Optimization of a method for soil sulphur extraction

Numerous methods for the determination of soil sulphur (S) have been developed and tested in field conditions, but so far none of them have shown a satisfying relationship to crop yield. Therefore, these methods are not suitable to be used to evaluate the sulphur supply or to determine the sulphur fertilizer demand. In this paper a successful approach was adapted and optimized for routine analysis in soils in humid conditions. Modifications included a comparison of soil incubation with shaking, changes in the concentration of the extractant, the soil-to-extractant ratio, the time of shaking, particle size of the soil and method of detection. The best results in terms of a high reproducibility and sensitivity of the method for soils with extremely low, but also high, sulphur contents were obtained when the soil was extracted in a 1:5 ratio with 0.025 M KCl, shaken for 3 hr and then filtered. The method is suitable for ICP and IC measurement, whereby IC is preferable on low sulphur soils because of the higher detection limit.