The growing of lettuce plants in tropical regions has been painful under high temperatures and ample luminosity, substantially affecting the crop cycle and yield. The effect of shading on lettuce seedlings production was evaluated in relation to three types of shading-net in four heights from the bed, under high temperature conditions and ample luminosity. An experiment was conducted in Mossoró, Rio Grande do Norte State, Brazil, in a completely randomized design in split-plot scheme, with three replications. The factor assigned to the plots was constituted by shading-net colors (white, green and black) plus a control (without net) and the other assigned to the subplots was constituted by net heights in the bed (20; 30; 40 and 50 cm above soil surface). Evaluations of plant height and diameter, number of leaves per plant, shoot fresh mass and plant growth rate were made on lettuce seedlings. There was a significant interaction between types of nets and their distances on leaf number per plant, shoot fresh mass and growth rate of lettuce seedlings. Seedlings grown under green net were significantly taller than those under white net. On the other hand, seedlings grown under green net were significantly larger than those under white and black net. Tallest and largest seedlings were obtained from lettuce cultivated under open sky. Highest quantity of shoot fresh mass and plant growing rate were obtained under white net shading at about 30 cm above soil surface.
Lactuca sativa; leaf production; growth rate
