Carbon is on the agenda, be it in the air or in the soil and quite rightly agriculture is highlighting the potential for soil to be one of the major sinks for atmospheric carbon. Along with this will come the possibility of carbon payments for locking up carbon in the soil.

It is well recognised that over the last 60 or 70 years, UK soils have lost a lot of organic matter and therefore carbon, carbon makes up 58% of the soil organic matter. It is likely that within the next five years schemes will be introduced to pay farmers for locking up carbon, so it’s important to know where your soils are starting from.

Recent changes in the way that laboratories measure soil organic matter has highlighted a problem for soils with either a high clay content or a high chalk level / high pH. Until recently the preferred method was Loss on Ignition (LOI) where a soil is heated to high temperatures burning off the carbon. Unfortunately, the presence of a high clay content that holds onto water at normal temperatures and the presence of calcium carbonates which when heated release carbon means that some measurements of organic matter may be overstated by up to 25%. The new test Soil Organic Matter by Dumas treats the sample prior to heating and measures the differing oxides given off when burnt and then converts this figure to soil organic matter.

If you are going to try and monitor soil organic matter over a period of years, then there are few key things to remember:
1. Make sure you chose a method that will give the most reliable results for your soils.
2. Always use the same laboratory to carry out the tests.
3. Carry out the soil tests at the same time of year and ideally at the same point in the rotation.

If you would like to discuss monitoring your soils, please contact William at w.waterfield@fcgagric.com or your local FCG Office.