Transport and Fate of Indicator Microorganisms Under Nutrient Management Plan Conditions

Irrigation water consisting of various combinations of dairy lagoon water and well water was applied to field sites to meet the evapotranspiration and nutrient requirements of several crops. The subsurface transport and survival of indicator microorganisms (total E. coli, fecal coliforms, Enterococcus, and somatic coliphage) in the lagoon water were subsequently studied under these nutrient management plan (NMP) conditions. When crops were irrigated using sprinklers at a rate that was 25% of the saturated soil conductivity, little transport of the indicator microorganisms was observed. Survival in the root zone was highly dependent on the microorganism type, with high survival rates for Enterococcus and much lower survival rates for total E. coli, fecal coliforms, and somatic coliphage. Additional NMP experiments were conducted in the field using furrow and drip irrigation systems, and complementary laboratory column transport experiments were also initiated using repacked and undisturbed field soil. These experimental studies and corresponding numerical modeling demonstrate the potential importance of irrigation regime, soil matrix, and soil structure on microorganism transport and survival. A preliminary inspection of these results indicate that the transport and survival of indicator microorganisms were minimized when irrigation water was uniformly applied to the field biweekly at rates that are lower than the saturated conductivity of the soil.