Articles
EFFECT OF ROOT ZONE WARMING ON TOMATOES GROWN AT DIFFERENT AIR TEMPERATURES
Grenadier, grown in recirculating solution at two night air temperatures, 18° and 13°C.
The minimum day temperature in both cases was 20°C. Solution warming gave a large increase in root size, raised the levels of minerals in the leaf but did not affect the development of early fruit or the early yield.
Reducing the night temperature from 18° to 13°C resulted in a lower early yield.
However, by the end of the experiment plants grown at the low air temperature in the heated solution produced 18.9 kg/m2 compared with 15.9 kg/m2 in the unheated solution.
Conversely, at the high night temperature solution warming reduced the yield from 19.8 to 18.2 kg/m2.
In the second year the same experiment was carried out except that the minimum night temperatures used were 13° and 5°C. Root zone warming increased shoot vigour and root size particularly at the lower night air temperature.
Early yield was not affected but after 10 weeks picking there was a significant yield increase from solution heating.
Plants grown at the low night temperature with root zone warming produced early and total yields as great as plants grown at the higher temperature.
The saving in fuel achieved by reducing the night temperature from 18° to 13°C was offset by a reduction in early yield and therefore monetary returns.
However, the results of the second experiment suggest that it may be possible to achieve greater fuel saving by further reducing the night temperature to 5°C without incurring any greater loss in early yield if root zone warming is provided.
Reducing the air temperature at night from 18° to 5°C would give an estimated overall fuel saving of 60% in the January-April period.