ROOT AND AIR TEMPERATURE EFFECTS ON GROWTH AND YIELD OF TOMATOES AND LETTUCE

In tomatoes the response curve shows a broad optimum in the region 25–30°C. The greater growth is associated with a larger leaf area and total dry matter production, increased length of the root system (but not necessarily the dry weight of the roots) and the absorption of larger amounts of N, P and K. The rate of transpiration is also increased at higher root temperatures. There is a reduction in the size of the root cortex and the formation of larger xylem vessels in the warmer roots.

Results obtained in NFT systems are still equivocal although there are no reasons why they should be different from those described above. At a nominal night temperature of 9°C in the mild winter of 1977–78 fruit yield was similar to that obtained under 'blueprint' conditions when the roots were heated to 23 or 26°C. In a subsequent experiment in 1978–79 the plants showed symptoms of nickel toxicity when the nominal night temperature was 8°C. There were no visual toxicity symptoms at night temperatures of 12 or 16°C although analyses showed greater concentrations of nickel than in control plants. The nickel was probably leached from the monel sheathing of the immersion heaters. The effects of nickel are being checked and the experiment on root heating will be repeated in the 1979–80 season using silica-sheathed heaters.

Download Adobe Acrobat Reader (free software to read PDF files)