The alpha (MIR) and XRF instruments are two different methodologies of analysis that are complementary and not overlapping: x-ray fluorescence (XRF) is an elemental method, measuring the elemental composition of material. Due to the intrinsic characteristics of the methods, light elements such as B, C, N cannot be detected. Alpha instrument measuring diffuse reflectance spectroscopy in the middle infrared (MIR) range (600 – 4000 cm-1) is a molecular method, measuring the light absorbance of specific molecules such as C- O, N-O, H-O, C-H, among others.
They have been designed to work together in the analysis of different soil elements because their complementarity enhances the strength and reduces the weakness of the properties’ predictions of such heterogeneous and complex media as soil. Though each instrument may work separately, there are expected differences in accuracy for each case due to the prediction capacity. For example, the MIR (alpha) uses an indirect prediction model through proxies such as clay content, organic material, to analyse the total elements while XRF uses direct prediction.
Because of the direct measurement of total elements used by the XRF, the XRF comes in to complement on the strength of the predictions in addition to elements whose predictions are not strong for the alpha instrument. For example, XRF is more accurate in the analysis of the total P than the alpha. This makes a complete LIAB a hybrid of measurement and prediction (see picture below).
Figure 1: Comparison of reference vs prediction for P exchangeable: XRF only (upper left), Alpha only (upper right) and fusion approach (below)
In essence, combining both data enhances the prediction providing results of the entire range of properties with a high accuracy. Therefore, the fusion approach of the two instruments is highly recommended for increased accuracy.