Making Manure-Borne Pathogens Stay
Put By Sharon
October 22, 2002
By filtering out pathogens in manure, grass buffer strips may be
a useful tool to prevent these organisms from washing into surface water from
farmland runoff, Agricultural Research
Service scientists report.
Microbiologist Daniel R. Shelton and his colleagues at the ARS
Animal Waste Pathogen
Laboratory in Beltsville, Md., are conducting a study in collaboration with
University of Maryland scientist Adel
Shirmohammadi to determine how effectively grass buffer strips filter out
Shelton's group constructed oddly slanted hills to simulate
different topographies bordering farm areas. The scientists planted grass
strips on two 20-foot-long, slanted slopes of a wedge-shaped, aboveground
mound. One slope had a clay loam soil, while another was covered with sandy
loam. Various indigenous grasses were planted on each soil type to test the
filtering effect. Bare slopes devoid of vegetation were used as controls.
The researchers applied fresh dairy-barn manure along the top of
the slopes, then used overhead sprinklers to simulate rainfall. Collection
tubes were placed at various points on the slopes to funnel samples of runoff
water to be analyzed for bacteria content.
Runoff from the bare clay loam slope contained virtually all of
the pathogens present in the manure. Sandy loam soil fared better: 75 percent
of the pathogens remained in the sandy loam slopes. Sand enables water and
microbes to move into the soil more quickly, rather than run off the surface.
By contrast, vegetated slopes held on to practically all of the
pathogens, leaving none in the runoff water from the sandy loam soil, and only
0.6 percent in the runoff water from the clay loam soil. Pathogens that remain
in the soil either become food for other soil organisms, or they settle into an
area between soil layers that doesn't support life.
A more detailed story appears in the
October 2002 issue of
Agricultural Research magazine.
ARS is the chief scientific research agency of the
U.S. Department of Agriculture.