Soil pH

Definition - What does Soil pH mean?

Soil pH is a measurement that indicates the alkalinity or acidity of soil. It is calculated by finding the negative logarithm of the concentration of hydrogen ions in the soil, and ranges from 0 to 14. The lower a soil’s pH the more acidic it is, and the higher the pH, the more alkaline the soil is. Soil with a pH of 7 is considered neutral.

Soil pH is an important measurement because the acidity or alkalinity of soil determines how easily plants can absorb nutrients from it.

MaximumYield explains Soil pH

A pH level of less than 4.5 is considered extremely acidic, and anything above 8.5 - 9.0 is considered strongly alkaline.

For a better idea of what this means, lemon juice has a pH level of 2.5 and stomach acid has a pH of 2.0. On the other end of the spectrum, ammonia has a pH of 11.1 and milk of magnesia has a pH of 10.5.

Plants take up nutrients from soil when the nutrients are dissolved in water. When the soil's pH is too acidic or too alkaline, some of those nutrients – including iron, nitrogen and others – are not able to dissolve as efficiently. When soil is too acidic (below about 6.0 pH), phosphorous, potassium and nitrogen cannot be properly dissolved and absorbed. When it is too alkaline, with a pH rising much higher than 7.5, then phosphorous, manganese and iron will not readily dissolve in the soil solution. Thus, most plants thrive best in soil with a pH of 6.0 - 7.5.

Soil pH levels are affected by a number of different factors, including temperature, rainfall and the type of vegetation that has grown in the soil previously. In general, areas with heavier rainfall will have more acidic soil, while areas with dry climates will have more alkaline soil. The soil pH for cultivated ground where specific crops have been grown may be very different from uncultivated soil that has only native vegetation.

Farmers and horticulturists can adjust soil pH with fertilizer, crop rotation and other techniques to obtain an ideal pH level to grow healthy plants.

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