Compost and cattle manure as sources of inorganic sulphur to soil

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 -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 -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 weeks, after which a rapid increase in -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 -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 accommodating 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-week incubation period, only CM improved soil arylsulphatase with respect to the control. A comparison between the trends of arylsulphatase activity and of -S release indicates that at low S concentrations a significantly greater level of arylsulphatase and, conversely, high S concentrations induced a decrease of the enzyme.