Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 1, 2001
Publication Date: April 1, 2002
Interpretive Summary: We measured the rate of survival of potential pathogens, including E. coli O157:H7, in various agricultural management systems. We looked at manure application as well as application of pathogens in contaminated runoff or irrigation water to unplanted soil as well as to soil planted with various cover crops. We looked at three diverse soil types and found very little difference based on soil type alone. Cover crops were a different story: rye, the only grass cover crop used, enhanced survival of the inoculated O157:H7 strain at least 100%. In simpler terms, O157:H7 survived for about 30 days in soil alone, but for about 60 days when the soil was planted with rye. Soil planted with alfalfa, hairy vetch or crimson clover showed only one instance where O157:H7 survival was enhanced, also to about 60 days for alfalfa in one of the soils. In addition, we looked at total coliforms which included O157:H7, as well as other potential pathogens. We found that tlevels decreased to background in inoculated treatments quicker than in those that were not inoculated, indicating that native coliforms existed in our samples and that they were longer-lived than those we introduced. In any case, the most significant risk of exposure from potential pathogens in soil, regardless of source or crop type, exists for 3 months or more after application. Subsequent land use, including planting or harvesting crops or use of the land for grazing should take this figure under advisement to prevent the risk of contamination.
Technical Abstract: The influence of manure application and cover crops on E. coli O157:H7 and total coliform survival was tested in three soils. Manure from a dairy operation was inoculated with strain B6914 of E. coli O157:H7 and applied to intact soil-core microcosms at six tons per acre for fallow soil and rye-planted treatments. Microcosms planted to alfalfa, crimson clover and hairy vetch received only O157:H7 with no manure, and a subset of fallow soil, rye and alfalfa microcosms received no inoculum. Leaching and runoff losses did not occur in the microcosms because they were maintained at a soil water-holding capacity of 60% with periodic irrigation. In fallow soil with or without added manure, O157:H7 survived to about 30 days. Rye roots with manure enhanced O157:H7 survival to 55-56 days in all soils. Alfalfa rhizospheres in the silt loam soil enhanced survival to 64 days, but there was no enhanced survival from alfalfa in the other soils, or from clover or rvetch in any of the soils. Total coliforms, which include species native t plants, declined significantly within two months for inoculated treatments, but often decreased more slowly in uninoculated treatments. The predicted survival of total coliforms declined in fallow soil 74-86 days with manure B6914, 25-69 days with only B6914, 64-104 days with only manure and 45-232 days with no amendments. Total coliforms persistence was often lower when manure or B6914 was applied or when there was a rhizosphere present. In summary, E. coli O157:H7 applied with manure or through irrigation or runof survives for about one month in fallow soil and up to two months in the presence of cover crops. Total coliforms in manured or inoculated treatment were at high levels for about three months. A longer period would then be appropriate for grazing or when harvesting crops after manure application.