REACTION OF CHRYSANTHEMUM "SUPER WHITE" TO SOIL HEATING RELATED TO PHOTOPERIOD

Young plants of chrysanthemum were grown under greenhouse from december 8 th. 1980, to the end of april 1981, with minimum air temperature of 12°C known as unsuitable to produce normal flowering. This temperature was used in order to study the interest of soil heating. Day temperature of the greenhouse was not regulated.

Four benches were used for this experiment :

1 - no soil heating, 2 - 20°C during all the cultivation, 3 - 20°C during the long day period, 4 - 20°C during the short day period. Heating was achieved by hot water in polyethylene pipe at 35 cm deepht.

At the end of the long day period, the height of plants, their stem diameter and dry matter were measured. The plants were significantly higher in the heated benches than in the non-heated one, nevertheless, the plants grew more dry matter. Soil heating had no effect ont the stem diameter.

Soil heating during the long day or the short day period delayed flowering, compared with plants heated all the cultivation long.

The consequences of this different way of soil heating were examinated.