Secrets Underground

Secrets Underground

Soil fertility, a fundamental element of agricultural production, refers to the ability of the soil to provide the essential nutrients required by plants for optimal growth. This ability is directly related to the presence and availability of nutrients such as nitrogen, phosphorus, potassium, calcium, magnesium, sulphur and other elements in the soil.

In addition, soil fertility is inextricably linked to several factors such as soil structure, organic matter content, soil pH and, of course, the presence of beneficial micro-organisms.

Classification of Soil Organisms by Size

Fertile soil is characterised by its ability to provide plants with the right amount and form of nutrients to grow healthily and produce high quality crops. Soil fertility is an essential pillar of agriculture and food production as it has a direct impact on crop yields and the long-term sustainability of agricultural land. Maintaining and improving soil fertility is therefore a key objective of agricultural management and environmental protection.

It is important to recognise that soil is a complex and dynamic ecosystem. The physical soil particles are saturated with living organisms that are in a state of continuous activity throughout the growing season.

Classification of soil organisms by size

Soil organisms can be divided into three main categories according to their size:

  • Microfauna: This category includes organisms of minute size, ranging from 0.02 to 0.16 mm. Examples of microfauna include bacteria, fungi, actinomycetes, protozoa and algae.
  • Mesofauna: Mesofauna includes organisms of moderate size, ranging from 0.16 to 10.4 mm. Examples of mesofauna are insects, springtails, mites, nematodes and molluscs.
  • Macrofauna: Macrofauna includes larger organisms, larger than 10.4 mm. Examples of macrofauna are earthworms, insects, arachnids and small rodents.
Classification of Soil Organisms by Size

Activities of soil organisms

Soil organisms play a crucial role in the functioning of the soil ecosystem and in supporting plant growth. Some of the main activities of these soil organisms are described below:

Decomposition of organic matter: Micro-organisms, such as bacteria and fungi, are responsible for decomposing organic matter in the soil, including fallen leaves and plant debris. This decomposition releases nutrients that are essential for plant growth.

  • Nutrient cycling: Soil organisms actively participate in nutrient cycling by breaking down and releasing elements such as nitrogen, phosphorus and potassium into forms that are readily assimilated by plants.
  • Improved soil structure: Earthworms and other burrowing organisms help improve soil structure by mixing and aerating the different soil horizons. This facilitates water infiltration and oxygen circulation, which benefits root growth.
  • Pest and pathogen control: Some organisms, such as predatory nematodes and certain fungi, play an important role in controlling pests and pathogens that can damage plants.
  • Humus formation: Organic waste processed by micro-organisms is converted into humus, a nutrient-rich substance that improves water retention and soil structure.
  • Nitrogen fixation: Some bacteria, such as those that form symbioses with legume roots, have the ability to fix atmospheric nitrogen in the soil, making it a nutrient available to plants.
  • Carbon storage: Soil organisms play a key role in storing organic carbon, which helps to mitigate climate change.

Abundance of Microorganisms in Soil

The number of micro-organisms in the soil is staggering. For example:

BacteriaThey break down organic matter, attacking cellulose and hemicellulose compounds in tissues and oxidising carbon. It also intervenes in nitrification processes so that it can be absorbed by plants.10,000,000,000,000 in 1 gram of soil
ActinomycetesThey degrade soils that are not attacked by fungi and bacteria; especially starch. They are involved in the humification process (they produce the “earthy smell”).100,000,000 in 1 gram of soil
SeaweedThey live in moist soils and need light to develop. They act as colonisers of rocks in the early stages of weathering. Others are able to fix atmospheric nitrogen and then release it into the soil.20,000 in 1 gram of soil
MushroomsThey act as decomposers of organic matter, especially cellulose; or as predators of other organisms (nematodes, bacteria, rotifers, protozoa, fungi).Between 10,000 to 1,000,000 in 1 gram of soil


Soil fertility is a fundamental factor in agricultural production as it determines the ability of the soil to provide the nutrients necessary for healthy plant growth. This fertility is related to the availability of essential nutrients such as nitrogen, phosphorus and potassium, and is influenced by several factors, including the presence of beneficial micro-organisms.

Soil is a complex ecosystem inhabited by a wide range of organisms, from micro-organisms such as bacteria and fungi to macro-organisms such as earthworms. These organisms play a vital role in soil health and fertility. They are involved in decomposing organic matter, cycling nutrients, improving soil structure and controlling pests. They also contribute to carbon storage and atmospheric nitrogen fixation in the soil.

The abundance of micro-organisms in soil is staggering, with hundreds of millions per gram of soil. These organisms are essential for maintaining and improving soil fertility, which in turn influences agricultural productivity and long-term sustainability. Agricultural management and environmental protection focus on preserving this diversity and function of soil organisms.

Leave a Reply

Your email address will not be published. Required fields are marked *

We use cookies to personalise content and ads, to provide social media features and to analyse our traffic. We also share information about your use of our site with our social media, advertising and analytics partners.

View more
Cookies settings
Privacy & Cookie policy
Privacy & Cookies policy
Cookie name Active

Who we are

Suggested text: Our website address is:


Suggested text: When visitors leave comments on the site we collect the data shown in the comments form, and also the visitor’s IP address and browser user agent string to help spam detection.

An anonymized string created from your email address (also called a hash) may be provided to the Gravatar service to see if you are using it. The Gravatar service privacy policy is available here: After approval of your comment, your profile picture is visible to the public in the context of your comment.


Suggested text: If you upload images to the website, you should avoid uploading images with embedded location data (EXIF GPS) included. Visitors to the website can download and extract any location data from images on the website.


Suggested text: If you leave a comment on our site you may opt-in to saving your name, email address and website in cookies. These are for your convenience so that you do not have to fill in your details again when you leave another comment. These cookies will last for one year.

If you visit our login page, we will set a temporary cookie to determine if your browser accepts cookies. This cookie contains no personal data and is discarded when you close your browser.

When you log in, we will also set up several cookies to save your login information and your screen display choices. Login cookies last for two days, and screen options cookies last for a year. If you select "Remember Me", your login will persist for two weeks. If you log out of your account, the login cookies will be removed.

If you edit or publish an article, an additional cookie will be saved in your browser. This cookie includes no personal data and simply indicates the post ID of the article you just edited. It expires after 1 day.

Embedded content from other websites

Suggested text: Articles on this site may include embedded content (e.g. videos, images, articles, etc.). Embedded content from other websites behaves in the exact same way as if the visitor has visited the other website.

These websites may collect data about you, use cookies, embed additional third-party tracking, and monitor your interaction with that embedded content, including tracking your interaction with the embedded content if you have an account and are logged in to that website.

Who we share your data with

Suggested text: If you request a password reset, your IP address will be included in the reset email.

How long we retain your data

Suggested text: If you leave a comment, the comment and its metadata are retained indefinitely. This is so we can recognize and approve any follow-up comments automatically instead of holding them in a moderation queue.

For users that register on our website (if any), we also store the personal information they provide in their user profile. All users can see, edit, or delete their personal information at any time (except they cannot change their username). Website administrators can also see and edit that information.

What rights you have over your data

Suggested text: If you have an account on this site, or have left comments, you can request to receive an exported file of the personal data we hold about you, including any data you have provided to us. You can also request that we erase any personal data we hold about you. This does not include any data we are obliged to keep for administrative, legal, or security purposes.

Where your data is sent

Suggested text: Visitor comments may be checked through an automated spam detection service.

Save settings
Cookies settings