Evapotranspiration and crop coefficients (Kc) of stevia [Stevia rebaudiana (Bertoni) Bertoni] under greenhouse conditions

The reference evapotranspiration (ETo) of a zone and the crop coefficient (Kc) represent important data necessary to determine the water requirements of plants. The objective of this study was to determine the crop evapotranspiration (ETc) and Kc of plants of stevia at different stages of development, as proposed by FAO, by employing four free-drainage lysimeters installed inside a greenhouse. The ETo was estimated using an atmometer ET gage model A. The lysimeters were 0.25 m effective depth, 0.4 m wide and 1 m long, and within each of them four plants of stevia were transplanted 25 cm apart in a row. The water balance in lysimeters was determined three times a week during nine weeks. After harvest, a similar second experiment was conducted. Plant height, canopy diameter, and stem and leaves dry weight were measured, and it was found no differences in growth between plants inside and outside lysimeters. The mean ETc was 1.47 and 1.12 mm.dia(-1) in the experiments 1 and 2. Mean values of Kc for stages I, III and IV were 0.35, 0.59 and 0.55, respectively, while the Kc for stage II increased from 0.35 to 0.59. Stages I, II, III and IV lasted 38, 14, 4, and 4 days, respectively, in both experiments.