Autumn 2023

Focus on soil organic matter

So you’ve got your soil organic matter (SOM) results back. But what do those results mean, and what value are they?
We have gathered six key things you need to know about organic matter.

  • What is organic matter?
    Organic matter is plant and animal residues at various stages of decomposition. About 58% of organic matter consists of organic carbon. Soil biology breaks down residues in the soil to form humus.
  • The importance of organic matter
    Without organic matter, soil simply can’t thrive. It plays a multi-faceted role by enhancing the soil’s physical, chemical and biological properties. Practically speaking, this means benefits such as enhanced aggregation, improved water-holding capacity, optimised nutrient cycling and the provision of food for living organisms in the soil.
  • What is a good result?
    Due to its nature, having been living or once-living material, SOM is highly variable – the average amount in UK agricultural soils ranges between 1 and 7%. The optimum organic matter is highly dependent on soil type. We expect organic matter to be higher in clay soils than in sandy soils. This is because clay particles’ binding capacity makes degradation more challenging.
  • Is it a good indicator of soil health?
    Soil is a complex ecosystem, so one parameter alone won’t tell you how healthy your soil is. By definition, soil health is a balance between soil physical, chemical and biological characteristics. Therefore using other measurements such as pH, micro nutrition and digging to look at soil structure is vital.
  • How can I improve soil organic matter?
    There’s no quick fix; building SOM levels is a long-term commitment. However, following the philosophy of ‘replacing what you remove’ is a good starting point. Whether that’s applying organic manures, incorporating crop residues or adding cover crops into the rotation.
  • When should I retest my organic matter?
    Organic matter takes a long time to change, so there is little value in testing for it every year. Typically, it is recommended that you test for soil organic matter once every 3-5 years.

To learn more about organic matter testing, please get in touch with your local agronomist.

You can find out more about organic matter in our latest article in CPM Magazine