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Nitrification Inhibition in Soil: II. Evaluation of Anhydrous Ammonia-Potassium Azide Solutions in Eastern Washington¹

ABSTRACT

The effectiveness of potassium azide (KN₃) as a nitrification inhibitor for field-applied anhydrous NH₃ was evaluated on a Naff silt loam in the winter wheat (Triticum aestivum L.) area of eastern Washington. Formulations of KN₃ in liquid NH₃ of 0, 2, and 6% (w/w) were applied to fallow soil in August 1969 at a rate of 112 kg N/ha (81-cm spacing) with a special field applicator. The 2% formulation was also applied at a rate of 224 kg N/ha. The NH₃ retention zone was sampled periodically through February 1970 and analyzed for NH₄⁺-N, NO₂^--N, and NO₃^--N. Both levels of KN₃ were effective in reducing the nitrification rate during the early post injection period, but the higher level was more effective at later dates. Two months after application, the amounts of NO₃^--N recovered from the retention zone as percent of total extractable N were 67, 48, and 36 for NH₃ alone, NH₃ + KN₃ (2%), and NH₃ + KN₃ (6%), respectively. Percentage amounts of NO₃^--N decreased with increase in N application rate. Nitrification inhibition due to KN₃ was still evident 6 months after application, particularly at the high N rate. The inhibitory effect of low soil temperature during the winter months was also apparent. These results indicate that KN₃ formulated with anhydrous NH₃ was an effective nitrification inhibitor for this N source.

¹ Contribution from the Soil & Water Conserv. Res. Div., ARS, USDA, cooperating with the Washington State Univ. Agr. Exp. Sta., Pullman, Wash., and the Louisianna State Univ. Agr. Exp. Sta., Baton Rouge, La. Presented before Div. S-3, Soil Science Society of America, Tucson, Ariz, Aug. 27, 1970. Scientific Paper 3576, Washington Agr. Exp. Sta.

² USDA, ARS, SWC, Pullman, Wash. 99163.

³ USDA, ARS, SWC, Baton Rouge, La.

Received for publication January 18, 1971. Accepted for publication March 16, 1971.