The evapotranspiration of Gergana long-fruit cucumbers was established in four years of field experimentation with drip irrigation, grown in greenhouse conditions on chromic luvisol soil in the Sofia region. Different irrigation regimes have been tested – from full satisfaction of the daily needs of the culture from water to irrigation with 20% and 40% reduced water application rates. The total evapotranspiration values for the study period were determined.
For the needs of practice and design, the ten-day values of the biophysical coefficient Z are calculated, which depends on the biological characteristics of the crop and the weather factors. On the basis of the established relationship between evapotranspiration and evaporation, the values of the coefficient of crop in unheated plastic greenhouses are calculated as the average for the cucumber vegetation curve Ki = 1.46.