Vineyard Site Selection
Soils for Grapes
Soil affects grapevine productivity and wine quality, but soil, like climate, it is made up of many components including physical, chemical, and biological properties. All of these variables may ultimately affect vine growth and wine quality, but precise relationships are not well characterized for all such variables. Furthermore, the influences of vineyard management, climate, varieties, and rootstocks as well as variation winery practices may easily obscure the unique soil contributions to wine quality. For these reasons, it is difficult to describe an ideal soil for a vineyard.
To begin identifying a soil type for a particular vineyard site the United States Department of Agriculture (USDA) soil survey maps should be referenced. Hardbound soil surveys for each county can be found at National Resource Conservation Service (NRCS) and usually at state cooperative extension offices, local libraries, or online.
Excavating Soil Profiles to Evaluate Soils
Once an area has been identified as potentially suited to vines, a detailed soil survey is carried out, often by digging pits with a backhoe. A thorough site evaluation uses a series of excavated soil profiles in different areas of the vineyard.
Soil Site Selection Factors
Grapes can grow successfully in a wide range of soils, although they do have some key soil requirements for good growth without excessive intervention.
Viticultural soils have traditionally been chosen by their physical properties. Moisture storage and drainage are considered important for good grape production, especially in areas where irrigation is unavailable or not permitted. Shallow, poorly drained soils tend to be susceptible to waterlogging and moisture deficiency with only average fluctuations in rainfall.
While soil type has long been appreciated as a wine quality determinant the direct influence of soil chemical properties on must and wine quality is a contentious area. Traditionally vineyard sites are picked on soil physical properties rather than chemical ones.
Typically vineyard site selection involves many different sources of printed information such as soil survey manuals, topographic maps, aerial photographs, vegetation surveys, flood maps, hydrology maps, soil analysis, and property surveys to name a few. Each source contributes an important characteristic to the final decision. However, it is a challenge to keep track of all this information at once, to understand the interrelationships, and to correlate multiple data sources at single locations. The development and implementation of precision viticulture has made it possible to better manage and analyze different levels of input by combining the global positioning system (GPS), geographic information systems (GIS), and remote sensing technologies.
Soil electrical conductivity (EC) has been widely used to interpret soil spatial variability. Initially used to assess soil salinity, the use of EC in soil studies has expanded to include: mapping soil types; characterizing soil water content and flow patterns; assessing variations in soil texture, compaction, organic matter content, and pH; and determining the depth to subsurface horizons, stratigraphic layers or bedrock, among other uses. Figure 4.4 displays variability in salinity across a vineyard, as measured by a ground electromagnetic induction (EM38) soil survey. Blue shows the lowest electrical conductivity of that vineyard at that time, it then grades through green and yellow and orange and red as conductivity increases.
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