Microbial biomass (MB) is the best single indicator of soil health (Doran, 2000). Microbes feed and protect plants, build soil structure which prevents erosion, increase water holding capacity, and build soil organic matter (SOM). MB is low in any situation that is harmful to plant growth (and vice versa) and protects against pathogens, thereby reducing the need for pesticides. MB can predict success before plant outcome. The Fungal:Bacterial ratio (F:B) of the MB provides crucial information regarding colonization by Arbuscular Mycorrhizal Fungi (AMF), and the recycling metabolic processes of saprophytic fungi (SpF).
Soil stewards all over the world are seeking to understand the microbial levels in their soil and the ratio of fungal to bacterial life. The higher the microbial biomass, the more nutrients will be available to plants naturally, decreasing or eliminating the need for chemical fertilizers. Higher fungal to bacterial ratios are critical for building soil structure that prevents erosion and runoff off of pollutant chemicals while building moisture holding capacity of the soil and sequestering carbon.
Soil health is fast becoming one of the most important factors in agriculture and in the growing efforts to improve the earth’s stock of agricultural land. Farmers, industry, and environmentalists are looking for cost-effective and reliable ways to measure soil health and to assess impacts of progressive changes to soil and harvest management.
Testing soil in homogeneous sections at similar stages of the growth cycle can set a baseline for microbial biomass and fungal to bacterial ratio. That baseline can be used to assess how different stewardship practices are impacting the soil and allow for refinement to soil management plans and show soil health improvement over time. While every soil steward’s situation is unique, microBIOMETER® can help measure, follow, and assess efficacy of improvement to soil health.
Many first-time cannabis growers don’t think too hard about the soil their plants will be growing in. If the soil looks healthy enough, it should be good to go, right? Well, it might be, but that isn’t enough information to tell for sure. If you really want to know whether your cannabis will thrive, you’ll have to see whether or not your soil contains a solid amount of microbes.
Microbes have a mutually beneficial relationship with the plants in their soil, and supporting microbes is one of the best ways you can support your cannabis. As we go along, we’ll be discussing the details of microbial presence in soil, the relationship between microbes and plants, and the specific organisms that make optimal growth possible.
Why Microbes Play a Vital Role in your Cannabis Plant Health
Microbes are key if you want your cannabis plants to grow as well as they can. If the idea of beneficial bacteria is strange to you, remember that we, ideally, have loads of bacteria in our bodies that keep us healthy. We’re not made of soil, of course, so things don’t work exactly the same, but the microbes in soil and those in our guts share key functions in common. Namely, as we’re about to explore, microbes provide vital nutrients to the plants in their soil, along with protecting them from harmful forces.
How Microbes and Cannabis Plants Work Together
With that in mind, let’s take a look at how the relationship between microbes and the cannabis plants you are growing play out in the soil. Plants need sufficient amounts of phosphorus, potassium, and nitrogen to survive and microbes have a direct hand in how much of those nutrients your plants receive.
While the nutrients may be in the soil already, they aren’t as accessible as they could be. Potassium, for example, is often shrouded in inorganic material. As microbes happen upon it, they’ll consume it, metabolize it, and excrete it in a form much more readily consumed by the plants. While the others aren’t as hard for the plant to get to, the microbes break them down nonetheless, and the plants benefit greatly from the enhanced access. This effort is further assisted by their ability to aerate the soil, ensuring there’s an even flow of water and nutrients.
The microbes aren’t only doing all this from the goodness of their heart, though. As the plants are fed, their roots excrete a collection of substances, called exudates, into the soil. These exudates, which include a variety of amino acids, organic acids, and sugars, happen to be a great source of nutrition for the microbes. With their microbe bellies full, the nutritional cycle is fully formed, and the plants are ready to thrive.
The Importance of Fungi for Growing Cannabis
While we think of fungi as separate from microbes, they’re part of the club too, and serve the same cause. To be clear, though, this is because they also partake in the exudates to stay fed.
Mycorrhiza fungi, in particular, can be found acting as the extension of plant roots, collecting nutrition from further down the soil than plants would be able to otherwise.
One type, ectomycorrhizae, acts as a sort of sheath for the root, extending out for nutrition. Endomycorrhizae, however, actually live inside the plant, helping to bring the nutrients straight into the root. To preserve them, ensure that you’re not being heavy-handed with fertilizers. Of course, you should also avoid fungicides entirely.
Microbial Dangers, and How Other Microbes Stop Them
As the fungi provide nutrients to the roots, they serve as a protective layer for them as well. But what, exactly, do they need protecting from? Well, among the beneficial microbes, there are thousands of microscopic worms, called parasitic nematodes, that feed on the roots of plants.
Looking from the outside, you’d notice roots facing attacks from ectoparasitic nematodes, which live in the soil right outside said roots (the rhizosphere). At the same time, endoparasitic nematodes are able to enter the roots themselves, breaking them down from the inside.
In anticipation of this threat, fungi will utilize their hyphae, which are the tiny strands that make up their mycelium. Using these strands, the fungi are able to locate and trap both types of nematodes, preventing them from further chewing at the root.
The fungi also receive help from, interestingly enough, other nematodes. They aren’t quite the same, though; while the others are parasitic, these are known as predatory nematodes. They, too, dwell in the rhizosphere, but only to eliminate plant-eating threats in the area.
How Earthworms Play a Part
Not every part of this underground battle is microscopic, though. In fact, the humble earthworm will be one of the main lines of defense for your cannabis plant. Parasitic nematodes happen to be a favorite prey of theirs, so they’ll munch up whatever your fungi and other microbes can’t catch. In turn, the waste they excrete contains nitrogen, phosphorus, and potassium (the three vital nutrients we mentioned earlier), along with calcium and magnesium. They also aerate the soil as they move around, ensuring the plant has easy access to the natural fertilizer.
How Benefits Show Themselves in Cannabis Plants
If you’re able to ensure optimal conditions for your soil microbes, you’ll notice it pretty quickly as your cannabis plants mature. Their leaves will be greener and fuller, they’ll end up on the taller side, and your buds will be notably larger and more resinous than average.
Your plant may be able to survive without a healthy amount of microbes, but it’ll look amateur in comparison. That’s not to mention the cost of those seeds adding up, leading you to lose money you could spend on expanding your growing operation. Armed with this new information, you won’t even have to worry yourself with the thought. Just keep those microbes and worms alive, and you’ll be on your way to hefty yields of potent buds!
microBIOMETER®, a rapid, on-site soil test, will help you determine the microbial levels in your cannabis soil as well as the fungal to bacterial ratio to ensure the healthiest environment for optimal growth of your plants.
Until now tests for microbial biomass were expensive and time consuming. microBIOMETER® costs $13.50 or less and takes 20 minutes with results read by your cell phone.
* Only microBIOMETER® identified soil health in a U. of Tennessee study of soil health test methods including Cornell, USDA, Alabama and other soil health panels costing ten times as much.
* There are >2 million academic articles that use microbial biomass laboratory tests as proof of soil health. However, lab tests cost $100 – $500. microBIOMETER® takes 20 minutes at an average of $10/test.
* Soil microbes quickly die when removed from the soil. microBIOMETER® reveals the microbial biomass of your soil as it exists. Lab tests use dried soil and we have demonstrated that 80% of microbes die upon drying.
* The low cost and simplicity of microBIOMETER® means you can use it to monitor what is happening in time to make necessary corrections.
* microBIOMETER® can tell you if you are increasing your soil organic carbon. For instance, an increase in microbial biomass of 100 ug MBC/g per acre of agricultural land is equal to an elephant’s weight in microbial biomass, which is about 400 lbs of microbial carbon or >1450 lbs of CO2 equivalents. This can be accomplished by switching from heavy chemical fertilizer use to regenerative practices.
Arbuscular Mycorrhizal Fungi (AMF) colonize 80% of crops. Their effect on plant growth can be positive, neutral or negative. It depends on many factors including the crop species and genotype, the species of AMF, and the characteristics of the soil. A low pH favors colonization of the plant by AMF while application of chemical fertilizers, especially phosphate, inhibits colonization by AMF. In the absence of chemical fertilizers and in the presence of low levels of pH, AMF provides the plant with phosphorous. AMF can extract P from rocks so it can get P from soil that tests low for P.
AMF can dramatically increase plant yield and resistance to pathogens and drought, as well as decrease irrigation needs and sensitivity to salinity. Thus, AMF can be of great assistance in transitioning from conventional to sustainable/regenerative agricultural. There are now many suppliers of AMF but there is no guarantee that any one product will be optimal for your crop and your soil.
The new microBIOMETER® test, which estimates fungal to bacterial ratios in soil, can help you decide which AMF works best with your plant and soil because it can detect colonization of rhizosphere soil for fungi within a month of AMF application.
Leifheit, E. F., Veresoglou, S. D., Lehmann, A., Morris, E. K., & Rillig, M. C. (2014). Multiple factors influence the role of arbuscular mycorrhizal fungi in soil aggregation—a meta-analysis. Plant and Soil, 374(1-2), 523-537.
Leeston Pastoral is a 5th generation, family owned farm in New South Wales, Australia. Historically, they have had a fine wool Merino & Hereford cattle breeding operation. Over the last 20 years they have moved to focus on cattle.
The 2019 drought forced them to reevaluate what operation they wanted to continue in. They decided to adopt a more regenerative approach and move from a cattle breeding operation to a cattle trading operation. They now have one large mob grazing holistically using short grazes and long pasture rest periods.
microBIOMETER® has allowed them to quickly, easily and inexpensively record existing benchmark measurements of their soil microbiology and now reassess the effects of stock movements and plant/soil amendments. They are excited to see the new F:B ratio measurement, as they want to make sure the soils stay fungally dominated so they can more effectively create stored soil organic matter.
They were happy to see their microBIOMETER® results showed an almost 30% increase in microbial biomass and fungal to bacterial ratio one month after holistic grazing. Studies have shown that a 1.5x increase in your soil’s F:B ratio can lead to a 3x increase in carbon sequestration. Thank you Adam for sharing your experience with us!
The Sítio Escola Portão Grande is a Brazilian NGO, nonprofit organization which was founded in October 2012.
Sítio Escola Portão Grande hosted students from the Mentoring and Language Acquisition Program (MLAB) for a full day immersion at the farm in Brazil which featured soil testing with microBIOMETER®. MLAB is a mentoring and language acquisition program for Harvard students and Brazilian high school students, with low income and high performance. In addition to mentoring, the program brings foreign students to an immersion in Brazil, exploring themes that motivate them.
The students were delighted to observe the use of microBIOMETER® to assess fertility based on the measurement of soil microbial biomass. It was explained to the students that microBIOMETER® is used monthly to assess the evolution of fertility due to the different inputs applied to the soil, the crops and harvests carried out, as well as throughout the seasons. Therefore, providing a database of great importance to make future decisions. In addition, due to its ease of use, microBIOMETER® also proved to be an good tool to assess the quality of the inputs we produce on the farm, such as bokashi and compost tea, allowing the tuning of the culture media we use for them.
A big thank you to Antonio Feres Neto for sharing this story with us! We love hearing how our customers are using microBIOMETER®.
Types of fungal spores. The sizes vary from microscopic to visable..
Arbuscular Mycorrhizal Fungal (AMF) are dependent on the plant for their food, therefore, they die when the plant dies. Lucky for us before they die they form spores that can live a long time in the soil.
When we have looked at the soil from vineyards in winter it is filled with fungal spores. Pictured here of some of the types of AMF spores. The size of these spores can vary from microscopic to visible.
The spore starts growing when it receives a chemical message from a nearby plant. It has a day or two to reach the plant, enter the root and build a little space called an arbuscule where it can get food from the plant. If it fails at this, the fungi dies. This is why we like to plant seeds with AMF. The plant feeds the fungi because the fungi send out long hair like structures called hyphae that bring minerals and water back to the plant. In fact, scientists have recently shown that the fungi and the plant actually barter with one another, i.e. when phosphorus is low, the fungi gets more food for delivery of phosphorus.
microBIOMETER® measures both fungi and fungal spores as well as bacteria. The lab methods of PLFA and Carbon Fumigation do not adequately measure spores. Standard microscopy also does not adequately measure fungi.
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.
