Enhancing the Soil Sponge Function and Reducing Soil Degradation in Mediterranean Vineyard Soil: Synergies between Biochar Application and Vegetation Cover

Abstract

Sustainable land management in Mediterranean vineyards faces several challenges, including land degradation, drought, and climate change impacts, often exacerbated by extreme weather events. We hypothesised that biochar enhances the soil sponge function, thus promoting vegetation growth, and that this synergy can significantly reduce runoff and soil erosion. To address these hypotheses, we conducted a random-block design box lysimeter experiment from September 2019 to October 2020 under natural rainfall conditions at a slope gradient 14.4. A Regosol soil type with sandy loam texture collected from the Bairrada’s Denomination of Origin region (Central Portugal) was used. Soil treatments consisted of untreated soil as the control and woody biochar-amended soil with the maximum sustainable concentration of 4% (w/w), both sown with a biodiverse pasture seed mixture. There was an improvement in soil physiochemical and hydrological properties, i.e. bulk density decreased by 12%, water infiltration and soil water content increased by 50% and 59%, and the soil pH increased to neutral conditions. Soil water repellency only in the biochar-amended treatment remained within wettable conditions. The vegetation cover and aboveground biomass increased by 235% and 198%, respectively. Vegetation cover significantly affected all erodibility parameters, i.e. reduced runoff and soil erosion (fine earth fragment) by 50% and 58%. This study suggested that a combination of biochar application and vegetation cover can improve the soil sponge function and mitigate erosion of vulnerable acidic soils. This approach offers a practical strategy for sustainable soil management, especially during hydrological seasonality (dry to wet conditions) in Mediterranean vineyards.

Keywords: Soil sponge function, Soil erosion, Soil hydrophobicity, Atmospheric River (AR), Nature-based solutions