How much carbon is in your soil?

There is currently significant attention focused on the potential to increase soil carbon stores for mitigating and offsetting greenhouse gas emissions. However, there are still many uncertainties in relation to the quantity of carbon that can be stored in UK soils, implications for other nutrient cycles and the permanence of soil carbon over time. What is perhaps less uncertain is the positive contribution soil organic matter (SOM) can have to a soil’s health and function, which can subsequently benefit wider ecosystem services.  Approximately 58% of SOM is carbon, with the remainder comprising other key nutrients (E.g. N, P, K, Ca etc), which is derived from the breakdown of leaf litter, crop residues, plant material, dead roots and animal wastes.

At any moment in time, soils comprise a mixture of SOM deposited and incorporated at different timescales and are at different stages of decomposition. This leads to a complex mixture of organic material that provides a wide range of functions, such as providing nutrients, aiding soil aggregation, water holding capacity, buffering pollutants and carbon storage.  There are therefore many advantages to conserving and/or increasing SOM through land management practices that promote good soil health.

There are a range of management practices recommended for improving soil health and many of these also contribute to SOM and soil carbon conservation and/or accumulation.  For example, a key practice is to maintain soil cover where roots help bind the soil (preventing physical loss through erosion) and the root and residue material provides organic matter to the soil system. In addition, optimising grazing and tillage management to reduce compaction and disturbance but maximises manure and residue incorporation to the soil.  To determine whether your soil is losing or gaining SOM and carbon, it is important to participate in soil testing to be able to monitor changes over time.

Dr Sarah Buckingham, Senior Environmental Consultant, SAC Consulting.

This article was first published in Jan/Feb 2024 edition of the the Farming Scotland Magazine.




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