Column Article from the March 2010 Magazine Issue
How Can a Vineyard Be Carbon Neutral?
by Cliff Ohmart
Unless he’s been in a cave for the past five years without access to any kind of media, it is impossible for a winegrape grower not to have been confronted with the concept of a vineyard’s carbon footprint, or to have come across someone claiming to have a carbon-neutral vineyard.
As a scientist by training and experience, I really like the concept of carbon footprint, because it is a performance measure based on quantitative data. While the concept of carbon footprint is a very simple one to understand—it’s the net amount of carbon dioxide equivalents produced in the growing and harvesting of a ton of winegrapes—the amount and detail of data required to calculate it is mind numbing.
When someone says he has a carbon neutral vineyard, what does that mean, and where did the data come from to justify that statement? I think it is important for winegrape growers to understand and appreciate the answer to this question, and I will therefore spend the next few paragraphs discussing some of the basic concepts of a vineyard’s carbon footprint.
Let’s first start with some facts. Most of you have read or heard discussions of why CO2 is one of the major factors in climate change, so I will not go into much detail about it here, other than to say it is a greenhouse gas. It is called that because CO2 in the atmosphere traps heat from the sun as it is re-radiated from the earth’s surface back to outer space, much like what happens inside a greenhouse. The higher the concentration of CO2, the more heat is trapped.
Two other gases, methane and nitrous oxide, are also greenhouse gases, because they, too, result in heat being trapped in the atmosphere. However, they both have many times the ability of CO2 to cause heat to be trapped. For example, nitrous oxide is 300 times more potent. For simplicity’s sake when discussing greenhouse gases, the impact of these two gases is measured by converting their impact into what is called CO2 equivalents.
A convenient way to look at calculating the carbon footprint of a vineyard is to think of it as an exercise in accounting. One accounts for how many CO2 equivalents are emitted by the activities used in growing grapes, and then compares it to the amount of CO2 that the vines sequester in their tissues during growth. Some carbon is also stored in the soil, if organic matter is added in the form of compost or plant residues.
On the surface it seems like accounting for all the CO2 it takes to produce a ton of winegrapes is a pretty straightforward job. The amount of CO2 produced from burning a gallon of diesel fuel or gasoline is well known. Therefore, calculating the amount of CO2 produced from the operation of tractors, ATVs, etc., is simply a matter of recording the amount of fuel used and converting this to CO2 equivalents using the proper formulae.
You need to record the hours of fuel burned in each vineyard. If gas or diesel pumps are used for irrigation, then the amount of CO2 released to irrigate a vineyard is known.
If you use an electric pump, things get more complicated. If the electricity was from a “green” source, such as solar panels, wind turbines or hydroelectric power stations, then no CO2 was released. However, if it is from a coal-fired electrical plant, then some was released.
What about the CO2 equivalents released to produce the metal stakes? (See Alternatives to Wood Posts on Page 36.) How about to produce the wire and the drip irrigation tubing?
We can’t forget the drippers, and don’t forget the CO2 equivalents it took to manufacture the tractors, sprayers and ATVs. What about the shop? How many CO2 equivalents were released to build the shop? Then we can’t forget how many are released to run the shop. We also can’t forget our office. And how much was released to manufacture the pesticides, fertilizers and compost put on the vineyard?
All of a sudden, the task for calculating CO2 equivalents for a ton of grapes seems endless. Fortunately, most of the things I have mentioned above are produced by manufacturing processes. Because of the great interest in carbon footprints for manufacturing facilities and processes, the CO2 equivalents are known for many of them. It is a matter of chasing down all the data required for the calculations. This kind of detail brings up an important point about how to calculate the carbon footprint of your vineyard: How thorough were the sources, and where did they get the data to make the calculations?
Once the amount of CO2 equivalents generated in the grapegrowing process is calculated, it is time to determine the amount of CO2 captured by the vineyard as it grows. Unfortunately, this part of the accounting equation is less well understood.
More research needed
In fact, until now, no one has determined this figure for a grapevine or vineyard. To do so will take detailed and expensive research on vine photosynthesis, respiration and nutrient cycling. Therefore, any models currently used for calculating the fixation of CO2 by vineyards is done using models created for other species of plants, then making assumptions of how these predict grapevine physiology and vineyard nutrient cycling.
While on the topic of insufficient knowledge of the biological component of the vineyard system as it relates to CO2 and the carbon cycle, another poorly understood process is the nitrogen cycle in the vineyard. It turns out that nitrous oxide is released in the vineyard as a result of microbial activity in the soil.
I mentioned earlier that nitrous oxide is 300 times more potent than CO2 as a greenhouse gas. Due to this potency, it is beginning to look like the nitrogen cycle in the vineyard could have a significant role in its carbon footprint. We already know, for example, that moist soil releases more nitrous oxide than dry soil, because microbial activity is higher. The amount released will also be related to the vineyard’s fertilization program, even if only natural fertilizers are used.
A significant amount of research needs to be done to provide the data necessary to accurately calculate the carbon fixed or sequestered in a vineyard. The carbon footprint concept is a great tool to help in measuring the sustainability of our vineyards. This is because it is a metric-based measurement of an outcome: the amount of CO2 equivalents released to produce a ton of winegrapes, which has a negative effect on climate change. It can be used over time to help opti mize the vineyard performance on this metric.
However, even with the lack of data I mentioned above, we know enough about the carbon cycles of permanent crops to predict that winegrape production will result in a net production of CO2 equivalents. So the idea of a carbon-neutral vineyard could be misleading: To achieve this neutrality in most, if not all, vineyards, some mitigation is necessary someplace else, either through buying carbon credits or planting trees.
There are many ways to reduce a vineyard’s carbon footprint. The California Sustainable Winegrowing Alliance’s publication on the topic is just one good source of information for winegrape growers. However, the reduction of greenhouse gas production in growing winegrapes is only one part of sustainable winegrowing. We cannot forget the other important components including human resources, water use, air quality, soil management, pest management and habitat management. To move along the sustainable winegrowing continuum, we need to be sure we focus on all the important issues.
Dr. Cliff Ohmart is vice president of professional services for SureHarvest. Previously he served as research/IPM director at the Lodi-Woodbridge Winegrape Commission. He has been writing on sustainable winegrowing issues for Wines & Vines since 1998. Contact him through firstname.lastname@example.org.
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