Long-term effects of compost amendment of soil on functional and structural diversity and microbial activity

We studied the effects of applying different composts (urban organic waste, green waste, manure and sewage sludge), mineral fertilizer and compost plus mineral fertilizer on chemical, biological and soil microbiological parameters over a 12-year period. The organic C and total N levels in soils were increased by all compost and compost + N treatments. Microbial biomass C was significantly (P £ 0.05) increased for some compost treatments. In addition, basal respiration and the metabolic quotient (qCO2) were significantly higher in all soils that had received sewage sludge compost. The Shannon diversity index (H), based on community level physiological profiling, showed a higher consumption of carbon sources in soils treated with compost and compost + N compared with the control. The utilization of different guilds of carbon sources varied amongst the treatments (compost, compost + N or mineral fertilizer). Cluster analysis of polymerase chain reaction-denaturing gradient gel electrophoresis patterns showed two major clusters, the first containing the mineral fertilization and compost treatments, and the second, the composts + N treatments. No differences in bacterial community structure could be determined between the different types of compost. However, the results suggest that long-term compost treatments do have effects on the soil biota. The results indicate that the effects on the qCO2 may be due to shifts in community composition. In this study, it was not possible to distinguish with certainty between the effects of different composts except for compost derived from sewage sludge.