Soil, a Living System

Soil, also commonly but mistakenly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that harmoniously work together to support life. Within a tablespoon of soil, there are more microorganisms than there are people on earth (1).

For a better representation, currently, there are about 7.8 billion human beings living on our planet.

It is worth mentioning that, although referred to as dirt many times, scientific definitions distinguish soil from dirt by restricting the latter term specifically to displaced soil(2). In simpler words, dirt is soil that is in the wrong place. J.L. Anderson, the writer of Industrializing the Corn Belt: Agriculture, Technology, and Environment explains dirt as “from the perspective of the people who raised the crops and livestock…the farmer ‘with the dirt on his hands and dung on his boots’”(3). When cut off from its ecosystem, subsequently losing its functionality, soil turns to dirt, and becomes no longer a productive member of the society. In order for soil to be productive, it has to stay alive and it has to remain healthy.

There are many definitions in the literature that define the term soil health, but FAO describes it as: “the capacity of soil to function as a living system”. Healthy soils maintain a diverse community of soil organisms that help to control plant disease, insect and weed pests, form beneficial symbiotic associations with plant roots, recycle essential plant nutrients, improve soil structure with positive repercussions for soil water and nutrient holding capacity, and ultimately improve crop production”(4).

Before going further into soil health, subsequently agricultural productivity, soil functionality must be covered first. Soil not only functions as a medium for plant growth, supply, purification, and storage of water, or as a habitat for organisms, but it also plays a vital role as a modifier of Earth's atmosphere. Healthy soil means cleaner air and water, fertile and rich crops and forests, productive pastures, and diverse wildlife. In other words, “better soil, better food, better life”. For soil to be considered healthy, it needs a rich and diverse living community: macrofauna such as nematodes, arthropods, and mollusks, and microorganisms such as bacteria, archaea, fungi, and protozoa. The second group, formed by tiny creatures living underneath the ground, is defined as the soil microbiome. These microorganisms carry out a range of processes important for soil health and fertility in soils of both natural ecosystems and agricultural systems, one of which is to transform organic matter into plant nutrients, along with converting the soil minerals into disease-suppressing compounds (5)(6).

Soil, as mentioned earlier, can regulate Earth’s atmosphere by fixing atmospheric gases, such as carbon dioxide among others. However, the soil can’t do that without its living part, the soil microbiome. To explain the carbon cycle in figures, the total carbon in terrestrial ecosystems is approximately 3170 gigatons. Of this amount, nearly 80% is found in soil (7). For a better visual representation, “a release of just 0.1% of the carbon now contained in Europe’s soils would be equal to the annual emissions from 100 million cars” (8).

In addition to carbon dioxide storing capacity, soil also plays a crucial role in balancing other greenhouse gases, such as nitrous oxide and methane. Nitrous oxide is almost 300 times more potent, and methane is about 20 times stronger than carbon dioxide (9). A major direct source of nitrous oxide is synthetic fertilizers. Due to intensive farming practices, nitrogen-based fertilizers are excessively used and as a result, pollute our air and water, and disrupt the carbon and nitrogen cycling capacity of the soil. This mention of the soil’s cycling and storage of carbon brings us to the term carbon sequestration. “Carbon sequestration is the process of capturing and storing atmospheric carbon dioxide. It is one method of reducing the amount of carbon dioxide in the atmosphere with the goal of reducing global climate change.”(10). One of the areas where one can see significant negative consequences of climate change is biodiversity. In recent years, the interconnection of climate change and biodiversity has been widely recognized. But what is not known to many is the significant impact of climate change on all the soil biodiversity and related services.

Soil biodiversity, also referred to as “factory of life” by the EU Commission in their report about soil biodiversity (11), plays an important role within the global system, because through microorganisms, soil can mitigate climate change, store greenhouse gases, purify water and prevent erosion. Remembering back the description of healthy soil, one can draw the conclusion between soil biodiversity and healthy soil (12), which brings back to the statement made earlier: “better soil, better food, better life”.

To conclude, the interconnected nature of ecosystems is an undeniable fact that lay in front of us. Ending with a quote  “Soil is at the bottom of the food chain, yet it is the cornerstone of life on earth.”

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Bibliography

(1) Food and Agriculture Organization:

http://www.fao.org/3/a-au887e.pdf

(2) Hans, Jenny. Factors of Soil Formation, A System of Quantitative Pedology:

https://www.nrcs.usda.gov/wps/PA_NRCSConsumption/download?cid=nrcseprd1330210&ext=pdf

(3) Gardner, Madelyn. Soil Ain’t Dirt: The Many Meanings of Soil in the Lives of Iowa Farmers:

https://www.grinnell.edu/sites/default/files/documents/madelyn_gardner_soil_aint_dirt.pdf

(4) Food and Agriculture Organization:

http://www.fao.org/agriculture/crops/thematic-sitemap/theme/spi/soil-biodiversity/the-nature-of-soil/what-is-a-healthy-soil/en/

(5) Food and Agriculture Organization:

http://www.fao.org/3/a0100e/a0100e0d.htm

(6) Schlatter Daniel,  Kinkel Linda, Thomashow Linda, Weller David, Paulitz Timothy. Disease Suppressive Soils: New Insights from the Soil Microbiome. The American Phytopathological Society,  Phytopathology:

https://apsjournals.apsnet.org/doi/10.1094/PHYTO-03-17-0111-RVW

(7) Ontl, T. A. & Schulte, L. A. (2012) Soil Carbon Storage. Nature Education Knowledge 3(10):35:

https://www.nature.com/scitable/knowledge/library/soil-carbon-storage-84223790/#:~:text=Soil%20Carbon%20Sequestration,in%20the%20form%20of%20SOC

(8) European Commision, Soil the hidden part of the climate cycle:

https://ec.europa.eu/clima/sites/clima/files/docs/soil_and_climate_en.pdf

(9) ibid 8.:

https://ec.europa.eu/clima/sites/clima/files/docs/soil_and_climate_en.pdf

(10) USGS, Science for a changing world. What is Carbon Sequestration:

https://www.usgs.gov/faqs/what-carbon-sequestration?qt-news_science_products=0#qt-news_science_products

(11) European Commision, The factory of life
Why soil biodiversity is so important:

https://ec.europa.eu/environment/archives/soil/pdf/soil_biodiversity_brochure_en.pdf

(12) Farm Advisory Service, Soil Biodiversity and Soil Health:

https://www.fas.scot/downloads/tn721-soil-biodiversity-and-soil-health/