Onions in the research plot have been irrigated with water inoculated with E. coli, some to extreme highs, Waite-Cusic said. The E. coli was applied during the last irrigation. In the sample of onions taken from the plots, the majority of them did not test positive for the bacteria, Waite-Cusic said.
In one of the latest samplings, onions were harvested one afternoon, put in bags and tested the next morning. Only 16 out of 150 onions tested positive for E. coli, Waite-Cusic said, and this from rows where the irrigation water had been artificially inoculated with 100,000 colony-forming units of generic E. coli for 100 milliliters of water.
“The soil does a good job of filtering,” experiment station superintendent Clint Shock said.
Testing showed that there was less E. coli as the water moved from the furrow or drop tape through the soil to the onion bulb.