Four different covers were tested to obtain a system to produce vegetables throughout the year under low tunnels without ventilation management. Lettuce, cv. Regina, was grown during thirteen plantings from October 1994 to July 1997. The winter treatments were: a) low tunnel with transparent polyethylene without perforations and with conventional management according to the meteorological conditions; b) low tunnel with 3% perforated transparent polyethylene and without ventilation management; c) umbrella-like, low tunnel with transparent polyethylene with open laterals throughout the year and without ventilation management; d) cropping without tunnel throughout the year, as a control. The treatments in the summer were similar to the winter treatments with conventional and perforated covers replaced by a black plastic screen with a 30% reduction in solar radiation. Results indicated that the umbrella-like tunnels can be used instead of conventional low tunnels, which need daily management. This technique allows lettuce to grow throughout the year and only requires the laterals adjustment, according to the year season.
vegetables; conventional tunnel; umbrella tunnel; perforated tunnel; plastic screen tunnel; ventilation
