Long-term soil functional differences between spontaneous cover cropping and tillage in a semi-arid vineyard

Context Soil degradation and water scarcity pose critical challenges for vineyard sustainability in semi-arid regions. Objectives This study evaluates the long-term effects of spontaneous cover cropping (CC) on soil health in a rainfed vineyard in central Spain, managed without irrigation or pesticides for over two decades. Methodology By comparing soils under CC and conventional tillage (TILL), we assessed changes in soil physical properties (porosity and water retention), nutrient content, and microbial function up to 30 cm depth. Stepwise regression analysis was used to explore management-driven relationships among CC, soil properties and nutrient dynamics. Results Soils under CC showed significantly higher organic matter content (1.74 ± 0.37% in the topsoil with CC vs. 0.83 ± 0.24% in TILL) and porosity (51.2 ± 2.5% vs. 44.0 ± 1.8% at 10–30 cm depth). Available phosphorus tended to be higher under CC (19.13 ± 0.60 mg/kg in CC vs. 14.13 ± 4.52 mg/kg in TILL), and this trend was further supported by stepwise analysis, which identified P availability as a variable influenced by management practices. Enzymatic activities were consistently elevated under CC, particularly in the topsoil; β-glucosidase (25 ± 9 mU/g) nearly doubled the value observed under tillage. Although soil water availability showed a non-significant trend in the topsoil (10 cm), it was higher in the subsoil (30 cm) under CC (29.0 ± 0.97% vs. 25.1 ± 0.32% in TILL). The stepwise regression analysis supported a management-driven model where CC influence soil organic matter (SOM) and nutrient availability. SOM and soil moisture strongly influenced extractable phosphorus (R² = 0.790, p =0.0047) and mineral nitrogen (R² =0.907, p =0.00018), with moisture at the time of sampling emerging as the dominant driver of nitrogen dynamics. Conclusions The analysis supports a management-driven pathway in which long-term vegetation inputs under CC enhance SOM accumulation. Soil water availability tended to increase in the subsoil under CC, while SOM together with short-term moisture conditions emerged as the main regulators of nutrient dynamics under semi-arid conditions. Implications By aligning ecological processes with practical agronomic outcomes such as nutrient retention and soil structure, these findings offer compelling evidence to support the broader adoption of sustainable ground cover practices in Mediterranean viticulture.