pH [2]

pH is a measure of the soil acidity and the scale ranges from 0 to 14. It is measured as the negative (decimal) logarithm of the hydrogen ion concentration of a solution. With the pH scale being logarithmic (base 10) each pH unit is 10 times the value of the previous value; thus pH 5 is 10 times more acidic than pH 6; whilst pH 5 is 100 times more acidic than pH 7.

Turfgrasses will grow over a wide range of pH levels, although optimum growth will take place over narrower parameters.

The more acidic soils with a pH of less than 5 will favour the fine fescues and browntop bent grasses. A very acidic soil will result in many nutrients being less available (being ‘locked-up); reduced micro-organism activity which will also result in reduced organic matter decomposition; typically the production of a thinner sward can result, although careful management can alleviate this arising; whilst there will also be less strongly growing turf, which is primarily due to reduced nutrient availability, however, this is not usually a particular problem for finer turf situations, in many cases it is a beneficial condition, plus earthworm activity, especially surface casting, is also reduced.

Slightly acidic to neutral soils, with a pH of 6.0 -7.0 will be suitable for Perennial Ryegrass, Smooth Stalked Meadow Grass plus the undesirable Annual Meadow Grass. Nutrient availability is typically optimum within this range, allowing for strong growth, although disease potential and earthworm casting can also be optimum.

Alkaline soils, with a pH of 7.0 or greater will result in more micro-nutrients being locked up and less available, affecting growth; in addition, there is also a reduction in phosphorus availability.

Where soils are too acidic for the desired turfgrass plant then lime (Calcium Carbonate) might be applied to help raise soil pH; and where the soil is too alkaline or not acidic enough then ground Sulphur can be used to help lower soil pH. The changing of pH on soil-based surfaces is problematic and prone to difficulties due to the complexity of soil variabilities. Often considerable quantities of material would need to be applied to make significant changes, which would be impractical in many turf situations as this would often negatively affect the sward cover and density.

BS ISO 10390:2005 is the International Standard for Soil quality – Determination of pH.

There are two main classifications used to describe soil pH, although the more common one used in the UK is probably that derived from Truog.