3.1. Vineyard Soil Characteristics

Regarding winemaking objectives, it is important to optimize support for high crop quality and quantity. It is a well-known fact that soils influence wine grape quality. In fact, the impact of soil, when combined with climate, topography, and grapevine variety, is referred to as the terroir effect [29]. Although soil is one of the most important factors in wine quality [29], globally speaking, grapevines are planted in an extremely wide variety of soils. Vogel [30] considered that each soil has a limited potential to deliver a certain soil function, and that soil health assessments should reflect soil status in relation to its potential. Sustainable, efficient soil use is essential for supporting continued vineyard production and quality. However, the scientific names of the soils being cultivated for growing wine in the Valdepeñas PDO are unknown, but their properties are known on a very detailed scale.

Soil morphological and physicochemical characteristics and mineral content provide us with important information for assessing soil type and, consequently, the sustainability of viticulture. Different properties lead to distinct soil types and impact management improvements. Based on the field description and laboratory data, the different soil profiles were classified according to Soil Taxonomy [28] and the Reference Base for Soil Resources [31], as observed in Table 1 and Figure 3.

Results provided evidence that vineyards develop and grow in soils with acceptable qualities. In this way, the soil pH (that provides information about the solubility and availability of nutrients for vine growth) range from 7.1 to 8.4, (Table 2) which are rated as moderately to slightly basic [32]. The CEC, with values of samples ranging from 13.3 to 19.5 (cmol+·kg?1), is dominated by the cation Ca2+, therefore always with a degree of saturation of 100%. Organic matter (that occurs in moderate to low contents, between 0.1 and 1.5%, typical of semiarid regions), is an important parameter that affects soil quality and agriculture sustainability; in no case are soil amendments, such as dolomite, used given the area’s predominantly carbonate nature. Soil texture is one of the major soil physical characteristics to determine vine growth. Vines should be grown on soils with good drainage, aeration, and permeability. Therefore, soil texture is not a limiting factor for vine production in the study area because most textures are clay loam and clay, which can be classified as suitable soil textures for vine production [33] (Table 2). Table 3 shows the mean values of the concentration of macronutrients in these soils, where moderate P and N contents are highlighted.

Vine needs soil that is well drained and not very wet. The drainage classes of the study area are classified as two soil permeability property classes: well drained and moderately drained. The color of Valdepeñas PDO soils is very striking because many are red, and others are white due to the high carbonate content (Table 2). According to Lazcano et al. [32], while soil temperature appears to be relevant for terroir, it has not often been associated with soil health assessments.

Several authors [34,35] have mentioned that vineyards in the old world were often established on marginal land, and the most fertile soils were reserved for growing cereals and other food crops, while extensive land availability in the new world offered deep, alluvial, fertile soils for vineyard establishment purposes [17]. As a result, vineyards arguably occupy a wider range of soil types than any other crop. In Valdepeñas, there are vineyards on very varied soils, but most are of good quality.

It is known that plant nutrients play an important role in plant physiology and metabolism. However, viticulturalists in this area have been unaware that they have been optimally managing soil nutrient supply because K deficiencies are not observed.

About 22–56 kg of N ha?1 is removed from wine grapes through harvest [17]. Soil N supply and retention are fundamental in viticulture because N is one of the most limiting nutrients for vine growth. Therefore, an adequate N supply is crucial for good vineyard productivity. Thus, as N and P contents are moderate (Table 3), farmers have worked without overapplying N fertilizer. Lazcano [32] stated that it is clear that vineyard N status must be very carefully managed to strike a vine health–grape quality balance.

The Valdepeñas PDO is a typical area with a semiarid Mediterranean climate. Therefore, water scarcity can become an issue, especially in the light of climate change [36,37]. There are generally no drainage problems, but managing water availability is somewhat more complicated if the aim is to improve productivity and quality. We should bear in mind that excessive water availability can promote vigor and cause direct and indirect negative effects on wine grape quality [17,38]. Many soils in the Valdepeñas PDO are finer-textured soils with a higher water-holding capacity compared to coarser-textured soils.

3.2. Vineyard Soil Management; from the Past to the Future through the Present in the Valdepeñas PDO Vineyard Soils

Common practices in Valdepeñas vineyards are plowing or tillage, mineral fertilization, irrigation and drainage systems, and weed management. Organic amendments with manure are also very common because they provide a direct C source for soil organisms and an indirect C source via increased plant growth and plant residue returns [39].

Soil functions for vineyard include: (1) supporting high yield and grape quality; (2) good water infiltration and the capacity to store water; (3) retaining and recycling nutrients efficiently, while supplying nutrients in correspondence with crop demand, which can also be demanded; (4) storing C and reducing greenhouse gas emissions; and (5) supporting diverse microorganisms and marked biological activity. Soil’s capacity to perform these functions can be assessed by many chemical, physical, physicochemical, biological, and biochemical parameters, but the most informative and reliable ones are generally selected [40,41]. Agricultural vineyard systems and management practices that ensure high production often have negative repercussions on soil health, quality, and fertility [30,42].

Viticulture is a long-standing tradition in the Valdepeñas PDO, and management practices have hardly changed for centuries. Evidently, vineyard soil management has implications for wine quality [43,44]. Indeed, soil conservation, weed management, improvement in soil nutrients, water content, pest control, and resource availability regulation (i.e., water, nutrients) are very important aspects for controlling vine vigor and vine growth, and for influencing desirable wine quality targets.

In the Valdepeñas PDO, it is customary to use conventional agriculture in such a way that the application of phytosanitary products and mineral fertilizers is frequent, but it has always been restricted. For this reason, although these applications cannot be considered ecofriendly because their overuse can cause soil and water contamination, their negative effects have not really been incurred because they are scarcely added. In the study area, which has a dry climate and low rainfall, the incidence of fungal diseases is very low. Therefore, fungicides are only applied in small quantities [45].

In the Valdepeñas PDO, vineyards are based on a combined edaphic and climatic terroir to produce high-quality grapes and, above all, good productivity. Consequently, it is possible to affirm that this is an ideal scenario for authentic ecological viticulture.

Nevertheless, the vineyard field land use in the Valdepeñas PDO can be classified from a highly suitable class to a moderately suitable class. Soil is still quite potent in developing vineyard fields, but the presence of calcium carbonate indicates that soil has not undergone an intensive leaching process. This does not mean that it does not require fertilization management, but rather the other way around; that is, it requires solid OM being added to improve soil aggregate.

Although vineyard land use is located in a marginally suitable class, from the obtained results (Table 2 and Table 3) it can be deduced that the soil type requires the addition of solid OM. Therefore, it is a matter of improving a series of soil properties to maintain nutrients in soil, reducing nutrient leaching to improve soil aggregate, etc. Finally, to increase production, the addition of chemical fertilizers is necessary.

Globally speaking, agricultural practices are intensely used, such as continuous soil tillage, mineral fertilizer inputs, application of low-quality irrigation water, and removal of pruning waste, which have determined soil fertility loss and the depletion of soil OM. All this has had negative effects on both productivity and soil conservation [46] in many areas worldwide, such as southern Italy, and perhaps in the Valdepeñas PDO.

The climate factor is key in the terroir concept; thus, a positive correlation between high soil temperature and N, K, C, and Mg uptake exists [47]. Without going into the functions performed by climate in detail, it is known that inter-row spontaneous vegetation in Valdepeñas vineyards is controlled by grazing, tillage, and exceptionally by the application of herbicides, as in other areas [48,49,50,51,52]. To a certain extent, this has been carried out ancestrally by farmers, who have passed their knowledge from generation to generation. Thus, for example, until approximately two decades ago, dry vineyards predominated. Today, the opposite occurs, and with increasing intensity. The reason for this is very simple: unfavorable soil conditions, such as low water content due to soil mishandling, can cause plant stress, which has negative effects on both growth and yield. Water deficit also decreases photosynthetical activity and can affect differentiation and berry sizes [53].

Since halfway through the past century, or even before, the application of organic waste, mainly from livestock, was commonplace in Spanish vineyards. As is known, the main effect of such addition is to improve soil health in vineyards [46,47]. It is no surprise today that the literature about using organic additions, particularly compost in vineyards, is vast [54,55,56,57,58,59].

The application of OM, manure, or other byproducts could facilitate vertical water movement in soil [60] by increasing functionality and soil biological fertility and, therefore, improving soil quality and vineyard productivity. It is also known that OM additions to vineyard soils typically lower soil bulk density, improve aggregation, and lead to improved soil porosity [61,62,63,64].

Increases in OM lead to higher total N contents [54,58,65] and revitalize the presence of P [66,67]. In the case of P, it is known that deficiency in wine grapes has been reported in certain soil types with less than 10 mg P per kg soil [68]. Although the Valdepeñas soils contain little P, and a substantial number of soils are carbonate in nature, the addition of OM easily compensates for this P deficit. The viticulturists of Valdepeñas have, thus, been working correctly for many decades before present day. Given the carbonate nature of a considerable number of soils in Valdepeñas, the P management carried out by Valdepeñas viticulturists has been correct.

Increases in OM are also known to improve soil aggregation, infiltration, and water-holding capacity, and to lower bulk density [54,61,64,69]. OM additions have been suggested to be a potential C sequestration practice [58,70], and improve microbial biomass activity by providing nutrient cycling with beneficial effects, especially in degraded soils [71].

It should be noted that K is the major cation in grape juice and must. It also has a significant effect on juice pH [72]. In a wide range of studies with many different sources, compost application usually increases soil extractable K [58,68,73,74,75].

Today, however, traditional OM application has been replaced with other organic materials, such as composted sewage sludge, mushroom compost, composted cattle manure, winery waste, vermicompost, or pruning waste, which routinely increase soil total N [54,58,65,76,77]. However, these techniques have not been well accepted and are, therefore, not implemented by most Valdepeñas winegrowers.

The study of the metals that accumulate in agricultural soils due to agricultural practices (i.e., manure fertilization and pest control spraying) has been addressed on numerous occasions [78,79,80,81,82,83].

Although, for climate reasons, Valdepeñas is not an area prone to fungicide use, misuse by repeated applications of Cu-based fungicides in both conventional and organic farming can certainly create environmental problems. Therefore, it should be taken into account that Cu accumulation in vineyard soils can alter some soil properties, which compromises their fertility and induces toxicity in plants that, ultimately, has detrimental effects on growth and productivity.

A specific example is that represented by Cu accumulation in agricultural soils in general, and vineyards in particular. Vineyard soils are prone to Cu accumulation by uncontrolled applications of metal-contaminated sludge and/or Cu-based fungicides for crop defense against pathogens. Although Cu is an essential micronutrient for vineyards, excessive Cu in soil can lead to toxicity symptoms, particularly in acid soils, as stated by Miotto [84] and Brunetto [85]. This is rare in our case because Valdepeñas hardly has any acid soils. The studied soils have an average Cu concentration of 25.7 mg·kg?1 on the surface horizon and 23.2 mg·kg?1 on the subsurface horizon (Table 3). These values are in accordance with the concentration of world soils (25 mg·kg?1) [86] and are higher than those published by Reiman [87] (13 mg·kg?1) for European agricultural soils.

Compared to other crops, vine requires less water to grow and mature. However, the expected climate change can intensify water stress on vine, particularly in regions with limited water availability, which is the case of Valdepeñas. Ideally, the best practice for each vineyard site should be determined mainly considering vineyard design, soil type, and the climate conditions of the vineyard site, as stated by Ripoche [88] and Sweet [89].

The amount of water available for access by grapevine roots depends on the soil type, particularly on its physicochemical properties (profile depth, texture, structure, OM content, salinity, etc.). The ease with which root development occurs in both depth and laterally determines the effective grapevine root volume and, therefore, determines the volume of water that can be taken up by grapevine. Water is a limited vulnerable resource in Valdepeñas and, hence, irrigation demands have been increasing to offset the effects of environmental stress on vineyard cultivation [90].

Given the region’s semiarid climate, water management in vineyards requires irrigation if plants are not subjected to water stress, at least at certain vegetative growth times. However, the implementation of these irrigation techniques can lead to changes in the status of the soil organisms’ diversity and abundance. It is necessary to bear in mind that some organisms, such as earthworms and generalist predators, spiders and ground beetles, prefer higher moisture content [91,92]. Without knowing this effect, the winegrowers from Valdepeñas are meticulous irrigation caretakers, and have unknowingly cushioned this effect. Likewise, after irrigation in mid-summer (when temperatures of around 40 °C are reached), preferential calcium carbonate accumulation can be observed, such as that which appears in Figure 4D (whitish spots). They are carefully dealt with via minimal tillage, which is frequently carried out manually. Regarding potentially resistant weeds (as Conyza Canadensis, Figure 4D), it is desirable not to rely on a single strategy, in such way that in CLM herbicides are generally only used when necessary. The viticulturist of this region also tends to rotate the application of herbicides. In any case, it is advisable to carry out mechanical weed control practices, applying minimum tillage. However, perhaps the most important thing is that the viticulturist maintains permanent control of new weeds, cleaning them manually.

3.3. Future in the Valdepeñas Vineyards and Suitability

Agricultural production plays a vital role in generating enough capital for farmers’ socioeconomic conditions. The Valdepeñas PDO can produce a lot of good wine. However, farmers wish to produce more to meet increasing wine demand. To produce more, better and sustainably, adequate vineyard soil management ensures that nutrients are not deficient or toxic to vine, and appropriate nutrients enter the food chain. Thus, soil management is important both directly and indirectly for vineyard productivity, environmental sustainability, and human health. Moreover, if farmers currently wish to achieve sustainable viticulture, modern techniques with the least environmental impact must be used in such a way that productivity and quality over time are compatible [93,94].

Cover cropping in vineyards has been a common practice in several areas in the world, particularly in Europe [95]. It has been found [44] that cover cropping can improve soil and vine health; may influence vine vigor while increasing juice anthocyanins, soluble solids, and other phenolic components; and can decrease titratable acidity.

Currently, viticulture is undergoing change in such a way that vineyard areas are being reduced in certain world regions, while others tend to increase, albeit very gradually. Thus, it is worth highlighting the application of smart precision viticulture paradigms, and their related technologies could allow the timely, localized, and balanced distribution of, for example, agrochemicals to achieve the required goals. However, given the smallholding nature of the viticulturists in CLM and, therefore, in Valdepeñas, smart precision viticulture technologies are not used by farmers, only by large wineries. The reality is that viticulturists go out of their way to work their vineyards themselves day by day, with constant monitoring to maintain the phytosanitary status, an adequate humidity level, etc., to avoid having to make large investments in new equipment and techniques.

Therefore, given the way that the farmers in the region work today, such investments may not be necessary because they work family plots, and they work tirelessly and permanently every day so that vineyards and farmers’ families practically coexist closely on a daily basis. In fact, if some modern techniques, such as precision equipment, were used, it would entail a cost that winegrowers could hardly afford. This agrees with Caffaro [96] and Tey [97].

Among the traditional techniques, we can mention the following: mechanical tillage using traditional implements (plow) and with mechanical traction; predominantly, organic fertilization with manure from livestock in the area, mainly sheep; absence of irrigation: cultivation mainly in dry land; traditional conduction systems in “gobelet”, with moderate productions; and scarce use of phytosanitary products except sulfur in dust.

Technical additions implemented in recent times include: alternative soil maintenance systems either with herbicides or with cover crops; predominantly chemical fertilization with formulated fertilizers and, if there is the possibility, incorporating through fertirrigation; and incorporation of drip irrigation system techniques.

In the Valdepeñas area, rainfall generally concentrates in winter and does not usually exceed 400–500 mm per year. In this context, where water is a very limited resource, traditional management is based on intensive weed control to avoid competition with grapevines for water and nutrients. Nowadays, many winegrowers use plant cover in vineyard agroecosystems, although the study of the benefits and ecosystem services supported by spontaneous flora in vineyard agroecosystems is certainly a novel topic [98]. Currently, in the Valdepeñas PDO, vineyard management ranges from barely any disturbance at all (permanent plant cover) to considerable disturbance (regular soil tillage or herbicide application), although the latter predominates (Figure 4). The fact that cover cropping has been found to increase soluble solids, anthocyanins, and other phenolic components of grapes [36,44], it leads to a bigger soil microbial biomass and controls grapevine canopy growth [99]. This means that winegrowers should be guided toward these procedures. Therefore, it is necessary to convince viticulturists about always seeing green roofs as competition in relation to nutrient and N supply. In fact, this has already been observed by Griesser in several European vineyards [100]. A Trifolium fragiferum (strawberry clover) cover crop could be implemented as an alternative for weed control under vines based on the success of an irrigated vineyard according to Abad [101].

Although the conditions for agricultural vineyard production and sustainability are optimal in Valdepeñas, viticulturists should be aware of the need to promote sustainable practices, which they have carried out for years, to not only increase grape productivity and quality but to also conserve healthy soil and water quality, and to increase the economic vitality in this rural area.

Following the criteria of the International Organization of Vine and Wine, sustainable viticulture must respect the environment and also integrate concepts of sustainable development. In this sense, it is necessary to minimize the risk of erosion, select vineyards in the most suitable soils, and carry out soil management in order to preserve biodiversity. However, it is also necessary to adapt to climate change. In this way, every day, the use of green cover (use of local plant species, adapted periods, etc.) becomes more common, as well as the rationalization of machinery use. However, perhaps where it has had the greatest success is in the use of adapted irrigation systems. In short, everything that leads to maintaining fertility, biodiversity, and structure of the soil will be seen as positive.

Examples of possible actions that winegrowers should take into consideration are: sustainable weed control, adaptation of the vegetable cover strategy, sustainable use of herbicides for reducing their impacts, protecting and improving soil organic matter and water retention capacity (where applicable), implementing a sustainable fertilization plan with best practices based on scientific assessment, the rationalization of machinery use, and the limitation of soil compaction. Other proposed actions are to increase the surface under the green cover and modernize the application techniques of plant protection products.

More winegrowers are increasingly paying attention to the ecological aspects of wine production. Indeed, sustaining ecosystem functions and services and testing sustainable farming practices are key issues in recent agroecological and biological conservation research and policies [102]. The problem lies in striking a balance between ecological and economic aspects.

Perhaps it would not be as important anywhere else as in Valdepeñas to apply and implement vinecology via the integration of ecological and viticultural practices, a term proposed by Viers [10]. Engaging the viticultural sector in conservation requires raising awareness about the ecological benefits of conservation, in other words, continuing to cultivate vineyards, but in close connection with nature conservation, and in such a way that they are complemented by a full range of the ecosystem services integrated into the wonderful Valdepeñas landscape.

New trellis driving systems with higher productions. Use of fungicide, insecticide and acaricide, phytosanitary products. who noted that the investments and/or operating costs required by the above-mentioned systems were rather high, particularly for small vineyards.

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Francisco Jesús