Quantitative analysis of different nitrogen isotope labelled nitrates in paddy soil using mid-infrared attenuated total reflectance spectroscopy

Abstract

Nitrogen isotope labelled technology with mass spectroscopy is commonly used to trace the fate of agricultural N in the environment. However, due to mass spectroscopy's cost, time consumption and long laborious preparation, Fourier transform infrared attenuated total reflection spectroscopy (FTIR-ATR) was employed to detect different isotope labelled nitrates in this study, and the feasibility of this method was investigated in paddy soil. The results showed that the RPD of a partial least squares regression (PLSR) model were 5.69 and 8.15 mg kg⁻¹ for ¹⁴NO₃–N and ¹⁵NO₃–N, respectively, and the RMSEP were 5.60 and 3.91 mg kg⁻¹, respectively, which indicated that the method could well predict the nitrate concentration. The model implementation indicated that the total nitrate concentrations from FTIR-ATR and mass spectrometry were almost the same, among which ¹⁵N labelled nitrate obtained by ATR was 3.58–10.02 mg kg⁻¹ lower than that from mass spectrometry, while ¹⁴N labelled nitrate from ATR was 6.75–13.68 mg kg⁻¹ higher. Compared with a control treatment, the mineralization and release of soil nitrogen were enhanced in a nitrogen treatment. Therefore, the technique of FTIR-ATR can be used as an alternative option in determining isotope labelled nitrate in paddy soil.