The long-term application of composted organic wastes caused a lasting increase in vineyard soil health and multifunctionality

As a consequence of climate change and unsustainable management practices, agricultural soils in the Mediterranean region are often degraded. The application of composted organic wastes is traditionally considered a beneficial practice to improve soil health. We studied the permanence of the beneficial effects of the long-term (20 years) application of composted organic wastes, versus mineral fertilization or no fertilization, on Mediterranean vineyard soil health. To this aim, four years after ceasing fertilization, a comprehensive analysis of soil physicochemical and biological properties, including prokaryotic diversity and functional traits by genome-centric metagenomics, was conducted to ascertain whether the beneficial effects of organic fertilization were maintained 4 years after its end. In general, but not always, soils treated with composted organic wastes showed significantly higher values of many physicochemical and biological properties (e.g., organic matter, Olsen phosphorus and extractable potassium), resulting in improved soil multifunctionality. However, despite such statistical significance, the quantitative magnitude of many of those differences was small. Fertilization regimes had a lasting strong influence on soil prokaryotic communities, as 70% of the 200 metagenome-assembled genomes and 86% of the prokaryotic functional traits showed significant differences among treatments. Organic amendments promoted nitrifying taxa such as Nitrosocosmicus oleophilus and Nitrospira japonica . In minerally-fertilized soils, resource acquisition and stress tolerance strategies were fostered among prokaryotic communities, possibly due to resource limitation and soil degradation, respectively. Stress tolerance traits were lower under organic fertilization, likely due to the improved soil properties and functions. The results obtained suggest that soil functions are influenced by microbial genes involved in nitrogen and carbon cycling, underscoring the central role of microbial metabolism in sustaining soil health and ecosystem functioning. This study demonstrates the lasting benefits of composted organic amendments in promoting soil multifunctionality in vineyard soils.