Comparison of three different methods of determining soil sulphur mineralization in relation to plant sulphur availability in soils

S mineralization in soils with different fertilizer histories [0, 188 and 3 76 kg superphosphate (SP) ha/year applied since 1952] and animal camping tr eatments (camp and non-camp soils) was determined simultaneously under the same glasshouse conditions using three different methods (i.e. open incubat ion, pots with and without plants). Results obtained showed that amounts an d patterns of soil S mineralized differed from one system to the other. In the open incubation system, the pattern of S mineralization showed a rapid release of S in the first 4 weeks followed by no substantial release during the remaining 20 weeks of incubation. In both pot systems, S mineralizatio n was slow initially and increased significantly with time. Total amounts o f S-32 mineralized in the open incubation system ranged from 7.5 to 11.9 pg S/g soil, while corresponding values for pot systems were 2.3-3.7 and 2.3- 5.9 pg S/g soil for pots with and without plants, respectively. Rates of so il 32S mineralization with time as fitted by regression models were differe nt in the three systems, showing the differential impact of leaching, crop removal and plant effects on soil S mineralization. Similar results were ob tained using radioactive S-35 tracer. Overall, the results suggested that c ontrary to commonly postulated ideas, soil S mineralization determined by p eriodic leaching of soil in the open incubation system does not simulate cr op removal of S or provide a means of predicting plant S availability.