Organic matter (OM) is a key component of healthy soil, but it often sparks debate between proponents of synthetic fertilisers and those who follow organic or biological farming principles. In truth, OM plays a vital role in soil health, though its exact functions and composition are still being researched.

What is Organic Matter?

Organic matter includes all organic materials in the soil, from fresh plant residues, straw, and manures to older, well-decomposed material. While often confused with humus, OM is a broader category.

What is Humus?

Humus is the stable, long-lasting component of organic matter. It is formed after plant and animal residues have been thoroughly broken down by soil microbes. Humus improves soil structure and helps retain moisture and nutrients.

Why Organic Matter Matters

Organic matter contributes to:

• Soil structure and stability

• Water retention

• Nutrient retention, especially nitrogen (N), phosphorus (P), potassium (K), and sulphur (S)

• Soil colour and texture

• Microbial activity that supports nutrient cycling

The Role of Soil Microorganisms

Microorganisms are essential to organic matter decomposition. A single handful of soil can contain more microbes than there are people who have ever lived. These organisms feed on organic compounds, breaking them down and releasing nutrients that plants can use.

The rate at which organic matter breaks down depends on:

• Soil pH (most microbes slow down in more acidic soils)

• Moisture levels

• Temperature

• Soil texture

In very acidic or waterlogged soils (like peat), decomposition is slower. This leads to a build-up of organic material but also creates challenges with nutrient availability.

The Takeaway

You do not need to subscribe to a particular farming philosophy to appreciate the importance of organic matter. Whether you are improving pasture, growing vegetables, or managing a small block, understanding and supporting the organic component of your soil will pay off in plant health and long-term productivity.

If you’d like to learn more about improving your soil and making the most of fertiliser use, our Soil & Fertiliser ebook covers the essentials in practical detail.