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Nitrification Inhibition in Soil: I. A Comparison of 2-Chloro-6-(trichloromethyl)pyridine and Potassium Azide Formulated with Anhydrous Ammonia¹

ABSTRACT

The relative effectiveness of 2-chloro-6-(trichloromethyl) pyridine and potassium azide as nitrification inhibitors, formulated and applied to soil with anhydrous NH₃, was compared in laboratory and growth chamber experiments. At an inhibitor level of 10 ppm, and after 14 days, NH₄⁺ concentrations 0 to 2.5 cm from the point of release of NH₃, NH₃ + KN₃, and NH₃ + N-Serve were 695, 810, and 887 ppm N respectively, while after 56 days corresponding values had decreased to 129, 316, and 609 ppm N. After 14 and 56 days of incubation in unplanted pots, KN₃ was 60 and 40%, respectively, as effective as N-Serve in suppressing nitrification. N-Serve was more effective than KN₃ during longer incubation periods because of its greater residual activity.

In general, yields of ryegrass (Lolium sp.) and cotton forage (Gossypium hirsutum L.) followed the order of NH₃ = NH₃ + KN₃ > NH₃ + N-Serve. The greater residual activity of N-Serve compared with KN₃ and the absence of root development in the center of the NH₃ + N-Serve retention zone, as well as the stunted and flaccid appearance of roots, was indicative of potential phytotoxicity of N-Serve in this particular mode of application.

¹ Contribution from the Southern Branch, Soil & Water Conserv. Res. Div., ARS, USDA, cooperating with the Louisiana State Univ. Agr. Exp. Sta., Baton Rouge, La. Presented before Div. S-3, Soil Science Society of America, Tucson, Ariz., Aug. 27, 1970.

² Microbiologist, Soil Scientist, and Chemist, respectively, USDA, ARS, SWC, Baton Rouge, La. 70803.

Received for publication November 2, 1970. Accepted for publication January 30, 1971.