The impact of biochar application on sponge function, water erosion, and vegetation cover in a Mediterranean vineyard soil

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, i.e. a combination of infiltration and retention of rainwater, thus promoting vegetation growth, and that this can be considered an indirect mechanism to 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 of 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. Biochar reduced runoff and soil erosion (fine earth fragment) by 50 % and 58 %. There was an improvement in soil physical and hydrological properties, i.e. bulk density decreased by 13.1 %, enhancing soil sponge function involving increasing water infiltration and soil water content by 50 % and 59 %. Soil water repellency only in the biochar-amended treatment remained within wettable conditions. The vegetation cover and aboveground biomass increased by 263 % and 198 %, respectively, due to an increase in soil pH to neutral conditions, improvement of essential nutrients (NPK) and the reduction of toxicity in biochar amendments. This study offers a practical strategy for sustainable soil management against traditional approaches, especially the observed biochar-vegetation synergy during hydrological seasonality (dry to wet conditions) in Mediterranean vineyards.