Inter-row floor management is a powerful factor for optimising vine balance in a non-irrigated organic Barbera vineyard in northern Italy

Floor management in organic viticulture plays a key role as weed suppression and soil health must be warranted through practices that minimise the recourse to extensive tillage and herbicides, while any resident vegetation or sown cover crop should exert moderate competition for water and nutrients towards the consociated vines. Lack of knowledge exists about the fraction of soil cover crop coverage (Scc) which might represent the best compromise between the above needs. A four-year study (2017–2020) was conducted in an organically managed cv. Barbera/420 A vineyard in the North-West of Italy, comparing five floor management treatments each having light tillage as the practice chosen to control the under trellis weed growth. Inter-row treatments were permanent grass (PG), tillage (T), alternate tillage and permanent grass every second mid-row (AGT), a variant of this last treatment, where the tilled mid-row was used for growing a temporary winter cover crop terminated in spring (AGC) and temporary grass (TG) where grass was disked post-harvest (mid-October) until natural growth resumption in late winter (mid-February). An assessment was made for soil profile and physicochemical composition, floristic analyses performed in T, PG, and TG treatments, vegetative growth, yield components, grape maturity at harvest, single leaf gas exchange as well as midday and pre-dawn leaf water potentials. While overall scant, mostly season-related differences were found for leaf function and water status, soil management heavily impacted vine performance. Year-round soil cover crop coverage (Scc) regressed towards total pruning weight/vine and yield/vine showed high linear correlation (R2 = 0.93) for pruning weight/vine (to be reduced by 38% at 75% Scc vs. 0% Scc of the T treatment), whereas yield/vine was quite poorly correlated (R2 = 0.21) showing a 15% decrease in PG vs. T. Regressing Scc vs total soluble solids (TSS), titratable acidity (TA), total anthocyanins and phenolics concentration disclosed mild linear correlation (R2 = 0.52) for the two technology ripening parameters and a much tighter fit for colour and phenolics (R2 = 0.79 and 0.90, respectively). AGT had an intermediate behaviour between its two extremes (i.e. T and PG) without assuring any significant marginal gain. Conversely, modulating PG into TG through a temporary removal of the resident vegetation in the fall and AGT into AGC by growing a winter cover crop terminated in the spring as mulching, gave the highest yield at adequate technological and phenolic ripeness. PG assured maximum grapes total soluble solids and total anthocyanin concentration at harvest; however, due to its low vigour, several shortcomings also followed, such as low yeast available nitrogen and malic acid concentration, as well as a tendency to accumulate high amounts of flavonols. Our work led to the conclusion that AGC and TG treatments are quite valuable choices under the specific environment for successful soil management in organic vineyards.