I was visiting an organic lemon grower recently. His lemon trees were full of fruit, rich in color and uniform in size. After I toured the property, we stopped and he dug a bit to show me the thick dark brown soil. He invited me over to smell it and it was musty, damp and full of life as you could see strands of mycorrhizae like tiny train tracks going in all directions. I think you could have planted your thumb and grown a person if you had wanted. It was truly beautiful.
What makes soil rich and dark and full of life? Well, it’s the building up of organic matter. In simple terms, microbes feed on plant exudations that are carbon in form of sugar. As the soil food web develops, everything becomes food for something else, every excretion builds a stronger carbon chain that over time turns the soil dark. The more this happens, the more carbon sequestration takes place, which can result in locking the carbon into the soil for over a decade.
Organic matter breakdown is not a single chemical transformation but a complex process. Breakdown starts almost immediately after an organism, or part of it, dies. The organic material is colonized by micro-organisms that use enzymes to oxidize the organic matter to obtain energy and carbon. Leaf and root surfaces are colonized by microorganisms even before they die.
Soil animals such as earthworms assist in the decomposition of organic matter by incorporating it into the soil where conditions are more favorable for decomposition than on the surface. Earthworms and other larger soil animals, such as mites, collembola and ants, fragment organic material, increasing its surface area and allowing more microorganisms to colonise the organic matter and decompose it.
The end result is humus, the dark, organic material that forms in soil when plants and animals (nematodes, protozoa for example) decay. When humus is in soil, the soil will crumble. Air and water move easily through the loose soil, and oxygen can reach the roots of plants.
Soil organic carbon is part of the natural carbon cycle, and the world’s soils holds around twice the amount of carbon that is found in the atmosphere and in vegetation. Soil organic carbon is the basis of soil fertility. It releases nutrients for plant growth, promotes the structural, biological and physical health of soil, and is a buffer against harmful substances.
As we all become greater stewards of the land, focusing on building better soil biology, the ground beneath will reward our efforts.