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Healthy soil is active, alive and moving.
Soil is more than something we walk on or a substance that holds our plants upright. It is a superorganism and home to the most densely populated communities on all continents. 90% of all organisms live underground. There are 10 000 and 50 000 species of microorganisms in less than a teaspoon of soil, holding more microbes than people on earth.
Soil is alive. In just one hectare of soil, there can be 2300kg of bacteria and fungi, 365kg of arthropods, 140kg of protozoa, and 50kg of nematodes (Kounang and Pimentel 1998).
What is a Superorganism?
A superorganism is a collection of living organisms tightly integrated with their immediate material environment, so the whole system behaves as an entity. Soil is a physiological system in which the microorganisms, inorganic particles, water and gases act together as self-entity, one capable of maintaining its chemical and physical state constant and suitable as a habitat. In this way, the soil is regarded as another of earth’s significant ecosystems.
Soil Organisms
Soil organisms are the bridge between the plant and the soil and can be regarded as the regulator of the soil-building and plant-feeding processes.
All soil organisms need energy to survive. The energy they need comes from eating something containing carbon. The carbon may come from plants, waste products, or the bodies of other organisms. It is an eat-and-be-eaten world in and on the soil.
Plants take up nutrients through their roots to feed their leaves. Photosynthesis produces exudate in the plant’s leaves and secretes it through the roots. Exudate is a unique blend of carbohydrates (sugar), proteins, hormones and other biological compounds. Their presence in the soil awakens and supports the growth of specific microbes that live on these exudates and the cellular material that sheds off as the plant’s root tips grow. All this takes place in the area immediately around the roots called the rhizosphere.
This area contains bacteria, fungi, nematodes, protozoa, and larger organisms such as earthworms and beetles. The diversity of beneficial microbes protects against pathogens around the rhizosphere. They also increase the availability of minerals & nutrients and produce organic compounds that plants use for growth & vitality. Microorganisms enhance aggregation, soil structure, water infiltration, aeration and water-holding capacity.
Soil bacteria are like microscopic bags of fertiliser. They absorb and hold nitrogen and other nutrients that they gain from root exudate and other organic matter. The soil protozoa and nematodes act as fertiliser spreaders by eating and releasing the nutrients locked in the bacteria and fungi. They digest what they need and excrete carbon and other nutrients in the plant’s root area. Living soil provides nutrients for living plants, while plants enhance the cycle by producing exudates. Insects, spiders, and arthropods, in turn, eat the protozoa and nematodes. Soil arthropods also eat each other and are the food of snakes, birds, moles, and other animals.
All these organisms work in synergy, creating soil structure. Bacteria produce sticky slime, so they don’t get washed away. Fungal hyphae bind the soil particles to create water-stable aggregates, creating pore spaces that enhance water retention and drainage. Worms, insect larvae, moles and other burrowing animals move through the soil for food, creating pathways allowing air and water to drain better.
A healthy food web keeps pathogens and competition in check and won’t allow one population to overtake. Mycorrhizal fungi have a symbiotic relationship with the roots, protecting them and providing them with water, phosphorus and other plant nutrients.
Soil Organisms and their function
Bacteria – Feed on organic matter, store and cycle nitrogen, and decompose pesticides.
Fungi – There are up to 3,000 species of fungi in the soil. Some feed on dead organic matter, like crop residues that are more difficult to break down, while others are parasites that attack other microbes. Some fan out from the root to get more nutrients and hold more water for the plant, delivering nutrients to the plant in exchange for carbon.
Protozoa – Eat bacteria, fungi, and algae. When they eat bacteria, their primary food source, they slowly unlock nitrogen released into the soil environment. They convert organic nitrogen to inorganic nitrogen that’s available to plants.
Mites – Decompose and shred organic matter as an essential part of the nitrogen cycle.
Nematodes – These microscopic worms are an important part of the nitrogen cycle. Most are non-pathogenic and don’t cause disease. They eat other organisms in the soil.
Earthworms – Expel partially decomposed organic matter, produce nutrient-rich casts, and make lubricated tunnels that aid soil structure and water movement in the soil.
Living soil – Better food
Soil microbes are essential in determining our food’s nutritional value. Soil with a wide diversity of life, especially bacteria, fungi, and nematodes, produces nutrient-dense food. The cooperation between bacteria, fungi, and plants’ roots (collectively called the rhizosphere) transfers carbon and nutrients from the soil to the plant and eventually to our plates.
Immunologists and allergists in Europe are uncovering another intriguing soil-health connection, the “farm effect.” Children raised on ecologically managed farms in Central Europe have much lower allergy and asthma rates than urban children or those raised on industrialised farms. In one study, researchers cultured farm children’s mattresses and found a mixture of bacteria—most of which are typically found in soil. Food grown in well-treated soil offer far more advantages when it comes to getting the best nutrients and building a healthy immune system.
Organic matter decomposition
Organic matter decomposition serves two functions for microorganisms. It provides energy for growth and carbon for the formation of new cells. Soil organic matter (SOM) is composed of the “living” (microorganisms), the “dead” (fresh residues), and the “very dead” (humus) fractions. The “very dead” or humus is the long-term soil organic matter fraction that is thousands of years old and resistant to decomposition.
Soil organic matter has two components: active (35 percent) and passive (65 percent) SOM. Active soil organic matter comprises the “living” and “dead” fresh plant or animal material which is food for microbes and is composed of easily digested sugars and proteins. The passive soil organic matter is resistant to decomposition by microbes and is higher in lignin.
Microbes need regular supplies of active soil organic matter in the soil to survive. Long-term no-tilled soils have significantly more microbes, more active carbon, more soil organic matter, and more stored carbon than conventionally tilled soils. A majority of the microbes in the soil exist under starvation conditions; thus, they tend to be dormant, especially in tilled soils.
Dead plant residues and plant nutrients become food for the microbes in the soil. Soil organic matter is all the organic substances (anything with carbon) in the soil, both living and dead. It includes plants, blue-green algae, microorganisms (bacteria, fungi, protozoa, nematodes, beetles, springtails, etc.) and the fresh and decomposing organic matter from plants, animals, and microorganisms.
Soil organic matter can be broken down into its parts. One hundred grams of dead plant material yields about 60–80 g of carbon dioxide released into the atmosphere. The remaining 20–40 g of energy and nutrients is decomposed and turned into about 3–8 g of microorganisms (the living), 3–8 g of non-humic compounds (the dead), and 10–30 g of humus (the very dead matter, resistant to decomposition). The molecular structure of soil organic matter is mainly carbon and oxygen, with some hydrogen and nitrogen and small amounts of phosphorus and sulfur. Soil organic matter is a by-product of the carbon and nitrogen cycles.
What Interferes with Healthy Soil Balance?
Turning up the soil through rototilling can disturb worm barrows, bringing them to the surface where they die. Worms play a vital role in the garden because they provide nutrients for the soil and aerate it. Rototilling also breaks up fungal hyphae and kills arthropods.
Air pollution, pesticides, fungicides, and herbicides also kill off a variety of microbe communities, or they move away. Soil compaction also destroys the food web by compressing the natural soil microbe habitat and the plant roots they depend on for nourishment.
Chemical fertilisers harm the soil food web by killing entire portions of it—once the microbe balance is disturbed, other food web members also disappear. Earthworms are irritated by synthetic nitrates and deprived of food, so they move out. Earthworms are one of the best shredders of organic material, and their absence is a significant loss.
As soil structure worsens, pathogens and pests establish themselves, watering becomes more challenging, and gardening becomes much more work. Avoid additives with high NPK numbers (Nitrogen, phosphorus and potassium), rototilling, or compacting your soil beds by walking on them. These activities can destroy or severely damage the soil food web.
How To Create a Healthy Soil Microbe Balance?
- Compost – Introduces new microbes and life into the soil.
- Trees, shrubs and perennials – Prefer soil dominated by fungi. Coarse, dry, brown organic material and mulch on the surface support fungi growth.
- Vegetables, annuals, and grasses – Prefer bacterial-dominated soil.
- To restore our soil, add microbes and feed them – The most persistent form of soil carbon is primarily from dead microbe bodies rather than leftover plant parts. Most of the old soil carbon has undergone microbial decomposition. Even though plants are the source of carbon for the soil, microbes control their fate by using it as food, ensuring that some of it will stay in the soil. Grow lactic acid bacteria (LAB) to speed the decomposition of dead matter in the soil. Make a probiotic tea to feed the microbes. Add bokashi, the fermentation that builds soil.
