Importance of Testing Soil pH

The importance of having the correct soil pH 

What effect does pH have on the availability of nutrients in the soil? There is no simple answer to this question, since the effects of pH are complex and vary with different nutrients; however soil pH is important because it influences several soil factors affecting plant growth. These factors will be discussed throughout this article as it aims to clarify the importance of soil pH and its relations to plant growth for many growers.

The first order of business is a quick run-over of pH and its associated terminology. Soil reaction and soil pH is an indication of how much alkalinity or acidity is present in the soil. This is measured in pH units, the pH units run on a scale from 0-14 with 7 being the neutral point. A pH reading below 7 is considered acidic and a pH reading above 7 is considered alkaline or basic. As the amount of hydrogen ions in the soil increases, the soil pH decreases, thus becoming more acidic. With this scale growers can get a broad idea on the acidity or alkalinity of their soil. 

As mentioned above, soil pH is important as it influences several factors affecting plant growth, this includes; soil bacteria, nutrient availability, nutrient leaching, toxic elements, and soil structure. Bacterial activity releases nitrogen from organic matter and in turn certain fertilizers are affected as bacteria operate best in the pH range of 5.5 to 7.0. Alternatively, plant nutrients leach out of soils with a pH below 5.0 a lot quicker than from soils in the pH range of 5.0 to 7.5. The best pH range for nutrient availability to the plants is in the pH range of 5.5 to 6.5. Certain metals such as Aluminium may become toxic to plant growth in soils with the pH value below 5.0. Some nutrients, such as phosphorus and molybdenum, become less available at lower pH values. It is clear that the pH of soil it vital in determining various nutrient uptake and availability. Be sure that the plants you are growing have the best pH value to absorb the specific nutrients needed to ensure optimal growth.

Certain soil structures, such as clay soils, are highly dependent on pH value. In the optimal range of 5.5 to 7.0 clay soils are granular and are easily worked, whereas if the pH range is extremely acidic or alkaline, clays tend to become sticky and hard to work with. This result alone proves the importance of pH in soils.

Although the pH value in the soil is not an indication of fertility it does affect the availability of fertilizer nutrients. A soil may contain adequate nutrients yet growth may be limited by a very unfavourable pH. Likewise, builder's sand, which is virtually devoid of nutrients, may have an optimum pH for plant growth.

The pH of soil is vital as it determines what nutrients are available at the plants roots. Nutrients such as Nitrogen, phosphorus and potash will not dissolve properly if the soil is too alkaline or acidic. Knowing the pH of your soil when planting garden/landscape beds, and the preferred pH that your plants like to grow in, will help the increase the success of your yields

How do I test my and adjust my soil pH?

There are several options on soil testing, we offer a soil pH meter and soil test kits to ensure accurate pH testing. See our YouTube video How to test pH of Soil for plants - Make Amendments for a run down on how to accurately test the pH of your soil.

 

Adjusting my soil pH

Raising and lowering pH takes time, so do not expect rapid changes. When your pH needs to be raised, you will want to apply Limestone or Hydrated Lime. To lower your pH, you will apply Iron Sulphate, Aluminium Sulphate or Ammonium sulfate.

To raise the soil pH and make your soil less acidic you will use lime, the amount of lime necessary to properly adjust the pH can only be determined by the above-mentioned soil test kit. Not all liming materials are equal, be sure to examine your test results to determine whether you will need calcitic lime or dolomitic lime. The difference between the two limes is a matter of what nutrients are released when adjusting the pH. Calcitic lime is mined from natural limestone deposits and crushed into a fine powder also known as agricultural lime, it releases calcium in your soil as it adjusts the pH.  Dolomitic lime derived in a similar way but from limestone sources that contain both calcium and magnesium. If your soil test comes back showing high levels of magnesium, use calcitic lime. If the test shows a magnesium deficiency, then use dolomitic limestone.

If you are looking to grow more acidic-loving plants it is vital that you lower your soil pH into the acidic range, this can be done by using elemental sulphur and aluminium sulphate. Elemental sulphate eventually becomes oxidized by soil microbes; however, it takes a few months to adjust the pH, thus working it into the soil will create better results as it is more rapidly processed. Spring applications are generally the most effective and it is far less likely to burn plants than aluminium sulphate products. Aluminium sulphate reacts quickly with soil and changes its pH value rapidly, this, however, increases the potential to burn plant roots.

Soil pH plays a big role in nutrient availability of plants and every grower should be aware of the pH value of the soils they are growing in to ensure maximum nutrient uptake can occur, resulting in better yields. Always keep the pH factor in mind when you are planning nutrient management programs, it is also advised to keep historical records of the soil pH in your fields. Soils tend to acidify over time, recent years have shown that pH decline is occurring rapidly in continuously cropped, direct-seeded land. On the other end of that spectrum, leaching of alkaline salts can raise the pH above the optimal range. A soil with an optimum pH today, may be too acidic or alkaline in the future, thus it is important to continuously check and manage your pH levels to ensure your landscape is the best breeding grounds for the plants you are cultivating. 

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