Carpool Lane to Carbon Zero

Mark Krasnow and Karen Peterson

I’ve been thinking about carbon sequestration [a lot] for a while now. But I’m writing this because I recently attended a conference with a session on the local sustainability program’s Road Map to Carbon Zero, and the carbon sequestration potential of vineyards seemed overlooked, and areas of improvement focused entirely on emissions. After the conference, I had a look at the proposed Roadmap to see what mention, if any, there was of sequestration in it. After all, it’s hard to cover a topic as huge as carbon in a half hour talk at a conference, and I wanted to make sure time constraints weren’t the reason sequestration was given such short shrift. In the report there was passing mention of “carbon removals,” and a suggestion that research work should start in vineyard “carbon removal” by 2040, there was no other mention of anything but emissions-based targets. They accepted carbon removal had to be part of the answer since all emissions could not be eliminated, necessitating something in the negative column to offset these. However, they did not define “carbon removal,” it could mean sequestration by vines and midrow plants, or it could mean burying biochar (or both).

It’s all a bit underwhelming and disappointing. Such intense focus on emissions not only undermines innovation in the sequestration space, but it sets the stage for vineyards and wineries to throw money at the problem, rather than looking hard at their practices and asking people to act/farm better. Pitched in the emissions only context, smaller growers who cannot easily or quickly electrify their fleet can end up feeling they can have no real impact. In reality, every grower can make some concrete changes to how they farm to do better in terms of balancing absolutely necessary emissions with enhancing carbon gains by the vineyard soils and vines.

What Do we “Know” About the other side of the equation - Sequestration?

Sequestration is the long term removal of CO2 from the atmosphere and storage in another form that does not contribute to climate change. All plants absorb carbon dioxide from the air, and thus at least temporarily sequester that carbon from the atmosphere in the body of the plant itself, and in exudates into the soil. How long those plants grow and how large they get determine how much carbon they sequester. Burying biochar is another type of sequestration, locking away that carbon long term.

Like forests, the paragon for carbon sequestration, vineyards have perennial species with extensive root systems which are in the ground for decades. While there is no work done in New Zealand, in Northeastern Italy (another adopted home of Sauvignon blanc) vineyards were shown to be moderate carbon sinks, sequestering about 8-9 tons CO2/ha per year (PItacco and Meggio, 2015). An approximate breakdown of how much of that carbon is sequestered in both the roots/soil, trunks, exported via fruit, or is found in canes and leaves (which may or may not stay in the vineyard post-harvest) are shown in Figure 1, but an appreciable portion (60% of the total carbon assimilated) is stored long term in the permanent structures and roots. Other studies have shown that much of the total sequestration comes from the midrow growth (Callesan et al., 2023), an area which can relatively easily be managed differently.

What Are Some Small and Actionable Changes that can Impact the Carbon Equation?

I see plenty of opportunity to reduce our carbon and overall ecological footprints with our practices, not just the type of equipment we use, the packaging we put our wine into, or type of electricity we purchase or generate. These gains can be achieved by all growers, regardless of size, variety, or location. This is the kind of stuff that I would love to have seen get some attention in the other Roadmap, so I’m outlining some of it here. Think of it as the Thoughtful Viticulture “Carpool Lane to Carbon Zero.” Now, we don’t have carpool lanes here in New Zealand, but the sentiment still applies – working collectively we can get to our destination faster, in this case Carbon Zero.

Nutrient Management

We’ve said it in a previous blog, and I’ll say it again, applying unnecessary fertiliser, or applying fertiliser at the wrong time, can have negative environmental impacts. To show I’m not alone on this soap box, the AWRI published a factsheet back in 2014 about vineyards and greenhouse gas emissions that touches on this. In short, Nitrous Oxide (N2O), yes – laughing gas, is a natural byproduct of the Nitrogen Cycle, and poorly timed or unnecessary applications of nitrogen fertilisers can increase the amount your vineyard releases. I cannot emphasise enough the importance of tissue testing to determine what, and how much, nutritional assistance your vines need. Adding more DOES NOT increase yield if your vines already have adequate amounts. Unnecessary Nitrogen not taken up by the vines is available to microbes and some is released as N2O. While the absolute quantity of N2O released is relatively small, the real kicker is the impact of N2O per molecule is about 300 times that of CO2 in terms of global warming.

Basic Midrow Management

Here in New Zealand, we are blessed in most of our wine regions with relatively regular rain, even over the summer. This means that we are able to have green stuff growing between our rows for all, or at least most, of the year. This presents a real opportunity for vineyards to do their part to help combat climate change, and potentially offset the carbon emissions not only from producing fruit, but from the rest of the wine production chain as well. The current standard in Marlborough is for grassed down midrows that are frequently mowed to keep the grass quite short. While this is undeniably better than tilling out every row or every other row, maintaining “bowling green” midrows is unnecessary in most cases. Worse, it adds emissions to maintain while also limiting the carbon sequestration potential of the vineyard, a double whammy to the carbon budget.

Reducing unnecessary mowing and tilling is the LOWEST of low hanging fruit. Allowing the grass to get a little taller (or be there at all) enhances the carbon sequestration potential of the midrow and improves the vineyard “carbon budget” with LESS effort, and a savings in diesel and employee time. To put it in perspective, with just under 30,000 ha of grapes in Marlborough, if every vineyard decided to skip ONE mowing pass, that would add up to over 100,000 km of tractor operation removed from the carbon footprint equation. But if that’s not enough to put it into perspective for farmers – at an average speed of 10km/h that’s roughly 10,000 man-hours & tractor hours. And that’s just counting rows, not headlands…

I know we can take it further than just letting the grass grow. Changes to midrow management to enhance carbon sequestration need to be tested regionally to determine best practice and ensure no negative effect on the vines or on wine quality. While we've done work here in Marlborough that shows you can have substantial midrow cover crop growth (i.e. meter tall plants) with no negative effect on yield or quality, this was just one study with a specific species, and more work is required (and some is ongoing) to establish best practice. Having data to back up best practice does not hurt anyone, and can have such a huge upside by encouraging more people to examine and change what they do.

Irrigation Management

I’d be remiss if I did not mention irrigation management. Irrigating vines in excess, promotes excess vegetative growth, which then requires trimming/hedging and canopy management passes. While it is true that water stress can limit yield, the timing and severity of the stress need to be considered. A little discomfort on the vine’s part around veraison discourages lateral and shoot tip growth, leaving more photosynthate for ripening fruit and permanent structures (i.e. sequestration). More water than necessary encourages growth, and hence the need to trim. Trimming is a double whammy like mowing, you’re burning diesel and reducing the sequestration of the vines at the same time. Changing irrigation, even if only for part of the season, is a small change any grower can make to improve their vineyard’s carbon footprint with a little measurement and experimentation.

What Now?

These are the first steps any vineyard can take towards this goal, and we encourage everyone to take a closer look at what they do and make incremental improvements when and how they can. I'm not saying to ignore emissions of course, I'm just encouraging a wider view of the issue. We can get to Carbon Zero a lot faster if people don’t go into the effort with the assumption that our current practices are perfect. Be thoughtful about how you farm. In addition to the emission reduction changes outlined in the Roadmap, adopting some small, concrete changes to management will help us achieve the goal by, if not before, 2050.

I think a quote attributed to Albert Einstein applies here: You cannot solve a problem with the same thinking that created it.

We need to think (and act) differently if we want a different result. In our fight against climate change, let’s not tie one hand behind our back, and address sequestration as seriously as we do emissions reduction.

Literature cited

Callesen, T. O., Gonzalez, C. V., Campos, F. B., Zanotelli, D., Tagliavini, M., & Montagnani, L. (2023). Understanding carbon sequestration, allocation, and ecosystem storage in a grassed vineyard. Geoderma Regional, 34, e00674.

Pitacco, A., & Meggio, F. (2015). Carbon budget of the vineyard–A new feature of sustainability. In BIO Web of Conferences (Vol. 5, p. 01024). EDP Sciences.

Photo credit: New Zealand Winegrowers Inc.