Soil video script (8m 24s)
“To understand how soil works is to understand how the universe works.”
The principle for the soil chapter is to build healthy soil. Soil is a dark brown material made of organic matter, minerals, water, air and a myriad of microorganisms.
We observe the soil dimension through soil horizons. We can look at a picture of a soil horizon, and see billions of years of work compacted in different layers.
On top you have leaf litter, this is the freshest layer, freshly fallen leaves and trees. Below, is Type A soil, the topsoil. It’s dark and nutrient-rich, useful for growing plants. B is the subsoil – it has less nutrients, lighter in color. And C is a parent material, a dense, compacted substance like clay, which is useful for supporting a foundation.
Soil food web
After a seed breaks out of its shell, it sends out two runners – one toward the sky and one into the soil, a stem and a root. The runner going toward the sky converts sunlight into chlorophyll, food for the roots, through the process of photosynthesis.
In the rhizosphere, the 1-5mm region of space around root tips, the roots put out exudates, sugars and carbs, hanging like bait to attract bacteria and fungi. Bacteria and fungi arrive and chew on the exudates.
The presence of bacteria and fungi attract larger microorganisms – nematodes and protozoa. They consume the bacteria and fungi and excrete nitrite and ammonium, NO3 and NH4, two forms of soluble nitrogen. The plant absorbs this nitrogen and channels the energy back into the stems, to grow more leaves, make more chlorophyll, which will produce more exudates, and the cycle continues.
The plant matures and eventually produces carbs and sugars above ground, in the form of… fruits and vegetables. These “fruits” attract insects, animals and people. We walk over, consume the fruits, and later return it to the soil in the form of nitrogen, phosphorus, calcium and carbon.
After enough nutrient exchanges, fungi and bacteria decompose this decaying organic matter into humus. Humus is the final stage of soil decomposition. This fine spongy soil has a great ability to store moisture and nutrients.
As soil matures, fungal nets form throughout the soil and increase nutrient distribution between species. And larger organisms like worms and beetles arrive and vertically aerate and redistribute the soil.
This is a very basic explanation of how soil works. But I think it provides some insight into the immaculate coordination of nature. This symbiosis between underground and above ground, is how plants have survived on this planet for so long.
And I think sometimes in our culture, it’s like we’re going into the forest, we’re looking and we’re chopping and cutting and searching, we keep trying to get this… to grab the essence of … the plant… of nature… there’s nothing there. There’s nothing in the forest… other than… they do produce fruits and flowers and mineral deposits over time… this is true and we can use these things to our advantage. But there’s nothing else there. It just happens.
And I think it’s important to take more of an observer’s role in this… theatre happening before us. So you observe for a minute and see oh okay this is how it works, and then you realize you’re human too, you’re consuming and living and dying just as all the other microorganisms are. And that’s what’s so amazing about being human… the fact that we can be aware this process, just as we are a part of it.
So I think our challenge as humans is to both figure out how to manage this place while we play the game. This is the challenge and debate and conversation we’re all having – How can we best manage the place, while we play the game.
Nutrients in the soil
Okay, so we’ve talked generally about what soil does and how it is formed. What about the elements in the soil?
There are three main elements in plants – carbon, hydrogen and oxygen. Carbon is the physical basis of all living organisms. Plants absorb carbon from the atmosphere, in the form of CO2 and, with help from nutrients in the soil… they materialise themselves out of thin air.
This guy Christian did this test in Auroville where he put 9kgs of soil in a jar and planted a watermelon seed. A few months later, he had 7kg watermelon, and 8.9kg of soil. The loss of soil came from the soil residue on the root stalks, he said.
Where did the 7kgs of watermelon come from? It came from thin air. This is plants do. They materialise themselves out of thin air.
Outside of carbon, hydrogen and oxygen, all plant nutrition comes from the soil. Major nutrients found in the soil are nitrogen, potassium and phosphorus – N, P, K.
Nitrogen builds green matter in leaves,
Phosphorus builds flowers and fruits,
Potassium builds roots.
N, P and K are the elements which build the roots, shoots and fruits of the plant.
These are also the main ingredients in chemical fertilisers. The thing with chemical fertilisers is that they only provide NPK. They neglect all this other element activity going on in the plant – the minor elements, the trace elements and the minor trace elements. And each of these other elements provide vital roles to plant nutrition.
Minor elements include calcium, magnesium and sulfur:
- Calcium strengthens cell walls
- Magnesium aids in the uptake of phosphorus
- Sulfur helps with protein and chlorophyll
Then you have trace elements like:
- Boron, which aids in the production of sugars and carbs and regulates the use of other nutrients
- Copper, important for plant reproduction and aids in root metabolism
- Chloride helps metabolism
- Iron helps to form chlorophyll
- Manganese – Activates plant enzymes needed for growth
- Molybdenum – helps to regulate nitrogen consumption
- Zinc – regulates sugar consumption
And then you have additional minor trace elements like strontium, vanadium, silicon and nickel, which also provide other essential mechanisms in the assembly line of soil food production.
Texture of soil
There are three main textures of soil – sand, silt and clay. And every type of soil is going to have a different amount of each texture. The soil textural triangle shows the range of soil textures. Loam is what we’re going for as far as ideal texture of soil goes. Loam is a spongy nutrient-rich soil with an even distribution of sand, clay and silt.
pH of the soil
pH means the power of hydrogen, it is a measurement of the dissolvability of the soil nutrients. Or more importantly, how easily roots can absorb nutrients from the soil.
The pH scale ranges from 0 – 14, zero being alkaline and 14 being acidic. You want your soil to be in the 5.5 – 7.5 range. If you’re unsure of the pH level or want to keep your soil in this 5.5 – 7.5 range, add compost. Adding compost neutralises the pH of the soil.
You can also use a litmus test where you dip paper in water. The change in color of the paper will tell you the pH of the soil. Also hydrangeas and other kinds of flowers grow a certain color reflecting the pH of the soil. If it is too acidic – add lime, seashells or bones. If it’s too alkaline – add sulfur, pine bark or woodchips. Just remember, adding compost neutralises the soil. This is what you want.
So to recap this chapter,
- Soil is a bunch of dead and decaying plants.
- The region below the soil works to feed the region above the soil, and vice versa
- The soil food web is an amazing microcosm of life, and
- And it works, it doesn’t need chemical fertilisers or any other products. And we can make soil, we can improve the soil at our site using compost.
And that’s what we’ll talk about next chapter. Okay, that’s it for this section of soil.