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Abstract
Dennis, S.O., T. Tsegaye, R.E. Harrison
and S.A.
Aburime. 2007. The fate of
entomopathogenic nematodes in nursery soils: implications on water quality.
JEMREST 3:237-252.
DOI: 10.4029/2007jemrest3no112
Entomopathogenic
Nematodes (ENs) are potential bio-control agents for soil-borne insects like
the Japanese beetle grubs. They could serve as alternatives to chemical
pesticides because of their negligible environmental hazard. Knowledge of
their fate in soils is important for their release into the soil environment.
The study seeks to examine the fate of Steinernema carpocapsae TN 18
strain, an entomopathogenic nematodes, in nursery soil at the column scale.
Two field soils were used to pack the columns; Decatur
silt loam (Rhodic Paleudult soil) and Waynesboro
sandy clay loam (clayey, kaolinitic, thermic, Typic Paleudult). These soils
had history of nursery crop production for at least ten years. A Darcian flux
(0.8 cm hr-1)
was used to facilitate movement (leaching) of the nematodes in disturbed soil
columns. Bromide concentration of 0.8 M, non-toxic to the nematodes was added
to the soil surface as a conservative tracer. Leachate samples were assayed
for nematodes and bromide concentrations. Bromide and nematode breakthrough
curves, as well as two adsorption models, were used to provide evidence of
entomopathogenic nematodes’ fate and transport processes in the soils.
Four kinetic models (first-order, second-order, Elovich equation, modified
Freundlich models) were used to test the time required for the ENs to reach
equilibrium state. The Elovich and the modified Freundlich kinetic models
tended to be superior to the other two kinetic models because of their
relatively higher R2 value of 0.84 and 0.86
respectively. However, none of them adequately described the kinetics of nematodes
sorption in our study. The kinetic study showed that equilibrium sorption of
the nematodes was reached after four hours. The amount of ENs sorbed to soils
was tested with two adsorption isotherms (Freundlich and Langmuir). A good
fit of the data was obtained with the Freundlich isotherm while the Langmuir
isotherm exhibited a non-linear fit. Relatively, the bromide and
nematodes’ BTCs indicate that the ENs movement was retarded in both
field soils, suggesting that sorption might be a key factor in determining
nematodes transport through soil. A mass balance ranging from 97-98% was
achieved for the applied bromide; while 99% of the nematodes remained within
the soil matrix.
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