Regional transferability of mid-infrared diffuse reflectance spectroscopic prediction for soil chemical properties

Mid-infrared diffuse reflectance spectroscopy (MIR-DRS, 2500 to 25 000 nm) can provide rapid, cheap and relatively accurate predictions for a number of soil properties. This paper examines the ability of MIR-DRS to predict various soil chemical properties with emphasis on the elucidation of possible mechanisms of prediction. Three datasets from the states of Queensland, New South Wales, and Victoria, Australia were used in this study. MIR is able to predict fundamental soil properties related to soil matrix or solid constituents and soil solution concentrations which are in equilibrium with the solid phases. Basic soil organic and mineral constituents are well predicted: cation exchange capacity, clay content, organic and total C, and total N. Chemical properties that are related to the mineral and organic components can also be predicted, including: total K, total P, elemental Fe, Si, and Al. Soil pH appears to be related to the soil constituents from its relationship with the exchange sites. Due to the differences in the origins of the soil and in the laboratory measurement procedures, calibration functions from one region do not perform well on another one. Local calibration is preferred to avoid the measurement biases between laboratories, and the calibrated functions are more specific to the soil types in an area.