THE USE OF PLASTIC FILM AS A GROWTH-STIMULATING FACTOR, ESPECIALLY ON GROWING OUTDOOR-CUCUMBER
Although the area of outdoor-cucumbers in Denmark is rather limited (some 800 ha per year), stabilization of yield is desirable and therefore different methods to improve the microclimate are being used as e. g. temporary shelters of rye, broad beans and sunflowers.
As a method to improve the microclimate, covering with plastic film is now being used to a steadily increasing extent.
In some preliminary experiments in 1965 with gerkins, covering with clear polyethylene film gave an increased yield of 82% in relation to uncovered. The best result was obtained where the cucumbers were sown at the bottom of an 8 cm deep furrow and covered immediately after sowing. The plastic remained all season through, being perforated at plant distance when touched by the plants, and the plants growing through the perforations. This method, however, is very laborious and weed control is very difficult.
These experiments were continued in order to investigate various methods of covering, including the less laborious method of removing the plastic, when the plants reach a certain stage, here the 3-leaves stage. The relation between plastic covering, sowing-time and sowing on ridges was investigated. On ridges, which are approximately 1.0 m wide and 15–20 cm high, the soil temperature raised more quickly because of an increased radiation on the greater surface in relation to soil volume. In all treatments the cucumbers were sown at the bottom of 10 cm deep furrows.
The treatments were:
- Covered with clear plastic film at sowing, perforated immediately (comparable with covering with perforated plastic film).
- Covered with clear plastic film at sowing, perforated when the plants are at the 3-leaves stage.
- Covered with clear plastic film at sowing and plastic removed when the plants are at the 3-leaves stage.
- Sowing app. 20th May, and 2. sowing app. 1st June.
- Sowing in furrows on level ground.
- Sowing in furrows on ridges.