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- Author or Editor: Gerald I. Moss x
Three rose cultivars, Ilona, Mercedes, Sonia, on Rosa multiflora rootstock were grown in a nutrient film technique (NFT) system for 2 years, with root-zone warming (RZW) to 25°C compared with ambient temperature roots. In the 1st season the night air temperatures were 18°, 12°, and no heating (9°); in the 2nd season, 18°, 14°, and 10°. Harvested flowers were graded according to stem length. In the 1st winter seasons RZW increased the proportion of long stemmed roses and increased the total yield, especially in ‘Ilona’. In the 2nd winter season, RZW again increased the proportion of long stemmed roses in ‘Ilona’ but increased the total number of blooms more in the other cultivars. The effects of RZW persisted into the summer period. Prevailing wholesale prices were used to calculate probable gross returns based on yields. Since RZW tended to give longer stemmed roses and more blooms than did ambient conditions, this treatment enhanced returns more than that of the increased air temperature treatments. RZW increased probable returns over the ambient for ‘Ilona’, ‘Mercedes’, and ‘Sonia’ by 49%, 69%, and 78%, respectively.
Equipment for measuring water use of a greenhouse crop of up to ± 1 kg h-1 over 30 m2 is described. It is based on growing a crop in nutrient film, with a nutrient tank replenished from a water tank, and controlled by accurate level sensors. The water tank is suspended from a load cell interrogated at frequent intervals by a data logging computer. Examples of data collected are given. Peak daytime transpiration rates varied from 50 mg s-1 m-2 to 150 mg m2 s-1 with a maximum error of 5%. With low transpiration rates, the errors were increased, but accuracy could be improved by calculating the rates over a prolonged time interval.