Possibilities of growing glasshouse vegetables in a closed system using common soil as a substrate.

Acta Horticulturae 633, 213-220.
Bleyaert P, Pollet S and Lemeur R (2004)



As a possibility to avoid the emission of nutrients in cultivation of glasshouse vegetables, a Dutch prototype of closed growing system (CS) was developed further. Normal soil rooting layer was simply separated from the subsoil by a sheet of plastic. Soil texture was sandy loam; depth of the growing layer was 0.40 m. In contrast to many hydroponic, soilless systems, this closed system allows free choice of vegetable growing. The CS was tested during six years for butterhead lettuce (Lactuca sativa L. var. capitata) in winter and cucumber (Cucumis sativus L.) in summer by comparison with simultaneous cultivation in the normal growing system. For lettuce, yield and crop quality for both growing systems were comparable. Tipburn sensitive cultivars should however be avoided and plant-dependent irrigation should be pursued. Cucumber yields in CS were very variable. Some evidence was obtained that accidental inferior yields were caused by conditions of poor soil aeration, presumably due to low substrate porosity, in combination with improper irrigation. Use of grafted plants and less frequent irrigation with higher irrigation rate improved CS-results. After six years of use, no abnormal compaction of soil layers in the closed system could be detected. This explains why a sandy layer (0.10 m) on top of the plastic lining could not improve growing results. The shallow soil layer in the closed system allowed more efficient soil disinfestation with quantities of methylbromide and steam much lower than normal.