One of the most important components of any farm is the soils – they provide a medium for growth, as well as a platform for supporting grazing and traffic movement.

Reflecting on the complexity of soils, over the last 20 years concerns have moved from just considering the nutrients that need to be applied to ensure the best crop yields, to taking into account of other aspects of soil health.

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Understanding the complexity and dynamic nature of soil is the key to monitoring and maintaining its overall health. The health of the soil is the interaction of the chemical, physical and biological components and these can all be measured, and monitored to ensure that the health is sustained.

Additionally, a healthy soil can reduce negative impacts from management, such as greenhouse gas emissions and loss of nutrients to rivers through diffuse pollution.

The chemistry of soil is still a good place to start when assessing soil health and recent work on the samples sent for analysis to the SRUC's commercial labs has shown that more than 50% had a soil pH below 5.8.

Maintaining a pH of the soil at around 6.0 for grassland and 6.2 for arable crops is essential to ensure optimum use of nutrients applied as fertiliser.

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The naturally acidic nature of Scottish soils result in a loss of pH through time and regular sampling and application of lime should prevent the pH declining. At a pH less than 5.4, root growth starts to be inhibited, therefore lower the pH the greater the yield loss for crops.

Damage to the physical structure of the soil, especially through soil compaction, can also result in yield loss. This has become more of a concern over recent years when summer rainfall patterns have been more unpredictable and as the machinery for cutting grassland or managing arable crops has become larger and heavier.

Research has shown that, on average, 70% of the damage done from machinery can be on the first pass.

Understanding and assessing any soil compaction that might have occurred is essential to managing the soil. The method developed by SRUC, a visual assessment of the soil structure, uses a spade to dig out a block of soil that can then be broken apart and evaluated.

A comparison with a simple information sheet, containing photos and descriptions, the Visual Evaluation of Soil Structure (VESS), is a method that anyone can try.

Studies on the effects of soil compaction on grassland in the South-west of Scotland at Crichton Royal Farm has shown a 14% loss of dry matter yield over three years (3 t/ha) through two passes of a heavy tractor when the soil was wet in autumn. This confirmed that even limited soil compaction effected soil health.

The biology of the soil is difficult to assess in the field as the soil microbes that help ensure a healthy soil cannot be seen with the naked eye. However, there have been proxy methods to overcome this with nematodes being extracted in a soil sample and identified in the laboratory or something as simple as counting the number of earthworms in a block of soil (the VESS soil block would be ideal for this).

Earthworms are a suitable indicator as they generally prefer similar conditions to crops, such as pH and soil moisture. The more a soil is disturbed, the fewer earthworms are seen, therefore you should find more earthworms in a grassland than an arable soil.

Additionally, as earthworms feed on dead and decaying material, the more organic matter in the soil should encourage greater earthworm numbers. Maintaining or increasing organic matter is a very important component of the soil health as this provides sites for microbial activity that provides a source of a slow release of nutrients that can be made available to the growing crops.

The organic matter in soils maintains moisture longer during dry periods but provides more porous areas in the soil to drain away rainfall to reduce water-logged soils during wet conditions.

Earthworms are sensitive to soil compaction and work in grassland has shown reduced earthworm numbers in areas of more traffic down by 19% in areas of light traffic to 100% in areas of heavy compaction.

Soil compaction can affect certain species more than others with Aporrectodea caliginosa, or the grey worm, shown to have a higher sensitivity, with a 42% reduction in numbers as a result of a compacted soil.

Through the AHDB GreatSoils project, a soil health card has been developed that provides not only the numerical results from the indicator measurements such as soil pH, P, K, Mg, VESS, earthworm numbers etc, but a coloured traffic light system (red for needs immediate attention to green good but continue to monitor) that highlights the good and poorer aspects of the soil sampled.

The complex nature of soil means you need to know your baseline from where you are starting to allow management decisions to be made. Thereafter, this should allow you to measure, monitor and improve your soils.