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Marci Spaw and Kimberly A. Williams

This decision case presents the issues a grower would face when deciding where to place and how to orient a high tunnel structure on a specific farm site. It provides a tool to teach site planning concepts on a small scale that are easily transferable to issues addressed when planning for construction of all sizes and types of protected-environment structures. In this case, the owner of Full Moon Farm must decide the placement of her high tunnels on a given farm site. Factors to consider include wind, snow, and ice loads as well as structural integrity, labor efficiency, and optimizing light levels. Ultimately, no one solution meets all recommended criteria, so the grower must prioritize the importance of various factors to come to a decision. This case study is intended for use in upper-level undergraduate horticulture courses, and although the principles are broadly applicable to site planning across geographic regions, it is most appropriate for climates above lat. 35°N. In particular, it may prove useful in courses such as greenhouse management and production courses for vegetables, cut flowers, and small fruits, where students assume the role of grower/farmer in the site planning process. This case study is supported by a website version with digital images, digital video, and maps that can be used both inside and outside of the classroom; all are downloadable from the website http://www.hightunnels.org/planningcasestudy.htm. The teaching notes present an unorthodox solution to the Full Moon Farm site planning dilemma.

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Kimberly A. Williams and Paul V. Nelson

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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Kimberly A. Williams and Paul V. Nelson

Soilless container medium components such as peatmoss and perlite have almost no capacity to retain PO4-P, and preplant amendments of triple superphosphate (TSP) are readily leached. Al amendments were tested to reduce P losses from these media. Al2(SO4)3 solutions at rates of 320 and 960 μg Al/cc were applied to a 70 peat: 30 perlite medium and dried at 70C. Adsorption isotherms were created at 25C for the Al2(SO4)3-amended media and an unamended control using solutions of Ca(H2PO4)2 at concentrations of P ranging from 0 to 500 μg·ml–1. Isotherms showed that P retention increased as Al concentration increased. In a greenhouse study, Dendranthema ×grandiflorum `Sunny Mandalay' was grown in these media with 100 g P/m3 from TSP incorporated into the mixes before planting. PO4-P, soluble Al, and pH were determined on unaltered medium solutions collected throughout the cropping cycle and foliar analyses were determined on tissue collected at mid- and end-crop. The highest rate of Al was excessive and resulted in low pH and soluble Al levels in the medium solution early and in the cropping cycle, which were detrimental to plant growth. When Al was applied at 320 μg/cc, soluble Al levels in medium solution were not significantly higher than in the unamended control, PO4-P leached from TSP was reduced, and sufficient PO4-P was released throughout the cropping cycle to result in optimal plant growth.

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Ellen T. Paparozzi and Kimberly A. Williams

Chat rooms and their use in everyday life are becoming increasingly common, and the technology may be a useful tool to link students with experts of a given subject material and each other. In our shared course Plant Nutrition and Nutrient Management, we experimented with using a chat room to link students with experts in the field of plant nutrition. Our main goal was to enhance the learning experience of the students by providing them with access to national and international plant nutrition researchers. Web CT was used to create and conduct the chat rooms and a chat etiquette evolved to prevent crosstalk and control the flow of the discussions. Positive outcomes of the chat room use included exposure of students to the technology and beneficial interaction between students and experts. Negative aspects of chat room use included the time involved to coordinate the overall effort and train experts to use the technology; the slow pace of some chats; effective grading; and the superficial coverage of some topics. We are developing modifications for future sessions to allow subjects to be explored in more depth and to improve networking between students and experts.

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Kimberly A. Williams and Paul V. Nelson

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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Kimberly A. Williams and Paul V. Nelson

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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Valerie M. Jonas and Kimberly A. Williams

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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Kimberly A. Williams and Ellen T. Paparozzi

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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Kimberly A. Williams and Paul V. Nelson

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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Kimberly A. Williams and Paul V. Nelson

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.