Leaching of Escherichia coli O157 : H7 in diverse soils under various agricultural management practices

Application of animal manures to soil as crop fertilizers is an important m eans for recycling the nitrogen and phosphorus which the manures contain, A nimal manures also contain bacteria, including many types of pathogens. Man ure pathogen levels depend on the source animal, the animal's state of heal th, and how the manure was stored or treated before use. Rainfall may resul t in pathogen spread into soil by runoff from stored or unincorporated manu re or by leaching through the soil profile, Steady rainfall consisting of 1 6.5 mm h(-1) was applied to 100-mm disturbed soil cores that were treated,v ith manure and inoculated with Escherichia coli O157:H7 strain B6914, The l evel of B6914 in leachate was near the inoculum level each hour for 8 h, as was the level of B6914 at several soil depths after 24 h, indicating that there was a high rate of growth. Bacterial movement through three different types of soil was then compared by using disturbed (tilled) and intact (no -till) soil cores and less intense rainfall consisting of 25.4 mm on 4 cons ecutive days and then four more times over a 17-day period. Total B6914 lev els exceeded the inoculum levels for all treatments except intact clay loam cores. B6914 levels in daily leachate samples decreased sharply with time, although the levels were more constant when intact sandy loam cores were u sed. The presence of manure often increased total B6914 leachate and soil l evels in intact cores but had the opposite effect on disturbed soil cores. Ammonia and nitrate levels correlated with B6914 and total coliform levels in leachate. We concluded that tillage practice, soil type, and method of p athogen delivery affect but do not prevent vertical E. coli O157:H7 and col iform transport in soil and that soluble nitrogen may enhance transport.