Features Applications Swine
Southern soils mitigate manure microbes

September 14, 2010 – That
swine manure sprayed on to fields adds valuable nutrients to the soil is well
known. But what is not known is whether all that manure is bringing harmful
bacteria with it.
September 14, 2010 – That
swine manure sprayed on to fields adds valuable nutrients to the soil is well
known. But what is not known is whether all that manure is bringing harmful
bacteria with it.

A new study looks at the
levels of nutrients and bacteria in soils of fields that have been sprayed with
manure for fifteen years or more. The research team, composed of scientists
from the USDA-ARS Crop Science Research Laboratory at Mississippi State, tested
soils inside and outside fields of five farms on twenty different soils types.
Their results are reported in the September-October 2010 Journal of
Environmental Quality, published by the American Society of Agronomy, the Crop
Science Society of America, and the Soil Science Society of America.

Manure sprayed fields were
found to contain higher concentrations of several types of bacteria. These
include measurements of total bacteria, fecal bacteria, Staphylococcus (a
common bacteria living inside animals and a potential human pathogen) and
Clostridium (common gut inhabitants and potential pathogens).

Two other types of
bacteria that are potential pathogens, E.Coli and Enterococcus, showed no
differences in between sprayed or non-sprayed fields. One type of bacteria,
Listeria, was found in higher concentrations outside, rather than inside, the
fields. Two gastrointestinal pathogens, Campylobacter and Salmonella, could not
be cultured in any significant amount from the fields, although DNA testing did
detect some bacteria, though there were no differences between sprayed and
non-sprayed fields.

The investigators also
analyzed public health data from three public health districts with similar
land areas, populations, and agricultural bases, but with varying numbers of
swine confined animal feeding operations (CAFOs), a typical source of swine
manure. Their analysis of annual reports of illnesses caused by Campylobacter
and Salmonella from 1993 through 2008 showed no relationship between reported
cases of these human illnesses and swine CAFO numbers.

The research team also
tested soils for nutrient levels. These tests showed higher pH and higher
levels of phosphorus, potassium, magnesium, sodium, copper, and zinc inside
spray fields compared to outside. These results were consistent with what was
expected for spray fields after long-term use. Finding differences between the
same soil types inside and outside confirmed that outside soils had not been
contaminated with manure and would provide good comparisons of bacteria.

“Finding low levels of
pathogens outside spray fields is not surprising, because these bacteria are
known to infect a wide range of wild and domestic birds and animals,” said team
leader Mike McLaughlin.

“Finding similar low
levels inside and outside the spray fields suggests that the low levels of
pathogens in [manure] are further diluted in spray fields and either do not
survive in soil or survive at low levels below cultural detection limits,”
added team microbiologist John Brooks.

This first report on spray
field bacteria in the region suggests that manure nutrient management plans
have been effective for nutrients and for bacterial pathogens. Future research
will focus on enhanced resolution of pathogen levels in manure and soils, on
pathogen survival and transport in soil and on plants, and on practical
solutions to further reduce or eliminate risks from these pathogens

The full article is
available for no charge for 30 days following the date of this summary. View
the abstract at https://www.agronomy.org/publications/jeq/abstracts/39/5/1829.