THE EFFECT OF SUPPLEMENTARY LIGHT AND ELECTRICAL CONDUCTIVITY ON GROWTH AND QUALITY OF CUT ROSES
The highest light level contributed to a photosynthetic active radiation during winter which exceeded the natural radiation during summer. Generally the yield increased as the PPFD level increased from 130 to 250 or 370 μmolm-2s-1, and this was the case during the whole period. The response of PPFD varied between the cultivars and as an average the yield increased 18, 41 and 53% at 190, 250 and 370 μmolm-2s-1 PPFD, respectively, compared to 130 μmolm-2s-1.
Raising the EC in the growing medium from 2-3 to 4-6 mS cm-1 increased the yield by 9 % as a mean. For two cultivars it was an increase of 26%, while for one it was a decrease of 8%. The quality of the roses increased with increasing PPFD by a higher proportion of class one shoots by longer stems particulary during mid-winter, and by an enhancement of the keeping quality. The content of macro nutrient elements in the leaves decreased with increasing PPFD, while no effect of the EC was found except for cv. Jaguar where the content of N and K was lower at high compared to normal EC.