Tech Tuesday: Organic Matter

Organic matter plays a central role in building healthy, resilient soils by improving structure stability, increasing water-holding capacity (WHC), providing nutrients, and delivering a whole cascade of biological benefits. Yet despite all the buzz around it, organic matter is often talked about without fully explaining why it matters so much.

What Is Organic Matter?
Organic matter is made up of living and previously living materials within the soil. This includes:
• Plant litter and crop residues
• Decomposing organisms
• Developing plant roots
• Added inputs such as manures

The ‘organic’ part means these materials contain carbon, as well as essential nutrients like nitrogen and phosphorus.

Why Is There So Much Fuss About Increasing Organic Matter?
One of its biggest impacts is on soil structure. As organic matter increases, soil aggregates become more stable, which means it can resist compaction better from things like machinery.

This increase in aggregate stability leads to multiple benefits:
• Better water infiltration
• Increased water-holding capacity
• Improved workability
• Reduced surface runoff and erosion

These improvements directly enhance a soil’s ability to withstand dry conditions, as the organic matter can act like a sponge, able to hold onto infiltrated water more easily, making higher organic matter levels a key factor in drought resistance. Adding organic matter to the soil also provides a supply of nutrients, as elements such as nitrogen, potassium, magnesium etc are also present in organic matter.

Organic Matter and Carbon Storage
A major reason organic matter is such a hot topic today is its role in carbon storage. As organic materials are added to soil, carbon is stored within that system rather than being released into the atmosphere.
Organic matter also feeds soil microbes. As these microbes consume it, it can drive higher mineralisation rates for nutrients and, when they die, their remains form what’s known as microbial necromass. This necromass is surprisingly stable and represents a significant longterm carbon store within the soil.

How We Measure Organic Matter
There are two widely used methods for determining organic matter content. Loss on Ignition (LOI) – The most common method is known as Loss on Ignition. In this process, a soil sample is first dried and weighed, then heated to very high temperatures. The heat burns off the organic matter, and the weight loss of the sample is measured. This loss is assumed to represent the amount of organic matter present in the soil. LOI is widely used because it is relatively simple and cost-effective, making it practical for routine soil testing. The Dumas Method – The Dumas method is considered the gold standard for measuring organic matter. In this method, soil is heated in an oxygen-rich environment, causing the carbon in the organic matter to convert into carbon dioxide CO₂. The amount of CO₂ produced is then measured and used to calculate the soil’s carbon content, which is converted into an organic matter value. Because it directly measures carbon, the Dumas method provides highly accurate and consistent results.

Our Approach to Testing
We use external accredited laboratories to analyse our organic matter samples. To ensure our results are compatible across different systems, we use both LOI and Dumas methods. This allows us to confidently compare organic matter percentages regardless of which method is referenced.

Understanding Your Results
Organic matter results are reported as a percentage and typically range between 1–10%, depending on soil type and management history. When you test with a PES Technologies unit, your results are reported back as a percentage and seen on a scale to see where your results sit in the spread of our results. However, it’s important to remember that organic matter is relative to your soil. For example, achieving 4% organic matter on a sandy soil may represent many years of improvement, while the same value on a heavier soil may be more typical.

Management
Methods proven to increase organic matter are often those that reduce cultivation and add biomass to soil, such as no-till practices and cover cropping. However, each field and soil type is different, to interpret and plan management it can be helpful to contact an agronomist. Cultivation generally reduces organic matter levels, so when testing soil, it’s good practice to take a reference sample from an uncultivated area of your field or land. Establishing a baseline and maintaining consistent reference points allows you to track change over time and clearly see how your management decisions are affecting your soil’s organic matter. Understanding where you started is just as important as
knowing where you are now.