COMPARISONS OF HOT WATER MICROCLIMATE HEATING AND CONVENTIONAL OVERHEAD HEATING ON THE DEVELOPMENT AND NUTRITIONAL STATUS OF SEEDLING GERANIUMS AS WELL AS FUEL CONSUMPTION OF THESE HEATING REGIMES

Scope of Study. Hot water microclimate heating as an alternative to conventional heating for the greenhouse crops was studied. Two crops of seedling geraniums (Pelargonium x hortorum Bailey) were grown for 16 weeks under the microclimate system using "Gro-Mat" ethylene propylene diene monomer (EPDM) tubing and a 10(DEGREES)C air -21.1(DEGREES) media temperature environment. Another crop was grown with conventional heating at 16.6(DEGREES) air temperature. Evaluations were made on growth, flowering, nutritional status, and energy consumed.;Findings and Conclusions. The microclimate system sporadically produced a taller plant during the first eight weeks of the October crop compared to the conventional heated crop; and the December crop was affected only twice during the initial eight weeks. This time the microclimate heating system produced a shorter plant. After week eight there were fewer differences in height. Switching the heating method on some eight week old plants caused no significant differences in height during weeks 10-16 of the October crop, but the plants that went from eight weeks of conventional to eight weeks of microclimate heat were significantly taller on week 10, 14 and 16 than plants that moved from microclimate to conventional heating. There was a cultivar x retardant interaction during weeks 10-16. Chlormequat caused a shorter plants and less dry weight, and 'Smash Hit' was affected more strongly than 'Ice Queen'. The same general pattern occurred on shoot dry weight. Chlormequat caused a lower root dry weight on 'Smash Hit' in the October and December crop. One of the principal differences noted in this study was that the conventionally heated plants flowered seven to ten days earlier than the microclimate plants. The elemental concentrations of the plants were affected by the type of heating system early in the life of the crop (week 8). In the October-sown crop conventional heat caused higher levels of N, P and K, but microclimate heat and chlormequat caused elevated levels of Ca and Mg but these increases were erratic. The December-sown microclimate heated plants had greater concentrations of N, P, K, Ca, Mg and Fe than the conventionally heated plants. Chlormequat increased elemental concentrations of all elements. By the end of the crop (week 16) few differences in elemental concentrations were detected between the two types of heating systems, and there was a significant cultivar x retardant interaction. The microclimate heating system used about 30% less natural gas than did the conventional system. It appears that microclimate heating systems are a possible alternative to conventional heating systems.