Soil pH
Soil pH is a measure of the acidity or basicity of a soil. Soil pH can be used as an important indicator to make analysis of both quantitative and quantitively regarding soil characteristics. In soils the pH is commonly measured as a slurry of soil mixed with water or a salt solution and normally falls between 3 and 10 with 7 being neutral. Alkaline soils are basic soils with a pH above 7, soils with a pH below 7 are acidic soils. Ultra-acidic soils with a pH < 3.5 and very strongly alkaline soils pH > 9 are rare but can occur. The soil pH can affect may chemical processes and it specifically affects plant nutrient availability and influencing the chemical reactions they undergo. The best pH range for most plants is between 5.5 and 7.5. Many plants have adapted to survive at pH values outside this range.
Soil pH ranges and classification
| Denomination | pH range |
|---|---|
| Ultra acidic | < 3.5 |
| Extremely acidic | 3.5–4.4 |
| Very strongly acidic | 4.5–5.0 |
| Strongly acidic | 5.1–5.5 |
| Moderately acidic | 5.6–6.0 |
| Slightly acidic | 6.1–6.5 |
| Neutral | 6.6–7.3 |
| Slightly alkaline | 7.4–7.8 |
| Moderately alkaline | 7.9–8.4 |
| Strongly alkaline | 8.5–9.0 |
| Very strongly alkaline | > 9.0 |
Methods of determining pH in soil
Observing a soil profile can reveal profile characteristics that can be possible indicators of acidic, alkaline or neutral soils.
- Poor incorporation of an organic surface layer with underlying mineral layer can indicate strongly acidic soils
- Columnar structure can be an indicator of sodic condition
- Presence of a caliche layer or a mineral deposit indicates the presence of calcium carbonates, which are present in alkaline conditions.