Keywords: Recirculation, hydroponics, recycled-water, ultra-violet radiation, slow sand filtration, ozonation, chlorination, pasteurisation, fungicides, disease control, Phytophthora, Pythium, Fusarium.
The increasing pressure on the availability of water for horticultural production world-wide has led to an increasing interest in methods of water conservation. The collection and recycling of used irrigation water or recirculation is one very effective method of reducing overall water consumption whilst at the same time avoiding ground water pollution from the leaching and disposal of nutrient-rich used water. One of the main difficulties with this technique is the high risk of rapidly spreading plant disease from a few isolated plants to entire nurseries via the recycled water. However, this disease threat is readily controlled by the use of water treatments that remove or kill pathogen propagules before the used water is recirculated. A number of different techniques are effective for this including ultra-violet radiation, slow sand filtration, use of chemicals such as ozone or chlorine and pasteurisation. In addition less proven technologies with promise for future, more sustainable, systems involve the introduction of microbial inoculants and even the manipulation of the natural disease suppression sometimes seen in recirculating systems. Due to the diverse nature of commercial horticultural production, the selection of an appropriate water treatment system for an individual nursery is very much a case-by-case decision based on water types, quantity and quality to be treated, space, work-force skill and capital available. Under the broad headings of heat-, chemical-, ultra-violet radiation-, filtration- and microbial inoculation treatments, this review considers the efficacy and suitability of the various treatments for recirculating water in both protected production or ‘closed’ systems and the more ‘open’ systems used for outdoor cropping of hardy plants.
Tim Pettitt, PhD., Horticulture Research International, Wellesbourne, Warwick, CV35 9EF, UK.
20 Pages, 3 Figures, 2 Tables, 74 References.