Mid-infrared diffuse reflectance spectroscopy for the quantitative analysis of agricultural soils

Soil samples were analyzed conventionally and by mid-infrared diffuse reflectance spectroscopy for total C, total N, pH, and measures of biological activity. Ground, non KBr diluted, samples (n = 180) from experimental plots (two locations, three replicate plots, under plow and no-till practices, three rates of N fertilizer, and from five depths) were scanned from 4000 to 400 cm(-1) (4-cm(-1) resolution, 64 co-added scans) on a DigiLab FTS-60 Fourier transform spectrometer using a custom-made linear sample transport (50 by 2 mm sample area scanned). Results using partial least-squares regression showed that accurate calibrations can be developed for the determination of a number of compositional parameters: total C, total N, pH, and many measures of biological activity. In general, the results achieved using mid-infrared spectra were at least as accurate as those found previously using near-infrared spectra and were sometimes significantly better, that is, pH.