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). 

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Monoculture vs. polyculture: When the obviously right choice isn’t


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Diversity is a good thing, right? “Respect diversity” ranks right up there with “natural is better.” And both platitudes say that monocultures are bad and polycultures are good. Monocultures are the standard way to grow commodity crops, but it’s voguish for the small/local/organic/biodynamic crowd to talk about the benefits of crop diversity. It’s pretty obvious that a diverse, natural, “wild field” mix is better for a cover crop in a rotating field system or between vine rows than planting just one thing.

The problem with obvious things is that they’re sometimes wrong. Not because they’re “common knowledge” instead of scientifically tested – plenty of old wives weren’t idiots – but because they rely on stereotypes that don’t work when you stop to think them through.

Andrew McGuire at Washington State University’s Center for Sustaining Agriculture and Natural Resources recently published a pair of blog posts (here and here) knocking down the sensible-sounding idea that mixed cover crops are better than carefully selected monocultures. “Better” here means “deliver more ecosystem services,” and ecosystem services are things like improving soil quality, attracting beneficial insects, and fixing soil nitrogen. He reviews a pile of research demonstrating that different cover crop species are best for each of these different services. When you mix them you don’t get more of everything, as you might expect; you just dilute each of their effects. In other words, mixes are great if you want a little nitrogen fixing, a little flowering for beneficial insects, and moderate biomass to fold back into the soil. But, you can’t cheat the system, plant five different species, and expect to reap the full benefits of all five; you’ll just get a little of everything. The more aggressive species in the mix will also out-compete the less aggressive species – your mix won’t remain a nicely balanced mix forever – and the resulting biomass (the mass of plants to be turned under to enrich the soil) will be lower than what the most vigorous species in the mix would have given you on its own. “Transgressive overyielding” – the idea that plants grown in mixtures benefit symbiotically from each other’s presence and outperform plants grown in monoculture – isn’t supported by the data.

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In transition

This isn’t really the Wineoscope, at least not as it was or as it will be. This is an awkward in-between creature that exists only while I’m getting my act together around a new site. So, please accept my apologies for this pimply adolescent phase, and look forward with me toward something a little less, well, awkward.