A comparison of the mineralization of nitrogen and of sulphur from decomposing organic materials

Abstract

The decomposition of a wide range of plant materials added to soil waa studied by measuring the production of carbon dioxide, and changes in the concentrations of ammonium and nitrate nitrogen and sulphate sulphur. The amount of sulphur mineralized depended on the sulphur content and the carbon/sulphur (C/S) ratio of the organic matter in much the same way as the amount of inorganic nitrogen depended on the nitrogen content and the carbon/nitrogen (C/N) ratio. For any given C/S or C/N ratio the sulphur or nitrogen mineralized varied within quite wide limits. With a 12 week decomposition period, initial C/S ratios of 200 and 420 were the minimum and maximum values at which no mineralization of sulphur occurred. The corresponding values for nitrogen were 16 and 44. Calculations indicated that the microbial residues from easily decomposed materials had a C/N ratio of 6–7 and a C/S ratio of 50–60, but with the residual organic matter from the more resistant materials the ratios were wider. Where large quantities of nitrogen were mineralized the decomposition of the native organic matter was stimulated.