Nitrogen Form Affects Foliage Plant Growth A Summary of Research at CFREC Apopka

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University of Florida,
Central Florida Research and Education Center-Apopka
CFREC-Apopka Research Report RH-92-27

K. Steinkamp, C.A. Conover and A.R. Chase*

Foliage plant producers most often use urea (CO(NH₂)₂), 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 Table 1.

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 temperatures.

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 which received fertilizer composed primarily of NO3 showed damage that resembled Fe or Mn deficiency symptoms.

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 NH₃ (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 NH₃ had fewest nodes per vine but cutting quality was slightly higher than quality of cuttings from plants fertilized with NH₄ or NH₄NH₃. 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.

Growing Medium

Another factor to consider is N availability for plant use. Plants absorb NH₃ and, in smaller amounts, NH₄ directly. Urea and most NH₄ need to be converted to NH₃ by microorganisms present in the growing medium before plants can absorb them. Conversion of urea and NH₄ to NH₃ in growing medium is dependent on potting medium composition and environmental conditions.

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.

Environmental Pollution

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 NH₃. However, nitrification converts NH₄ fairly rapidly, and at a somewhat slower rate urea, to NH₃.

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 size.

Plant quality was unaffected by fertilizer treatment. Leachate pH decreased over time forall 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 NH₃ had lowest electrical conductivity.

Leachate analysis showed few differences in NH₃ 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 NH₃. Leachate with highest concentration of NH₃ after twelve weeks was collected from pots receiving fertilizer formulations containing some NH₃.

Disease Control

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 NH₃ 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 NH₃ 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% NH₃ 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 NH₃ 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 NH₃. Foliage of plants fertilized with 100% NH₃ 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. dieffenbachia were grown in two tests, using the same three ratios of NH₃ 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.

Economics

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 NH₃.

Conclusions

Increasing NH₄ or urea and decreasing NH₃ 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 NH₃. 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 NH₃ 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% NH₃ 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.

References

1. 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.
2. Chase, A . R. 1989. Nitrogen source and rate affect severity of xanthomonas leaf spot of Hedera helix. Nursery Digest 23(4):18-19.
3. Chase, A.R. 1988. Effect of nitrate-ammonium ratio on growth of Syngonium podophyllum 'White Butterfly' and susceptibility to Xanthomonas campestris pv. syngonii. Nursery Digest 22(9):44.
4. Chase, A.R. and R.T. Poole. 1990. Effect of nitrogen source on growth and susceptibility of Anthurium hybrids to Xanthomonas campestris pv. dieffenbachia. Foliage Digest 13(12):3-4.
5. 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.
6. 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.
7. 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.
8. 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.
9. 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.
10. 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 medium leachate.
11. 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.

Table 2. Fertilizer components and percentage of total N three N forms supply, in nine fertilizers, used to produce salable size foliage plants, in several experiments conducted at CFREC-Apopka.

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.