Cultivar, Rootstocks, and Trellis Blocks of the W-MEA Viticultural Model

I began the "fleshing out" of the Wine -- Mise en abyme (W-MES) Viticultural Model with an elaboration of the Site Complex and a comparison of the best practices elements to the Masseto site conditions. In this post I continue this "fleshing out" by detailing the elements of the Vineyard Establishment Complex (identified below within the red oval). As before, I will attempt to identify best practices and compare them against the Masseto conditions where data are available.

Variety
A number of factors are considered in selecting the variety (or varieties) to be planted: (i) experience of other vineyards in the area; (ii) the quality of the variety; (iii) the speed at which it completes its annual reproductive and vegetative cycles and how do those cycles match to the climate of the region; (iv) the yield potential; (v) adaptation to climate; (vi) adaptation to soil conditions; (vii) its resistance to disease; and (viii) the varieties that are allowed by existing legislation (in an area where that is a concern).

The climate of a grape-growing region will determine, to a large extent -- and all things being equal -- both the grape varieties that can be grown and the styles of wine that can be produced. The climatic requirements for successful viticulture include: a growing season long enough to mature both the fruit and vegetative aspects of the plant; production of sufficient carbohydrates to ripen the fruit as well as to maintain future productive potential; and an adequate supply of water.

The common wisdom holds that varieties produce at their best when grown at the coolest margins of viable ripening. Grapevines are selected either through mass or clonal selection and cuttings are grafted onto rootstocks based on the attributes required.

Rootstock
Most of the world's quality wines are based on vitis vinifera, a species which, when grown on its own roots, will succumb to attacks from phylloxera and parasitic nematodes. This problem has been solved by grafting the vitis scion onto phylloxera- and nematode-resistant rootstock.

Vine vigor and soil capacity are additional important inputs into the rootstock-choice decision. Varieties with large canopies (high-vigor varieties) can become less fruitful over time (thus reducing the capacity of the vine) due to reduced cluster number and size. Dr. Andy Walker of UC Davis defines vine capacity as "the ability to grow and produce foliage, roots, and fruit and to establish a trunk." According to Dokoozlian and Kliewer (AJEV 46, 1995, pp. 209-218), vigor is used to describe the growth capacity of grapevines, with those having "large dense canopies and low sunlight exposure ..." being referred to as high-vigor vines. Dense canopies can be detrimental to vine yield in that (i) the plant is deploying its resources in "unproductive" areas and (ii) they reduce the amount of light getting to internal leaves. And human activity (with the related costs) is required to reduce this physical manifestation of vine vigor and re-direct the vine's resources to more productive use.

Soil capacity is a function of the water-holding capacity and mineral wealth of the soil. Vine capacity, on the other hand, is the soil capacity plus the levels of carbohydrates stored in the vine trunk and cordons. Growers seek to blunt the upside of vine capacity by employing low-vigor rootstocks but, in most cases, capacity will trump vigor.

Rootstock(s) utilized in the vineyard environment should be (http://iv.ucdavis.edu/files/24347.pdf):

• Resistant to present and potential soil pests
• Suitable for the soil’s texture, depth, and fertility
• Compatible with soil chemistry (pH, salinity, lime content)
• Favored for the anticipated soil water availability, drainage, and irrigation practice
• Appropriate for the vineyard design
• Appropriate for the fruiting variety’s growth and fruiting characteristics.

Trellis
The rationale behind vine training systems is (i) an understanding that increasing the exposed leaf area improves fruit quality, (ii) that exposure of leaf area can be manipulated by training, and (iii) training alters the microclimate of the canopy. The amount of leaf area that can be exposed to the sun is a major consideration in the choice of a training system. It is affected by (Reynolds, Andrew G., and Justine E. Vanden Heuvel, Influence of Grapevine Training Systems on Vine Growth and Fruit Composition: A Review, Am. J. Enol. Vitic. 60(3), 2009, p251):

• The disposition of the bearing units
• the Trellis height
• The associated type of training.

Growth, yield, and quality are directly proportional to the ratio of exposed leaf area to fruit weight with a range of 7 - 14 cm² total leaf area/gram of fruit required to achieve full fruit maturity. The higher end of the range should be pursued in colder climates in order to ensure that the vine can complete its important physiological functions (Reynolds and Vanden Heuvel).

The trellis serves as the framework within which the vines are trained and supported and must (Paul Domoto, Constructing a Vineyard Trellis, Presentation, Iowa Grape Growers Conference, 2002):

• Be strong enough to support large crops and withstand high winds
• Last for 20 or more years with routine maintenance.

One of the most important considerations in trellis selection is the size of the canopy that it will be supporting. The vines growth potential has to be taken into consideration in order to ensure that it will bear the weight of the vine at maximum vegetative growth. The factors which drive vine growth potential are as follows (http://www.ucanr.org/sites/intvit/files/24348.pdf):

• Temperature
• Annual rainfall
• Sunlight exposure
• Winds
• Soil texture
• Vine rooting depth
• Pre-Plant soil preparation
• Cultivar
• Rootstock
• Cultural practices

Other elements that factor into the trellis decision are (Reynolds and Vanden Heuven):

• Plant and row spacing
• Row orientation
• Establishment costs
• Equipment requirements
• Desire for mechanization.

The details of the model elements for the W-MEA Model Vineyard Complex are provided in the table below. Red-colored text indicates a best-estimate.

      Masseto Vineyard Versus the W-MEA Viticultural Model -- Vineyard Complex

Block	Component	Element	Optimal Value	Masseto Position
Variety	Nomenclature		Depends	Merlot
	Climate Adaptation		High	High
	Soil Adaptation		High	High
	Local Custom		N/A	Compliant
	Variety Quality		High	High
	Yield Potential		Balanced	High
	Disease Resistance		High
	Allowed by Regulation		Compliance	Compliant
Rootstock	Nomenclature		Depends	N/A
	Soil Pest Resistance	Phylloxera	Med-High	Med-High
		Nematodes	Med-High	Med-High
	Soil Qualities Suitability	Texture	Loam, sandy loam	Clays
		Depth	Ø  3 feet	N/A
		Fertility	Low-Med	High
	Soil Chemistry Compatibility	pH	6.0-6.8	N/A; assumed high
		Salinity	Threshold 1500 μmho/cm	N/A
		Lime Content		N/A
	Water Availability	Drought Conditions	Adaptable	N/A
		Wet Soils	Adaptable	Inhibits performance
Trellis		System	Depends	Spurred Cordon
		Strength	Wind resistant; supportive of vine growth potential	Compliant
		Longevity	Ø  20 years	N/A
		Plant and Row Spacing	2.5 m between vines in Bolgheri	3 m x 0.85 m
		Row Orientation	Depends	Perpendicular to the fall line of the slope
		Set-Up Costs		N/A
		Equipment Requirements		N/A
		Mechanization Plans		N/A

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