Improving Soil Fertility With Fungi

Deano Martin
Tuesday, 3rd March 2015

Deano Martin explains how he makes his own fungal compost to increase his soil fertility.

Making a more fungal compost has been an aim of mine for some time. One of the ways that I do that is to not make 'hot' compost, keep the proportion of high carbon materials high, and to not turn unless it's needed. However recently I set up a truly fungal mix of ingredients and this post is about how that went.

Why make a fungal compost?

I first started thinking about making a more fungal compost after starting to make actively aerated compost tea. Some of the compost tea recipes call for a fungally dominant compost, and the forums were full of ideas of how to make that happen. I made leaf mould, and really good compost, but recently I've been thinking more about building my soil fertility without compost.

Soil fertility without compost

I have been continuing to learn more about soil. How it works, how nutrients are cycled, and what drives these processes. I keep coming back to an idea that when I compost I'm not building soil fertility, merely redistributing fertility that has already been made. If I make a conventional compost I am mixing carbon and nitrogen rich materials in a ratio of around 30:1. By the time that the compost is ready the ratio has dropped to around 10:1, meaning that 2/3rds of the carbon has been lost.

Now many of the cycles in soil work both ways. A good example of this is Nitrogen. It is both fixed and lost from the soil, but which of the two is prevalent depends on the carbon:nitrogen ratio in the soil. It takes energy for microbes to fix nitrogen, so if there are supplies of useable nitrogen in the soil, the nitrogen fixers use it, along with other soil life. It is only when the ratio of carbon to nitrogen increases that significant amounts of nitrogen is fixed by microbes. The phosphorous cycle works in a similar way. If the ratio of carbon to phosphorous is 200:1 or less, available phosphorous is bound up and becomes unavailable to plants. At a ratio of 300:1 or higher, microbes make available phosphorous that is bound up. Inbetween these figures both processes are taking place. Taking these into account, adding compost at a ratio of 10:1 doesn't make sense. I will be doing the work that microbes in my soil could be doing instead.

Growing carbon

If the key to building my soil fertility is carbon I need to do two things.The first is to produce the carbon, and the second is to ensure that the microbes that I need to utilise that carbon are present in my soil. The grain polycultures that I am growing will produce the carbon, both in the form of cellulose rich, lignified straw, and from root exudates. The point of the fungal compost is to ensure that the microbes that I need, predominantly fungi and actinomycetes, are present to deal with the raw materials that I will provide. The picture below is from one of my vegetable beds, and suggests that some of what I need is probably already there.


Indigenous Microorganisms and Biofertilizer

Indigenous Microorganisms (IMOs)

One way to get a wider range of microbes into my soil is to culture them. You can do that by collecting microbes from healthy environments, culture them, and then add them to the growing space. I used a version of the method described by Gil Carandang for making beneficial indigenous microorganisms, also known as Indigenous Microorganisms (IMO) in the Korean Natural Farming system. The next link gives a more accurate description of what I did (IMO). In fact I followed a cheat version as described in a series of youtube clips this is the first in the series.

The picture below shows the third stage, which is IMO3. What you can see is wheat bran that has been colonised by microbes that I collected on rice initially. As well as being added to my soil, some of this has been added to a special fungal compost mix which I'll describe shortly.



Recently I started making biofertilizer. These are microbial ferments designed to convert minerals into plant available form. It's a bit like replicating what would happen in the soil, but doing it under optimum conditions, and more concentrated. After repackaging the biofertilisers I poured the sloppy residue onto my fungal compost mix, and the lead picture (above) shows the result.

However I couldn't determine whether the fungal hyphae were present in the residue, or came from the compost mix. The fungal hyphae are too small to see with the naked eye, but the picture below shows a fungal fruiting body present in the fungal compost.


Fungal compost experiment

I decided to try and identify where the fungus was coming from so I mixed some of the diluted IMOs (IMO2 from the video series above), and added it to some wheat bran. I divided the bran into two containers, and added some of the fungal compost to one of the containers. From the other I took a handful of the bran and spread it on the top of the fungal compost. I left it for around five days. The pictures below show the results.

The first picture shows the bran only mixture. There are no visible signs of fungal hyphae, although there was some warmth from the center of the mixture.


The picture below is of the bran mix that had some of the fungal compost added. All of the bran has been colonised. The broken texture is just where I wanted to check how far the mycelium extended. Only a small amount of the fungal compost was added. Less than 10%.


The picture below shows the bran spread onto the fungal compost mix. Wherever there was bran there was fungus. This makes it pretty clear that the fungus is coming from the fungal compost mix, exploiting a new food source. It also indicates that the mix is a really efficient way of inoculating bran, and then using the bran to introduce the fungus to the soil or container. However the bran alone may not be the best way of getting a wide range of fungi and other microbes into the soil, as it may only be colonised by a small proportion of the decomposers present. Using a wide range of fungal food sources will increase the range that can be potentially cultured.


My Fungal Compost

In order to get a fungal compost mix, I added a range of high carbon sources, many of them already colonised by fungi, to an old bathtub kept in an outbuilding. The primary source was some well rotted leaf mould. This would have had fungi that were able to utilise lignin as a food source. Lignin is the resistant material in wood, and stiff stems like straw. To this I added shredded miscanthus grass. This is a source of lignin and cellulose, like straw, but already mechanically shredded. With these two materials I included some of my best compost. This was a cold compost, made with lots of high carbon materials, and was two years old. After the batch was started I added some of the IMO3 bran and mixed it in. As the primary material that will be added to my soil is straw, I will continue to feed the mix with more straw-like materials. I would also like to add some more woody materials, perhaps some shredded branches. Eventually I will divide the fungal compost into smaller batches, mix them with straw and bran, and when colonised, add them to my vegetable beds, probably before returning harvested straw.

This article originally appeared here:

Further resources

Plants and fungi - using beneficial mycorrhizal to boost plant growth