Special Issue: ‘Sustainable Viticulture: Soil Fertility, Plant Nutrition and Grape Quality’

1. Introduction

Sustainable viticulture is the practice of growing grapes indefinitely—for winemaking, juice production, or fresh or dry consumption—while upholding the highest standards of product quality and environmental stewardship [1,2,3]. Achieving this goal requires the adoption of integrated soil, water, nutrient, vine, and post-harvest management practices that enhance vineyard health, protect the environment, and promote consumer well-being, in line with the “One Health–One World” paradigm [4].

While the concept of sustainability in viticulture is readily defined, its practical implementation is considerably more complex. The multifaceted interactions among viticultural production factors, coupled with the wide variability of grape-growing conditions globally, present significant challenges for viticulturists [5]. Striking a balance between production and grape quality objectives, while optimizing the vineyard’s edaphoclimatic potential, requires careful management to avoid compromising long-term vineyard viability and environmental sustainability [6,7,8], [Contribution 10].

Therefore, addressing the challenge of sustainability in viticulture requires a robust foundation of knowledge, and it is not surprising that science can serve as the critical source of insights capable of driving meaningful progress. This need has been clearly recognized by the agricultural research community, as evidenced by the remarkable rise in scientific publications tackling the subject of viticulture sustainability, from only 1 paper in 1999 to 214 in 2024 according to a SCOPUS search for the words viticult* and sustainab* in the title, the abstract and keywords of papers indexed therein.

It is within this context that this Special Issue was conceived. It was launched with the aim of gathering a representative collection of recent research advances in the pursuit of sustainable viticulture. As a result, it features ten new studies focused on the impacts of several practices dealing with soil, water, nutrients, vines, and grapes on the health of viticultural systems.

These investigations vary in their methodological approaches depending on the specific research questions addressed in each case, encompassing three of the most commonly used types in scientific research: primary experimental [Contribution 1, Contribution 4, Contributions 8–9], primary observational [Contributions 2–3, Contributions 5–7], and secondary research [Contribution 10]. Notably, primary modeling research is the only major category not represented.

Furthermore, the primary investigations in this Special Issue originate from a variety of viticultural regions scattered throughout the world within the 34–43º N and the 22–31º S latitude belts, featuring three continents, in which Europe is the most represented, with four works developed in southern Italy [Contribution 1], northwestern Spain [Contributions 7–8], and northern–central Spain [Contribution 3]; followed by the Americas with three works developed in southwest USA [Contribution 2] and southern Brazil [Contribution 6, Contribution 9]; and finally Asia, with two works developed in northern–central China [Contribution 5] and southern–central Turkey [Contribution 4].

As a result of their global distribution, the investigations presented in this Special Issue reflect substantial diversity in environmental conditions, which in turn influence management strategies for grape cultivation. These include vineyard altitudes ranging from 50 to 1400 m and climate characteristics—according to the soil temperature and moisture regimes defined by Soil Survey Staff [9]—spanning from mesic to thermic temperature regimes and from perudic to aridic moisture regimes, encompassing all the intermediate udic, ustic, and xeric, leading to a range of water management strategies from rainfed to fully irrigated systems. Finally, the soil properties also vary widely, with pH values ranging from 4.6 to 8.1, clay varying from 10 to 35%, sand from 30 to 70%, and soil organic matter (SOM) from 0.3% to 9.0%.

In the next section, an overview of the research articles included in this Special Issue is provided. For clarity and ease of reference, the articles are grouped into three thematic categories: (1) Soil Management for Vineyard Health, (2) Soil Water, Nutrients, and Vine Management for Grape Yield and Quality, and (3) Post-Harvest Treatments for Grape Quality.

2. Overview of the Published Articles

2.1. Soil Management for Vineyard Health

The adoption of conservation and regenerative agricultural practices (CRAPs) is essential for improving soil health both on site and beyond. For perennial crops like grapevines, soil-centered minimum-to-no-tillage CRAPs can be broadly categorized into four main types. These are (i) mulching with organic materials, (ii) incorporating organic matter into the soil, (iii) inoculating the soil with beneficial organisms, and (iv) establishing cover crops [Contribution 10]. In this Special Issue, the impacts of these four soil-centered minimum-to-no-tillage CRAPs in viticulture are reviewed [Contribution 10]. In addition, this Special Issue also includes newly focused studies about the effects on soil health of two of these CRAPs, namely mulching [Contribution 1] and cover crop establishment [Contribution 8]. Additionally, novel investigations addressing the effects on vineyards’ soil health of irrigating with untreated wastewater [Contribution 2] and of SOM in zinc-polluted vineyards [Contribution 7] are presented.

The synthesis of primary research by Visconti et al. [Contribution 10] reviews the factors that affect a vineyard’s soil health in depth. This is a narrative review in which the authors address the concept of soil health from a holistic perspective and how it applies to the special case of viticulture. In fact, wine, the most precious produce of vineyards, boasts obtaining some of its most distinctive traits from the soil on which grapevines are cultivated. These traits are wrapped within the terroir; however, since viticulture also makes harsh impacts on soils, is the terroir not threatened? The authors try to address this inconvenient question by presenting the different aspects into which soil health splits, how conventional agricultural practices affect soil health, how it could be enhanced, how it is related to the terroir, and how soil health status can be assessed.

One significant threat to soil health in vineyards is copper (Cu) accumulation, resulting from its widespread use as the active ingredient in grapevine fungicides [10,11,12]. In this Special Issue, the primary experimental, climate-chamber-based study by Vázquez-Blanco et al. [Contribution 8] explored the potential of perennial ryegrass (Lolium perenne L.) to enhance soil health, including its likely capacity for Cu phytoremediation, across a broad range of soils representative of the renowned northwestern Spanish viticultural region. Perennial ryegrass is revealed to exhibit a notable ability to exclude Cu uptake, and therefore it is attributed with a low potential for effective phytoremediation. However, viewed from another perspective, the strong performance of perennial ryegrass across diverse soil types, ranging from acidic to mildly alkaline, and with varying levels of Cu pollution, suggests that it may be highly suitable as a cover crop, particularly where soil Cu is high. Specifically, its use could contribute to soil health improvement in vineyards, capitalizing on the multiple soil ameliorating effects of cover crops [13,14,15], while posing minimal risk of Cu mobilization to the other environmental compartments. Particularly significant in this regard is its role in protecting the biota from Cu toxicity.

Zinc (Zn) accumulation poses another heavy metal risk to vineyards’ soil health, primarily due to its use as an alternative or complement to Cu in managing fungal diseases in viticulture [16]. In this Special Issue, the primary observational, survey-based study by Pérez-Rodríguez et al. [Contribution 7] investigates Zn availability in vineyard soils and how it may shift following afforestation resulting from vineyard abandonment. Interestingly, SOM, particularly its degree of transformation (humification), as indicated by decreasing carbon-to-nitrogen (C/N) ratios, emerges as a key factor influencing Zn bioavailability and mobility in the environment. This occurs because, as SOM mineralizes, it releases low-molecular-weight, water-soluble organic ligands that complex Zn²⁺, stabilizing this heavy metal in the soil solution and hence increasing its availability and mobility. This investigation, therefore, highlights a case in which an increase in SOM might negatively impact soil and environmental health, by enhancing the mobilization of potentially toxic elements [17,18].

In addition to cover crop development, organic mulching is another CRAP that can promote soil health recovery in vineyards, since it has been shown to be particularly effective in mitigating raindrop impact and in buffering thermal and moisture soil regimes, with eventual SOM-enhancing effects in agriculture [19,20]. This Special Issue features a primary experimental, field-based study by Blanco et al. [Contribution 1], which examines the impact of mulching with municipal solid waste (MSW) compost on the row line soil health of a 5-year-old vineyard situated on flat terrain in southern Italy. The cooling effect of MSW compost on soil temperature in this hot summer environment was clearly evident. However, the anticipated SOM-increasing impact from this thermal buffering was less apparent. It is hypothesized that the likely SOM boost may be offset by a “microbial inoculation effect” associated with the MSW compost, potentially stimulating SOM decomposition. Notwithstanding, further research is needed, as the potential contribution of the MSW compost itself, as well as that of vine residues, to the fresh SOM pool, and consequently to overall SOM enhancement, was not assessed in this investigation.

In addition to solid organic materials like composts, untreated wastewater may serve as an effective source of both organic matter and nutrients to improve vineyard SOM and soil nutrients’ concentrations in available form [21]. In this Special Issue, Mpanga et al. [Contribution 2] explore this possibility through a primary observational, field-based study conducted in a 20-year-old vineyard in central–northern Arizona (USA). The vineyard is irrigated with two types of water, ditch and fishpond, at an approximate rate of 3.3 mm per week. Although both water sources are similar in physicochemical properties, the fishpond water appears to contribute organic matter to the soil due to its algae content. This characteristic may explain how soils irrigated with fishpond water outperform those receiving ditch water in terms of SOM, phosphorus, and soil respiration, factors that are ultimately associated with a remarkably enhanced grape yield. However, further research is required, given the inherent limitations of observational studies in establishing causal relationships [22,23], and also given the associated health hazards that untreated wastewaters may bear [21].

2.2. Soil Water, Nutrients, and Vine Management for Grape Yield and Quality

Soil management is not the only factor influencing vineyard health and terroir—soil water and canopy management also play crucial roles [Contribution 10], above all under water scarcity conditions. Therefore, a comprehensive approach that integrates all three aspects is essential for developing sustainable viticultural systems. Specifically, the management of the physical and chemical fertility of the soil significantly regulates vine vigor, berry development, and ultimately, grape yield and quality [24,25]. Additionally, the regulation of grapevine fertility through pruning has a substantial impact on these same traits [26,27,28]. In this Special Issue, three newly focused studies explore the effects of soil physical fertility attributes and pruning practices on grapevine performance.

First, the study by Martínez-Vidaurre et al. [Contribution 3] examined how water stress—assessed through the model-simulated ratio of available soil water (ASW) to soil water-holding capacity (SWHC)—influences vine nutritional status, vigor, yield, and grape and wine composition. This primary observational field-based study was conducted in four rain-fed Vitis vinifera cv. ‘Tempranillo’ vineyards, aged 20 to 35 years, located in Spain’s Rioja wine region, whose vines were grown over five seasons. The results showed that soils with a higher SWHC increased the ASW-to-SWHC ratio, thus reducing grapevine water stress, particularly during the critical fruit set to ripening stage, which in turn enhanced nutrient status, vine vigor, and grape yield, but led to lower total soluble solids (TSSs) in the grapes. Specifically, the period between veraison and ripening was identified as particularly sensitive to water stress, as increases in the ASW-to-SWHC ratio during this stage led to higher berry weight and acidity, alongside reductions in the anthocyanin concentration and total polyphenols. Interestingly, the effects of water stress on grape composition were reflected in the wine for anthocyanins and polyphenols, but not for TSSs (i.e., alcohol concentration) or acidity.

Consistent with the findings of Martínez-Vidaurre et al. [Contribution 3], Uriarte et al. [29] have observed in a mega-analysis that lower water stress—typically associated with higher irrigation rates—leads to overall increased yield and vigor, but to reduced TSSs and concentrations of anthocyanins and phenolics in grapes. Regarding the impact of water stress timing, Theocharis et al. [30] observed that when it happens prior to veraison, it can enhance anthocyanin accumulation in red grape varieties.

Therefore, the findings of Martínez-Vidaurre et al. [Contribution 3] reinforce the broader consensus on the effects of water stress on grapevine development and quality, and that the effects on grape composition—and consequently on wine quality—are modulated by the phenological stage at which the stress occurs. Furthermore, the study by Martínez-Vidaurre et al. [Contribution 3] underscores the importance of developing integrated water management strategies that consider the SWHC, which depends on the product of the soil effective depth (SED), one minus the coarse fragment fraction (1—w_CF), and the difference between the soil water content at field capacity and at wilting point (ϴ_FC–ϴ_WP). Therefore, this study suggests that rising SED, 1—w_CF or ϴ_FC–ϴ_WP —such as by regeneratively avoiding soil compaction, removing gravels, stones, and cobbles from the subsurface soil layers, and increasing SOM —will be essential for sustaining grape yield and quality amid increasingly variable and arid climatic conditions, thereby supporting the long-term sustainability of viticulture, particularly in the context of climate change.

The ASW depends, in addition to the SWHC, on climate wetness. However, edaphoclimatic conditions may impact grapevines not only through their effects on the ASW, but through the rest of the soil properties that traditionally define fertility and, specifically, chemical fertility and, furthermore, through all climate features. In this issue, Andrade et al. [Contribution 6] investigated how grapevine, soil, and climate characteristics influence yield variation by means of several statistical methodologies with the aim of reducing the uncertainty of grape yield predictions during pre-harvest negotiations, thus supporting more informed decision-making throughout the viticultural supply chain. This primary observational field-based study was conducted on rain-fed grapevines aged 2 to 40 years, encompassing 27 cultivars grown for 14 seasons in a commercial vineyard located in the Campanha Gaúcha emerging wine region in southern Brazil. Among the most influential factors driving yield variation were plant age, plot location, start-of-dormancy temperatures, and the available soil concentrations of key nutrients (Zn, Cu, potassium (K), and manganese (Mn)). Interestingly, SOM did not emerge as an influential factor, which may be due to the overall low average SOM content (0.75%), in conjunction with its narrow range of variation in the study area (0.5–1.5%). Regarding the macronutrients, the absence of N data in the study dataset unfortunately prevented the evaluation of its effect, while the likely sufficient supply of P in the vineyard, due to the site’s commercial management, may have masked any potential impact.

Besides Andrade et al. [Contribution 6], the impact of soil characteristics on grapevine performance is further explored in this Special Issue by Li et al. [Contribution 5]. Their primary observational field study was conducted across six Vitis vinifera cv. ‘Cabernet Franc’ vineyards located in the rapidly developing wine-producing region on the Eastern Foothills of the Helan Mountains in China. In contrast to the study by Andrade et al. [Contribution 6], the work by Li et al. [Contribution 5] expands the analysis beyond overall yield to include yield components and grape quality traits, encompassing both technological and phenolic ripeness characteristics. Yet, consistent with Andrade et al. [Contribution 6], Li et al. [Contribution 5] found that SOM —with an average of 1.2% and a range of 0.3–3.7%—was not associated with grape yield, despite being strongly associated with the soil concentrations of macronutrients—nitrate nitrogen (N-NO₃⁻) and P—as well as with available micronutrients such as iron (Fe) and manganese (Mn). However, SOM emerged as particularly linked to grape quality.

Interestingly, grape technological ripeness traits were separated into two groups: TSS was moderately associated with Mn and Zn, while acidity-related traits were more strongly linked to SOM and its associated nutrients in the study area (N, P, Fe, and Mn), along with Zn. Phenolic ripeness traits also exhibited a split: tannins and anthocyanins were moderately associated with SOM and its related nutrients (N, P, Fe, and Mn), whereas flavonol concentration was also associated with SOM and the same nutrients, but more strongly, and additionally, to soil pH.

The study concludes that tailored soil management strategies focusing on SOM enhancement and balanced macronutrient levels can optimize grape composition and quality. In this regard, limits for optimal berry traits were calculated—e.g., SOM between 2 and 3% and total nitrogen (TN) above 0.1%—thereby offering actionable guidelines to improve phenolic richness and acidity balance in wine grapes [Contribution 5].

In addition to the management of soil, soil water, and nutrients, canopy management plays a vital role in developing sustainable viticultural systems [Contribution 10]. Particularly, pruning stands out as one of the most influential management practices on grapevine health and performance by impacting disease susceptibility, vigor, yield, and grape quality [28,31].

In this issue, Sánchez et al. [Contribution 9] examined how pruning severity, i.e., the number of buds left per cane, at two levels, namely, short (spur) and mixed (a combination of spur and cane pruning), affects the duration of phenological stages, thermal requirements, and ripening progression in three grape juice cultivars (‘Bordô’, ‘BRS Cora’, and ‘BRS Violeta’). This primary experimental, field-based study was conducted on irrigated grapevines over two growing seasons in a vineyard located in São Paulo, southeastern Brazil, under a humid subtropical climate. The results showed that there were no significant differences between short pruning (one to three buds left per cane) and mixed pruning (a combination of one to three and four to twelve buds left) with regard to the duration of phenological stages, thermal requirements, or the progression of ripening with the exception of the ripeness index, i.e., the ratio of TSSs to titratable acidity (TA), which was overall significantly lower for mixed pruning.

The diminishing effect of mixed pruning on the ripeness index warrants further investigation, particularly in wine growing, as it may help to counteract the climate change-driven trend of increasing the TSS-to-TA ratio in grapes, which runs counter to the preferences of wine consumers [32]. Moreover, severity is only one of several parameters that define the pruning of grapevines. Another key factor is, e.g., the pruning aggressiveness, which is determined by the amount of protective wood left between the pruning cut and the vine’s permanent structures, as well as whether the vine’s preferential sap flow pathways are preserved [31]. Therefore, future studies should explore both the individual and combined effects of the factors that define the pruning technique on vine yield and grape quality across diverse training systems, cultivars, trellis designs, and climates. The goal is to refine pruning practices to better align with specific growing conditions, grape yield and quality objectives, and vineyard health priorities.

2.3. Post-Harvest Treatments for Grape Quality

Complementing previous research on soil properties, water availability, nutrient dynamics, and canopy management, Kaya et al. [Contribution 4] investigated how post-harvest treatments, differing in environmental sustainability, impact grape quality. Specifically, they examined the effects of two alternative shade-drying methods on the phytochemical composition of grapes destined for raisin production. This primary experimental study, conducted in Hadim and Karaman (southern–central Turkey), focused on the phenolic profiles of ‘Gök Üzüm’ grapes subjected to hot dipping in either oak ash or potassium carbonate (K₂CO₃) aqueous solutions prior to shade drying.

Oak ash, a by-product of oak wood burning, represents an a priori more sustainable alternative to K₂CO₃, which is an industrially produced chemical. Using advanced analytical techniques (HPLC-DAD-MS and UHPLC-MS/MS), the authors quantified key grape constituents, including anthocyanins, flavonoids, phenolic acids, and phytoalexins.

The results revealed that grapes treated with oak ash exhibited significantly higher levels of most phenolic compounds. For instance, anthocyanidins reached 215 mg/kg under oak ash treatment, compared to 154 mg/kg with K₂CO₃. Similar enhancements were observed for flavonols (68 vs. 50 mg/kg), flavanones (15.1 vs. 11.0 mg/kg), catechins (61.6 vs. 39.8 mg/kg), and resveratrol (33.8 vs. 23.2 mg/kg). Delphinidin-3-O-glycoside, a key anthocyanin, was also significantly more abundant in grapes subjected to oak ash treatment. Principal Component Analysis further supported these compositional differences, showing clear clustering of samples based on the pre-treatment applied.

While both treatments altered the berry composition, oak ash consistently enhanced attributes linked to antioxidant capacity and color stability—critical factors for raisin quality and consumer appeal. In contrast, K₂CO₃ treatment was associated with elevated levels of certain hydroxybenzoic acids (gallic, vanillic, etc.), which feature antioxidant, anti-inflammatory, cardioprotective, neuroprotective, anticancer, and antimicrobial potential [33,34], although overall phenolic retention was lower. These findings highlight the sensitivity of grape composition to brief chemical pre-treatments and underscore the importance of aligning processing methods with desired nutritional and functional outcomes in grape products.

Future research might also explore the potential introduction of harmful substances into the food chain resulting from the use of wood ashes in post-harvest treatments. These ashes may be enriched with heavy metals and some xenobiotic organic compounds, depending on the wood’s composition and its combustion conditions [35]. Furthermore, upcoming studies might incorporate comprehensive Life Cycle Assessments (LCAs) and Carbon Footprint analyses to ensure a thorough evaluation of environmental impacts. By addressing these critical aspects of grape, raisin, grape juice, and wine production, holistic “One Health” assessments can be developed, ultimately maximizing viticultural and societal benefits.

3. Conclusions

As demonstrated by the studies in this Special Issue, modern viticulture is inherently multifaceted. The effective management of soil, water, nutrients, pruning, and post-harvest practices is essential not only for optimizing grape yield and quality, but also for promoting environmental sustainability.

To frame the subject, Visconti et al. [Contribution 10] examined the pivotal role of soil health in sustaining vineyard productivity and terroir expression. Their work highlights the detrimental impacts of conventional viticultural practices on soil properties, the benefits of enhancing SOM and soil biological activity, and the pressing need for sustainable management strategies to ensure long-term viticultural and environmental viability.

In this context, SOM consistently emerges as a key determinant of vineyard health throughout the contributions to this Special Issue. As shown by Mpanga et al. [Contribution 2], SOM plays a crucial role in improving soil physical, chemical, and biological fertility. However, as Pérez-Rodríguez et al. [Contribution 7] illustrate, SOM may also contribute to undesirable outcomes, particularly in vineyards affected by heavy metal pollution (e.g., Zn contamination), emphasizing the need for site-specific management approaches.

Addressing soil biological fertility, Blanco et al. [Contribution 1] demonstrated the potential of MSW compost in mitigating soil temperature fluctuations, thereby enhancing soil microbial activity. These effects may bolster plant resilience and support environmental sustainability in grapevines, particularly when exposed to warm climates. In parallel, Vázquez-Blanco et al. [Contribution 8] explored the use of cover crops in vineyards with coarse-textured soils and acidic to mildly alkaline pH values, showing their potential to improve soil and environmental health, particularly where elevated soil Cu levels have become a concern.

Beyond soil management, several studies emphasized the critical role of soil water availability. Martínez-Vidaurre et al. [Contribution 3] demonstrated how soil water status influences vine health and berry composition, underscoring the importance of sustainably enhancing the soil water-holding capacity and precisely managing plant water stress during key phenological stages to balance yield and grape quality. Advancing the field, Andrade et al. [Contribution 6] showcased the application of machine learning algorithms to predict grape yield in support of early marketing decisions, illustrating the potential of data-driven approaches in viticultural management. Similarly, Li et al. [Contribution 5] examined the influence of soil characteristics on grape yield and quality, further emphasizing the importance of site-specific soil management.

In addition to soil, water, and nutrients, pruning practices also play a significant role in vineyard sustainability. Sánchez et al. [Contribution 9] investigated how different pruning methods affect berry chemistry, particularly in subtropical climates, providing insights into how canopy management can influence grape maturation and quality. Finally, Kaya et al. [Contribution 4] explored the modulation of grape phytochemical composition through post-harvest treatments, particularly comparing two shade-drying methods of differing environmental sustainability for raisin production.

Collectively, these studies reflect a clear and ongoing shift towards sustainable viticultural practices, particularly regarding soil fertility, plant nutrition, and grape quality. We believe that this collection of articles provides both valuable insights and practical guidance for viticulturists, agronomists, and researchers striving to enhance vineyard performance while fostering resilient and eco-friendly viticultural systems.