Comparison of methods to evaluate the sulphur status of soils

The sulphur status of 98 soils was assessed using nine methods, some of which were designed to include mineralizable sulphur. A close correlation was found between various direct extraction methods all using phosphate, though the turbidimetric method of analysis appeared to overestimate soil S values. Extractions following short term incubation with cysteine correlated significantly with direct extraction methods indicating that the soil sulphate pool is directly related to the soil's ability to mineralize readily available organic 5. In contrast, incubation with elemental S gave no correlation. A respirometric method following amendment with cellulose gave only a poor correlation with two other methods. A Neubauer plant bioassay was most closely correlated to Ca (H₂PO₄)₂-extractable 5, CaCl₂-extractable 5 and to extractable S following incubation with cysteine. The value of the various methods for routine use is discussed.