Concern about microbial contamination of ground water from foraging dairy cows has increased as spray irrigation practices in New Zealand have increased over the years. Bacteria capable of living in both animals and humans are commonly found in cow manure. Addressing the lack of research on the topic, a team of New Zealand researchers studied the transport of microbes from two spray irrigated dairy pastures into ground water supplies.

The research team, reporting in the May-June 2010Journal of Environmental Quality and published by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, found little to no transport of microbes due to spray irrigation application.

When irrigation applications were increased to simulate irrigation plus heavy rainfall, there was a small increase some forms of bacteria, notably E. coli. But other common bacteria were only detected at very low levels when fresh cow pats where subjected to this treatment. The results of the study indicate a minimal impact of dairy farm pastures on microbial quality of ground water as a result of spray irrigation.

Previous studies of flood irrigation, which apply much more water less efficiently than the spray irrigation systems used in this study, have been shown to cause high levels of ground water contamination. No difference was noticed between two different spray irrigation systems, a traveling irrigator and center pivot. The researchers suggest that converting from flood irrigation to spray irrigation will reduce microbial contamination of ground water and reduce environmental health risks.