THE OPTIMIZATION OF AIR TEMPERATURES FOR GREENHOUSE CUCUMBERS - AN EVALUATION OF DIFFERENT FARMING STRATEGIES

From 1985 to 1988 experiments were carried out in a greenhouse consisting of eight individual chambers to examine the impact of different air temperatures on cucumbers. The experiments focused on a method of optimization based on a yield model which allows temperatures to be optimized during 9-d periods over the whole period of yield formation.

The main variants were:

• a standard routine with a constant night temperature of 14 °C as a basis for comparison;
• an optimized temperature routine based on a fixed outdoor climate (standard climate) (off-line strategy);
• an optimized temperature routine based on actual outdoor temperatures (on-line strategy) with and without CO₂-enrichment.

In addition a temperature routine including a decrease in night temperatures from 20 °C down to 11 °C within four weeks after the beginning of the experiment was tested along with a strategy where the mean temperature value fixed for each month had to be approximated as close as possible by way of set-point correction.

The tests were carried out with the cucumber varieties 'Saladin', 'Polo' and 'Stella'. Planting took place between mid and end January.