Alumina-Buffered Phosphorus Fertilizer

Jonathan P. Lynch, Kathleen M. Brown, and Gary Moorman

Penn State University

Executive Summary:

With financial support from AFE, we have developed a novel fertilizer technology for container plants that provides continuous, optimal levels of phosphorus to plant roots based on actual plant phosphorus requirements, while eliminating leaching from the container. Plants grown using this alumina-buffered phosphorus fertilizer are of equal or better quality than conventionally grown plants and have improved tolerance to drought stress.

We would like to continue research on this novel fertilizer to provide information needed for its eventual commercializafion and use by the floriculture industry. In this project, we propose to conduct postproduction evaluafions of poinsettias, florist azaleas, and chrysanthemums grown with alumina-buffered phosphorus or conventional fertilizer, in cooperation with Dr. Terrill Nell at the University of Florida and Yoder Brothers. In addition, we will evaluate the effects of alumina- buffered phosphorus on susceptibility of geraniums to Botrytis and Pythium, in cooperation with Dr. Gary Moorman in the Plant Pathology Department at Penn State.

If successfully implemented, this technology would significantly reduce nutrient effluent from greenhouses and nurseries, increase efficiency by simplifying nutrient management, and improve plant performance by providing optimum quantities of phosphorus for plant growth. These benefits would improve the efficiency and compefitiveness of greenhouse crop production while protecting water resources.

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Description and Objectives

Soilless growth media such as perlite, rockwool, vermiculite, and peat have generally good water holding characteristics, cleanliness, and convenience, but they share an inability to retain and release plant nutrients (Nelson 1991) and are known to be very conducive to Pythium root rot development. Crop requirements for specific nutrients change during the growing season, are affected by environmental conditions, genotype, etc., and are difficult to continuously monitor. Consequently, container crops are supplied with high levels of fertilizer throughout their growth cycle. The resulting high fertilizer levels can be detrimental to plant quality and stress tolerance (Anghinoni and Barber 1980, Sheldrake 1991, Marschner 1995) and render plants more susceptible to Pythium root rot (Gladstone and Moorman, 1989). Furthermore, runoff of nutrients from intensively fertilized horticulture operations is an environmental threat to surface and ground water resources, and increasingly is subject to regulation by state and federal agencies.

With support from AFE, we have developed a novel solution to this problem by creating a solid-phase-buffered phosphorus fertilizer (Al-P). This new technology allows controlled release of P into the potting medium throughout the life of the plant, in amounts determined by actual plant need, without the need for grower monitoring and without nutrient leaching. Solid-phase buffering of phosphorus is provided by a solid aluminum oxide compound, formulated in granules the size and shape of sand grains. The alumina is treated with phosphorus, then added to the growing media in very low concentrations. Our work with peatlite soilless mixes indicates that addition of phosphorus~harged alumina at 1% of the volume of the dry medium is sufficient fQr optimal plant performance of floriculture crops ~in et aL 1996). The phosphorus bound to the solid alumina releases a very low concentration of phosphorus into the surrounding solution, in the range of concentrations encountered in natural soils, about one thousand times lower than conventional horticultural nutrient solutions.

Because soluble phosphorus concentrations are very low, even if large quantities of water are flushed through the medium, negligible amounts of phosphorus are lost. In the systems we have tested, leaching has been reduced to less than 1% of that in conventionally fertilized plants (Borch et aL 1998, Lin et aL 1996). This means that there is less nutrient waste to be dealt with in greenhouse and nursery wastewater streams, greatly reducing potential for pollution of ground and surface waters. Although the solid alumina releases very low concentrations of phosphorus, it acts as a buffer; that is, it will tend to maintain that concentration under any condition (chemically speaking, it establishes an exchange equilibrium). In this way the release of phosphorus from the fertilizer is proportional to the phosphorus requirement of the crop: a vigorously growing crop will acquire more phosphorus from the buffer, while a slowly growing crop will acquire less. Thus, the alumina can be used to provide optimal phosphorus nutrition over time, without the need for

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grower monitoring, and without the need for any additional phosphorus fertilization, while minimizing phosphorus leaching from the container. This is in contrast to slow-release fertilizers such as Osmocote, which can maintain adequate phosphorus concentrations in the root zone over extended periods of time, but which release phosphorus as a function of pellet dissolution rather than plant requirements, and do not prevent phosphorus leaching (Havis and Baker 1985).

Performance of plants grown with buffered Al-P fertilizer was equal or better than conventionally fertilized plants. In some cases, plants were more compact or had more branches (Borch et al. 1998; Lin et aL 1996). Bedding plants (marigold and impatiens) grown with Al-P showed improved drought tolerance, which may have been a result of better root distribution within the container and smaller leaves (’3orch et al. 1998). The morphological and physiological changes produced by Al-P may also be important for other aspects of quality. For example, postproduction quality of flowering plants depends on good production practices, including light and adequate but not excessive nutrition ~ell, 1993). We believe that phosphorus levels used in commercial horticulture are excessive, and that use of Al-P to supply lower but still adequate phosphorus will improved quality.

The specific objectives of this project are:

I) To conduct ~05 tproducti on evaluation of poinsettia, florist azalea, and chrysanthemums grown with Al-P.

2) To determine whether Al-P fertilizer affects resistance to Botiytis infection of foliage or Pythium root rot.

Progress to Date and Future Anticipated Benefits

We have made substantial progress in developing and evaluating alumina-buffered phosphorus (Al-P) fertilizer. We have shown that the technology is effective for growing geraniums and marigolds in commercial peatlite media. In these studies the use of alumina reduced P leaching to 2% compared to 74% in conventionally fertilized plants ~in et aL 1996). Alumina was effective at media concentrations as low as 1%, which would represent a very small cost for the alumina substrate per pot (approximately 5 cents per pot, at the retail cost of the alumina; scaled up for commercial manufacturing, the alumina would be less expensive since it could be purchased at wholesale prices). In no case did we observe inferior growth of the alumina-fertilized plants compared to conventional fertilizer, and in some cases we observed superior growth and flowering.

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The quality of bedding plants was improved when the plants were grown with buffered phosphorus fertilizer. The most important improvement was an increase in drought tolerance. Marigold and impatiens plants grown with the Al-P fertilizer took longer to wilt when water was withheld than plants grown with a conventional, high-P fertilization regime (13orch et aL 1998). We have seen similar improvements in drought resistance of poinsettia (Miller et al, unpublished). Some species are also more compact when grown with the buffered-phosphorus fertilizer (Borch et aL 1998).

In this project, we will continue and extend our previous work on the effects of Al-P on quality of flowering plants. As part of our 1997-98 project, we have trials underway at Yoder Brothers in Florida testing the effects of Al-P on growth and quality of florist azalea and chrysanthemum. Some of these plants will be sent to the University of Florida for postproduction evaluation in their specialized facility. In addition, poinsettias produced at the University of Florida will be included in postproduction evaluations.

Excessive fertilizers are well known to render some plants more susceptible to disease. Our current project includes evaluation of Pythium root rot susceptibility, which has been shown to increase with increasing phosphorus levels when standard fertilizers are employed (Gladstone and Moorman 1989). Our preliminary data, based on one experiment, indicates that Al-P does not result in less Pythium root rot susceptibility. This experiment is being repeated. We will also test the foliage of plants for susceptibility to Botiytis, since progression of gray mold is affected by nutrition ~lad and Evensen 1995).

Materials and Methods

Postproduction experiments. Florist azalea plants (4 cultivars) are currently being grown at Yoder Brothers facility in Alva, FL using conventional fertilization or Al-P amendments. Plants from these experiments will be sent to the University of Florida for evaluation in their postproduction evaluation facility. We are planning a similar trial of chrysanthemums with Yoder Brothers; plants from these experiments will also be sent to UF for postproduction evaluations.

Dr. Terrill Nell (University of Florida) is planning evaluations of several poinsettia cultivars at the University of Florida. Some plants in these trials will be grown with Al-P instead of conventional fertilization and tested in the postproduction facility. Dr. Nell has agreed to cooperate in these experiments on a trial basis for this year. If the results are promising, we will submit a new proposal with joint budgeting for further experiments next year.

Disease resistance. Geraniums will be grown in a soilless medium in a climate~ontrolled greenhouse at several P levels. Control plants will be fertilized with conventional horticultural nutrient solutions (1-2 mM phosphate), and low P treatments provi4ed by solid-phase-buffered media (in the range of 10-100 ~IM phosphate). Standard production practices will be followed.

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Seedlings will be tested for Pythium susceptibility by transplanting them from plug flats into potting mix and inoculated with Pythium mycelium one week after transplant. Plant mortality will be recorded weekly after inoculation. Upon termination of the experiment, root rot and root quality will be rated for each surviving plant.

For tests of Botiytis susceptibility, leaf disks will be removed from plants grown with conventional P treatments or Al-P. The disks will be inoculated with botrytis spores and incubated. The percentage of disks that become infected will be recorded (Moorman and Lease, 1992).

In all cases, a sufficient number of plants will be evaluated to permit statistical analysis of the results.

Literature Cited

Anghinoni I, SA Barber. 1980. Phosphorus influx and growth characteristics of corn roots as influenced by phosphorus supply. Agronomy Journal 72:685-688.

Borch K, KM Brown, JP Lynch. 1998. Improvement of bedding plant quality and stress resistance with low phosphorus. HortTechnology 8:20-24.

Elad Y, K Evensen 1995. Physiological aspects of resistance to Botiytis cinerea. Phytopathology

85: 637-643

Gladstone LA, GW Moorman. 1989. Pythium root rot of seedling geraniums associated with

various concentrations of nitrogen, phosphorus, and sodium chloride. Plant Disease 73: 733-

736

Havis JR, HJ Baker. 1985. Phosphorus availability in peat-sand media fertilized with several phosphorus sources. Journal of Environmental Horticulture

3:153-155.

Lin, YP, EJ Holcomb, JP Lynch. 1996. Marigold growth and P leaching from media amended with P-charged alumina. HortScience 31:94-98.

Marschner H. 1995. Mineral Nutrition of Higher Plants, 2nd edition. Academic Press, New York.

Moorman, GW and RJ Lease. 1992. Residual efficacy of fungicides used in the management of

Botzytis cinerea


on greenhouse-grown geraniums. Plant Disease 76:374-376.

Nell, TA. 1993. Flowering Potted Plants. Prolonging Shelf Performance: Postproduction Care and Handling. Ball Publishing, Batavia W.

Nelson PV. 1991. Greenhouse Operation and Management. Prentice-Hall, Inc., New Jersey. Sheldrake R. 1991. Control height with low P. Greenhouse Grower 9:77-80.

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Project Leader Qualifications

Jonathan Lvnch, Associate Professor of Plant Nutrition, Department of Horticulture, Penn State. Dr. Lynch would bring expertise in plant nutrition and 14 years of experience with buffered fertilizers to the project. Dr. Lynch has several ongoing projects on practical and basic aspects of the N, P, and K nutrition of horticultural crops in his research group.

Kathleen Brown, Associate Professor of Postharvest Physiology, Department of Horticulture, Penn State. Dr. Brown would bring 17 years of experience in postharvest and postproduction physiology to the project. Dr. Brown has several collaborative projects with Dr. Lynch on how phosphorus nutrition influences postproduction quality and stress tolerance of floricultural crops.

Gary Moorman, Professor of Plant Pathology, Department of Plant Pathology, Penn State. Dr. Moorman has worked with the effects of fertilization on Pythium root rot of geraniums, poinsettias, impatiens, and begonias for over 15 years. He has also worked extensively on Botiytis epidemiology and control as well as its fungicide resistance in commercial greenhouses.

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Estimated Budget Submitted by The Pennsylvania State University to the American Floral Endowment September 1, 1998 - August31, 2002

Year 1

9/1/98-

8/31/99

A. Salaries and Wages
Co-Prin. mv. J. P. Lynch 0
Co-Prin. mv. K. M. Brown 0
Co-Prin. mv. G. Monman 0
Research Teelmician, R. Snyder, 24%, 12 mos. 7,999
Total Category I 7,999
wages, technician 2,000
Total Category Ill 2,000

Total Salaries and Wages

9,999

B. Fringe Benefits
Category I @ 27.34% 2,187
Category Ill @ 7.64% 153
Total Fringe Benefits 2,340
C. Total Salaries, Wages, & Fringe Benefits 12,339
D. Equipment ($5,000 and greater) 0
E. Materials & Supplies 500
F. Travel 1,500
G. Publication Costs 0
H. Computer Costs 0
I. Other Direct Costs 0
J. Total Direct Costs 14,339
Budget Notes: JK~.1:7I2t)~x

Estimated salary costs are based on current salary rates (fiscal year 1997-98) escalated approxin’atcly 4% leginning July I of each subsequent year. University policy has been to award salary increases on the basis of mcrit only.

Fringe Benefits: Rates are computed using the fixed rates of 27.34% applicable to Category I salaries. 12.23% applicable to Category II graduate assistants, and 7.64% applicable to Category Ill salaries and wages I;()r the current fiscal year of July 1, 1998 through June30, 1999. If this proposal is funded, the rates quoted abt’ve shall. at the time of funding, be subject to adjustment for any period subsequent to June 30, 1999 if superseding Government approved rates have been established. The fringe benefit rates are negotiated and approved by the Office of Naval Research, Penn State’s cognizant federal agency.

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