Design of sustainable hydroponic systems in relation to environment-friendly disinfection methods

The last few years Dutch horticulture has changed from a classical production-oriented market to a customer-oriented market. It is no longer the grower who decides about amount and quality of the product. Now, the consumer, and for vegetables more specifically the supermarket prescribes. One of the results is a change from large amounts of a single quality and bulk products to a very segmented presentation of products with different qualities and with added values. In this situation it is important for the grower how the consumer looks at the sustainability of cultivation methods. The enormous boom in system development in the Netherlands has come to a standstill. This enables us to look back to see if there are differences between the former basic assumptions of a “safe, sustainable and competitive” horticultural sector and the commercial application of hydroponic systems. It became clear that many growers choose a certain system for economic reasons. Factors such as low investment, clean restart, labour input are more important than the environment, low annual costs, reuse of materials and substrate. In former years it was said that all circulating nutrient solution had to be disinfected and sterilised to avoid the risk of rapid dispersal of soil-borne pathogens. Now, it is said that the microflora present in the circulating nutrient solution plays an important role in suppressing of root diseases. In that case it becomes more important to eliminate pathogens in such a way that the microflora keeps alive. It has to be determined whether active methods (heat treatment, ozone, UV) can play this role or whether a passive method such as slow sand filtration, which eliminates pathogens group specific, has better prospects. In this paper the commercial application of hydroponic systems will be discussed in relation to the role the natural microflora may have, to suppress soil-borne diseases in the nutrient solution