Evaluation of the Quality of Solid Fertilizers by Portable X‐Ray Fluorescence

ABSTRACT The growing global demand for food necessitates an increase in the supply of fertilizers that enable greater crop productivity in a sustainable manner, minimizing environmental impacts. The increasing availability of fertilizer products and formulations has raised concerns about compositional quality, which cannot always be adequately verified. Generally, fertilizer quality evaluation is rarely incorporated into agronomic management, which tends to focus on soil analysis, irrigation water analysis, and foliar analysis for determining nutrient dosages. For this reason, the quality of solid inorganic fertilizers was evaluated using energy‐dispersive X‐ray fluorescence (XRF) for the determination of elements from Mg to Fe. The results between XRF and the reference methods were compared for the elements P and K, using a sample of 27 fertilizers drawn from a population of 100 samples analyzed over a three‐year period. The element Nitrogen was determined by colorimetry. Elemental concentrations were determined directly by portable energy‐dispersive X‐ray fluorescence. Of the 27 samples evaluated, only five were consistent with the compositions declared on their commercial labels. A paired Student's t ‐test for phosphorus and potassium confirmed no significant differences between XRF and the reference methods. The XRF technique proved to be an effective tool for quality control of solid inorganic fertilizers, enabling the simultaneous multi‐elemental characterization of samples without requiring acid digestion. This capability allowed us to infer adulterating matrices—including phosphogypsum, clay, and silica—as well as the inference of elemental sources, such as potassium chloride as the primary potassium carrier, information that is not readily obtainable through conventional single‐element methods.