The protected and hydroponics cultivation are increasing in Brazil, demanding a better knowledge of crop performance in this environment. Plant dry matter accumulation as a function of solar radiation, temperature, relative humidity and other weather parameters in greenhouse is different when compared with field cultivation. With the purpose of proposing models to characterize the temporal variation of leaf and total dry matter production of hydroponics-grown lettuce (Lactuca sativa L.) and to determine the flowering period and the maximum dry matter accumulation rate as a function of plant relative development (relative degree-days), solar radiation and effective thermal index, two experiments (Spring and Autumn) were carried out in the greenhouse, at Santa Maria, Rio Grande do Sul State, Brazil. Growth and development models are useful in obtaining basic information on the plant <FONT FACE=Symbol>´</FONT> environment interactions, maximizing the use of resources in greenhouse, as well as, to define the best form of crop management. The cultivar Vera was chosen as function of its earliness. Models were proposed to estimate the temporal variation of dry matter accumulation, where the best results for relative development were obtained using effective degree-days, characterizing the importance of the air temperature for the vegetative phase and the solar radiation for the reproductive. The yield and quality of the lettuce seeds evidenced a high potential of hydroponics technique.
modeling; dry matter; plastic-greenhouse