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Soils

Overview

Grapevines will tolerate a wide range of soils; however some writers claim that each soil imparts its own unique taste and mouth-feel to a given variety. Soil properties affect the root system of the grapevine: roots absorb and conduct most of the vine's water and nutrient requirements to the aerial parts of the plant. Variables that provide a means to describe soils in terms of attributes meaningful to viticulture are essential in characterizing the Texas AVAs. Site characterization, of soils in the Texas AVAs involved analyzing factors of pH, soil depth, soil texture, available water capacity, permeability, and bulk density.

Soil pH

Soil pH is a measure of the acidity or alkalinity of the soil. The pH results from the interaction of soil minerals, ions in solution, and cation exchange. Soil pH gives an indication of fertility and nutrient balance with the ideal range being 5.5-8.0.

Depth

The location of bedrock with respect to the land surface is often needed in surface and subsurface environmental modeling applications. Deep soils allow the development of an extensive root system, buffering the plant against fluctuations in rainfall and potential drought thus allowing for a more consistent grape quality from year to year. Adequate depth for successful grapevine growth ranges from 75cm to 100cm. A deep soil (>90cm) offers greater volume of potential soil moisture than does a shallow soil (<30cm).

Bulk Density

Bulk density (g/cm3) is the ratio of the mass of soil to its total volume (solids and pores together). It is a measure of the total mass of a moist soil per unit volume. Generally, lower bulk density values have implied more pore spaces and better internal drainage of soils which consequently allows more rapid root development. This is a measure of the compactness of the soil which naturally interferes with internal drainage and could restrict root growth.

Permeability

Soil permeability is a measure of the ease with which air and water move through the soil. A consistent and moderate supply of water, along with deep and spreading root growth are some of the benefits of good drainage or permeability. Unimpeded soil drainage is often associated with the highest quality wine. The internal water drainage and hence permeability of vineyard soils is the most important soil physical property and the desirable value is >5cm/hr.

Texture

Texture is the primary soil property that determines a soil's moisture holding capacity. There are a wide range of soil texture types capable of fulfilling the moisture requirements of grapevines. These include gravelly alluvials, limestone -based soils and clays due to high water-holding capacity.

Sands are not particularly suited to vine growth (due to poor moisture retention) unless large amounts of rainfall and ample irrigation is available. The direct effects of soil texture on wine quality are poorly defined, but indirect effects of texture on soil hydrology are more important. Texture affects water-holding capacity of the soils and internal water drainage hence ideal vineyards would have loam, sandy loam, or sand clay loam textures.

Available Water Capacity (AWC)

This is the volume of water that should be available to plants if the soil, inclusive of rock fragments, were at field capacity. The effect of Available water capacity (AWC) on vine performance is dependent on soil physical properties and management of vineyards. AWC affects yield, as well as fruit quality both directly and indirectly. The major effects are indirect and act via vegetative growth due to direct effects of leaf water potential, turgor, translocation or organic and inorganic substances and canopy photosynthesis. The indirect effects of AWC dominate in the oversupply of water while the direct effects dominate in the undersupply of water.

Data Descriptions

Climate
Topography

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Bell Mountain
Escondido Valley
Fredericksburg (THC)
Mesilla Valley
Texoma
Texas Davis Mountains
Texas Hill Country
Texas High Plains

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Texas High Plains Texas Hill Country Texoma Mesilla Valley Escondido Valley Fredericksburg (THC) Bell Mountain Texas Davis Mountains


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