Soil nutrients and fertility

Soil fertility is about how well your soil supplies nutrients for healthy plant growth.

When the levels of nutrients in soil are right, the soil:

• stores more carbon
• holds more water
• feeds your plants naturally.

Soil nutrition is linked to soil carbon and organic matter. 

1. Through photosynthesis, plants provide energy-rich organic compounds into the soil as energy for the soil ecosystem.
2. The soil ecosystem in turn drives the cycling of organic and inorganic matter (carbon and nutrients) in the ground.
3. It mineralises organic materials, it converts minerals into plant usable forms and it structures the soil particles so that water, air and roots can get down deep.
4. This feeds microbes, which recycle nutrients and build soil structure.

The cycle is simple:

Plants grow → feed soil life, which builds structure → stores carbon and nutrients for more healthy soil → stronger, more resilient plants.

Nutrient needs vary with soil type, rainfall and enterprise so it is important to always test your soil and get local advice before changing your program.

The role of plants

Plants are the engine of soil health. Deep roots and diverse species:

• feed soil biology
• improve structure and water infiltration
• build organic matter and carbon.

Keeping groundcover and green growth year-round keeps your soil life active. That’s how you build lasting fertility — not just short-term gains.

The role of legumes

Legumes (like clovers and medics) fix nitrogen from the air through their roots. They work best in a mixed, perennial pasture.

Too much clover can cause bare patches, acidity and even animal health problems.

Aim for balance with enough legumes to supply nitrogen without taking over.

Healthy soil biology also supports free-living nitrogen-fixing bacteria, which thrive when there is plenty of root activity.

Nitrogen - the fuel for growth

Nitrogen drives growth, but too much synthetic nitrogen can backfire.
Heavy use can “burn through” soil carbon, leaving your soil hungrier over time.

Good nitrogen management includes:

• growing legumes to add nitrogen naturally
• keeping living roots in the ground
• avoiding overuse of fertiliser
• using organic matter or composts where practical.

A balanced approach builds soil carbon and long-term fertility.

Phosphorus and potassium

Most Australian soils are low in phosphorus, which plants need for strong root growth. Before adding fertiliser, do a soil test and it is important to only apply what’s needed. 

• Phosphorus should match your soil type, rainfall and production goals.
• Potassium is usually fine unless you’re cutting hay or silage, which removes nutrients.

Using fertiliser wisely

Fertiliser is a tool, not a fix. It can support productivity and soil carbon if used strategically. Avoid sudden changes to fertiliser programs as soils need time to adjust.

Tips:

• base your program on soil test results.
• match fertiliser rates to your goals and rainfall.
• reassess every few years.
• combine with good grazing and plant diversity.

Making and transporting fertiliser produces carbon emissions. Using 50 kg of superphosphate creates around 14.5 kg of CO₂. Using it efficiently saves money and helps the climate.

Building soil carbon

The best way to build soil carbon is through living, healthy plants.

Grazing management that allows recovery, green cover and root growth feeds the soil life that stores carbon. Fertiliser can help, but plants do most of the work.