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Growers Give Soil-Building Tips

Speakers at Organic Winegrowing Conference discuss ways to enhance soil fertility

by Paul Franson
organic growing horse
Spottswoode Estate Vineyard & Winery, host of the Organic Winegrowing Conference, is looking into replacing tractors with horses such as this draft horse, Ben.
St. Helena, Calif.—The Napa Valley Grapegrowers held their sixth Organic Winegrowing Conference last week at Spottswoode Estate Vineyard & Winery, which has been growing organic winegrapes since 1985.

The sold-out crowd of 160 attendees—30 more than the 2011 venue, Frog’s Leap Winery—heard experts discuss many topics in growing grapes organically, from improving soil fertility to managing pests.

They also learned from Spottswoode’s Beth Novak Milliken that the winery is experimenting with replacing tractors with horses for farming, and met a draft horse named Ben.

The first speakers discussed building soil fertility.

Malcolm Morrison of Sonoma Biologics tackled the topic first, warning, “When blocks are struggling, there is no silver bullet. There is no such thing as an organic fertilizer. When you apply biologic fertilizers, the nutrients are not immediately available, unlike soluble synthetics. It takes time for the bacteria and fungi in the soil to break them down—and those elements may be low in struggling blocks. You need to build that workforce of microbes.”

Morrison pointed out that soil analyses generally include mineral content—but not protozoa, bacteria and fungi, the biologic elements in the soil. The soil may be anaerobic, too, which encourages pathogens.

Building soil fertility
Compost is among the steps to building the soil’s fertility. Rather than buying compost, Morrison recommends building it with the native microbes from your ranch. “You don’t need to spend a lot of money on compost,” he said. Morrison added that commercial compost providers rarely provide biologic analyses, just mineral content. If it smells like ammonia, it’s outgassing vital nutrients, too.

He strongly recommends using cover crops, saying, “I don’t like to see bare soil. It’s an entry for damaging microbes.” He also encourages biodiversity, including animals, but warns, “Too much of any one thing is not good.”

Following Morrison’s talk, “Amigo” Bob Cantisano, a legend among organic growers, discussed how to “fix” problem areas and desired qualities in compost.

Cantisano said he has worked with 160,000 acres of organic and transitional crops in California. “You can make an organic system work,” he said, “and we are.” He noted that the biggest improvement he’s seen in Napa Valley over the years is increased use of compost and cover crops.

He said that generally, only parts of a block are struggling, and claims, “The problem is rarely fertility. It’s often other things caused by humans or other conditions.”

Cantisano listed a half-page of potential reasons for poor growth or yields, with compaction being a prime candidate along with pests from nematodes to deer, improper irrigation, pruning, row orientation, soil depth and variety and rootstock.

He also noted that little research has been conducted about organic growing; most focuses on commercial synthetic fertilizers. “Ninety-nine percent of lab tests are on conventional farming, and you can’t take conventional lab analyses and standards and apply them to organic farming,” he stated. “The standards were conducted in 1975 on Thompson seedless table grapes yielding 15 tons per acre in the San Joaquin Valley. You can’t apply that to Pinot Noir in the North Coast.”

He recommends that growers who suspect soil or crop fertility take soil and/or plant tissue samples for lab analysis. He recommends doing both.

Microbial analysis may be important: Use a lab or Sani-Check test kit. It’s important to compare normal areas from your property with suspect areas using separate sample sets. Get professional assistance with analysis unless you are knowledgeable, and take corrective action using mineral and biologic organic fertility additions.

He warns that severe problems like high nematode pressure may take two to three years to correct.

Cantisano claims that many varieties require more trace elements than those generally recommended. He uses simple instruments like a refractometer to measure sap sugar, a pH meter and nitrogen and potassium meters to evaluate plants and soils.

He notes that growers are now finding far more damaging nematodes than they used to; it might be because they’re looking harder for them, but possibly due to farming practices. “Some farming practices like driving tractors on multiple passes discourages the biology,” he said, suggesting adding attachments to tractors to reduce passes. He also felt most growers till too early.

He added, “Some of the most widely used cover crops used in Napa Valley aren’t appropriate here,” even though he developed the mixes.

Cantisano listed common soil fertility issues that can limit yields, and how to deal with them. Almost all are improved by additional organic matter.

Anaerobic biology can be corrected with good compost, deep-rooted cover crops like daikon radish, tilling or ripping, compost teas and irrigation management. It’s often a result of wet conditions.

Excess boron can be buffered with increased organic matter, or it can be leached with gypsum. If there’s a deficiency, increase organic matter or use Fertibor or Solubor supplements.

He finds that seven of 10 vineyards are low in calcium, especially on the North Coast. “The standards of 1.5%-2% are too low,” he claimed. The solution is to add calcitic limestone and organic matter. If a field does have an excess, organic matter, soil sulfur and a different rootstock can help.

Excess magnesium is very common in the clay soils in the North Coast. Again, add organic matter, limestone or gypsum or till deeply. If there’s a shortage, add dolomite, Sul-Po-Mag supplement or organic matter.

Santisano says that excess nitrogen is a common problem, and that recommendations are often too much. “All that lush growth is the antithesis of vine quality. It leads to bigger berries containing more water.”

Competitive cover crops and skipping tillage helps. A deficiency can be corrected with legume cover crops, good compost, tillage providing an oxygen flush or protein fertilizers. In an emergency, you can fertigate or spray foliar solutions.

The solution to a shortage of organic matter is obvious: compost, cover crops, crop residues and not tilling.

If the pH is off, adjust with limestone, gypsum, dolomite or soil sulfur.

And finally, correct a deficiency of phosphorus with soft rock phosphate, legume cover crops, organic matter, compost or guano.

Like Morrison, Cantisano is not enthusiastic about most commercial compost. “It’s mediocre; it’s not finished,” he said, adding, “Grapevines need more fungi in the soil, not bacteria.”

He also said that if you have to hedge more than twice per season, something is wrong. “You have too much nitrogen. The ideal is not to have to hedge at all.”

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