Bacteria from manure may get into crops

8 Jul 2009 Unit: Plant Research International Bacteria in manure that are harmful to humans may reproduce around the roots of plants and get into the groundwater. This has been demonstrated by Dr. A.V. Semenov, researcher at the chair group Biological Farming Systems, in a recently published article in the scientific journal ‘Applied and Environmental Microbiology’. When manure is ploughed down or injected into the soil – methods used to reduce the emission of ammonia – bacteria survive longer than when the manure is applied on the soil surface without incorporation. Salmonella bacteria that are mixed into the topsoil layer via manure can still be traced 66 days after application down to a depth of ten centimetres. E. coli survives about fifty days in the topsoil layer. This has been found in laboratory tests where the health risks of soil treatment with manure infested with Salmonella and E. coli have been investigated. The survival period is shorter in case of surface application of slurry (manure mixed with urine) but larger amounts of bacteria penetrate into deeper soil layers. Particularly injection of slurry into the soil, however, was found to increase the spreading of the pathogenic bacteria into deeper soil layers. The experiments have been repeated on soil on which lettuce was grown. Little difference was found between the use of slurry or ‘solid’ manure. Both cases showed a distinct increase in the amount of cells of the pathogens near the lettuce roots. This indicates that larger amounts of pathogens are to be expected in the presence of lettuce, also deeper in the soil treated with infested manure. It may be concluded that risks associated with the presence of human pathogens in manure depend on type of manure and method of application. A risk model, based on these data, has been prepared which can be used to minimise the chance of possible infestations with human pathogens via manure.   This research, financed by the STW Technology Foundation, has been set up to identify the health risks of the use of fresh manure on crops for human consumption. Download: Percolation and Survival of Escherichia coli O157:H7 and Salmonella enterica Serovar Typhimurium in Soil Amended with Contaminated Dairy Manure or Slurry (pdf)

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