Abstract
Hanan and Holley (6), in 1960. published on a simple air temperature control system for research purposes. However, present climate control systems have completely revolutionized the manner, quality, and efficiency of research carried out in greenhouses. Reports by Willits et al. (8, 9) showed that building a system with equipment extant in 1975 would be difficult for a practicing horticulturist. There are possibly now more than five companies in the United States marketing environmental control “computer” systems for the greenhouse industry. Within the past 10 years, interest in the potential of sophisticated climate control has been marked (1–4, 7–9).
Abstract
Most systems used for controlling rootzone temperature (RZT) involve grouping plants in each treatment together in one temperature-controlling apparatus (3, 5). The power of experiments using systems with grouped plants is limited because the groups constitute single experimental units during data analysis. Some systems have overcome this problem, but reports may lack fabrication details (2) or indicate a limited RZT range was used (1, 4). We designed a precise, inexpensive system capable of achieving a wide range of RZT in which individual plants are discrete experimental units.
Abstract
An inexpensive, well-stirred chamber for measuring net fluxes of CO2 and H2O vapor from single leaves was constructed from readily available materials. It incorporates a fan that maximizes air turbulence and boundary-layer conductance. Leaf temperature can be maintained within ± 0.5°C of air temperature. Temperatures can be varied for experimental purposes or can be maintained constant even under varying heat loads using a temperature-controlled water circulator. When used in conjunction with such a circulator and CO2 and H2O vapor analyzers, this chamber can become an inexpensive yet useful component of a gas-exchange system.
Tulip bulbs are produced in the Netherlands and are shipped to United States during the months of July and August in temperature-controlled shipping containers. Each shipment is often composed of a mixture of many cultivars. Mechanical failure of temperature controls may result in high temperatures that ultimately may reduce forcing quality of the bulbs. When such accidents occur, an immediate decision must be made about whether to invest more time and money on these potentially damaged bulbs. Such a decision is not easy because symptoms of heat damage are often delayed until months later. Research on a single cultivar, `Apeldoorn', has shown that heat stress can cause flower abortion and other abnormalities. However, cultivars undoubtedly vary in their response to heat stress. Thus in the 2002 and 2004 forcing seasons, ≈45 cultivars were screened for response to a standard heat stress of 4 days at 35 °C. Prior to the heat stress, bulbs were held at 17 °C or 9 °C for 4 weeks, mimicking conditions used for late and early forced bulbs, respectively. Flower and leaf height, percent flower abortion, and flowering date were evaluated. Heat stress caused flower abortion and reduced plant height in sensitive cultivars. Across all cultivars, cold storage prior to the heat stress significantly increased bulb's sensitivity to heat stress. Using percent flower abortion, cultivars were grouped into three categories: resistant, moderate, and susceptible. With this information, we hope that damage assessment may become easier and fewer bulbs wasted.
A cooling system using the principles of heat transfer was designed to provide a temperature difference of 6C between root and shoot zones and to study the effect of this difference on growth, yield, and phenology of `TI-155' sweetpotato [Ipomoea batatas (L.) Lam.] grown using the nutrient film technique in a greenhouse. Treatments were temperature control (20C) and variable temperature (26C) in a randomized complete-block design with two replications. A modified half Hoagland's nutrient solution with a 1 N: 2.4 K ratio was used and was changed every 2 weeks. Nutrient solution pH was maintained between 5.5 and 6, and electrical conductivity, salinity, and solution temperature were monitored at regular intervals. Storage root fresh and dry weights (except for fibrous root dry weight) and foliage fresh and dry weights were not significantly influenced by root zone temperature. Leaf expansion rate and vine length were lower for root zone temperature control plants; stomatal conductance, transpiration, and leaf unfolding rates were similar for both treatments.
bract color, and anthesis, as well as an average color rating of the uppermost five bracts on each stem (the three primary bracts and the two uppermost stem bracts). Significance of treatment means relative to the moderate-temperature control were
Abstract
‘Atlas’ and ‘Monika’ alstroemeria (Alstroemeria hybrida L.) were grown in cooled (12 to 16C) and noncooled (15 to 18C) gravel substrate in four temperature-controlled greenhouse compartments having mean day/night air temperatures of: 20/14, 20/13, 22/13, and 24/14C. Total flower production of ‘Atlas’ in all compartments was 1.6 times greater than for ‘Monika’. The greatest production of ‘Atlas’ occurred with 20C average daytime air temperatures combined with root substrate temperatures 12C to 14C, which favored year-round production. Warmer day temperatures tended to improve flower grade and stem length of ‘Monika’; however, the higher yield in cooler air temperatures outweighed the contributions of warmer air temperatures to quality. ‘Atlas’ stems were significantly longer and of better quality than ‘Monika’ in all temperature regimes.
`High-temperature controlled-atmosphere (high CO2/low O2) conditioning was investigated as a possible treatment to delay the incidence of internal breakdown of peaches and nectarines (Prunus persica L. Batsch) during subsequent cold storage. Maintaining an atmosphere of 5% to 15% CO2 added to air or to 1% to 5% O2 while conditioning peaches for 2 days at 20C partially prevented fruit ripening (compared to fruit conditioned in air), as measured by flesh softening and loss of green pigment, while no off-flavors were detected. Conditioning of peaches at 20C for 4 days in air or in air + 20% CO2 was detrimental to fruit quality, as indicated by flesh softening or detection of off-flavors.
The successful germination of triploid watermelon seeds depends largely upon three factors; moisture control, planting depth, and temperature control. The planting medium must be moistened until it is humid, but not wet enough for free water to be squeezed from a handful. This level of humidity must be maintained until germination is complete. The planting depth should be 1.25 to 2.5 cm. This reduces the number of seeds that “push” themselves from the medium and also facilitates correct moisture maintenance. Seeded trays should be placed in a germination room and held 48–72 hours at a temperature of 30 to 32 °C and a relative humidity of 90% to 95% until germination begins. When germination is complete, the plants can be watered normally.
Four types of media [coir, 1 coir: 1 peat (by volume), peat, and sandy loam soil] were evaluated for their effects on plant growth and nitrate (NO – 3) leaching in the production of oriental lilies (Lilium L.) `Starfighter' and `Casa Blanca'. Twenty-five bulbs were planted in perforated plastic crates and placed on the ground in temperature-controlled greenhouses. The potential for NO – 3 leaching was determined by placing an ion-exchange resin (IER) bag under each crate at the beginning of the study. After plant harvest (14 to 16 weeks), resin bags were collected and analyzed for NO – 3 content. Plant tissues were dried, ground, and analyzed for N content. Results indicated that the use of coir and peat did not significantly influence plant growth (shoot dry weight) relative to the use of sandy loam soil; however, substrate type influenced the amount of NO – 3 leached through the media and N accumulation in the shoots for `Starfighter', but not `Casa Blanca'.