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University of Florida, IFAS,
Central Florida Research and Education Center-Apopka
CFREC-Apopka Research Report RH-92-6
A.R. Chase and R.T. Poole*
Fertilizer recommendations change periodically when new research findings on application rate, balance of fertilizer elements, or application interval identify potential improvements in plant production. Many ornamental plant producers changed fertilizer formulations to maximize profits when source of nitrogen (N) was not shown to affect growth of most foliage plants (3, 4, 5). Additional work demonstrated that containerized Epipremnum aureum (golden pothos) stock plants grew well when fertilized with 28 or 56 mg N from NH4NO3 Materials and Methods
Experiment 1. This test began on 18 April 1990, using well rooted golden pothos cuttings obtained from a commercial nursery. Cuttings were potted, 10 per pot, into 6-inch standard containers filled with Vergro Container Mix A without superphosphate (Verlite Co., Tampa, FL 33680). Plants were grown in a greenhouse where maximum light intensity was 2000 ft-c at leaf level and air temperatures ranged from 65 to 90°F. Plants were watered as needed to maintain healthy growth, usually twice a week. Immediately after placement in the greenhouse, containers were top dressed with 39-0-0 urea formaldehyde fertilizer at rates of 1, 2, 3, 4 or 5 g/6-inch pot, with ten replicates per treatment.
Potting medium leachate soluble salts levels (umhos/cm) were measured on 5 May and 13 June. Number of leaves and vines, and total vine length were recorded on 13 June. On 18 June, plants were rated for top quality using the following scale: 1 = dead; 2 = poor quality, unsalable; 3 = fair quality, salable; 4 = good quality, salable; and 5 = excellent quality, salable. Color was also rated on the following scale: 1 = no variegation, solid green color;
2 = poor variegation; 3 = fair variegation; 4 = good variegation; and 5 = excellent variegation. The number of necrotic leaves per plant was recorded on 18 June. Vines were cut back to pot rims, fresh vine weights were recorded and vines were utilized for cuttings.
The unrooted cuttings obtained from experiment 1 were planted, 10 per 6-inch standard pot, in the same medium used for the stock plants. Each container was top dressed with 6 g 19-6-12 Osmocote (Grace/Sierra Co., Milpitas, CA 95035). Five replications per treatment were established under mist in a greenhouse where light level was 1500 ft-c and temperatures ranged from 65 to 90°F. Experiment 1 ended when cutting quality was rated (using the same scale employed to determine top quality grades of stock plants) on 19 July 1990.
Experiment 2. The second test, conducted in 1991 during the summer months, was very similar to experiment 1; therefore, only differences between the two tests are listed below. Six rates of fertilizer were tested, with containers receiving 1, 2, 3, 4, 5 or 6 g/6-inch pot urea formaldehyde 39-0-0 on 7 June. Potting medium leachate soluble salts (µmhos/cm) were measured on 18 June, 23 July and 18 August. Top quality and color (using previously given scales) were evaluated on 19 July with vine length and fresh weight of vines recorded on 23 July. The experiment was completed with final vine lengths, vine weights, top quality and color recorded on 21 August. No cuttings were evaluated in experiment 2.
Experiment 3. The final test was a 3 x 4 factorial design with 10 replications per treatment, and was begun on 11 September 1991. Good quality golden pothos liners were potted into 6-inch standard containers using the same growing medium as in experiments 1 and 2. Plants were placed in a greenhouse under 1500 ft-c maximum light intensity where temperatures ranged from 65 to 90F and were watered 2 or 3 times per week as needed. Containers were top dressed with the same urea formaldehyde fertilizer at rates of 0, 2, 4, or 6 g/6-inch pot. Potassium from 0-0-45 was added at the rate of 0, 3 or 6 g/6-inch pot. All containers received 4 g/6-inch pot of single superphosphate to supply phosphorous requirements.
Soluble salts of potting medium leachate were measured every 4 weeks. Plant quality was graded (based on the same scale used in experiments 1 and 2) on 22 November. Total vine length and number of vines per plant were also determined on 22 November. Total vine weight was recorded on 25 November, the day cuttings were taken from the fresh vines as described under experiment 1. Cuttings were graded (using the same scale as in experiment 1) 10 January 1992, the day experiment 3 was terminated.
Results and Discussion
Experiment 1. Stock plants receiving urea at 4 g/6-inch pot had more leaves, fewer damaged (marginal burning) leaves and higher top quality grades than stock plants fertilized at the other rates tested (Table 1). Lower application rates apparently resulted in leaf necrosis as a result of N deficiency. Number of vines and vine length were not affected by urea rate in this test (Table 1). Electrical conductivity of leachate collected from golden pothos with the highest top quality grades was measured at about 2500 µmhos/cm on 4 May and 850 µmhos/cm on 13
June 1990. Cuttings from stock plants receiving urea at either 4 or 5 g/6-inch pot were of higher quality than those obtained from stock plants fertilized at the 1, 2 or 3 g urea /6-inch pot rates; although differences were not statistically significant (Table 1).
Experiment 2. Plant growth as indicated by vine weight and length generally increased as urea rate increased up to the 4 g urea/6-inch pot (Table 2). Top quality was better overall at the initial rating on 19 July, indicating that available N had reduced significantly by test completion a month later. Electrical conductivity of leachate from containers of golden pothos fertilized with 6 g urea/6-inch pot was measured at about 4000 µmhos/cm on 18 June, but had decreased to 1600 µmhos/cm, on 23 July 1991. Highest quality plants on 21 August were those receiving 6 g urea/6-inch pot, the highest rate tested in experiment 2 (Table 2).
Experiment 3. The correlation between top quality grade and electrical conductivity (soluble salts) was significant. Top quality grades increased as electrical conductivity of the leachate increased to about 4,000 µmhos/cm, regardless of N:K ratios, but decreased gradually as leachate electrical conductivity increased further to about 6000 µmhos/cm (Fig. 1). A similar trend for vine length, weight and number of vines occurred (Fig. 2), although highest ratings were found at different combinations of N to K. Greatest vine length occurred on stock plants fertilized with 3 or 6 g of K and O g N or O and 3 g of K and 2 g of N (Fig. 2). Most vines were produced with any rate of Kand O g N, 3 and 6g of K and 2g N or O or 3g Kand 4g N. Finally, total vine weight was highest when plants received 6 g K and O g N, O and 3 g K and 2 g N, or O g K and 4 g N. Apparently, the effects of K and N are additive for these growth parameters on golden pothos with over fertilization effects controlled by both K and N rate. With such differing responses to the same treatments, it becomes difficult to determine optimal fertility regimes. Quality of cuttings from these stock plants was dramatically affected by treatment. Plants receiving no K and no urea produced no cuttings due to lack of vine production. Some cuttings were produced by plants receiving intermediate rates of K and urea. Although some plants produced salable cuttings, no treatment gave consistently high quality cuttings in this test. Over fertilization resulted in poor cutting production characterized by both low yields and low quality cuttings. Fertilization at the 6 g urea/6-inch pot rate caused severe reductions in cutting production levels regardless of K rate. Best cuttings in, as well as best overall-stock plants were produced when plants received 2 or 4 g urea/6-inch pot and 3 g K/pot. Although these results might suggest applying no potassium or no nitrogen, this recommendation has not been supported by the other research reported here or in the literature.
Best quality plants in experiments l and 2 were grown with 4 g urea/6-inch pot. In an earlier test, comparable quality plants were grown with NH4NO3 at rates of 42 to 56 mg N/6-inch pot/week soluble fertilizer (6, 9). In experiment 3, N:K ratios did not have a significant effect on golden pothos stock plant growth, although total of N and K applied greatly influenced plant growth parameters. This was reflected by the correlation between leachate electrical conductivity and top quality.
Cutting quality was significantly affected by the fertilizer regime of the stock plant. In experiment 1, cutting quality increased as rate of urea increased to 5 g/6-inch pot. In experiment 3, best cuttings were produced when plants received 2 or 4 g urea/6-inch pot and 3 g K/pot. These experiments indicate that nitrogen may be somewhat more important in affecting both stock plant and cutting quality, although potassium must be available in moderate amounts to give optimum growth. Finally, urea can serve as a good source of nitrogen for growth of golden pothos stock and cuttings.
*professor of Plant Pathology and Professor of Environmental Horticulture, respectively. CFREC-Apopka, 2807 Binion Rd., Apopka, FL 32703-8504.
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2. Chase, A.R. and R.T. Poole. 1991. Effect of potassium and potting medium on growth of golden pothos. Univ. of Fla., IFAS, CFREC-Apopka Res. Rpt. RH-91-14.
3. Conover, C.A. and R.T. Poole. 1983. Influence of nitrogen source and growth and tissue content of three foliage plants. Proc. Fla. State Hort. Soc. 95:151-153.
4. 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.
5. 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.
6. Poole, R.T. and A.R. Chase. 1991. Growth of pothos cuttings affected by nitrogen fertilization of stock plants. Univ. of Fla., IFAS, CFREC-Apopka Res. Rpt. RH-91-12.
7. Poole, R.T. and C.A. Conover. 1982. Fertilization of birdsnest fern, Asplenium nidus L. Proc. Trop. Reg. Amer. Soc. Hort. Sci. 25:81-87.
8. Poole, R.T. and C.A. Conover. 1985. Nitrogen, phosphorus and potassium fertilization of Brassaia actinophylla, Calathea makoyana and Chrysalidocarpus lutescens. J. Environ. Hort. 3(1):1-3.
9. Reyes, Trinidad, A.R. Chase and R.T. Poole. 1990. Effect of nitrogen level and light intensity on growth of Epipremnum aureum. Proc. Fla. State Hort. Soc. 103:176-178.