Background research for this topic consists of studying existing wine grape growing regions to determine the scientific basis for the concept of terroir and apply that concept to other areas, namely Calumet County in Wisconsin. Locating the best potential viticultural areas is important because growing specialty crops is a better way for farmers to make ends meet, therefore conserving agricultural land. Calumet County is unique because of its excellent agricultural soils, but unfortunately, there is a problem of aquifer susceptibility in some areas (Gotkowitz, M.B. and Gaffield, S.J.). This means that there are some soils in the county that allow infiltration of impurities to the groundwater. More research needs to be done concerning the effect that grape growing would have on the groundwater issues, but it is certain that a vineyard would erode less and grapes would not need the large amounts of nitrogen (manure) that other crops need. Also, many of us enjoy the occasional glass of wine, so it is important to promote the local wine industry for two additional reasons. As the upcoming climate change threatens existing vineyards in California and other warm areas (White, et. al.) there is an opportunity for other growers to succeed. Another reason for promoting Wisconsin wine is that it is becoming costly to ship wines all over the world. As people become more aware of where their food is coming from, more of us will consciously buy local products. This project was intended to describe the status of the viticultural industry in Calumet County,Wisconsin.
In my quest to find potential terroir in Wisconsin, I had to first define terroir. The French describe it as the “taste of the soil” that is reflected in the wine. For me, terroir has come to mean the integration of all of the factors that contribute to growing excellent quality wine grapes. But, it is also important to note that terroir develops as a result of growing the wine grapes in an interaction between the vines and the land over time. Nonetheless, a good place to start my research is in the areas in which excellent grapes are already being produced.
Excellent wine grapes are not grown in a prime environment for the grapevine. If a grapevine grows in a situation where it has an abundance of the necessary plant nutrients, it will not produce good grapes, if any at all. The grape grower has to strike a balance between the healthy plant and the perfect fruit. He does this with various pruning techniques, trellising, and a little help from Mother Nature. In addition, grapevines are sensitive to temperature extremes. Heat accumulation is very important, but if the temperature gets too hot, photosynthesis halts and sugars start to break down (White, et. al.). Likewise, if the temperature gets too cold, the fruit may not form, it may not ripen, or the vines may suffer irreparable damage (MSU-ext). Some areas may have temperatures in the correct range, but humidity can become a limiting factor. However, there are many breeders working on these issues and there are already hundreds of varieties of grapes (Minnesota Grape Growers Association). Depending on where the grower lives, there is usually a selection of grape cultivars that will work in that area. This research focuses on the cold-hardy wine grapes suitable for our climate in Wisconsin with long, cold winters and somewhat humid summers (Lawrie, 2005).
The idea that water regulation is part of the answer to the question of terroir has come up many times and it is very important for producing quality grapes. However, if I have learned anything throughout my studies, it is that in a natural system there are so many inputs and outputs to consider that one can never assume that there is only one factor influencing an organism. Fortunately, there is a lot of information available as to the best way to grow grapes. It was important for me to learn what the requirements for grapevines are in order to find out where they would likely grow well. In making a list of land characteristics I have turned to local vineyard owners, many books and websites (too many to mention), and I even have grapes growing in my yard.
The methodology for my project is designed around another project that I came across. John D. Boyer from Virginia Polytechnic Institute and State University did an analysis of viticultural potential in Virginia. His analysis was initially based on climate and was much more complicated because it included all of the microclimates in Virginia (due to the elevation differences found there). After finding regions that have good climate, he then concentrated on the physical aspects of the land. Similarly, the analysis of viticultural potential for Calumet County was first an examination of the climate in the area. Instead of choosing areas where the climate was amenable to grapes, I chose the varieties that would do well in the area. Incidentally, none of the varieties that can take the Northeastern Wisconsin climate are known to be of premium wine quality. Vinifera (European) type grapes cannot tolerate our cold winters (Lawrie, 2005), so I could only recommend a series of cold-hardy grapes that were bred by Elmer Swenson and the University of Minnesota.
The climate factors studied include the amount of rainfall, growing season length, growing degree days (heat accumulation), and lowest winter temperatures. Some of the data was readily available in the Green Bay area for a history of 100 years, but could not be found in Calumet County. Since these areas share the same climate region, I used Chilton and Green Bay data from individual weather stations in the analysis and other regional data from the Wisconsin Climatology Office. Averages between Chilton and Green Bay were quite close so seems that the climate should be very similar. The lowest temperatures are within the ranges of some grape varieties. Surprisingly, there are now quite a few varieties that can handle our cold winters, some of which are hardy to -40 F.
Calumet County’s rainfall amounts from 29-35 inches would guarantee that no irrigation would be needed. This amount of precipitation is sufficient for viticulture (Roper, et. al.). The growing season length presented some problems due mostly to late spring and early fall frosts.
Late spring frost is detrimental to the forming bud and causes decreased yield of fruit. Early fall frosts can be harmful as well cutting ripening short (MSU). Because of this, only the ultra-early varieties would be suitable for commercial production in Calumet County, even these have had some of their seasons cut short. It is fine to experiment with riskier varieties, but a commercial vineyard represents a large investment and it is not advisable to have a crop that does not leave much room for nature’s variances.
Growing degree days are a way of measuring the amount of heat energy available to a crop. Grapes only grow at temperatures above 50 degrees Fahrenheit and they need a certain amount of heat accumulation to ensure sugar production. It turns out that Calumet County has a sufficient amount of growing degree days for the early varieties to ripen.
With the grapevine requirements in hand, I turned my focus to analyzing land characteristics that offer the best conditions for wine grape growing. The characteristics I chose, in order of importance, are: land use (only agricultural land was included in the analysis), soil drainage, depth to groundwater, soil composition, depth to bedrock, slope, and slope aspect. Everything that I have read emphasizes the fact that grapevines need good drainage (Roper, et. al., Minnesota Grape Growers Association, MSU, and Double A Vineyards). Also, since grapevines will not last long in standing water and a vineyard represents such a large investment, I added twice as much value to soil drainage and depth to groundwater in the final suitability equation (explained below). Soil composition by particle size indirectly affects the flow of water and the capacity to hold it. It is quite important but was not given weight because grapes are somewhat forgiving to physical soil composition. Also, it seems that with the exception of the Niagara Escarpment outcrop, soil depth to bedrock in Calumet County is consistently greater than 60 inches, sufficient for growing grapes. Slope was included in the analysis because of increased water drainage, air flow, and sun exposure. Slope aspect is not a limiting factor, but in the right direction, it can increase solar radiation enough to ensure ripening of the fruit. The East Central Regional Planning Commission and Calumet County supplied data for the project, and ArcGIS software was used to bring it all together.
Soils data provided access to soil type (musym) polygons. It was possible to look up characteristics of each soil type using Web Soil Survey through the Natural Resources Conservation Service. To determine soil drainage, I used the drainage class listed for each soil type. Finding soil composition was a matter of looking up percent clay and percent sand for each soil type and classifying it into groups labeled excellent, fair, and poor. An excellent soil composition would have close to a 1:1:1 ratio (~30%) of clay:sand:silt. A poor soil would have more than 50% of one component or less than 25% sand, 15% clay, or 5% silt. A good soil would be anything in between 25-30% or 40-50% sand, 10-25% or 36-50% clay, and 10-25% or 36-50% silt. The soil depth information was already categorized according to how the data was recorded. Depth to bedrock was either less than or greater than 60 inches and depth to groundwater was less than 2 feet, 2-6 feet, or greater than 6 feet. Each category received a score between 0-5 that corresponded to the requirements of the grapevine. It was also possible at this point to make maps of the different characteristics in Calumet County.
Contours provided slope and aspect data. The spatial analyst extension in ArcMap allows land information to be converted into slope and/or aspect data from contours or DEMs of the area.The contours were separated by township, so when it came time to run the suitability analysis, it was important to make sure that each area was classified the same. Percent slope values were scored as follows: 0-2.49% =1, 2.5-4.99%=2, 5-7.49%=3, 7.5-9.99%=4, 10-12.49%=5, 12.5-15%=4, and anything over 15% was eliminated. Aspect values were scored accordingly:flat=1, N=1, NE=2, E=3, SE=4, S=5, SW=4, W=3, and NW=2. The highest scores reflected the potential for solar radiation. The weighted overlay tool layered all of these scored characteristics, put double the weight on soil drainage and depth to groundwater, and put them into a final suitability equation that resulted in a map that totals the score in each area (pixel). I then classified the scores as most suitable to least suitable. Out of a possible 45 points, Calumet County scored a range from 10 to 45 with an average score of 28. Anything that scored below 20 was eliminated from consideration and the rest of the ratings were as follows:21-30 was classified as least suitable, 31-35 was moderately suitable, 36-40 was considered quite suitable, and 40-45 was most suitable.
As you can see, the most suitable areas for viticulture in Calumet County are highly associated with the Niagara Escarpment Area.
Interestingly, these areas are also associated with some areas of aquifer vulnerability in the county. Shallow, well-drained soils in this area are known to increase the potential for bacteria and pollutants to find their way into the groundwater. Current agricultural use of this land involves the spread of manure, compounding the problem. Grapevines are known to be quite sustainable in that they require little fertilization, and if grown in the proper areas, they are resistant to disease. Wine grapes may be an option for agriculture in the area because they will cut back erosion and need no irrigation after established. Also, if the site is located in an appropriate environment, the need for fungicides and pesticides is greatly reduced.
Each potential site must be physically examined and other factors such as soil chemistry should be taken into consideration before planting vines. It is best to site vineyards in an environment in which it will have the proper conditions so that the grower can practice sustainability. However, I do not intend to criticize areas that are not marked as “potential grape growing sites.” After all, amendments can be made to soils that could turn a moderately suitable area into a quite suitable area. Nevertheless, if a grower is considering sustainable agriculture, this type of information would be valuable for any proposed crop.
In light of the correlation between the Niagara Escarpment Area and the most suitable wine growing soils and topography; and the fact that there are other great vineyards located along the Niagara Escarpment inCanada and New York, I have decided to extend the land analysis to the remaining counties along the Niagara Escarpment in Wisconsin.
This content reflects the personal opinions of the author. It is accurate and true to the best of the author’s knowledge and should not be substituted for impartial fact or advice in legal, political, or personal matters.
© 2012 kpelkey