Many farmers wonder why their plants are growing slowly, why leaves are turning yellow, or why plants are wilting. Often, these issues can be traced back to fluctuations in soil pH, making it crucial to check and amend the soil.

In this article, we will explore what soil pH is, how it affects plant growth, and methods for testing soil pH to ensure timely interventions for your field.

1. What is Soil pH?

- Definition: Soil pH measures the acidity or alkalinity of soil, ranging from 1 to 14. It reflects whether the soil is acidic, neutral, or alkaline. Most soils have a pH between 5.0 and 8.0. Each plant species has an optimal pH range; if the pH deviates from this range, plants may experience stunted growth, yellowing leaves, wilting, or even death.

- Soil Classification by pH:

• pH = 7: Neutral soil, suitable for many crops.
• pH > 7: Alkaline soil, which may cause yellowing in new growth, indicating the need for soil improvement.
• pH < 7: Acidic soil, which may be hard and cracked, requiring remediation.

 Soil pH scale and how it affects plants

2. When to Check Soil pH?

• New Planting Area: Initial pH measurements help determine suitable crops or necessary amendments for optimal growth.
• During Cultivation: Regular pH checks guide appropriate soil management practices to foster healthy plant development.
• When Plants Show Symptoms: Signs of distress such as slow growth, yellowing leaves, or poor root development warrant a pH assessment to implement timely corrective measures.

Note: Measure soil pH at any time, but avoid testing immediately after applying lime, fertilizers, or organic matter, as this can skew results.

3 stages need to check soil pH

3. Identifying Soil Issues Through pH Levels.

Soil pH can serve as an indicator of various soil problems. Timely identification allows for appropriate interventions to prevent crop damage.

Table evaluating the influence of pH on fertilizer use efficiency.

Effects of pH on Nutrient Availability:

• pH < 5.0: Aluminum (Al), iron (Fe), and manganese (Mn) become soluble, potentially toxic to plants. Symptoms may include calcium (Ca) and molybdenum (Mo) deficiency.
• pH < 5.5: Symptoms of molybdenum (Mo), zinc (Zn), and sulfur (S) deficiencies appear.
• pH > 7.5: Aluminum, zinc, and iron toxicity may occur.
• pH > 8.0: Formation of calcium phosphate that plants cannot absorb.
• pH > 8.5: Elevated sodium (Na) levels lead to salt toxicity and signs of zinc and iron deficiency.

The impact of soil pH on the soil environment.

4. Methods for Measuring Soil pH.

a. Direct Soil pH Measurement.

- Create a hole in the soil using a drill or ruler (ensure consistent depth for each measurement).

- Add distilled or deionized water to moisten the soil, avoiding excess water.

- Insert the pH meter probe into the hole and wait for the reading.

b. Measuring pH from Soil Samples.

- Collect representative samples from various locations in the planting area, including near plants and at least two samples further away.

• Take five samples from the four corners and one from the center.
• Ensure all samples are taken from the same depth, digging a hole 50 x 50 x 50 cm and removing a thin layer of soil down to 40 cm.

- Mark the pH at sampling points, as nutrient levels and soil type can fluctuate.

- Mix about 0.5 kg of soil, let it dry, then crush and weigh 0.1 kg for testing.

- Place the sample in a 0.5-liter beaker, add 2/3 water, and stir until dissolved.

- After 30 minutes, pour off the upper layer of water for testing.

5. Measure soil pH using measuring tools.

a. Using pH Testing Strips.

- Dip a pH test strip into the solution until the paper is fully saturated. Wait one minute for color change.

- Compare the strip color with a pH color chart to determine soil pH.

• Advantages: Inexpensive and easy to use.
• Disadvantages: Dark-colored solutions can make readings difficult, and results can vary due to lighting and angle. The error of the measurement result is 0.5, so it affects inaccurate soil reclamation.

b. Using a pH Meter.

- Mix soil with distilled water in a measuring container, adding a few reagents.

- Follow instructions to see color changes indicating pH levels.

• Advantages: Provides accurate readings and is user-friendly.
• Disadvantages: Subjective readings may occur, and results can vary by 0.5-1 pH unit. The amount of included reagents is limited, usually only enough for 5 measurements. Handling this chemical requires safe measures.

c. Using Advanced pH Measurement Devices

- Digital pH Meters: These provide accurate readings displayed on an LCD screen, are less affected by solution color, and have a lower error margin (0.01-0.1).

- pH Testing Kits: Offer high precision but require careful handling and are more expensive.

- Laboratory Chemicals: For precise testing, requiring a lab setting and knowledgeable personnel.

• Methyl Red: The solution turns red when pH < 4, yellow when pH > 7, in the range 4 < pH < 7, the chemical changes from red to orange-red, orange and finally yellow.
• Bromthymol Blue: The solution turns yellow when pH < 6, blue when pH > 8 and from 6 < pH < 8, the solution appears yellow, yellow-green, green, blue respectively.
• Phenol phthalein: The solution retains its color when pH < 8 and pH > 10 then turns red.

Top 5 most accurate ways to measure soil pH.

Conclusion:

Soil pH significantly impacts both soil health and plant growth. By understanding soil pH, you can manage and enhance the growth of your crops effectively.

This guide aims to help you recognize the signs of plant distress such as wilting, yellowing leaves, or slow growth, enabling you to check soil pH and assess its effects. With this knowledge, you can implement the appropriate measures to restore your field’s health.

For further advice on handling acidic or alkaline soil conditions, consult ATW’s additional resources or contact our support engineers 24/7 at hotline 032 988 6079.