What is biological soil health, and why is it important?

by Juan Vicente Beneitez Lajas on 10/Aug/21

Biological soil health refers to the continued capacity of soil to function as a vital living ecosystem that sustains plants, animals, and humans by supporting the diverse community of microorganisms, including bacteria, fungi, archaea, and nematodes, living in the soil. These microorganisms play a key role in soil quality, nutrient cycling, disease suppression, and the overall health of plants by decomposing organic matter and material, storing energy and nutrients used by plants, creating biodiversity, and supporting natural soil food webs.

Additionally, soil biology is essential for the functioning of the nitrogen and phosphorus cycle, among others. In addition to the phosphorus and nitrogen cycles, soil biology is also essential for the functioning of other important nutrient cycles. These include:

Carbon cycle: Soil biology plays a critical role in the carbon cycle by decomposing organic matter and releasing carbon dioxide into the atmosphere. At the same time, soil microorganisms can also store carbon in the soil, contributing to soil fertility and mitigating climate change.
Sulfur cycle: Sulfur is an essential nutrient for plants and soil microorganisms. Soil bacteria and fungi play a crucial role in the sulfur cycle by breaking down organic matter and releasing sulfur compounds into the soil.
Water cycle: Soil microorganisms also play an important role in the water cycle by enhancing soil structure and porosity, improving water infiltration, and reducing runoff and erosion. This helps to maintain healthy soil moisture levels and support plant growth.
Nutrient cycling: Soil biology also involves cycling other essential nutrients such as potassium, calcium, and magnesium. Soil microorganisms help to break down organic matter and release these nutrients into the soil, where they can be taken up by plants.

Functional Groups

Soil microorganisms can be classified into functional groups according to the biological function they take on in a given ecosystem. For example, “all microorganisms that act in the N cycle (e.g., diazotrophic, nitrifying, denitrifying, ammonifying and proteolytic bacteria, etc.) and C cycle (e.g., cellulolytics, amilolytics, proteolytics, etc.) are examples of functional groups''. Here, the focus is not the individual species themselves, but the role they play collectively in an environment. Regardless, all of the biological components or biological communities of soil such as plants, animals, insects, earthworms, nematodes, arthropods, protozoa, fungi, and bacteria, are crucial components of soil health.

Microbial Community

Because the microbial community or microbiome are responsible for much of the recycling and transport of nutrients and water that occurs in the soil, they too are essential for overall soil health and productivity. According to Cardosa et al., “a teaspoon of soil can contain a billion bacterial cells, several to hundreds of yards of fungal hyphae, thousands of protozoa, and 10-20 nematodes (Ingham, 2018).”. As an example of some of the benefits of this microbial community, Rhizobium bacteria fixes nitrogen in legumes such as soybeans. Arbuscular mycorrhizal fungi (AMF), a group of beneficial fungi, form close bonds with plants and help them absorb nutrients.

Soil Biological Buffering

Contrary to chemical and physical properties, soil biological components can help with resistance, which is the ability of communities or populations to remain unchanged when stressed by a disturbance. Because “soil with high microbial diversity has more chance to keep the ecological processes after a disturbance.”.

Biochemical Indicators

Besides microbial activity and biomass, biochemical indicators i.e. soil enzymes, are another useful indicator of soil health. They are similarly responsive to changes in soil use and management. During carbon and nutrient cycling in soil, enzymes act as catalysts in different reactions. Additionally, soil respiration, production of carbon dioxide via soil organisms, has also been used widely as a bioindicator of soil health.

Importance of Biological Properties

“Biological properties” as expressed by one noted agronomist “are a forgotten and neglected dimension during more than a century of intensive agriculture practises.” But now that biological properties have gained more and more scientific evidence to support their importance, we can arrive at the conclusion that a combination of all three properties will ultimately lead to ideal soil health and productivity.

What is the relationship between soil biology and plant health?

The relationship between soil biology and plant health is complex and multifaceted. Healthy soil biology can support healthy plant growth by providing nutrients, improving soil structure, and suppressing diseases. Conversely, unhealthy soil biology can lead to nutrient deficiencies, poor soil structure, and increased susceptibility to pests and diseases. Optimal chemical, biological, and physical properties promote healthy soils, which occur when their soil organisms are balanced and diverse.

Soil organisms contribute to nutrient cycling, which is essential for plant growth and development. Plants and microorganisms obtain their nutrients from the soil and change soil properties through organic litter deposition and metabolic activities. Beneficial microorganisms facilitate the cycling of organic matter and nutrients, allowing the soil to continue supporting life. Changes in root architecture, induction of root-based transport systems, and associations with beneficial soil microorganisms allow plants to maintain nutrient uptake. Overall, soil biology plays a critical role in plant health by providing the foundation for healthy soil and supporting the nutrient cycling and root development necessary for healthy plant growth.

How can I assess the biological health of my soil?

There are several methods to assess the biological health of the soil, such as using biological soil testing methods, such as soil microbiome analysis can provide information about the types of microorganisms in the soil and what functions they provide. Also, earthworm counts, soil respiration, and examining plant root systems can offer simple ways to assess soil biological health.

You can also examine the root systems of plants, which can provide clues about the health of the soil, and use plant growth and yield as indicators of soil health.