Soil organic matter and soil carbon are currently the centre of attention for several important reasons as repeatedly discussed in this newsletter, but soils have differing potential to store carbon.

An analogy that I like, is to compare your soil with is a cruise liner. Is your soil a mega liner with thousands of passengers – a heavy soil, or a little tourist junk – a light soil. The soil organic matter can be regarded as all the people on board (crew and passengers), the heavier soil able to hold more organic matter, and the soil carbon as the crew on board. Soil carbon is a fixed proportion of the organic matter (58%) whilst the really important members of the crew “the chefs” represent the active carbon in the soil. It is the active carbon that enables nutrient transfer to the plant’s roots.

Obviously, the mega liner has the potential to hold many more passengers and soil organic matters in excess of 10% are not unheard of on heavy clay soils, whilst a little tourist junk holding 100 passengers is like a sandy soil with a capacity of only 3-4% organic matter.

Soil classification can be undertaken as part of a standard soil analysis and only needs doing once.

The Soil Quality Index devised by scientists at Rothamsted and discussed in a previous article, allows the direct comparison of soils between different soil types. Look at Field 1 and 3 which have a similar clay content but differing levels of organic matter rating one as moderate and the other as degraded.

Likewise compare soils 2 and 4 where the same levels of organic matter on different soil types allows one soil, number 4 a lighter soil, to be designated as moderate and number two, a medium heavy soil to be defined as poor.

For more information or a fresh look at assessing your soils, contact William at w.waterfield@fcgagric.com or your local FCG Office.