What is the soil microbiome?
The soil microbiome is a term used to describe the collection of bacteria, fungi, protozoa, nematodes, earth worms and many others that live in the soil. Healthy soil is one of the most diverse ecosystems on earth and there are more soil microbes in a single gram of soil than human on the planet.
These microscopic creatures provide valuable services that support healthy plants, decompose organic matter, release of nutrients from sand, silts and clays and produce compounds that cause soil aggregates to form, which helps with water infiltration and prevents erosion.
Why should we care about soil?
Soil and its microbes provide over 98.8% of food for humanity (1). When you start to think about it, everything that is in your kitchen fridge comes from the soil. Admittedly it wouldn’t be there without the incredible input of hard-working farmers and food producers, but those vegetables came from the soil, the cheese and milk were provided by the cow that ate the grass that grew in the soil, the bottle of wine whose grapes grew on vines that sprawled across Mediterranean soils.
The challenge we face is that over the past 60 years, it’s estimated that 1 ton of soil per hectare in France is lost to erosion every year (2). The increased production that has resulted from the mechanisation of agriculture and widespread use of inorganic fertilizers, herbicides, pesticides, and insecticides has not been without a cost. Soil has literally been washed away by the rain and blown away by the winds. And once it has gone it takes a long time to create new soil. INRAE (France’s National Research Institute for Agriculture, Food and Environment) estimates that the speed of the formation of soils is between 0,02mm – 0.1mm per year, which is very slow (3). The soil microbiome may also have been severely impacted to the extent it is no longer provides the vital nutrient cycling services to plants.
The good news is that by taking a regenerative approach to our soil we can reverse the damage that has been done. Working to restore and enhance soil microbiology on degraded and eroded soils can speed up the rate of soil production. Bacteria and fungi literally break down the bed rock with enzymes making nutrients available to plants and increase soil organic matter through decomposition. We can also increase plant uptake of nutrients because they are being made available by the soil food web and because pH is at optimum levels which ensure that vital plant macro- and micro-nutrients are not locked up in the soil. Improved plant nutrition triggers higher levels of resistance to pathogens, pests, and diseases, which in turn means that there is increased photosynthesis. Increase photosynthesis in turn, increases the amount of root exudates released by plants into the rhizosphere which help support microbial life.
What is the soil food web?
The soil food web is the network of interdependent microbes, protozoa, nematodes, arthropods, small mammals and birds that together cycle nutrients, minerals, and organic matter in the soil. Dr Elaine Ingham, a leading researcher and soil microbiologist who discovered many of the intricate relationships between plants and the world beneath our feet, has shown that the soil food web performs multiple functions. These include:
Cycling nutrients in rocks, sands, silts, clay and organic matter into plant available forms.
Retaining nutrients in soil so nutrient loss from leaching and erosion does not occur.
Protecting plants from diseases and pest and parasite attacks. This includes all surfaces of the plant.
Decomposing chemicals and other potential plant toxic materials into plant beneficial materials.
Building soil structure by converting dead plant residues into structured, aggregated organic matter. This enables the movement of atmospheric gases e.g. oxygen and nitrogen, water and roots through the soil. (4)
Did you know plants are not vegan!
Plants have evolved in symbiosis with this soil food web. Research has identified multiple ways in which plants can access the nutrients they need at different times throughout their lifecycle. These include:
Ionic exchange: Plants actively seek to cultivate beneficial bacteria and fungi by releasing 30-40% of the simple sugars they produce through photosynthesis into the soil profile around their roots. This encourages the proliferation of bacteria and fungi communities which are subsequently consumed by predator organisms – protozoa and nematodes. When the predators excrete their waste, e.g. excess nitrogen in the form of ammonia, plants can absorb these nutrients through their roots. (5)
Rhizophagy: Plants are not vegan, they feed on bacteria and fungi that are present in the root zone. They do this by the release of exudates that encourage the proliferation of bacteria and fungi in the root zone. When the bacteria or fungi subsequently enter the root, they are bombarded with a superoxide which oxidizes their cell walls and causes them to leak nutrients directly into the roots! The plant gets a tasty meal and any remaining bacteria escape through the root hair to feed and reproduce on more exudates (6).
Endo- and ecto-phytes: Approximately 90% of plants partner with mycorrhizal fungi – either endophytic (within the root itself) or ectophytic (around the root). These fungi form a mutualistic interface between the plant, soil, other plants and the rest of the soil food web through their extensive network of hyphae which can extend a plant root zone by 10,000 times. The mycorrhizal fungi will actively translocate nutrients for the plant in return for additional exudates to support their own growth. (5)
If you would like know what how your soil food web is supporting your plants, get a soil microbiology test. Send us an email to find out more andy@resiliencesoil.com
Resources
1. Kopittke PM, Menzies NW, Wang P, McKenna BA, Lombi E. Soil and the intensification of agriculture for global food security. Environ Int. 2019 Nov 1;132:105078.
2. Mathieu C. Planet-Vie. 2020 [cited 2024 Apr 23]. La dégradation des sols en France et dans le monde, une catastrophe écologique ignorée. Available from: https://planet-vie.ens.fr/thematiques/ecologie/gestion-de-l-environnement-pollution/la-degradation-des-sols-en-france-et-dans
3. Ruellan A. Des sols et des hommes: Un lien menacé [Internet]. IRD Éditions; 2010 [cited 2024 Apr 24]. Available from: http://books.openedition.org/irdeditions/8293
4. Soil Food Web School. Soil Food Web School - Regenerating Soil. [cited 2024 Apr 24]. Restiring Nature to the World’s Soils. Available from: https://www.soilfoodweb.com/
5. Powers M. Regenerative Soil. 2021.
6. White JF, Kingsley KL, Verma SK, Kowalski KP. Rhizophagy Cycle: An Oxidative Process in Plants for Nutrient Extraction from Symbiotic Microbes. Microorganisms. 2018 Sep 17;6(3):95.
FAQs
1. What is the soil microbiome? The soil microbiome refers to the diverse community of microorganisms including bacteria, fungi, protozoa, nematodes, and earthworms that inhabit the soil. It plays a crucial role in supporting healthy ecosystems by facilitating nutrient cycling, decomposing organic matter, and enhancing soil structure.
2. Why is the soil microbiome important? The soil microbiome is essential for sustaining life on Earth. It contributes to over 98.8% of food production for humanity by supporting plant growth and providing nutrients. Additionally, it helps prevent soil erosion and promotes water infiltration, making it vital for maintaining agricultural productivity and ecosystem health.
3. How has human activity impacted the soil microbiome? Over the past 60 years, human activities such as mechanized agriculture and the use of inorganic fertilizers, pesticides, and herbicides have led to soil degradation and erosion. This has negatively affected the soil microbiome, reducing its ability to provide essential services like nutrient cycling and soil formation.
4. What is the soil food web? The soil food web is a complex network of interconnected organisms, including microbes, protozoa, nematodes, arthropods, and small mammals, that interact to cycle nutrients, decompose organic matter, and support plant health. It plays a critical role in maintaining soil fertility and ecosystem resilience.
5. How do plants interact with the soil food web? Plants have evolved symbiotic relationships with the soil food web, accessing nutrients through mechanisms such as ionic exchange, rhizophagy, and partnerships with mycorrhizal fungi. By releasing exudates and forming alliances with soil microorganisms, plants optimize nutrient uptake and enhance their growth and resilience.
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