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Nitrogen Form Affects Foliage Plant Growth--A Summary of Research at CFREC-
K. Steinkamp, C.A. Conover and A.R. Chase'" "
University of Florida, '. o 19.
Central Florida Research and Education Center-Apopka
CFREC-Apopka Research Report RH-92-27' irsity Florida
Foliage plant producers most often use urea (CO(NH2z)), ammonium (NH4) or nitrate
(NO3), alone or in various combinations to supply crop nitrogen (N) requirements.
Determination of best N form for foliage plant production should be made after weighing several
factors including cost, availability, plant response under various environmental conditions and
ground water pollution potential. A number of experiments have been conducted at CFREC-
Apopka to provide growers with information useful in making these fertilizer decisions.
Plant Growth and Quality
Ideally, the most important factor deciding choice of N form should be plant growth
response. In one experiment, seven fertilizers containing different forms of N were used to
grow schefflera (Brassaia actinophylla), peacock plant (Calathea makoyana) and philodendron
(Philodendron selloum) for nine months (Conover and Poole, 1982). Fertilizer formulations and
percentages of nitrogen derived from NO3, NH4 and urea for the seven fertilizers are shown in
Growth data were recorded after six months to evaluate response when plants were grown
in fall and winter light intensities and temperature regimes. Growth data were measured again
three months later to determine plant response to higher summertime light intensities and
Height, plant grade and foliar color of schefflera and philodendron were not influenced
by N form. All fertilizer treatments produced good quality plants and tissue levels of macro-
and micronutrients were within the ranges recommended for production of healthy plants (Poole
and Conover, 1976). Temperature and light intensity ranges appeared to have no effect on
which N form produced best growth.
Growth of peacock plant was influenced by N form. Best plant, root and color grades
were assigned to plants fertilized with 100% urea or 75% NH4:25%NO3. Foliage on plants
'Editorial Assistant, Center Director and Professor of Environmental Horticulture, and
Professor of Plant Pathology, respectively, Central Florida Research and Education Center, 2807
Binion Road, Apopka, FL 32703.
which received fertilizer composed primarily of NO3 showed damage that resembled Fe or Mn
In another test, the nine fertilizer formulations shown in Table 2 were used to grow
'Silver Queen' aglaonema (Aglaonema 'Silver Queen'), 'Camille' dieffenbachia (Dieffenbachia
maculata 'Camille'), 'Dania' zebra plant (Aphelandra squarrosa 'Dania'), parlor palm
(Chamadorea elegans), 'Florida Ruffle' fern (Nephrolepis exaltata 'Florida Ruffle'), peperomia
(Peperomia obtusifolia) and heart-leaf philodendron (Philodendron scandens oxycardium)
(Conover and Poole, 1986b). Individual species were grown from rooted cuttings, seedlings or
offsets, from February 6, 1981 until crops reached salable size. Although slightly better quality
'Silver Queen' aglaonema and heart-leaf philodendron were grown with 100% NH4, all foliage
plants in this test were salable and N form did not greatly influence plant growth.
Tissue analysis showed potassium (K) levels in 'Silver Queen' aglaonema and heart-leaf
philodendron dropped when percent NO3 in fertilizer decreased. Tissue from plants receiving
100% urea, 100% NH4 or the 75% combination of NH4 with NO3 (the treatments producing the
best quality heart-leaf philodendron or aglaonema) had slightly lower K levels than those of good
quality foliage plants produced in earlier research (Poole and Conover, 1976).
Fixation of K by NH4 in growing medium of tomato plants was observed previously
(Maynard et al, 1968). Results of the preceding test indicate that K nutrition may have to be
monitored or increased when NH4 or urea are the only N forms used for production of long term
crops or maintenance of aglaonema and heart-leaf philodendron stock plants.
Golden pothos (Epipremnum aureum) stock plant fertilization was examined in a year-
long test conducted in 1990 (Poole and Chase, 1991). Stock plants were grown from cuttings
using the three fertilizer formulations listed in Table 3 and growth was measured during the
summer and winter months.
Nitrogen form did not influence stock plant growth or cutting quality during the summer
months. Growth and cutting quality during fall and winter was slightly influenced by N form.
Golden pothos receiving only NO3 had fewest nodes per vine but cutting quality was slightly
higher than quality of cuttings from plants fertilized with NH4 or NH4NO3. However, influence
of N form on growth of golden pothos stock plants and quality of cuttings would probably be
considered insignificant for stock plants maintained for commercial purposes.
Another factor to consider is N availability for plant use. Plants absorb NO3 and, in
smaller amounts, NH4 directly. Urea and most NH4 need to be converted to NO3 by
microorganisms present in the growing medium before plants can absorb them. Conversion of
urea and NH4 to NO3 in growing medium is dependent on potting medium composition and
Low levels of organic matter and aerobic bacteria, low temperature, low pH and high
moisture all reduce the rate of nitrification. Levels of organic matter and aerobic bacteria as
well as water holding capacity can vary greatly among growing media used in plant production,
thereby affecting plant growth.
An experiment was conducted to determine whether interactions between commonly used
growing media and N form affected foliage plant growth. The nine fertilizer formulations shown
in Table 2 were used to grow parlor palm, 'Camille' dieffenbachia and peperomia (Peperomia
obtusifolia) in four different media (Conover and Poole, 1986a). Growing mixes were: (1)
Florida sedge peat, (2) Florida sedge peat: Pine bark (1:1, v/v), (3) Metro Mix-300 (sphagnum
peat moss, vermiculite, perlite, granite sand and pine bark; Grace/Sierra Co., Milpitas, CA
95035) and (4) Vergro Container Mix A [sphagnum peat moss:vermiculite:perlite (2:1:1, v/v);
Verlite Co., Tampa, FL 33601]. Liners or seedlings were grown in 6-inch pots from August
17, 1984 until individual species reached salable size.
Potential interactions between commonly used growing mixes and N form did not affect
plant growth. Height and quality of parlor palm and peperomia were not affected by N form.
'Camille' dieffenbachia height was slightly influenced by N form, with tallest plants (20 inches)
receiving mostly NH4 and shortest plants (18 inches) receiving fertilizer containing urea. Such
small differences in height would probably be considered insignificant in commercial production,
especially since plant quality and root growth remained unaffected.
Another factor influencing choice of N form should be amount of nitrogen leached from
containers. NH4 carries a positive charge that helps make it more resistant to leaching than the
negatively charged NO3. However, nitrification converts NH4 fairly rapidly, and at a somewhat
slower rate urea, to NO3.
In an experiment conducted in 1991, all leachate generated from 6-inch pots containing
'Petite' spathiphyllum (Spathiphyllum 'Petite') fertilized with the nine fertilizer formulations
listed in Table 2 was collected and analyzed (Poole and Conover, 1991). The crop production
cycle lasted approximately nineteen weeks during which time plants grew from liners to salable
Plant quality was unaffected by fertilizer treatment. Leachate pH decreased over time
for all nine fertilizer formulations tested, but leachate from containers receiving formulations
containing 100% to 75% NH4 had the lowest pH. Leachate from containers fertilized with
formulations of 50% or more NH4 had highest electrical conductivity (soluble salts) readings and
leachate from pots receiving mostly NO3 had lowest electrical conductivity.
Leachate analysis showed few differences in NO3 concentration among the nine fertilizer
formulations tested for the first twelve weeks of plant growth. After twelve weeks, containers
fertilized with 100% urea or 100% NH4 produced leachate lowest in NO3. Leachate with highest
concentration of NO3 after twelve weeks was collected from pots receiving fertilizer formulations
containing some NO3.
Effective disease control measures often combine a chemical spray program with control
of several environmental conditions such as air temperature, fertilization, watering method or
air circulation patterns unfavorable for pathogen development and spread. The results of ten
experiments conducted to examine effects of NO3 to NH4 ratio on severity of damage on five
foliage plants infected with Xanthomonas campestris bacteria are given.
In two tests, 'White Butterfly' nephthytis (Syngonium podophyllum 'White Butterfly')
were grown with the following five ratios of NO3 to NH4 100:0, 75:25, 50:50, 25:75 and
0:100 (Chase, 1988). Plants were inoculated with X. campestris pv. syngonii, which causes
blight on nephthytis. Fourteen to twenty-one days after inoculation, severity of disease was
estimated as the percentage of the leaf surface water-soaked, chlorotic and/or necrotic.
Symptoms of blighting, plant height and quality were not significantly affected by N ratios.
When Brassaia actinophylla, inoculated with campestris pv. hederae were grown in four
experiments using the same five N form ratios, plants fertilized with either 100% NH4 or 100%
NO3 were less damaged by bacterial leaf spot (Blake and Chase, 1988). Plant growth and
quality were unaffected by ammonium:nitrate ratio treatments.
Severity of bacterial leaf spot on 'Brokamp' English ivy (Hedera helix 'Brokamp'), also
caused by X. campestris pv. hederae, was influenced similarly by N form in two experiments
(Chase 1989). Plants fertilized with 100:0, 50:50 or 0:100 ratios of NO3 to NH4 were
inoculated with the pathogen. When number of lesions per plant was determined about fourteen
days after inoculation, plants fertilized with 50:50 N form had more lesions than plants receiving
only NH4 or NO3. Foliage of plants fertilized with 100% NO3 was least affected by the disease.
Nitrogen form did not affect 'Brokamp' English ivy total vine length or fresh weight of foliage.
However, when 'Princess' (Anthurium 'Princess') or 'Southern Blush' (Anthurium 'Southern
Blush') anthuriums inoculated with X. campestris pv. dieffenbachiae were grown in two tests,
using the same three ratios of NO3 to NH4, N form did not consistently affect severity of
Xanthomonas blight (Chase and Poole, 1990). Both anthurium cultivars produced good quality
comparable growth, regardless of N form fertilization.
All three N forms are currently available individually, but are most commonly found in
products where at least two N forms are used to furnish nitrogen requirements. Since
application costs of fertilizers containing the three N forms are comparable, the major economic
consideration is cost of the product itself. For the past several years, urea has remained the least
expensive of the three N forms commonly used in foliage plant production, followed in order
of increasing price by NH4 and NO3.
Increasing NH4 or urea and decreasing NO3 in fertilizers improved growth or quality of
'Silver Queen' aglaonema, peacock plant and philodendron. Little or no visible differences were
seen in growth or quality of 'Dania' zebra plant, schefflera, parlor palm, 'Camille'
dieffenbachia, 'Florida Ruffle' fern, peperomia, heart-leaf philodendron, spathiphyllum, 'White
Butterfly' syngonium and 'Brokamp' English ivy receiving different N forms.
Golden pothos stock plant growth during winter was affected by N form, with cutting
quality slightly enhanced by NO3. Although results were significant statistically, they would
probably be considered insignificant on commercial crops.
The low K levels in tissue of 'Silver Queen' aglaonema and heart-leaf philodendron,
grown for twenty-six and nineteen weeks, respectively, with 100% urea or NH4 did not appear
to injure plants, but must be monitored. These findings, along with the results of the nineteen
week leachate monitoring test, which showed the acidifying effects of NH4 on medium leachate,
indicate that long term crops, interiorscapes and stock plants fertilized with NH4 may benefit
from a regular medium monitoring program.
Plant growth was unaffected by interactions of N form and growing medium composition
and results of the leachate monitoring test seem to indicate N form would also be relatively
unimportant in regard to NO3 content of leachate since effects of fertilizer rate and irrigation
level had a much greater effect.
The importance of N form as a component of disease control programs is still unclear,
but fertilization with 100% NO3 or 100% NH4 did result in lower levels of disease for two of
the foliage plants tested. More research with major economic foliage plant crops is needed to
determine the potential usefulness of specific N forms to benefit disease control efforts.
Based on current market prices and research results, NH4 and urea, alone or in various
combinations, are logical choices for fertilization of many foliage plants.
Blake, J.H. and A.R. Chase. 1988. Effect of ammonium-nitrate ratio on growth and quality
of Brassaia actinophylla susceptibility to Xanthomonas campestris pv. hederae. Proc.
Fla. State Hort Soc. 101:337-339.
Chase, A.R. 1989. Nitrogen source and rate affect severity of xanthomonas leaf spot of Hedera
helix. Nursery Digest 23(4):18-19.
Chase, A.R. 1988. Effect of nitrate-ammonium ratio on growth of Syngonium podophyllum
'White Butterfly' and susceptibility to Xanthomonas campestris pv. syngonii. Nursery
Chase, A.R. and R.T. Poole. 1990. Effect of nitrogen source on growth and susceptibility of
Anthurium hybrids to Xanthomonas campestris pv. dieffenbachiae. Foliage Digest
Conover, C.A. and R.T. Poole. 1982. Influence nitrogen source on growth and tissue content
of three foliage plants. Proc. Fla. State Hort Soc. 95:151-153.
Conover, C.A. and R.T. Poole. 1986. Effects of nitrogen source and potting media on growth
of Chamaedorea elegans, Dieffenbachia maculata 'Camille' and Peperomia obtusifolia.
Proc. Fla. State Hort. Soc. 99:282-284.
Conover, C.A. and R.T. Poole. 1986. Nitrogen source effects on growth and tissue content
of selected foliage plants. HortScience 21(4):1008-1009.
Maynard, D.N, A.V. Barker and W.H. Lachman. 1968. Influence of potassium on the
utilization of ammonium by tomato plants. Proc. Amer. Soc. Hort. Sci. 92:537-542.
Poole, R.T. and A.R. Chase. 1991. Influence of nitrogen source and rate on growth of
Epipremnum aureum stock plants and quality of cuttings. Univ. of Fla., CFREC-
Apopka, Res. Rpt. RH-91-16.
Poole, R.T. and C.A. Conover. 1991. Unpublished results of experiment #91-10: Influence
of nitrogen source on growth on 'Petite' Spathiphyllum and nitrogen composition of
Poole, R.T. and C.A. Conover. 1976. Chemical composition of good quality tropical foliage
plants. Proc. Fla. State Hort. Soc. 89:307-308.
Table 1. Fertilizer components and percent of total N each of three N forms supply in seven
fertilizers used to grow Brassaia actinophylla, Calathea makoyana and Philodendron selloum
for nine months.
% Nitrogen form
NH4N03, NaNO3, KN03
NaNO3, Ca(N03)2, KNO3
(NH4)2S04, CO(NH2)2, K2S04
Table 2. Fertilizer components and percentage of total N three N forms supply, in nine
fertilzers, used to produce salable size foliage plants, in several experiments conducted at
NH4NO3, NaNO3, KN03
NaNO3, Ca(N03)2, KNO3
NaNO3, CO(NH2)2, KN03
NaNO3, CO(NH2)2, KNO3
NaN03, CO(NH2)2, KN03
% Nitrogen form
UNIVERSITY OF FLORIDA
3 1262 05836 2095
Table 3. Fertilizer components and percentages of total N three N forms supply in three
fertilizers, used to grow Epiprumnum aureum stock plants, in two experiments in 1990.
% Nitrogen source
Fertilizer components NO3 NH4
(NH4)2SO4, KCL, H3P04 0 100
NH4NO3, KCL, H3PO4 50 50
KNO3, NaNO3, Ca(N03)2, KCL, H3PO4 100 0