June 2006 Issue of Wines & Vines
 
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The Dangers Of Soil Salinity

 
by Tim Teichgraeber
 
 
The Dangers Of Soil Salinity
In his salinity research, Cramer also experimented with fast-growing maize: the third plant from the left displays the stunting effect of excess soil salinity.
 
    HIGHLIGHTS
     

     
  • In arid climates, salt will accumulate in the soil. Soil salinity has become a worldwide concern in places like Australia, and closer to home, Paso Robles.
     
  • Dry regions with highly saline soils also tend to have ground water that is high in salts. Irrigating saline soils with salty ground water tends to exacerbate the problem and cause dehydration.
     
  • There are various ways to cope with soil salinity, which include giving vines a good soaking with rainwater or low-salt mountain runoff river water. Another tactic is drenching irrigation sufficient to wash out the accumulated salts and restore a healthy balance to the soil.
The dirt doctors at the University of Nevada, Reno and Texas Ag Extension Service have been known to spin some salty yarns--morbid tales of leaf burn, chloride phytotoxicity and boron-blackened vines. Their stories of vine decline and slow death are ones to which California growers should bend an ear, ere they see their own vineyards quietly poisoned and steathily dispatched by saline soils below.

Biochemistry professor Grant Cramer, of the University of Nevada, Reno, says that soil salinity is either a significant concern or a major problem in most winegrowing regions.

"Anywhere you have arid climates, you're going to accumulate salt in the soil," Cramer says. "Australia has significant salinity problems, and I would imagine some of the North African grapegrowing areas have significant salinity issues too. It's a worldwide problem. Certainly the San Joaquin Valley would also have problems."

Salts are more than just the sodium chloride you might use to garnish your margarita or make your strip steak really pop. They're a whole class of ionic compounds made up of positively charged cations and negatively charged anions that are neutral when combined. Some are organic, some are inorganic, some are basic, and the most troublesome have a dogged tendency to accumulate in soils and plants unless they are thoroughly flushed out with fresh water low in salts. They contain vital micronutrients, some of which turn toxic at high levels. Among the potentially phytotoxic salt components are sodium, chloride and boron, all of which can cause crippling decreases in vine vigor or even vine death at elevated levels.

Not surprisingly, arid regions with highly saline soils also tend to have ground water that is high in salts. Irrigating saline soils with salty ground water tends to exacerbate the problem and cause dehydration--the most basic salt accumulation problem for plants.
 
A thirsty vine is like a shipwreck survivor bobbing along in a life raft. "If you drink seawater, by osmosis you become dehydrated. It's like a catch-22, and eventually it becomes toxic," Cramer says.

When salt levels get high enough in the vine, the leaves start to display "leaf burn" or browning, as they do with some other vine afflictions like Pierce's disease.

Another salt accumulation problem is caused by the way salts change the structure of the soil itself, and the effect that has on plants. "(Salt) also changes the way the roots grow," Cramer says. "Normally the soil clumps in a way that leaves pores." Those clumps and spaces allow the soil to hold water and also allow roots to penetrate the soil. "The salt breaks down those clumps--we call that deflocculation."

Chloride, Sodium And Boron

Aside from your run-of-the-mill dehydration and soil deflocculation problems, leaf burn may also indicate specifically toxic levels of sodium, chloride or boron.

Dr. George Ray McEachern of the Texas Agricultural Extension Service described some symptoms of salt toxicity in a 1995 article that is available online (http://horticulture.tamu.edu/ newsletters/vine/abv1095.html), but did not return my phone calls requesting an interview. Soil salinity is a major issue across the state of Texas, so papers from authorities there should be accorded due respect, especially given that state's significant experience in viticulture.

According to McEachern, vines with toxic levels of chloride display leaf burn, but chloride doesn't really affect the roots. High levels of chloride slow the absorbtion of nutrients and interfere with photosynthesis, stunting productivity of the plant. Chloride can subtly decrease health and vigor, and by the time the vine displays obvious leaf burn, the damage may be tough to reverse. Subtle decreases in vigor may make chloride poisoning difficult to recognize until late in the game.

Sodium toxicity is not terribly well understood, at least as far as I can gather. Some speculate that it has a negative effect on leaves, and according to McEachern, the negative effects on soil structure are well documented.

One salinity test measures the soil's sodium absorbtion ratio (SAR). If a soil's SAR is above 4, the soil is borderline-suitable for grapegrowing. If the SAR is above 7, grapevines will likely sicken over time. McEachern cites as examples Texas vineyards that were planted in soils with SARs of 16, 20 and 43, all of which failed.

Boron toxicity tends to manifest itself in vine leaves turning black. McEachern says that where irrigation water boron readings are greater than 1 part per million, vines should be closely monitored for decreased vigor and wells should be tested regularly.

McEachern points out that what makes soil salinity so scary is its ability to slow down a vine and have a negative impact without any visual symptoms other than poor performance. Without regular testing of soil and irrigation water salt levels, salt toxicity can be hard to diagnose. By the time you are aware of the problem, salts may have done irreparable damage to the vines.

Cramer, a UC Davis graduate, says that his salinity studies have to date been largely limited to laboratory situations and that more field studies are needed. "I think there's a lot more studying to be done, and that's why I'm going to Australia."

Coping With Saline Soils

A good soaking with rainwater or low-salt mountain runoff river water are two ways to flush the salts out of problem soil. Another tactic is drenching irrigation sufficient to wash out the accumulated salts and restore a healthy balance to the soil.

Fresh water rainfalls are integral to keeping saline soils in check in coastal regions. Inland regions like Nevada or Texas often have more serious salinity problems because they seldom see a good drenching. "In Nevada, we don't have rivers to wash the salt out into the sea," Cramer says.

If it's possible to flush the excess salts out of saline soils with mountain runoff, there are parts of Western Nevada that might flourish as grapegrowing regions just the way Mendoza has in Argentina, provided that the mountain runoff is used efficiently. Both are desert regions on the leeward side of mountains that see substantial rainfall.

Cramer says that it may be possible to wash the salts out of previously barren soils in areas with adequate drainage. "One guy was planting a vineyard in Fallon and the guy had used it as his ice skating rink in the winter time. The water he was using (to freeze for ice skating) was high in boron. Initially when we planted the vines there were signs of boron toxicity. Then we leached it with canal water from Lake Tahoe that was very low in boron.

The Dangers Of Soil Salinity
Professor Grant Cramer experiments on soil salinity's effect on grapevines in his University of Nevada, Reno, laboratory.
"Soils are very heterogenous--they vary a lot. In a particular region you can have good soils and bad soils. The biggest factor is whether you've got quality water to irrigate with or significant rainwater to leach the soil," Cramer says.

Drip irrigation of saline soils with saline water throughout the growing season is ill advised. This technique only tends to increase the buildup of salts in the soil to the detriment of vine health.

Regular testing of both soil salt and irrigation water salt levels is advised in any region with salinity issues, especially because the effects of low-level toxicity can be slow to emerge, but hard to reverse.

Soil Salinity In Paso Robles

Paso Robles is one of many grapegrowing regions where soil salinity is an important consideration, though maybe not a matter of life or death. West Side vineyards get more rainfall, which helps decrease salt retention. Eastern regions of Paso Robles, depending on the weather, have to pay more attention to salinity issues.

Don Brady, winemaker for Robert Hall Winery in Eastern Paso Robles, is a veteran of Desert Ridge, Llano Estacado and Cordier Estates in Texas. Brady says that salinity issues are less grave in Paso Robles, but they're still an issue.

"It's just something that affects the vines, but it's not something that is life threatening," Brady says. "It's economic. It's not a situation where the vines can't grow because of the salinity, but there are places where the soil is too salty and it becomes limiting to the vines."

Brady recalls how precarious salinity issues were in Texas, and one specific occasion when a freak accident tipped the scales.

"Someone was outside the vineyard quail hunting and they shot into the vineyard and punctured the drip hoses. Wherever the water contacted the vine it killed the foliage of the vine because of the salt in the water," Brady says.

The quality of well water there and elsewhere can vary substantially. "It depends on where you are in the aquifer," Brady adds. "There were 16 wells, and the best was 400 ppm dissolved solids and the worst was 2,400 ppm. At 2,400 it's salt water." There are situations that not even a vine can suffer, when alternative crops should be considered. "There were places there they'd grow shrimp," he says.

Brady says that it's hard to match the benefits of a good rain. "An acre-inch of rainfall is a hell of a lot more than what you can put on with irrigation." Fortunately, Brady says, Paso Robles is also blessed with good irrigation water. "We have great water. Great quality of water and great quantity of water, and we're able to use that water to leach our soils."

Brady believes that some varieties may be more tolerant of saline conditions. "We've got Orange Muscat that seems to be salt intolerant. I think Zinfandel is salt intolerant. Syrah could be also. Some of the thicker-skinned varieties like Cabernet, I think, are more tolerant of saline conditions. You're talking about vine stress, whether it's caused by salinity or other things. Some (varieties) are more hardy to environmental stresses."

East Side veteran Jerry Lohr echoes Brady's sentiment that there's no substitute for a good rain when it comes to combating soil salinity. After five years of drought, Lohr says he's "feeling really good," after 12-plus inches of rainfall so far this year.

Lohr says that well water quality varies in Paso Robles and that not all of it is good for irrigation. "We're operating 17 wells at present with different levels of salinity. We're treating the water in different ways. One well we felt wasn't treatable, so we dug another one half a mile away."

Lohr says that treating irrigation water with gypsum helps to reduce the negative effects of accumulated salts on soil structure. "If you see the damage you're well too far gone. If you have a vine where the soil conditions are such that the vine can't extract potassium, it's too late."

Selecting salt resistant rootstocks should also be considered in areas with salinity issues. "1103 Paulsen seems to be one of the most salt tolerant rootstocks available," Lohr says. He isn't sure whether variety choice is important. "We haven't seen an effect on varieties in our vineyards. I don't have soil that is so saline that I see damage in the varieties."

Even Lohr is quick to admit that salinity issues may have subtle effects that aren't yet known. "I think we're probably more into studying these things than some other places because we're a young area. We don't know what we don't know yet."

(San Francisco resident Tim Teichgraeber is the regular wine columnist for the Minneapolis Star Tribune, a frequent contributor to The Wave Magazine, and books the remainder of his schedule as an entertainment lawyer for the likes of Dillinger Four and Har Mar Superstar. Contact him through edit@winesandvines.com.)
 
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