One of the greatest threats to soil health is compaction from machinery.

This is an avoidable consequence of modern agriculture, with its heavy mechanical loads passing over the land several times in a season, by using the correct tyres. Understanding the relationship between tyre type, inflation pressure and tractive force can limit the effects and improve productivity.

The Farm Advisory Service (FAS) has predicted that compacted, or poorly drained soils can reduce yields by 14- 35% and increase nutrient run-off losses by approximately 40%.

“Using the correct tyre and pressure can mitigate the damage to soil, which is increasingly important as conditions become more variable,” said Zach Reilly, of SAC Consulting, part of Scotland’s Rural College (SRUC), and facilitator of 'Farming For A Better Climate’s Soil Regenerative Agriculture Group'. “In recent years, there have been major developments in tyre technology which can help farmers to manage this vital aspect of their business.”

Very high flexion tyres, or VF tyres, can reduce ground pressure by up to 40% compared to standard tyres as the carcase of these tyres flex, creating a larger contact area for the machinery with the soil, reducing ground pressure.

“The advantage of VF tyres is that they adapt easily between terrain, saving time on changing the tyre pressure when you leave the field. If investing in VF is not appropriate, adjusting the pressure of existing tyres is another option,” explained Mr Reilly.

“You can’t just let tyres down, though. You need to ensure your tyre pressure is safe for the operating conditions – usually slow in the field and quick on the road.”

As a rule of thumb, a high weight with a low pressure creates a small problem deep down, and a low weight with a high pressure creates a large problem near the surface. A target ground pressure of less than 10 psi should be aimed for, to ensure minimal crop loss. This is due to the fact many roots can survive when exposed to a pressure between 7 and 9 psi.

Soil structure is the arrangement of soil particles and the air and water gaps between them. Each soil has a different carrying capacity and this will vary with soil texture and change based on environmental factors, particularly the moisture levels within the soil.

Wet soils are generally more plastic, meaning they can be moulded without fracturing, and high plasticity can cause soils to become impermeable if compact.

When looking to safeguard soil structure, Mr Reilly added that it is also important to consider the whole picture between the soil and machinery, including:

* Wheel slip which can cause shear failure and smearing in the soil;

* machinery ballasting which can influence wheel slip and machinery efficiency;

* Also the set-up of the implement, including the critical depth of a tine and the rake angle of discs or coulters.

James Hopkinson, at Cloud Farming, had been exploring the most effective methods of soil regeneration both independently and as part of the FFBC Soil Regenerative Agriculture Group, the discussion forum facilitated by Mr Reilly between five progressive farmers in the East of Scotland.

He has been using VF tyres for a number of years, and commented: “When sowing a field, up to 85% of the field will be driven on depending on implement width and tyre size. When you consider the whole crop production cycle, from primary cultivation to spraying to harvest many parts of the field can be driven on several times.

"Using flexible tyres alongside our reduced tillage regime has improved water and root movement within the soil and the pore space is much better within the soil profile.”

Alongside the benefits observed at Cloud Farming, improved soil structure can also have an environmental benefit. Soil microbes can cause nitrous oxide emissions, a potent greenhouse gas, when they are exposed to anaerobic environments.

Mr Reilly explained: “The process of denitrification is a complex one with several stages. When soil microbes respire without oxygen several gases can be emitted, and soil compaction can cause this.

"Soils with a high water filled pore space can emit N2, which is not harmful. However, soils with between 40% to 100% water filled pore space can emit N20, a greenhouse gas with a global warming potential approximately 300 times that of carbon dioxide.”

Mr Reilly concluded: "Looking after your soils is, therefore, important from a productive and environmental benefit, and small changes to processes, such as changing tyre pressure, can mitigate long term damage and losses."