Soil conservation benefits of biochar in Mediterranean vineyards: enhancing soil sponge function and mitigating erosion

Soil erosion by water poses major environmental challenges to the European viticulture sector. Biochar is recognised as a sustainable tool for combating land degradation, but few studies have been conducted in Mediterranean vineyards with hilly terrain and heavy rainfall. This study assesses the potential of biochar to support soil conservation by enhancing sponge function, i.e. water retention and infiltration, and reducing erodibility in sloping sandy loam soil under natural rainfall conditions. An 18-month outdoor box lysimeter experiment was conducted using bare soil, including soil amended with 4% (w/w) biochar from a Portuguese vineyard. Over the monitoring period, biochar application significantly ( p <0.001) reduced the runoff coefficient by an average of 45%. Biochar reduced coarse fragment erosion by 67%, fine-earth erosion by 43%, and splash erosion by 34%, all affected ( p <0.05) by rainfall intensity. The erosion rate in vineyard soil was 3 times lower ( p <0.001) in biochar-amended than in control (3.7 vs. 11.1 t ha ⁻¹ yr ⁻¹ ). Improved soil structure led to a 7% reduction in bulk density, an average increase of 73% in stored water, and a 28% increase in infiltration rate. During drier periods, the biochar-amended soil stored 171% to 303% more water than the control soil. We recommend a minimum monitoring period of a full hydrological cycle under natural rainfall to comprehensively capture the effect of biochar on the soil sponge function. Observed seasonal trends and atmospheric river (AR) events suggest that studies using rainfall simulations without considering antecedent soil moisture and AR variations will yield skewed data on effects.