Enzyme activity and microbial biomass in a field soil amended with municipal refuse

Summary Changes in enzyme activity levels, in biomass-C content, and in the rate of fluorescein diacetate hydrolysis were measured in a loamy soil to which solid municipal refuse had been applied as compost over a 3-year period at two different rates. Addition of the compost caused significant increases in the activity of all enzymes tested. The increases were much higher at 90 t ha^-1 year^-1 than at 30 t ha^-1 year^-1. Significant increases were also observed in the biomass-C content and in the rate of fluorescein diacetate hydrolysis. Significant correlations among changes in biomass-C content and the rate of fluorescein diacetate hydrolysis and the changes in all enzymes tested were found.Two activity indices were calculated; a biological index of fertility and an enzyme activity number. No correlations were found between the biological index of fertility and the changes in the various enzyme activities. However, significant correlations were found either between enzyme activity number and most of the changes in enzyme activity, or between the enzyme activity number index and the biomass-C content (r=0.850). The use of a new activity index, the hydrolysis coefficient, is proposed. This coefficient was significantly correlated with biomass-C content (r=0.925) and with the enzyme activity number index (r=0.780).