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Sustainable soil management of orchards can have positive effects on both soils and crop yields due to increases in microbial biomass, activity and complexity. The aim of this study was to investigate medium-term effects (12 yr) of two different management practices termed ‘sustainable’ (ST) and ‘conventional’ (CT) on soil microbial composition and metabolic diversity of a rainfed mature olive orchard in Southern Italy. ST included no-till, self-seeding weeds (mainly graminaceous and leguminosae), and mulch derived from olive tree prunings, whilst CT was managed by frequent tillage and included severe pruning with residues removed from the orchard. Microbial analyses were carried out by culture-dependent methods (microbial cultures and Biolog®). Molecular methods were used to confirm the identification by light microscopy of the isolates of fungi and Streptomyces. Significantly more culturable fungi and bacteria were found in ST than in CT. The number of fungal groups in ST was also significantly greater than in CT. Overall and substrate-specific Biolog® metabolic diversity indices of microbial communities and soil enzyme activities were greater in ST. The results demonstrate that soil micro-organisms respond positively to sustainable orchard management characterized by periodic applications of locally derived organic matter. This study confirms the need to encourage farmers with orchards in the Mediterranean basin to practise soil management based on organic matter inputs associated with zero tillage to improve soil functionality

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The aim of the present work was to evaluate the effects of two soil management systems so called sustainable treatment (ST) and conventional treatment (CT) on the composition and on genetic, functional, and metabolic diversity of soil microbial communities in a Mediterranean olive orchard. The ST system included no-tillage, integrated chemical fertilization, and organic matter inputs from drip irrigation, spontaneous cover crops, and pruning material. Microbial analyses were carried out by an integrated approach of culture-dependent (microbial cultures and Biolog) and culture-independent methods (denaturing gradient gel electrophoresis [DGGE]). After 7 years of treatment, average olive yield was 8.4 and 3.1 t ha j1 year j1 in ST and CT, respectively. Conventional treatment had a significantly higher number of total culturable bacteria and actinomycetes compared with ST, whereas fungi were significantly lower. In ST, the number of ammonifying bacteria, proteolytic bacteria, and Azotobacter in the wetted areas under the drippers (ST-WET) was significantly higher than along interrows (ST-INTER). The DGGE analysis of microbial 16S/18S rDNA showed differences between ST and CT, whereas 16S/18S rRNA DGGE bands of ST-WET clustered differently from those of CT and ST-INTER. Some Biolog metabolic indexes 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 microorganism activity and improve olive yield and fruit quality.

The equilibrium adsorption and binding of DNA from Bacillus subtilis on complexes of montmorillonite–humic acids Al or Fe hydroxypolymers (Al–M–HA or Fe–M–HA) at different M/HA ratios, the desorption of DNA, the capacity of bound DNA to transform competent cells of B. subtilis in vitro, and the protection of bound DNA from degradation by free and organomineral‐bound DNase I are reported. Adsorption was rapid (maximal after 2 h), occurred from pH 3 to 10, and was higher on Al–M–HA than on Fe–M–HA. Saturation of the sites on the surface or between the layers of Al– or Fe–M–HA occurred with only some complexes, depending on how the complexes were prepared. Essentially no desorption under stringent conditions was observed. Bound DNA transformed auxotrophic competent cells of B. subtilis, although at a lower frequency than free DNA. Bound DNA was protected more than free DNA against degradation by DNase I, and differences in resistance to degradation between free and bound DNA were more evident when DNase was also bound on the organomineral complexes.

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