How to modify and adjust soil pH? (scientific and practical solutions)

Crops and garden crops will reach their maximum yield in the right soil, irrigation, air and fertilization conditions. The soil condition at the time of planting and holding the crop must be constantly checked and changed according to the crop’s needs. One of these things is adjusting or correcting the soil’s pH or the soil’s acidity or alkalinity level. Each crop may require a certain amount of soil acidity, and farmers adjust soil pH according to the needs of that crop.

By adjusting soil pH through amendments such as adding lime (to increase pH) or sulfur (to decrease pH) and other minerals and chemicals, farmers can optimize soil conditions for their specific crops and maximize crop performance. They also support beneficial soil microorganisms and ensure the health of the products.

Why do we need soil pH adjustment?

Adjusting soil pH is important for agriculture for several reasons:

• Nutrient Availability: Soil pH affects the availability of essential nutrients for plant growth. Most plants grow slightly acidic to neutral soil pH (about 6.0 to 7.0). At low or higher pH levels, some nutrients are less available to plants, which leads to nutrient deficiency and reduced crop yield.
• Microbial activity: Soil pH affects the activity and diversity of soil microorganisms, such as bacteria and fungi. These microorganisms play an important role in nutrient cycling, organic matter decomposition, and soil structure formation. Maintaining an optimal pH range supports a healthy and diverse soil microbial community.
• Soil structure: Soil pH can affect soil physical properties such as compaction and porosity. Optimal pH levels create stable soil aggregates that improve soil aeration, water penetration, and root penetration.
• Product-Specific Requirements: Different products have different pH preferences. For example, plum trees thrive in acidic soils, while alfalfa and tomatoes prefer slightly alkaline conditions. Adjusting soil pH to match crop needs ensures optimal growth and productivity.
• Reduced toxicity: High pH levels can increase the solubility and availability of potentially toxic elements such as aluminum, manganese, and heavy metals. Adjusting the pH can help reduce the toxicity of these elements and create a more favorable growing environment for plants.

How do we measure soil pH?

Before we learn how to adjust soil pH, we need to know how to measure soil pH correctly. To measure soil pH, there are different methods, the most accepted of which include the following:

Using soil pH test kit:

These kits include chemical reagents and a pH spectrum that allow direct measurement of soil pH. The pH can be easily determined by using a soil sample and mixing it with distilled water.

Using the pH meter electrode:

A pH meter electrode is an electronic device that accurately measures soil pH. We mix the soil sample with distilled water and place the electrode in this solution. The device shows the pH directly, making this method more accurate than the test kit.

Laboratory:

Send the soil sample to a specialized laboratory, and they will measure the soil’s pH using precise equipment. This method is the most suitable for accurate soil analysis and determining its needs.

Correct soil sampling and accuracy in conducting tests are the keys to success in soil pH determination. Proper planning can be done by accurately measuring pH to correct soil pH and increase crop productivity.

Correction of alkaline soil pH

After testing, if we find that our soil is alkaline (that is, its pH is higher than 7.0), but the product we want to grow requires a more acidic environment, we can increase the amount by adding minerals and chemicals to the soil. Reduce the pH of the soil and adjust the pH of the soil.

We can use the following solutions to reduce soil pH (increase acidity):

Use of sulfur:

Adding sulfur to the soil produces sulfuric acid and lowers the pH. To achieve the desired effect, sulfur should be added gradually and according to soil tests. For this purpose, fertilizers such as sulfate can be used. When dissolved in the soil, sulfate turns into ammonium (NH4+), which leads to an increase in soil acidity.

Use of organic fertilizers:

Organic fertilizers such as vermicompost, peat moss, and cow manure can lower soil pH. These fertilizers increase acidity by producing organic acids and increasing the activity of soil microorganisms.

Use of nitrogen fertilizers:

Nitrogenous fertilizers such as ammonium sulfate and ammonium nitrate reduce soil pH after breaking down into weak acids. These fertilizers should be used carefully and according to the plant’s needs.

Use of acids:

Sulfuric acid, phosphoric acid, and nitric acid can lower soil pH. This method should be done carefully and based on soil tests to avoid damage to the plant.

In any method, the amount and time of use of modifiers should be adjusted according to the soil test results and the plant’s needs to achieve the best results.

Correcting the pH of acidic soil

But what can we do if we find out that the soil is too acidic after the test? As there are solutions to reduce the soil’s alkalinity, there are also effective solutions to reduce the soil’s acidity.

Use of lime (calcium carbonate):

Adding lime to soil neutralizes acids and increases pH. The amount of lime required should be determined based on soil testing.

Use of other lime materials:

Other calcareous materials, such as dolomite (calcium and magnesium carbonate) and zeolite, can also increase pH and improve the soil’s physical and chemical properties.

Use of alkaline fertilizers:

Alkaline fertilizers such as potassium sulfate, magnesium sulfate, and sodium nitrate can increase pH. These fertilizers reduce acidity by providing alkaline cations in the soil.

Use of organic materials:

Adding organic matter such as compost, vermicompost and peat moss to the soil can increase the pH. These organic materials increase the buffering properties of the soil by producing alkaline compounds.

• Important point: Here, the question may arise: Why is the use of organic materials such as vermicompost recommended both to increase soil pH and to decrease soil pH? No mistake has occurred! The initial condition of the soil determines how organic fertilizers work.
• Increasing pH (reducing acidity): In acidic soils (with low pH), adding organic fertilizer to the soil increases pH and reduces acidity.
  Reducing pH (increasing acidity): Organic fertilizers usually contain humic and fulvic acids, which can reduce pH after decomposition in the soil. Consequently, in alkaline (high pH) soils, adding these substances can lower the pH.

Conclusion

In this brief and useful article, we examined the need to adjust soil pH during the stages of planting and growing crops and garden crops. We also introduced methods for checking soil pH before doing anything.

Solutions for increasing or decreasing soil pH were also introduced and reviewed. In this way, information about soil pH modification and regulation was presented in brief.

In the end, it should be mentioned that before using any kind of fertilizer or additives in the soil, you should test the soil and be well aware of its acidity level. Also, getting help from an expert can be very helpful in these cases.