Biochar

Soil in the rain forest is some of the poorest on earth. Plants absorb the nutrients they need through their roots, relying heavily on the plants being soluble in water. A rain forest, true to its name, rains almost constantly. That rain picks up the nutrients in the soil and washes them away. The various living organisms try to hold on to those nutrients by locking them away in their bodies, but eventually those nutrients are returned to the soil. The soil cannot hold on to them. So when explorers discovered lenses of dark, black, fertile soil in the interior of the Amazon Basin, it came as a big surprise.

The soils came to be called terra preta soils and have been the subject of much study. Due to the high concentration of pottery sherds, bones, charcoal, and other indicators of human life, it was obvious that the soils were made by a previous civilization. But it was initially unclear why the soils retained such a high degree of fertility, with fertility possibly even increasing over time instead of degrading as would be expected. It turned out that the cause was the concentration of charcoal in the soil that was doing it.

The study of this soil led to the discovery of biochar, a form of charcoal produced by pyrolysis, creating the charcoal at high temperatures and in a relatively low oxygen environment. The physical and chemical structure of biochar acts a lot like the carbon commonly used in water and air filters. It is extremely porous, leading to a high surface area, one that is really good at cation exchange. For the lay person, that means it bonds with a wide variety of compounds, holding them in place. In a carbon filter, this means it bonds with soluble lead, arsenic, and chlorine, things you want removed from the water so it is safe to drink. In soil, this capability is more applicable to nitrogen, phosphorus, and potassium. Biochar in soil can hold on to the very nutrients that plants need to survive and thrive.

The benefits don't stop there, though. Because of biochar's porosity, it is also very good at retaining water. Interestingly, the open structure of biochar seems to be an ideal support for microbial life. Beneficial bacteria and fungi thrive in the environment created by biochar. The nutrients bound to the biochar are easily accessible to the microorganisms crawling all over the surface, where they can become a part of the life cycle of the soil, eventually to end up in plants.

So what does it mean for food production? Biochar has a huge potential in agriculture. One of the great frustrations of modern agriculture is that soil fertility is falling. To combat that, soils are heavily treated with synthetic fertilizers. Those fertilizers wash away readily in the rain, meaning that more need to be added. But it also causes a problem downstream. All that fertilizer in the water causes an algae bloom. That algae bloom is followed by the algae dying. As the algae in the water column starts to rot, it steals oxygen from the water, killing fish, crustaceans, and anything else, creating a dead zone. The annual dead zone on the Gulf of Mexico reached 6400 square miles in 2015. All that fertilizer used to make that dead zone was purchased by farmers, each one hoping that that fertilizer would go to their plants.

So what if something could be added to the soil that helped all that fertilizer stay in place? What if that amendment also increased water retention, thereby increasing drought tolerance? What if it also increased beneficial microbial activity, the very activity that supports plant growth? And where does it come from? We really like having trees in our cities, and we like them to be well trimmed. Those trimmings typically head for the landfill. What if we diverted that waste product instead and made our soils better? That biochar could be added to farmland, and just like in the Amazon Basin, that fertility could be realized for hundreds of years. Biochar can take hundreds or even thousands of years to degrade in a natural environment, and it improves the soil that whole time.

But what about more modern, higher tech growing methods? Could biochar be used as media for hydroponics or aquaponics? I have seen a lot of discussion of the possibility online, but very little actual data on whether it works or not. I think that an analysis of what biochar does and how it would apply to hydroponics and aquaponics might be in order.

Again, biochar absorbs nutrients and holds on to them. It will do this with huge amounts of nutrients. Now, biological activity can access those nutrients (remember the "exchange" part of cation exchange) and help feed them to the plants. But that means two things for aquaponics and hydroponics. The first is that the biochar is going to absorb a LOT of nutrients until it is filled up. In land-based agriculture, the biochar is typically "charged" or pre-filled with nutrients before being added to the soil. In hydro- and aquaponics, that doesn't necessarily have to happen, but the grower needs to know that the biochar will take its fill before the plants can get it, and that process can take some time, perhaps weeks or months.

The second thing to recognize is that it is the biological activity that exchanges all those cations. Fungi is particularly active in that process, but bacteria are also important. Without that living system, the biochar will just act as a nutrient sink that will have to be filled before a regular nutrient profile can be maintained.

Biochar in a properly alive media would have a stabilizing force on the nutrient load of the media. Once it is full, the bacteria and fungi can access it if nutrients drop too low and it will absorb when nutrient loads are too high. Adding it while a tank is cycling might help lessen the stress on the fish, but the grower might want to refrain from adding plants until the nitrate level starts to climb, indicating that the biochar filter is full. Also, adding it as a supplement to the media rather than as a media in itself would be a good idea, perhaps 20% or less.

As for me, I do aquaponics with soil. The soil I create is a vibrant, living community that holds its own nutrients pretty well and should have no trouble accessing nutrients held in the biochar. I am working on expanding and creating new aquaponics beds and will be trying biochar as a supplement to the soil in the system, probably at around 20% of total volume. I will report back on how that worked when I have more information.

Primary vs. Secondary Decomposing Mushrooms

Shaggy manes, a great example of secondary decomposers

There are many different kinds of mushrooms out there, classified by their source of food. Parasitic mushrooms attack living organisms. Mycorrhizal mushrooms form a symbiotic relationship with plants, trading nutrients for sugar. But when it comes to the world of mushroom cultivation, the real species of interest are the saprophytes, the mushrooms that decompose dead tissue. But even those come in several different varieties. There are primary, secondary, and tertiary decomposers. Tertiary decomposers are mushrooms that live in soil, scraping out a living on the little scraps of nutrition they can find here and there. Very few are of culinary significance. Primary and secondary decomposers, on the other hand, are the species that compose the majority of our culinary mushrooms.

When a tree falls in the forest, it is the primary decomposers that move in and start the process of turning the body of the tree back into soil. Think about the trunk of a tree. While the tree is alive, there isn't much living inside the tree, besides the tree, of course. Plus, it is made of solid wood (weird how that works, eh?) and most living creatures can't penetrate through to get to the energy stored in the wood. Fungal species are quite adept at it, though, and among the mushrooms, there is still lots of competition for any new food source. Once the primary decomposer detects an available food source, it throws all its energy towards occupying it. Growth is very rapid and it grows a huge amount of tissue in a fairly dense concentration.

Once it has colonized what it can grab, the primary decomposer produces a flush of mushrooms, then proceeds to decompose as much of the food source as it can.

Chunk of wood that has been fully decomposed by white rot
fungus, still looks like wood

However, primary decomposers are not particularly complete in how much they decompose. Most are either brown rot fungus, which means they decompose the cellulose and leave the lignin behind, or white rot fungus, which means they decompose the lignin and leave the cellulose behind. Either way, the wood still looks pretty much like wood when the fungus is done with it. It is just a whole lot softer and lighter.

The secondary decomposer moves in and picks up where the primary decomposer left off. It certainly feeds on the cellulose and/or lignin that is left over, but it also decomposes the other compounds present in the tree.

The biggest difference between the two is the type of environment they prefer to grow in. The primary decomposer is adapted to the inside of a freshly fallen log. They prefer an environment with little to no competition. They produce ideally on pasteurized sawdust, straw, or something similar. Secondary decomposers are a little different. In nature, once the primary decomposers have finished, insects, soil bacteria, and all kinds of other organisms have started invading. It provides a richer micro-ecosystem. This is the preferred habitat of the secondary decomposers. Some won't even produce mushrooms in sterile substrate. Several even prefer a well-composted substrate that still has some woody/fibrous components to it.

The same piece of wood as above, just squeezed to show
how soft it is. It is ready for a secondary decomposer

As for how to tell the difference, just look at the growing requirements. If the mushroom will fruit off of just sawdust, vertical or horizontal surface, it is probably a primary decomposer. If it requires a casing layer and only fruits from a horizontal surface, it is probably a secondary decomposer. Examples of primary decomposers are shiitake (Lentinula edodes), oyster (both Pleurotus and Hypsizygus species), reishi (Grifola frondosa), and pioppino/black poplar (Agrocybe aegerita). Examples of secondary decomposers are button/portobello (Agaricus brunescens), king stropharia (Stropharia rugoso-anulata), and shaggy mane (Coprinus comatus).

Considering my current projects, what are the implications of this information? Well, the main thing is that when mixing mushrooms and gardening, the information about what habitat the mushrooms like is very important. So when you are doing it in aquaponics, like I am, there need to be some minor adjustments to how you do it. For example, if you are doing traditional aquaponics, using media, primary decomposers are going to be your best bet. But rather than sawdust/woodchip blocks, which is the usual preferred method, partially buried logs would be best. The worms would gobble up the blocks too soon, whereas they would do no appreciable damage to the logs.

On the other hand, if you are doing aquaponics with soil, both primary and secondary decomposers can be used. The primary decomposers will still do better in logs, but the active soil in an aquaponics system can be really beneficial for secondary decomposer mushrooms. Plus, they would add additional filtration for the water.

A little over a year ago I created a woodchip bed in my aquaponics system using king stropharia mushrooms. The results were better than expected. They obviously thrived in that environment. I intend to keep experimenting as often as I can manage. I think there are great combinations out there yet to be discovered.

GeekDad: The Best Garden Supplement Is as Natural as Your Plants

I have a new blog post up at GeekDad this morning. It is all about mycorrhizal fungus. You can check it out here.

Mycorrhizal Fungus

If I had to pick what is the most important thing to do for your plants to ensure their health and vigor (other than basic needs, like sunlight, water, etc.), it would be really hard to choose between compost and mycorrhizal fungus. In the end, though, I would probably choose mycorrhizal fungus, just because there are more plants that are adapted to rocky, nutrient poor soils than there are plants adapted to life without mycorrhizal fungus.

Mushroom-producing fungus (hereinafter abbreviated to "mushrooms") fall primarily into three categories: parasitic, saprophytic, and mycorrhizal. Parasitic mushrooms harm and/or kill other living organisms. Saprophytic mushrooms break down organic matter that is already dead. Mycorrhizal mushrooms are a bit more complicated to define and are the subject of this post.

The discovery of mycorrhizal mushrooms, exactly what they do and how amazingly important they are is a relatively recent one. Scientists have discovered that the root system of plants doesn't really do what we thought it does, at least for most plants. It turns out that roots aren't all that good at collecting water and nutrients from the soil. The roots' main purpose is to connect up to networks of fungus that live in the soil nearly everywhere called mycorrhizae. The plant then forms a symbiotic relationship with the fungus. The plant provides sugars to the fungus through its root system, in some cases sending as much as 80% of the sugar the plant produces. The fungus, in turn, does what it does best. It sends filaments far and wide to search out the nutrients that the plant needs, break them down, and deliver them right to the roots of the plant. Think of it like a living fertilizer, getting the most out of the soil. It also seeks out and concentrates water, delivering that to the plant as well, increasing the drought tolerance of plants. It turns out that approximately 90% of all plants on earth, including all or nearly all of our cultivated, food-producing plants, are evolved to take advantage of this relationship. Plants that have the appropriate mycorrhizal mushrooms in the soil with them will be healthier, grow faster, resist pests and diseases better, be more drought tolerant and have a much better chance of surviving stressful conditions.

My first attempt to use mycorrhizal fungus was a dramatic one. I have a tree aloe in a pot. When I got it, it was about 4 inches tall. Over the next 4 or so years, it grew to be about 8 inches tall. I finally decided it needed to be repotted. About this time, I bought my first treatment of mycorrhizal mushrooms. When I repotted the tree aloe, I inoculated them with the mycorrhizal mushrooms. Normally when you repot a plant, it sits there for about two weeks in transplant shock while it repairs its root system and adjusts to its new environment. My tree aloe showed obvious new growth the next day. Over the next 6 months it grew from 8" high to nearly 2' high.

The most dramatic example I have heard of regarding what these amazing mushrooms can do was from an experiment performed by mycologist Paul Stamets. He went out in the woods in the Pacific Northwest and found two trees growing side-by-side, one a deciduous tree, the other a conifer. They were able to confirm that the same individual mycorrhizal fungus was growing on the roots of the two trees, connecting them. They then tented both trees. One tree got a clear tent and a supply of carbon dioxide with a special, traceable isotope of carbon. The other tree was tented with black plastic to block all access to light. They allowed time to pass and then tested the tissues of the stressed tree. The tissues of the tree showed significant quantities of the carbon isotope they had provided to the other tree. The only way that is possible is if the mycorrhizal fungus in the soil had been accepting the sugars from the healthy tree and providing them to the stressed tree in an attempt to nurse it back to health.

Mycorrhizal fungus are present in the soil in nearly every natural environment in the world. However, human activities of moving and compacting soil from activities such as plowing and construction destroy native populations of mycorrhizal mushrooms. Fortunately, you can buy supplements to restore populations of mycorrhizal fungus. One such source is the website of the mycologist mentioned above, www.fungi.com. There, he sells a product called Mycogrow(TM), that restores the mycorrhizal mushrooms to the soil.

It is also worth mentioning that while some of our best culinary mushrooms, such as truffles and chanterelles, are mycorrhizal mushrooms, these have proven very hard to cultivate as they are evolved to pair with a particular tree in a particular ecosystem. The mycorrhizal mushrooms that you can buy spores for will produce mushrooms, but only tiny, inedible ones. They are more for helping the plants than for producing edible mushrooms.