The effect of three types of polyethylene screens (white, green and black) under four heights from the soil surface (20; 30; 40 and 50 cm) was evaluated on the yield of lettuce (Great Lakes cv) under high temperature and luminosity conditions of Mossoró, Rio Grande do Norte State, Brazil. The control treatment consisted of the cultivation of the lettuce under open sky. The experimental design was of randomized complete blocks in a 3x4+1 factorial scheme, with four replications. Three types of shading-net colors (white, green and black) and four heights in the bed (20; 30; 40 and 50 cm above soil surface) besides a control (without net) were evaluated.Plant height and diameter, number of leaves/plant, yield, shoot dry matter and plant growth rate were obtained from plants. A higher number of leaves/plant and lettuce yield was observed using the white screen. The highest lettuce yield (80,5 t.ha-1) was obtained with the screen placed 44,6 cm from the soil surface. There was a significant interaction between types of screen and screen heights from the soil surface on the quantity of shoot dry matter and plant growth rate. The highest economic indicators were registered with the white screen at 40 cm from the soil surface.
Lactuca sativa; shading; growth rate; economic indicators
