EVAPOTRANSPIRATION AND PRELIMINARY CROP COEFFICIENT OF GERBERA SOILLESS CULTURE GROWN IN PLASTIC GREENHOUSE.

Evapotranspiration (ET) and crop coefficient measurments have been estimated in gerbera soilless culture in perlite, sand, zeolite and rockwool substrates, under plastic greenhouse, in the Agricultural Research Center of Northen Greece.

The method of solar radiation, modified for greenhouses, was used to estimate the potential ET. The actual ET was measured from the water balance formula and the crop coefficient was calculated as the ratio of potential and actual ET.

Preliminary results are reported as follows:

• The potential and actual ET follow the same pattern, the actual one being always lower than the potential.
• The highest rate of actual ET was recorded in May 1992 (0.5l per plant for sand and zeolite and 0.61 per plant for perlite and rockwool). The lowest one was observed in November 1991 (0.15l per plant for sand and zeolite and 0.22l per plant for perlite and rockwool).