The fundamental of the effects of water, organic matter, and iron forms on the pXRF information in soil analyses

•Soil mineralogy plays a fundamental role in pXRF patterns.•Selective dissolution of SOM and iron forms can be detected by pXRF.•Low contents of SOM did not interfere in pXRF analyses.•Soil moisture must be considered for pXRF analyses in field.•Soil fertility and soil particle size distribution are related to pXRF data. Portable X-ray fluorescence (pXRF) has great potential for numerous applications in soil science. However, the basic knowledge about the effects of soil properties on pXRF spectra are still poorly studied, which may lead users to biased interpretations of mathematical models. The present study aimed to evaluate the outcomes of moisture, soil organic matter content (SOM), and iron forms on pXRF data. The work was conducted with seventeen soil samples from the central region of São Paulo state (Brazil). Three selective dissolution treatments were applied to remove: (i) soil organic matter (−SOM), ii) SOM and poorly crystalline iron forms (−o), iii) SOM and poorly crystalline plus well crystalline iron forms (−d). One additional treatment iv) including water addition (+W) was also carried out. The effects of treatments were evaluated for sandy and clayey samples. Soil particle size distribution and elemental content affected the bremsstrahlung and characteristic peaks counts. In +W, there was a generalized decrease in counts mainly for the light elements (magnesium, aluminum and silicon). Regarding the selective dissolution procedures, alterations were verified, reflecting mainly the removal power of reagents. Generally, the most pronounced alterations occurred for −d and moderate alterations for −SOM and −o. The pXRF data showed high correlation with particle size distribution and mineralogy attributes. The kaolinite, gibbsite, Fe2O3, Al2O3, SiO2, TiO2 and MnO contents were quantified with satisfactory accuracy (0.61