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 65EFFECT OF ERADICANTS ON THE MICROBIOLOGICAL 
PROPERTIES OF NURSERY SOILS' 
D. J. PERSIDSKY and S. A. WILDE2 
 Current nursery practice employs a large number of toxic compounds, or eradicants,
for the control of destructive insects, parasitic fungi, and noxious weeds.
The application of these chemicals is not without adverse influence upon
the beneficial soil organisms, state of soil fertility, and the growth of
nursery stock. This study aimed to detect the effects of commonly used eradicants
upon microbiological characteristics of soils which serve as indicators of
unimpaired soil productive capacity. 
 The trials were conducted in greenhouse cultures with outwash siliceous
sand possessing a reaction of about pH 5.0, exchange capacity of 1.9 m.e.
per 100 g., and 0.7 per cent of organic matter. The biocides studied included
chlordane, benzene hexachloride, calomel, thiosan, aluminum sulfate, formaldehyde,
allyl alcohol, and Stoddard solvent. These were applied at the rates slightly
exceeding those used in current nursery practice. Such treatments were justified
in view of the local concentration of chemicals resulting from their uneven
distribution under conditions of actual soil management. The following microbiological
characteristics were investigated: the relative ' density of micropopulation,
rate of cellulose and protein decomposition, nitrification capacity, rate
of carbon dioxide evolution, growth of excised roots under the influence
of volatile substances emitted by the soil, growth responses of Aspergillus
niger, and the development of mycorrhizal short roots. Monterey pine, Pinus
radiata, was used as a test plant and a carrier of symbiotic organisms. The
extreme poverty of the soil, the use of enclosed containers, and fluctuating
content of soil moisture, unavoidable in watering by hand, all undoubtedly
contributed to the adverse effects of biocides. 
 The number of microorganisms present in untreated and biocide-treated soils
was determined on the basis of colonies develo'ped on the molecular membrane
filters (Clark et al., 1951). 
1 Contribution from the Soils Department, Wisconsin Agricultural Experiment
Station, Madison, Wisconsin. This study was carried out with the assistance
of a 
grant from the Research Program on the U.S.S.R. (East European Fund, Inc.,
New 
York City). Publication approved by the Director of the Wisconsin Agricultural
Experiment Station. 
2 Research Associate and Professor of Soils, respectively.