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  • Author or Editor: Kimberly A. Williams x
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A series of experiments were conducted to determine the ranges of irrigation frequency and N and P fertilization regimes that produce ivy geranium (Pelargonium peltatum L.) plants of optimum commercial quality. Two cultivars, `Sybil Holmes' and `Amethyst', were grown. Data collected included fresh and dry weights, ratings, leaf area, height, width, ratings, and nutrient tissue content. Individual pots were weighed daily and irrigated when weight of pots dropped by 15%, 30%, 45%, or 60% of container capacity (CC). Leaf water potential was measured using a pressure chamber. At both mid and end of crop, plants irrigated when pot weight dropped by 30% of CC were under least water stress (e.g., water potential of –7.0 to –4.7 MPa). Irrigation frequencies at 15%, 45%, or 60% of CC had similar water potentials (e.g., –9.9 to –9.1 MPa). At 15%, a plausible explanation of the stress is that oxygen was limiting in the root zone due to water-logging; at 45% and 60%, water was the limiting factor. Single factor experiments with N at five concentrations ranging from 2 to 32 mm and P at five concentrations ranging from 0.08 to 2.56 mm were conducted. Quadratic equations were fit to curves of growth responses plotted against concentration of N or P applied. As an example of results, N fertilizer rates of 16 and 32 mm for `Amethyst' resulted in similar, commercially acceptable dry weights (37g), but different N tissue concentrations of 3.4% and 3.9% respectively. For `Sybil Holmes', N fertilizer rates of 10 and 26 mm resulted in similar dry weights (21g) but different tissue concentrations of 2.8% and 3.4%, respectively.

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A model for the creation of shared synchronous courses between universities has been developed based on our experiences during the development and delivery of an upper-level undergraduate/graduate course in Plant Nutrition and Nutrient Management offered by Kansas State Univ. and the Univ. of Nebraska–Lincoln. The course was conducted during the Spring 1999 semester using two-way compressed video so that instructors and students at both sites could see and hear each other in live time. Our model is set up as a flow-chart and currently has 10 steps that include areas such as “Identifying the Need,” “University Must-Do's,” “Distance Class Technology Requirements,” and “Advertising the Course.” Each step details procedures to follow, offers ideas and suggestions, and includes examples taken from our course. Also included is information about web site development and chat room use. The model is easily adapted for use with distance technologies similar to two-way compressed video such as Internet 2. An electronic version of the model can be accessed at http://www.oznet.ksu.edu/dp_hfrr/Floriculture.

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Nutrient solution with a molar ratio of 10 N: 1 P: 3 K was applied in scheduled intervals at rates of 0.5, 1, 4, or 20 mm N (NO3 + NH4) to Dendranthema ×grandiflorum (Ramat.) Kitamura `Sunny Mandalay' plants seven (7/day) or 14 times/day (14/day). These plants were compared to a 20 mm N control in which nutrient solution was applied when the soil moisture tension reached 30 kPa. Plants with 7/day had significant quadratic relationships for height, width, and dry weight, with the lowest responses at the low nutrient concentration. With 14/day, height and dry weight did not differ, although width did increase linearly with nutrient solution concentration. However, linear regression slopes for all three variables were much lower with 1Vday than with 7/day. At midcrop in both experiments, significant regression curves indicated that the lower concentrations of nutrient solution resulted in lower tissue N and K levels; however, slopes of the linear regressions were lower with 14/day than with 7/day. With 7/day, the water content (percentage) of plants in the schedule-fertilized treatments was higher in plants receiving higher nutrient concentrations, as indicated by the significant linear and quadratic regression curves. With 14/day, the water content was linearly related to solution nutrient concentration, but with a lower slope than with 7/day. These three trends indicate that steady-state nutrition was more closely achieved in a commercial-style substrate with 14/day applications of nutrient solution. These results suggest that plant growth that meets commercial expectations can be achieved at lower soil solution nutrient concentrations than currently applied.

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Soilless substrates have little capacity to sorb PO4. One way to reduce PO4 leaching during production is to increase the substrate retention of PO4. Adsorption isotherms were created at 25 C for alumina (aluminum oxide); the 2:1 calcined clays arcillite (montmorillonite plus illite) and attapulgite.; and a medium of 70 peat: 30 perlite using solutions of KH2PO4 at rates of P ranging from 0 to 20000 μg·ml-1. Material sorbed at the rate resulting in maximum P adsorption was then desorbed 22 times. Sorbing concentrations necessary to establish an equilibrium P concentration of 10 μg·ml-1 in the substrate solution were estimated from these curves. Materials were-charged with P at these estimated rates and evaluated in a greenhouse study in which each material was tested at 10 and 30% by volume of a 70 peat: 30 perlite substrate used to produce Dendranthema × grandiflorum `Sunny Mandalay'. Phosphate, K, and pH were determined on unaltered soil solutions biweekly throughout the cropping cycle and foliar analyses were determined on tissue collected at mid- and end-crop. Isotherm and greenhouse data indicated that alumina, arcillite, and attapulgite effectively retained and slowly released K as well as PO4 over time. Alumina was most effective at retaining P, sorbing 16800 μg/cc compared to 3100 and 7800 μg P sorbed/cc for arcillite and attapulgite, respectively, when sorbed at P concentrations resulting in an equilibrium concentration of approximately 10 μg P/ml.

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Many soilless root media have limited ability to retain nutrients. Zeolites are minerals that have substantial nutrient buffering capacity and can be precharged with K, and possibly PO4, and combined with soilless media to provide these nutrients during crop production. The zeolite clinoptilolite was precharged with K and PO4 at two rates that were estimated from sorption isotherms to result in equilibrium root medium solution concentrations of P at >1 μg·ml–1 (low rate) and K at 125 μg·ml–1 (high rate). Precharged clinoptilolite was mixed with a 7 sphagnum peat: 3 perlite root medium to comprise 20% (v/v) and evaluated as the sole source of K and PO4 during production of Dendranthema ×grandiflorum (Ramat.) Kitamura `Sunny Mandalay'. Phosphate, K, Na, and pH were determined on unaltered bulk medium solutions collected over the course of the cropping cycle, and foliar analyses were determined on tissue collected at mid- and end of crop. Plants that relied on K release from precharged clinoptilolite at the low and high rates and received a N/P/-K fertilizer produced growth and tissue K concentrations that were not significantly different than the control which received a complete fertilizer. Plants that relied on PO4 release of precharged clinoptilolite did not result in growth or tissue P levels similar to those of the complete control. Phosphate levels in the root medium solution were adequate only during the first month of the cropping cycle, but PO4 release should be taken into consideration when developing a fertilization program using precharged clinoptilolite to provide other nutrients. Using precharged clinoptilolite at the low rate reduced K losses through leaching to 26% of the amount leached from control plants receiving K at 176 mg·L–1 at each watering.

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Soilless container root media have little capacity to retain P, and preplant amendments of triple superphosphate (TSP) and water-soluble fertilizer (WSF) P applications are readily leached from them. A soilless medium modified with Al2(SO4)3 was tested to reduce such P losses. Aluminum sulfate solutions were applied to a 70 sphagnum peat: 30 perlite (v/v) medium to result in 0.32, 0.96, and 1.92 kg Al/m3 and dried at 70C. Adsorption isotherms (25C, 0 to 500 mg P/liter) showed that P retention increased as the rate of Al addition increased. In a greenhouse study, plants of Dendranthema ×grandiflorum (Ramat.) Kitamura `Sunny Mandalay' were grown in Al-modified media and an unmodified medium in factorial combination with P from preplant amendment of 0.1 kg TSP-P/m3, or P applied at each watering as WSF at rates of 5.5 or 21.8 mg P/liter. The two highest rates of Al were excessive and resulted in low pH and excessive soluble Al levels in the root medium solution early in the cropping cycle, which were detrimental to plant growth. When the root medium was modified with 0.32 kg Al/m3, soluble Al levels in medium solution were not significantly different than in the unmodified control. TSP-P that leached was substantially reduced by the addition of Al, yet sufficient P was released throughout the cropping cycle for adequate plant growth. Plants grown in Al-modified medium with 0.1 kg TSP-P/m3 did not differ from control plants in unmodified medium + 0.27 kg TSP-P/m3 and were larger than plants grown in unmodified medium + 0.1 kg TSP-P/m3. Aluminum modification of the root medium substantially reduced P leaching when used with WSF containing P. In addition, growth of plants in unmodified medium fertilized with 5.5 vs. 21.8 mg P/liter was similar.

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A sustained release nutrient source suitable for maintaining steady, low (1 mM) N concentrations in the soil solution was sought as a component to be used in a system for reducing nutrients in the effluent of an open greenhouse cropping system. Several nutrient sources were evaluated as a N source incorporated singly in a medium of 1 sphagnum peat moss: 1 vermiculite and used to produce Chrysanthemum × morifolium `Sunny Mandalay'. All nutrients except N were applied additional to the sources tested. Sources tested included specific non-viable bacterial (B) and fungal (F) organisms from commercial biotechnological production lines, a microbial sludge mixture (S) from waste-water treatment, poultry waste-methane generator sludge (PS), mico-Osmocote (O), unsteamed bonemeal (BM), poultry feather meal (FM), and three-yeer aged pine needles (PM) at rates from 0.15 to 1.3 kg N·m-3. Based on periodic vacuum extracted soil solution analyses, leaf analyses, and plant growth, the efficacy of sources was in the order B, O> BM> S> PS> F, FM> PN. The 3 best sources provided sufficient N for 6 weeks; however, growth parameters did not differ from a complete liquid fertilization control until after 9 weeks. N in soil solution from the bacterial cells was at weeks 1, 3, 5, and 7: 142, 200, 73, and 3, mg·l-1, respectively.

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In commercial interior green walls, plant trimming and replacement necessitated by stem elongation under low interior light levels is labor intensive and costly. Antigibberellin plant growth regulators (PGRs) may slow stem elongation and thus reduce maintenance costs in this environment. In Expt. 1, two PGRs were applied as foliar spray or drench to three spiderwort selections [two of zebra plant (Tradescantia zebrina) and one of inch plant (Tradescantia fluminensis)] immediately before installation in a green wall, each at three rates: ancymidol (ANC) foliar spray at 25, 100, and 200 mg·L−1; paclobutrazol (PBZ) foliar spray at 20, 80, and 160 mg·L−1; and PBZ drench at 1, 4, and 8 mg·L−1, along with an untreated control. In Expt. 2, 80 mg·L−1 PBZ foliar spray, 1 mg·L−1 PBZ applied via subirrigation four times, and the combination of these two treatments, was evaluated on ‘Burgundy’ zebra plant. In both experiments, plants were placed in a vertical modular tray interior green wall. Change in total stem and specific internode length were measured every 14 days after installation for 3 months to calculate growth per month. Antigibberellin application slowed internode elongation of spiderwort selections during the first month after installation. Antigibberellins were more effective in zebra plant at reducing overall stem growth rate and less so on inch plant. Across the three spiderwort selections, 25 mg·L−1 foliar spray of ANC resulted in no difference in growth rate when compared with the control, although 100 to 200 mg·L−1 foliar spray was effective. Based on the results of both experiments, moderate and high rates of PBZ, applied both as a foliar spray and drench, resulted in similar reduction in stem elongation. PBZ applied as 20 to 80 mg·L−1 foliar spray, 4 mg·L−1 drench before installation in the wall, or a combination of an 80 mg·L−1 PBZ pre-installation foliar spray and recurring 1 mg·L−1 via subirrigation (four times) were effective at growth suppression of spiderworts for at least 3 months. Even rates of PBZ of 160 mg·L−1 foliar spray or 8 mg·L−1 drench did not show phytotoxicity in treated plants and could be considered for use. We recommend a pre-installation application of 80 mg·L−1 foliar spray or 4 mg·L−1 drench for controlling stem growth across spiderwort selections. Application of antigibberellin PGRs to plants before installation in green walls slows stem growth and can contribute to reduced maintenance costs.

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Hydrogen peroxide (H2O2) is a well-known oxidizing agent often used as a remedy by consumers to treat algae and root decay from presumed root disease on interior plants, as well as to encourage root growth and health. To characterize the phytotoxic effects and define the safe concentration threshold for H2O2 use on ‘Vivaldi’ hybrid phalaenopsis orchid (hybrid Phalaenopsis), root systems were dipped for 3 minutes in 0%, 3%, 6%, or 12% H2O2 one time and observed in greenhouse conditions for the following 27 days. Root systems of each plant were assessed over time for percent visible root damage; ratings of root health on a scale of 1 to 5 points, with 5 points indicating “very healthy”; and final fresh and dry weights. To determine when symptoms manifested above the root zone, foliage and flower damage was evaluated over time by assessing percent visible foliage damage, ratings of foliage health, percent foliar wilt, flower/bud count, and final foliage and flower fresh and dry weights. Over the evaluation period, the root health rating of the ‘Vivaldi’ hybrid phalaenopsis orchids treated with 12% H2O2 decreased from 5 to 1.13, whereas those treated with 3% H2O2 only decreased from 5 to 4.13. H2O2 concentrations of 6% and 12% damaged root health permanently, whereas the 3% H2O2 concentration only caused minor damage to overall root health. However, algae were not killed at the 3% rate. Neither foliage nor flowers were seriously affected during the 3 weeks after application, but foliage wilt did result in the 6% and 12% treatments by week 4. As H2O2 concentration increased, fresh weights decreased in roots and leaves. Although a single 3% H2O2 root dip did not result in severe symptoms of phytotoxicity, the treatment’s long-term plant health effects are unknown. Because the 3% H2O2 root dip caused minor plant health setbacks and failed to subdue algae populations in the root zone, consumers should be wary of using H2O2 to improve orchid (Orchidaceae) root health and should instead focus on altering care and watering practices.

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Student learning from producing crops in recirculating culture for a 6-week module in the Fall 2013 course HORT 570 Greenhouse Operations Management at Kansas State University was assessed. The module design followed Kolb’s experiential learning model, with teams of students responsible for production of lettuce (Lactuca sativa ‘Green Oak Leaf’) or basil (Ocimum basilicum ‘Italian Large Leaf’) and chives (Allium schoenoprasum ‘Purly’) crops in either a nutrient film technique (NFT) or in-pot recirculating culture system. Goals were to discern if this class experience would 1) improve student confidence and understanding of not only recirculating solution culture systems, but also general crop nutrient management; and 2) improve higher-order learning (HOL) skills of applying, analyzing, and evaluating information. Student learning was evaluated by administering the same survey, which included questions to evaluate student perception, lower-order learning (LOL), and HOL, at four separate times during the semester: 1) before mentioning plant nutrition, hydroponics, or recirculating solution culture; 2) after plant nutrition lectures but before the experiential module; 3) immediately upon completion of the experiential module; and 4) at the end of the semester. An increase in student confidence related to managing crop production in recirculating solution culture and nutrient management was perceived by students upon completion of the module. A significant increase in LOL occurred after the material was presented during the course lectures with an increase also occurring upon completion of the experiential module. In contrast, HOL did not significantly increase after the lecture material was presented, but significantly increased upon completion of the module. Both LOL and HOL was retained at the end of the semester. This evidence supports the role of experiential learning in improving student understanding and fostering HOL.

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