Organic Fertilization Induces Changes in Soil Nitrogen Mineralization and Enzyme Activities

In this study, we addressed the reuse of two organic waste products as fertilisers. To this end, soil fertilised with the spent mushroom substrate (SMS) or with an anaerobic digestate (DIG) was subjected to an incubation assay, and the results were compared with those from soil treated with a mineral fertiliser (MIN) and an unfertilised soil (CO). The soil was sampled after fertilisation and after 90 days of aerobic incubation. Nitrogen (N) mineralisation (NH4+ and NO3-) and oxidable carbon (OC) were determined. The impact of the treatments on the soil was evaluated by measuring the enzymatic activity of arylsulfatase (ARYL), ß-galactosidase (GAL), and urease (URE). The highest OC content was observed in the SMS treatment. After 90 days of incubation, the SMS treatment showed a lower mineral N content than the CO treatment. This finding was associated with N immobilisation. However, mineral N significantly increased ARYL activity in the DIG and MIN treatments, and URE activity was always higher at both sampling times in the SMS treatment. Initially, GAL activity was notably high in the DIG treatment but decreased after incubation, reaching similar values to those registered in the CO treatment. Organic fertilisation treatments induced different effects on soil N mineralisation, showing changes in the activity of the enzymes analysed.