Aren’t all soils alive? Most of the time, yes.
In nature, all soils are teeming with life; from plant roots and bulbs to insects and worms and the whole universe of microscopic organisms that are interlocked in a web of life, all of it breathing, moving, feeding; living, breeding and dying.
These days, though, the term ‘living soil’ is usually used to refer specifically to the microbial life in a soil. The distinction is made to draw our attention to this all-important and often overlooked component of the soil. But what exactly do these tiniest members of the soil food web do, you ask?
In a healthy soil, microbes:
• recycle nutrients — microbial activity makes nutrients available to plants by breaking down organic matter as well as fixing atmospheric nitrogen.
• exclude pathogens — when plant roots and microbes co-exist in soils, they tend to work together symbiotically to exclude bacteria and fungi that are harmful to them, thus forming a stable and healthy soil ecosystem.
• build more soil — as microbes decompose complex organic matter like woody material, they form humus. Humus has amazing water- and nutrient-holding capabilities which causes soils to become more fertile and robust as more and more humus is formed.
The healthier the microbial ecosystem, the healthier the soil and the plants that grow in it. And since we all daily rely on plants for food (even when we eat meat), it follows that we would want to protect and encourage the growth of soil microbes. Farm them, essentially. But how do you farm herds of microscopic cattle? Tend fields of microscopic crops?
Let’s start right at the beginning…
What is soil?
The stuff we know as soil in our vegetable gardens, flower pots and in the beautiful, wild places out there like mountains, forests and jungles all have some things in common. Soil is the place where plant roots take up nutrients and is made up of varying proportions of
• weathered rock / sand (plants draw necessary trace elements and minerals from here)
• organic matter in various states (provides nutrients for plant growth)
• and microorganisms (or microbes) in their billions
What are microorganisms?
Microorganisms (or microbes; same thing, shorter word) is a collective name for millions of different types of extremely small, often single-celled organisms that occur everywhere around us. Even though they are so small that we can’t see them with the naked eye, without microbes, life as we know it would not exist.
Some important soil microbes include bacteria, fungi and protozoans:
bacteria — break down fresh organic matter, can live with or without oxygen, fix atmospheric nitrogen and form symbioses with plant roots
fungi — break down woody and lignified organic matter and make phosphorous available to plants
protozoa — are often predators of other microbes, playing an important part in releasing the nutrients into the soil that microbes lock up in their bodies as they grow and reproduce
All life on earth has evolved from single-celled microbes. Somewhere in the evolution from these single-celled beings to multi-cellular organisms like plants and animals, the cells that make up these larger organisms lost a lot of the abilities that they used to have. This means that all multi-cellular and fairly complex organisms are still completely reliant on microbes for such basic things as fixing nitrogen and breaking down organic matter (both absolutely essential to plant growth). A great example of this is right inside our stomachs, where we host hundreds of different types of microorganism that helps us to digest our food and get nutrients from it.
Beneficial microbes (fungi in this case, the white stuff) decomposing woody as well as fresh organic matter.
Similarly, we can start to think of soils as the ‘stomach of the earth’ (credit to the Alternative/Natural Farmer Joel Salatin for this idea). Our stomachs take in organic matter (vegetables, fruits, nuts, steaks etc.) via our mouths and then digest it to release the nutrients and minerals that allow our bodies to grow and live. Soils take in organic matter from fallen leaves and animal droppings and then digest it to release the nutrients and minerals that allow plants to grow and live. In much the same way that I can’t get nutrients from a carrot by holding it in my hand, but need to chew it and get it in my stomach first, plants need soil microbes to act as the digesters of their food.
Stated differently, because they can’t directly extract nutrients from organic matter, plants need soil microbes to digest organic matter for them.
As microbes digest (or decompose) organic matter, the nutrients that were bound up in complex organic molecules when that organic matter was a living plant or animal, now becomes mineralised and available to plants.
Farming with microbes
Even though soil microbial ecosystems are complex and diverse, there are some basic practises that help microbes to flourish.
The two cornerstones of maintaining healthy soil life is making sure the microbes have adequate water and food (much the same as any other living thing). Providing these two go hand in hand in natural growing systems.
First of all, we want to make sure that the water that enters our soils, whether by rain, dew or irrigation, is kept there for as long as possible, so that it can provide for as many microbes as possible. To do this, we add organic matter like dead leaves and stalks of plants (green or brown) to the soil surface. This is known as ‘mulching’ or adding mulch.
Mulch decreases evaporation from bare soils, prevents erosion and water run-off and also absorbs water, acting as a reservoir for microbes and plant roots to drink from as they need it.
The mulch also acts as a food source for the microbes, because they immediately start to break down any organic matter that they come into contact with, releasing nutrients into the soil.
Additionally, we can avoid tilling or cultivating our soil. Disturbing the natural soil layers that form is extremely detrimental to soil microbial life. The microbes closer to the soil surface like oxygen and the deeper ones dislike oxygen. When we mix these layers, microbes get taken out of their preferred environment and take a lot of time to get back into a healthy balance again.
When we remove plants from a patch of soil, it is best to cut the plant at the base of the stem and leave the root system intact and the soil undisturbed. As microbes decompose the roots of the plant, deep soil structure is built and organic matter and nutrients are added to the soil.
The final practise we can adjust to benefit microbes is that of fertiliser application. Because microbes make plant nutrients available by excreting it as waste products, it follows that adding a lot of plant-available nutrients to a soil in one go is like adding a lot of microbial waste to your soil. Microbial populations, as with all organisms, die off when surrounded by too much of their own waste, so we must apply fertilisers judiciously and sparingly. We can do this by using slow-release organic fertilisers, where the soil microbes regulate the rate of nutrient release as well as not being too heavy-handed with manure applications, especially fresh poultry-manure and the like.
When we do apply fertilisers to our soils, we can keep in mind the maxim of ‘feed the soil, not the plant’. Our annual vegetable crops often represent short-term goals that we’re trying to achieve, so it is tempting to try and feed them as much as possible. But it makes more sense, especially when you consider all the future crops you want to harvest from that same soil, that you want to feed the soil to be healthy. Think of your soil as a living entity, not just a container for your plants and right practise will follow.
Applying compost teas and vermicompost are also ways to feed your soil with populations of beneficial microbes and have the added benefit of being good for the environment and relatively easy to make.
Go forth, tend your microbial herds well, and watch your soils prosper!
Words by Hannes Wiese