Why Does Soil Ph Matter?
 | Author:
Allison Kosto, MSU Broadwater County Extension Agent
MSU Broadwater County Extension Agent |
Why Does Soil pH Matter?
Allison Kosto
MSU Broadwater County Extension Agent
Soil should not be confused with dirt. Dirt is unclean; it gets underneath your fingernails. Soil, on the other hand, is a dynamic material that has living parts. Soil is comprised of minerals, water, gases, organic matter and microorganisms. All of these components give soil its unique characteristics. Soil is not the same in Montana as it is in Florida. In fact, it may not be the same on one side of your yard as it is on the other.
The environment, along with soil composition and parent material, attributes to the soil pH. I’m sure you are somewhat familiar with pH. The pH scale ranges from 0 to 14 with 7 as neutral. Numbers less than 7 are acidic and numbers greater than 7 are alkaline or basic. Lemon juice is acidic, and bleach is alkaline.
In Montana, we tend to have soils with a high pH (alkaline), usually ranging from 6.5 to 8.5. There is a lot of science behind why and how soil develops a certain pH. However, without getting too complicated, the primary reason that soil in Montana tends to be more alkaline is that it contains a large quantity of calcium carbonate (lime). This is especially true in Broadwater County (remember the lime plant?!). Due to our low average precipitation, these carbonates also leach into the groundwater, which also gives our water a high pH too.
The best way to find your soil pH is to use a reputable lab. Based on samples received in my office, our native soils in Broadwater average a pH of about 8.0. Home testing kits are available for pH and other nutrients. However, their accuracy is questionable. A list of labs is available from the Extension Office, and we can even send the sample for you. A basic garden soil analysis is about $17 plus shipping.
Soil pH has an ability to affect plant growth by influencing nutrient availability. It affects how the soil attracts and releases nutrients. In high pH soils, iron, manganese and boron are not as accessible to plants. Iron is the most common nutrient deficiency due to alkaline soils. Some plants, including many trees, are more susceptible to iron deficiencies. An iron deficiency shows up at interveinal chlorosis. This means that leaf of the plant is yellow while the veins stay bright green. In acid soils, magnesium, calcium and phosphorus tend to be limiting.
Generally, most plants grow well when the soil pH is 6 to 7 (slightly acid to neutral). However, some plants may prefer a certain pH range. For example, blueberries prefer acidic soils. If you’ve ever tried to grow blueberries in Broadwater County, you may have discovered that they simply don’t grow or produce well here. This is because of our alkaline soil.
If you have a high pH soil, one of the first questions you’ll likely ask is, “How do I change it?” Unfortunately, it’s not easy. Because of our calcareous soils, it is difficult, expensive and often impractical to lower pH significantly. The two most common amendments to lower pH are elemental sulfur and aluminum sulfate. Aluminum sulfate works more quickly, whereas elemental sulfur can take several months. Routinely adding organic matter can also improve pH. Always be cautious when adding fertilizer and soil amendments. Too much of a good thing isn’t always a good thing. Use your soil test to determine how much fertilizer or organic matter should be used.
Acidic soil and the need to raise pH is uncommon in Montana. Cropland in some areas of Montana is starting to have an issue with soil acidification due to high fertilizer inputs for many years. Additionally, areas in northwest Montana have a lower pH due to parent material that is high in silica, as opposed to carbonates east of the divide. Limestone is the common amendment used to raise pH in areas of low pH.
Even with amendments, it is extremely difficult to cause a major change in your pH. However, by knowing and understanding your pH, you can make better management decisions. For example, if you have a pH of 8.0 then you may have to come to terms with the fact that blueberries simply won’t produce well. You also may need to fertilize your trees with iron annually.
If you have any questions about soil testing, fertilizers or soil amendments, stop by your local MSU Extension Office at 416 Broadway or contact us at 406-266-9242 or allison.kosto@montana.edu.
