Sulphur biochemistry in agricultural managed soils using 34S

To gain a better understanding of sulphur transformation within soil, stable sulphur and oxygen isotopes were used. Four soils with different histories of fertilizing were studied under field conditions to observe the influence of fertilizing on the isotopic composition of different sulphur forms in soils. In laboratory experiments the behaviour of these soils observed under sulphur deficiency and sulphate fertilization conditions was investigated. The natural sulphur isotopic composition of inorganic sulphate in the four soils shows a difference with respect to organic sulphur in soil and precipitation sulphate which is attributed to fractionation during transformation processes. Mineralization was recognized as a biochemical process which affects the 18O content of sulphate. The irrigation experiment showed that sulphate is mineralized at different rates, depending upon the content of soil organic matter (SOM). Whereas in soils with high SOM mineralization is the predominant mechanism, in soils with low SOM sulphate can be immobilized. (author). 11 refs, 2 figs, 2 tabs