I. BASIC PROBLEMS OF WATER RELATIONSHIP - ENERGY BALANCE AND WATER SUPPLY IN GLASSHOUSES IN THE WEST-NETHERLANDS
Approximately 50% of the global radiation inside non-heated glasshouses appeared to be used to evaporate water. The energy supplied by artificial heating in heated glasshouses is to a lower percentage used for this purpose. As an exact calculation of the energy balance components is not yet possible it is estimated that 25 to 30% of the heating energy was used for evapotranspiration.
Data on water supply to tomatoes, cucumbers, roses and carnations in heated glasshouses from a large number of holdings were in a good agreement with the calculated requirements. Solar radiation was the most important factor when calculating the needed water supply.
Some limitations were made to the use of the found relationship between the to be given additional water supply and global radiation in heated glasshouses. Account should be taken of soil and glasshouse type as well as ventilation frequency and heating intensity. Checks on moisture content of the soil and evaluation of crop growth remain necessary.