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

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 (FTIRATR) 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 (NO3)-N-14-N and (NO3)-N-15-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 N-15 labelled nitrate obtained by ATR was 3.58-10.02 mg kg(-1) lower than that from mass spectrometry, while N-14 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.