In situ evaluation of net nitrification rate in Terra rossa soil using a fourier transform infrared attenuated total reflection15N tracing technique

Nitrification and mineralization of organic nitrogen (N) are important N transformation processes in soil, and mass spectrometry is a suitable technique for tracing changes of15N isotopic species of mineral N and estimating the rates of these processes. However, mass spectrometric methods for tracing N dynamics are costly, time consuming, and require long and laborious preparation procedures. This study investigates midinfrared attenuated total reflection (ATR) spectroscopy as an alternative method for detecting changes in14NO3-N and15NO3-N concentrations. There is a significant shift of the v3 absorption band of nitrate according to N species, namely from the 1275 to 1460 cm-1 region for14NO3 - to the 1240-1425 cm-1 region for15NO3 -. This shift makes it possible to quantify the N isotopes using multivariate calibration methods. Partial least squares regression (PLSR) models with five factors yielded a determination error of 6.7-9.2 mg N L-1 for aqueous solutions and 5.9-7.8 mg N kg-1 (dry soil) for pastes of a Terra rossa soil. These PLSR models were used to monitor the changes of15NO3-N and 14NO3-N content in the same Terra rossa soil during an incubation experiment in which [15NH4]2SO 4 was applied to the soil, allowing the estimation of the contributions of applied N and mineralized N to the net nitrification rate, the potential losses of the applied15NH4-N, and the net mineralization of soil organic N. © 2009 Society for Applied Spectroscopy.