizer
management practices are being investigated for
citrus, corn, potato, pepper, tomato and forages. The
objectives of this program are to i) to improve our
understanding of root growth, crop nutrient uptake,
and accumulation dynamics; ii) use this information
for improved matching of crop nutrient supply, root
interception capacity and crop nutrient demands; iii)
provide a scientific base for enhancing nutrient
uptake efficiency and thus minimizing the risk of
nutrient contamination of surface and groundwater
resources. Using tubular microrhizotrons maximum
root depths and effective root depth (ERD, the depth
at which 90% of the total root length occurs) for
sweet corn under optimal conditions were determined
to be 70 vs 89 cm and 30 and 55 cm at 14 and 21
days, respectively. Maximum root elongation rates
were 4.7 cm/day. Under field conditions, root
densities for sweet corn were greatest in the row
middles and the upper 15 cm of the soil profile. Root
density increased with N-rate and in-the-row root
densities at 21, 35 and 56 days were 0.28, 0.90,
0.96; 0.43, 2.19, 2.68; and 0.58, 2.50, and 2.73
cm/cm3 for the 0, 133, and 266 kg N rates,
respectively. Corresponding between-row root
densities for the 266 N rate were 19, 47 and 82% of
those in the row. Use of covercrop residue promoted
root growth. Root densities showed an exponential
decay pattern and densities below 30 cm and 45 cm
soil were on the order of 0.2-0.4 and 0.02-0.05

cm/cm3, respectively. Use of subsurface irrigation
placed at 23 and 33 cm increased ERD at maturity
from 28 cm (surface irrigation) to 39 and 51 cm,
respectively. Maximum root densities (MRD) for
pepper at the 0-15, 15-30 and 30-45 cm soil depth
were 2.3, 0.7 and 0.6 cm/cm3, respectively.
Corresponding values for tomato were 3.0, 0.9 and
0.7 cm/cm3. For tomato MRD values outside the
wetting area were 0.7 compared to 3.8 cm/cm3. For
potato root concentrations for the upper 15 cm at 0,
15, 30 and 45 cm from the row-center were 1.2, 1.2,
0.2, and 0.1 cm/cm3 respectively and ERD was
between 20 and 30 cm. A comprehensive literature
review along with field data showed that biomass and
N accumulation for annual crops generally follows
logistic patterns. Maximum biomass and N
accumulation rates occurred between 1/3 and 2/3 of
the growth duration and N recovery for most annual
crops ranges from 36-82%. Root uptake capacities of
annual crops increased overtime and approached
maximum values at 35-56 days. Fertilizer uptake
efficiency can be increased by applying nutrients in
phase with crop demand and via sound irrigation
practices to retain nutrients within the upper 30-45
cm of the soil profile. Root distributions for citrus
followed bimodal patterns and root densities ranged
between 0.1 and 1.5 cm/cm3. Daily maximum N
uptake capacities increased as soil N concentration
increased and were 8-10 kg N/day under optimal
conditions. The above information will be integrated
in PC-based management tools to facilitate more
efficient N use on vulnerable soils in Florida.

Fig. 3. 4-year-old grapefruit tree grown on a
flatwoods soil with sufficient N fertilizer and 200 Ibs
K20 per acre per year. (Notice more branching,
expansive tree canopy with visible grapefruits.)

Importance of Potassium in a Florida Citrus
Nutrition Program
Continued from page 8

Fruit size increased with increasing K fertilizer rate, but
brix was maximized at about 200 to 250 Ibs K20/acre.
Therefore, it is important to supply sufficient K for fruit
sizing, but too much can perhaps cause the brix to be
less than maximum. Peel thickness also increased as K
fertilizer rate increased, indicating that adding K does not
provide positive results for everything. Growers must
consider all factors and strike a balance between them
when deciding on the rate of K fertilizer to apply.


The Potato Root Distribution and its Role in Nitrogen Uptake Efficiency
Fernando Munoz, Rao Mylavarapu, Soil & Water Science, Chad Hutchinson, Horticultural Science

Potato is a shallow rooted crop that is grown on sandy
well-drained soils where nitrate leaching from N
fertilizers has been identified as the reason for increase
of nitrate concentration in groundwater, rural wells, and
streams, particularly in the St. John River watershed of
northeast Florida. Part of this problem may be because
farmers tend to apply higher rates of N as an insurance
against yield reduction. Enhanced uptake is one of the
proposed strategies to minimize nitrate leaching,
reducing fertilizer rates at the same time. In the short
term this could be accomplished by timely and precise
placement of the fertilizer in soil regions where it could
be quickly absorbed by the roots. In the long term, the
development of potato cultivars with high uptake and use
efficiencies by plant breeding could be a part of the
solution to nitrate leaching from potato fields. In both
cases a detailed knowledge of the root system is
required. The precision of fertilizer placement on time
and space is especially important for nutrients such as
nitrate characterized by high mobility in the soil. In order
to begin the collection of information about the potato
root system a two-year study of the potato root
distribution was initiated.

The objectives of this study were: to propose and to test
a new methodology to get a representative sample from
the potato root system in order to study vertical and
horizontal root distribution, to study the effect of three N
rates on the root system of Atlantic, a potato variety
used extensively by the farmers in the tri-county
agricultural area located in the St. Johns River
watershed and to generate information that could be
used to enhance fertilizer placement in order to
maximize uptake and minimize nitrate leaching.

This device, 'slicer' is composed of 2 sharp-edged metal
sheets. Three wooden pieces holds the sheets in place
with an even separation of 4 inches. The "slicer" is
buried into the soil (Picture 2) Two slices, one including
a plant and another one between plants, were taken in
each plot. Afterward, each slice was split in 14 sub-
samples (Fig.1), weighed and labeled individually.

................... - - - -4

S20. cm 15" 5-- 15A 1-- t-15Ai --- 20.8cm 10. cn

Fig 1. Spatial distribution of the samples.

The roots were separated from the soil by washing on a
screen (Picture 3) and pulled out of organic matter
debris. The soil samples containing roots were stored in
a cooler at 45 F during the washing process.

Picture 1.

In order to accomplish the proposed objectives a
device to get a representative sample of the potato
root system was designed (Picture 1).

Continued from page 10


Roots were kept in plastic bags containing a solution of
sodium azide (0.02%) as preservative and stored in a
refrigerator. Roots were scanned in translucent
Plexiglas trays containing water. Root images obtained
in this way were saved and further analyzed for root
length and root surface area using GSRoot, specialized
software for root analysis (Picture 4). Subsequently,
roots were oven-dried at 105 C and their weight
recorded. Root variables studied are: -Root Length
Density (RLD) cm root / cm3 soil. -Root Area Density
(RAD) cm2 root surface / cm3 soil. -Specific Root Length
(SpecRL) cm root / mg biomass. -Specific Root Area

(SpecRA) cm2 root surface / mg biomass. -Marketable
and total tuber yield (kg/ha). Additionally bulk density
and soil strength using penetrometer were also
Preliminary Results:

The applied nitrogen rates did not show any significant
effect on the root parameters evaluated RLD and RAD
were highly correlated (0.91, <0.0001), which is normal
because N rates had no effect on root system traits.
Furthermore, just one potato variety was evaluated.

RLD was statistically different for relative position
(vertically) and, slice (horizontally) at 1% and 5%
respectively (Fig. 2). RLD was lower for the slice
between plants than the slice including the plant (Fig. 2).

RAD was statistically different both horizontal and
vertical positions at 1% in both cases. RAD was lower in
the slice between plants than in the slice with the plant
(Fig. 3).

These facts mean that the crop root system in the region
of soil between plants has less capacity to explore the
soil. Therefore, any nitrates in this region could be
susceptible for leaching.

Figure 2 Root Length Density (RLD) in cm root/cm3soil. Means on distinct color are statistically different.
In the slice p < 0.0001. Between slices p < 0.03

Figure 3 Root Area Density (RAD) in cm2 root/cm3 soil. Means on distinct color are statistically different.
In the slice p < 0.0001. Between slices p < 0.005

I Continued page 12

Nu t M E Pe 1 o

Continued from page 11
SpecRL and SpecRA were highly correlated (0.90,
<0.0001). These two parameters showed statistical
differences vertically only (Fig. 4, 5). This is a foreseen
response for just one variety evaluated under a
fertilization regime that may not be affected root traits.

Root deformation due to soil compaction was observed
(Picture 5.). Root swelling and increase in the root
tortuosity occurred in regions with a soil strength close to
15 psi (0.1 MPa). The compacted layer was uniformly

distributed throughout the field at a depth of near 24 cm.
Statistical differences (<0.0001) were observed among
the average soil strength observed in each evaluated
soil depth (Table). There was no difference in
marketable and total yield under the fertilization rates
applied. Soil compaction could be responsible in part for
the lack of yield response to increase in the fertilization
rate. More detailed studies are recommended in order to
estimate the effect of soil compaction on potato yield.

Current assessments indicated that the performance of
the root sample devise (slicer) was satisfactory,
validating its use for future studies. Lack of any influence
of nitrogen application rates on the evaluated
parameters of the root system and yield suggests that N
uptake at these application rates and under the site
conditions depends more on the rate of nitrogen influx to
the plant than root response in terms of length and root
surface area. Root deformation by soil compaction could
be limiting potato root efficiency to scavenge nitrates
from the soil. Timing and precise placement of the
fertilizer instead of higher N rates probably maximize N
uptake and correspondingly minimize any potential for
nitrate leaching.

Figure 4 Specific Root Length (SRL) in cm root/mg biomass. Means on distinct color are statistically different. In
the slice p<0.0001. The difference was no-significant between slices.

Figure 5 Specific Root Area (SRA) in cm2 root surface/mg biomass. Means on distinct color are statistically different. In
the slice p<0.0001, the difference was no-significant between slices.

Evaluating Leaching Potential for Nutrient Management Planning in Sandy Soils
V.D. Nair, W.G.Harris, R.D. Rhue, D.A. Graetz, and R.S. Mylavarapu, Gainesville

Several Soil and Water Science faculty are involved
in research projects addressing nutrient management
issues in the Suwannee River Basin (SRB). These
projects assess risks associated with nitrate and
phosphate applications. Highlighted in this write-up
are some aspects of research in the Suwannee River
Basin with respect to the application of a nutrient
management tool -- the Florida P-Index -- with
special emphasis on the leaching potential of these
sandy soils. The study involves four sites, two dairy
and two poultry operations.

Karst landscapes of the SRB may require further
refinement of leaching criteria based on water moving
preferentially through breaches in Bt horizons.

Risk assessment of P for leaching-prone
soils requires that a valid and practical
indicator of the affected depth be included in the
assessment protocol
for nutrient management using the Florida P-Index. A
"P quick test" has been developed to provide a
simple and practical field method for the assessment
of the P-affected depth. The test involves mixing a
small amount (1.0 g) of soil in a ceramic test plate
with reagents used in the phosphomolybdate blue
colorimetric method for P determination.

Performing the P quick test in the field

Soil profile showing redoximorphic
features at the Bt horizon

The use of Ground Penetrating Radar (GPR) scans
provide continuous images of subsurface interfaces
and will indicate breaches in the Bt horizon through
which P could move.

Example of the colorimetric procedure
used in the P quick test

6- -

R ".a

The GPR at work at one of the dairy
sprayfields in the study

Nutrient Man I to Pg 1 l Sn1r

Continued from page 13

Water Soluble P, mg kg

0 5

15 20 25 30

Byrd -Oak Grove Dairy Barnes Sympson Poultry
Uairy Poultry

0 50 100 150 200

20 -


Depth, 8p






F Byrd -OakGrove Dairy Barnes *Sympson Poultry
Dairy Poultry

The above figures show depth to background P
(horizontal lines) for the four sites as determined by the
P quick test and their relationship to water soluble P and
Mehlich 1-P concentrations. Depth to background P is
the depth recorded when the blue color fades.

Soils have a finite capacity to retain P before
elevated pore water concentrations occur. This
finite concentration can be estimated by relating
extractable P to extractable Fe and Al. That is
because Fe and Al oxides correlate highly with P
retention in Florida soils. The critical P saturation
ratio (PSR) indicated by data collected in Florida
is approximately 0.15; i.e if the molar ratio of P
to Fe+AI is greater than 0.15, there is an
elevated risk of P loss from the soil. We can
calculate the amount of P to reach this critical
PSR from the expression, (0.15-soil PSR) x
(moles of Fe+AI). For details on this concept,
refer to Nair et al. 2004. Journal of
Environmental Quality 33:107-113.

Another basis for estimating the lifespan of a soil
is to calculate the degree to which a soil retards
vertical P movement. Our project is comparing
the prediction of P based on the retardation
approach with the capacity prediction explained
above. Thus far, the results of the two
approaches have been comparable.

This research was supported in part by a grant
from the USDA-IFAFS. We take this opportunity
to thank the graduate students involved in this

With graduate students at one of the field

I P 15 of 16UNutrient Management Education

The Green Industries Best Management Practices:
Education Program and Future Research
L.E. Trenholm, Environmental Horticulture Department

It has been almost two years since the Green Industries
Best Management Practices (BMP) manual was
completed. This document was developed in conjunction
with UF-IFAS, Florida Department of Environmental
Protection, Water Management Districts, and
representatives from many facets of the lawn care and
fertilizer industry. The primary goal of the manual is to
provide the commercial lawn and landscape industry
with guidelines on how to perform their jobs with minimal
impact on Florida's environment. Preservation of both
water quality and quantity are the desired outcomes.

To get the educational message of the manual out to all
segments of the industry, the BMP Educational Program
was developed. In 2003, over 1,000 workers were
trained in BMPs in training sessions held throughout the
state. Training materials include copies of the manual, a
summary guide, and CDs with PowerPoint presentations
and other references. Survey and quiz responses to
these sessions include:

97% of respondents felt that the program met
their expectations
96% knew more about the topics than they
previously did
87% felt prepared to teach the topics to other
98% felt that the training materials would be
used in training programs
Average pre-test scores were 68.4%, while post-
test scores averaged 86.6%

Training continues in 2004. New audiences are being
targeted for this year's programs, including city and
county government officials, landscape designers and
installers, irrigation specialists, and environmental
specialists. A Spanish version of the manual is to be
published later this year.

In conjunction with development of the manual and
educational program, FDEP has recently awarded a 5-
year grant to turfgrass researchers to verify
effectiveness of the BMPs. Beginning in 2004, research
will begin in Gainesville, Jay, and Ft. Lauderdale to
evaluate nutrient leaching on various home lawn
turfgrass species in response to varying rates of nitrogen
and irrigation during the turf establishment phase and on
established grass. Ninety lysimeters will be installed in
each location in year one and sampling will be
conducted throughout the growing season for nitrates
and phosphates. Future work in this project includes
evaluating specific turfgrass P requirements and
determining phosphate leaching from varying rates of P,
effects of winter fertilization on leaching, and nitrogen
source and timing effects on nutrient leaching. Drs.
Bryan Unruh, John Cisar, George Snyder, Jerry Sartain,
and Laurie Trenholm are collaborating on this state-wide

T . .........

Figure 1. Pump used to collect
leachate from turf plots

Figure 2. Turfgrass BMP research

Nutrientanagn o Pe 1 o 16

Silver Bullets and Phosphorous
Mary Beth Hall, Animal Science Department

Animal Sciences faculty have made a concerted effort to
work with dairy farmers and their nutritionists to
understand that they can have a huge impact on
reducing the amount of phosphorous that is excreted by
cows and thus reduce the potential impacts of the farm
on the environment. Through meetings, articles, and on-
farm discussions, we discuss basic concepts about
* It is an element. It does not convert into anything
* It is not volatile. Unlike nitrogen, it will not volatilize.
* Cows have a basic requirement for phosphorous to
maintain health and productivity.
* Like other animals, cows cannot use phosphorous
with 100% efficiency so none is excreted, but efficiency
may be improved.
* What goes in does come out: Phosphorous is used
for growth to make tissue, for bone, for pregnancy, for
milk, and for manure.
* The phosphorous content of milk is about 0.09%,
and it does not change much.
* For milking cows, roughly, the intake of
phosphorous, minus that in milk equals the amount of
phosphorous in manure.

In the discussions with the dairy industry, we emphasize
that the best way to reduce the amount of phosphorous
you have to deal with in manure is to feed less
phosphorous to your cows meet their requirements,
but limit excesses. At normal dry matter intakes, Dr.
Larry Satter of USDA recommends feeding phosphorous
as 0.35% of ration dry matter to meet the gram
requirements of the cow for phosphorous. Reaching this
amount often means feeding more forage and carefully
selecting the byproduct feeds you use. Many of the high
protein byproduct feeds (wheat midds, distillers grains
for example) tend to be high in phosphorous. Hominy
contains roughly twice the phosphorous (0.65%) that
ground corn does (0.30%). Often, no additional
phosphorous from mineral sources needs to be added to
rations to meet the animals' phosphorous requirements.
We recognize that one of the challenges to reducing
phosphorous in the diet is that byproduct feeds are often
a very good buy to bring needed nutrients into the diet.
The dairy farmer and their advisors have to decide how
to formulate to meet a variety of goals for the diet. To
date, the Florida dairy industry has removed most if not
all excess phosphorous mineral supplementation from
the diets, with a attendant reduction in phosphorous
importation onto farms.

Another topic we address with the dairy industry is that
increasing feed efficiency can reduce phosphorous in
manure: if the farm gets more pounds of milk out of each
pound of feed the cow consumes, they can export more
phosphorous off the farm. This can be done by making
certain that the diet consumed by the cows is properly
balanced for all nutrients, provide the cows with a
comfortable environment to live in, and maintaining good
animal health. Accomplish these goals, and the cow has
potential to produce more milk from a fixed amount of
feed. With a fixed amount of phosphorous consumed
each day, each additional pound of milk the cow
produces ships 0.4 grams more phosphorous off the
farm. That's a small amount, but multiply the increase in
milk by the number of cows for 365 days in a year, and
the additional amount adds up to a mass that matters.

A topic we address with the farmers is the array of
products that promise to make phosphorous disappear.
Rarely say never, but if someone offers a product that
reduces phosphorous in manure or in the lagoon without
changing the amount of phosphorous being fed into the
system, the farmers are told to inquire as to what
happened to it. Even in cows, phosphorous is neither
created nor destroyed. Through the discussions on
phosphorous, people in the dairy industry are
encouraged to rely on sound, science-based information
to make decisions, and recognize that, through feeding,
they can change phosphorous loading on their farms.

This newsletter was created to disseminate
information on current projects in the Nutrient
Management area. If you would like to submit
an article for inclusion in a future newsletter
please contact:

Susan Curry
PO Box 110290
Soil & Water Science
University of Florida
Gainesville, FL 32611
(352) 392-1951

Nurin Maaemn Edcto

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