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  • Author or Editor: L. Art Spomer x
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This paper describes a simple laboratory exercise for demonstrating the direct relationship between container soil volume and plant growth in a way that avoids complications caused by soil geometry (shape and depth). This is accomplished by mixing different amounts of gravel into each container soil thereby excluding different volumes of soil from otherwise identical containers.

Open Access
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A simple temperature control system constructed from a $10 homemade, precise, solid-state, proportional thermoregulator, resistive heating element, and insulated enclosure is described. It is intended as one of a series of small heated units, each set to a different temperature and placed in a single, large, refrigerated area, such as a large cooler or air-conditioned room, but can be modified for cooling in a heated area. Its demonstrated temperature control precision over 24 hr was ± 0.02°C at the thermal sensor at a set point of 25° and ambient of 19° ± 2.5°. Control temperature precision, range, and span are determined by thermoregulator components, enclosure construction, and ambient conditions. This or similar systems have been used successfully in seed germination, postharvest, cell culture, and nutrient release studies.

Open Access
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A method utilizing small, bouyant particles in a floating mat for the hydroponic germination and growth of small plants is described. The bouyant mat supports the seeds and small plants on the culture solution surface and allows easy, non-destructive removal of the plants analysis and re-insertion. This method was used successfully to germinate and grow seedlings of bluegrass (Poa pratensis L.)

Open Access
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The quantity of amendment required to ensure adequate aeration in container soils is usually determined by empirical tests on a series of mixtures containing different amounts of the amendment In this study, the “threshold proportion” or minimum amount of amendment required before aeration improvement begins, was demonstrated to be controlled by amendment interporosity. This concept is the basis for a method of predicting total and aeration porosity of any container soil mixture.

Open Access
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The soil water distribution pattern in a container soil is simulated using cellulose sponges as an analog of container soils. Two classroom exercises are presented that have been successful in both classroom and extension presentations to horticulturists.

Open Access
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Soil physical amendment (soil mixing) is a widespread horticultural practice. Unfortunately, it is often done with little understanding of the principles involved or the physical effects produced. Three simple demonstrations are described which have proved helpful in explaining the physical effects of soil amendment in classroom and extension presentations. These exercises use simple volume measurements and require commonly available supplies including containers, a volume measure, a sieve, plastic sheets, and media components such as soil and sand. The differences between component and mixture water retention are used to demonstrate the effect of amendment on porosity, water retention, and aeration. Some sample results and discussion questions are included.

Open Access
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The importance of water to plant growth is well-recognized (13, 35, 37, 48, 49, 50, 58, 63, 80, 97, 130, 141, 143, 160) and has been studied for over 300 years (62, 106). Despite this long history, relatively little is known about the specific water requirement for most horticultural crops. Water requirement is the minimum amount of water required to provide optimal yield. The amount required is determined by the type of yield, the critical limits of deficiency relative to yield, the limits of tolerable yield reduction, the size and permeability of the plant’s evaporative surface, the plant’s growth stage, and the environmental factors affecting growth and transpiration. Actual water requirement therefore is defined by a combination of human motivations, plant physiological responses, and physical environmental factors.

Open Access
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Water stress resulting from inadequate soil water retention following transplanting is a major cause of container-grown transplant failure. The relatively small water supply contained in the soil containers used in nursery and bedding plant production is reduced further by enhanced drainage following transplanting. This drainage phenomenon, which has received little previous attention, was investigated under controlled laboratory conditions. Samples of 2 suitable container soils were embedded in simulated ground bed soil and retained in a container; water retention of the embedded soil, surrounding ground bed soil, and contained soil was monitored simultaneously to determine if the embedded soil (analogous to a container-grown transplant’s soil) retained less water than the contained soil. The embedded soils lost 30% to 85% of their estimated available water within a few hours, whereas contained soils lost the same quantity only after 3 or 4 days of surface evaporation. A simultaneous increase in water content in the surrounding ground bed soil indicated that the rapid water loss from the embedded soil was due to water movement into the surrounding soil. A similar water loss following subsequent irrigation of the embedded and ground bed soils indicated that this embedded soil water loss is primarily a drainage phenomenon. This effect was concluded to be a potentially significant factor affecting transplant survival.

Open Access

Horticulture Research Methodology courses are an important if not essential introduction to research for beginning graduate students. Such courses are often characterized by presentation of a series of experimental techniques, lacking continuity and out of context with real-world research situations. In the described course, students gained expertise with a range of environmental and plant measurement techniques within the framework of a semester-long experiment. The experimental techniques were introduced and incorporated into the experiment at appropriate stages. Each student engaged in hands-on participation in development of a proposal; experimental set up, implementation, and daily maintenance; and data accumulation, analysis, and reporting (in HortScience manuscript format). In addition to direct experience with all subject techniques, each student had individual responsibility for characterization of a. selected plant (or environmental) parameter. This format successfully accomplished the provision of direct and coherent experience with a wide variety of important horticultural research techniques within a real-world setting.

Free access

Osmotic adjustment in response to decreasing media water availability was observed for in vitro Chrysanthemum morifolium Ramat. cultivars Bright Golden Anne, Deep Luv, and Lucido. Water stress was induced by increasing sorbitol (0, 0.1, 0.2, 0.3, 0.4 M), mannitol (0, 0.1, 0.2, 0.3, 0.4 M), and sucrose (30, 45, 60, 75, 90 g·l-1) concentrations in modified MS media (2 mg·l-1 BA and 0.1 mg·l-1 NAA). Osmotic adjustment was evidenced by a significant reduction in measured cell sap osmotic potential (R2 = 0.78, 0.96, 0.91 for sucrose, sorbitol, and mannitol respectively) in all cultivars. Shoot length, weighted density (apparent mass), and proliferation were significantly reduced by sorbitol and mannitol treatments. Sucrose reduced shoot proliferation, increased length, and had an inconsistent effect on weighted density. Cultures grown on media without hormones showed tremendous increase in root number up to 60 g·l-1 sucrose. Sorbitol had a negligible effect on rooting at 0.1 M but no roots developed at higher sorbitol concentrations or in any mannitol treatments. Plants transferred to a non-water-stress media after they had experienced in vitro water stress exhibited no change in osmotic properties from the stress treatments.

Free access