Comparison of some extraction methods for determination of sulphur in soils of the Czech Republic

Input of sulphur in soils from atmospheric depositions has been substantial ly reduced during the last decade. On the other hand the area of crops with high demand of this element has risen. That is the reason why sulphur is b ecoming the element of interest for plant nutrition in the Czech Republic. The study was focused on the incorporation of the determination of sulphur into the regular soil testing scheme which is based on Mehlich III extracti on method. Extraction of finely ground soil (particles < 0.250 mm) with wat er according to ISO 11048 was the method used for the determination of sulp hur most frequently. The influence of soil particle size for water extracti on and Mehlich III extraction, the relationship between sulphate sulphur an d total sulphur in water soil extracts and relationships between water, Meh lich III and aqua regia soil extracts were studied. 147 soil samples collec ted from the soil monitoring plots were used for the evaluation of the rela tionships between the extraction methods (water extraction, Mehlich III and aqua regia) and between sulphate sulphur and total extracted sulphur. 29 t opsoil and 29 subsoil samples from the South-Moravian region were used for evaluation of the influence of soil particle size on extraction of sulphur. The increase of sulphur extraction for finely ground samples (< 0.250 mm) for water and Mehlich III extracts was only 4 to 6% (R-2 = 0.98) compared t o ordinary prepared soil samples (< 2 mm). Linear relationship (R-2 = 0.91) between the sulphate sulphur and the total sulphur extracted by water was found. Extracted sulphate sulphur was determined by capillary zone electrop horesis and total extracted sulphur by ICP-AES. Approximately 70% of the to tal extracted sulphur was present as sulphate sulphur. Between water extrac tion and Mehlich III extraction a statistically highly significant linear r elationship was found (R-2 = 0.62). Conversion equations may be used for re calculation of criteria but field and pot experiments will be necessary to establish a more precise relationship between determination of sulphur in M ehlich III soil extracts and the plant uptake. Between content of sulphur i n aqua regia extracts and the other studied extraction methods no relations hip was found.