M.R. Hardgrave
Trials were carried out over a 2 year period as part of a project to develop practical recirculation systems for greenhouse salad crops. In cucumber and tomato trials the standard rockwool growing system (with excess solution running to waste) was initially compared with a simple recirculation system.

For cucumbers total fruit yield was higher from the recirculation treatment in Year 1 and there was an indication that there were lower plant losses due to stem diseases (Mycosphaerella & Botrytis). In Year 2 levels of stem disease were again reduced when nutrient solution was recirculated but differences in humidity between the treatments were shown not to be the reason for the variation. Total crop yield was influenced by the spread of Pythium aphanidermatum in the recirculating system in the second trial.

In the tomato crop it was more difficult to maintain optimum nutrient levels and in Year 1 final yields showed a slight reduction for recirculation compared with run to waste. In the second year the treatments aimed to control nutrition very closely or to allow wider fluctuations from target levels before adjustments to stock solution nutrient levels were made. Again yields from the recirculation treatments were slightly lower than those from the standard system. Closer control of nutrition gave no benefits over the more flexible system.

The project is continuing to work towards finding the link between recirculation and stem disease in cucumbers and to eliminate yield losses in tomatoes.

Hardgrave, M.R. (1993). RECIRCULATION SYSTEMS FOR GREENHOUSE VEGETABLES. Acta Hortic. 342, 85-92
DOI: 10.17660/ActaHortic.1993.342.10

Acta Horticulturae