1 Department of Agroecology - Climate and Water, Department of Agroecology, Science and Technology, Aarhus University2 Department of Agroecology - Soil Physics and Hydropedology, Department of Agroecology, Science and Technology, Aarhus University3 GEUS, Copenhagen4 Department of Agroecology - Soil Fertility, Department of Agroecology, Science and Technology, Aarhus University5 Miljøkemi og Fysik6 Department of Agroecology - Climate and Water, Department of Agroecology, Science and Technology, Aarhus University7 Department of Agroecology - Soil Fertility, Department of Agroecology, Science and Technology, Aarhus University8 Department of Agroecology - Soil Physics and Hydropedology, Department of Agroecology, Science and Technology, Aarhus University
The spreading of manure on agricultural land is an economic and practical solution for improving soil quality; however, animal manure frequently contains zoonotic pathogenic bacteria, such as certain Eschericia coli, Salmonella spp. and Campylobacter spp. The present experiment was conducted as a large multidisciplinary project. Pig manure with a natural content of Tetracycline resistant bacteria and fecal indicator organisms was followed in soil columns and a field scale experiment. In the field experiment pig manure was injected into agricultural soil. The distribution and survival of natural occurring indicator bacteria around a manure slurry slit in the soil was followed. During a period of two months, sections of soils with different distance to the manure string were assayed to obtain information on survival and spread of bacteriophage, faecal indicators (Enterococci, Bacterioides, E. coli) and Tetracycline resistant bacteria. The die-off of the different organisms was quantified showing an extended survival close to the manure string. Genomic DNA from 400 Tetracycline resistant bacteria was isolated and their phylogenetic relationship was established using BOX PCR showing that the main Tetracycline resistant bacterial species is E. coli. Drainage water from the field sites were collected weekly from one year prior to manure application, where no Tetracycline resistant bacteria were detected. For a period of 11 months following the first manure application, drainage water was sampled proportional to the flow and collected weekly. Selected storm events were intensively monitored by the collection of subsamples for every 2 mm of drainage runoff, using a refrigerated ISCO sampler. Drainage samples were tested for Tetracyckline resistant bacteria and fecal indicators. The highest concentration was found in the first drainage sample following manure application; however a fast decrease in cell numbers in the following drainage samples was seen. For the Tetracyckline resistant bacteria concentrations up to approximately 100 CFU ml-1 was detected. In conclusion, the survival and environmental spread of indicator organisms show that the upper soil and drainage water are impacted by the microorganisms natural originating from pig manure under natural conditions.