Soil pH It is considered one of the fundamental parameters in agriculture, as it directly influences the development, health, and productivity of crops. Maintaining the pH in the optimal range facilitates the absorption of nutrients main (nitrogen, phosphorus, potassium, calcium, magnesium, sulfur) and essential micronutrients, impacting the harvest and final quality of fruits and vegetables.
What is soil pH and why is it so important?
El soil pH It is the measure that indicates the concentration of hydrogen ions (H+) on the ground, indicating its degree of acidity or alkalinity On a scale of 0 (most acidic) to 14 (most alkaline), with 7 being neutral. Below 7, the soil is acidic; above XNUMX, it is alkaline or basic.
This variable directly impacts:
- The availability and assimilation of nutrients for the plants.
- Microbial activity responsible for mineralizing organic matter and fixing key nutrients.
- The chemical balance of the soil, determining which elements are available or blocked.
- The structure, porosity and physical quality of the substrate.
For example, in acidic soils, metals such as aluminum, iron, and manganese can reach toxic levels, while in alkaline soils, excess calcium and carbonates can retain phosphorus and micronutrients, making them difficult for crops to utilize.
Optimal soil pH ranges for different crops
Ideal pH values can vary depending on the crop. Most cultivated plants thrive in soils slightly acidic to neutral (between 6.0 and 7.5). However, there are species that require more specific conditions:
- Wheat: pH 5.5 - 7.5
- Barley: pH 6.5 - 8.0
- Rye: pH 5.0 - 7.0
- Corn: pH 5.5 - 8.0
- Alfalfa: pH 6.0 - 7.8
- Sunflower: pH 6.0 - 7.0
- Almond: pH 6.0 - 7.5
- Potato: pH 5.0 – 5.5 (prefers more acidic soils)
- Tomato: pH 5.5 - 7.0
- Eggplant: pH 5.4 - 6.0
- Orchid: pH 4.0 - 4.5
How is soil pH determined?
There are several ways to check pH:
- Portable pH meter: Simple and quick tools, suitable for approximate measurements and field work.
- Test strips or colorimetric kits: Economical, for an overview, although with less precision.
- Sending samples to a specialized laboratory: The most reliable method for accurate diagnosis, essential before major plantings or fertilization adjustments.
The recommended procedure involves taking several representative samples of the soil, drying them, sieving them, mixing them with distilled water, and measuring the pH after a brief resting period. This analysis should be repeated periodically, as fertilization, rainfall, and other factors cause pH to fluctuate throughout the annual cycle.
Factors that determine soil pH
The pH value is dynamic and can vary due to the influence of several elements:
- Parental material: Acidic rocks generate acidic soils, calcareous rocks produce basic soils.
- Climate and precipitation: Heavy rainfall often results in acidic soils due to leaching of bases (calcium, magnesium).
- Texture and organic matter content: Sandy soils are more susceptible to fluctuations; clayey and humus-rich soils have greater buffering power.
- Irrigation type: Water with high alkalinity can increase the pH.
- Agricultural practices: Fertilizer applications, amendments, and crops gradually change the pH balance.
Human activities—from fertilization to waste management and over-tillage—alter the natural acidity or alkalinity of the soil. Therefore, understanding the soil's history and monitoring it periodically is part of professional agronomic management.
Effects of pH on nutrient absorption and plant health
When the soil has an inadequate pH for the cultivated species, nutritional imbalances occur:
- Very acidic soils (pH < 5.5): Increased levels of toxic aluminum and manganese, calcium, magnesium, and phosphorus deficiencies, and short, thickened roots. Trace elements may be in excess, which can be harmful.
- Neutral soils: Greater balanced availability of all nutrients, optimal microbial activity, favorable structure.
- Alkaline soils (pH > 7.5): Micronutrients such as iron, zinc, manganese, and copper become less available; there is a high risk of iron chlorosis and nutritional deficiencies. Phosphorus is bound in insoluble forms.
Symptoms in plants can be confused with diseases: chlorosis, stunted growth, wilting, leaf necrosis, among others. Thus, regulating pH not only improves nutrition but also facilitates the diagnosis and treatment of agricultural problems. Here you can learn more about how to analyze soil conditions to optimize your plant health.
Soil pH management and correction
Adjusting the pH is possible with strategies adapted to each case:
- For acidic soils: Add calcium amendments (agricultural lime, dolomite, controlled wood ash, crushed eggshells). The type and particle size of the product affect its speed and effectiveness. It is important to calculate the dosage based on the soil texture and organic matter.
- For alkaline soils: Apply organic matter (compost, worm castings), elemental sulfur, nitrogen fertilizers in ammonium or sulfate form, micronutrient chelates, and occasionally agricultural gypsum to displace sodium in sodic soils. The process is slow and requires monitoring to prevent excessive acidification.
Soil classification according to pH and associated problems
Soils can be classified as follows:
- Strongly acidic: pH less than 5.5, with risk of metal toxicity and low phosphorus availability.
- Slightly acidic to neutral: pH between 6.0 and 7.5, ideal for most plants.
- alkaline: pH greater than 7.5, tendency to micronutrient deficiencies and blocked phosphorus.
- Sodium or calcareous: Highly alkaline soils, which are difficult to correct and where physical problems such as crusting and low permeability are often seen, in addition to iron, zinc, and manganese deficiencies.
Recommendations for efficient pH control
To maintain proper pH over the long term and avoid harmful fluctuations:
- Conduct periodic soil analysis at different points and depths of the ground.
- Use organic matter to improve the buffering capacity of the soil, promote microbial life and favor the structure.
- Choosing crops and fertilizers suitable for the natural pH of the soil.
- Record tillage and fertilization history to anticipate changes and make informed decisions.
pH management is a key tool for ensuring crop health and maximizing productivity and harvest quality. Understanding these processes will allow us to anticipate deficiencies or toxicities, save on long-term corrective measures, and promote a balanced and sustainable agroecosystem.