Application of near-infrared spectroscopy in analysis of soil mineral nutrients

The feasibility of using near-infrared reflectance spectroscopy (NIRS) was investigated for the analysis of pH, electrical conductivity (EC), phosphorus (P), sulfur (S), calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), iron (Fe), and manganese (Mn) in 28 Canadian soil samples from three boreholes down to 10 m in depth. Field moist soil samples were scanned for pH and EC, and air-dry samples were scanned for the analysis of the elements. Calibrations were developed between the near-infrared spectral data and results obtained by conventional analyses. The NIR-predicted values were highly correlated to the measured values obtained by the conventional methods (r(2)>0.9) for P, Ca, Mg, K, Fe, and Mn, and almost as highly correlated (r(2)>0.8) for S and Na. Results for pH were somewhat less successful (r(2)>0.6), and appeared to be useful only for screening purposes, whereas EC was not successfully predicted by NIRS in this study. It appeared that NIRS could be a useful method for the rapid, non-destructive, simultaneous analysis of elemental concentrations in dry soils, useful in routine analysis.