How Soil Work: Its Composition, Layers & More


It is crucial that the soil include all of the components that are contained in the plant itself, and that it keep these elements for a sufficient amount of time for the plant to be able to absorb them throughout its existence. Nitrogen, phosphoric acid (phosphorus), and potash are the three chemical components that plants need the most and that are at the greatest risk of running out quickly (potassium). (This is the standard N-P-K ratio that can be seen on the label of any and all commercial containers or bags of fertilizer.)

There are, of course, a variety of additional chemical components, but they make up such a negligible portion of human activity that they are seldom depleted from the surrounding environment. Only after being dissolved can the plant make use of the components.

Acid vs. Alkaline

In addition to affecting fertility, the acidity and alkalinity of the soil have a role in selecting the kind of plants that may be successfully cultivated there.

When there are more hydrogen ions than hydroxyl ions in a sample of mixed soil and water, the soil is said to have an acidic pH level. When the soil-water combination has an equal quantity of hydrogen ions (acid) and hydroxyl ions, we say that the soil is in a neutral state (alkaline). For a soil scientist, all of this information makes perfect sense; however, a gardener’s main concern should be the pH scale. The pH scale is a method that was developed to indicate the acidity or alkalinity of solutions, such as the soil-water solution.

The majority of plant species, fortunately, do best when grown on soil that is slightly acidic to neutral or slightly alkaline. Although the level of acidity or alkalinity of the soil may sometimes be to blame for poor plant development or death, it is a fallacy to believe that adding additional limestone to the soil would solve the problem if this is the case. Either a home gardener utilizing one of the kits that are available from garden stores or mail-order nurseries, or a professional should do the initial soil test. A home gardener may use one of the kits (consult your county agent or State agricultural school outreach). The findings of the test, which were represented in terms of the pH scale, show how much lime has to be added in order to bring the pH up to the desired level.

In spite of the fact that an excessive amount of lime may be detrimental to soils and plants, there are unquestionably some advantages to using lime in addition to the fact that it alters the pH of the soil. It does things like provide calcium, make porous soils more compact, and promote the activity of microbes in the soil that are helpful.

In addition to testing for acidity, it is also possible to determine the amounts of the essential plant food elements in the soil by applying certain chemicals to a small amount of soil (or to water that has been allowed to leach through it) and observing the reaction. This can be done in conjunction with an acidity test. These types of tests should be carried out in a laboratory utilizing complex equipment, and the results should be analyzed in conjunction with a thorough assessment of the land’s physical condition, the crops it bears, and the management practices that are in place. Only then will the tests be truly accurate and of the greatest use. These kinds of examinations are often carried out by state agricultural experiment stations and sometimes by county agents. There are low-cost kits available with step-by-step instructions specifically for gardeners.

A graphic that illustrates in a very understandable way how the availability of different nutrients varies depending on the pH of the soil. Even while essential nutrients are present WITHIN the soil, the pH must be at the appropriate level in order to make them “accessible” for the plants to take in.

The Nature of Soil

The following are the five primary components that make up soil:

  1. mineral particles
  2. humus
  3. micro flora and fauna
  4. air
  5. water

The size of the mineral particles is the primary factor that decides the mechanical properties of soil, which are referred to as its texture.

The nature of the mineral particles and the quantity of humus in the soil both have a role in establishing the relative fertility of the soil. The quantity of humus present also has a significant role in determining the relative populations of the various species of microflora and microfauna.

The size of the mineral particles, the presence of humus, as well as the types of microflora and microfauna in the soil all contribute to the total quantity of air in the soil. Out of these three aspects, the size of the mineral particles is most likely the one that matters the most.

The size of the mineral particles in the soil is the primary factor that decides how much water can move through the soil. The quantity of humus, also known as organic matter, in the soil is the primary factor that determines how much water the soil is able to hold onto.

None of these five aspects, on their own, should be given excessive weight in the decision-making process. The proportional amounts that each component makes up of the whole are the only ones that really count.

The Origins of Mineral Particles

The fundamental rocks that make up the earth’s crust are where the mineral particles in soil come from. Soil is made up of these rocks. The kind of rock that the mineral particles in soil originated from is one of the most important factors in determining the fertility of the soil. Extreme climatic circumstances, such as glaciers, have, over the course of many years, been responsible for breaking these rocks down into ever-smaller shards. The process of rocks being worn away by the elements, such as wind, rain, sun, and ice, as well as other agents, such as lichen and mosses, is an ongoing process.

The Function of Humus

Remains of animals and plants are progressively broken down by the elements as well as by creatures that live in the soil. The material that is left behind after the partial decomposition of this organic matter is referred to as humus. It is a tiny, colloidal substance that is dark and black in color and contains lipids, carbs, and proteins. It is a very complicated material.

In these four ways, humus contributes to the overall health of the soil as well as the plants that grow in it:

1) It works as a storage facility for plant nutrients, which have a propensity to cling extremely tenaciously to the surface of humus particles. This makes it less probable for these nutrients to be removed from the soil as a result of drainage. Nitrogen can only be stored in the soil in the form of humus.

2) It prevents the erosion of mineral particles caused by wind and water and makes clay soils simpler to deal with by binding the mineral particles together.

3) It not only acts as a storage facility for water in the ground but also works to promote drainage and the flow of air through the soil.

4) It supplies a source of food for the flora and animals that live in the soil, which is itself necessary for the establishment of healthy plants.

An increase in the quantity of humus that is already present may bring about a significant improvement in the quality of many soils.

Microscopic Flora and Fauna

There are many different kinds of plants and animals that may be found in soil. These creatures range in size from the tiniest bacterium to bigger, more obvious ones like earthworms and millipedes. All of these factors contribute in some way to the transformation of decomposed animal and plant waste into humus, to the preservation of open spaces for air and water in the soil, and to the overall upkeep of a healthy soil environment.

It is very desirable to have a microbial population that is both abundant and diverse in the soil. Microorganisms flourish in the same circumstances that allow plant roots to flourish, and they compete with one another for the same nutrition sources. The microorganisms in any soil that has a high concentration of organic matter and a diverse population of microorganisms are in a constant state of competition with one another. Because of this, it is impossible for a single specialized disease organism or fungus to acquire the upper hand. As a result of the actions that they carry out, the organisms in the soil make a great deal of nutrients accessible to plants in a form that is simple for the plants to make use of (nitrogen fixing bacteria are a well-studied example of this).

The Layers of Soil

There is no chemical formula that can be used to describe the composition of soil, and two samples of the same soil, even if they come from the same garden, will never be identical to one another. In spite of this, the majority of gardens have two very different layers of soil. The top layer, which is often a dark hue and composed of rich soil, is the first layer. The lighter-colored, less fertile subsoil that lies under this layer is often sterile.

The top layer of soil is of primary significance to gardeners since here is where the plants’ feeding roots are located. Plants’ anchoring roots may be able to penetrate the subsoil, but this layer, which is often sterile and should never be brought to the surface, must be avoided at all costs. Most of the time, when gardeners talk about soil, they are just talking to the top layer of the soil.

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