Dirt Made My Lunch

A trip through the food system and its externalities

by Docker Clark

Credit: Rick van der Haar on Unsplash

When I was in grade school, in the sprawling suburbs of Kansas, I often hummed a song called “Dirt Made My Lunch”. I had learned the song in my school’s choir one fine April, on Earth Day, and the lyrics stayed anchored in my brain for years. Short of the tune being catchy enough to get stuck in my 7 or 8 year old head, I didn’t think much of it. With almost twenty years of hindsight, I realize that wasn’t just a memorable song about dirt; it was the prologue to my professional life–my opening credits.

🎶 🎶
Dirt made my lunch
Dirt made my lunch
Thank you dirt, thanks-a-bunch 
For my salad, my sandwich, my milk and my munch
‘Cause dirt, you made my lunch
🎶 🎶 

My name is Docker Clark, and I am currently a researcher in NYU’s Department of Environmental Studies. Under the mentorship of the department (notably, my PI Matthew Hayek), I have been doing work surrounding climate and animal agriculture, particularly as it pertains to beef. You may then wonder why I told you about the dirt song which, upon further investigation, is a 1987 release from a band called the Banana Slug String Band-a group of musicians and educators passionate about nature. Who knew! Well, my first-ever true research project, my undergraduate thesis, was on soil contamination in New York City and how plants might be used to remedy that (a process called phytoremediation). After that, I began working and researching in the food sector and, as the song so rightly states, it all comes back to the soil. Not sometimes, pretty much always.

🎶 🎶 
“Dirt” is a word that we often use
When we’re talkin’ bout that earth beneath our shoes. 
It’s a place where plants can sink their toes
In a little while, a garden grows
🎶 🎶

In this issue of Who Wants Seconds, I’d like to take you on a journey from the dirt to your dinner plate through the lens of my current research area, regenerative agriculture. I am a scientist, if a beginner one, so I would be remiss not to include some facts and figures for you. Let’s get started!

STOP #0: BARE ROCK

Ok, ok, I know this is not where I said I’d start, but I want to at least give some respect to where soil itself begins, and that’s as rocks! It is erosion that turns bare rocks into mineral soil (that is, the part of the dirt which does not include any organic matter). Wind, water, plant roots, and symbiotic organisms called lichens break down the rocks into smaller and smaller particles until, with a healthy dose of dead organic matter, you have soil! This may seem a bit obvious to some, but I bring up erosion for a reason. Erosion can, in many agricultural systems, be a huge problem which leads people from farmers to agroecologists to demonize it as a whole. Remember: without erosion, we don’t have soil. 

STOP #1: DIRT

Dirt vs. Soil

As we begin our journey through food production,. I want to first address something that is glaringly wrong with this song if you’re a soil person like me. Dirt and soil, while often used interchangeably, are not the same thing. Soil is a complex mixture of micro and macro organisms, decaying organic matter, and sediment particles of varying size classes (from largest to finest: sand, silt, and clay). It is, by definition, impregnated with a web of life which helps it maintain its structure, absorb and hold water, and support life. “Dirt” is the word for small particles of soil (organic or inorganic) that lack the components or the structure to support plants (for example: 7 year-old me constantly had soil under my bare feet, and dirt under my fingernails… and all over my clothes). With that being said, I still love the song and we’re all going to cut the Banana Slug String Band (who, by the way, are still making music to inspire kids.) some due slack. Soil made my sandwich doesn’t have the same ring, and frankly, would be hard to rhyme.

Soil Fertility

You may think that once we have soil, the next logical step in our agricultural journey is to plant a seed, and while sometimes that is true, many farmers choose to apply a significant portion of fertilizer before ever planting. These fertilizers are nitrogen-based, often ammonium compounds like ammonium-nitrate (NH4NO3) which can be synthesized from the nitrogen in our atmosphere in a process called Haber-Bosch. The production of nitrogen fertilizer accounts for 1.4% of global carbon dioxide emissions and consumes 1% of the world’s total energy production. Nitrogen is, among many many other things, the backbone of DNA and the primary component of amino acids and by extension proteins. None of the food we eat could exist without nitrogen, so it makes sense to add it to the soil.

Though necessary to produce enough food to feed our population, the application of nitrogenous fertilizers is the main cause of eutrophication (when an overabundance of N runs off of fields and into waterways, where it over fertilizes the aquatic plant life and causes algal blooms which wreak havoc on aquatic ecosystems). You may have heard of the “Dead Zone” in the Gulf of Mexico; well, too much fertilizer is how it happened. 

From NOAA and LSU. Darker colors indicate areas where overproduction of algae has resulted in hypoxic (low-oxygen) and anoxic (no-oxygen) conditions.

🎶 🎶
A farmer’s plow will tickle the ground. 
You know the earth has laughed when wheat is found.
The grain is taken and flour is ground 
for making a sandwich to munch on down.
🎶 🎶

STOP #2: TILLING, PLANTING, AND GROWING

In order to grow our food, farmers need to plant seeds. According to the Food and Agriculture Organisation, if you’re a farmer in the Americas, you’re likely going to plant corn. If you’re in Europe, you’re more likely to grow wheat. Asia? You’re probably growing rice. I mentioned earlier that soil has a “structure”, and in order to give your seeds the best chance of survival, you are likely going to need to mechanically break this structure (albeit temporarily) by tilling. Tillage has been an agricultural practice since the birth of agriculture, but it too has its downsides. Left to its own devices, soil and the plants it supports will tend to stay put; vast networks of plant roots and mycorrhizal fungi (think mycelium–the roots of fungi) hold the dirt particles together. When farmers till the soil, that network is damaged, allowing rain or wind to carry free soil particles (which, remember, are carrying the fertilizer we just applied).  

In addition to the nitrogen runoff from these fields, we also have carbon loss to worry about here. Soils change in composition as you go deeper with the top layer soil containing the most organic material (it’s called the O-Horizon by scientists for this very reason). With a lot of organic matter comes a lot of carbon. This carbon can be washed away or oxidized (turning back into gaseous CO2) as a result of tillage, especially in agricultural systems which perform tillage every year.. This has marked negative effects on soil fertility, soil structure, and can result in a given field needing even more N and C inputs next growing season. We’ll talk more about soil carbon at our next stop on this journey, “Your Lunch”. 

It goes without saying that different crops have different relationships to the soil.  Leguminous crops such as beans or lentils are nitrogen-fixers, meaning they take advantage of symbiotic relationships in nodules on their roots to convert atmospheric nitrogen (N2- Not available to be absorbed by plants) into ammonia (NH3- usable by plants). In doing this, they are adding something back into the soil in exchange for all of the benefits, nutrients, and security that a healthy soil can provide. Corn's extensive, fibrous root system can help provide soil with the structure that is routinely lost with tillage and harvest. I could go on, but the point is you don't get something for nothing in the environment. This is all part of a complex web which relies on direct and indirect interspecies cooperation. Too much intervention to weigh the food scales in our favor (tilling, intensive irrigation, fertilization, and let not even get started on pest- and herbicides) is likely to cascade through the system and be felt elsewhere (probably more than one elsewhere). 

PIT STOP: REGENERATIVE AGRICULTURE

Let’s talk a little bit about some of these agricultural practices which have been a hotter and hotter topic among the scientific-agricultural community. First, and perhaps most importantly, “regenerative agriculture” for the purposes of this post is an umbrella term for a whole suite of different agricultural methods and practices which prioritize the “regeneration” or healing of the land, most often focusing on the soil as the baseline for all terrestrial ecosystems. Each farmer, scientist, non-profit, and “climate visionary” appears to have their own specific definition of the word “regenerative” in this context. Naturally, the word “regenerative” has become a buzzword which means anything and nothing, but in a general sense, practices which call themself regenerative are soil-focused. Here are some examples of agricultural practices that have been called “regenerative”.

• Cover-cropping

  Planting a non-cash (often nitrogen fixing/leguminous) crop on fallow fields to [1] reduce soil erosion and [2] add some nutrients back to the soil. This also allows for soils to maintain a more complex structure. A colleague and friend of mine recently published about the interplay between cover cropping and crop yields. Check her study out here.

• Reduced- or no-till farms

  Sowing seed without plowing or tilling first (and/or prioritizing crops which grow perennially without needing to be started from seed every year).  

• Ley rotations

  Think cover cropping with more steps (multiple rotations of mixed-species cover-crops between cash crops).

• Silvopasture

  Grazing animals on a mixture of pasture and forest (forest soils can far FAR more carbon than typical pasture soils not to mention cropland soils).

• Rotational Grazing of Livestock

  There are many different types of rotational grazing, some include “Adaptive Multi-Paddock” (AMP) grazing, Mob grazing, management-intensive grazing (MiG) and so on.

Given the fact that animal agriculture (meat, dairy, eggs, leather/hides, etc.) accounts for a disproportionate share of food-system GHG emissions, it makes sense that “regenerative animal agriculture”, also known as “regenerative grazing”, would become a particularly sought-after avenue for the climate-weary farmer attempting to reduce GHG emissions. Like “regenerative agriculture”, “regenerative grazing” does not have an agreed-upon definition. Most “regenerative grazing” practices involve some attempt on the part of the rancher to mimic the natural nomadic grazing pattern of bovine animals. In short: we’re usually looking at dense herds of cattle, constantly moving from place to place as a group. This differs from conventional grazing management (especially in the US) where large herds of cattle are allowed continuous access to a large pasture for the entire grazing season (sometimes supplemented with some hay).  

Why–I hear you ask–would it be better for animals to be constantly moved from small paddock to small paddock, rather than grazing a vast expanse at their leisure? Well, claims vary widely on this, with some saying cows prefer to graze in tight groups (they feel safer), and others saying it is merely more stimulating for them to have the excitement of a new paddock each day. What is sure is that, given the opportunity to graze a huge pasture at their will, cows will tend to over-graze certain areas and under-graze others. Essentially, the cows will choose their favorite place to graze (tastier grass/underbrush species, less sun exposure, closer to water, whatever the reason) and they will eat up and trample over that grass vastly more than other patches. Grass that has been overgrazed and soil that has been over-trampled can have a much harder time recovering from that trampling, leading to a gradual decline in pasture productivity (pasture quality). Grazing the herd on a small subsection of pasture for a short period of time, ensures that the animals have a similar effect on the entire pasture AND allows plenty of time for that subsection of pasture to recover (the amount of time it takes the cows to visit all other subsections). 

🎶 🎶
A stubby green beard grows upon the land.
Out of the soil, the grass will stand.
But under hoof it must bow
for making milk by way of a cow
🎶 🎶

The idea behind this being “regenerative” stems from the belief that this type of short-duration, intense grazing will allow plants plenty of time to prioritize growing more roots (which, among many other things that I am simplifying for brevity, helps pull carbon into the soil–soil carbon sequestration). Higher carbon sequestration in soil = less CO2 in our atmosphere. The potential of a practice like this is immense given that–on a global scale–the amount of C stored in the soil is more than the atmosphere and all plants combined.

Now, this is an exciting possibility, and contrary to what you might think after reading the rest of this section, I don’t think it’s impossible. But the reality is the data we have don’t point in that direction. There are several low and mid- quality scientific assessments of soil organic carbon (SOC) responses to regenerative grazing (and their predicted yearly SOC sequestration are widely varied), but these either [1] make no direct comparison between that and conventional grazing, [2] only collected a soil carbon measurement once (meaning they have no way to say how much was sequestered since they started grazing), [3] conducted their studies on sites which were recently converted to pasture from some form of annual row cropping (meaning they already had incredibly degraded soils and they would have seen sequestration regardless of the strategy they used to graze their animals), or some combination of the three.  

Here’s what good evidence that regenerative grazing can sequester soil carbon would look like. 

• Start with at least two (ideally many more replicates) pastures which are right next to each other and have the exact same land use history (bonus points if they've been grazed by cattle for the past 50+ years).

• Before ever starting the regenerative grazing system, take baseline SOC measurements at all sites

• Randomly designate half of these sites as regenerative and begin grazing cattle on them based on your desired regenerative or rotational method. Leave the other half as conventionally grazed.

• Take another soil measurement at every site, every year (at the same time each year), for 5 to 10 to 20 years.

• Compare the soil carbon from the baseline measurement, to the most recent measurement at that site (Year 5 or 10 minus year 0).

• THEN compare that 5 or 10 or 20 year difference between all regenerative and conventional sites.

As of now, only a handful of studies have done this (or something comparable) and, unfortunately for the beef farmers, results are pretty darn near zero. As in, due to regenerative grazing management, ~0 more tons of carbon were sequestered in regenerative pastures than in conventional ones. This is not to say that sequestration isn't possible for regenerative grazing, it just means that (A) we need more longitudinal data in different climates and circumstances and (B) the data we do have, don’t support some of the exciting claims re: regenerative grazing. Importantly, this all could change! While I certainly take issue with the idea of a single silver-bullet solution to any multifaceted problem such as food emissions, I certainly do not take issue with improving our practices for the sake of improving them, or hey, maybe because it's the right thing to do by the animals. Let’s continue to improve our science so that it can better inform our decisions! With that, let’s talk finally about food.

STOP #3: YOUR LUNCH

So, we’ve grown our plants and now it's time to harvest the food. Let’s talk a bit about processing and transport. The transport of food accounts for nearly 6% of total food system emissions (OWID), and transport of vegetable and fruit consumption contributes nearly twice the amount of greenhouse gases released during their production (Li et al. 2022). This, obviously, has more to do with international trade than it does with production, but it is a part of the food system often forgotten by well-meaning farmers and scientists who tout certain “carbon negative” agricultural practices or technologies.

Whether you’re flexitarian or carnivorous, paleo or vegan, it’s important to have an understanding of your food and the processes behind producing, distributing, and disposing of it. Each of these steps involves certain assumptions, emissions intensities, and associated wastes, and they all lead back to the soil. It makes sense, then, that the closer you eat to the soil (that is, the fewer steps involved to produce your food) the more efficiently you're eating. This goes all the way back to an ecological principal called Lindeman’s law or the law of 10%. The law of 10% states that, on average, only about 10% of the energy in a given trophic level (as in: producers=plants, consumers = herbivores, secondary consumers = carnivores) makes it up to the next level. This creates a sort of ecological food pyramid not unlike the food pyramid you probably saw in primary school classrooms, where each level is only 10% as energy dense as the level below it. This doesn’t mean that meat (say, a steak) has 10% the calories of a salad. It means that, generally, the cow had to eat 10 salads to produce that many calories of steak. So cut out the middle man every once in a while and enjoy some food that came straight from the soil!

🎶 🎶
Dirt made my lunch
Dirt made my lunch
Thank you dirt, thanks-a-bunch 
For my salad, my sandwich, my milk and my munch
‘Cause dirt, you made my lunch
🎶 🎶