Dig a hole, study the soil and help to lock away more greenhouse gas

ADOPTING the latest technologies and sustainable land use practices could allow soil to play a key role in locking away huge quantities of greenhouse gases. Plants, through the process of photosynthesis, have the ability to extract carbon from the air and feed it to the soil through their roots.

A team of scientists from the universities of Edinburgh and Aberdeen have produced a study which suggests land could store an extra eight billion tonnes of emissions globally, helping to limit the impact of climate change.

Developing such farming systems will also improve returns. Soil structure describes the way sand, silt, clay and carbon particles are clumped together to form aggregates of varying size. Soils with good structure are friable (crumbly) so the soil breaks up evenly when squeezed.

Carbon derived from decaying plants and animals, plus secretions from soil organisms like earthworms and bacteria, is the ‘glue’ that binds soil particles together to form aggregates. The right blend of large and small aggregates creates pore spaces important for plant growth. Pore spaces regulate the movement and storage of air and water for the living organisms in the soil which influence root development and affect nutrient availability.

Soils with low carbon content are more prone to compaction and erosion because the glue in the form of carbon that forms aggregates and allows pore spaces between them is absent. This can lead to poor water infiltration (influencing plant water availability and susceptibility to erosion) and low oxygen availability.

Soils are alive, and there are more living organisms in a teaspoonful of soil than there are people on the planet. As with all living things, soils can become unwell, and even die, if they are not cared for properly.

Biota describes all the animal and plant life in the soil. A diverse biota is required to maximise soil health and crop potential, reduce reliance on artificial inputs and achieve better disease resistance in crops. In an arable rotation, reduced cultivation techniques can be a good practice to help maintain soil organic matter, especially in the soil surface tilth.

The best tool to help understand the condition of the soil on a farm is a spade. Whilst soil type and its key characteristics do not change, the soil structure will vary across the farm from year to year depending on things such as crop rotation, machinery use, livestock density and the weather. The best way to understand the structure is to dig holes across the farm and take a look. This approach also gives a feel for the organic matter content and begins to identify any compaction.

Compaction describes when soil has been compressed by, for example, machinery or livestock into a solid impermeable layer, either at the surface or within the topsoil. Root development can be restricted, which affects yield and plant health, and reduces drought resistance and crop nutrient response.

All farmers should make pedology – the scientific study of soils – their particular care. Fertile soils contain adequate supplies of plant nutrients such as nitrates, phosphates, potash and sulphates as well as trace elements like manganese, copper, cobalt and selenium. Above all else, a fertile soil will be free draining – cultivated crops in our climate can be grown only on land that has been drained of excess water.

Good, fertile soils are formed by the sediments deposited by flooding rivers in low-lying areas – so drainage is essential if crops are to benefit from the fertility that has accumulated over the years. Lime is also very important in maintaining fertility.

According to QMS Head of Industry Development, Douglas Bell, much of Scotland’s permanent pasture is suffering from a lack of lime, with only three per cent of managed grass in Scotland given lime every year. “We’ve fallen behind England and Wales because our soils are pretty acidic. We should be putting more lime on our soils,” said Mr Bell.

Agronomist Steve Townsend from Soil First Farming says livestock producers needed to follow in the footsteps of their arable neighbours and manage their soils better. Grassland was suffering as a result of too much artificial nitrogen being applied, poaching (trampling), poor drainage and short-grass grazing.

Mr Townsend says building up reserves of carbon in the soil is key to improving grassland and this could be achieved by growing a bigger root mass and introducing a grazing strategy where livestock intensively graze for short intervals on a rotation.