Soil looks simple. But a small clump contains an entire world teeming with life. Understanding microbial life in soil changes how people think about growing plants.
Microbial biomass carbon varies around a median of 206 micrograms per gram of soil.
The Invisible Workers Underground
Soil microorganisms, including bacteria, fungi, and archaea, drive essential soil functions such as nutrient cycling, organic matter decomposition, and disease suppression.
Bacteria often represent the most numerous group. They break down dead plant material and transform nutrients into forms plants can use. Some bacteria fix nitrogen from the air, turning it into fertilizer that plants need for growth.
Fungi contribute heavily to soil structure and the break down organic matter, significantly contributing to the conversion of carbon to stable organic matter. This makes fungi extremely efficient at building long-term soil health.
How Do Bacteria Help Plants Grow?
Bacteria do several important jobs in soil. As they decompose organic matter like leaf litter or dead roots, nutrients locked inside dead material are released and become available for plants to use.
Nitrogen-fixing bacteria work with plants in special partnerships. Bacteria like Rhizobium form symbiotic relationships that fix nitrogen, converting atmospheric nitrogen gas into usable ammonia that plants absorb through their roots. This free fertilizer helps plants grow strong without chemical additions.
Some bacteria dissolve minerals in soil. Bacteria such as Micrococcus, Enterobacter, and Pseudomonas play crucial roles in phosphorus solubilization, making phosphorus available for plant uptake. Plants need phosphorus for root development.
Understanding Fungi’s Critical Role
Fungi look different from bacteria; not only are they larger, but they have slightly different pigments. Fungal biomass is necessary for healthy soil—their size and structure give them special abilities.
Fungi break down tough plant materials like wood and tree bark. They produce special enzymes that dissolve lignin, the substance that makes wood hard. This decomposition creates rich, dark soil called humus that holds moisture and nutrients.
How Farming Practices Affect Soil Microbes
Fungi and bacteria keep each other in check through symbiotic relationships. Different plants prefer different ratios of fungi to bacteria. Annual crops may prefer lower fungal-to-bacteria ratios, while perennials prefer higher ratios. Forests have the highest ratios because trees depend heavily on fungal networks for nutrients.
According to a study by Lori et. al. in 2017, organic farming systems show 32 to 84 percent greater microbial biomass compared to conventional systems. Adding compost, manure, and cover crops feeds soil microbes and helps grow their populations.
Chemical fertilizers and pesticides harm soil microbial communities. Fungicides kill both harmful and helpful fungi. Without beneficial fungi, plants struggle to access nutrients and water. This forces farmers to add more chemicals, creating a cycle that damages soil health.
Understanding Soil as a Living System
Soil microbial biomass represents the foundation of productive agriculture and healthy gardens. When people protect and feed these microscopic workers, they foster plant-soil interactions and receive a stronger and healthier soil community.
Learning about soil microbes transforms how people garden and farm. Every decision—from whether to till, what to plant, and how to fertilize—affects billions of organisms working underground. Making choices that support microbial communities creates healthier soil, stronger plants, and better harvests that last for generations. Use the microBIOMETER® soil test to estimate your soil microbial biomass and ensure you have the healthiest soil possible.
Overton Environmental Enterprises, Inc. is a Canadian company that develops innovative biotechnology solutions that reduce reliance on chemical fertilizers and pesticides.
Their EcoTea™ products and research are focused on helping farmers work with soil ecosystems instead of against them. In their years of research they have proven direct results from using broad spectrum biology but the impacts in the soil and changes in soil quality have been harder to showcase.
Three seasons ago they discovered the microBIOMETER® testing system. These tests have given them a way to benchmark pre application conditions, the post application changes and most importantly the improvements over time. This real-time way for farmers to see the unseeable has given them confidence in the value of biology for their soils and programs. They use microBIOMETER® to augment field data (i.e. help correlate scores with plant health data and yield). microBIOMETER® has allowed them to show how EcoTea™ can influence root bacterial to fungal ratios and determine (at least in part) the amount of resources the plant is allocating to the rhizosphere.
The microBIOMETER® has given us another way to showcase how re-introducing biology can help our soils and the hard-working communities that rely on them.”
EcoTea™ is a biological product with biodiversity like no other, built on the vision of soil biodiversity enhancing professional success. EcoTea™ combines a wide array of plant-supporting microorganisms fortified with added biostimulants to enhance soil quality and nutrient function. Diversity is the key, allowing our products to adapt and meet your individual site needs, based on plant response and requirements. Our proprietary process built with ecological engineering provides the functional microbial community associated with healthy crops and soil.
BioHub Solutions, an Australian company that provides biological solutions to the agricultural industry, has incorporated microBIOMETER® into their business. BioHub Solutions believes measurements should be simple whenever possible to ensure their implementation and repeatability. microBIOMETER® has become an integral part of the BioPlan processes. Growers also like it because it provides instant feedback and accountability for Biohub’s biological strategies.
“Our trees continue to do well against the control in areas such as average plant height growth, trunk to height ratio, and fungi to bacteria ratio utilizing microBIOMETER®. This is pleasing so far and we will continue measurements.”
Green bean study in North Queensland.
Green bean trial in North Queensland (above). Initial samples taken 2 weeks before harvest. So far overall bean numbers are 36% improved over control. More importantly, marketable sized numbers are improved by 52%. This is where the margin is for the grower. Microbial biomass is also 28% higher than control which is pleasing. Looking forward to the full harvest figures if they reflect the initial samples taken.
Olive rootstock (below). The data has indicated on average, a 17% increase in stem diameter over the control. Root weight improvements of 47%, biology biomass improvements of 46% and fungal to bacterial ratio improvements of 56% over control. This illustrated that the BioHub solution achieved results in the manner the team had predicted. Photo depicts an example of the treated plug on the left and control on the right.
Olive rootstock – treated
Olive rootstock – control
Different methods measure different fungal and bacterial populations. The chart below, adapted from Wang et al review of 192 different F:B ratios, illustrates how three different methods came up with three different F:B ratios for Forest, Farmland and Grassland. Note that microBIOMETER® correlates well with the gold standard, microscopy. By plate culture, forest F:B is about 1/3 that of farmland, whereas PLFA forest F:B is slightly higher, and microscopy and microBIOMETER® forest F:B are 10 times higher than farmland.
Soil microbes are tightly bound to and often covered in soil making them very hard to evaluate by microscopy. The special magic of microBIOMETER® is the extraction powder and whisking process that separates most of the microbes from the soil. And during the 20 minute settling time allows the soil particles to precipitate leaving the extraction fluid >95% microbial.
This allows microBIOMETER® to examine 100 – 1000 times more microbes than any other method. When you apply extraction fluid to the membrane in the test card the colored microbes are captured on the surface of the membrane. A cell phone picture of the card is analyzed by the app and the intensity of the color of the microbes indicates their quantity – this is the basis for all laboratory colorimetric tests. We discovered that the fungi in soils are a slightly different color than bacteria, and so the app is able to distinguish between bacteria and fungi.
Click here to see a full video tutorial of microBIOMETER® soil testing.
Source: Food Web and Soil Health
The graph pictured here from the USDA website depicts the ratio of fungi to bacteria as a characteristic of the type of system it is in. An excerpt from the article:
“Grasslands and agricultural soils usually have bacterial-dominated food webs – that is, most biomass is in the form of bacteria. Highly productive agricultural soils tend to have ratios of fungal to bacterial biomass near 1:1 or somewhat less. Forests tend to have fungal-dominated food webs. The ratio of fungal to bacterial biomass may be 5:1 to 10:1 in a deciduous forest and 100:1 to 1000:1 in a coniferous forest.”
If you are measuring soil attached to the roots colonized by mycorrhizal fungi, your ratios should be much higher than is shown for agricultural soil. Also the saprophytic fungi population increases when there is a lot of litter for digestion, so you would expect to see different ratios at different times of the year and under different conditions.
The graph pictured below based on USDA website information shows the expected fungal to bacterial ratio for various plants.
Please visit our Using the Fungal to Bacterial Ratio with microBIOMETER® on YouTube for more information on fungal to bacterial analysis.
