Soil particles are very heterogeneous in microscopic scale, which is manifested the double-layer structure made of the soil organic matter and mineral matter. In this work, Fourier by transform infrared photoacoustic spectroscopy ( FTIR-PAS) combined with independent component analysis ( ICA) was utilized for in situ depth-profiling of the manmade complex film, in order to lay a foundation of in situ characterizing the heterogeneous soil organic-mineral complex. The complex film was composed of the PE preservative film and office adhesive tape. The moving velocity of infrared photoacoustic spectrometer was set to 0. 16 cm/s, 0. 32 cm/s and 0. 64 cm/s, respectively. Independent component analysis ( ICA ) was performed on the photoacoustic spectra of the heterogeneous complex film. Results showed that the depth-resolved information of the complex film could be derived by changing the moving velocity, and the estimated thickness of PE film was 5. 4-7. 6 μm, which was close to the actual thickness 7 ± 1 μm. Moverover, the spectral features of the polyethylene ( PE) preservative film and office adhesive tape were extracted from the photoacoustic spectra of the heterogeneous complex film by means of ICA. Depth profiling of complex film samples showed that FTIR-PAS could be used as a new analytical tool to study heterogeneous soils, especially soil organic-mineral complexes.

The nitrate-N content in KNO3 solution and soil was rapidly predicted using techniques of mid-infrared spectroscopy, in which 15 NO-3 and 14 NO-3 were distinguished and predicted. The results showed that the characteristic band of nitrate in solution and soil was 1200-1500 cm-1 , and compared with 14 NO-3 , the red shift of characteristic band of 15 NO-3 was about 35 cm-1 . In the characteristic band of nitrate, absorption band increased with the nitrate nitrogen concentration with less interference absorption. The linear regression was made between the first principal component of characteristic band and nitrate-N content, and correlation coefficient was more than 0 . 9840 , indicating that the technique of mid-infrared attenuated total reflectance spectroscopy could be applied for rapid monitoring of nitrate in solution and soil. Meanwhile, based on the red shift characteristic of 15 NO-3 absorption band, the method of partial least squares were involved to predict the nitrate-N of different N-isotope labeled in solution and soil, resulting that all the prediction models reached excellent levels. For 14 NO3-N and 15 NO3-N in solution, the correlation coefficients ( R2 ) were 0. 9980 and 0. 9982 respectively, and ration performance to standard deviations ( RPD ) were 6. 44 and 4. 76, respectively. While for 14 NO3-N and 15 NO3-N in soil, the correlation coefficients ( R2 ) were 0. 9794 and 0. 9679, and RPD were 5. 75 and 4. 78, respectively. Therefore, the technique of mid-infrared attenuated total reflectance spectroscopy can be applied for rapid monitoring different N-isotope labeled nitrate in solution and soil, to provide a new in situ and fast time method to study nitrification process in soil.