ROOT-ZONE WARMING AS A MEANS TO SAVE ENERGY IN THE PRODUCTION OF GREENHOUSE CROPS IN AUSTRALIA

In 1980 tomatoes at a root temperature of 25°C gave 13% higher yield than those with roots at ambient temperature, and a 16% greater yield in 1981. This effect was greater at the lower night temperature (10, 12°C) and with no heating (8, 9°C) compared with 15 and 18°C. Thus in southern Australia, greenhouse tomatoes may be grown with root warming only. This represents a calculated energy saving of 68%.

Kentia fosterana palms were grown for 9 months from seedlings and compared at root temperature of 25°C with ambient root temperature at night minimum temperatures of 18, 12 and 9°C. Root-zone warming to 25°C increased growth by 31% and total leaf area by 33%. Growth and leaf area at the lower night temperature with root warming were only slightly less than with ambient roots at 18°C night temperature.

'Sonia' rose cultivar on R. multiflora rootstock was grown in nutrient film and production with 25°C root temperature compared with ambient root temperatures at 18, 12°C night temperature and with no heating (9°C). Over the winter period root warming resulted in 52% more blooms and 13% longer stems. 'Sonia' with root warming gave 42, 28, 66% more blooms at 18, 12 and 9°C night temperatures respectively. The yield at the lower night temperatures with root warming was similar to that at 18°C with roots at ambient temperature. Although the combination of low night temperature and root warming represents a considerable energy saving, with roses the use of root warming at the higher night temperature might be preferred because of the high yield and more consistent production, so that energy use per bloom is reduced by root-zone warming.

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