The Nature-Nerd Nuts & Bolts of Soil

Factors of Forming the Foundations of Life

Bushing off my shoes or cleaning the car, dirt just seems like something that’s best to steer clear from: It sticks to everything. It’s dusty when it’s dry. It’s muddy when it’s wet. It’s annoying when it gets into bed.

That being said, from the point of view of the tomatoes and trees, dirt is a much more valuable thing. Indeed, none of us would be here without it. In every way imaginable, soil is our foundation.

So, let’s get to know this magic substance a little better, not only as the foundation for all life, but also for the hopeful metaphors that it provides.

Let’s start with the fact that there are lots of different kinds of dirt, so many that some might consider themselves connoisseurs (you can even become a Dirt Doctor¹). Still, many people distinguish “dirt” from “soil” by saying that dirt doesn’t have the nutrients to support life² that soil has. But, in this article I’m gonna use those terms interchangeably because it’s fun, and also because it’s fair; indeed- there’s a plant that has evolved to grow in dirt everywhere³ (though they’re often considered weeds, gotta hand it to hearty). Anyway- let’s start with the basics:

What is Soil?

The first thing to know about soil is that it’s made of many things⁴. To the naked eye it might look just like a bunch of dusty stuff, but there’s actually a lot going on there. Here’s the general categories of what makes up dirty things:

• Minerals (which often come from broken down rocks, but not always)

• Organic material (like leaves, poop and dead meat -which is why most people try not to get dirt in what they eat).

• Living organisms (such as the invisible microbes who help organic materials decompose)

• Air (which is necessary for microbes)

• Water (which is also necessary for microbes)

What makes each soil unique is the ingredients that contribute to each category. For example, some soil may have more minerals while others may have more poop. With that in mind, different soils are created in different places under different conditions that offer different ingredients. So-

Here are the 5 “factors of formation”⁵:

The first two factors have to do with the actual soil ingredients:

1. Parent Materials might be called the baseline of soil (as they make up a big percentage of it⁶). The parent materials are the clay, sand, and silt that mostly come from rocks over thousands of years as they’re eroded by weather (like rain, ice, and wind). The size and amount of the parent materials determines the soil’s texture so that it might be rocky, sandy, dusty, or thick with clay.

2. Organisms are the other big source of ingredients for soil. There are generally three categories of organisms that affect soil:

• Plants contribute to soil in a few ways. Firstly, their roots help hold it in place (so that it doesn’t get washed or blown away). Plants also cycle nutrients by taking minerals from the soil (as part of their food) and by adding nutrients to the soil (when they drop leaves or die). Finally, decomposing plant matter creates a layer of mulch on top of the soil that protects it from erosion and keeps the moisture in the ground.

• Animals also contribute to soil through their poop (which provides lots of microbes and nutrients) and their dead bodies (which also offer nutrients). Some dirt-dwelling animals also aerate the soil by moving it around when they dig and burrow (like gophers⁷ and worms).

• Microbes⁸ (like bacteria and fungi) secrete enzymes that help break down all the dead and poopy stuff into smaller and more stable forms of plant nutrients (such as carbon, nitrogen, phosphorus and potassium).

The next three factors of formation address how the soil’s ingredients are created and collected:

3. Climate is a major factor of how soils are formed. Firstly, temperatures affect how fast the organic matter is decomposed; cold slows decomposition down and heat speeds it up⁹.

   Also, the amount of precipitation has a big impact in a couple ways: Firstly (and obviously) precipitation waters plants. If there’s lots of rain, then there’s lots of plants, and if there’s lots plants, then there’s lots of food for animals (which means more dead meat, bones, and poop for the soil). Plus, lots of plants also means that there’s lots of dead leaves and roots (that also decompose into soil). Generally speaking, more water equals more organic material in the soil.

   Also, when rain pounds onto rocks, or ice moves on top of them, the pressure slowly dissolves the rocks into smaller pieces that the water moves around through run-off. This is often how the soil’s parent materials are formed.

4. Terrain also has a big impact on soil composition. There are different kinds of terrain, such as mountains, plateaus, valleys, and plains¹⁰. Different terrains tend to have different kinds of soil. For example, steep mountain slopes tend to have more shallow soil as run-off carries it downhill to the bottom of the mountain. The valley, then, catches all the minerals and organic material, which gives it richer soil as a result. (you can dork-out on valleys here)

5. Finally, soil takes time. Landslides, glacial retreats, and volcanic eruptions all create new soils that mature over time, changing as they mature. Newer soils have grittier textures with less plant and animal matter. Older soils are finer and often have more plant and animals matter. With this in mind, the ground has different layers of soil at different stages of development, which are called “soil horizons.¹¹”

   Here’s how the soil horizons are layered, starting with from the top layer (that touches the air) and moving down into the ground:

• The tippy-top layer is called the organic layer. This is where all the new poop and dead stuff starts breaking down.

• The second-to-top layer is the topsoil (or humus layer), where the microbes and worms do their decomposition work. This layer is where seeds germinate and where plants get a lot of their minerals.

• The middle layer is called the subsoil, which consists mainly of leached minerals from the upper layers, and is often more clay-like.

• Underneath, there’s the parent rock (which is bedrock that’s been broken-down).

• Finally, the bottom layer is bedrock, which are the big rocks that break down to create the parent rock (over very long periods of time).

Why Soil Matters

Once soil has been created, it serves multiple functions within the ecosystem¹²:

• It supports plant life. While plants make their own food from the sun and air through photosynthesis (whoa), they also need water and minerals -which they absorb through their roots in the soil.

• It supports water quality: Soil filters and regulates water by slowing it down and absorbing it for use.

• It stores carbon: soil captures and stores carbon from the atmosphere in a process called carbon sequestration, which works like this¹³: plants absorb carbon through photosynthesis (whoa). Then, when they die, the carbon that’s stored in their leaves and roots decomposes into the soil (and stays in the soil until it’s dug up and released into the atmosphere again).

• It facilitates decomposition: By providing habitat for dirt dwelling animals (who relish the opportunity to chow down on dung or fruit that’s rotten), soil makes sure that we’re not wading through crap everywhere.

Nature’s Soil Care

All things considered: dirt is pretty valuable stuff, which is why nature naturally protects it from erosion (which is when soil stuff -such as rock, sand, and organic materials- are worn away by wind, rain, running water, ice and landslides¹⁴). In order for soil to stay in place and stay healthy, it needs the support of plants (who help hold it in place, keep it covered, keep it moist, and replenish it with new organic material). With this in mind, different kinds of ecosystems offer different kinds of soil care. In forests, fallen leaves, trunks and branches provide a constantly refreshed layer of mulch¹⁵ that maintains moisture and protects the soil from the wind and water. In prairies and meadows, grasses¹⁶ and ground covers do the same trick. Even in deserts, the soil has protection with what’s called bio crusts¹⁷, which are communities of algae, lichens, mosses, bacteria and fungi that reside on the surface of the soil to make sure that it stays in place. Naturally, human care of soil aims to mimic nature’s care through mulch, ground covers and compost.

Making Rich Soil with Compost

What makes a "perfect” soil is totally debatable as it depends on the needs of the plant. Plants adapt over time (through what’s called adaptations¹⁸) to thrive in different soil conditions (such as salty soil by the ocean, or dry and low-nutrient soil in the desert). With this in mind, the nutrients and conditions that plants need reflect what’s available in their native habitat (learn more about native plants here).

That being said, generally speaking, soil is considered more fertile when it has more organic matter, minerals and microbes. That’s why farmers and gardeners make and use compost. Compost is a mixture of decaying and decomposing plant and animal products that offer a broad base of the most essential plant-nutrients¹⁹ (in which each nutrient helps with a different part of growth such as root growth, photosynthesis, and forming seeds²⁰). Plants hold all the nutrients that they’ve absorbed (through their roots) in their tissue. Then, when they decompose, those nutrients are recycled into the soil to become available for more plant growth.

Microbe Magic

Decomposition doesn’t happen on its own; it requires microbes. Microbes are everywhere: in the air, in the water, and in the dirt²¹. They are a free and invisible force of nature that flourishes by the billions as soon as conditions for growth are provided (did you know that “there are more microbes in a teaspoon of soil than there are people on the earth²²”?). To thrive, microbes need the right combination of air, water, and threes times as much carbon to nitrogen²³, which can be found in simple ingredients: dried up plant waste (including cardboard) is rich in carbon (and is called “browns”), and green plants, kitchen scraps, and poo are rich in nitrogen (and are called “greens”²⁴).

With the right ratio of “browns” and “greens”, all the compost needs is a good stir periodically (to give the microbes air), and some water (to give the microbes moisture)²⁵. If the compost is out of balance²⁶, it will either seem like nothing is happening or it will be stinky and slimy. If the compost pile is degrading too slowly, the pile might need more greens or water. Conversely, if the pile gets kinda stinky, the pile might need more browns and/or air.

In the process, compost goes through 3 stages: the warm-up, the hot-stuff, and the cool-down cure. Each stage has its own special crew of microbes²⁷. In the warm-up, the microbes get turned-on. Then, in the hot-stuff, the microbes heat up the pile to help burn away any pathogens or weed seeds. Getting the temperature right is important in this phase because if it’s stirred too much, it’ll lose the heat that this crew of microbes need to thrive (and they like it hot). However, if it’s not stirred enough, the microbes won’t have enough air to breathe.

Then, once the microbes have done the bulk of their job, the compost will start cooling naturally. This is the sign of the last phase of composting: the cool-down cure. In this phase, the compost will seem pretty much done: it will look and feel like rich soil. But, to be sure that it's ready to offer plants, it’s important to let it really finish, or it could burn them (too much semi-decomposed matter can be harmful²⁸). You can test when your compost is done by the “bag test²⁹” where you “put a handful of moist compost into a zip-lock bag”, press out the air, leave it for three days, then open it back up. If it still stinks, it’s not done.

Finally, once you’ve fully cured the compost, you can sprinkle it anywhere. Signs that the soil could benefit from a compost boost³⁰ are: leaves that are yellowing, bronzing or falling, or growth that seems stunted. However, compost can also be overdone (which, unfortunately, has somewhat similar symptoms³¹. So, I tend to play it safe with application). Just remember: compost is not a substitute for soil; it’s an amendment. Well-balanced soil also needs ingredients that help it drain well and retain moisture³².

A Hopeful & Unifying Conclusion

When it comes to the foundations of life, there’s nothing that inspires more hope than soil. On this ground level of biology, life is rooted in recycling³³, where everything has value (in all stages of its existence), and prosperity is rooted in the ability to use what’s been broken; nothing is ever lost or gained -only rearranged.

Here, the unity of life couldn’t be clearer:

the dirty truth is that we’re made of each other.

---

Hear More Songs & Stories of My Dirt Devotion

---

Stay In Touch for New Content and Ways to Join Me

1. https://www.scimagoir.com/rankings.php?area=1111&sector=Higher%20educ.

2. https://www.thespruce.com/soil-vs-dirt-7089792#:~:text=Soil%20is%20not%20dirt%20because,Plants%20cannot%20grow%20in%20dirt.

3. https://www.epicgardening.com/plants-for-poor-soil/

4. https://www.nature.com/scitable/knowledge/library/what-are-soils-67647639/#:~:text=Soil%20is%20a%20material%20composed,mineralogy%20of%20soils%20is%20diverse.

5. https://geo.libretexts.org/Bookshelves/Geography_(Physical)/The_Physical_Environment_(Ritter)/11%3A_Soil_Systems/11.05%3A_Factors_Affecting_Soil_Development

6. https://www.maswcd.org/Youth_Education/StudyGuides/Soils_study_guide.htm#:~:text=An%20average%20soil%20sample%20is,distinguished%20with%20an%20ordinary%20microscope.

7. https://www.wildlifeexperts.com/pocket-gopher-soil-health/#:~:text=Soil%20Aeration,continually%20tamp%20down%20the%20soil.

8. https://decode6.org/articles/what-do-microbes-do-in-the-soil/#:~:text=Microbes%20secrete%20enzymes%20that%20help,increase%20soil%20organic%20matter%20content.

9. https://www.bbc.co.uk/bitesize/guides/zw4n97h/revision/7#:~:text=At%20colder%20temperatures%20decomposing%20organisms,killed%20and%20decomposition%20will%20stop.

10. https://www.worldatlas.com/articles/what-is-terrain.html#:~:text=The%20common%20ones%20are%20plateau,to%20flat%20and%20icy%20wastelands.

11. https://www.sciencefacts.net/soil-horizons.html

12. https://www.soils4teachers.org/role-of-soils/#:~:text=Soils%20absorb%2C%20hold%2C%20release%2C,Soil%20Science%20Society%20of%20America

13. https://www.energy.gov/science/doe-explainsthe-carbon-cycle#:~:text=Plants%20constantly%20exchange%20carbon%20with,carbon%20dioxide%20when%20they%20decay.

14. https://education.nationalgeographic.org/resource/erosion/#

15. https://www.cnps.org/gardening/prepping-and-planting/mulching-basics#:~:text=Mulch%20reduces%20soil%20water%20losses,Healthy%20soil%20means%20healthy%20plants!

16. https://allnativeseed.com/the-role-of-native-grasses-in-soil-health-and-erosion-control/

17. https://www.nature.org/en-us/about-us/where-we-work/united-states/utah/stories-in-utah/growing-biocrust-in-utah/#:~:text=Just%20centimeters%20off%20the%20ground,the%20soil%20surface%20of%20drylands.

18. https://www.thinktrees.org/wp-content/uploads/2019/07/Plant-Adaptations.pdf

19. https://convoyofhope.org/articles/plant-nutrients/#:~:text=First%2C%20let's%20talk%20about%20what,reduced%20yields%2C%20and%20weak%20stems.

20. https://extension.missouri.edu/publications/mg4

21. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9986037/#:~:text=Microorganisms%20were%20the%20first%20form,of%20every%20form%20of%20life.

22. https://ohioline.osu.edu/factsheet/SAG-16#:~:text=There%20are%20more%20microbes%20in,Fungus%2C%20Protozoa%2C%20and%20Nematodes.

23. https://compost.css.cornell.edu/chemistry.html

24. https://www.charlottesville.gov/704/Backyard-Composting#:~:text=See%20the%20list%20below%20of,to%20your%20backyard%20compost%20pile.

25. https://www.epa.gov/recycle/composting-home#:~:text=Microorganisms%20feed%20on%20the%20materials,materials%2C%20and%20oxygen%20to%20breathe.

26. https://www.washingtonpost.com/home/2023/06/27/compost-mistakes-common-avoid/

27. https://calrecycle.ca.gov/organics/homecompost/microbes/#:~:text=The%20most%20productive%20members%20of,material%20they%20find%20themselves%20on.

28. https://extension.umn.edu/nutrient-management-specialty-crops/correct-too-much-compost-and-manure#:~:text=While%20adding%20compost%20to%20your,available%20in%20high%20pH%20soils.

29. https://earthmatter.org/wp-content/uploads/2016/08/tip-sheet-how-to-use-compost-cpts-htuc-f.pdf

30. https://www.nparks.gov.sg/nparksbuzz/oct-issue-2020/gardening/identifying-nutrient-deficiency-in-plants#:~:text=Deficiency%20symptoms%3A%20Chlorosis%2C%20bronzing%20or,bronze%20spots%20in%20younger%20leaves.

31. https://www.rivulis.com/6-signs-you-are-over-fertilizing-your-plants/#:~:text=Yellowing%20and%20wilting%20of%20lower,Slow%20to%20no%20growth.

32. https://sfyl.ifas.ufl.edu/lawn-and-garden/homemade-potting-mix/

33. https://www.snexplores.org/article/recycling-dead#:~:text=The%20decomposition%20that%20follows%20the,It's%20nature's%20way%20of%20recycling.