Organic soil amendments for a sustainable vineyard management: linking microbiome responses to soil biochemistry

Products obtained from various organic wastes recycling processes can represent sustainable alternatives to traditional fertilizers in vineyard management. In this study, three organic-based amendments were applied consistently for the first three years from plantation in an experimental vineyard in Northern Italy. The amendments included municipal organic waste compost, sewage sludge compost, and 'plasters' derived from alkaline hydrolysis and pH neutralization of sludges. The study aimed at exploring the effects of these amendments on soil biochemistry, including soil physicochemical properties and main enzymatic activities, together with soil microbiome variations. Microbial community composition was analyzed by bacterial 16S and fungal ITS regions sequencing and microbial network analysis, also studying its correlations to changes in soil carbon and nitrogen pools. Results showed that the matrices did not act as microbial inocula. Instead, they stimulated specific autochthonous microbial populations and had a deep and varied impact on the cumulative fungal and bacterial network of microbial interactions. Compost-based amendments, which represent a source of recalcitrant carbon, significantly promoted soil biodiversity and increased microbial biomass. Conversely, sludge plasters were a more easily degradable source of carbon and nitrogen. This matrix promoted the proliferation of copiotrophic bacteria and unexpectedly resulted in a deep rearrangement of the fungal population, which led to increased laccase activity. These results confirm that compost-based organic matrices, especially municipal compost, can represent a valuable alternative to mineral fertilization in vineyards. Conversely, the potential and the long-term effects of sludge plasters on grapevine cultivation need to be further explored.