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What is Soil?
What is Soil?
Outside the seas, soil is the top layer of the Earth's crust - along with terrestrial tock, bare sand , bare salt flats , valley glaciers and ice sheets. It is a complex structure of minerals, amorphous inorganic matter including mineraloids, organic matter, and living organisms. It provides a vital medium for plant growth and support by supplying nutrients, surrounding roots, and regulating water and gas flow. Soil creates various ecosystems upon which most of the Earth's terrestrial biodiversity depends, along with being essential for agriculture, and various human activities. Its composition varies widely, influenced by factors such as climate, geology, and vegetation, and based on several unique important processes like decomposition..
Natural Body
Natural Body
In the early 1800s soil was considered to be like a bin with dead dirt in it that transfers nutrients (fertilisers) to plants. Later that century, Russian scientists considered it more of a 'living entity'. Dokuchev introduced the concept that soil is a natural body formed by specific factors such as climate, organisms, topography, parent material, and time.
I consider soil a natural body as it has distinct living form, somewhere between an organism and an ecosystem. I used to see soil a living entity with structure like a scaffold, where the soil particles are stuck together with glues, like buildinbg blocks and cement, with the organisms inside. Yet, seeing soil more as a natural body, I have come to see the structure more like a skeleton, which interacts continuously with the bones supporting and interacting with the rest of the body around.
Dirt
Dirt
Many people would say soil is 'dirt' - something to scrape off your shoes or wash off your hands. This is not new. In the 1890s, Shaler pointed out,that: ‘The greater part of mankind, those who are well instructed as well as the ignorant, look upon soil as something unclean... . A chance contact with this material fills them with disgust, and they regard their repugnance as a sign of culture’ ‘Origin and Nature of Soils' (download)
If we trouble to look into soil, we soon find there is a lot more to it..
Structures
Structures
Soil improves interaction with both air and water, and the soil structures with their 'peds and pores', provide a massive increase of surfaces to make more life, albeit v small. As life evolved above ground, so it must have underground. It is just we haven't talked about it before. Some if us see soil as a lump of dirt. Dead, static. Yet many now see it is a dynamic living entity, and as a 'natural body' must have evolved. More on soil structure
Spaces
Spaces
There are tens of thousands of very small creatures in every cubic metre of soils, interacting with many more fungi and plant roots and debris, as well as bacteria, archaea, and viruses within all these organisms. They can exist within strong stable structures that provide a unique living environment, dark and damp. How did all this happen? How has soil withstood all sorts of extreme conditions, bombardments, and catastrophes? It is a fascinating - largely untold, story.
Components
Components
The primary components of soil include:
Mineral Particles and colloids: These are the inorganic components of soil, such as sand, silt, and clay and amorphous matter. The relative proportions of these particles help determine the soil's texture.
Perhaps the key component is clay. Clay particles and minerals have been around for billions of years, and gradually interacted with the various organic forms developing over the last half billion (500m).
Organic Matter: This includes both live matter like roots and fungi but also decomposed plant and animal material, microorganisms, and other solid organic substances, like humus. Organic matter contributes to soil fertility, structure, and water retention.
Water: Soil contains varying amounts of water, which is essential for plant growth and other soil processes. The water-holding capacity of soil depends on its texture and organic matter content.
Air: Spaces between soil particles allow for the movement of air. and creatures. Adequate aeration is crucial for the survival of soil organisms and the exchange of gases necessary for plant roots.
Living Organisms: Soil is teeming with life, including bacteria, archaea, viruses fungi, protozoa, roundworms and potworms, springtails, mites, insects, and earthworms. These organisms play vital roles in nutrient cycling, decomposition, and maintaining soil health.
Photo Global Soil Partnership
Types
Types
At the simplest, soils can be classified according to their clay, loam and sand content. Soils are changing and forming, a process called 'pedogenesis', according to the climate, topography, organisms over several thousand years. There are various recognised 'types' which can be classiified in a similar way to plants and animals. The most general level - the main groups - are called 'Orders' which then get divided into more speciific types. The US classification is simpler than the Europeano, basedn the world classification.
Processes
Processes
There are over 2 dozen essential soil Processes including enabling plant growth, regulating water and air flow and filtration, supporting biodiversity, and participating in nutrient cycling. There are physical chemical electrochemical and biological processes carried out in a wide range of circumstances from warm/cold, wet/dry, freeze/thaw and aerated/anaerobic. Processes in detail
This site asks how this complex of functions came to be here, where and when these various functions arose. They could not have all have arrived together, yet they work together and provide the ways we live. If we understood this interaction better, we may be able to put these functions to work better.
Biome
Biome
The soil biome refers to the community of plants and animals living in the soil.
Nearly 2/3 of the world's biodiversity lives in the soil (Anthony et al., 2023) You may have heard that there are 'billions of bacteria' in a gram of soil, and that underground fungal forests can go on for miles. There are also quadrillions of small arthropods - creatures with eyes legs and mouthparts moving around. In the UK alone there is an estimated 12 quadrillion .
Somebody has recently estimated that the world's weight of tiny springtails springing around underground adds up to much more than all the dogs running about above ground. (Potapov 2023)
There is twice the weight of worms (0.2Gt of C) in the world than all domesticated animals. Together springtails and mites weigh much the same as earthworms, but they do a lot more running around. More about mass weight and volume in Biome.
I say 'estimated' as they would take a long time to count. I know counting them is hard as I counted and identified over half a million arthropods.
If you went at my pace - 1/2m in 3 years, it would take you about 70 b years - well over 15 X the life of this planet - to count the small arthropods in British soils.
12 quadrillion UK soil arthropods (ones with legs)
12,000,000,000,000,000/500,000
= 75,0000,000,000 yrs
=15X 4.5Billion years of planet earth.
How do all these arthropods and worms interact with the rest of the wood wide web? The impact of quadrillions of small animals, with massive biomass, are often ignored, with relatively little known about how these creatures relate with fungi, bacteria, other microbes, and the soil itself. Here we are going to try to rectify that and put them all together and say it is a new, more holistic, science. It requires a paradigmatic shift in the way we see soil.
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