Evapotranspiration, water use efficiency and crop coefficient of three lettuce varieties grown in a tropical region

Three field experiments were carried out in a tropical environment in Brazil in order to evaluate the effect of planting date on crop evapotranspiration (ETc), crop coefficient (Kc) and water use efficiency (WUE) of three lettuce (Lactuca sativa L.) cultivars grown in different seasons (autumn, winter and summer) under tropical climate. ETcvalues were obtained through the soil water balance method and reference evapotranspiration (ETo) through the Penman-Monteith method, using data collected in an automatic weather station located close to the experimental area. The results of the research showed that the mean values of ETc and Kc for lettuce were 3.5 mm day-1 and 0.82, respectively. The curly cultivar showed the highest yield (40.8 kg ha-1) during the autumn transplanting date. Results also showed that the three lettuce varieties have different responses to the climatic conditions. The greatest WUE was observed for the three lettuce varieties when they were grown during the autumn growing season, and the lowest values occurred during the winter growing season.