LAUSR

Colorimetry is a conventional method for the determination of soil nitrification rates, and it demands pretreatments and chemical reagents, which make it time and cost consuming. Fourier transform infrared attenuated total reflectance spectroscopy (FTIR-ATR) as a simple and fast method was employed in this study, and the feasibility of determination of nitrate contents by FTIR-ATR under different soil conditions was investigated. It was found that the second-order derivatives of nitrate characteristic bands (1270–1320 cm−1) were proportional to nitrate contents, and an excellent correlation coefficient of 0.9751 was obtained, indicating that FTIR-ATR combined with second-order derivatives could be well used for quantification of nitrate. The nitrate-N contents determined by FTIR-ATR and colorimetry increased with increasing incubation time under different treatments including soil temperature, moisture, pH and nitrogen application rate; in most cases, the values obtained by FTIR-ATR were slightly higher than those obtained by colorimetry after 50% incubation. The abiotic immobilization of nitrate and Fe interference in the colorimetric procedure might contribute to this difference. Thus, FTIR-ATR combined with second-order derivatives can be used as an alternative option for fast determination of nitrate under varied conditions in paddy soils.