Transport of bacteria from manure and protection of water resources

Survival and transport of pathogens from manure in the environment depend on a number of complex phenomena. An important question is how the properties of such a complex environment as the soil-manure medium impact the persistence of bacteria within the vadose zone. First, manure can change the partitioning of precipitation water between infiltration (enhanced by solid manure) and surface runoff (stimulated by liquid manure). Components of manure, such as straw and coarse organic matter, can strain and filter micro-organisms from the transporting water. After infiltrating the soil, the retention of bacteria depends on the physical configuration of soil, the soil chemistry, and the properties of the microbial cells. Transport of bacteria in soils obeys the general laws pertinent to macropore flow and the interaction between particles and surfaces of variable charge. Detailed characterisation of the variable properties within the structured soil profile is a difficult task. Application of manure can result in significant changes in the physical and electrochemical properties of the soils and microbial cells. Such changes can affect the interaction between bacterial cells and soils in several ways: increase filtration, modify the kinetics of the physico-chemical interactions between charged surfaces, and alter the competition for retention sites between suspended soluble and particulate compounds. Survival of faecal bacteria is affected by the physical and chemical conditions existing prior to manure application as well as by conditions imposed by mixing soil and manure. Competitive interaction with native soil bacteria, in the soil-manure mixtures, is an important aspect governing survival of introduced organisms. (C) 2003 Elsevier B.V. All rights reserved.