5
© G.L. Creasy and L.L. Creasy 2009. Grapes(Creasy and Creasy) 75
sought. In doing this, the site with the lowest risk is a vineyard that is already known to consistently produce high-quality grapes. For example, if one were to want to produce ‘Champagne’, then land within the Champagne region in France must be used. However, these sites also cost the greatest amount of money, if they can be purchased at all! In some cases there will be reasons to look at planting in untested sites, where the risk is higher but the cost of the land is less.
The concept of matching the vineyard site to the grape product is an important one to work toward. This will also narrow down the potential areas that need to be investigated, and provide a basis through which to evaluate potential sites. Chapter 3 reviewed the environmental factors that are important to vine growth and productivity, and in site selection the pros and cons of a particular site must be evaluated with regard to the target outcome (i.e. grapes matching a particular set of quality criteria, refer to Table 2.2).
Now information about what will be required of a site in order to produce the target product can be gathered. For example, if the market demands ‘Flame Seedless’ table grapes, then a vineyard site that will be capable of growing, sustaining and ripening the ‘Flame Seedless’ variety is needed ⫺there is no point in looking at a site that is too cold, does not have enough water or does not have access to the labour required to allow its production, etc.
To make the best decision about a potential site, the requirements of the variety must be determined and then compared with those that are available at the potential site. Common factors to be considered are heat accumulation, winter minimum temperatures, water availability and soil characteristics.
There are modifiers that a site may also possess, such as a slope (related to air drainage and frost incidence), the slope’s aspect (influencing sun exposure and temperature), proximity to a large body of water, elevation, etc.
It is difficult to say which of these many factors are the most important, as each may be essential in a particular aspect of grape production. A discussion on the most important factors follows.
Climate
The basic parameters the vines need, as laid out in Chapter 4, apply here. As temperatures are so critical to grapevine survival and production of the desired cultivar and composition of the grape, having access to long-term weather information at the site makes it much easier to make a confident decision about the site’s suitability. Often, however, sufficient weather information is lacking, which increases the risk associated with developing that site. At a minimum one should be confident that enough heat will accumulate at the site to produce grapes of the desired composition, as well the knowledge that damaging winter, spring or autumn temperatures do not occur with a frequency that will mean economic ruin.
Large bodies of water can also assist in changing the mesoclimate. As water stores a lot of heat, in the winter it can increase air temperatures nearby and also act in causing air to circulate, which can prevent the accumulation of freezing air and grapevine damage (Newman, 1986; Shaw, 2001). In the spring, relatively cool air coming off the water can delay budbreak, meaning less risk of damage from early-season frosts.
The amount and timing of rainfall is relevant to the need for an irrigation system, or to aid vine spacing and rootstock decisions. Rainfall occurring close to and during harvest season can be particularly detrimental, as it can degrade fruit quality (e.g. through decreased fruit sugar and flavour concentration or increased disease incidence) and hinder human and machinery traffic in the vineyard.
Soil
Soil is an important consideration for site selection because, like climate, its basic properties cannot be altered much. The soil serves several purposes for the vine. At its most basic, it anchors the plant to the ground. However, it is also the medium through which the plant obtains the vast majority of its water and nutrients. Chapter 2 discussed what roots are, but here how roots interact with the soil is examined.
Grapevines can grow in many and varied soil types. There is no one soil type that is best for grapevines. Indeed, with the use of rootstocks a single cultivar, if grafted, can have roots that are completely different, and even then there can be particular rootstock/cultivar combinations that are best suited to certain sites. With this in mind, when evaluating soils it is best to confirm that the most deleterious characteristics are not present. These include flooding, impervious layers, excessively low or high nutrient levels or pH and insufficient organic matter. Soil testing (for nutrients and water-holding capacity at a minimum) is an integral part of evaluating a potential vineyard site, and should be performed in a comprehensive manner (Thomas and Schapel, 2003). To some extent, each of these soil-based problems can be mitigated with pre-planting management decisions.
Interacting with these are factors such as rainfall and/or water availability on the site. Irrigation water may be lacking or expensive. If the site has ample water supply for irrigation, then very sandy or gravelly soils can work well, whereas if there is not enough water for irrigation then they would not be. This is another demonstration of how complex and interrelated the components of the system can be.
So, from the overall point of view, it is very easy to identify potential locations for vineyards. What becomes more difficult is to decide which soils match which rootstocks and cultivars for which end uses. Regional soil maps, though widely available, are rarely detailed enough to provide enough information for
rootstock/cultivar planting decisions. As soils can vary considerably over a short distance, having a soil expert walk the area and take soil cores as necessary is a valuable exercise, as is having a look at the soil profile in a soil pit (see Plate 21).
Additional information can be gained by remote sensing techniques (Smith, 2002), such as aerial photography (both at visible and infrared wavelengths), satellite imagery or electromagnetic (e.g. EM-38) (Reedy and Scanlon, 2003) or ground-penetrating radar determination of soil water content (Huisman et al.
2003).
The water-holding capacity (WHC) of the soil is important in assessing a potential vineyard site. Together with the amount of annual rainfall, this provides the vines with their water supply for growth. The amount of water a soil can hold is the difference between the amount at field capacity, where any additional water drains out somewhere else and the permanent wilting point, where plants can no longer extract water from the soil. The values for these will vary depending on the soil type, with sandy soils not holding very much water but almost all of it being easily extracted by plants. High-clay soils will hold lots of water, but a larger proportion of it will be held too tightly for the roots to extract it. High WHC is not necessary for vine growth, but there must be an alternate supply of water for the vines if it is unlikely that natural rainfall will supply enough to satisfy vine needs.
Since plant rooting depth changes the volume of soil from which water can be taken, soil depth is also an important consideration. Increased depth means more potential for water and nutrient supply, which has effects on grape quality parameters (Coipel et al., 2006). Note that, though vine roots can penetrate to significant depths and find water, there may be little in the way of nutrients available at those depths due to the lack of proper soil to carry them.
Changes to soil depth or even texture across a site, as well as the presence of clay pans, are also causes of vineyard variability, which can complicate management of the vines due to differences in vine performance caused by the soil (Trought, 1997). The installation of tiles to drain excess water from the soil, as with perched water tables caused by impermeable layers, is important in soils that waterlog in the winter or spring as vines prefer well-drained soil (see Fig. 5.1).
Soil pH is relevant because of its influence on the availability of essential nutrients. At low pH, macroelements such as phosphorus and potassium become less available, while at high pH, microelements like iron and zinc become scarce (Marschner, 1986). V. labruscavines are known to be more tolerant to acidic soils than is V. vinifera(Himelrick, 1991), probably because the former species evolved in an area with soils of lower pH. Soil pH can be altered through the addition of lime (increase) or gypsum (decrease), but these are temporary measures as the soil pH will tend to revert to its natural state over time (Himelrick, 1991). Nutrient status of the soil can also be changed, and soil organic matter is a large contributer to soil WHC as well as nutrient- carrying capacity. For more details on these aspects, see Chapter 7.
If a vineyard is being replanted there can be issues with carry-over effects (Westphal et al., 2002). These can range from depleted soil nutrients, nematodes or insect populations to pathogens left in the soil and remaining plant roots.
Proper soil testing and preparation is essential to avoiding these problems.
Slope and aspect of land
In many areas, higher-quality grapes can be grown on sloping land (see Fig.
5.2). In cooler climates there is a benefit in terms of water and air drainage, as well as increased sun exposure if the slope faces the noon-time sun. However, sloping land also brings difficulties with machinery access and vineyard uniformity. There are many examples of very successful vineyards on both flat and sloping land but, in areas that are pushing the boundaries of economically viable sites, slopes are generally regarded in a positive way.
Other factors
Other factors to take into account include land cost/availability/zoning, likely pests and diseases, proximity to existing industry infrastructure, presence of skilled and unskilled labour, accessibility to markets or shipping ports, reputation of the region, pollution concerns from neighbouring activities or Fig. 5.1. This wet spot in a springtime vineyard is a problem for machinery and human traffic, as as well as keeping vine roots in anaerobic conditions.
previous cropping, water availability and quality, natural rainfall and its timing through the year. As some vineyard activities ⫺such as bird-scaring, frost-fighting, early morning fungicide spraying, etc. ⫺may not be expected by neighbours, it is best to resolve these issues before planting the vineyard to avoid conflict.
Knowledge of other plants and their phenological stages in relation to grapes can also help predict the performance of vines not yet planted. If there are reliable data for time of budbreak, flowering and ripening in grapevines and other crops, including ornamentals, in one region, the relationship between phenological dates of those other crops and grapevines can be used to predict when grapes will reach certain stages of development. For example, if it is known that in one region grapevine budbreak coincides with first bloom of
‘Red Delicious’ apple, then if that same apple is growing in another area that is being evaluated for grape production and the date that the apple trees bloom is also known, this leads to a good predictor of when budbreak will be for grape in that area. Advance knowledge of all the important phenological stages can be estimated using this technique, leading to a better risk assessment for the type of grapes needed to be produced. Unfortunately, the detailed information needed to be able to use this technique is rarely available.
In scouting new vine-growing areas, the use of aerial photographs to look for vegetation differences, Global Positioning Systems (GPS) for accurately marking out sites and elevation determination, and Geographical Information Fig. 5.2. Sloping vineyard site in Oregon, USA. Excellent air drainage keeps cold air from accumulating near the vines.
Systems (GIS) to help organize the data into a useful form and plan out blocks, is increasingly common (Smith, 2002).
Being thorough and methodical in investigating a site is vitally important, but predicting its potential to produce quality grapes, even with the increased level of knowledge and experience available today, is still quite difficult.
However, it is worth this effort to try to get it right since, once the vineyard is planted, alterations to many aspects of production become almost impossible.
It is helpful to remember that management inputs can overcome many deficiencies a vineyard may have, but this may result in decreased fruit quality or increased site costs through the life of the vineyard.
At the end of all this, there are two questions to answer: (i) are there one or more factors associated with the site that will prevent it from growing the grapes the market needs? (ii) if so, then what grapes could be grown, how best should they be managed and will it be economic?
The alternative is to investigate another site. However, if the site is appropriate, then it is time to move to the next stage of development, determining how the site will be planted out.