Articles
INFLUENCE OF TEMPORARY COVERING WITH PLASTIC ON TIMING, YIELD AND QUALITY OF ICEBERG LETTUCE
The treatments involved were types of polyethylene (P.E.) sheets with different perforation – 250, 500 and 750 holes of 1 cm in diameter per square meter.
A new type of plastic sheet – polypropylene – with net structure has been compared to P.E. Each type of plastic sheet were left on the crop for 4, 5 and 6 weeks respectively after transplanting.
The results from two growing seasons are discussed concerning the effect on soil temperature and the final yield and quality of harvested plants.
By selective harvest of lettuce plants when reached marketable size the most pronounced effect was 8–10 days earlier harvest by covering with a P.E. sheet in 5 or 6 weeks from the transplanting until mid-May.
The earlier harvest of the lettuce increased in 1981 the gross return per hectare with approx. 40.000 D.kr. and compared to additional expenditures of about 10.000 D.kr. for covering with plastic gave a considerable increased profit.
Under Danish growing conditions covering the lettuce with plastic after mid-May increases the existence of physiological disorders like tip-burn and marketable yield is decreasing.