Soil Yourself: 'Reconstructing' Soil from Readily Available Commercial Products
In this post, I will 'reconstruct' a soil by using its constituent parts and readily available commercial products. The purpose of this exercise is not to offer an accurate description of what a soil actually is, but simply to provide a different perspective on how to approach a soil. Obviously, it doesn't come close to realizing the final nature of actual soils.
Granular Material
The main component of soil is its granular composition―its particular combination of sand, silt, and clay. These particles are all small pieces of disintegrated rocks―caused either by physical breakdown or chemical decomposition usually over thousands of years by natural phenomena―and the main difference between them is their particle size. Sand consists of loose particles that are visible to the naked eye and range in size from 2.00 to 0.05 mm, silt is a dust-like sediment made up of particles that vary in size between 0.002 and 0.05 mm, and clay is extremely fine-grained material composed of microscopic and sub-microscopic particles that are smaller than 0.002 mm. The granular composition defines the soil texture and can influence many soil properties such as its water-holding capacity, permeability, and plasticity/workability.
Soil Organic Matter (SOM)
Soil organic matter consists of any material that originated from a living organism and, regardless of its decomposition stage, is added to the soil (for our purposes, we will exclude the still living organisms from this category). Examples of SOM are numerous: Sphagnum peat, fish meal, sawdust, leaf litter, manure, biochar, compost, etc.
There are two main functions of SOM: to act as a bank of nutrients and to modify the soil structure. Since SOM originated from living organisms, it usually contains many of the nutrients necessary for life and releases them into the soil as decomposition progresses. However, the nutrient content varies greatly depending on the type of SOM and certain types may in fact contain negligible amounts of nutrients (e.g. sphagnum peat). Beyond nutrient content, SOM is also important because it can alter the soil structure. Similar to the granular composition of soil explored earlier, SOM can influence soil properties such as water-absorption capabilities, binding of soil particle, water filtration and aeration. However contrary to a soil's granular composition, organic matter progressively decomposes over time and therefore these properties are not necessarily static.
There are two main functions of SOM: to act as a bank of nutrients and to modify the soil structure. Since SOM originated from living organisms, it usually contains many of the nutrients necessary for life and releases them into the soil as decomposition progresses. However, the nutrient content varies greatly depending on the type of SOM and certain types may in fact contain negligible amounts of nutrients (e.g. sphagnum peat). Beyond nutrient content, SOM is also important because it can alter the soil structure. Similar to the granular composition of soil explored earlier, SOM can influence soil properties such as water-absorption capabilities, binding of soil particle, water filtration and aeration. However contrary to a soil's granular composition, organic matter progressively decomposes over time and therefore these properties are not necessarily static.
Nutrients (Non-organic Fertilizer)
In order to support life, a soil needs to contain some of the essential elements that organisms require for their development. Some of these elements may be naturally present due to the parent material of the granular composition or the content of the SOM described earlier, but a soil may nevertheless require additional nutrients. If we want to add these nutrients without adding more SOM and changing the soil structure, we can add non-organic fertilizers (this doesn't mean that it isn't ecofriendly, it just means that it is not carbon-based). The most common example are the widely-available fertilizers that increase the amount of nitrogen (N), phosphorus (P), and potassium (K) in the soil.
pH Adjusters
In order to make certain nutrients available or to help certain plants thrive, you may find that the concentration of soluble hydrogen ions (pH) of the soil needs to be adjusted. To decrease the soil pH (make the soil more acidic) you can add products such as sulfur whereas to increase the soil pH (make the soil more alkaline) products such as lime (calcium carbonate) can be added. Although these additives do adjust the pH of the soil, whenever possible the pH should be a result of the intrinsic properties of the soil (e.g. choice of organic matter) since additives do not tend to change the pH permanently.
Life
A healthy soil teems with diverse, often tiny organisms including various species of bacteria, fungi, protozoa, nematodes, and arthropods. Here I do not mean life on top of the soil, but life within the soil: In fact, it is believed that there are more lifeforms by weight in the soil compared to the weight of the animals that the soil supports above-ground. One lifeform you can add to your soil from the local nursery is Mycorrhizae―beneficial fungi that interact with plant roots and play an important role in plant nutrition, soil biology, and soil chemistry.
Now just add water, mix, et voilà! We've got soil.
Important Concluding Remarks
When studying soils, the whole is usually broken down to understand its constituent parts―we take a soil sample and perform chemical tests to determine pH, observe lifeforms under the microscope, calculate organic matter by the change in burnt weight, and sift the remaining granular material to determine its texture. Here I did something different: I simply enumerated its individual parts in order to 'make up' the whole. Needless to say, my friends who are experts in soils may not be very happy with this approach given that soils are extremely complex and―just like the adage "the whole is more than the sum of its parts" from the Gestaltian school of psychology―this approach will not do justice to the extraordinary nature of soils. However, I believe there is value in 'reconstructing' soils this way―so long as we resist the urge to consider this a checklist that satiates our quest for knowledge and instead use these points as orienting principles to build knowledge upon.