Soil Organic Carbon Is The Carbon That Is Stored in Soil. It’s Important For Gardeners & A Vital Part of Soil Organic Matter, It’s That Simple. This Article Explains Soil Carbon’s Importance.

The roots on this rocket plant are extensive and can contribute to soil carbon retention when the plant dies
The roots on this rocket plant are extensive and can contribute to soil carbon retention when the plant dies

Global warming is intrinsically tied up with atmospheric carbon but part of the answer lies in the soil, and could become part of the soil. Soil Organic Carbon is part of that answer and gardeners can influence it.

When a plant photosynthesises it uses the carbon dioxide from the air, soil elements plus energy from sunlight to produce organic matter. That organic matter is the leaves, stems, branches, fruit and roots produced as part of plant growth.

When plants are harvested the carbon is also harvested and is consumed. Some waste also falls to the floor as autumn leaves or falling petals. And some remain in the roots.

The autumn leaves can be pulled into the soil by worms and become part of the soil carbon. Roots left after harvest, or when the plant dies, also become soil carbon.

Much of this soil carbon can be locked into place for hundreds of years. Sometimes thousands of years or even longer. But every time we disturb the soil carbon is released. Ploughing releases vast quantities of carbon each year. So does digging. that’s one reason I like No Dig. It retains soil carbon.

 Soil as Carbon Reservoir

Soil is one of the biggest carbon reservoirs we have. It can contain much more carbon than it currently stores. But sadly, over recent centuries we have allowed soil carbon levels to drop. We’ve destroyed jungles, ravaged peat reserves and constantly ploughed land. Each of these actions release carbon into the atmosphere. That has increased carbon dioxide levels in the atmosphere and contribute to global warming.

The good news is we can increase soil carbon levels. We can all contribute to this. And the second piece of good news is that if we do so our soils become healthier and more productive. Our gardens, allotments and farms will be able to be more productive. And in a time of food insecurity that is essential.

It should be noted that though in this article I deal with carbon in soil organic matter, carbon can also exist as mineralised carbon. Coal is an extreme example of mineralised soil carbon but there are others

Does Soil Organic Carbon Remain In the Soil Forever?

Forever, no. But it can be locked away for millennia if conditions are right.

Once carbon returns to the soil an equilibrium is largely established.  The carbon will stay there until something prompts it to leave. Things like ploughing, rotovating or digging.

It is however true to say that something like 50% of soil carbon is retained short term and will dissipate in 10-20 years. It is replaced though so not a total loss. The other 50% will last for millennia.

BUT, though some is short term the overall quantity can increase over many years.

How Much CO2 could Soils Store?

Exact figures are impossible to give. But we know the figure is huge. We are talking about millions of tons of carbon across the UK. That alone is not going to solve global warming but is a very useful contribution to it. So, in the Dig for Victory ethos, perhaps we should say No Dig for Victory!

Soil Carbon Storage Potential

If you have read my soil articles you’ll know not all soils are equal. And they all have different soil carbon potential. Clay soils have the potential to hold much bigger volumes of carbon than sandy soils. That’s partly because clay soils have a bigger surface area on which carbon can be “adsorbed” (fixed). And of course organic matter levels affect carbon holding potential. The more organic matter the more carbon.

Roots penetrate the soil and sequester organic soil carbon when they die
Roots, such as this mooli, penetrate the soil and sequester organic soil carbon when they die

Rainfall also has an impact as does temperature. Frozen permafrost can’t grab as much carbon as warmer soils (though it contains vast amounts of carbon). And temperature impacts plant growth so has more potential but organic matter breaks down faster in warm soil.

In essence it’s complicated. But to simplify it the more plants we grow and the more we reduce soil cultivation by ploughing etc the more we can raise soil carbon levels.

Interestingly, research shows that carbon levels under hedges have higher carbon levels. That confirms the fact that soils that aren’t cultivated intensively have increased soil carbon.

More research is needed on soil carbon but it is clear that as gardeners we can have a positive impact of soil carbon.

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