Before any changes are made to increase soil organic matter (SOM) or soil organic carbon (SOC), it is crucial to know how much you have in the soil to start with
Using laboratory analysis gives a concise numerical percentage, yet should be combined with observations of soil characteristics to fully understand soil health.
If using laboratory analysis, it is important to understand how to correctly take the sample. Terrafarmer offers a detailed sampling service that can assess the organic matter at varying depths and give a geospatial reference to each sample location.
We also provides crucial after-sampling support so you’re not left in doubt about what to do next.
The amount of organic matter that any soil can store is limited by two key factors.
Soil texture
Soils with a higher clay content will store more SOM as clay (with its largely negative charge) can form bonds with SOM (largely positive charged) and form a protective barrier around it to prevent further degradation. The sandier the soil, the lesser the bonding potential and the more air can infiltrate, which increases the rate of SOM decomposition.
Some target organic matter levels based on soil type are listed in the table below. Bear in mind that tillage and cropping practice will also have a significant effect, with reduced-tillage settings and pastures able to achieve the higher end of the range. It is also possible to go beyond the target levels (to a point) in some instances, the ranges below are merely a guide.
| Soil type | Approximate SOM range |
|---|---|
| Light/Sandy | 2-4% |
| Mineral/Medium-textured | 4-5% |
| Heavier/Clay-rich | 5-10% |
| Peat Soils | >20% |
Climate and topography
The higher the climate temperature, the faster the soil processes work to decompose organic material. This results in an increased rate of losses back to the atmosphere. Higher temperatures also typically promote longer periods of drought and lower soil moisture levels which limit the amount of plant growth, so less organic material is available to be cycled into SOM.
Conversely, in areas of high rainfall (such as the west of the UK), higher SOM levels are frequently observed. These areas tend to have high soil moisture levels, and if not drained freely or they are low-lying, can even fall waterlogged for long periods of time. This greatly reduces the amount of oxygen within the soil, which reduces the rate of SOM lost by oxidation. These wetter areas also promote a faster rate of plant growth, increasing the amount of organic material available.
Get in touch
Our soil health assessment services, which can be combined with soil scanning and soil sampling, will give you the knowledge you need to improve your soils. Get in touch to find out more.
