Microclimatic modifications and productive responses of the Iceberg lettuce (Lactuca sativa) in protected environments

Experiments were carried out in Ponta Grossa - PR, Brazil, in the winter and spring/summer periods with iceberg lettuces cultivars Lucy Brown and Raider Plus. The objectives were to assess the lettuce productive responses and the intensity of the microclimate modifications in five cropping systems as under shade nets Aluminet 40-O® (AL) and ChromatiNet Vermelha® 40 (CR), a low tunnel covered with transparent polyethylene (TU), direct cover white nonwoven (NW) and natural conditions (NT). A complete randomized design was used for both the experiments with five treatments placed in a 5x2 factorial arrangement (cropping systems x cultivars) and four replications. The photosynthetically active radiation and air temperature were monitored by installing probes in a datalogger system. In the winter both cultivars under NW and TU produced 21 days earlier compared to the other environments but they presented fresh commercial head similar to NT at the end of the cycle and superior to CR and AL. In the spring/summer there was no difference in the lettuce cycle regardless of the cultivar and the cropping systems. The Lucy Brown cultivar presented smaller sized heads for the winter cropping but did not differ from Raider Plus during the spring/summer. The mean air temperature of the air under NW was higher than in the other environments in both experiments. The use of the different covering materials reduced the photosynthetically active radiation available to the plant but did not prevent commercial head production of Iceberg lettuce