Horticultural operations are increasingly using recirculating subirrigation systems and runoff water collected in catchment basins to supplement decreasingly available potable water sources for irrigation (Obreza et al., 2010). Irrigation water that is collected for use in catchment basins (capture-and-reuse) or recirculating (ebb and flood) irrigation systems are characterized by elevated levels of physical, chemical, and biological contaminants that result in lower water quality, compared with potable water (Gilbert et al., 1980; Runia , 1994). When irrigating with low quality water, the combined physical, chemical, and microbial variables can result in microirrigation emitter and filter clogging and promote biofilm formation on critical surfaces within the water distribution systems (Bucks et al., 1979; Ravina et al., 1997). A report by Hong and Moorman (2005) compiled research that identified 16 species of Phytophthora (including the plant pathogen Phytophthora ramorum), 26 species of Pythium, 10 viruses, waterborne plant pathogens, and other microorganisms in irrigation water samples collected from nursery and greenhouse operations.
Sanitation technologies are incorporated into horticulture irrigation systems to provide control of pathogens, improve plant health and prevent the development of secondary inoculum or protective overwintering structures (Agrios, 1997). These technologies include filtration, chlorination, copper ionization, ozonation, UV light, use of activated peroxygens, chlorine dioxide, heat, or other technologies to provide disinfestation of irrigation water (van Os, 2009). Water quality variables such as suspended particles, dissolved organic and inorganic molecules, and microbes create a demand on sanitizing agent active ingredients, thereby reducing the efficacy of water treatment technologies for control of microbes, pathogens, and algae (Copes et al., 2004; Ravina et al., 1997; Sutton et al., 2006).
Monitoring of biological, physical, and chemical variables is necessary to ensure water quality is adequate for its intended use. For example, a standard evaluation for health and operational safety at food and beverage processing and recreational swimming facilities monitors biological variables such as counts of aerobic bacteria and fungi to indicate contamination or ineffective treatment [American Public Health Association (APHA), 1995; Maier et al., 2009]. The reduction of bacterial counts from water samples collected before vs. after water treatment is used as a measure of effective control by a sanitizing agent, according to the U.S. Environmental Protection Agency (USEPA, 1999). Physical contaminants from plant debris, peatmoss, sand, and insoluble salts can restrict water flow, create a sanitizing agent demand, reduce UV transmission, and shield target pathogens from contact with a sanitizer (Copes et al., 2004; Gauthier et al., 1999; Pettygrove and Asano, 1985; Pirovanni et al., 2004; Rogers et al., 2003). Chemical aspects of water quality, including pH, total dissolved solids, alkalinity, and nitrogen, can decrease the efficacy of sanitizing treatment to provide pathogen and pest control. High solution pH and reduced forms of nitrogen in organic and inorganic compounds, such as ammonium in water-soluble fertilizers, can reduce the availability of strong oxidizers such as hypochlorous acid (APHA, 1995; Feben and Taras, 1955; Heibling and VanBriessen, 2008; Tanwar et al., 2008).
Surveys have been conducted to assess chemical water quality (Argo et al., 1997) and pathogen presence in ornamental greenhouses and nurseries (Hong and Moorman, 2005). Water quality information is lacking on whether levels of water contaminants such as suspended solids, aerobic bacterial density, and COD meet recommended guidelines. If physical, chemical, and microbial load are outside of recommended guidelines, there is increased risk that treatment technologies will not provide effective control of target pathogens, algae, and biofilm in recirculated irrigation systems.
The objective of this study was to quantify physical, chemical, and microbial load and overall sanitizing demand at key sampling points within irrigation systems, using a field survey approach at multiple greenhouse and nursery locations. These values were compared against published irrigation guidelines for effective sanitation treatment for control of pathogens, algae, and biofilm, and for adequate nutrient management of horticultural crops.
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