Soil analysis is important in farming to encourage optimal crop growth, allowing for the efficient use of nutrients, reduce the risk of leaching and lower carbon footprints.

The Farming for a Better Climate’s Soil Regenerative Agriculture group has been analysing its soils and looking at chemical, physical and biological soil health indicators.

The starting position for soil analysis is the pH – the scale of how acidic or alkaline it is. In Scotland, the target pH for grassland soils is between 5.8 and 6.0, with arable soils slightly higher at 6.0 to 6.2.

As Scottish soils are generally acidic, they usually require a liming material to be applied periodically to increase the pH and optimise crop growth. Acidic soil below a pH of 5.6 will have soluble aluminium which will inhibit root growth and limit yield.

Several agricultural practices and natural processes, including the use of nitrogen fertiliser and rainfall, can lower pH values and therefore it is necessary to analyse soils every four to five years to identify if there is a need to correct the soil pH.

Alongside pH, it is important to test for phosphorus (P) and potassium (K), as these are major nutrients required for crop growth. Phosphorus boosts root development, early seedling growth, plant maturity and seed development. Potassium regulates water content, resists stress, and increases the strength of straw.

Maintaining an optimal level of both P and K in the soil will ensure adequate nutrients for crop growth, without having excessive nutrients which pose an environmental risk.

When the Soil Regenerative Agriculture Group analysed its soils, the pH and phosphorus was within the target values, but the potassium indices ranged from low to high (Table 1).

Scottish soils are usually analysed using the Modified Morgan methodology, which has been adapted to analyse the plant-available nutrients in acidic soils. This presents realistic soil P levels which reflect what plants can extract and accurately removes the right amount of K from both sandy and heavy clay soils alike, which is more suited to fields with variation in soil type.

The use of incorrect soil analyses can lead to inaccurate reporting of soil nutrient levels, particularly soil P, which in turn can result in the under-fertilisation of crops.

Conversion tables are available in SAC Technical Notes 715, 716, 717, 718, (depending on region), however these conversion factors are less accurate than using the correct methodology to analyse soil initially.

Beyond the soil analysis discussed above, soils can also be analysed for trace elements, which is particularly valuable if a deficiency is suspected or for a more comprehensive soil check-up.

In recent years, there has been increasing interest in soil analyses which focus on the physical and biological components of a soil. These include a CO2 burst or more basic in-field analysis such as earthworm identification and counts.

Read more: Farm Carbon Toolkit – how best to understand soil health

A CO2 burst measures the carbon dioxide from a soil which can indicate the level of microbial activity. This method of analysis usually involves a period of soil incubation so that the temperature can be regulated.

The soil is also mixed with a source of energy to boost activity. However, this test does not distinguish between organism types, and is therefore a basic measurement.

Often the most straightforward way to investigate the biological health of a soil is by counting earthworms in field. A healthy soil is considered to have eight worms – from the three environmental groups: endogeic, epigeic and anecic – per spade (20cm x 20cm x 20cm).

(More information on earthworms, including how to identify adult worms, go to

Analysing the physical properties of soil is also important. Heavy machinery and sub-optimal working conditions can lead to compact soils which prevent plant roots developing and can subsequently reduce yield.

Often the best way to track the physical properties of a soil are to dig in the field regularly, performing the visual evaluation of soil structure (VESS) several times across the field. This allows for the topsoil and subsoil profile to be assessed and ranked on a score of 1 to 5, with 1 being a friable soil without any issues and 5 being a very compact soil that requires immediate restoration.

The Soil Regenerative Agriculture Group also analysed the biological and physical aspects of its soils and found that all the soils have a high level of microbial activity. However, there was a wide range in the VESS scores and in earthworm numbers and species (Table 2).

Soil analysis can help to identify ways to increase productivity and ensure that inputs such as fertiliser are effectively targeted. Regular analysis can also help to track changes and, when considered alongside farm management practices, can identify operations which have had both positive and negative impacts on soil health.