Inquiry-Led: What’s That Smell?

It’s a crisp October day in the Midwest. Campus trees have put forth kaleidoscopic canopies and are beginning to shed, while one of Iowa’s trademark blue skies is glittering high and wide. You step out of your residence hall en route to a dining hall bagel and schmear, and instead of the intoxicating leaf musk scent you expect, your nostrils are assaulted by the dulcet aroma of … poop?

It’s warm and earthy and suspended thickly in the atmosphere. Sort of sickly sweet. The smell makes me think of microbes. The pungent odor descends on campus for only a couple of days each year and, after a few hours, I hardly notice it. Nonetheless, it’s a rite of passage for Grinnellians to inhale and ask, “What is that smell?”

The quick answer? Manure. After all, Iowa is home to 25 million hogs, 56 million hens, nearly 4 million cattle, and the considerable poop those animals produce.

I’ve lived in Grinnell for five years, though, and my curiosity isn’t resolved by “manure.” I want to know where the manure smell is coming from. And how does it reach Grinnell? And why is it so … potent?

I want more than a simple answer for this fetid phenomenon — I want an explanation. And in this inaugural installment of “Inquiry-Led,” I’ve set out to find one.

Manure: Friend of Farmers

My investigation begins with a lengthy email [Subject: Seeking Manure Wisdom] to Jon Andelson ’70, senior faculty of anthropology and environmental studies. When it comes to Iowa phenomena, Andelson always knows a guy. Sure enough, by way of response to my inquiries, he introduces me to his friend, Howard McDonough, a lifelong Grinnell-area farmer. Back in the day, Andelson tells me, McDonough was one of the first farmers to jump on the “natural fertilizer” wagon. In Andelson’s sunny office, passing around an ear of rainbow flint corn, the two give me a crash course on fertilizer.

As plants grow, they guzzle up the elements nitrogen, phosphorous, and potassium from the soil. In fields which are constantly replanted, these elements become depleted and, to replenish these essential nutrients for the next round of crops, farmers add fertilizer to their fields.

For years, McDonough explains, most farmers applied commercial fertilizers — synthetic blends of nitrogen, phosphorous, and potassium. But in the ’70’s, he tells me, “Pioneer Seed was doing all kinds of research where they’d put manure onto cornfields instead of commercial fertilizers. The more often they applied manure, the more the yields went up.” Manure wasn’t simply as good as synthetic fertilizers. It was better.

When I was a student in biology courses, the topic of feces came up a lot. Ecology? Microbiology? Immunology? Poop is relevant to it all. So, I know that manure, like commercial fertilizers, contains nitrogen, potassium, and phosphorous. The organic matter also contains a wealth of micronutrients that benefit soil and plants ­— it’s like a seven-course meal for young corn.

But what McDonough tells me really sets manure apart as a fertilizer is the way it slowly releases its nutrients as it breaks down, rather than dumping them all at once. “Manure put down 20 years ago might still be benefitting plants grown today,” he says. For soils stripped of nutrients by monoculture farming year after year, manure is a gift that keeps on giving.

Inspired by the findings of the early manure studies, McDonough began collecting manure from a chicken facility in Prestage, Iowa, and hauling it to his fields and other farms in the area. It was a win-win situation: the chicken facility got a sustainable outlet for their animal waste, while farmers like McDonough received free, effective fertilizer.

McDonough tells me that manure has become the preferred fertilizer for many farmers in the decades since his initial foray into manure in the ’70’s. Manure is cheaper than commercial fertilizer (though no longer free), more sustainably sourced, and, in epicenters of livestock agriculture like Iowa, readily available.

Does manure’s knack for fertilization explain the mystery at hand? I prepare to close the case, asking McDonough if, when we smell manure on campus, it’s a result of it being spread onto nearby fields as fertilizer.

“Occasionally,” he replies, “but rarely.”

Brutal.

Something Fragrant This Way Comes

Fertilizer application is certainly a part of the story, McDonough assures me. In the fall and the spring — after harvest and before planting — manure is spread on fields across the Midwest. Depending on the temperature and the speed and direction of the wind, the freshly spread manure can be smelled from near and far.

When it’s not fertilizer season, however, McDonough believes we’re smelling manure straight from the source. Specifically, he says that the odor of chicken feces is often borne in on westward wind from poultry facilities east of Grinnell.

His claim puzzles me.

Grinnell is surrounded by livestock operations. The smell of pig manure occasionally wafts in from farms south of town, and the odor of cattle manure from a dairy farm west of Grinnell. (“I’ve trained my nose to smell the difference between chicken manure and pig manure,” I’m told by Shannon Hinsa-Leasure, professor of biology. Niche talent or curse? You decide.) Amidst all this omnidirectional animal husbandry — why should chicken be the primary culprits? Why was McDonough pointing the finger at poultry facilities to the east? To vet his hypothesis, I turn to Iowa’s atmosphere and the open road.

For years, Iowa State University meteorologists have collected data about wind speed and direction in Iowa. They’ve determined that the prevailing winds in Iowa — the strongest and most common winds ­— blow from the southeast to the northwest. This means that winds are far more likely to carry odors from the east to the west than in any other direction.

The wind data checks out with McDonough’s hunch regarding the leading source of the smell, but I don’t want to assess his hypothesis with meteorological theory alone. So, on a 34-degree day in November, with twenty miles per hour winds blowing from the southeast, I head east out of Grinnell on Highway 6. I roll my car windows down. I wear two coats, gloves, a knit hat, but no scarf: I need my nose free.

Nine miles east of town, there is a major egg-laying facility. Picture, if you will, a few million hens — all eating and laying eggs and pooping nonstop. I want to see how close to the facility I have to get before I can smell that familiar chicken sh*t refrain.

About three miles from the facility, the scent hits me. After 10 minutes of frigid en plein air driving, my sense of smell is probably not the strongest, but the tangy, sweet odor is undeniably familiar.

The smell had travelled far to reach me, but I’d travelled far too. If they were the source of the occasional campus stink, these manure odor molecules would have to journey six additional miles westward to reach Grinnell. Was that journey likely? It depends upon temperature.

Cold days (such as the one I’d ventured out in) aren’t nearly as conducive to spreading scents as are hot days. At warmer temperatures, liquids and solids turn into gasses more readily, drastically increasing the number of odor-causing molecules in the air. If the odorous molecules from chicken manure can extend at least three miles east in nearly freezing conditions, it certainly seems plausible that they would grace the town of Grinnell on a seventy degree, windy, September day.

A Sensitive Defense

At this point, I am fairly convinced that the occasional campus stink is — at least most of the time — of the chicken poop persuasion. And it’s led me to one final question:

How can I possibly be so sensitive to smells produced nearly 10 miles away?

After all, none of this investigation would have occurred if not for the simple fact that I (and many) find the stench of manure … offensive.

I decide to bring my question to Liz Queathem, professor of biology. She was trained as a comparative physiologist and functional morphologist — she studies why animals have the form and structure that they have. I figure she might know something about the human nose and its beef with feces.

Queathem explains to me that, as feces decomposes, it produces gasses including ammonia (NH3) and hydrogen sulfide (H2S). In high concentrations, both compounds are extremely toxic. Our noses are carefully evolved to detect and protect us from these gasses.

Just how sensitive is the nose? Well, the Occupational Safety and Health Administration sets the limit for acceptable exposure to hydrogen sulfide at 20 parts per million. The human nose, however, can detect it at concentrations of 0.05 parts per billion. That’s 1/400,000th of the concentration at which hydrogen sulfide would be dangerous to our health.

If there’s a smell that is going to set off alarm bells in our brains — it is manure. In fact, Queathem says it’s pretty much impossible to develop a detector for the stinky component of poop that is as sensitive as the human nose. Out of everything I’ve learned in my manure investigation, I find this the most comforting.

Sure, the smell is bad. Frankly, if you’re already having a bad morning and it turns out to be a manure day, it can be viscerally upsetting. But I like knowing that the scent is only so offensive because my organs are trying their absolute best to keep me safe.

Right now, Iowa is home, and it’s a home I share with a lot of livestock. We all poop. My scent receptors may be taking it too far. I appreciate their trying.

I hope this cleared the air.

— Anika Jane