Soil biology

Beneath every paddock is a bustling community of organisms, from microscopic bacteria to earthworms, all working together to build structure, recycle nutrients, and support plant growth.

Key points:

• Soil biology drives nutrient cycling and supports plant growth.
• A diverse soil ecosystem makes your soil more resilient to drought and stress.
• Disturbance, chemicals and bare soil reduce biological activity.
• You can support soil life by minimising tillage, maintaining groundcover and adding organic matter.

What lives in soil?

A single teaspoon of healthy soil can contain over a billion living organisms. Together, these creatures form what’s called the soil food web, a complex network that drives nutrient cycling and builds soil health.

How soil biology works

Soil organisms depend on plants for energy. Through photosynthesis, plants send carbon-rich sugars into the soil via their roots. This feeds microbes, which in turn release nutrients, build organic matter, and improve structure.

As larger organisms like protozoa, nematodes, and arthropods feed on smaller ones, nutrients are cycled and made available to plants. This natural recycling process is what keeps soil fertile without relying solely on inputs.

Good biology means:

• More nutrient cycling
• Better soil aggregation and structure
• Higher water-holding capacity
• Stronger, deeper roots
• Improved resilience to drought and erosion

Most soil life is concentrated near plant roots in the rhizosphere. This is where roots, microbes, and fungi interact most intensely.

Roots exude sugars, enzymes, and organic compounds that attract microbes. In turn, microbes:

• unlock nutrients like nitrogen and phosphorus
• improve root growth and health
• help plants resist disease
• influence soil pH and structure.

Healthy root systems equal healthy soil biology. Anything that encourages strong, diverse root growth boosts life in the rhizosphere.

Managing soil biology

Soil biology responds quickly to management — for better or worse. You can enhance it by working with natural processes.

Do more of:

• Testing your soil to identify limiting factors.
• Keep living roots in the ground year-round. Perennials, cover crops, and diverse pastures feed soil life continuously.
• Maintain 100% groundcover. This keeps soil cool, reduces evaporation, and buffers temperature swings.
• Increase plant diversity. Different species support different microbes, boosting resilience.
• Add organic matter. Compost, manure, or green manure crops feed microbes and improve structure.
• Graze with purpose. Short, high-density grazing followed by long recovery promotes strong root systems and microbial “pulses” of activity.
• Minimise soil disturbance. Excessive tillage breaks up fungal networks, depletes carbon, and harms structure.
• Use fertiliser only when guided by soil tests and in balance with biological management.
• Rotate species to build diversity and break pest cycles.

Do less of:

• Overusing of chemicals. Many herbicides and pesticides disrupt microbial communities and slow down soil processes.
• Limiting heavy fertiliser use. Relying on high rates of inorganic fertiliser can make soil biology “lazy.” When plants get nutrients directly from fertiliser, they reduce root exudates — starving the microbes that normally feed them.

Does fertiliser help or harm soil biology?

It depends on how it’s used.

In some cases, balanced fertiliser use can actually stimulate soil biology, especially if it corrects a limiting factor like pH or nutrient deficiency. For example, trials have shown that lime or moderate fertiliser applications can increase microbial carbon, water infiltration, and organic carbon.

However, overuse of inorganic fertilisers reduces the need for plants to interact with microbes, weakening biological networks over time. The key is to balance chemical inputs with practices that feed soil life including organic matter, good groundcover, and diverse root systems.