Qualitative and quantitative changes of soil microbial communities as a result of sustainable agricultural practices in an Italian olive grove

The aim of the present work was to evaluate the effects of two soil management systems, so called ‘sustainable’ (ST) and ‘conventional’ (CT) on the composition, genetic diversity and carbon substrate utilization of soil microbial communities in a Mediterranean olive orchard. ST system included no-tillage, limited chemical fertilization, and organic matter inputs from drip irrigation with wastewater, spontaneous cover crops and pruning material. CT system was characterized by soil tillage, chemical fertilization, no irrigation and heavy pruning. After seven years of treatments, average olive yield was 8.4 and 3.1 t ha–1 yr–1 in ST and CT, respectively. CT had a significant higher number of total bacteria and actinomycetes if compared to ST, whereas fungi were significantly lower. In ST, the number of the bacteria involved in the nitrogen cycle isolated from the wetted areas under the drippers (ST-WET) were significantly higher than in inter-row areas (ST-INTER). The patterns of denaturing gradient gel electrophoresis of microbial 16S/18S rDNA showed differences between ST and CT, whereas those of 16S/18S rRNA evidenced that ST-WET clustered separately from CT and ST-INTER. Diversity indexes evaluated by Biolog® assay were significantly different between ST and CT. The results revealed qualitative and quantitative changes of soil microbial communities in response to sustainable agricultural practices that stimulate soil micro-organisms and improve olive yield and quality.