Soil Biology The Life Cycles within Soil 1

Soil Biology The Life Cycles within Soil

Soil biology is a guide to understanding fungi, bacteria, nematodes, and Actinomycetes. To maximize your yields it is crucial to have a basic understanding of the biology of soil!

Soil Biology Soil


One thing’s for sure; the soil is full of life. Each of the species living in the soil either depends on it for food, shelter or even both.

Regardless, Soil Biology and Chemistry is a pretty complex aspect.

Many would say, the soil is like the stomach of the earth.

That is because it is responsible for consuming, then digesting and cycling the organisms and nutrients in the environment.

In most cases, people will perceive the soil as just an inert material that we build, walk and grow plants on.

However, there is more to soil than just that. Soil consists of many living organisms, all of which are important aspects that make up the environment.

But that’s just a spectrum of the whole composition.

That is why this article will help you get a better understanding of Soil Biology and other related aspects of the soil. Shall we get started?

Soil Biology and Chemistry

Soil biology basically refers to the living organisms found within the soil.

On the other hand, soil chemistry refers to the chemical composition or chemical characteristics of the soil. So, let’s start by talking about soil biology.

Soil Biology Basics

There are different living organisms in the soil. That said, these organisms have been grouped into:

Soil Biology Your soil is alive

Image credits Kellogg Garden

Microbial decomposers and consumers
Decomposers are organisms that obtain their foods by breaking down dead organic wastes.

On the other hand, consumers are organisms that obtain their food by eating other organisms.

Soil is full of microbial decomposers and consumers in charge of breaking down dead or even living organisms that might have dropped to the soil.

In short, decomposers are not able to make their own foods, as producers do.

So, they have to depend on other organisms for food.

In that case, decomposers depend on dead organic wastes for food. These decomposers are microscopic hence they can only be viewed under a microscope.

Only 5% of what is produced by plants is typically consumed by animals.

About 95% of what plants produces is consumed by microorganisms.

That said, there are millions if not billions of bacteria in every gram of soil.

These bacteria also come in different types, and a large percentage of them are still not discovered.

Majority of the bacteria living in the soil are aerobic. That means that they use oxygen found in the soil’s atmosphere.

On the other hand, there are bacteria in the soil that don’t live on oxygen while others can live with or without oxygen.

The development and growth of these bacteria are limited to the availability of food in the soil.

Additionally, the soil consists of fungi and they vary in size, type, shape and color.

You will also find mycelium which are underground roots of mushrooms that are able to absorb water and nutrients from the soil.

These roots are able to decompose acidic materials in the forest.

Soil Animals
There are different living organisms found in the soil. These soil animals can be considered as consumers and decomposers. This is because they feed on organic matter and decompose them, in their digestive system.

Some of the animals feed on each other while others feed on roots.

If you would like to know more about these soil animals, then keep on reading. I will give you examples of soil animals and how they benefit the soil.

Soil Chemistry

Soil chemistry is a pretty broad topic that I wouldn’t even know where to begin but let’s start with its definition.

That said, soil chemistry is basically the chemical composition of the soil.

These characteristics affect the soil’s mineral composition, environmental factors and organic matter.

On top of that, soil chemical composition is the reason why we have different types of soils.

Each of the soil types that exist today typically have a different chemical composition from the other.

This difference is manifested in the form of color, texture and even water retention.

What’s more, you will be able to note that soils are different using their color or texture and in some cases the vegetation that grows on them.

One of the earliest studies of soil chemistry was through soil PH. That is basically the acidity of the soil. Changing the PH of soil was aimed at enhancing the supply of nutrients to the crop.

This section also includes soil minerals and how they can help plants grow.

As you’ve already figured out by now, the soil is full of different nutrients.

What’s more, these nutrients are easily utilized by plants in different forms. In that case, these nutrients are grouped into micronutrients and macronutrients.

Macronutrients are types of nutrients that plants require in large amounts whereas micro nutrients are nutrients that plants require in small amounts.

Regardless, both types of nutrients are relatively important to the healthy growth of plants.

On top of that, these nutrients need to be in a specific balance in your soil.

What is Soil?

There is a chance that one, two or more times, you have thought about the soil that’s just below your feet.

I must agree that the complexity that comes with the soil is something that amazes most people.

Well, basically soil happens to be the material that is found on the surface of the earth that consists of both organic and inorganic materials.

More to that, soil tends to have varying compositions and structures in its particles.

And both of these factors are essential to farmers who are looking for the ideal soil to farm in.

Also, the factors apply to engineers who wish to know the soil’s capability of holding up under different circumstances.

Although soil is vital to the sustainability of the ecosystem, it’s also a great natural medium for growing any sorts of vegetation.

That is why soil is exactly defined as the inorganic and organic materials on the earth’s surface that provide the medium for growth of plants.

Over time though, the soil could slowly develop and vary in its composition.

The inorganic materials in the soil may include minerals and probably weathered rocks.

In short, non-living things. The weathering process happens when the rocks are broken down to smaller pieces.

During this chemical process, the smaller pieces of rock tend to mix with other organic materials which originate from the living organisms in the soil.

Types of Soil Organisms

Soil organisms have a very essential role in the ecosystem. They have a significant impact on the physical properties of the soil.

The biological processes and the cycling of nutrients too.

When it comes to the soil organisms, their effect on the physical properties of the soil increases with their body size.

Soil organism can be categorized into Macrofauna and microorganisms.

The Macrofauna consists of termites, ants, earthworms, and others.

The macrofauna is known to have a great effect on the soil porosity.

That is because they tend to create macro pores as well as tunnels in the soil that help to allow preferential aeration of the soil.

This also allows the flow of water into the soil profile.

At the same time, it helps to perfectly mix the minerals in the soil from one horizon to the other.

This has an effect on the texture, density and content of organic matter in the soil.

The microbes (microorganisms) on the other hand play a different role in the well-being of the soil composition.

The microorganisms are the primary components of the soil community.

They include fungi and bacteria which helps to regulate all processes that lead to decomposition and cycling of nutrients in the soil.

Microbes can be dormant at times but under the right environmental conditions, they quickly become active.

Here are some of the major microorganisms that live in the soil;

soil algae

Soil Algae Bacteria, Nematodes, and Actinomycetes

Soil Algae
Credits: brewbooks from near Seattle, USA [CC BY-SA 2.0 (]

The soil algae can be categorized into eukaryotes and prokaryotes.

They will grow abundantly especially in locations that have adequate moisture and light.

Algae has a very diverse role in the soil ecosystem.

Actually, we have seen how much soil algae can revolutionize the agricultural sector through the use of cyanobacterial fertilizer.

In addition to that, soil algae have been used to reclaim any sodic soil.

For instance; sewage treatment, alkaline soil and so much more.

Some of the prominent genera of the soil algae include; Aulosira, Nostoc, Tolyphothrix, Anabaena among others.


Soil Biology The Life Cycles within Soil 2

Agrobacterium spp

Bacteria are like the most crucial workforce of any soil types.

Also, they are the smallest unicellular prokaryotes that are found in the soil.

Bacteria are the most abundant group of all other microorganisms living in the soil.

The cells will vary mostly between 108 and 1010 as per every gram of soil.

Bacteria, unlike other soil organisms, do not just occur freely in the soil.

In most cases, they will be closely attached to the soil particles.

Or in some cases, they are embedded into the soil organic matter.

Even when you add dispersing agents in the soil, they still aren’t distributed as an individual cell.

Bacteria also play a very vital role in the final stage of breaking down the nutrients in the soil and breaking them down to the roots.

That is why most researchers refer to them as the most vital life forms that are found in the soil.

Bacteria are also involved in the decomposition of organic matter, nitrogen fixation, production of biogas and biotransformation.

Some of the prominent genera include; Pseudomonas, Nitrobacter, Rhizobium, Agrobacterium, Bacillus, Nitrosomonas, Thiobacillus, Clostridium, Alcaligens, Aethrobacter among others.


Biology of soil Fungi

Credits: Dominicus Johannes Bergsma [CC BY-SA 4.0 (]

Just like bacteria, fungi also live in the root zone of plants.

Hence, they are responsible for making the nutrients available to the plants.

Especially in most of the cultivated soils, fungi make a major part of the microbial biomass.

That is because they tend to have an extensive network of mycelium and a larger diameter.

However, the numbers of fungi in the soil will differ according to the composition of the soil as well as the isolation procedure used.

Fungi derive nutrients from organic matter in order to boost their growth.

This may include; arthropods, protozoa and nematodes or in some cases living plants.

The fungi that tend to inhabit the roots has two phases.

A parasitic phase and the saprophytic phase that happens after the invaded host dies.

However, the fungi that inhabit the soil lacks the ability to survive as a soil saprophyte.

The good thing with the specialized saprophytes is that they have developed a way to survive without having to cause any damage to the inhabited host.

However, the distribution of these specialized parasites will depend majorly on the host.

The soil saprophytes include; Gliocladium, Alternaria, Dematium, Cladosporium, Humicola among others.

On the other hand, the fungi associated with diseases that affect plants include; Verticillium, Pythium, Plasmodiophora, Fusarium, Armillaria, Ophiobolus, Rhizoctonia, Sclerotium among others.


Nematodes are basically a broad phylum of organisms that occupy different niches in the environments.

A large percentage of nematodes can be found in the soil while others are parasitic to other animals for instance humans.

These group of animals are particularly difficult to distinguish one from the other.

That makes it quite hard to find out the number of species in this phylum. However, a rough estimate shows that there are over 25,000 species in this group.

Nematodes can also be referred to as roundworms. But that doesn’t mean that they are even related to the true worms.

These organisms have a smooth and unsegmented body.

The ones that live in the soil feed on plants and algae.

There are also some nematodes that feed on fungi and bacteria while others feed on other nematodes.

Nematodes can easily be grouped into:
1. Bacterial feeders: eat bacteria
2. Predatory feeders: consume nematodes and protozoa
3. Fungal feeders: feed on the cell wall of fungi
4. Omnivores: they have a different diet almost in every stage of their lives.

Nematodes help distribute protozoa and bacteria in the soil and along the roots. They are also food for higher level predators in the soil.


This category of soil microorganisms tends to share both the characteristics of fungi and bacteria.

Most people refer to them as ray-fungi as they have a very close affinity to fungi. They tend to release antibiotic properties to the soil.

The actinomycetes are more populated in Pasteur soils and grassland as compared to cultivated land.

The most limiting factor to the presence of actinomycetes in the soil is the ph. They will mostly be available in alkaline or neutral soils.

Some of the common members of actinomycetes include; Nocardia, Actinoplanes, Actinomyces, Streptomyces among others.

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