Effects of day and night humidity on yield and fruit quality of glasshouse tomatoes(Lycopersicon esculentumMill.)

Two spring crops and one autumn crop of tomato (Lycopersicon esculentum Mill.) were grown under natural light conditions in a glasshouse at different day and night humidity levels. A high or low humidity by day was combined with either a high or low humidity by night. Vapour pressure deficits (VPD), achieved over the period in which the treatments were applied, ranged from 0.35 to 1.0 kPa by day, from 0.21 to 0.71 kPa by night, and the 24 h mean from 0.2 to 0.8 kPa. Temperature differences between treatments were restricted to less than 0.7°C. Calcium deficiency and concomitant leaf area reduction was most severe under continuously high humidity. Stomatal conductance was significantly increased by high humidity. Early yield was higher at high humidity by day, but final yield was reduced by either a high humidity by day or night. Mean fruit weight and keeping quality were reduced under high humidity. Final yield and mean fruit weight were significantly related to 24 h mean VPD. It is concluded that yield losses under high humidity are due to restricted fruit growth. Humidity control with tomato should concentrate on the avoidance of long periods with high environmental humidity.