Archives May 2020

Key Facts We Should Know About Soil

Soil is the fragile, friable layer of the earth’s crust that covers the continents, between the surface and the bedrock. It is formed by mineral particles, organic matter, water, air and living organisms. It is the interface between earth, air and water and hosts most of the biosphere.

Soil provides us with food, biomass and raw materials, serves as a platform for human activities, our landscape and our heritage and plays a central role as a habitat and gene pool. It stores, filters and transforms substances such as water, nutrients and carbon.

Soil is a key, largely non-renewable and very complex natural resource and yet it is increasingly damaged by certain human practices.

Here are some key facts  about soil

1. Soil makes up the outermost layer of our planet and is formed from rocks and decaying plants and animals.

2. Soil has varying amounts of organic matter (resulting from the decomposition of living organisms), minerals and nutrients.

3. It helps clean the water we drink and the air that we breathe — for free!

4. An average soil sample is 45 % minerals, 25 % water, 25 % air and 5 % organic matter. Different-sized mineral particles, such as sand, silt and clay, give soil its texture.

5. Topsoil is the most productive soil layer.

6. Ten tonnes of topsoil spread evenly over a hectare is only as thick as a one Euro coin.

7. Natural processes can take more than 500 years to form two centimetres of topsoil.

8. In some cases, five tonnes of animal life can live in one hectare of soil.

9. Fungi and bacteria help break down organic matter in the soil.

10. Earthworms digest organic matter, recycle nutrients and make the surface soil richer.

11. Roots loosen the soil, allowing oxygen to penetrate. This benefits animals living in the soil. They also hold soil together and help prevent erosion.

12. A fully functioning soil reduces the risk of floods and protects underground water supplies by neutralising or filtering out potential pollutants and storing as much as 3 750 tonnes of water per hectare.

13. Soil scientists have identified over 10 000 different types of soil in Europe.

14. Soils worldwide contain 1 550 billion tonnes of organic carbon (to be compared with an atmospheric carbon pool of 760 billion tonnes and 560 billion tonnes of carbon in living organisms and plants).

15. Soil captures about 20 % of the world’s manmade carbon dioxide emissions.



Restoring soils could remove up to ‘5.5bn tonnes’ of greenhouse gases every year

Replenishing and protecting the world’s soil carbon stores could help to offset up to 5.5bn tonnes of greenhouse gases every year, a study finds.

This is just under the current annual emissions of the US, the world’s second largest polluter after China. Around 40% of this carbon offsetting potential would come from protecting existing soil carbon stores in the world’s forests, peatlands and wetlands, the authors say. In many parts of the world, such soil-based “natural climate solutions” could come with co-benefits for wildlife, food production and water retention, the lead author tells Carbon Brief.

Ground up

The top metre of the world’s soils contains three times as much carbon as the entire atmosphere, making it a major carbon sink alongside forests and oceans. Soils play a key role in the carbon cycle by soaking up carbon from dead plant matter. Plants absorb CO2 from the atmosphere through photosynthesis and this is passed to the ground when dead roots and leaves decompose. But human activity, in particular agriculture, can cause carbon to be released from the soil at a faster rate than it is replaced. Few countries record data on soil-carbon loss directly from agriculture, according to the Intergovernmental Panel on Climate Change’s most recent assessment report, making it difficult to understand the degree to which soil carbon losses are contributing to climate change. The new analysis, published in Nature Sustainability, takes a look at how protecting and replenishing soils – both in agricultural and natural landscapes – could instead help to combat warming. If finds that, if techniques to improve soil carbon were rolled out at the maximum assumed level worldwide, they could remove up to 5.5bn tonnes of CO2e a year.

Counting carbon

For the analysis, the authors built on an earlier study which looked at the global greenhouse gas removal potential of all “natural climate solutions”. The term is used to describe a range of negative emissions techniques that aim to enhance the ability of natural ecosystems to remove CO2 from the atmosphere. The research finds that a quarter of all the greenhouse gas removal ability of natural climate solutions comes from soil-based techniques, such as protecting and restoring forest soils, peatlands and wetlands.

The chart below shows the greenhouse gas removal potential of various soil-based natural climate solutions. The figures are shown in billion tonnes of CO2e per year.

The research shows that the largest greenhouse gas removal potential comes from protecting existing forests and reforestation. This technique could offset 1.2bn tonnes of CO2e a year, when only forest soil carbon is considered.

Forests soils are a globally important carbon store. They can be particularly carbon-rich because they absorb high densities of dead plant matter. Forest soils also play a significant role in absorbing methane. Another soil technique with large potential is “biochar”, according to the research. Biochar is a carbon-rich charcoal which, when sprinkled on land, can boost soil carbon storage.

Peatlands are carbon-dense boggy environments made up of partially decomposing organic matter. They cover just 3% of the world’s surface, but hold up to a third of its soil carbon. Restoring wetlands could also have an important role in removing greenhouse gases from the atmosphere, according to the research. Like peatlands, wetlands contain water-logged carbon-rich soils. A recent study found the Amazon’s wetlands are twice as carbon rich as its rainforests, with soils holding the majority of this carbon.

Co-benefits and costs

The study also explores the likely costs and co-benefits of each soil-based natural climate solution.

The chart below shows the proportion of CO2e removal for each technique that would be low-cost (black), cost-effective (grey) and not currently cost-effective (white). The techniques are grouped into three categories: forests (top), agriculture and grasslands (middle) and wetlands (bottom). A colour key indicates if the technique is likely to have co-benefits for air (yellow), biodiversity (green), water (blue) and food (red).

The chart shows how avoiding the degradation of forests, peatlands and wetlands would be the most low-cost way to mitigate greenhouse gas emissions on a global scale.

However, it is worth noting that ecosystems still face major threats in many parts of the world. For example, recent satellite data shows that Amazon deforestation could reach a record high in 2020. Meanwhile, the world’s largest tropical peatland is being threatened by a plan to drill for oil.

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