Two experiments were carried out in the Escola Superior de Agricultura de Mossoró, in Brazil. The first experiment, from October to November 1999, evaluated the performance of three lettuce cultivars grown at the nursery stage under shading and three types of polyethylene net, and the second experiment, from December 1999 to January 2000, compared the lettuce yield under shading and no shading. The experimental design in both experiments was a randomized complete block. Treatments in the first experiment were factorial combinations of three types of polyethylene net (2 x 2 mm white and green nets and half-shade black net) and three lettuce cultivars (Great Lakes, Verônica and Regina) replicated four times. Treatments in the second experiment were these three types of polyethylene net plus one where lettuce cultivar Verônica was grown under no shading (control) replicated three times. The lettuce spacing in both experiments was 0.20 x 0.20 m. The performance of lettuce was evaluated through plant height and diameter, leaf number per plant, shoot dry matter content, yield, relative growth rate, gross and net incomes and rate of return. Shading and cultivar interaction affected plant height. Plant diameter and leaf number per plant were affected only by cultivars. Shoot dry matter content and yield were affected by shading as well as cultivars. White polyethylene net shading associated with lettuce cultivar Great Lakes provided the highest economic indices when compared to no shading.
Lactuca sativa; production of seedlings; polyethylene net
