Long-term effects of municipal solid waste compost application on soil enzyme activities and microbial biomass

A long-term field experiment utilising barley received four different treatments prior to sowing: municipal solid waste (MSW) compost at either 20 t ha−1 (C20) or 80 t ha−1 (C80); cow manure (MA) at 20 t ha−1; mineral fertilizer (MIN) or NPK (400 kg ha−1); and NH4NO3 (150 kg ha−1). The effects of these applications on soil enzyme activities and microbial biomass at crop harvest were measured after nine years. In comparison with the control (no amendment) MSW addition increased biomass C by 10 and 46% at application rates of 20 and 80 t ha−1, respectively, while MA treatment increased microbial biomass C by 29%. The ratio of soil microbial C to soil organic C was the lowest at the high rate of MSW application. Oxidoreductase enzymes, such as dehydrogenase and catalase, were higher in the MSW treatments by 730 (C20) and 200% (C80), respectively, and by 993 and 140% in MA treatments than in the unamended soil, indicating an increase in the microbial metabolism in the soil as a result of the mineralization of biodegradable C fractions contained in the amendments. The addition of MSW and MA caused different responses in hydrolase enzymes. Phosphatase activity decreased with MSW (±62% at both rates) and MA (±73%), to less than those in the mineral fertilization and the control treatments. Urease activity decreased by 21% (C20) and 28% (C80), possibly being affected by the heavy metals contained in the MSW. However, β-glucosidase and protease-BAA increased in all the organic treatments, especially with MA (by 214 and 177%, respectively). This is attributed to the microbial stimulation by the organic C and is correlated with the increase in dehydrogenase (r2=0.882) and catalase (r2=0.654) activities.