Effect of Nitrapyrin on Nitrogen Transformations in Soil Treated with Liquid Swine Manure 1

Applications of animal manure to soil result in nitrification of applied NH + 4 — N and eventual loss of applied N through leaching and/or denitrification processes. In theory, one way to reduce the leaching and/or denitrification losses is through the use of a nitrification inhibitor. Therefore, a field experiment was conducted during the summer of 1979 to determine the effects of nitrapyrin [2‐chloro‐6(trichloromethyl)pyridine] on N transformations occurring within a band of soil‐applied liquid swine manure (LSM). Liquid swine manure (60 t ha −1 ) containing 0 or 50 mg nitrapyrin active ingredient/liter was injected into Chalmers silty clay loam (fine‐silty, mixed, mesic Typic Haplaquoll). The LSM application provided about 156 kg ha −1 of plant‐available N and nitrapyrin addition rates were 0 and 3 kg ha. −1 Periodically during the 24‐week experiment soil samples were obtained from the LSM application band and analyzed for NH + 4 — and NO − 3 — N. From 40 to 50% of added organic N was mineralized in the LSM application bands. Ammonium present in bands of LSM not treated with nitrapyrin was oxidized to nitrate within 7 weeks after application. Addition of nitrapyrin to the LSM delayed nitrification for up to 15 weeks after application. Essentially all of the inorganic N had been lost from the LSM that did not receive nitrapyrin by the 11th week after application, probably as a result of sequential nitrification and denitrification. However, in the nitrapyrin‐treated LSM high amounts of inorganic N remained during the entire experiment and greater than 50% of the inorganic N initially present was recovered after 24 weeks. These findings suggest that nitrapyrin was effective in inhibiting nitrification in manure‐treated soil and addition of the inhibitor reduced N losses following manure application.