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Building Soil Health with Volcanic Basalt

Organic and sustainable farmers have long relied on rock dust, including volcanic basalt, as an all-natural way to improve roots systems, increase yields, and promote general plant health in a wide variety of crops and conditions. Yet it has taken the rapid depletion of our global soils to bring rock dust to the attention of modern agricultural science. The good news is that there is undeniable evidence that rock minerals can help restore soil health, minimize crop deficiencies, and boost resistance to pests and disease.

Origin of Volcanic Basalt 

On May 18, 1980, Washington’s Mount St. Helens awoke from 120 years of dormancy and erupted, sending volcanic ash into the atmosphere and depositing it in 11 states. It was difficult to imagine at the time that any signs of life could emerge from the surrounding landscape, which was covered with dark gray ash and resembled the moon.

Despite the destruction, though, nature’s regenerative abilities quickly took over. In some cases, agricultural farmlands that were downwind of the eruption saw long-term beneficial effects as a result of the mineral-rich rocks that the eruption deposited on their soil in the form of ash. This helps explain why people throughout history have been willing to settle near active volcanoes despite the potential dangers.

Not all rock dust is alike, however. Basalt stands out from other rock materials for its ability to balance overall soil health. Created through the cooling and solidification of dense viscous lava, basalt is the rock that underlies much of the Earth’s oceans. Some regions of the world are blessed with surface extrusions of basalt. Compared to volcanic rocks, which are high in quartz, basalt weathers relatively quickly. This means that it begins to release nutrients to plants as soon as the roots make contact. Additional nutrients become available with ongoing decomposition, thereby resulting in a steady flow of nutrients over time.

volcano cloud
Cloud of volcanic ash from Sakurajima Kagoshima Japan

Decades of Research

Research into the use of volcanic basalt as a soil amendment dates back to the 1930s, when scientists in Europe used finely-ground basalt to treat and improve the productivity of degraded forestlands. One of the most comprehensive studies on the benefits of crushed basalt came from D’Hotman de Villiers, who conducted a series of long-term field trials on highly degraded soil on the island of Mauritius. He found that adding volcanic basalt led to increased sugarcane yields.

The tests started as early as 1937 and resumed later in the 1940s and ’50s at the Sugar Cane Research Station of Mauritius. Scientists commenting on de Villiers’ work note several reasons behind basalt’s effectiveness as a soil amendment, including improved silicon nutrition, enhanced trace element supply, alteration of soil’s physical properties, and modification of mycorrhizal populations. Further studies have shown that basalt’s ability to increase soil function and productivity is a major mechanism influencing positive crop response, as measured by cation exchange capacity (CEC).

In addition, the concept of paramagnetism as developed by Dr. Philip S. Callahan points to the beneficial aspects that volcanic rock minerals add to soils and plants. Callahan’s research led to the conclusion that the healthiest agricultural soils are paramagnetic; this paramagnetism facilitates the flow of electromagnetic forces from the atmosphere to organic plant materials. In soils where this paramagnetic force has been eroded away, adding ground volcanic basalt can reestablish the balance necessary for increased biological activity and the resulting plant growth.

Boosting Resistance

The latest research focuses on rock dust’s ability to enhance the innate resistance of plants to a multitude of physical and biological stressors. Silicon (Si), which occurs naturally in volcanic basalt and is a key component of cell walls, strengthens stems and helps plants stand tall to capture more light and maximize photosynthesis. Silicon has also been identified as playing a particularly significant role in helping plants stay healthy and boosting their resistance to pests and disease.  Plants that don’t have access to adequate silicon in the soil are stressed out, weak, and unable to resist injuries caused by insects and pests.

Jian Feng Ma of the Faculty of Agriculture at Kagawa University in Japan cites extensive evidence to support the conclusion that silicon is “likely the only element able to enhance the resistance to multiple biotic and abiotic sources of stress.” Ma’s research shows that the beneficial effects of silicon are dependent on a plant’s ability to accumulate silicon in its stems, leaves, and buds. The more silicon in a plant’s shoots, the better its ability to resist the stresses that cause pests and diseases that lead to decreased crop health and vitality.

Sounds relatively straightforward, right? After all, silicon is the second-most abundant element in the Earth’s crust after oxygen. And yet crops around the world show signs of silicon deficiency. The problem — and the potential solution — lies with the form of silicon that can be absorbed by plants. Only a small fraction of silicon in our agricultural soils is soluble and readily available for plant growth.

One of nature’s best sources of soluble silicon is volcanic basalt. Adding silicon back to soil that has been depleted of this essential element not only makes it easier for plants to ward off plant-eating insects, but it also improves plant resistance to leaf and foliar diseases and makes them stronger in the battle against environmental and climate stress.

One believer in the resistance-boosting benefits of volcanic rock dust is Bob Wilt, owner and operator of Sunset Valley Organics. Located in the middle of the Willamette Valley in western Oregon, Sunset Valley Organics is a family farm producing great-tasting, nutrient-dense organic berries that require minimal processing because they are grown in healthy soil that teems with beneficial microbes. Unlike many other berry growers in the region, Sunset Valley Organics’ blueberry crops have not been affected by the dreaded spotted wing drosophila (SWD). Wilt has never had to spray against the insect; he attributes this to healthy growing conditions and plants with Brix levels of 12 and better.

Wilt has been using volcanic basalt for the past two years as part of a holistic, organic soil management plan and has seen good growth and healthy plants with fewer insects and disease. He attributes this to a balanced system of carbon, rock minerals, and microbes. He plans to continue using volcanic basalt as part of his farm’s healthy soils program.

“It’s all about getting our soils together,” he says. “We need to replace what we take out, and rock minerals are essential because minerals are food for microbes.”

Volcanic basalt may also be helpful in treating iron chlorosis, which can stunt plant growth and, in the case of fruit-bearing trees, leads to smaller fruits with bitter flavors if left untreated. While there are many different iron compounds available for treating chlorosis, university studies have shown that the iron in all-natural volcanic basalt is more effective at correcting deficiencies than synthetic iron products. For orchardists throughout the West, where high bicarbonate levels in irrigation water contribute to iron deficiency, volcanic basalt is being tested as a safe and effective way to deal with its symptoms.

Some sustainable farmers are also incorporating volcanic basalt as part of an integrative and non-chemical approach in the ongoing battle against slugs. Ground to preserve variable grit size, volcanic basalt acts as a physical barrier that slugs are loathe to cross and provides shelter for nematodes, earthworms, and other biological organisms that are essential to soil health and productivity. At the same time, essential rock minerals are slowly released back to the soil, further enhancing microbial activity.

Biology & Geology

By definition, organic farming is a system of agriculture that strives to mimic the natural ecosystem and its focus on building healthy soil. Healthy soil in turn is derived from a marvelously complex interaction between biology and geology in which rock material decomposes and reacts with soil microorganisms and plant material to release minerals and nutrients that are essential to optimal plant growth and increased agricultural yields.

By mimicking the Earth’s own method of producing healthy soil, rock dust helps support the biological processes required for optimal and sustainable plant growth. For evidence we need only observe the self-preserving behavior of plants themselves.

Plants are not nearly as passive as they seem. Given the opportunity, plants will actively seek to acquire nutrients from their surroundings to overcome imbalances. Recent research shows that fine roots will attack rock particles as a physiological consequence of mineral deficiency. In soil that is properly mineralized, however, plants don’t have to work nearly as hard to survive. Across a variety of conditions, volcanic basalt has been proven to minimize deficiencies, improve root systems and help grow stronger crops with higher yields and higher levels of nutrition.

For generations of sustainable farmers, volcanic basalt’s benefits have been indisputable. Today, scientists across the globe continue to validate the benefits of rock dust. Brazil has even made soil remineralization part of its agricultural policy — a major step forward in generating global awareness and interest in the importance of rock minerals. Now it’s up to the rest of the agricultural world to treat rock minerals for what they are: The building blocks of healthy soil.

Rich Affeldt holds an M.S. in agronomy from the University of Wisconsin-Madison and is the senior agronomist at Central Oregon Basalt Products, the maker of Cascade Minerals Remineralizing Soil Booster (RSB). Made of 100 percent finely-milled volcanic basalt from Central Oregon, RSB is listed by the Organic Materials Review Institute (OMRI) for use in organic production. For more information visit  www.cascademinerals.com. This article appeared in the April 2016 issue of Acres U.S.A.


Jian Feng Ma (2004) Role of silicon in enhancing the resistance of plants to biotic and abiotic stresses, Soil Science and Plant Nutrition, 50:1, 11-18, DOI: 10.1080/00380768.2004.10408447; bit.ly/1QrFDmk

According to the University of California’s Integrated Pest Management Program, “barriers of dry ashes or other abrasives heaped in a band 1 inch high and 3 inches wide around the garden also can be effective:” ipm.ucdavis.edu/PMG/PESTNOTES/pn7427.html

Paramagnetism by Philip S. Callahan, Ph.D. available from Acres U.S.A.