Pictures of the fractions of carbon from rapidly decomposable raw pieces of plants and micro-organisms scanned using electronic microscopy.

Fractions of carbon from rapidly decomposable raw pieces of plants and micro-organisms scanned using electronic microscopy.

Why Soil Organic Matter matters

Soil organic matter contributes to a variety of biological, chemical and physical properties of soil and is essential for good soil health.

  • 21 November 2008 | Updated 14 October 2011

Soil health is important to optimise productivity in agricultural systems.

Healthy, productive soil is a mixture of water, air, minerals and organic matter.

In turn, soil organic matter is composed of plant and animal matter in different stages of decay, making it a complex and varied mix of materials.

Functions of soil organic matter

Soil organic matter (SOM) is a key indicator of soil health because it plays a role in a number of key functions. These functions can be divided into three types:

  • biological functions of SOM
    • provides nutrients and habitat for organisms living in the soil
    • provides energy for biological processes
    • contributes to soil resilience (the ability of soil to return to its initial state after a disturbance, for example after tillage).
  • chemical functions of SOM
    • measure of nutrient retention capacity
    • provides resilience against pH change
    • main store of many key nutrients especially nitrogen and potassium.

      Soil organic matter
      is a key indicator of soil health because it plays a role in a number of key
      functions.

  • physical functions of SOM
    • binds soil particles into aggregates improving soil structural stability
    • enhances water holding capacity of soil
    • moderates changes in soil temperature.

There are often strong interactions between these different functions. For example, the biological function of providing energy that drives microbial activity also results in improved structural stability and creates organic materials that can contribute to nutritional capacity and resilience to change.

Optimising the benefits of soil organic matter

Managing soil organic matter for a maximum contribution to soil health and resilience can present a conundrum.

Decomposition and mineralisation of organic matter are required for functions such as provision of energy and nutrients. However, the maintenance or increases in organic matter help to maintain its positive effects on soil chemical and physical properties.

So, when managing soil organic matter the never-ending turnover and the need to replace and rebuild is a constant demand of good agricultural practice.

When selecting management scenarios to optimise the benefits of soil organic matter the following needs to be considered for each particular site:

  • what are the most important functions that organic matter provides?
  • how big is the contribution of organic matter to soil health and resilience?

Management actions that optimise the provision of these functions and maintain the contribution to soil health and resilience will ensure maximum benefit from soil organic matter.

Read more about Factors which influence soil carbon levels.