Determination of Soil Cation Exchange Capacity Via Portable X-Ray Fluorescence Spectrometry.

Soil cation exchange capacity (CEC) is one of the important soil properties evaluated, especially in the context of soil fertility. Current methods for measuring soil CEC are arduous and require laboratory analysis. Whilst accurate, laboratory approaches are destructive in nature, require sample modification, and take considerable time to complete. Therefore, the potentiality of using portable x-ray fluorescence (PXRF) spectrometry to predict soil CEC was investigated. PXRF is a proximal sensing technique, which facilitates in-situ quantification of elemental data in seconds. In this study, 450 soil samples were collected from active farm fields in California and Nebraska, USA representing a wide variety of soil textures. The samples were subjected to PXRF scanning followed by standard laboratory characterization. The dataset was divided into both modeling and validation sub-datasets. Multiple linear regression was applied to the modeling dataset to develop a predictive model associating pure elemental data from PXRF where Ca, Ti, V, Cr, Fe, Cu, Sr, and Zr were used in the model. A second model also included auxiliary input data (soil clay, pH, organic matter) as potential modeling variables. Both models were shown to perform similarly, with the auxiliary input model providing slightly higher R² (0.926 vs. 0.908) and slightly lower RMSEs (2.236 vs. 2.498) compared to the pure elemental data model. Validation via correlation analysis supported the significance of the developed models which was compelling for both the pure elemental model (R=0.904) and the auxiliary input model (R=0.953). Summarily, PXRF shows considerable promise for rapid prediction of soil CEC with reasonable accuracy thereby minimizing the need for tedious laboratory determination for many applications.