Estimation of sulfate and amino acid sulfur in plant material by X‐ray spectrometry

The SKα shift between the valences of sulfur has been used to determine by X‐ray spectrometry the two main forms of sulfur present in plant material, viz: oxidised S (S6+) and covalently bonded sulfur (Sc). S6+ and Sc were shown to correlate closely with sulfate, as determined by reduction with hydriodic acid, and cysteine+methionine S, respectively. The method is rapid and reliable provided the X‐ray spectrometer is stable and has high reproducibility in goniometer setting. The use of S6+ and Sc is recommended as an alternative to chemical methods for assessing the sulfur status of crops and the sulfur amino acid content of diets.