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Effect of 2-Chloro-6-(Trichloromethyl)Pyridine and its Hydrolysis Product 6-Chloropicolinic Acid on Soil Microorganisms¹

ABSTRACT

The influence of nitrapyrin [2-chloro-6-(trichloromethyl)pyridine] and 6-chloropicolinic acid on soil microorganisms was studied in a series of pure culture and soil incubation tests with concentrations of chemicals ranging from 0 to 1,000 ppm.

Pure culture studies with 59 species of bacteria, fungi, and actinomycetes showed no inhibition of growth by nitrapyrin at concentrations < 10 ppm. Two species were inhibited between 10 and 100 ppm, 38 between 100 and 1,000, and 10 species showed no growth reduction at the highest concentration of 1,000 ppm nitrapyrin. Of 45 species studied, 6-chloropicolinic acid inhibited one species at concentrations < 1,000 ppm. Forty-one species did not show growth reduction in the presence of 1,000 ppm of this chemical.

Population counts of bacteria and fungi in seven soils incubated in the presence of nitrapyrin or 6-chloropicolinic acid at concentrations of 1,000 ppm snowed little inhibitory influence. No consistent trend in terms of stimulation or suppression of carbon dioxide formation during soil respiration was evident for either chemical at 1,000 ppm.

6-Chloropicolinic acid at 1,000 ppm had little if any effect on soil mineralization, variable effect on ammonium oxidation, and little or no effect on nitrite oxidation. Suppression of ammonium oxidation by 6-chloropicolinic acid varies with soils, and appears most likely to be observed at concentrations of 100 ppm or more.

Key Words: N-SERVE nutrient stabilizer • nitrapyrin • nitrification inhibition • microbial inhibition

¹ Contribution from Ag-Organics Research, The Dow Chemical Company, Walnut Creek, CA 94598.

² Research Specialist, Senior Research Biologist, Microbiologist, Research Technician, Research Specialist, Director Ag-Organics Research, respectively.

Received for publication January 29, 1974.