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  • Soil Health

  • Chemical


Soil pH indicates the soil’s acidity or alkalinity. Its inherent value is influenced by the chemical composition of the soil, but it can change due to both natural factors and agricultural activities. The soil’s pH influences the accessibility of nutrients in the soil by plants, affects microbial activity, influences flora and fauna species diversity, and has been associated with leached soils (Cardoso et al., 2013; Creamer et al., 2016; Gardi et al., 2009; Merrington, 2006).

Soil pH has direct associations with several critical ecological aspects, including but not limited to biomass production (including for food and fibre), filtering, buffering, transformation of substances within the soil matrix, and safeguarding genetic diversity within ecosystems. Furthermore, it exhibits indirect connections, influencing human health via impacts on the uptake of heavy metals into plants and the availability of micronutrients in food plants, impacting water quality, and playing a role in climate control (Guerra et al., 2021).

Methodology summary

Soil pH is measured on a scale of 0 to 14, with pH level below 7 being acidic while pH level above seven is alkaline (or basic). A pH of 7 is considered neutral (neither acidic nor alkaline) (Soil Testing Methods Global Soil Doctors Programme, FAO).

Soil pH is usually measured by glass electrode in a slurry of 1 part by weight of soil to 2.5 parts water. Measure soil pH in a weak salt (0.01–0.1 M) solution of calcium or potassium chloride, rather than just water, to reduce the influence of varying electrolyte concentration because it is then small relative to the total salt concentration in solution. The use of CaCl2 has been recommended for a range of practical and interpretive reasons (Schofield, 1955; Archer et al., 2003; Merrington 2006).

Normally pH measurements are conducted in a laboratory, but they could also be measured on-site if necessary equipment is available.

Detailed information on soil sampling such as where to take the samples from, how many, the best time to sample, and depth of sampling, can be found at the Farm Carbon Toolkit.

Metric threshold or direction of change

  • Thresholds are context (habitat, vegetation type, soil type, etc) dependent.
  • DEFRA have produced targeted pH for arable and grassland soils for light sand soils, medium soils, deep clay soils, deep clay silty soils, organic soils (10-25% SOM) and peats (25%+ SOM).
  • Feeney et al., 2023 have also benchamarked pH for some habitat types and soil types in the UK.

  • Agricultural
  • Forest
  • Grassland
  • Peatland
  • Saltmarsh
  • Wetland


  • Community


  • Low


  • Tier 1

Technical expertise

  • Low

Standardised methodology

  • Yes