Scottish soils are a valuable store of carbon, particularly the peat soils of the uplands and islands.
In Scotland, more than 60x more carbon is stored in our soils than vegetation and between them, these carbon stores hold about 125x the total amount of CO2 emitted each year in Scotland. It is essential that we protect soil carbon reserves and play our part in meeting Scotland’s greenhouse gas (GHG) reduction targets .
Soil carbon can be lost in a variety of ways including :
- Ploughing and other cultivations expose soil organic matter to oxygen – this breaks the soil carbon down to carbon dioxide – a greenhouse gas.
- Water-logging of plant material can cause it to rot in the absence of air causing the release of methane, another powerful greenhouse gas.
- Higher overall temperatures speed up the various soil carbon breakdown processes.
Soil carbon increases when the soil organic matter (SOM) accumulates faster than it is being lost. And SOM is one of the keys to soil health and fertility and is worth to boost the soils’ productive capacity and crop yields.
Soil management for carbon, therefore, matters to all farmers, whether organic or conventional
Managing Soils to boost Soil Carbon
- Reduced tillage drastically cuts down on soil carbon losses. It won’t work for every farm in every year. Note it can also reduce on-farm fuel use, cutting costs.
- Minimising soil erosion keeps soil in the field.
- Incorporating crop residues after harvest returns much of their carbon to the soil. This boosts soil fertility directly through the residue’s nutrients as well as providing better water holding capacity and boosting activity of soil biota.
- Where straw is required for bedding, returning it later as manure helps to maintain SOM.
- Growing cover crops, particularly legumes, on otherwise bare ground can benefit soil carbon as well as perhaps “soaking up” excess nutrients
- Good irrigation practice helps avoid waterlogging and boosts SOM.
- Nutrient management using long-term manure applications boosts soil carbon whilst making good use of resources
- Crop rotations with a variety of plant families helps SOM through a variation in rooting depths and styles from year to year. In particular, including grass in the rotation is helpful.
- Improving grazed pasture through drainage, soil aeration, compaction reduction and improved diversity of forage species can all help SOM.
- Afforesting highly degraded or marginal soils will significantly improve carbon sequestration compared to sub-optimal grazing or arable use of those soils.
The hidden carbon in the manufacture, transport and application of pesticides and fertilisers and the employment of tillage and irrigation must be taken into account when determining the case for land use change.
Carbon Storage is Long term
Accumulating carbon in the soil is a long-term process. The life-time of stable soil organic matter is 250-1900 years but it can be lost in a moment, for instance through erosion.
To speed up sequestration either :
- INCREASE the rate at which you apply organic matter particularly from off-farm (e.g. composts) or
- DECREASE the rate of oxidation of soil carbon and decomposition of soil organic matter, for instance by using reduced tillage systems
Soil Quality Improvement
In a trial comparing soils that had a diverse rotation including grass, or had significant manure additions or were in continuous wheat, after five years the soils in diverse rotation and the manure-amended soils had :
- increased levels of organic matter
- more fungal activity
- better porosity
- greater compaction resistance
Higher soil carbon and better soil structure will be critical for soils to be able to cope with increased climate variability with, for instance better drainage and drought resistance.
Top tips for EVERY farm
- Keep off wet soils – working wet soils causes compaction and reduces yields.
- Dig to assess soil structures – structure will change over time.
- Soil test regularly – particularly for pH and P.
- Maintain soil organic matter.
- Take steps to prevent erosion.
- Irrigate to the crop’s requirements and not more.
- Maintain field drains. )