The foundation upon which nearly all plants grow is soil.  Knowledge about the nature and properties of soil will give a better understanding of how to use soil more effectively to support healthy plant growth and an overall healthy environment.

Using Soil

When growing a plant one of the main considerations is its growing medium. In certain specialized settings various mediums are used like plug trays, or a nutrient solution as in hydroponics; however, for nearly all plants the growing medium is going to be soil. Plants do process sunlight into food, but to make that process work the plants need to uptake complementary nutrients, and in that process plants actually mine nutrients from the soil. So for a plant to be healthy it not only needs some light exposure but it also needs soil that helps supply it with its building blocks.

There are many commercially available soils which serve well to support the healthy growth of plants. A bag of soil at the local nursery which is organic and indicated for vegetables will likely have everything needed to get started. Because vegetables often grow quick and take a lot out of the soil, soils specifically recommended for vegetables will often be well fortified for most growing situations. Once the soil is available it can be used for growing plants from seed, for transferring starts into that soil, or for using the soil in a garden or other raised bed. However, if the area is somewhat large it might be more economical to look for nurseries that will sell soil in bulk, instead of just in bags.

These commercially available soils are usually well off in terms of nutrients, but are often very dry, so should be wet slightly prior to transplanting so that any roots do not dry out; and again after any transplanting plants should always be well watered in. The soils should not look or feel dry, but also not be so wet that water can be squeezed out of it.

If you grow a plant in a pot, the pot should be filled with soil no closer than one inch from the rim of the pot, as this will allow room for water as it soaks into the soil. The soil should be well packed down without being too firm, this may sound somewhat vague, but just thinking about how to best use the soil to tuck in a little growing plant with care, often results in just the right touch. If planting seeds this same firming in of the soil is helpful. The pressure ensures that the rots are in contact with the soil which helps prevent unnecessary drying out, and the gentleness helps ensure that the soil is not too compact and unnecessarily difficult for growing root to penetrate.

Now that you have an understanding for how to work with the soil to support the health of plants there is a more in depth explanation around the various aspects of soil; specifically where soil comes from, what are the chemical components of soil, what are the biological components of soil, and how all of these elements come alive and result in inactive dirt becoming dynamically active soil.

PARENT MATERIAL

All soils have the origin story in geology. It is from rocks where soils originate and, over vast spans of time, in combination with the weathering effects of the sun, water, wind, and freezing temperatures rocks have been broken down into smaller and smaller pieces. This weathering process has also been influenced by biological processes like those carried out by fungi and lichens which secrete acids allowing for the rock to become bio-available for the organisms to eat. As the parent rock is broken down into smaller and smaller pieces it can transition from being a boulder, to a rocks and gravel, to sand, silt and finally clay. It is often spoken of sand being so small it will just slip through the gaps between one’s fingers, but sand particles can be 40 times larger than silt particles and silt particles can themselves be over 25 times larger than clay particles. These mineral particles compose about 45-50% of soil; in addition to the roughly 0-5% of biological matter, and another 50% of pore space filled with water and air.

The minerals that are contained within the soil results in the soils color and there are entire books like the Munsell Soil Color Charts, which contain color charts, like paint swaths, that are used to determine the mineral constituents and possibly how well draining the soil has been in the past. For example, a soil that had a reddish color could be an indication of high quantities of iron. These colors and ultimately the mineral composition of the soil will provide a basic understanding if the soil presents any excesses or deficiencies when beginning to grow plants. Where geological process move very slowly, with an understanding of what is needed in soils an individual is able to amend the soil with the correct quantity of necessary elements so that the plants and everything else thriving in the soil is able to have everything that is needed for life.

ELEMENT

Just as with plants and animals it is appropriate to think of there being essential nutrients for healthy soils. A child might be able to run around for much of the day after eating a bunch of sugary foods and energy drinks, but this is not the recipe for lasting sustained growth. Similarly, plants are able to show a flurry of activity after the application of artificial fertilizers, but this is not going to result in sustained growth for the plants or the planet. There are three nutrients that have long received the focus as being the most important for healthy growth, this is what is seen on the sides of bags of fertilizer; and these are Nitrogen (N), Phosphorus (P), and Potassium (K). These three primary nutrients are very important, but there are others that are also very important such as the secondary nutrients Calcium (Ca), Magnesium (Mg), and Sulfur (S); and the seven micro-nutrients Zinc (Zn), Manganese (Mn), Iron (Fe), Boron (B), Chlorine (Cl), Copper (Cu), and Molybdenum (Mo). And where we might not yet understand how or why the other elements are important it has been suggested by soil scientist that through the long process of evolution that the soil biology has found a productive use for all of the elements.

BIOLOGY

Without there being some biological activity within the soil there would be merely dirt. Life, in fact, is one of the main components for there being soil, and the amount of life in soil is very significant. There are more living organisms in a teaspoon of soil than in all of the humans who have ever lived on Earth.

Soil is a dynamically active ecosystem populated with incredibly vast numbers of organisms.  In healthy soils these organisms consist of bacterial, fungi, protozoa, nematodes, arthropods and worms, and collectively their numbers can be in the trillions in just a cup of soil.  The role of these organisms is very important for maintaining the health of the soil, and their interactions are often reflected through the term ‘soil food web’.  The ‘soil food web’ moves the thinking beyond the outdated notion of a food chain and recognizes that everything is a means of food for something else. Being that most things make their way to the ground, with all the diversity of life, there is something that can consume nearly everything natural including bacteria, viruses and many pollutants that wash down drains and into oceans.  The essence of this soil food web relationship can be identified by considering the sources of input into the soil system.

The soil biology works in a reciprocal relationship with the plants, specifically the roots but also the leaves, fruit and eventual dead tree that falls to the ground, to share resources gathered from the sun with resources gathered from the Earth.  Plants feed on sunshine, however that is not all they need.  Through sunshine, water and the carbon dioxide that is taken in from the air, the plants convert the carbon, oxygen and hydrogen in to carbohydrates or plant sugars.  More than half of the carbohydrates that are produced by a plant are actually given off by the roots like a waste product.

These precious resources produced by the plant are not merely wasted however; the sugars are emitted by the roots and serve as food for soil microorganisms.  Fungi in the soil take the carbon from the plant sugars and form strands that can stretch 250 yards forming connections to different plants.  The ability of the fungi or mycorrhizae ('myco' - fungi and 'rrhizae' - root) to extend out is so vital for plants as it can expand the surface area of the plant's roots by over 50 times due to the sharing that takes place around the rhizosphere (the miniature ecosystem right around the plants roots).  With this increase in surface area the root is able absorb far more water and nutrients than it would be able to with just its roots alone.  The fungi tip or hyphae can produce digestive substances which it uses to break down parent rock material.  The fungi do not have a mouth so it breaks up the minerals to the point that they are able to be absorbed through its cell walls.  These minerals are then able to be transported anywhere throughout the strands of the mycorrhiza.  The mycorrhiza receives a good meal from plant roots, but if the plant is not healthy it will not receive a good meal; so the mycorrhiza in detecting a lack of some soil nutrient around a plant will transfer the minerals to plants so as to keep the system in balance.

The concept of companion planting and plant communities also utilizes some of these reciprocal relationships and in some cases it has been observed how some nutrients are even able to be shared from one plant to another over 100 feet away through the transport relays set up by the mycorrhiza.  And as all of these process go on in the soil they are being supported largely by the plant sugars coming as root exudate, and it is through this process that carbon originally taken from the air is able to be locked up by the plants and sequestered in great quantities into the soil. 

So, for healthier plants and cleaner air and water it is important to understand how the countless numbers of organisms are functioning under every bit of Earth. 

This understanding of the relationships influencing these organisms is also important because similar to beautiful animals going extinct on the land and in the seas, there are also whole soil systems or series which are going and have recently gone extinct.  Unlike a single animal which may go extinct, when a soil series (a series is a classification for a soil in an area) goes extinct it can mean that tens of thousands of different species that have formed a unique adaptive relationship are going extinct.  When an animal is threatened with extinction it can be brought to a zoo or some sanctuary and cared for, however with a soil series they cannot be removed from their unique environment.  If there is real interest in saving animals from extinction, there needs to be attention paid to ensuring the animals have food to eat to survive. When traced back to their source photosynthesizing plants are the base of nearly all food, and for nearly all plants to survive there needs to be healthy soils.  So to help stop species loss, it is important to help protect soils and ensure that the rates of soil loss are reduced as much as possible and stopped as soon as possible.

DEPLETION, EROSION AND DEATH

There is a direct relationship between the growth that is seen in a plant and what is being extracted from the ground around the plant. Therefore as the plant increases in size the surrounding soil decreases in the quantity of nutrients. If this was the whole story it would not be good for the plant; however, evolution has supplied ways for keeping this from becoming a real issue. In a natural setting there are typically several plants growing together, often called a plant community. People over time have modeled naturally forming plant communities with specifically chosen plants and came up with beautiful beneficial plant groupings, such as, the ‘three sisters’ combination of corn, beans and squash. These plants, in this example, are planted together and work together. The corn grows tall and provides a vertical support for the beans to climb upon. The large squash leaves cover the ground to help retain moisture in the soil and prevent weed seeds from germinating. While, the beans fixing nitrogen help fertilize the soil. In nature, similar arrangements have naturally worked themselves out and what is seen is a mostly contained loop where the plants grow in the area and some part or all of the plant falls back to the ground and acts to continue feeding the rest of the members of the group.

Historically many of the world’s most fertile regions for agriculture have been in river valleys. Similarly, the fertility of these areas is the result of plants falling to the ground and breaking down into food for soil microorganisms and therein for plants. The unique feature about these river valley areas is that the nearby rivers would pick up all of these nutrient accumulations from the ground and deposit them along the flooded areas near the rivers. Unfortunately, many of these rivers have been diverted or damned for irrigation or navigation, and therefore, have been substantially diminished due to changes in their head waters, furthermore, this has prevented the regular deposit of nutrients by the river. This situation leads to a slow decline of the soil, because the plants continue to take material out of the soil when the river no longer deposits nutrients back into to the soil. The depletion of nutrients in the soil prevents it from maintaining optimal health, and therefore, does not allow the soil to support growing healthy plants.

Some of these degrading soils can be artificially supported for some time by bringing in and adding fertilizers, but these fertilizers often diminish the health and quantity of the soil microorganisms, which result in the need for more and more fertilizer to generate the same level of output. To a greater consequence, in the areas where the soils are the most severally damaged due to unsustainable agriculture or industrial disregard, we are seeing vast numbers of cases where soils are going extinct. This is a very alarming situation, because soils are harmonious collections of thousands to millions of different species of organisms; so as a soil series goes extinct it is not just reflecting the loss of a single species, but the loss of untold numbers of species. The formation of soils is cultivated through the long processes of evolution. Currently, we are unable simulate this natural evolutionary process to grow these soils in labs outside of their native habitat, even if there was a desire to support and preserve these important natural resources and health allies.