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- Author or Editor: J. N. Walker x
An analysis of using an air-earth heat exchange for controlling the environment in a greenhouse was conducted. For purpose of the analysis, a small greenhouse (2.75 m wide and 4.25 m long) connected to 30.5 m of 45 cm diameter pipe was assumed. In terms of heating, the air-earth heat exchanges proved to be inadequate except for the very southern parts of the United States, and even in these locations the temperature had to be limited to a relatively cool temperature of 10°C. A similar analysis for summer showed that the air-earth heat exchange could effectively limit the occurrence of high temperatures in a greenhouse throughout the United States.
Setup and administration of comprehensive live plant identification (ID) tests in horticulture classes is time-consuming and costly. The curricular goal of this study was to integrate Web-based plant ID self-tests and computer-graded tests into floriculture potted plant production classes to potentially replace live plant ID tests. This research was conducted during 2000 and 2001 with students enrolled in Hort 4051 at the University of Minnesota, St. Paul. All plant ID tests were mandatory, constituting 12% of the grade. In 2000, only Web-based ID tests were used, while both Web-based and live plant ID tests were used in 2001. Two separate self-tests were designed as study aids with 34 randomized photographs/test. Correct spelling was mandatory to receive full credit for genus, species, and family. Self-tests could be taken ten times each per student. Students then completed two for-credit (graded), unmonitored Web-based tests. Students completed a Website evaluation form at the end of the semester. The two live plant ID tests were conducted with the same materials and were monitored. Mean student scores for the Web-based ID tests in 2000 ranged from 73.5 to 99.5% with a class average of 91.9%; there were no significant differencesamong students' scores. Student Web-based ID test scores for 2001 had a similar range with a high class average of 93.8%. In contrast, the 2001 live plant ID tests had a wider score range of 21.7% to 100.0% and lower class average (72.2%). Web-based and live plant ID tests, students, and their interaction were all highly significant. Web site course evaluations demonstrated interesting trends in student perception of Web-based and live plant testing. The implications for future class use and potential modifications for continued Web-based instruction are presented.
The environment created by ventilating a greenhouse with mine-air was suitable for the production of high quality spray chrysanthemums (Chrysanthemum morifolium Ramat.) and snapdragons (Antirrhinum majus L.) from mid-February through November without any additional energy requirement. The environment created in the greenhouse from December to February was extremely humid and favored botrytis development and physiological problems which reduced crop quality.
A greenhouse environment, heated and cooled with air drawn from a coal mine, was modified to reduce high humidity and dripping condensate. Polyethylene covered chambers, constructed within the mine-air greenhouse, were ventilated with mine-air, heated above mine-air temperature and ventilated with mine-air, or heated above mine-air temperature and ventilated with air drawn from outside the greenhouse. Heating the chambers above mine-air temperature did not reduce relative humidity significantly. However, polyethylene glazing on the chambers protected plants growing within the chambers from condensate dripping from the outer covering of the mineair greenhouse, which reduced the disease potential. Snapdragon and lettuce crops were produced in the chambers from early fall through spring. Snapdragon and lettuce grown in chambers ventilated with mine-air generally were of equal or better quality than plants produced in chambers provided with additional heat and ventilated with either mine-air or air drawn from outside the mine-air greenhouse.
A near-infrared reflectance (NIR) technique was developed that provides a rapid, nondestructive, nonchemical analysis of ground apple (Malus domestica Borkh.) leaf tissue for predicting total N content. Leaf tissue samples of apple with known (chemical) leaf N concentrations ranging from about 1.6% to 2.9% N were used in the calibration of the NIR technique. The NIR technique was highly correlated (r = 0.923) with the chemically determined total leaf N content. Prediction of tissue N values was performed with a standard error of estimate of about ±0.10% N. This value compares favorably with the standard error obtained for duplicate determinations preformed by a tissue analysis facility employing standard chemical (Kjeldahl) digestion methodology.