Fact Sheet: Soil pH
They key to plant vitality
Introduction to Soil pH
Soil pH is a measure of the acidity or alkalinity of the soil and is one of the most important soil properties that affect plant growth and nutrient management. It influences the chemical forms of nutrients, their availability to plants, and the microbial processes in the soil.
Types of Potassium Tests.
Types of Soil pH Tests
We conduct two types of pH tests for you, which help in understanding how pH varies under different conditions:
pH (1:5 Water)
Method: This test involves mixing soil with distilled water at a ratio of 1:5 (soil to water) and measuring the pH of the resultant solution.
Importance: The pH measured in a water solution provides a direct and straightforward indication of the soil's pH in its natural state, reflecting how plants will likely experience the soil.
pH (1:5 Calcium Chloride - CaCl2)
Method: This test is similar to the water pH test but uses a calcium chloride solution instead of water. The ratio is again 1:5.
Importance: The pH measured in a calcium chloride solution is typically lower than the water pH. It is considered more stable and less affected by soil organic matter and the salt content of the soil. This measure can be more indicative of the soil’s actual ionic strength and gives a better indication of the nutrient availability and potential toxicity issues.
Interpreting Results
Acidic Soil: pH less than 7.0
Effects: Increased availability of some nutrients like iron and manganese, but potential toxicity of these elements and decreased availability of others like phosphorus and molybdenum.
Management: Application of lime (calcium carbonate) can raise the pH to a more neutral level, improving nutrient availability and microbial activity.
Neutral Soil: pH around 7.0
Effects: Most nutrients are optimally available at this pH level, and microbial activity is at its peak, supporting robust plant growth.
Alkaline Soil: pH greater than 7.0
Effects: Decreased availability of essential nutrients like iron, zinc, manganese, and phosphorus.
Management: Elemental sulfur or aluminum sulfate can be used to lower the pH, improving the availability of these nutrients.
Factors Affecting Soil pH
Parent Material: The mineral composition of the parent rock from which the soil was formed can greatly influence its pH.
Rainfall: High rainfall regions tend to have more acidic soils due to leaching of basic cations.
Fertiliser Use: Some fertilisers can acidify the soil, especially those containing ammonium.
Actionable Recommendations
Regular Testing: Regular pH testing helps monitor changes and manage soil pH effectively.
Tailored Amendments: Based on the pH test results, apply appropriate soil amendments to modify the pH to suit the specific needs of your plants.
FAQs
Why test pH in both water and CaCl2?
Testing in both media provides a more comprehensive understanding of the soil’s pH conditions, helping anticipate plant responses and manage nutrient availability more effectively.