Title: TropicLine
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Title: TropicLine
Series Title: TropicLine
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Language: English
Creator: Fort Lauderdale Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida
Publisher: Fort Lauderdale Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida
Place of Publication: Ft. Lauderdale
Publication Date: July/September 1995
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Bibliographic ID: UF00089450
Volume ID: VID00010
Source Institution: University of Florida
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TropicLine Vol.8(1)


TropicLine Volume 8, Number 1, July-September, 1995

Editor: Alan W. Meerow
Christine T Stephens, Dean, Cooperative Extension


Nitrate, Phesphate, and Petasium Leaching from Two

Species of Centainer-grown Follage Plants Fetilized

by Different Methods

Timothy K. Broschat
Research Horticulturist

Environmental contamination from nitrate and phosphate has become an important concern
in many areas of the United States. Nitrate levels greater than 10 ppm in drinking water are
considered unsafe for humans (U.S. Environmental Protection Agency, 1982) and
phosphate is often associated with algal blooms and eutrophication of lakes and ponds
(Wetzel, 1975). Although phosphate is considered to be rather immobile within many soils,
it is much more readily leached from container media composed of pine bark, spaghnum
peat, vermiculite, or sand (Yeager and Barrett, 1984; Marconi and Nelson, 1984). Nitrate is
readily leached from container media (Handreck and Black, 1984). Although K is not
usually considered an environmental pollutant, leaching losses of K from the soil may
affect plant growth and quality.

Fertilizers are often applied at high rates to tropical foliage plants, yet little is known about
the leaching of nutrients from the containers into the environment. Controlled release
fertilizers have been used to reduce nutrient loss from leaching. Although many studies
(see Maynard and Lorenz, 1979) have compared growth and quality of ornamental plants
fertilized with controlled release, liquid, or soluble granular fertilizers, no studies to date
have used the same nutrient sources and ratios in their fertilizer treatments. Such
comparisons are less valid due to N, P, and K source differences, as well as slightly
different elemental ratios among the various fertilizer treatments. The purpose of this study
was to determine the total amounts of nitrate, phosphate, and K leached from
container-grown tropical foliage plants during a 6 month production period and to
determine if fertilization method affects the amounts of these nutrients leached during that
time.

Materials and Methods


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Liners of areca palm (Chrysalidocarpus lutescens H. Wendl.) from seed and Spathiphyllum
Schott. 'Mauna Loa Supreme' from tissue culture were planted into 3.5-liter polypropylene
containers using a 5 pine bark: 4 sedge peat: 1 sand medium (by volume) amended with
880 g Micromax, a complete micronutrient blend (Grace-Sierra Hort. Prod., Milpitas, CA)
and 4.9 kg of dolomite/ m3, hereafter referred to as the "container medium'. Pots
containing one plant each were fertilized with a total of 7.65 g N, 1.37 g P, and 4.5 g
K/container/6 months, or no fertilizer (control). Four fertilizer treatments utilizing the same
raw material uncoatedd 21N-3P-12K prills derived from ammonium nitrate, ammonium
phosphates, calcium phosphates, and potassium sulfate, Grace-Sierra Hort. Prod.) were
applied in the following manner: 1) liquid form (LF) --1.4 g of prills dissolved in 50 ml of
water and applied weekly to the medium surface of each container, 2) soluble granular
fertilizer (SGF)-- 6.1 g of prills applied monthly to the medium surface of each pot, 3)
lightly-coated controlled release fertilizer (LCCRF)--13.4 g of Osmocote 19N-3P-10K (3-4
month release at 20C) applied every two months to the surface of the medium, and 4)
heavily-coated controlled release fertilizer (HCCRF)-- 45.0 g of Osmocote 17N-3P-10K
(12-14 month release at 20C) applied once to the surface of the medium. Each treatment
was replicated ten times.

This experiment was performed under typical subtropical production nursery conditions.
The palms were grown in a shadehouse having a maximum PPFD of 840 uE.m-2.sec-1 and
spathiphyllum under 225 uE.m-2.sec-1. All plants received about 2 cm of water from
overhead irrigation daily. The water used for irrigation contained .54 ppm nitrate, <.5ppm
phosphate, .83 ppm potassium, and 41.5 ppm calcium. All leachates were collected from
each container by setting the growing container on a 15 cm azalea pot inverted within a
4-liter polyethylene bucket. This system excluded virtually all non-pot irrigation and rain
water from the leachate collection container. The accumulated leachates from each
container were measured for volume weekly and a sample analyzed for nitrate using a
nitrate electrode, phosphate using the ascorbic acid method, and K using atomic absorption
spectrophotometry. Total mg of each nutrient ion leached per week was calculated from
the total volume and sample ion concentrations. At the end of the 6 month production cycle
shoot dry weight was determined for each plant. Data were analyzed using analysis of
variance with mean separation by the Waller-Duncan k-ratio method.

Results and Discussion

Nitrate leached per week from the container medium fertilized with SGF decreased rapidly
from nearly 350 mg for week 1 to about 10 mg for week 5. Reapplication during week 5
(Fig. 1) resulted in a rapid increase followed by another decline 4 weeks later. Subsequent
oscillations were considerably reduced in amplitude. Container media fertilized with LF
weekly showed generally increasing nitrate leaching up through week 6, followed by
smaller peaks approximately every 2-4 weeks. Container media fertilized with LCCRF
leached from 50-100 mg nitrate /week except during weeks 6, 13, 17, and 22, when


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somewhat more nitrate was leached, presumably in response ot higher rainfall during those
weeks (Fig. 1). HCCRF-fertilized container media also showed considerable weekly
variation in nitrate leached, although nitrate leaching generally decreased over time. This
trend toward reduced leaching over time for these controlled release fertilizers may be due
to increased plant uptake by the larger plants, coupled with a reduced release rate from
these fertlizers. Hershey and Paul (1982) described a similar trend in pot chrysanthemums.
These data suggest that reducing concentrations of soluble fertilizers during the first part of
the growing cycle could significantly reduce nitrate leaching losses without reducing plant
growth.

Leached phosphate from the container medium generally increased over time for all
fertilizer treatments, although leachate phosphate from LCCRF and HCCRF declined after
week 22 (Fig. 1). Leachate phosphate was almost always higher for LF and SGF than for
the two controlled release formulations.

K leached per container fertilized with LF gradually increased to a maximum of about 190
mg K at week 6, but from weeks 8-22 remained relatively constant at about 40-80 mg/week
(Fig. 1). After week 22, K leached from all fertilizer treatments decreased to less than 25
mg K/week, presumably in response to increased plant uptake at that time. As with nitrate
and phosphate, K leached from SGF-fertilized container media peaked every 4 weeks as it
was reapplied. The height of these peaks decreased somewhat over time as plant size and
uptake increased. The LCCRF-fertilized containers showed rather low (<50 mg K/wk), but
constant K leaching except for a higher peak at weeks 6 and 7. Potassium leached from the
HCCRF-fertilized containers at higher rates than LCCRF for the first 16 weeks, but at
lower rates thereafter. Similar responses were reported by Rathier and Frink (1989) and
Cox (1993) for nitrate leaching from a single application versus multiple applications of
controlled release fertilizers.

Leaching data from this experiment generally indicated variable rates of nitrate, phosphate,
and K leaching over time for most of the fertilization methods. Unusually high rainfall
starting on week 6 resulted in much larger amounts of all three ions being leached from
these containers, but other factors also may have contributed to the week to week variation.
Based on these data, it appears that leachate sampling at any one time may not be a good
predictor of total nutrient leached during the production cycle.

After six months, dry weights of spathiphyllum grown in the container medium and
fertilized by the four methods were equivalent, and all fertilizer treatments produced much
larger plants than the unfertilized controls (Table 1). For areca palms, however, plants
fertilized with LF were larger than those fertilized with SGF. The controlled release
fertilizers produced palms equal in size to those grown with LF, but no better than those
receiving SGF. Thus, in terms of plant growth response, there was relatively little
difference among fertilization methods in the container medium.


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The total amount of nitrate leached from the container medium was significantly greater
for both spathiphyllum (Table 1) and areca palms (data not shown) fertilized with SGF. LF
produced the second most nitrate in the leachate for both species and the controlled release
fertilizers the least. The percentage of N lost to leaching in the container medium ranged
from 28% for LCCRF to 52% for SGF.

Relatively little phosphate leached from any fertilizer treatment. Since phosphate should
not be retained, plant utilization or precipitation must be responsible for the majority of
phosphate losses. From 11 to 28% of the applied phosphate was lost due to leaching from
the containers. Leachate phosphate amounts did differ among the fertilizer treatments,
however. Among fertilizer treatments, LCCRF resulted in the least phosphate leaching for
both species.

For both species, the highest amounts of K leached from containers fertilized with SGF
(Table 1). Liquid fertilization resulted in significantly less K leaching than SGF, and
LCCRF resulted in the least.

This study showed that nitrate, phosphate, and potassium leaching losses from a typical
foliage plant nursery are substantial. Assuming a density of 80,000 pots/ha, use of SGF in
the container medium would result in annual losses of 666 kg of nitrate, 49.4 kg of
phosphate, and 337 kg of potassium/ha. Use of controlled release fertilizers can
significantly reduce these leaching losses, however. These data support the findings of
Yeager and Cashion (1993) that leachate nitrate concentrations vary considerably during
the production period and sampling at any given time will probably yield misleading
results in terms of overall nitrate or phosphate input into the environment. Furthermore,
leachate volume must also be considered in order to determine the total amount of nitrate
or other ion input into the environment.

Literature Cited

Cox, D.A. 1993. Reducing nitrogen leaching-losses from containerized plants: The effectiveness of
controlled release fertilizers. J. Plant Nutr. 16:533-545.

Handreck, K.A. and N.D. Black. 1984. Growing media for ornamental plants and turf. New South Wales
Univ. Press., Kensingtion, Australia.

Hershey, D.R. and J.L. Paul. 1982. Leaching losses of nitrogen from pot chrysanthemums with controlled
release or liquid fertilization. Scientia Hortic. 17:145-152.

Marconi, D.J. and P.V. Nelson. 1984. Leaching of applied phosphorus in container media. Scientia Hortic.
22:275-285.

Maynard, D.N. and O.A. Lorenz. 1979. Controlled release fertilizers for horticultural crops. Hort. Rev.
1:79-140.


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Rathier, T.M. and C.R. Frink. 1989. Nitrate in runoff from container grown juniper and Alberta spruce under
different irrigation and N fertilization regimes. J. Environ. Hort. 7:32-35.

U.S. Environmental Protection Agency. 1982. Manual of individual drinking water systems. US EPA Office
of Drinking Water, Washington, DC. EPA-570/9- 82-004.

Wetzel, R.G. 1975. Limnology. W.B. Saunders Co., Philadelphia.

Yeager, T.H. and J.E. Barrett. 1984. Phosphorus leaching from 32P- superphosphate-amended soilless
container media. HortScience 19: 216-217.

Yeager, T.H. and G. Cashion. 1993. Controlled release fertilizer affects nitrate nitrogen runoff from container
plants. HortTechnol. 3:174-177.


Table 1. Spathiphyllum and areca palm dry weights and total nitrate, phosphate, and
potassium leached per spathiphyllum container over six months when grown in a pine bark,
sedge peat and sand medium and fertilized by four different methods.

Spathiphy Iltim Areca palm
Method dry wt dry wt Nitrate Phosphate Potassiium
(,U) ( ) ( ,L ) ( L ) ( 1U)
Control 0.8bz 28.5a 13e 3e 75e

LCCRFY 31 3 77 I0 222' 15 847'

SGF 27 5 73 9b 4160 309 2106

LF 29.7a 92.9a 3710b 382a 1747

HCCRF 32.6a 75.0ab 2655C 237C 1256C




zMean separation within columns by Waller-Duncan k-ratio method, k=100.

YLCCRF=Lightly-coated Controlled Relesae Fertilizer, SGF=Soluble Granular Fertilizer,
LF=Liquid Fertilizer, and HCCRF=Heavily-coated Controlled Release Fertilizer.


Figure


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