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United States Department of Agriculture

Agricultural Research Service


Location: Application Technology Research

2010 Annual Report

1a. Objectives (from AD-416)
Objective 1: Evaluate plant nutritional requirements to optimize production and enhance quality. Sub-objective 1a: Elucidate the optimal tissue concentration of P and B in different light environments for major production species and how their susceptibility to foliar and root pathogens are influenced by nutrient status and light. Sub-objective 1b: Determine the uptake, accumulation, and potential benefit of silicon in ornamental crops and explore the potential for its use as a buffer to Cu toxicity and an alternative approach to pathogen control. Objective 2: Develop new and/or improved methods to detect, quantify, and manage biotic and abiotic stresses in ornamental crops grown in soilless and/or hydroponic greenhouse culture. Sub-objective 2a: Evaluate the use of existing non-destructive sensor technology and develop new molecular probes to measure and predict the impact of biotic and abiotic stresses on ornamental crops. Sub-objective 2b: Improve the Virtual Grower software model to enable growers to optimize their production systems by making more informed economic decisions about energy use, plant growth, pest management, and other production inputs. Objective 3: Evaluate existing and alternative growth medium amendments to determine the potential to deliver Si and buffer pH without negatively impacting beneficial microorganisms or crop growth.

1b. Approach (from AD-416)
Impatiens, geranium, vinca, and zinnia will be grown in media amended with different concentrations of phosphorus and boron under different light environments to determine optimum supply and tissue concentrations of these nutrients. Plants containing different amounts of these nutrients will then be inoculated with Pythium, Phytophthora, Botrytis, and powdery mildew to determine host susceptibility. These same plant species will also be grown with supplemental silicon in the fertilizer solution or incorporated into the substrate as rice hulls or Si-containing slags, and inoculated with the same pathogens or expose them to elevated Cu concentrations in the rootzone to determine if Si plays a role in a plant’s ability to withstand pathogen attack and Cu toxicity. Plants grown in different amounts of light and exposed to the aforementioned pathogens will be monitored with various sensors (e.g. digital cameras, infrared temperature probes, fluorometers, chlorophyll meters) and molecular tools to detect initial onset of stress symptoms. Finally, the production methods developed within these tests can be incorporated into the existing computer decision support software Virtual Grower to help growers make decisions in crop management.

3. Progress Report
Studies investigating the role of light on phosphorus uptake and plant requirements were completed; light had little influence on potential P uptake and only when P supply was also low. There were no species differences in light response to P uptake. Columbine, corn, sugar beet, soybean, and six cultivars of lantana were grown in Si-containing and Si-free nutrient solutions, harvested, and quantified for silicon concentration. Overall, about half of all species evaluated have accumulated significant (greater than 0.1% dry weight) Si in leaf tissue. No differences were observed in reflectance signatures of species fed differing amounts of P or B. However, molecular tools are being developed that show promise in distinguishing among specific nutrient stresses. Virtual Grower 2.6 was released in June, 2010. It has 40 species to simulate growth and development, supplemental lighting, improved calculations for the impact that shade/energy curtains can have on energy conservation strategies, opportunities to add new and theoretical greenhouse coverings or fuels to test for energy performance, and real-time weather “calls” in which the next two days of weather at a grower’s U.S. site can be simulated within the model. Virtual Grower 3.0 is under development. Alternative substrates including crop residue (primarily wheat straw), rice hulls, biofuel crops such as miscanthus and switchgrass, and woody species such as willow chips, bark, and bamboo were tested for their potential as peat replacements and for Si delivery. It was found that some can provide sufficient Si to allow some species to benefit from improved Si uptake compared to peat-based and unamended substrates, as well as potentially provide early, reversible growth regulation. The cooperative agreements that helped develop the Floriculture Research Alliance strengthened existing ties and developed new connections among the group. Progress was made in characterizing plant photosynthesis response to short-term heat stress on finished plants, as well as general, non-stress photosynthetic response to CO2 and temperature, which will be added to Virtual Grower software to improve species-specific models. Additional crop development rates have been characterized for temperature and daily light integral response, which will also be folded into Virtual Grower software for distribution. A better understanding of the amount and duration of stress that young plants (unrooted cuttings) undergo in the first week of production, and methods have been developed to minimize that stress during shipping and initial reception of the cuttings. Thorough surveys of water quality have been performed in several U.S. grower’s facilities to determine the longer-term impacts of efficient re-use of water with different treatment practices. Alternative substrates utilizing composed dairy cow manure were characterized and can produce a high-quality crop with less risk of pH drift during production. Work has begun to characterize part of the Ornamental Plant Germplasm Center’s begonia collection for less-than-optimum temperatures.

4. Accomplishments
1. Virtual Grower En Español and Virtual Grower 2.6 were released. Growers of greenhouse crops face many complex, interrelated systems on a daily basis wherein one decision influences others in sometimes counterintuitive ways. Virtual Grower software allows users to build greenhouses with many different types of materials, select from different fuel types, simulate heating needs and costs, and see the impact of those decisions on the growth and development of some commonly grown greenhouse crops. This version of the program has added additional crops to already existing capabilities to simulate supplemental lighting, the ability to add more fuels and materials for testing, improved calculations for energy curtains, and real-time weather “calls” in which the next two days of weather at a grower’s US site can be simulated within the model. The software was translated into Spanish and is freely available for download on our webpage. This software has assisted both large and small growers in identifying energy (and money) saving strategies in their operations, improved efficient scheduling of crops, and helped growers obtain energy efficiency improvement grants through various funding sources.

2. The critical B and Ca tissue concentrations for pansy, petunia, and gerbera plugs were determined. The cause of distorted plant growth was investigated in a series of experiments in cooperation with researchers at North Carolina State University. Boron deficiency was identified as the elemental problem which caused the stunted growth, thus eliminating calcium as an element of concern. Further investigation studied the causes of why the deficiency was occuring in these small plants. This narrowed to the primary cause of boron deficiency to be a physiologically induced deficiency caused from over irrigation of plants with limited root substrate volume and the lack of environmental conditions which encouraged water uptake and transpiration. Through a series of presentations, scientific articles and magazine articles, greenhouse operators are now aware of the steps required to better manage irrigation based on the transpirational needs of the plant instead of on a timer which resulted in waterlogged conditions.

3. The visual symptoms of essential element deficiency for floriculture crops were determined. Floriculture crops require a high degree of management to achieve a market ready product. Fertilizer inputs are an important component of the production cycle, yet most floriculture crops lack critical tissue standards and adequate descriptions of the symptomology when nutritional disorders occur. In cooperation with scientists at North Carolina State University, individual nutritional disorders were induced in fourteen floriculture crops and when incipient symptoms occurred, they were recorded, photographed and tissue samples were taken for analysis to determine the nutritional levels. Through publication of results in both scientific journals and grower magazine articles, plus grower presentations in the U.S., these nutritional evaluation criteria are available to the greenhouse industry to aid in the diagnosis of nutritional disorders.

4. Novel bi-layer hydrogel was developed for floriculture production. The goal of this project was to develop hydrogels to mitigate the effect of biotic and abiotic stress induced by lack of soil hydration and nutrient availability over several days. In cooperation with scientists within the Department of Bioengineering at the University of Toledo, a bi-layer hydrogel was developed to separate the swelling requirement from that of low dehydration rates and mechanical strength. This would consist of a soft inner layer surrounded by a hard outer layer. A final version was created that replaced a PAAm outer layer with polyurethane. The polyurethane-coated gels produced the best results maximizing the water absorption of the inner layer while retaining sufficient compressive strength and reduced dehydration time of over a week. The development of these hydrogels could assist in not only more water-efficient production strategies, but improved nutrient delivery as well in containerized plant production.

5. Energy-efficient management of greenhouse temperature was developed. Energy for heating is a significant expense in the production of greenhouse bedding plants. In collaboration with scientists at Michigan State University, a variety of annual bedding plant species were characterized in how they grow and develop in response to a range of greenhouse temperatures. Species-specific models were then generated that predict the effect of temperature on time to flower. Using that information, greenhouse growers can predict crop timing at different temperatures to meet market dates. Growers can use that information with the Virtual Grower computer program to identify production temperatures that consume the least amount of energy based on their greenhouse characteristics and location. As a result, growers can potentially lower their energy bill by 10 to 20% or more and improve their scheduling accuracy. This information has been disseminated to greenhouse growers at regional and national grower meetings and through a 12-part “Energy-Efficient Annuals” series that appeared in Greenhouse Grower magazine in both print and on their website.

6. Survey made of commercial propagators’ water use practices. In collaboration with Clemson University, in February and March 2010, the peak propagation month for the spring season, water output of fifty different propagation systems were measured at 20 commercial greenhouses located in 10 different states. These data showed a 10-fold difference in water output per unit area per mist event amongst the propagators. The data also showed the variance that occurs within each propagation system due to engineering limitations with the current propagation equipment. This information will help identify systems that can be improved to reduce water use during propagation.

7. Water use of poinsettia cuttings in the propagation environment was determined. In cooperation with Clemson University, gas exchange measurements, including photosynthesis, transpiration and stomatal conductance, were recorded on poinsettia stock plants and then on cuttings throughout the propagation environment. These data show that stomatal functioning is disturbed as a result of the removal of the shoot from the stock plant and the function gradually returns to allow for more efficient water use as the cuttings are on the propagation bench. The differences in stomatal functioning are only observed during the night or when the cuttings experience water stress. Thus, it is clear that the stomata are not properly closing during the initial days in propagation. As a result, the water use requirements are much higher on the first night in propagation compared to the seventh night (before root initiation), even though the ability of the cutting to uptake water through the severed stem has not changed. For example, when water stress is induced on a one-day old cutting, it will wilt in one hour while a seven day old cutting will wilt in three hours. Once root initiation takes place (between days 7 and 10), water use efficiency has improved dramatically; however, photosynthesis does not return to the stock plant levels until the cutting is fully rooted in the fourth week of propagation. This information will help identify strategies to minimize water stress of newly propagated cuttings to improve rooting success.

8. pH and plant nutrition research was refined. Out-of-range media-pH and nutrient levels in growing media are common horticultural problems, and leaching and runoff of nutrients following over-application of irrigation water cause negative environmental impacts. In a project with the University of Florida, a new website ( was developed for transmitting research results to clientele from this collaborative project. The LimeR series of laboratory testing protocols for horticultural limestone were uploaded under the “what we’ve done” section of and were presented to an international science conference on growing media. Two refereed publications on lime and plant nutrition research were published, along with seven related trade publications, and five science conference presentations. One Ph.D. and one M.S. student were graduated in 2009 with thesis research on this topic. Seven horticulture growing media companies are now using these LimeR protocols to develop media with improved pH characteristics.

9. Photosynthetic responses of important ornamental crops were characterized. Growers do not have information on what environmental factors affect photosynthesis of important floriculture crops with which to make environmental and lighting management decisions. A lack of this information likely results in increased energy costs and/or reduced quality of yield. In a cooperative project with the University of Minnesota, the response of photosynthesis of greater than 20 important ornamental crops to light, temperature and carbon dioxide were identified in order to develop environmental strategies to maximize photosynthesis to increase crop quality and yield. These data are being integrated into a USDA-ARS model (Virtual Grower) to allow application throughout the U.S.

10. Environment influences efficacy of plant growth retardants. Plant growth retardant efficacy varies in different parts of the U.S., between different growers, and between different application days. The basis for this variation is not understood and results in over and under application of these chemicals. We identified the impact of temperature and humidity on efficacy of five plant growth retardants and identified that slow drying environments at the time of spraying results in the greatest efficacy. This information has been presented at multiple grower meetings and is being used to increase plant growth retardant efficacy to reduce chemical use.

11. Species suitable for northern U.S. green roofs were identified. Installation of green roofs is a new strategy to reduce the environmental impacts of buildings while reducing building energy costs. In cooperation with the University of Minnesota, we identified what species (forty two of eighty eight) can survive on rooftops in the Twin cities area (cold northern climate) and the impact of each of those species on a variety of desirable environmental impacts that could reduce building operating costs was tested on a rooftop in Minneapolis. This information is being integrated into the Minneapolis planning departments building code requirement related to green roofs.

12. Identifying new heat and/or drought tolerant ornamental crops. It is reasonable to expect that our environment will and is becoming warmer and dryer, therefore, it is desirable to identify ornamental crops that can be produced or used in the landscape that can withstand heat and that do not require irrigation. In collaboration with University of Minnesota, heat and drought tolerant species were screened (over one hundred species) that have potential as new floriculture and/or landscape crops. We selected fifteen cacti species and five succulents species with significant potential as new crops and identified the flowering requirements of those crops to allow forcing as floriculture crops.

13. Lettuce seed quality was enhanced by altering light and temperature during seed production. Collaboration with Ornamental Plant Germplasm Center and Ohio State University scientists examined the influence of light quality and temperature in the maternal environment on the quality of lettuce seed. Uniform stand establishment is important for high yields. The study demonstrated that altering the red:far-red ratio of light during plant development and growing plants at higher temperatures resulted in seeds with greater germinability and longevity, providing a potential procedure for improved yield and quality of selected horticultural crops.

14. X-ray technology was used to assess quality of Rudbeckia hirta seeds. Rapid assessment of seed quality is important in germplasm conservation. Traditional techniques such as chemical tests or germination can be time-consuming. Collaboration between Ornamental Plant Germplasm Center and Brazilian scientists demonstrated that X-ray analysis could be applied to seeds of the popular ornamental plant Rudbeckia hirta. The results validated the use of this method to quickly assess the physical and physiological quality of Rudbeckia seeds.

15. Efficacy of the Rhizon vacuum substrate solution sampler was compared to conventional methods. The Rhizon sampler provides a minimally invasive method for extracting unaltered root substrate solution ideal for research. Since solution is drawn from a very small area and nutrient gradients occur in the substrate profile, positioning in the profile is critical. In a collaboration with North Carolina State University scientists, the Rhizon sampler was characterized for sampling efficacy in container culture. Vertical positioning of the sampler yielded electrical conductivity (EC) readings similar to the mid-point in the profile and pH levels equivalent to the bottom 20 percent of the profile. Rhizon and pour-through extracts had similar EC levels but different pH levels. Saturated media extracts had lower EC and pH levels than the other two methods. The Rhizon sampler functions well and shares the same EC standards as the pour-through extracts but requires different pH standards. Saturated media extracts require different standards for pH and EC from each of the other two methods. This research provides a new approach in sampling and evaluating root substrate, potentially in a smaller target volume within the rootzone, to the more general all-rootzone-encompassing pour-through and saturated media extract methods.

16. Impact of composted dairy manure on pH management of soilless substrate was determined. Dairy manure compost offers the potential to provide buffering against substrate pH decline during cropping time, one of the largest production challenges. In a collaboration with North Carolina State University scientists, the use of dairy compost manure was evaluated for inclusion in containers for pH stabilization. Levels of 0 to 30 percent compost as a partial substitute for peat moss in a 3 peat moss : 1 perlite mix (volume basis) without addition of liming material resulted in initial pH levels of 3.1 to 6.5 . Although pH declined during plant production, the decline was similar in the agricultural limestone and the 20 to 30% compost treatments that had similar initial pH levels. Thus, pH buffering capacity of compost was similar to the limestone. Potential exists to use a small amount of limestone in combination with compost to stabilize pH during crop production.

17. Nutritional contribution of mature dairy manure compost was determined. In ongoing work with North Carolina State University scientists, mature dairy manure compost was used as a partial substitute for peat moss in a 3 peat moss : 1 perlite (v:v) mix used to grow an 11 week crop of pot mums. End of the crop tissue analysis indicated that compost resulted in higher leaf concentrations of potassium, sulfur, copper, iron, and manganese, lower, but adequate, calcium and magnesium, and similar nitrogen, phosphorus, boron, and zinc concentrations. Leaching tests on similar fallow compost mixes showed that the greatest release of nutrients from compost was at time zero and declined in an asymptotic fashion thereafter. Results indicate that downward adjustments in fertilizer application are needed when using compost and that the adjustment is more important in the pre-plant fertilizer formulated into the substrate than in post-plant fertilization

18. Impact of 13 floricultural crops on soilless substrate pH was determined. Prevention of substrate pH shifts during crop production is a major challenge. A small body of evidence suggests that plant species differ in their impact on pH shift during production. Research in collaboration with North Carolina State University evaluated 13 floral crops for their effect on pH. The crops, when fertilized with neutral reaction fertilizer, lowered pH between 4 and 78 days after transplant by the following amounts: petunia (0.14), begonia (0.19), osteospermum (0.43), pansy (0.51), impatiens (0.79), New Guinea impatiens (0.89), geranium (0.97), vinca (1.00), tomato (1.17), Reiger begonia (1.46), pot mum (1.56), sunflower (2.44), and kalanchoe (2.45). Clearly, species plays an important role in pH shifts. Crop species should be blocked according to their level of impact on substrate pH and the blocks treated differently. Different fertilizers could be selected for each block according to the potential acidity/basicity rating of the fertilizers, thereby holding all blocks within the same pH range during production.

19. Calcite (CaCO3, also known as lime) requirements of sphagnum peat moss was determined from pH titration curves. A series of time-consuming incubations of peat:lime mixtures are typically used to determine the liming rate to achieve a desired pH. A project with North Carolina State University developed a rapid, acid-based titration method for predicting lime requirement of sphagnum peat moss. In the method, peat moss with an initial acidic pH was titrated up to pH 11 and down to pH 3. These titration curves were averaged to predict lime requirements. This method was compared to the conventional method where peat was inclubated with calcite for 13 days in plastic bags until a steady-state was established. The two methods agreed with one another up to a pH of 6.2. Nevertheless, the acid-base titration is a quick method for accurately predicting calcite requirements of acidic peat moss for target pH levels up to 6.2.

Review Publications
Brunings, A.M., Datnoff, L.E., Palmateer, A.J., Locke, J.C., Krause, C.R. 2009. Exserohilum Leaf Spot on Tigergrass. Plant Health Progress. DOI:10.1094/php-2009-1215-01-RS.

Taylor, M., Nelson, P., Frantz, J., Rufty, T. 2010. Phosphorus Deficiency in Pelargonium: Effects on Nitrate and Ammonium Uptake and Acidity Generation. Journal of Plant Nutrition. 33:701-712.

Pasian, C., Frantz, J. 2009. Evaluating Performance and Stability of Polyethylene Terephthalate (PET) and Cellulose Polymer as Soilless Mix Components. Acta Horticulturae. 843:289-295.

Ka Yeon, J., Whipker, B., Mccall, I., Gunter, C., Frantz, J. 2009. Characterization of nutrient disorders of gerbera hybrid 'Festival Light Eye Pink'. Acta Horticulturae. 843:177-182.

Ka Yeon, J., Whipker, B., Mccall, I., Frantz, J. 2009. Gerbera Leaf Tissue Nutrient Sufficiency Ranges by Chronological Age. Acta Horticulturae. 843:183-190.

Kim, S., Iyer, G., Nadarajah, A., Frantz, J., Spongberg, A. 2010. Polyacrylamide Hydrogel Properties for Horticultural Applications. International Journal of Polymer Analysis and Characterization. 15: 307-318.

Last Modified: 06/21/2017
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