What is Soil pH?

pH stands for potential hydrogen. It refers to the excessive amount of hydrogen ions that block exchange sites in the soil and prevent minerals and nutrients from being absorbed by the grass.

The pH level of the soil is vital to growing lush, green lawns. On a scale of 1 to 14, a pH of 1 is very acidic and a pH of 14 is very alkaline (or basic), while a pH reading of 7 is neutral.  Lawns grow best in a soil that is slightly acidic to neutral (between 6.2 and a 7.0 on the pH scale).

Even small changes in pH reading can mean big changes for the lawn grass plant because the pH scale is logarithmic. This means that a pH reading of 5 is 1o times more acidic than a pH reading of 6 and 100 times more acidic than a pH reading of 7, and so on.

Why Test Soil pH?

Correct soil pH is essential to ensure optimal plant growth and crop yield, because it allows nutrients to be freely available for plants to take in. Testing the pH of your soil helps to determine what plants are best suited for that area.

Sometimes soil needs supplements, like fertilizers and soil pH adjusters, for plants to be able to thrive. Measuring the pH can help you figure out what and how much you need.

Things That Affect Soil pH

Many things can affect the pH of your soil. The most common factors are climate and weather, other plants in the area, the pH of your irrigation water, soil type, the kind of fertilizer you use, and nutrient availability.

Climate and Weather

Temperature, precipitation, sunlight, and seasonal weather changes all influence the soil pH. High precipitation, for example, will wash essential nutrients out of the soil. Many nutrients, such as calcium carbonates, are basic so as these nutrients leave the soil, it becomes more acidic.

Water coming into contact with decaying material in the soil (like leaves, for example) can also cause the pH to drop, because decaying matter releases carbon dioxide. When carbon dioxide mixes with water, acids can form.

Drier climates or regions going through a drought will have a more alkaline soil pH. Because there isn’t as much water moving through the soil, minerals and salts become concentrated, increasing the pH.

Plants

Native plants and local ecology can determine the starting pH of your soil. Soil underneath grasses is usually less acidic, while soils formed under trees tend to be more acidic. This is due to there being more decaying matter (leaves) near trees. The very crop you are growing can even alter your soil’s pH.

Irrigation Water

The water that you use to irrigate your crops will also influence the pH of your soil. If the water used is more acidic or more basic than the soil it is irrigating, the pH of the soil will shift.

Soil Type

Did the soil in your region form from granite, limestone, or shale? These parent materials will determine if your soil is more acidic or more basic. Areas with a lot of shale tend to be more acidic, while areas rich in limestone are more basic.

The texture of your soil will also determine how easy or how difficult it is to adjust the pH; this is known as the soil’s buffering capacity. Sandy soils have a lower buffering capacity while soils with more clay will have a higher buffering capacity. It’s harder to change the pH of soils with higher buffering capacities.

Fertilizer

Fertilizing soil is very important to get the best crop yields. Because pH will affect how easily available nutrients are to plants, it’s important to check soil pH before and after adding any type of fertilizer. By knowing your pH you can decide how much and what type of fertilizer you need.

Artificial nitrogen fertilizers tend to lower pH the most in soils. Organic fertilizer will acidify the soil once they come in contact with water, because of the soluble organic acids they contain.

Nutrient Availability

Plants cannot absorb nutrients if the soil pH is too low or too high. When soil pH is off, nutrients such as calcium and phosphorus will bind up with other things in the soil. When the nutrients become bound up, plants will not be able to take in what they need to grow.

Most nutrients are available when the soil is slightly acidic, but different plants thrive in different pH ranges depending on their specific nutrient requirements. If the pH is too low, aluminum toxicity can occur. When this happens, aluminum becomes unbound and the plants take it in at toxic levels.

If the pH is too high, nutrients like iron become bound. Without adequate iron uptake, plants will lose their chlorophyll and start to turn yellow, indicating the plants can no longer make food for itself. Molybdenum poisoning can also occur in soils with alkaline pH, resulting in stunted crops.

Methods of testing soil pH

In summary, there are two main methods exploited by soil pH testers:

1. Direct ground measurement – This is where soil pH is sampled using an electrode that’s placed directly in the ground. This method is terrific for nursery and field testing but care is needed to ensure you don’t damage your tester’s electrode. Where the soil you wish to test is firm to hard, it’s recommended that you first use an auger to disrupt the soil and then dampen the soil using distilled water before taking your measurements.
2. Soil slurry or dilution method – This technique is slightly more time consuming but less damaging to the electrode probe.It involves mixing your soil with distilled water in a container before using your pH tester take a measurement.

How a soil pH tester works

Portable Soil pH testers will have one of two main designs. They will either incorporate an electrode in the body of the device (all-in-one design), or the electrode will be connected to the main body by a wire.

Irrespective of the design, the principle behind the technology is the same. The pH electrode that takes the pH measurement consists internally of a reference electrode, reference solution, reference junction and a glass bulb with a hydrated gel layer. When your electrode is submerged in the diluted sample or pressed into the soil an electrical current is triggered. The tester then calculates the charge of the reference solution inside the bulb and compares it to the soil medium outside of the gel layer. This comparison results in a pH measurement which is displayed on the pH meter’s screen – all within a matter of seconds.

How to Test the Soil pH With a Digital pH Meter?

Gardening is like gambling — you plant and hope for a big payoff in produce or flowers, often sweetening the pot with an investment in soil amendments. Testing your soil’s pH improves your odds of garden success by letting you know ahead of time if a plant is likely to thrive as is or needs specific changes to soil chemistry. When soil pH is too high or too low for a plant, either the plant can’t access nutrients already in the soil or the nutrients become toxic to the plant. A digital soil pH meter takes the guesswork out of matching plant to site and tells you which soil amendments are needed in a matter of seconds.

What to look for when selecting your soil pH meter

There are many types of soil pH meters in different shapes and sizes to suit all applications, ranging from meters for the avid home gardener to large agricultural operations. When selecting the right soil pH meter for you here’s a list of things to consider.

1. Portability. Will you need a pH meter that is lab-based, field-based or a combination?
2. Method. Can soil be sampled directly or is dilution required?
3. Functions. Are other built-in functions required? For example, soil moisture and conductivity.
4. Length of the probe. The minimum sample depth is generally 20cm. Different plants and crops require measurements to be taken at varying depths.
5. Accuracy. Traditionally direct soil sampling is less accurate than the dilution method.
6. Calibration. Does the device come with any buffer solutions to calibrate your meter?
7. Sampling time. How long does it take to get a result?
8. Device and electrode durability. Take care as direct ground measurement can damage the glass within an electrode.