Microbial transport from dairying under two spray-irrigation systems in Canterbury, New Zealand.

Transport through the soil and vadose zone to groundwater of Escherichia coli, fecal coliforms, and Campylobacter spp. from pasturing of dairy cows was studied on two working dairy farms under a traveling irrigator and a center pivot system. Leachate was collected from 1.5 m depth using a large linear lysimeter over a period of 4 yr after rainfall or irrigation applied using a traveling irrigator. There was little transport of fecal coliforms or Campylobacter from irrigation applications of 55 mm. There was some transport of fecal coliforms at applications of 80 mm (corresponding to irrigation plus heavy rainfall) but no detectable Campylobacter. When fresh cow pats were placed on half of the lysimeter plots with an 80-mm water application, there was transport of fecal coliforms and Campylobacter, but levels of Campylobacter were low (<or=4 MPN L(-1)). Groundwater at the farm with center pivot spray irrigation was monitored monthly from September 2001 to June 2007, with 60% of samples being collected from downgradient wells. Escherichia coli were detected in 5.4 and 2.8% of samples from upgradient and downgradient wells, respectively, at concentrations of >or=1 cfu 100 mL(-1). Campylobacter was detected in 0.7% of samples over the study period, with equal percentages from up- and downgradient wells. The results indicate minimal impact of dairying at these sites on microbial quality of groundwater as a result of spray irrigation using traveling irrigators at rates of approximately 55 mm every 2 wk or center pivot irrigators at 18 mm every 3 to 4 d.