AERATION OF LOW PLASTIC TUNNELS. EFFECT OF THE POSITION OF THE PERFORATIONS
At 30 cm from the ground the maximum air temperature in tunnels with ridge perforations were 2–4°C lower than in the tunnels with side perforations : the minimum temperatures were the same in both treatments.
The ground temperature, at 5 cm depth, was 2–3°C higher in the tunnel with the top perforations. The leaf surface temperatures, and the green and dry weight of the plants, was not affected by the position of the perforations.
The mean percentage of set flowers was 5% higher (three first trusses) and 15% higher (4th to 8th trusses) in the tunnels with the top perforations. The accumulated yield, up to 24 July 1972, was 5 kg/plant in the top-perforated tunnels compared with 3 kg/plant in the lateral-perforated tunnels.
The temperature modifications observed have been small but have been very beneficial to the plants in the top-perforated tunnels. These results must be determined by other modifications of climate affecting the surface and interior temperatures of leaves and stems, which are connected with the changes in air turbulence under the tunnels. Such modifications are more difficult to characterise than the air temperature.