Understanding Soil pH and its Impact

What is Soil pH?

• Soil pH is the measure of the acidity or alkalinity.
• The pH scale ranges from 0 to 14, where 7 is neutral.
• A pH below 7 is acidic, and a pH above 7 is alkaline.
• Soil pH directly affects nutrient availability, microbial activity, and plant growth.

Soil pH and Availability of Nutrients

• Plants' nutrient absorption is influenced by pH.
• Acidic soils (pH < 7) have more available iron, manganese, and aluminum.
• Acidic soils (pH < 7) have lower availability of calcium, magnesium, and phosphorus.
• Alkaline soils (pH > 7) have limited phosphorus, iron, and certain micronutrients.
• Neutral soils (pH 6-7) provide a balanced availability of most nutrients.

Soil pH and Microbial Activity

• Soil microbes thrive in specific pH ranges.
• Acidic or alkaline soils disrupt nutrient cycling and overall soil health by reducing microbial diversity and activity.

Types of Microbes Based on pH Preference:

• Acidophiles thrive in acidic conditions (pH < 7), with an optimum pH of 2 to 5; sulfur bacteria, acid-loving fungi, and acidophilic bacteria are examples.
• Neutrophiles prefer neutral conditions (pH 6 to 8), with an optimum pH of 6.5 to 7.5; most soil bacteria and fungi are examples.
• Alkaliphiles thrive in alkaline conditions (pH > 7), with an optimum pH of 8 to 11; alkaline-loving bacteria, alkaliphilic fungi, and cyanobacteria are examples.
• Extreme Acidophiles thrive in highly acidic environments (pH below 2); Ferroplasma and Sulfolobus are examples.
• Extreme Alkaliphiles thrive in highly alkaline environments (pH above 9 or 10); Bacillus alcalophilus is an example.
• Microbes thrive in acidic, neutral, alkaline, or very acidic/alkaline conditions.

Soil pH and Plant Health

• Extreme pH levels can lead to poor growth, yellowing leaves, or nutrient deficiencies.
• Some plants have a narrow pH tolerance.
• Plant choice is important for soil pH.

Soil pH and Soil Structure

• Extreme pH can cause poor soil structure, compacted soils, and reduced water infiltration.
• It affects soil structure by influencing the charge and binding of soil particles.

Soil pH and Toxicity Levels of Elements

• Aluminum can become toxic in acidic soils.
• Iron or zinc may be less available in alkaline soils.

Ideal pH Range

• Most plants prefer a soil pH between 6.0 and 7.5 (neutral to slightly acidic).
• Acid-loving plants prefer a pH closer to 5.0–6.0.
• Alkaline-loving plants thrive in soils with a pH closer to 7.5–8.0.

Adjusting Soil pH

• Lime (calcium carbonate) raises the pH of acidic soil.
• Sulfur or peat moss lowers the pH of alkaline soil.

Impact of Soil pH on Soil

• Soil pH affects how easily plants absorb nutrients.

Nutrient Availability

• Acidic soil (pH < 6.0) has higher availability of iron, manganese, and aluminum, and reduced calcium, magnesium, and phosphorus.
• Alkaline soil (pH > 7.0) has limited iron, phosphorus, and zinc, but molybdenum may be abundant.
• Microbial activity is impacted by soil pH; it disrupts nutrient cycling, decomposition, and soil structure due to extreme acidity or alkalinity.
• The soil structure is affected by highly acidic or alkaline soils.
• Very acidic soils cause valuable minerals to leach.
• Alkaline soils cause poor aggregation and excessive crusting.

Impact of Soil pH on Plants

• Plants have optimal pH ranges for growth (pH 6 to 7 is preferred).

Growth and Health

• Signs of nutrient deficiencies or toxicities appear when pH is outside the optimal range.
• Acidic soils are suitable for some plants like blueberries and azaleas, while others prefer neutral to slightly alkaline conditions
• Alkaline soils hinders iron uptake for some plants.

Toxicity

• Root damage and impaired plant growth occurs in acidic soils due to high levels of aluminum and manganese.
• High levels of calcium or sodium can harm plants in highly alkaline soils.

Impact of Soil pH on the Environment

• Water quality is affected by runoff and leaching of nutrients and pollutants.
• Aluminum and other metals contaminate water bodies in acidic soils.
• Nutrients bind to minerals in alkaline soils making them unavailable to aquatic ecosystems.
• Extreme pH levels lead to soil erosion.
• Soils with neutral or slightly acidic pH aid in long-term carbon storage.
• Highly acidic or alkaline soils increase carbon dioxide emissions.

pH Management

• Soil pH is adjusted by adding organic matter, sulfur, or ammonium based fertilizers(to drop) and adding lime or wood ash (to raise).
• Regular soil testing ensures optimal plant growth and sustainability.

Soil pH Principles

• Soil pH impacts nutrient uptake.
• Maintaining an optimal pH balance is crucial for healthy plant growth.
• Plants have specific pH requirements.
• Plants suited for the soil’s pH is important or adjust the pH to meet plant needs.
• Soil pH influences microbial populations, nutrient availability, and organic matter breakdown.
• A balanced pH promotes good soil structure enhancing water retention, root growth, and nutrient absorption.
• Soil pH influences toxic substance and nutrient leaching into the environment.
• Soil's ability to resist pH changes affects the speed and effectiveness of pH adjustments
• Optimal plant growth is achieved through pH management, but care should be taken by testing understanding soil conditions.
• Maintaining an appropriate soil pH is essential for long-term soil health and sustainability to preserve soil fertility and ecosystem balance.

Soil pH and Nutrient Availability

• The availability of plant nutrients in soil depends on it's pH.
• Soil pH between 6.0 and 7.5 is ideal for most plants for optimal nutrient availability.

Optimal Soil pH Range (6.0 - 7.5)

• Most plants thrive in this range for the availability of a broad spectrum of nutrients.
• Most nutrients (nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, and trace minerals) are available.
• Soil pH of 6.5 is often "neutral" and ideal for balanced nutrient availability.

Nutrient Availability by pH Range:

• Acidic soils (pH < 6.0) have soluble levels of iron, manganese, and aluminum, and lower levels of calcium, magnesium, and molybdenum.

• Neutral soils (pH 6.0-7.0) provide the best range for nutrient uptake.

• Alkaline soils (pH > 7.0) have nutrients which are less soluble and harder for plants to absorb but contain abundant calcium and magnesium.

Soil pH and Fertilizers

• The efficiency of nutrients from fertilizers is highly impacted by pH.
• Soil pH determines nutrient solvency and effectivity upon utilization.

Nitrogen Fertilizer

Ammonium-based fertilizers

• These promote the release of ammonium, more efficient in slightly acidic to neutral soils.
• Ammonium is more stable and available for plant uptake in acidic soils. Nitrate-based fertilizers
• Provides nitrate, more available and efficient in neutral to slightly alkaline soils.

Phosphorus Fertilizer

• Phosphorus is affected by pH.
• It can react to form insoluble compounds in acidic soils becoming less available.
• In alkaline soils, phosphorus binds with calcium to form insoluble calcium phosphates increasing its availability.
• Optimal pH range for phosphorus availability is where phosphorus fertilizers work most effectively, ensuring that phosphorus remains soluble and available to plants.

Potassium Fertilizer

• Potassium fertilizers are less affected by pH compared to other nutrients.
• Soils may reduce potassium’s mobility and uptake.
• Potassium is most readily available in slightly acidic to neutral soils.

Micronutrients

• Iron (Fe), Manganese (Mn), Zinc (Zn), and Copper (Cu) are sensitive to pH changes.
• They're soluble and readily available to plants in acidic soils (pH < 6.0),
• In alkaline soils (pH > 7.0), micronutrients can become less available, leading to deficiencies like iron deficiency.

Calcium, Magnesium, and Sulfur Fertilizer

• The availabilty of Calcium and Magnesium is affected by the soil's pH.
• Calcium tends to be more available in alkaline soils but calcium in alkaline cause nutrient imbalances..
• Magnesium follow a similar pattern but are more available in in neutral to slightly acidic soils.
• Sulfur is typically available across a wide pH range.

Lime and Acidifying Fertilizers

• Lime (Calcium Carbonate) raises pH (reduces soil acidity).
• This improves the availability of phosphorus, calcium, and magnesium.
• Acidifying fertilizers lower pH can increase the availability of nutrients like phosphorus and micronutrients in alkaline soils.

Soil pH Influence on Fertilizer Efficiency:

• Acidic soils (pH < 6.0) work best with ammonium nitrogen fertilizer , phosphorus fertilizer, and micronutrients.
• Neutral to slightly acidic soils (pH 6.0 - 7.0) work best with phosphorus, and nitrogen fertilizers
• Add soil/base to Alkaline soils (pH > 7.0) to increase phosphorus, micronutrients (iron, manganese, zinc), and fertilizer uptake.

Soil pH Computation

• Compute with hydrogen ions to measure how acidic or alkaline a solution is. Formula: pH=−log[H+] Where: H+ is hydrogen concentration in moles/liter. log is the logarithm.
• Acidic solutions have < 7, while alkaline solutions have > 7 hydrogen ion concentration.

pH Calculation

• Soil pH Calculation requires specialized equipment.
• Take composite soil sample from collection of soil from area
• Mix known amount of soil (10 g) with distilled water (25 mL).
• Determine the the ion concentration Use a pH meter or indicator strips Apply the formula -log[H+] if you were measuring H+ concentration directly
• pH Meters
• Indicator Solutions
• Testing Kits
• The concentration of H+ ions is1 × 10-6 mol/L,pH=-log (1×10-6) yields pH =6.

Soil pH Testing Methods

pH Test Kit

• You will test with a pH test kit includes solutions ,pH test strips or testing fluid.
• Obtain multiple soil samples in garden area.
• Use the testing solution or soil-water slurry mixture and test pH level.
• Evaluate soil with indicator for pH based the color presented.
• It is simple inexpensive and quick method and it’s also generally less accurate than other .

Digital pH Meters

• You need to calibrate the device to a standard buffer solution.
• Apply the meter into the soil-water slurry.
• Evaluate the pH based in the readings on the digital readout.
• While accurate it is often more, pricier and needs periodical maintenance. .

Laboratory Soil Testing

• Have a soil analysis sent to the local laboratory
• They are high in testing ability based on the multiple soil properties that are calculated.
• This processes takes longer and is more costly than other forms of DIY analysis.

DYI Method

• Make sure that equipment will be available using the baking soda/vinegar methods.
• Add samples into containers plus apply soils for each test.
• You are analyzing for the fizziness if your soil samples are alkaline/acidity respectively.
• It’s the Cheapest but least test for evaluations.

pH Test Strips

• Evaluate test with your chosen soil.
• Dip test paper based on the instructions plus read with colors.
• It is quick plus simpler less precise. Use the list depending on your soil parameters .

Procedure

Use pH strips

• You need strips plus distilled water.
• Prepare soil-water slurry with samples of soil from four to six inches deep, mix in a cup amount of the soil.
• Dip testing into the mix.
• Evaluate that mixture from testing strips. Interpretation is based on results:
• pH is based on acidity or alkaline of the soil.

Vinegar and Baking Soda Method,

• Make sure you have the soils with vinegar plus Baking soda based on instructions
• Look during test to see if soils react to base/acid solution.
• pH is based on testing for soils acidic qualities or base components.