Long-term effects of heavy metals from composted municipal waste on some enzyme activities in a cultivated soil

A 3-year field experiment on a calcareous Fluventic Xerochrept planted with corn (Zea mays L.) was carried out to evaluate the effects of amending the soil with high and low rates of composted municipal waste on soil enzyme activities (alkaline phosphomonoesterase, phosphodiesterase, arylsulphatase, dehydrogenase, and L-asparaginase). These enzyme activities all increased when compost was added at rates of up to 90 t ha-1, and the phosphatases continued to show a linear increase with compost rates of up to 270 t ha-1. The addition of mineral fertilizer increased enzyme activities in unamended soil, and masked the stimulating effect of compost on the amended soils. Heavy metals did not affect soil enzyme activities up to a compost addition of at least three times the amount specified by Italian law.