Abiotic and Biotic Factors in Slow Filters Integrated to Closed Hydroponic Systems

Selected abiotic (electric conductivity, pH, oxygen content, chemical oxygen demand, dissolved organic carbon) and biotic (general bacterial and fungal microflora, fluorescent pseudomonads, filamentous actinomycetes, Fusarium oxysporum, Pythium aphanidermatum, biochemical oxygen demand, enzyme activities) factors have been monitored in two distinct commercial hydroponic systems with tomato and ornamental plants with integrated slow filters in supernatant, filter skin and effluent in two successive years. In six small scale experimental systems with two slow filters each (nutrient film technique, crop: tomato) the same parameters were followed to establish possible correlations with filter efficacy against Fusarium oxysporum f. sp. cyclaminis. In half of the systems, the filter skin was enriched with fungal cell wall preparation. Nutrient solutions of the systems showed biggest differences concerning the chemical oxygen demand (COD) (commercial tomato system >> experimental system > commercial ornamental system) and dissolved organic carbon content (DOC). Both factors were positively correlated in supernatant and effluent (e.g. supernatant: r2=0.813; p