6 Principles of Soil Health: Living Roots

Back to Your Roots

Millions of families have utilized the services of ancestry websites to better understand the history of their families. Now, why on earth would folks spend their hard earned money to learn about people that are long-gone and out of the picture? Aside from being good, clean fun, I believe the answer is roots. Each of us are on the receiving end of the traditions, knowledge, skills, and beliefs passed along in a generational relay race from ancestor to ancestor. This reminds me of the intimate relationship that the shoots of plants share with their below-ground counterpart. Of course, it differs because they are two different parts of the same organism, but I think the analogy still holds true. Our ancestors are a part of us not only spiritually, but also physically through the transfer of genetics and their experiences by way of epigenetics.1


For those of you who don’t already think this is all too philosophical, let me take it a step further. Not only are leaves and roots part of the same organism (duh), soil scientist Ray Archuleta goes so far as to say that “the soil and plant are one.” I believe he’s exactly correct. Living roots are the two-way underground bridge that allow food and energy to cross into the soil ecosystem while simultaneously bringing underground minerals and water into the visible, above-ground world. In other words, soil health cannot flourish without living roots and living roots cannot flourish without healthy soil. Cut off the soil from living roots and we descend down a spiral of negative compounding effects, just as we humans do without understanding our societal and familial roots.

Erosion Control

Soil erosion in the United States is estimated to be in the ballpark of 2-4 tons/acre annually2,3 and global rates vary from 1-5 tons/acre annually4,5 due to lack of accurate modeling and measurement in many nations.  While we don’t know exact figures, the fact is that erosion of topsoil is a serious issue that should stopped and reversed. Fortunately, living roots provide a simple solution that do just that. Research shows that cover cropping likely reduces erosion most out of various conservation practices, including agroforestry, reduced tillage, no-till, and residue return.6 Additionally, adaptive multi-paddock (AMP) rotational grazing was found to decrease bare soil compared to more conventional grazing7, which would help explain another study showing that AMP grazing decreased soil sediment loss to runoff by 34%, total nitrogen loss by 33% and total phosphorus loss by 31% in a north Texas watershed.8


One reason living roots reduce erosion is their ability to physically anchor soil in place. Erosion occurs when soil particles and organic matter are separated from the pack and are light enough to be carried away by water or wind. Living roots, particularly fibrous grass roots, create an underground mesh that embed themselves within and around soil particles. Soil fungi create an even finer mesh with their thin, spindly hyphae. Whereas we humans put food in our bodies, roots and fungi put their bodies in their food. Their strategy is to come into contact with as much surface area as possible in order to absorb the nutrition they need to survive. Together, this root-fungi duo behaves a little like the skeleton of the soil by providing necessary rigid structure to clump things together and hold them in place.  This massively reduces the possibility that soil will leave the land.


Increased microbial activity on and around roots also reduces soil erosion. Like a snotty 2 year old, microbes and roots constantly exude sticky substances that glue soil particles together. Clay, silt and decaying organic matter form small microaggregates as they stick together. Fungal hyphae and roots are necessary to bring the microaggregates into contact with one another and coat them with a sticky substance, thus forming a macroaggregate. These cottage-cheese looking structures attract and hold on to water more efficiently, making them that much more cohesive as a unit. Combine this with protection from wind and water by plant cover and it becomes nearly impossible for anything short of a tornado to take soil off of this land.


Tisdall & Oades, 1982

Oasis in the Desert

Although there are 100,000,000,000 bacterial cells in a gram of fertile soil, you might be surprised to find out that bacteria only inhabit less than 1% of available soil surface.9 Research shows that bacterial cells  can survive for long periods of time in the soil in a state close to starvation, while their relatives close-by are reproducing like mad with the proper resources available. The authors write that this would be like modern humans living at the same time with our medieval ancestors or even earlier!10


So, where is the 1% that soil microbes live? Just like any organism, they prefer  to live where there is available food, water and shelter.  Living roots and decaying organic matter are the two oases in a desert of resources. The rhizosphere (the 1mm zone surrounding the root) is especially hot real estate because roots exude sugars, amino acids and other organic acids that are easily consumed and metabolized. Some of these exudates are released passively due to pressure differences in the soil solution and root cells. Others  are strategically released to recruit specific beneficial microbes11 or to coat the root itself in a sticky “mucilage” for protection, moisture control and nutrient acquisition12. These “primary metabolites” are mostly located at the root tip, where the lack of cell differentiation favors diffusion of metabolites to the soil.13 Lastly, cells from the actively growing region of the root slough off to minimize frictional forces that would otherwise damage the root, providing microbes with yet another source of fresh food to decompose. In exchange for this flush of building material and energy, microbes scavenge for water and nutrients useful to the plant in what David Montgomery and Anne Bikle call the “biological bazaar.”


Bacteria are not the only beneficiaries of the rhizosphere. Fungi have developed an intimate relationship with growing plants and their roots the world over. In fact, 80-90% of all plants species on Earth have developed a symbiotic relationship with one or multiple species of soil fungi.14 Because the fungus-root love story is so common, we have a word for it: Mycorrhizal (“Myco=Fungus, Rhizae=root). Reported benefits to mycorrhizal plants include increased pathogen resistance, drought tolerance, water uptake, nutrient uptake and transplant survival rates.14 Soil health also benefits greatly from this dynamic duo with the secretion of glomalin from a special type of mycorrhizal fungus that infects root cells in the shape of microscopic trees. For this reason, they are called arbuscular mycorrhizal fungi (“Arbor” in Latin means tree). Glomalin is a glycoprotein, meaning it is a combination of  sugars exuded from the plant root and proteins exuded from the fungus.15 This  cements microaggregates together to form macroaggregates, as previously mentioned for its role in reducing erosion. Additional benefits macroaggregates provide to the soil include greater soil organic carbon accumulation compared to bulk soil16, water infiltration rates, water-holding capacity, aeration, rootability and yield.15,17

An "arbuscule" of an arbuscular mycorrhizal fungi looks like a microscopic tree inside a root cell!
Microscopic view of round mycorrhizal fungi spores germinating and infecting a corn root. Green dye indicates the presence of the glycoprotein glomalin.
Microscopic view of glomalin coating soil macroaggregates.

A boom of bacteria and fungi populations in the rhizosphere inevitably attracts creatures that consume them. Nematodes and protozoa are the first in a long chain of predators that eventually leads to us humans. These subaquatic hunters thrive in the water that macroaggregates attract and hold so well.18,19 Like wolves to deer, protozoa and nematodes control the population of rhizobacteria in a top-down manner,19 increasing mineralization of nutrients near the plant root with their micro-manure.20 Unsurprisingly, plant performance was found to increase with protozoa and nematode predation.21


Predator-prey relationships are essential for healthy soil. They maintain populations in healthy ranges, thereby ensuring the whole system moves forward. Ecosystems in nature are healthier when they find a balance between stagnation and an unsustainable pace of change. Think about water. Stagnant water becomes contaminated and can harbor deadly agents. Additionally, raging waters from a flood contain enough force to carry away a house in no time. Gently moving streams are a nice middle-ground as they provide clean water without the risk of losing your home. The soil food web works in the same way and it all starts with living roots in the soil. Living roots are the key to shaping an environment where energy, water, nutrients and life are cycling efficiently and at a sustainable pace by various life forms in the soil. These processes come to a halt with bare soil. It’s like Ray Archuleta says: “Bare soils are naked, hungry, thirsty and running a fever!” Once again, I think Mr. Archuleta is exactly correct.

Producers, consumers and decomposers are all essential players in the soil food web.


Societies that sever themselves from their roots often do so at their own peril. They have nothing to anchor themselves to when the storms of life come their way. Similarly, farms and ranches that sever the soil from living roots do so at the risk of decreasing soil health dramatically over time. Acutal storms will come and whisk away anchor-less topsoil, removing precious nutrients and organic matter. In addition, a dearth of living roots means that our hardest working employees, soil microbes, do not receive the food and energy they require in order to provide their services that benefit the land so greatly. For human civilization to cut the land off from living roots as many days as possible is to destabilize the very foundation upon which it rests. As today’s generation of land managers, it should be our goal to improve the soil through the use of living roots before we pass the baton off to our children and grandchildren.