6 Soil Health Principles: Diversity – groundedregenerativeblog.com

6 Principles of Soil Health: Diversity

Diversity of Diversities

Imagine 100,000 freshly minted lawyers gathering together and deciding to start a country. “We’re young, brilliant lawyers. Surely we can figure out how to run a country well. How hard could it be?” They invest in some real estate and name it something like Litigation Nation. Brilliant. Now, how many hours do you think would pass before their country fails? My guess is two and a half to get all the paperwork done.

Litigation Nation wouldn’t function well because every single person is alike. As a whole, they don’t possess the diversity of skillsets required to run a prosperous society. Which of them would volunteer to handle the nation’s garbage? Who’s going to fix the plumbing when issues arise? Nothing against lawyers, but I doubt anyone would be thrilled to take over either of those positions after enduring the rigors of law school.

Similarly, soil functions properly when its citizenry is composed of a diversity of organisms with a diversity of skillsets. Growing a plant or animal may seem simple on the surface, but there are an unfathomable amount of chemical and physical processes that need to be done every second of every day for the soil to be able to support healthy plants and animals. Every single bacteria, fungi, protozoa, insect, earthworm, bird, cow and all the rest of our trillions of employees work like spokes inside of a bicycle wheel to provide some sort of service, making sure the system will roll on smoothly. Not only that, diversity within groups ensure that there are enough workers for each task and that one species does not grow out of control by monopolizing food and energy.

Microbial Diversity

Felipe Bastida and his team of researchers wrote in 2021 that, “The diversity and biomass of soil microbial communities are the major regulators of fundamental ecosystem processes, such as organic matter decomposition, nutrient cycling, and gaseous fluxes.”¹ Let’s start by looking at organic matter decomposition and nutrient cycling.

All living organisms require an intake of nutrients to build their bodily structures and energy to power their bodily processes. Life is pretty simple when you think about it this way. Food and energy comes packaged in many different forms in the soil, with some packages easily degraded and others much harder to wriggle loose. Different species of soil microbes have developed wildly different strategies over time to unlock and consume these forms of nutrients and energy. Recycling nutrients from dead organisms (organic matter decomposition) is primarily the job of bacteria and fungi. In general, bacteria prefer low carbon-to-nitrogen ratio organic matter like fresh-cut, green grass. Many bacteria species specialize in the breakdown of cellulose, and for good reason! This major component of plant cell walls is the most abundant organic compound on Earth. Fungi, on the other hand, produce and excrete acids and enzymes strong enough to break apart high carbon-to-nitrogen ratio compounds, like wood and dried leaves. Other soil microbes bust apart nutrients from the structure of dead, non-living material like rocks, deepening the total pool of nutrients available for life! Once these decomposers excrete waste, other groups of diverse organisms are right there to consume and transform the nutrients further.

Now, as everyone knows, nature is also full of predator-prey relationships where one living organism consumes the body of another living organism (or a freshly killed one). One of the most important predators in the soil is the protozoa. Protozoa feed primarily on bacteria, who can be thought of as nutrient-rich bags of fertilizer swimming around. Protozoa, and other soil predators, don’t use all of the nutrients they consume. A good portion of these excess nutrients are excreted and enter back into the soil combined in a different configuration, often in plant-available forms, in a type of micro-manure.² These predator-prey relationships continue all the way up the food chain, resulting in nutrient and energy transformations each step up the ladder.

One other important aspect of diversity is the principle of redundancy. Some species of microbes eat the same thing and compete with others for access to the same piece of food. While this may seem like a negative to the soil community, it actually creates resiliency because species vary in their response to different disturbances.³ When one gets knocked down by tillage, for example, we need to have others that can pick up the slack and continue the cycling of life or else soil ecosystem functions come to a screeching halt while injured microbial populations recover. In addition, fighting for resources among microbes decreases the likelihood of one species overwhelmingly dominating the resource base. This diversity acts as a self-policing mechanism that holds disease-causing microbes in check, whether they be in crops⁴, animals⁵ or humans.⁶

All of these examples are obviously massive oversimplifications, but hopefully I got the point across that there is a great variety of food sources in the soil, each bringing with it one or many species that consume it. Other soil functions, such as forming aggregate structure, water infiltration, and gas exchange are largely positive side effects of living organisms finding and consuming diverse forms of food and energy. It should come as no surprise, then, that agricultural practices such as crop rotation⁷, no-till⁸, and animal integration⁹ all increase soil microbial diversity by increasing soil carbon content, a known predictor of greater soil microbial diversity.¹

Insect Diversity

Dr. Jonathan Lundgren, founder and director of Ecdysis Foundation and Blue Dasher research farm, might just be the world’s leading biodiversity entomologist. If you have a minute, his story dealing with Big Ag intimidation is quite the read. Dr. Lundgren’s 20+ years of research shows without a shadow of a doubt that the vast majority of insect species are either neutral or beneficial for crops and livestock. Only a tiny fraction of all insects are what we would call “pests”. What’s even more eye-opening is that the behavior of those “pests” is greatly influenced by insect population diversity, which is greatly influenced by… drumroll please…. human management of the land. By the rules of the transitive property, this means pests are encouraged to be pests largely as a result of farm management practices that reduce insect diversity. Harmful management practices that promote pest abundance include insecticide use¹⁰^,¹¹, tillage¹², and a lack of plant diversity.¹³ Neonicotinoid insecticide use is particularly harmful to pollinators and generalist predators, while at the same time very ineffective against soybean aphids in the Northern Great Plains.¹⁴ Talk about a lose-lose.

Another important research paper from 2015 from Dr. Lundgren found that, “Species diversity within the arthropod community is negatively correlated with pest abundance on maize farms. Specifically, pests declined as species diversity and community evenness increased.”¹¹ Among the reasons listed for this are diversity-dependent predation of pests, as well as competition between pests and species for similar habitat and abiotic resources, like water. If that isn’t enough, insect diversity also helps reduce weed pressure through weed-seed consumption (“granivory” for us science nerds)!¹⁵

As you will read in the section below, healthy plants are integral for the building of soil health, so devastation of a crop aboveground is a matter of soil health. In addition, belowground insect diversity plays an integral role in forming soil structure and building organic matter levels, such as in the case of dung beetles breaking down and dragging manure in the soil.

Let us return one final time to Dr. Lundgren’s work to learn how to increase insect diversity on the farm. He writes, “Our research suggests that agronomic practices that promote high levels of arthropod diversity fundamentally require fewer agronomic inputs.”¹⁶ These include reducing tillage, increasing vegetation diversity (extending crop rotations and adding cover crops, for example), as well as reducing pesticide and synthetic fertilizer inputs. No fancy contraptions. No expensive inputs. His advice: Let it bee. 🙂

Boiling down the importance of insect diversity for soil and ecosystem health to a few lines is a fool’s errand. Insects have such a massive impact on this planet and we tend to only notice them when things are going wrong. I encourage you to learn more about insects by checking out the great work done by Ecdysis Foundation and Dr. Lundgren’s very informative Ted Talk.

Plant Diversity

We all have a pretty good idea why plants are important, right? We’re taught these things in grade school. They provide us with food, fiber, shelter, and even the oxygen we need to survive! These are the benefits we can literally see because they are all above the soil surface. Don’t get me wrong, food and oxygen are essential to human survival, but I think it’s high time that plants get the recognition they deserve for their impact on the world below our feet. Let’s dig a little deeper and learn how a diversity of plants improves the health of the soil.

Soil Science 101 tells us that soil contains stuff (sand, silt, clay, living and dead organisms) and pore space (air and water). Squeeze out the pore space and we get compaction. No water, no air… no good. Plants are among the best biological tools in our regenerative toolkit in reducing compaction and aerating the soil. The tip of growing roots have a structure similar to the metal or plastic encasings on the end of shoelaces (“aglets” for anyone wondering) called the root cap. The root cap is made of tough material and can break through incredible levels of compaction as it continues its search for nutrients and water. Similar to earthworm channels, these root channels open up the soil and allow air and water to infiltrate, especially when the root dies and gets consumed by decomposers.

Diversity of plant species becomes critically important at this point because different plants contain different rooting architecture. Taproots, like those of the tillage radish and other broadleaf plants, descend deep into the soil profile with one main root and small hairs projecting from its sides. Plants with taproots benefit soil health by breaking up some compaction, as well as drawing up water and nutrients from deeper in the soil profile. Fibrous roots, like those of grasses, do not have one main root. As the name implies, their roots create a dense, fibrous network of material that typically stays closer to the soil surface compared to taproots. Because of the sheer number of roots, fibrous roots are especially good at breaking up compaction and holding soil in its grasp, thus reducing erosion. Combining the benefits of taproots and fibrous roots is one of many reasons why diverse rotations and diverse cover crop mixes can be greatly beneficial to soil health.

Aeration and holding the soil in place are not the only benefits plants and their roots provide to the soil. Plants, like all organisms, require different nutrients in different quantities to become what they are genetically programmed to become. This means that monocultures will deplete certain nutrients over time, while leaving others less affected. This creates imbalances, which often leads to disease pressure¹⁷ and a need to supply external fertilizer to make up for deficiencies. Polycultures, or at the very least extending rotations of monocultures, allows the soil to better maintain nutrient balance, which leads to better plant growth. As always in nature, the benefits ripple out further, as you can read about in the Rule of Compounding. Vigorous plant growth aboveground leads to more food production through photosynthesis, which provides more growing material for roots belowground. Plant roots, however, are not able to uptake all of the additional nutrients and water that plant growth requires, so they recruit microbes to do some of the job for them. In exchange for these nutrients, plants exude up to 40% of their photosynthetically fixed carbon into the soil surrounding their roots.¹⁸ Carbon is used as both an energy source and building material for cells, so what’s really happening is that plants are taking energy from the sun, placing it in the bonds between carbon from carbon dioxide, and sending that carbon and energy into the soil to stimulate life. Soil health greatly benefits from this whole process as the interaction of roots and microbes create biotic glues, such as glomalin, that create the macroaggregates necessary to maintain pore space, provide habitat for soil biology and reduce erosion.

This is where I will leave the story for now. My aim in this section was to provide a small appetizer describing the necessity of plant diversity for the healthy functioning of a soil ecosystem. There is much, much more to discuss (more revenue streams, more secondary and tertiary phytonutrients, healthier animals…), but just remember for now that plant diversity helps prevent and fix compaction, reduces erosion and fosters incredible amounts of soil biological diversity.

Dig into the main courses of plant information by reading about living roots, which is the fifth principle of soil health, and various articles on all things plants.

Animal Diversity

We conclude our tour of the wonders of diversity with our feathery and furry farmyard friends. Try saying that five times fast!

One reason why animal diversity increases soil health is their differing dietary preferences. Multiple species of herbivores selectively consume different plants, whereas one species of animal munches the same plants down over and over again, while leaving others untouched. This is why you might have heard someone say a pasture can be both under- and over-grazed simultaneously. Soil health is degraded over time as the roots and shoots of overgrazed plants shrivel up and die, leaving bare soil, while undergrazed plants oxidize into hardened material that can no longer photosynthesize, thus stopping soil microbial feeding through root exudates. We definitely don’t want that! Instead, we can utilize the cow’s preference for grass²⁰, sheep’s preference for forbs and goat’s preference for woody species²¹ to tailor a grazing plan that positively affects all plant groups. Of course, each class of livestock consumes each of the plant groups, especially when feeling pressured by their own species²³, but this gives you an idea of the differences in their feeding habits.

As for our non-herbivore livestock, pigs will eat most any plant in the pasture and are especially useful in orchard or permaculture operations, as pigs will gladly consume nuts and fruits that fall to the ground. Chickens also consume a wide variety of food when given the chance. They will eat pasture plants, seeds, worms, and insects. Many operations use this to their advantage by following their cattle with chickens to allow them to scratch in the manure patties so they can consume the larvae found inside. This reduces future insect pest loads and speeds up the incorporation of manure into the soil.

Another soil health benefit to multi-species systems is the diversity of microbes that each animal introduces to the plant and soil microbiome.²⁵ This is called “microbial shedding”. Once again, diversity begets more diversity! Grazing animals carry trillions of microbes in their fur, on their skin and, importantly, in their saliva. In fact, cows produce up to 50 quarts of saliva each day, with each drop containing millions of microbes. Sheep saliva is also chock full of microbes and plant growth-promoting compounds.²⁶ The vast array of beneficial microbes in livestock saliva likely explains why plants clipped with saliva regrew more vigorously and with more buds compared to plants clipped only with non-living salivary components!²⁷ And, as we know, this benefits soil health because more growth means more food and energy sent to the soil, which means more microbial activity and better soil functioning. Interestingly, we don’t see the same magnitude of effects when we substitute machinery for animals. Mowing a pasture instead of grazing with livestock, for example, may provide some benefits and may be the appropriate practice for that time and location, but it’s important to think of the compounds that machinery could shed as they work across the land: metallic material, hydraulic fluid, oil, and harmful gases in the exhaust. Inoculating our soils with beneficial microbes brings positive compounding and cascading effects, while industrial chemicals and compounds often have the opposite effect.

The final benefit I will touch on concerns parasites. Many parasites are host-specific, meaning they have developed a liking for one species of livestock. Cattle and sheep are two well-known dead-end hosts for many of the parasites that afflict one another²⁸. This means that a cow parasite inside of a sheep does not harm the sheep and the parasite eventually dies of starvation. The reverse is also true as many sheep parasites starve inside of a cow. In my mind, this draws direct comparisons to the pest and disease benefits of crop rotation, once again proving the universal importance of diversity to keep biology balanced and in-check. Just as with healthy crops, healthy livestock managed properly will positively influence soil health.

To learn more about the benefits of combining sheep, goats and cattle into a “flerd”, check out this very informative slideshow from the University of Nebraska-Lincoln.

Summary

One of the realizations that I’m coming to by studying regenerative agriculture is the undeniable interconnectedness of life. It’s actually very difficult to separate topics into discrete categories and write about them. Microbes rely on insects, which rely on plants, which rely on animals, which rely on microbes, on and on and on. You can mix-and-match and put those words in any order and it would make equal sense. Everything relies on everything else, which is a much different perspective than the dog-eat-dog, competitive paradigm modern agriculture was formed around. Yes, competition is fierce out there. Yes, nature is red in tooth and claw, but this doesn’t change the fact that a richly diverse planet functions better than a less richly diverse one. The alternative of a barren planet with little diversity leads to much worse outcomes for everyone. Soil health and function is a prime example proving this point. It’s up to us to create and foster a diverse environment full of life through our management practices.