What is Soil pH? Factors and How to Measure It!

Joko Warino S.P M.Si

What is Soil pH Factors and How to Measure It!

Soil pH is a crucial factor in determining the health and productivity of soil. It measures the acidity or alkalinity of the soil, which can significantly influence plant growth, nutrient availability, and microbial activity.

Understanding soil pH is essential for farmers, gardeners, and environmental scientists as it helps in selecting appropriate crops, optimizing fertilization practices, and maintaining ecological balance.

This article explores the importance of soil pH, how it affects various aspects of soil health, and practical ways to manage and adjust soil pH for optimal agricultural and environmental outcomes.

What is Soil pH?

Soil pH is a measure of the acidity or alkalinity of soil, expressed on a scale from 0 to 14. A pH value of 7 is considered neutral, while values below 7 indicate acidic soil, and values above 7 indicate alkaline soil.

The pH level of soil affects the chemical form of nutrients, influencing their availability to plants. For instance, certain nutrients are more accessible in slightly acidic soils, while others are more available in neutral to slightly alkaline conditions. Therefore, maintaining an appropriate pH level is crucial for optimal plant growth and health.

The pH of soil is determined by the presence of hydrogen ions; soils with more hydrogen ions are more acidic, while those with fewer hydrogen ions are more alkaline.

Soil pH can be influenced by various factors, including the parent material from which the soil is formed, rainfall patterns, organic matter decomposition, and agricultural practices.

Regular testing and adjustment of soil pH can help in achieving the desired conditions for specific crops, enhancing nutrient uptake, and promoting beneficial microbial activity. Understanding and managing soil pH is a fundamental aspect of sustainable soil management and agricultural productivity.

Why is Soil pH Important?

Here are the reasons why Soil pH is important:

1. Nutrient Availability

Soil pH directly influences the availability of nutrients to plants. Essential nutrients such as nitrogen, phosphorus, and potassium are most readily available in soils with a pH range of 6 to 7.

When the soil is too acidic or too alkaline, these nutrients can become chemically bound in forms that plants cannot absorb.

For example, in highly acidic soils, phosphorus forms compounds that are not soluble, making it inaccessible to plants. Similarly, in highly alkaline soils, micronutrients like iron, manganese, and zinc become less available.

Adjusting soil pH to the optimal range can significantly improve nutrient uptake, leading to healthier plants and higher yields.

Farmers and gardeners often lime their soils to raise pH levels or add sulfur to lower them, depending on the specific needs of the crops they are growing. Regular soil testing can help monitor pH levels and ensure that nutrient availability is maintained for optimal plant health.

2. Microbial Activity

The pH level of soil also affects the activity and diversity of soil microorganisms. Beneficial microbes, such as bacteria and fungi, thrive in specific pH ranges.

These microorganisms play a critical role in decomposing organic matter, cycling nutrients, and promoting plant health. For instance, nitrogen-fixing bacteria, which convert atmospheric nitrogen into forms plants can use, are most effective in neutral to slightly acidic soils.

In acidic soils, the activity of these beneficial microbes is often inhibited, leading to slower decomposition of organic matter and reduced nutrient cycling.

Conversely, alkaline soils can limit the availability of certain nutrients, affecting microbial processes. By maintaining an appropriate soil pH, farmers can create a conducive environment for microbial activity, enhancing soil fertility and plant growth.

3. Soil Structure

Soil pH impacts the physical structure of the soil, which in turn affects water retention, aeration, and root penetration. In acidic soils, the presence of excessive hydrogen ions can lead to the breakdown of soil structure, resulting in compacted and poorly aerated soils.

This can hinder root growth and reduce the soil’s ability to hold water and nutrients. On the other hand, in alkaline soils, the presence of sodium can cause soil particles to disperse, leading to poor soil structure and reduced water infiltration.

Maintaining an optimal pH level helps in preserving good soil structure, which is essential for healthy root development and efficient water and nutrient uptake.

Good soil structure promotes aeration, allowing roots to breathe and access the nutrients they need. It also improves the soil’s ability to retain moisture, reducing the need for frequent irrigation and promoting sustainable water use in agriculture.

4. Plant Health and Productivity

The health and productivity of plants are closely linked to soil pH. Plants grown in soils with an inappropriate pH level are often more susceptible to diseases and pests.

Acidic soils can lead to toxic levels of certain elements, such as aluminum and manganese, which can harm plant roots and stunt growth.

Alkaline soils can cause deficiencies in essential micronutrients, leading to symptoms such as chlorosis (yellowing of leaves) and poor overall plant health.

By managing soil pH, farmers and gardeners can create optimal growing conditions that enhance plant vigor and resistance to diseases and pests.

This not only improves crop yields but also reduces the need for chemical inputs such as pesticides and fertilizers. Healthy plants are better able to withstand environmental stresses, contributing to more sustainable and resilient agricultural systems.

5. Environmental Impact

The pH level of soil has broader environmental implications beyond plant health and productivity. Acidic soils can lead to the leaching of harmful metals such as aluminum into groundwater, posing risks to water quality and aquatic ecosystems.

Alkaline soils can contribute to soil salinity, which can degrade arable land and reduce its agricultural value. Managing soil pH is therefore important for preventing environmental degradation and preserving ecosystem health.

By maintaining appropriate soil pH levels, farmers can mitigate the environmental impact of agricultural practices. This involves using soil amendments judiciously, practicing crop rotation, and employing conservation tillage techniques.

Sustainable soil management not only enhances agricultural productivity but also protects natural resources, supporting the long-term viability of farming and the health of surrounding ecosystems.

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Factors that Affect Soil pH

Below, I explain the factors that affect soil pH, including:

1. Parent Material

The parent material from which the soil is formed significantly influences its pH. Soils derived from limestone or other calcium-rich materials tend to be more alkaline, while those formed from granite or sandstone are generally more acidic.

The mineral composition of the parent material determines the natural pH range of the soil, affecting its initial acidity or alkalinity.

Over time, weathering processes can alter the pH of soil derived from different parent materials. For example, acidic parent materials can lead to the formation of acidic soils as minerals break down and release hydrogen ions.

Understanding the parent material helps in predicting and managing soil pH levels for agricultural and environmental purposes.

2. Rainfall

Rainfall is a crucial factor that affects soil pH. In regions with high rainfall, leaching of basic cations (such as calcium, magnesium, potassium, and sodium) occurs, leaving behind more acidic components like hydrogen and aluminum ions. This process leads to a gradual acidification of the soil over time.

In contrast, arid regions with low rainfall often have soils that are more alkaline. The lack of sufficient water reduces leaching, allowing alkaline salts to accumulate in the soil.

Managing soil pH in these areas involves addressing the effects of rainfall patterns and their impact on soil chemistry.

3. Organic Matter Decomposition

The decomposition of organic matter can influence soil pH through the production of organic acids.

As plant and animal residues decompose, they release organic acids that can lower soil pH. The extent of this acidification depends on the amount and type of organic material being decomposed.

Conversely, the decomposition process can also lead to the release of nutrients that buffer the soil and mitigate pH changes.

For instance, the decomposition of certain plant residues can release calcium and magnesium, which can help neutralize acidic soils. Managing the addition of organic matter is crucial for maintaining balanced soil pH levels.

4. Agricultural Practices

Agricultural practices such as fertilization, crop rotation, and irrigation can significantly impact soil pH. The use of ammonium-based fertilizers, for instance, can lower soil pH as they convert to nitrate and release hydrogen ions.

Continuous cropping of certain plants can also deplete specific nutrients, altering the soil’s pH over time.

Irrigation with water containing high levels of dissolved salts can increase soil alkalinity, while practices like liming can be used to raise the pH of acidic soils.

Farmers need to carefully select and manage their agricultural practices to maintain optimal soil pH for crop health and productivity.

5. Pollution and Acid Rain

Environmental pollution, particularly acid rain, can dramatically affect soil pH. Acid rain, which is caused by the release of sulfur dioxide and nitrogen oxides into the atmosphere, can lower the pH of soil when it falls to the ground.

This acidification can lead to the leaching of essential nutrients and the mobilization of toxic metals like aluminum.

Industrial activities and emissions from vehicles contribute to the formation of acid rain, posing a threat to soil health.

Monitoring and mitigating pollution sources are essential steps in protecting soil pH and maintaining a healthy growing environment for plants.

Methods for Measuring Soil pH

To measure soil pH, you can use several methods, including:

1. pH Test Strips

pH test strips are a simple and cost-effective way to measure soil pH. These strips are coated with a pH-sensitive dye that changes color when it comes into contact with a solution.

To use pH test strips for soil, a small soil sample is mixed with distilled water to create a slurry. The pH test strip is then dipped into the slurry, and the resulting color change is compared to a color chart provided with the strips to determine the pH level.

Although pH test strips are easy to use and provide quick results, they may not be as accurate as other methods. The accuracy of the reading can be influenced by the quality of the strips and the precision of the color comparison.

However, for general gardening purposes, pH test strips can be a handy tool for getting a rough estimate of soil pH.

2. Digital pH Meters

Digital pH meters provide a more precise and reliable method for measuring soil pH. These devices use an electrode to measure the hydrogen ion activity in the soil solution.

To measure soil pH with a digital pH meter, a soil sample is mixed with distilled water to form a slurry. The electrode is then inserted into the slurry, and the meter displays the pH reading on a digital screen.

Digital pH meters are known for their accuracy and ease of use, making them popular among farmers, gardeners, and researchers.

Regular calibration of the meter with standard pH solutions is necessary to ensure accurate readings. Although digital pH meters are more expensive than pH test strips, their precision and reliability make them a worthwhile investment for those who need consistent and accurate soil pH measurements.

3. Laboratory Soil Testing

For the most accurate and comprehensive analysis of soil pH, laboratory soil testing is the preferred method.

Soil samples are collected and sent to a laboratory, where they are analyzed using standardized procedures and sophisticated equipment.

Laboratory testing not only provides precise pH readings but also offers additional information on soil nutrient levels, organic matter content, and other important soil properties.

Laboratory soil testing is particularly valuable for large-scale agricultural operations and scientific research, where precise soil management is crucial.

While this method can be more time-consuming and expensive compared to at-home testing methods, the detailed and accurate results it provides are essential for making informed decisions about soil management and fertilization practices.


Understanding and managing soil pH is crucial in agronomy and land management.

By knowing the soil pH, farmers can make better decisions regarding crop selection, fertilizer application, and corrective actions to ensure that the soil remains productive and supports healthy plant growth.

Measuring and managing soil pH is a fundamental step in achieving sustainability and efficiency in agricultural production.



Joko Warino S.P M.Si

Allow me to introduce myself, my name is Joko Warino, a lecturer at one of the universities in Indonesia (Faculty of Agriculture and Animal Husbandry, UIN Suska Riau Indonesia). My field of expertise is soil science.

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