Comparison of soil microbial community between soils amended with or without farmyard manure

Comparison of microbial properties were made between soils amended with chemical fertilizer (CF-soil) and with CF and farmyard manure (FYM: CF + FYM-soil) for more than 10 years in an attempt to elucidate microbiological characteristics of the soil with the repeated application of FYM. The numbers of total bacteria were not significantly different between the CF- and CF + FYM-soils, while those of culturable bacteria were two to six times higher in the CF + FYM-soil than in the CF-soil. Microbial community structure on a broad scale was estimated by molecular methods: %G + C profiles of soil community DNA and sequencing of 16S rDNA of clones. There was a shift in the %G + C profiles toward a greater proportion of higher %G + C classes in the CF + FYM-soil. 16S rDNA clone library was obtained from the community DNA of the two soils and phylogenetic analysis of 77 clones was made. While 16S rDNA clones in the CF-soil were dominated by alpha-, gamma- and beta-proteobacteria (36, 28 and 10%, respectively), those in the CF + FYM-soil by gamma- and alpha-proteobacteria, Actinobacteria and Acidobacterium (26, 21, 13 and 11%, respectively). Phospholipid fatty acid analysis (PLFA) showed a seasonal variation in the soil microbial community structure, but clearly differentiated the CF + FYM-soil from the CF-soil. These results suggested that different soil microbial community structure developed by the repeated application of FYM. Carbon utilization profiles using Biolog GN plates showed that the CF + FYM-soil had a higher utilization ability of the substrates, especially l-proline and phenyl ethylamine, α-cyclodextrin, cellobiose and d-serine. Microbial community specific to soil amended with FYM is discussed in a combination with the results obtained by the different methods.