This laboratory study was conducted to compare the mineralization of sulphur in a soil amended with cattle manure (CM) and green waste compost (GWC). Compared to control, values of SO42--S ranged from -46.8% in soil amended with the high dose of CM to -14.7% in soil treated with the low dose of GWC, indicating an immobilization of sulphur in the differently amended soil. Soil treated with GWC showed a steady linear release of SO42--S with time over the entire incubation period, with a decrease in mineralization at increasing rate of addition. Cattle manure showed a slow S mineralization over about 8 wk, after which a rapid increase in SO42--S release was observed. The cumulative S values were higher in CM than in GWC-treated soil but, when expressed as percentages of the added S, the release of SO42--S was higher in GWC-treated soil than in CM-treated soil. Kinetic model of net mineralization showed a different release of S between CM and GWC. In soil treated with CM, the Gompertz equation was a suitable model for accomodating the lag phase and the successive increase in S mineralization. An initial increase of arylsulphatase activity up until week 2 was in the soil treated with the two organic materials, especially when applied at the highest rate but, at the end of the 24 wk incubation period, only CM improved soil arylsulphatase with respect to the control. A comparison between the trends of arylsulphatase activity and of SO42--S release indicates that at low S concentrations corresponded a significantly greater level of arylsulphatase and, conversely, high S concentrations induced a decrease of the enzyme.
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