A Survey of the Physical, Chemical and Microbial Load In Nursery Irrigation Water

The objective was to analyze physical, chemical and biological water quality in horticulture irrigation systems, from a survey of 24 ornamental plant nurseries in the U.S. (“Locations”).  Within each Location, water was collected from up to five points (“Sample Types”) which included “Source” from municipal or well supplies, “Tanks” from enclosed storage containers, “Subirrigation” from water applied to crops in ebb and flood systems, “Furthest Outlet” which were irrigation emitters most distant from the Source, and ‘Catchment Basins’ from open outdoor retention areas.  On average, Source water had the highest physical and microbial water quality of the Sample Types, with the highest UV light transmission (85%), lowest total suspended solids (3.1 mg·L^-1), and lowest microbial density of aerobic bacteria (1108 colony forming units [CFU]·mL^-1).  Average quality of recirculated water from Subirrigation or Catchment Basins did not meet recommended levels for horticultural irrigation water, in terms of UV transmission (68 to 72% compared with recommended 75%), microbial density (>100,000 CFU·mL^-1 compared with recommended <10,000 CFU·mL^-1), and chemical oxygen demand (48.2 to 61.3 mg·L^-1 compared with recommended <30 mg·L^-1).  Irrigation water stored in Tanks or applied at Furthest Outlets had lower physical and biological quality than Source water, and microbial density did not meet recommended quality standards.  Compared with a published clogging index for small irrigation emitters, microbial density was a greater risk in recycled sources than physical and chemical parameters, indicating more effective  microbial water treatment is needed when recirculating water.