Evaluation of the Survivability of Fecal Coliform in Soil after Winter Application of Dairy Slurry on a Transitional-organic, Grazing Based Dairy. 1 2 3 4

ABSTRACT. The lifespan of soil bacteria can affect the potential of bacterial transport to surface waters and therefore influence policy decisions for land application of manure. The persistence of fecal coliform and Escherichia coli in the top 3.8 cm of soil was evaluated after spreading dairy slurry during winter months on a transitional-organic, grazing based dairy in southwestern Washington. Two applications of dairy slurry were applied, once in December 2003 and again in January 2004, by broadcast manure applicator to pastureland in an area approximately 3 to 4 times greater than routine farm practice. Soil cores were taken from plots in a setback zone or slurry application area using a 6 cm diameter soil probe at a depth of 3.8 cm and included surface material. Background soil samples were taken prior to slurry applications to establish baseline levels of fecal coliform and E. coli. Soil samples for determination of fecal bacteria were taken daily for 7 and 4 d, respectively, after the December and January slurry applications and on a weekly basis until bacteria levels were near background concentrations. Bacteria counts increased in the soil with slurry application and a subsequent increase in fecal coliform numbers occurred two to three days after slurry application. Fecal coliform numbers declined over 3 log(10) CFU per 100 g of soil within 52 days after the December slurry application and 42 days after the January slurry application. Fecal coliform bacteria had a relatively short lifespan after application on grassland during the winter months