Waste-derived 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 waste-derived 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 the alkaline hydrolysis and pH neutralization of sludges. Aim was exploring the effects of these amendments on soil biochemistry, including 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 network analysis, also studying its correlations to changes in soil C and N pools. 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 interactions. Compost-based amendments representing a source of recalcitrant carbon, significantly promoted soil biodiversity and increased microbial biomass. Sludge plasters, a more easily degradable C and N source, promoted the proliferation of copiotrophic bacteria and unexpectedly resulted in a deep rearrangement of the fungal population, leading to increased laccase activity. Although the organic matrices were applied considering their different susceptibility to release available N over time, by applying different mineralization coefficients, significant differences were found in the accumulation of soluble forms of N and C in soil, with the consequent differences in microbial compositional and functional responses. These findings suggest the need for in-depth studies to formulate specific guidelines for the use of compost-based matrices, and especially sludge plasters, in the field. Compost-based matrices behaved like soil amendments, while sludge plasters behaved like mineral fertilizers. Together they could be used to maintain soil fertility and meet plant nutritional needs.