How to improve livestock soils with biological approach

Soil is a precious resource, but it very quickly becomes a pollutant and a problem once it reaches watercourses. It has to be kept on the farm.

This is the message of plant and soil health educator Joel Williams, who says whatever the exact figures, statements such as “one-third of the world’s soil is degraded” and “24 billion tonnes of soils are lost each year” are alarming (see “Types of soil degradation”).

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“If we’re not keeping the soil where it is, we can forget about other conversations. It’s fundamental,” he says.

To start the process of improving soil health, Joel suggests thinking of soil as being like a three-legged stool.

One leg of the stool represents soil chemistry, another, soil physics, and the third, soil biology. If one leg is wonky, the stool – or the soil – is unstable.

“If you’re not intentionally working to improve these three components, then, like the wonky stool, you won’t have resilience,” he says.

Power of plants

The very fact of growing plants can change soil chemistry, physics and biology, he adds. Plants not only take in carbon dioxide but excrete it into soil through root exudates (compounds released from living plant roots).

Many root exudates are sticky, so they help soil aggregation by gluing soil particles together.

In addition, these exudates are highly digestible forms of carbon for micro-organisms. They also include a lot of organic acids, which solubilise nutrients.

So optimising root production and root exudates feeds soil biology.

A further benefit is that as plant roots are growing, some of the soil bacteria move into the root cells and grow there. Plants can then extract the nutrients from these bacteria (the rhizophagy cycle).

Most soil biology cannot get sustenance from air – it needs plants, composts and manures to feed it, says Joel.

The period when plants are in their most vegetative stage of growth, until they are about to switch to their reproductive stage (the first four to eight weeks of the growing season), is when most root exudates are produced.

After this, plants slow down or switch off root exudate production.

However, where the vegetative stage is restarted through grazing, root exudate production remains switched on, he adds.

Recovery periods

It is important to build in sufficient plant recovery times after grazing or cutting, particularly with diverse swards, to maximise photosynthesis and root exudate processes, so energy and reserves can be sent to root systems.

Joel advises that a sward is ready for regrazing once the plants have regrown and are about to move into the reproductive stage.

“I know this is hard, especially in dairy systems, and you may have to use reseeding and varieties better suited to multispecies swards. [Plant] breeding goals reoriented towards persistence would help, but this will take time,” he says.

Plant defences

Plants employ physical defences, such as producing a thicker “skin”, to make it harder for pests and pathogens to penetrate. They also marshal biochemical defences.

These result in altered root microbiome activity, which antagonises pathogens.

However, when plants are deficient in nutrients, they are undermined and cannot produce physical or biochemical defences. This is because macro- and micronutrients are needed to support photosynthesis.

“It all starts with priming photosynthesis, which then drives benefits below ground,” says Joel.

Integrated approach

To improve soil health by transitioning from a chemical approach to a biological one, he advises using integrated nutrient management.

This brings together as many tools as possible to manage fertility to reduce dependency on artificial inputs.

Integrated nutrient management involves a combination of the following:

• Strategic fertiliser use
• Organic inputs (composts, manures)
• Biostimulants
• Cover crops
• Companion crops/intercropping
• Crop residues
• Biofertilisers/microbial inoculants
• Integration of livestock and grazing.

“Be mindful of being overly focused on productivity,” he says. “You can also be more profitable by reducing inputs and saving on costs. There are lots of opportunities to be more efficient.

“Even simple changes are very effective. For example, undersowing maize with grass, or any kind of cover, is fantastic compared with not undersowing.”

Signs of improvement

Joel suggests farmers can expect to see functional changes in degraded soil in three to five years.

However, some signs and metrics can be visible very quickly. For example, soils growing diverse cover crops, even in the first few weeks and even if the field is heavily tilled, will show signs of aggregation.

“That shows you’re going in the right direction, driving repair and recovery,” he says.

Joel Williams was speaking at a recent AHDB workshop, Soil Secrets with Joel Williams, in Herefordshire.

Further resources and online courses: integratedsoils.com and ahdb.org.uk/greatsoils