How to improve the Fungi : Bacteria Ratio in soil

Understanding and measuring the microbe biomass in soil is crucial to growing healthier plants, with bigger yields and nutrient-rich produce that’s more disease resistant. 

In simple terms, it’s identifying and measuring the range of little critters and analysing the dominant microbes – fungi and bacteria.

The higher the number and the greater variety then the stronger the relationship between microbes and plants, trading nutrients to support healthy plants, produce, immunity and life as we know it.

However, the critical component of a functioning soil ecosystem and its underground community is often overlooked.

Scientists and researchers are digging deeper into understanding healthy soil and how microbes play a key role in this. It’s the backbone of regenerative agriculture – growing healthy plants, crops and produce – and it’s becoming increasingly clear that maintaining a diverse range of soil microbes and a balanced fungi to bacteria (f:b) ratio is critical to sustain and protect life – food production, filtering and absorbing pollutants, greater immunity to disease and weather extremes for healthy growth.  

In this article, we examine the significance of microbes, and specifically the fungi to bacteria ratio, to support a high-functioning soil ecosystem, just as nature intended.

The Fungi to Bacteria Ratio of soil microbes

In healthy soil, there’s a dynamic interaction between the different types of microbes (bacteria, fungi, protozoa, nematodes and arthropods) and the distinct roles they each perform in a highly efficient, but complex trading relationship with plants. 

Fungi and bacteria are the most abundant, each playing important roles in the soil ecosystem. Fungi, with their thread-like structures called hyphae, form an underground network around plants that enhances nutrient absorption and water retention capabilities by expanding their reach. They excel at breaking down complex organic matter such as plant residues, creating a more nutrient-rich environment for plants. Bacteria, on the other hand, are largely responsible for the rapid decomposition of organic matter, making nutrients more readily available to plants.

The ideal fungi-to-bacteria ratio in soil depends on various factors, including the type of plants being cultivated and the soil’s specific requirements. However, a balanced ratio is generally considered to be around 1:1 or slightly higher in favour of fungi. This equilibrium creates a healthy soil structure, promotes nutrient availability, and supports robust plant growth.

Why the Fungi to Bacteria Ratio is Important

Nutrient Cycling: Fungi and bacteria perform different roles in breaking down organic matter. Fungi decompose complex compounds like lignin and cellulose to release essential nutrients to plants, while bacteria rapidly oxidize organic matter, converting it into plant-available nutrients. A well-balanced fungi-to-bacteria ratio ensures efficient nutrient cycling, making essential elements more accessible to plants.

Soil Structure and Aggregation: Fungal hyphae create a complex web-like structure that binds soil particles together, improving soil aggregation. This network enhances soil porosity, water infiltration, and root penetration. Adequate fungal activity helps create a stable soil structure, reducing erosion risks and waterlogging while promoting healthy root development.

Disease Suppression: Certain fungi in the soil form beneficial relationships with plant roots, known as mycorrhizae. Mycorrhizal fungi enhance nutrient uptake, improve plant resilience to stress, and even provide natural defence against soil-borne pathogens. Maintaining an optimal fungi to bacteria ratio encourages the proliferation of these beneficial fungi, thereby contributing to disease suppression and healthier plants.

4 ways to Improve the F:B Ratio

1. Organic Matter Amendments: Incorporating organic amendments like compost, cover crops, and crop residues to enrich the soil with diverse carbon sources, encouraging fungal growth.

2. Reduced Tillage: Minimising soil disturbance through reduced tillage practices preserves fungal networks and prevents disruption of their hyphal structures.

3. Proper Nutrient Management: Balancing nutrient inputs and avoiding excessive nitrogen applications helps maintain a healthy fungi to bacteria ratio. High nitrogen levels can favour bacterial dominance, while moderate levels promote fungal growth.

4. Incorporate Mycorrhizal Inoculants: Introducing mycorrhizal inoculants during planting can help establish beneficial fungal associations with plant roots, enhancing nutrient uptake and disease resistance.

Understanding the fungi-to-bacteria ratio and its significance in soil health is crucial for achieving bigger yields and healthier plants and produce. By maintaining a balanced ratio, farmers and growers can optimise nutrient cycling, improve soil structure, and support disease suppression. By implementing practices that promote fungal growth and considering the specific crops being cultivated, we can harness the power of the soil foodweb, rather than working against nature, reducing or even eliminating reliance on synthetics, pesticides, and chemicals.


A well-balanced f:b ratio helps with nutrient cycling, increases yield, improves soil structure, increases plant immunity and resistance to weather extremes and disease. It can result in reducing or eliminating the use of synthetics, pesticides, and chemicals, which can disrupt the soil community and starve soil microbes, having a significant impact on plant growth and production for different plant species.

The fungi-to-bacteria ratio (F:B ratio) in soil is a critical component for growing healthy plants and producing high-quality crops. Fungi and bacteria are both microorganisms that play essential roles in the soil ecosystem, but their relative abundance can significantly impact soil health and plant growth. In this blog post, we’ll explore the importance of F:B ratio and why you should test the ratio of your soil.

Fungi and bacteria are critical to soil health and plant growth because they perform many essential functions in the soil. Bacteria decompose organic matter and make nutrients available for plant uptake, while fungi form beneficial relationships with plant roots, helping them absorb nutrients and water more efficiently. Fungi also help to bind soil particles together, improving soil structure and reducing erosion.

While both fungi and bacteria are essential, they have different characteristics that can impact soil health differently. Fungi tend to be more slow-growing but form larger and more complex structures, like hyphae, which can penetrate deeper into the soil and break down more complex organic matter. Bacteria, on the other hand, tend to grow quickly and are more efficient at decomposing simpler organic matter, like sugars and amino acids.

The ideal F:B ratio for plant growth can vary depending on the type of plant and the growing conditions, but generally, a balanced ratio of around 1:1 is considered optimal. When the F:B ratio is skewed too far in one direction, it can negatively impact plant growth. For example, when bacteria dominate, they can quickly consume available nutrients, leaving less for plants to absorb. When fungi dominate, they can decompose complex organic matter too slowly, leading to nutrient deficiencies.

To ensure that your soil has a balanced F:B ratio, you should test the ratio periodically. There are a few different methods for testing F:B ratio, but one of the most straightforward methods is using a soil food web analysis. This test measures the levels of different microorganisms in the soil, including fungi and bacteria, and provides a comprehensive view of the soil ecosystem.

If you find that your soil has an unbalanced F:B ratio, there are several steps you can take to correct it. Adding organic matter, like compost, can help to promote fungal growth, while reducing soil disturbance can help to promote bacterial growth. Using cover crops and crop rotation can also help to balance the F:B ratio over time.

In conclusion, the fungi-to-bacteria ratio is critical to growing healthy plants and producing high-quality crops. It’s important to examine and support the soil microbes that manage this. By testing the F:B ratio of your soil, and taking steps to balance it, you can help to ensure that your plants have the nutrients and support they need to thrive.

Testing the F:B ratio

The microBIOMETER® soil test gives you the total microbial biomass and breaks it down into the % fungal and % bacterial. This new data allows you to assess if your efforts to increase soil fungi are working.

Finally, there is a way to measure if soil or related products actually team with microbes! The microBIOMETER® is an advancement in measuring soil food web activity that finally lets us know if our inputs are working. It is an invaluable new tool with tremendous potential to improve our soils

Jeff Lowenfels – Author of “Teaming with Microbes”, “Teaming with Fungi”,
and “Teaming with Nutrients”.

Available at

The microBIOMETER® soil test is now available in New Zealand at Available is the starter kit and two sizes of refill kits. Order today and get more accurat information about your efforts to improve your soil.

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