Soils are not just the ground we walk on or a medium to plant into – they are dynamic, living energy systems with a host of inputs and outputs.

“If we think of soil as an energy system, with inputs, outputs, storage, and losses, we can redesign farming systems that recharge rather than deplete our soils,” explains independent soil consultant David Purdy.

“Think of the Earth as a huge chemical battery. The sun provides energy, and photosynthesis is the trickle charger, turning sunlight, carbon dioxide (CO2), and water into sugars,” says David.

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At the centre of this system is carbon, which is captured through photosynthesis. This carbon is stored, released, or lost through our soils.

The flow of carbon and energy starts with CO2 entering plants which is converted into sugars. These sugars move through the plant’s shoot and root systems and are released into the soil as root exudates.

“Farmers and growers are on a journey powered by photosynthesis.

Sugars are not just plant food – they are energy-rich compounds that feed soil life, store carbon, and perform vital functions like nutrient cycling and water retention,” says David.

“Ideally, we want to create agricultural systems that leave more carbon behind in the soil than they lose.

“But so far, our management systems have largely failed to do this, often increasing the loss of soil organic carbon. We’ve mined the soil for its carbon reserves instead of replenishing it,” he says.

The electrical analogy

To understand this dynamic, think of soil and cropping as an electrical system:

• Plants act as solar panels, capturing sunlight and converting it to energy
• Soil is the battery itself
• Stable carbon forms the compartments of the battery
• Biological activity (like microbial and root processes) is the charge level of the battery
• Soil oxidation and human disturbance such as cultivations and tillage are the battery discharging.

The more stable carbon in the soil, the more energy in the form of nutrients, water, and biological function the system can store.

Heavier soils with higher clay content can store more energy than sandy, lighter soils.

However, regardless of soil type, it is possible to influence the number of compartments and rate of discharge of the soil “battery”.

This can be achieved by promoting practices that build carbon and minimise losses.

Capturing energy and protecting soil

Cover crops and reduced tillage are two key practices that build soil health. “While species selection and tillage method are important, the single most influential factor for cover crop success is planting date,” says David.

Cover crops play a vital role in capturing solar energy, especially in off-seasons when cash crops are not growing.

Drill date is the single most influential factor for cover crop success © GNP

They maintain living roots in the soil, enhance biological activity, increase stable carbon, and reduce soil discharge as a result of reduced tillage which in turn reduces oxidation.

However, cover crop effectiveness depends heavily on the timing of establishment and termination.

“Aim to establish cover crops as early as possible and destroy them early around January or February.

“A study carried out at Agrovista’s flagship trial site: project Lamport revealed a difference of up to 300kg/ha/day greater biomass when comparing cover crops established in early to mid-August, rather than mid-September,” he says.

Living roots and post-cultivation recovery

Disturbing soil through cultivation disrupts its structure and biology.

Too much mechanical energy in  – such as intensive tillage – leads to biological energy out, which depletes the system’s structure and resilience.

To mitigate this, David recommends introducing living roots as soon as possible after cultivation.

© Tim Scrivener

“If you perform a tillage event, which destabilises soil, it must be followed with living roots to re-build soil structure, aggregation and biological activity. A living plant protects the soil. Do not leave soil bare,” he says.

“As CO2 leaves the system, the tiny pores underneath plant leaves, known as stomata can recapture some of this carbon, reducing losses,” he says.

Soil Structure and bulk density

Soil structure is essential for supporting both plant performance and carbon storage. Bulk density – the mass of soil per volume – determines porosity, affects root growth and microbial habitats.

Heavy soils naturally compact more than light ones, but poor management increases this compaction, limiting function.

Cover crops have been shown to reduce bulk density, particularly at 15-30cm depth, improving water infiltration and biological activity.

Redox is a vital part of soil chemistry © Tim Scrivener

Optimum bulk density is about 1.3g/cu cm, which provides 50% porosity for water and air. “Pores are the hotspots for microbial activity,” says David.

“Tillage creates large soil pores, but it’s the biology: worms, roots and fungi that create a diverse range of pore sizes that improve overall soil function.”

By viewing soils as living energy systems – with solar-powered inputs, microbial storage, with carbon at the centre, cropping can be managed more strategically.

Practices such as timely cover cropping, reducing tillage, maintaining living roots, and understanding redox processes (see “The importance of redox and soil chemistry”) can offer opportunities to rebuild soil function.