A very interesting aside in the 2005 ASEV paper “Soil and Winegrape Quality in Biodynamically and Organically Managed Vineyards” is that an annual ryegrass green manure crop was cultivated into the soil in 1996 and in 1997 the vineyard was composted: “organic matter spiked in 1997 and then fell back to pre-compost levels by 2000.” We don’t know how much or what the material was, but composting lasting only three years is consistent with my experience. My reading of Biodynamic literature indicates great emphasis is placed on soil building, with composting and “preparations” as the main ingredients of that program. Composting appears to be the main vehicle for adding Nitrogen to the soil for the growing of Biodynamic crops. Certainly modest levels of composting will enhance the soil organic matter and in my experience the study’s results showing about a three year enhancement is about right for a single treatment. But modest levels of manure compost may not provide sufficient Nitrogen for that farm. IMO, Biodynamic principles are at risk here because the notion of a self-contained, composted farm is simply not practical without bringing in large amounts of compost and manure from other sources. The Demeter Association allows up to 100 lbs of Nitrogen per acre under normal conditions and up to 150 lbs. of Nitrogen with “inherently nutrient-deficient (farms)…” To add 100 pounds of Nitrogen with a 2% Nitrogen content requires 5,000 pounds of compost per acre per year.
Here’s what I’m getting at: a vineyard produces shoots, leaves, stems and berries. At Smith-Madrone the canes are chopped and returned to the soil, the leaves fly wherever the leaves want to fly, the stems are composted and represent about 5% of the total weight and the pomace is returned directly to the vineyard with only the grape juice being permanently removed. However, the amount of pomace we generate and return to the vineyard is quite small when compared to the entire vineyard. While it helps with sustainability, our pomace is not sufficient to build “healthier” soil. One ton of grapes contains about 200 gallons of liquid (we get on average about 165 gallons out of the press with the rest going back to the vineyard with the pomace); this leaves an estimated 300 pounds of dry weight pomace and stems. That 300 pounds times our three tons to the acre results in a whopping 1/3 ounce of pomace and stems per square foot of vineyard. Look at it another way; what is 900 pounds of pomace in the top six inches of soil when the average top six inches of soil weighs 2 million pounds per acre?
I suspect our cover crop produces more dry weight organic matter than the pomace and our prunings provide even more organic matter. However, since we are a non-till vineyard all three sources of organic material must decompose slowly on the surface as opposed to being disked or plowed under the soil where the microorganisms have an easier way of getting to that organic material.
Gardeners compost at rates that would be multiple times what our vineyard generates, maybe even hundreds of times greater. So you can see that while returning everything to the vineyard in a closed system may be sustainable, it means very little to building a healthier soil. That’s fine with me because I believe that soils are, by my definition, inherently healthy and need only an adjustment or so.
But there is the problem of how to define a “healthy” soil? Most farmers would agree that Class 1 Yolo Fine Sandy Loam may be some of the finest soil on earth. But when we think of premium wine grapes those are not the soils of choice. Gravel, rocks, bench, upland, mountain, mineral, low fertility and well drained are words that define great vineyard soils. One soil is superior for traditional crops and the other soils are superior for unique agriculture such as wine grapes. Are the deep, rich and fertile soils healthy and the rocky, gravelly mountain soils un-healthy?
The paper also touches on the issues of soil fertility, soil depth and root penetration—three very important issues for vineyards. Grapevines are deep rooted and in the sandy soils of the San Joaquin Valley grapevine roots have been found at the 100 foot depth by water drilling rigs. There are almost no roots in the top 12 inches because of either cultivation turning over the soil to that depth, or with non-till the permanent cover crop roots tend to get that moisture first. So the effective rooting zone for most of our vineyards is the one to five foot depth: this is where the real action is happening, this is where the vine gets its moisture and nutrition, not in the top inches of soil. So earth worms munching through the soil, composting and green manure are great for the shallow rooted plants but they do little for the deep rooted vines and trees. Remember that compost and green manure take time to break down into a form that the plants can use. Unfortunately, the timing is off because the nitrogen becomes available only in late summer when we want the vines to stop their vegetative growth cycle and start the ripening cycle. It takes the winter rains to drive those released nutrients down into the root zone.
Growers spend a great deal of brain power trying to figure out which rootstock will match best with both the soil and the intended grape varietal. Could Biodynamics’ emphasis on soil building and health actually be misplaced and counterproductive to wine quality? I believe the answer is yes, but to be fair, that yes answer would apply to any grower who tries to change the soil characteristics by using too much compost and green manure. Here’s what could happen with too much compost:
- Organic content becomes too high – 1% up to 4%
- Water holding capacity increases
- Nitrogen content becomes too high
- Potassium content becomes too high
- Soil acidity becomes too low
- Calcium and Magnesium become out-of-balance
- Vine growth becomes too vigorous, especially in the short run
- Vine growth becomes out-of-balanced
- Natural soil system is disrupted
- Rootstocks no longer match original soil conditions
- Wine quality suffers
- Grower now thinks soil is “healthy”
- Grower is now polluting the environment
Soils have natural levels for nutrients, and if some of those nutrients like Nitrogen exceed the background levels then pollution begins. Organic matter breaks down into the negatively charged nitrates which are easily leached from the soil and this is an especially harmful pollutant near water sources. Phosphorus has similar issues. Small amounts of manure compost to help with the soil organic matter may be helpful as one of many tools available to the farmer, but relying on the manure compost as the sole source of nutrition and Phosphorus can result in problems. If I believe our vineyard or cover crop needs Nitrogen then I think it is more responsible to add just what is needed – it is the rifle vs. the shotgun approach. And after all, the Nitrogen we use comes from the air, not from oil by products.
Why are we messing with Mother Nature anyway? Why are we trying to make a sow’s ear into a silk purse, when the sow’s ear makes great wine and the silk purse doesn’t? What happened to the idea that wine grapes should struggle in poor, rocky, well drained soils? Historically, it was the wine crafted from those difficult soils that gave us wines of distinction, character and uniqueness – what I call a sense of place and what others call terroir?