Agriculture Reference
In-Depth Information
sheep, pig, and cattle feces; ovine stomach content; abattoir houses; sewage treatment
plants; or commercial creameries (Van Renterghem and others 1991; Dowe and others
1997; Avery and others 2004, 2005). The persistence of the pathogens varied among
different wastes and even the wastes of similar origins, highlighting the variable nature
of organic wastes.
Rates and Ways for Manure Application
Manure is abundant with microorganisms and nutrients. After incorporation into soil,
the introduced nutrients become available for existing soil microorganisms to grow.
The inhibitory effect of soil microorganisms on manure-borne pathogens was reported
by a few studies. Lazarovits (2001) demonstrated that organic manure application to
soil increased the overall populations of soil microorganisms by up to thousandfold
and reduced populations of plant pathogens. The intensive application of manure to
soil (e.g., 1 part manure to 10 parts soil vs. 1 : 25, 1 : 50, or 1 : 100) generally results
in greater inactivation of
E. coli
O157:H7 at both 15 and 21 °C but not that much at
5 ° C (Jiang and others 2002 ).
The application methods used for animal wastes can affect the persistence of
manure-borne pathogens. Hutchison and others (2004) have shown that the popula-
tions of
Salmonella
,
L. monocytogenes
,
Campylobacter,
and
E. coli
O157:H7 declined
signifi cantly slower in samples with animal waste incorporated into the soil immedi-
ately than in samples with the waste left on the soil surface. In contrast, another study
reported that
Salmonella
survival was signifi cantly longer when the hog slurry was
surface-spread as compared with results from thoroughly mixed manure treatment
(Holley and others 2006). Results from Gagliardi and Karns (2000) indicated that
E.
coli
O157:H7 can travel below the top layers of soil for more than 2 months after
manure application to a soil core, regardless of disturbed (tilled) or intact (untilled)
soil core. In considering the extended survival of pathogens in manure- amended soil,
fresh animal manure should not be applied to the land before adequate treatments are
applied to reduce the bacterial populations signifi cantly.
The Length of Time Pathogens Persisted in Manure-Amended Soil
Due to the declining nature of enteric pathogens in soil, initial bacterial load is a key
factor to predict the length of pathogen persistence. Fenlon and others (2000) applied
cattle slurry inoculated with 30 CFU
E. coli
O157:H7/100 ml to arable and grass plots
on a clay loam soil. They could detect
E. coli
O157:H7 only in the soil and on the grass
during the fi rst week after application. In contrast,
E. coli
O157:H7 with very high
application rates survived for at least 130 days on manure-amended soil cores with a
grass cover at 18 °C (Maule 1999). Under fi eld conditions,
E. coli
O157:H7,
Salmonella
,
and
Campylobacter
persisted for up to 1 month, and
L. monocytogenes
for more than
1 month in both sandy arable and clay loam grassland soil fertilized with livestock
manure. Survival times for
Salmonella
spp. were up to 300 days in soils spread with
cattle slurry and 259 days for soils amended with animal feces (Jones 1986).
Survival of Naturally Occurring Pathogens in Manure-Amended Soil
Most pathogen survival studies used bacterial cultures cultivated in laboratory media
for soil inoculation. Due to the sudden change of environment, the behavior of those