RESULTS IN AIR-SUPPORTED PLASTIC GREENHOUSES WITH SPRING VEGETABLE CROPS

Three air-supported plastic greenhouses with an area of 190m² were used. One, in 1971, was made of polythene film, and two, in 1972, were made of PVC and polythene film respectively. The greenhouse was kept erect by means of a centrifugal fan of 220w (870m³/h), placed at one end of the greenhouse. The fan effected two changes of air volume per hour in the greenhouse.

Ventilation was brought about by a helicoidal fan of 1 kw and a capacity of 2000 m³/h, capable of 20 air changes per hour.

The observations were concerned with the climatic conditions inside greenhouses, the effects on the crops (tomatoes 1971 and peppers 1972), and the cost of installation.

In 1971, crop-raising began on 14 April with the transplanting of Marmande tomatoes to a density of three plants per m² and with pinching at the 3rd truss. In 1972 crop-raising began on 4 April with the transplanting of "Quadrato d'Asti" peppers to a density of 2,5 plants per m².

The most important results are :

1. Because of the absence of supporting frames, the thermal and lighting performance of the air-supported plastic greenhouses proved to be better than for the traditional greenhouses.
2. The continuous influx of air into the greenhouse prevents thermal inversions during the night and the modification of the CO₂ content of the air in the greenhouse.
3. It was observed that between the two ends of the greenhouse there was a difference in the maximum temperature of 1–4°C, and in the minimum temperature of 0,5–2°C. The lowest maximum and the highest minimum temperatures were found near the fan.
4. The observed thermal gradients determined differences in production in the various positions in the greenhouse.
5. Growing conditions worsened considerably during the months of June-July because of the excessive increase in the maximum temperature, and because of insufficient ventilation. Therefore, it is necessary to take away the protecting film during this period.
6. The installation costs were Lire 600 per m²; the maintenance costs Lire 0,85 per m² per day during April, and Lire 1,1 per m² per day during July.