Water Treatment
Soilless cultures
Many greenhouse crops are to a large extent produced in soilless cultures. These are either ‘bag’ cultures using a solid medium such as pumice, sand, sawdust, peat, bark, perlite, vermiculite, rockwool or a mixture in bags, tubes, slabs or troughs, or water cultures (‘true hydroponics’) including nutrient film technique (NFT) and deep flow technique (DFT).
Open or closed systems
Cultures on a growing medium can be either in an ‘open system’ or ‘run-to-waste’ or in a ‘closed system’ or ‘recirculation system’. Closed systems use 20-40% less water and fertilisers than run-to-waste systems, and cause much less pressure on the surrounding land and water environment. Closed or recirculating systems are the future.
Root diseases
Soilless cultures were initially employed as a method to get away from soil-borne diseases (and also to improve the quality of the plants and produce). However, it soon became clear that crops in soilless cultures are affected by the same (or similar) pathogens as crops in soil. Pathogens are fungal structures, viruses, bacteria or nematodes. Pythium, Phytophthora, Fusarium and Rhizoctonia are examples of fungal diseases that occur in soilless-grown crops. Bacteria, viruses and nematodes can cause diseases in plants in soil as well as in soilless cultures.
Root disease control
Any pathogen present in a closed system potentially can spread all through the whole greenhouse via the recirculating nutrient solution. Also in open systems diseases can spread. The advantage of soilless cultures above soil cultures is that the roots are confined to a small volume of medium or water, and that pathogens can be controlled relatively easily. The media can be replaced or sterilised after usage.
Water treatment techniques
The nutrient solution can be treated, for which there are many different methods available: heating, UV, ozone, hydrogen peroxide, slow sand filtration, biofiltration and more. These techniques are discussed in a series of articles.
Further reading
Reasons for water treatment in soilless systems (1999)
Quality of source water for soilless cultures (1999)
Water volumes to be treated for soilless cultures (1999)
Sterilisation: heat treatment for pathogen control in water for soilless cultures (2000)
Sanitation and hygienic husbandry to prevent root rots (2000)
Pythium only successful in stressed plants (2000)
UV for sterilisation of water for soilless systems (I) (2000)
UV for sterilisation of water for soilless systems (II) (2000)
Hydrogen peroxide for cleaning irrigation system (2000)
Ozonation in soilless cultures. Part I: techniques (2000)
Ozonation in soilless cultures. Part II: dose and contact time (2001)
Ozonation in soilless cultures. Part III: growers’ experiences (2001)
Bio-filters and slow-sand-filters for soilless cultures (2001)
’Bio-filters’ and more for water treatments in soilless cultures (2001)
Biological control of root diseases - especially with Trichoderma (2001)
