Sustainable management for increasing soil microbial diversity in a Mediterranean agro-ecosystem

Olive can be considered a paradigm species for Mediterranean agro-ecosystems. In conventional olive growing, adopted by the majority of the farmers, frequent soil tillage has reduced soil microbial diversity and microbiota complexity that strongly contribute to the overall soil fertility. Therefore, the conventional agronomic practices should evolve in a more sustainable olive management addressed to improve soil microbial diversity. A better understanding of the ecology of soil microorganisms could lead to identify agricultural management practices that stimulate and select the soil microorganisms having beneficial purposes in agriculture, such those interested in nitrogen cycle. The aim of this study was to evaluate the effects of sustainable practices (grass cover and pruning residues recycling) on soil microbioligical quality in a Mediterranean olive orchard. The trials were carried out in a mature olive grove (Olea europaea L. – cv Maiatica) located in Basilicata Region (Southern Italy.) and managed for 13 years (medium-term) according to two different soil management systems: the sustainable treatment (ST) and the conventional treatment (CT). Soil microorganisms in the two systems were monitored by both microbiological cultural-dependent and molecular methods, and by microscopy. In the ST olive orchard, soil microbiota showed a higher complexity and metabolic diversity. The adoption of ‘innovative’, sustainable, agricultural practices had positive effects on soil microbiota and its biodiversity, which in turn can influence soil fertility and plant growth by increasing nutrients availability and turnover. The results of this study encourage the use of sustainable agricultural practices able to enhance physico-chemical and microbial soil fertility and promote good-quality fruit production without detrimental effects on water and soil resources. The role of the identified microorganisms in the soil microbial netwo rk is discussed, in order to provide a detailed view of the impact that man-made selection had on soil microorganisms of agricultural relevance in a typical Mediterranean agronomic biosystem.