Monitoring irrigation water quality in horticulture

The biological quality of water used for horticulture irrigation affects risk of crop losses from waterborne pathogens, algae, and biofilm. Efficacy of treatment technologies such as chlorine used to control biological contaminants in water is affected by other quality parameters including water chemistry, physical particles, and sanitizing agent concentration. The first objective of this research was to determine physical, chemical and biological irrigation quality in horticultural greenhouses and nurseries. The second objective was to determine whether a dehydrated culture media (Petrifilm) was a suitable onsite monitoring tool to quantify colony forming units (cfu) per ml of aerobic bacteria and fungus. The third objective was to determine free chlorine, total chlorine and oxidation reduction potential (ORP) when sodium hypochlorite was added to nutrient solutions that contained different sources of nitrogen. Results from the first objective showed that recirculated irrigation had lower physical and biological irrigation quality than source well or municipal water. Recirculated water had low ultra violet (UV) transmission (68% to 72% compared with recommended 75%) and high concentrations of aerobic bacteria (above the 10,000 cfu˙mL-1 recommended for controlling biofilm clogging of irrigation equipment). For objective 2, the density of aerobic bacteria (cfu˙mL-1) from irrigation water samples estimated on Petrifilm-AC at 3 days was lower than estimates on Reasoner and Goldrich agar (R2A) culture medium by a factor of 2.92. Concentration (cfu˙mL-1) of a single strain culture of Xanthomonas campestris pv. Begoniaceae cultured on Petrifilm-AC were also significantly lower (P<0.05) than counts on R2A culture medium or using a hemocytometer, but was not different from counts on Potato-Dextrose Agar (PDA) culture medium. Zoospores of Phytophthora cactorum did not culture on Petrifilm-YM, whereas PDA and vegetable agar with antibiotics were able to culture Phytophthora. When chlorine from sodium hypochlorite was added at 2.6 mg˙L-1 Cl to nutrient solutions at 100 mg˙L-1 N, there was a rapid decrease of free chlorine to near zero within 2-min, because of complexation of hypochlorous acid with ammonium. Main findings were that improved monitoring and treatment of recirculated water is needed, Petrifilm-AC is a useful onsite monitoring tool for aerobic bacteria in irrigation water, and chlorination efficacy is likely to be affected by interaction with water soluble fertilizer.