Soil pH: Why It Matters More Than Fertilizer for Crop Growth

By Zahid Hussain (M.Sc. Plant Pathology)

 Soil pH: Why It Matters More Than Fertilizer for Crop Productivity

Soil pH, which refers to the acidity or alkalinity of soil, is one of the most critical factors determining agricultural success. It directly controls whether plants can absorb essential nutrients from the soil or not. Many farmers believe that poor crop performance is mainly due to insufficient fertilizer application. However, in reality, if soil pH is not within the optimal range, even the best and most expensive fertilizers will fail to deliver results.

When soil becomes excessively acidic or overly alkaline, nutrients remain present in the soil but become chemically unavailable to plants. As a result, plant roots are unable to absorb them, leading to weak growth, nutrient deficiencies, and reduced yields. This makes soil pH management far more important than simply increasing fertilizer doses.

Understanding Soil pH and Nutrient Availability

Soil pH is measured on a scale from 0 to 14.

A pH below 7 indicates acidic soil

A pH of 7 is neutral

A pH above 7 indicates alkaline (calcareous) soil

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Most agricultural crops grow best in soils with a pH between 6.0 and 7.5, where nutrients are most readily available. Outside this range, chemical reactions occur in the soil that lock nutrients into forms that plants cannot use.

This explains why two fields receiving the same fertilizer program may show completely different results—the difference lies in soil pH, not fertilizer quantity.

Problems Caused by Acidic Soils

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Acidic soils are commonly found in areas with high rainfall, intensive cropping, or long-term use of ammonium-based fertilizers. When soil pH drops below 6.0, several serious problems arise.

1. Nutrient Unavailability

Essential nutrients such as phosphorus, calcium, magnesium, and potassium may be present in the soil, but acidic conditions reduce their availability to plant roots.

2. Aluminum Toxicity

One of the most damaging effects of acidic soil is the release of aluminum (Al³⁺) into the soil solution. Aluminum becomes toxic to plant roots, inhibiting root elongation and branching. This leads to shallow, weak root systems that cannot absorb water or nutrients efficiently.

3. Reduced Microbial Activity

Beneficial soil microorganisms responsible for organic matter decomposition and nitrogen fixation perform poorly in acidic conditions. This further limits nutrient cycling and soil fertility.

4. Poor Crop Growth

Plants growing in acidic soils often show stunted growth, poor tillering, weak stems, and reduced resistance to drought and disease.

Problems Caused by Alkaline (Calcareous) Soils

Alkaline soils are widespread in arid and semi-arid regions, including most agricultural lands in Pakistan, India, and the Middle East. These soils typically have a pH above 7.5 and contain high amounts of calcium carbonate.

1. Micronutrient Deficiencies

In alkaline soils, micronutrients such as iron (Fe), zinc (Zn), manganese (Mn), and copper (Cu) become chemically fixed. Even though they are present in sufficient quantities, plants cannot absorb them.

2. Iron Chlorosis

One of the most visible symptoms of alkaline soil is iron deficiency, which causes yellowing of young leaves while veins remain green. Farmers often apply more fertilizer, but the problem persists because the issue is chemical unavailability, not nutrient absence.

3. Poor Fertilizer Efficiency

Phosphorus fertilizers rapidly react with calcium in alkaline soils and become unavailable. This leads to low fertilizer-use efficiency and economic losses for farmers.

4. Soil Structural Problems

Highly alkaline and sodic soils often suffer from poor structure, surface crusting, low infiltration, and reduced root penetration.

Fertilizer Is Not the Problem — Soil Chemistry Is

These issues clearly demonstrate that nutrient deficiency symptoms are often caused by unfavorable soil pH rather than lack of fertilizer. Adding more fertilizer under such conditions does not solve the problem—it only increases production costs and environmental risks.

The correct approach is to test soil first, correct pH, and then apply fertilizer. When soil pH is balanced, even small amounts of fertilizer produce excellent results because plants can absorb nutrients efficiently.

Importance of Soil Testing

Soil testing is the foundation of proper nutrient management. A simple soil test reveals:

Soil pH

Salinity and sodicity levels

Macro- and micronutrient status

Without soil testing, fertilizer application is based on guesswork, which often leads to poor yields and wasted resources. Every farmer should test soil at least once every 2–3 years.

Methods to Correct Soil pH

Soil pH correction depends on whether the soil is acidic or alkaline. Each condition requires a different management strategy.

1. Managing Acidic Soils (pH below 6.0)

Acidic soils contain excessive hydrogen ions, which must be neutralized to raise pH. This is achieved by applying lime-based amendments.

Agricultural Limestone (Calcitic Lime)

Agricultural lime is the most common and effective material used to neutralize soil acidity. It reacts with hydrogen ions and increases soil pH, improving nutrient availability.

Dolomitic Lime

Dolomitic lime contains both calcium and magnesium. It is especially useful where soils are deficient in magnesium along with low pH.

Wood Ash

Wood ash has alkaline properties and can reduce soil acidity. However, it should be used cautiously and in limited quantities, as excessive application may raise pH too rapidly and create nutrient imbalances.

Benefits of Liming

Neutralizes soil acidity

Eliminates aluminum toxicity

Improves root development

Enhances microbial activity

Increases fertilizer efficiency

Liming effects are gradual but long-lasting, often improving soil conditions for several years.

2. Managing Alkaline and Calcareous Soils (pH above 7.5)

Alkaline soils require a different approach because lowering pH is more difficult and gradual.

Gypsum (Calcium Sulfate)

Gypsum is one of the most effective amendments for alkaline and sodic soils. While it does not drastically lower pH, it improves soil structure, reduces sodium hazards, and enhances water infiltration and root growth.

Elemental Sulfur

Sulfur is biologically oxidized by soil microorganisms into sulfuric acid, which slowly reduces soil pH. This process takes time and depends on soil moisture, temperature, and microbial activity.

Organic Matter Addition

Organic materials such as:

Farmyard manure

Compost

Green manures (e.g., sunn hemp, sesbania)

help lower soil pH gradually. As organic matter decomposes, organic acids are released, which increase micronutrient availability and improve soil health.

Use of Chelated Micronutrients

In alkaline soils, applying chelated forms of iron and zinc is more effective than conventional fertilizers, as chelates prevent nutrient fixation.

Role of Organic Matter in pH Balance

Organic matter plays a crucial role in buffering soil pH. It:

Reduces pH fluctuations

Improves nutrient retention

Enhances microbial activity

Improves soil structure and water-holding capacity

Soils rich in organic matter are more resilient and productive, even under challenging conditions.

Long-Term Benefits of Balanced Soil pH

Maintaining optimal soil pH provides long-term advantages:

Higher crop yields

Better fertilizer efficiency

Stronger root systems

Reduced nutrient deficiencies

Lower production costs

Improved soil sustainability

Balanced soil pH allows plants to fully utilize applied nutrients, making farming more profitable and environmentally sustainable.

Conclusion

Soil pH is the hidden foundation of crop productivity. Many nutrient-related problems observed in fields are not due to lack of fertilizer, but due to imbalanced soil chemistry. Excessively acidic soils damage roots and release toxic aluminum, while alkaline soils lock essential micronutrients like iron and zinc.

The solution is simple but often ignored:

Test the soil, correct the pH, and then fertilize accordingly.

When soil pH is properly managed, even small fertilizer inputs produce remarkable results. Healthy soil leads to healthy crops—and healthy crops lead to sustainable agriculture and food security.