Nitrification Kinetics and Nitrous Oxide Emissions Following Co-Application of Urea Ammonium-Nitrate and Nitrapyrin (Instinct) in Long-Term Tillage Systems.

Understanding the nitrification kinetics of applied nitrogen (N) fertilizers in long-term tillage systems can help management decisions to improve N use efficiency, and reduce nitrous oxide (N₂O) emissions during crop production.  Field studies were conducted in 2013 and 2014 near West Lafayette, IN, to determine rate of nitrification and N₂O emissions in long-term no-till (NT), strip-till (ST), chisel (CP), and moldboard plow (MP) systems following urea ammonium-nitrate (UAN) application, with and without nitrapyrin (Instinct).  Soil samples were taken weekly to the 30cm depth for up 10 weeks, analyzed for ammonium- and nitrate-N concentrations, and appropriate kinetic model fitted to the data.  Nitrous oxide emission was measured twice weekly for 8 weeks, and thereafter weekly for additional 12 weeks, using the static vented chamber procedure.  Nitrification was best described by 1^st order kinetics with and without nitrapyrin, and regardless of tillage system.  Without nitrapyrin, N₂O emission was greatest under CP and MP, and was smallest for NT.  Across tillage systems, N₂O emission was reduced by nearly 20% with Instinct application, and magnitude of emission reduction was generally in the order: MP>ST>NT>CP.