Research on reassembling: Root systems, soil structure, and wine quality

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If your usual reaction to scientific research involves muttering about taking things out of context, take heart. Historians will look back on our time and call it the era of systems. After a century or so of studying factors in isolation, wine research is now full of studies trying to put them back together again. You’d expect research on terroir to be at the front of that move, and it is. New research out of Friuli in northern Italy is a good example, tying soil type and root structures together with wine quality. Their findings – that wines have the most character when vines can develop large roots through the full soil depth – aren’t shocking, but it’s one more tally mark on the “soil structure matters” side of things.

The researchers found 14 vineyards on different soil types, all Friulano* (same clone, same rootstock), a white variety common in the region, all between 15 and 20 years old, and all pruned and cultivated in the same way with herbicided undervine strips and ground cover between the rows. And then they got busy. They used some pretty elaborate apparatus to measure soil water content. They dug a lot of holes to investigate soil structure. They measured transpirable soil water, reflecting not just how much water is in the soil but how tightly the soil is holding on to that water and how available it is to vines. It’s been shown that that measure corresponds to leaf water potential, which shows how well-hydrated the vine is and, indirectly, how well it’s able to take up water from the soil. They dug three meter-deep trenches in every vineyard to document the full root structure. They did this for three years, and each year they made 200 kg batches of wine, then had a trained panel taste them yearly for three years after bottling (the wines were made in 2006-2008). Usefully, of the three years they collected data, one was drier than usual, one wetter, and one about average, and the weather was essentially the same over the whole study area.

This study is praise-worthy for having measured root development in multiple ways and for using real vineyards while still controlling for a lot of non-soil factors. But their results are more reinforcing than revolutionary (which, you could say, is reassuring). The vines with the weakest, shallowest root systems yielded the weakest wines, lacking “elegance” and with wimpy aromas. Vines with the best-developed root systems yielded the most intensely aromatic and “elegant” wines. Differences were most obvious in the driest of the three years. The key point, the researchers concluded, was that soils that allowed for full, deep root development produced consistently good wines, and that the root structures were a better determinant of wine quality than the soil type. Differences between the soils could mostly be explained by their structures: clay-sand content and size of particles.

How would growers use this research? Let’s say you’re planting a new vineyard, maybe chardonnay. Instead of trying to find chalky soils to echo the fabled lands of Champagne, focusing on the composition of the soil, this article suggests that you should be paying more attention to the structure of the soil. Put it that way and this doesn’t seem like news. The iceberg theory of grapevines – what lies below the surface is as important or more so than what lies above – is enjoying a well-deserved moment. But, no doubt many of us have seen the waste of failing vines being pulled out to make way for a more suitable variety, all because someone sat at a desk and matched a few statistics to a variety without going out and grubbing around underfoot a bit. Perhaps this sort of research can help the Decision-Makers-Who-Sit-at-Desks crowd ask for different statistics and think a bit differently about their would-be vineyard sites.

The study didn’t document much grape chemistry: just sugars, pH and TA. The sensory analysis was rudimentary, with a small (eight-member) trained panel providing the wine quality judgements responsible for the paper’s main findings. And the study was limited to a single grape variety in a single location, with no good assurance that a different variety in a different location with a different range of soil types would yield the same results. Under that light, it’s difficult to make sense out of this paper as anything other than a snapshot of one terroir. All of that said, it’s still more comprehensive than much of the research connecting soil to vine and wine. Maybe the best use of this paper is as an example of how research can – with a lot of measuring and a cooperative environment – say something meaningful – scientifically and practically meaningful – about soil in all its glorious, grubby complexity.

*The papers’ authors refer to the variety as Tocai Friulano, but this name was banned from bottle labels in 2008 after Hungary joined the European Union and raised a ruckus about other wine names that might create confusion with their famous sweet Tokaji wines.

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