Comparison of methods to investigate microbial populations in soils under different agricultural management

The microbial community in sludge-treated and nearby untreated soils was in vestigated using direct microscopic counting, plate culture, carbon substra te utilisation (Biolog (TM)), and fatty acid methyl esters. Long-term sewag e sludge applications had resulted in higher concentrations of organic carb on and had altered other factors in the soil, including the concentration o f metals. Bioluminescence was inhibited in assays of the sludge-treated soi l, although microbial counts were similar in all soils. A detailed analysis of carbon substrate utilisation patterns and fatty acid methyl esters show ed qualitative differences in the microbial populations. This work shows th at a variety of approaches are required to assess microbial communities in soil where, despite large differences in land management, the populations a re similar in size and overall composition. (C) 2000 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights r eserved.