Urban community garden in Philadelphia in the United States

My shovel hit the earth with a ka-chunk. My friend and I were digging trenches to lay down a line of asparagus on a stretch of urban territory in Washington DC. We didn’t get far. The ground consisted of a thin layer of grass covering gravel mixed with burnt-orange clay.
Until a person starts digging, the depletion of the ground underfoot goes unnoticed. Yet the soils spread beneath us are important historical artefacts. The search for mineral nutrients has propelled colonisation, while the crises over depleted soils had a lot to do with the creation of both the social welfare state and 21st-century global capitalism. Since the 19th century, conservationists, economists, nationalists and environmental historians have written about soil quality and the “rape of the land”.

My experiment in trying to farm on disturbed urban territory got me thinking about how history might be changing with the molecular turn in biology. Scientists no longer think of soil as a collection of mineral elements. Molecular biologists have shown that billions of microscopic organisms dwell in healthy soils to form a superorganism of wondrous complexity. As I dug through rock and clay, I wondered how a history of this soil microbiome would read. Is it possible to populate the ground beneath my feet with the story of the tiny lives down there?

I looked under my spade. I had little to go on. There was almost nothing alive on this tuft of land on the edge of a primary school. The site had been a staging ground for a major construction project lasting two years, removing plants and earth, compacting the ground. After the renovation was complete, workers rolled out nylon landscaping nets, dumped a layer of commercial topsoil, pumped on some liquid nitrogen fertiliser and broadcast grass seed. It was good enough for a lawn but not for a vegetable garden.

Lawns are often dead zones that don’t feed native birds, bees, butterflies – or people. My friend Wesley and I wanted to see how many edible trees, shrubs and cover crops we could coax into life on the narrow banks of grass. We’d become friends while gardening on ground to which we had no claim. In a few years, we turned a patch of no-man’s land into a flower-and-vegetable-filled garden. Making an edible forest around the school was a bigger project for which we had no budget or staff – other than ourselves.

Urban regeneration

As spring warmed the ground, we began to plant. The school was closed so hardly anyone was around. Once started, we had trouble stopping. Wes and I spaded up the fringes of the school’s community garden, setting down seeds of kale, spinach, rocket and wildflowers. We moved on to the east side to plant strawberries and asparagus. We spaded up ground for hardy berry bushes and fig trees along the school’s southern facade, which bakes as hot and dry as any Italian olive grove. We climbed the padlocked courtyard fence to slip in native pawpaw and persimmon trees, while thumbing seeds of corn, beans and squash into the soil. These new edibles took root among struggling imported plants that the landscapers had laid down.
Wesley grafted fruiting apple branches onto ornamental trees and nestled tomato starts among decorative shrubs. We hoped the strawberry plants would spread as a cover crop to replace the English ivy where great clouds of mosquitoes breed. A city tree-cutter gave us freshly-cut white oak logs. We inoculated them with the spawn of shiitake mushrooms and stowed them in the shade of holly trees. Finally, we moved on to the marginal land on the west side of the school, where the cranes and trucks had rolled.

There, the soil had nothing to it. I dug in and lifted my spade to reveal a terrain of mass extinction. The ground held no worm, bug, root nor fungi. Nothing. As we dug, we unearthed only “foreign” elements – glass, plastic, brick and rust-iron nails. For a historian, it comes as no surprise that we live on ruins left by our predecessors, but my eye was on the future: building soil, restoring dead ground to life during a pandemic.

Flattened ground aerates poorly and has trouble both holding water and draining it. Even grass and invasive weeds had a hard time growing on the west side plot. Healthy soils are springy, lined with hair-thin roots and densely populated with a world of life in the form of insects, tiny animals, bacteria, viruses and fungi. Fungi send food and messages that zoom around the underground realm. Specialised bacteria ally with root tips, which serve as the command centre of plants. Azotobacter produces growth-stimulating chemicals. Rhizobium and Glomus work with roots to reduce disease in soils. Another bacteria, streptomyces, rescues thirsty plants during droughts. If drought conditions continue, root bacteria can even mutate to alter their metabolism to help plants along. Other bacteria and fungi quarantine plants from insects and pests. Not all bacteria and fungi are beneficial; some cause disease. Others are no more than freeloading parasites. It’s like any community – we take the good and the bad.

Wesley and I debated what to do. We had no money or desire to buy sterile plastic bags of topsoil. So far, we’d nourished our seedlings with leaf mulch and compost from kitchen scraps. That meagre stream had run dry. Wes pointed to an alley running along the forested park where trees drop leaves and branches on brick. Bacteria and worms had eaten those droppings and left behind a two-inch layer of soil. We scraped away, mining three buckets, barely enough to line an asparagus bed.

James Scott and early agriculture

Our problem of ravaged soils is one of the oldest in the history of agriculture. The first agricultural Homo sapiens farmed and foraged on small islands in alluvial deltas, semi-watery places that flooded regularly. Spring deluges brought fresh nutrients to river basins. Early humans engineered their settlements so that the hydraulic forces of rivers brought nutrients to them.

When humans settled down to farming 11,000 years ago, they enticed some animals to live with them. The Yale professor James Scott argues that most ancient farming communities, especially ones that relied on wheat or rice-based diets, invented lasting social institutions like social hierarchies, taxes and slavery. Compared to the easy life of hunting and gathering, farm work is repetitive, dull, physically taxing and time-consuming. Hunter-gatherers were taller, fitter and healthier than their farming neighbours. If our ancestors had a choice, they chose foraging.

According to Scott, farming had one main advantage. Wheat and rice can be stored for long periods like money in the bank. Elites forced other people to do the boring farm work so they had time for “civilisation”– poetry, law, painting and science. The walls around early city-states, Scott speculates, functioned as much to keep enslaved workers in as to fend off invaders. Animals helped with the heavy lifting. Pigs and chickens roamed and ate the garbage that mounted in crowded villages. Animals, birds and humans consumed plants, turning them into manure that decomposed into refreshed soils to feed plants.

This human-animal-crop system hiccupped along for millennia with lots of misstarts and collapses, caused in part by soil degradation and famines themselves triggered by plant, animal and human epidemics. In the 18th and 19th centuries, the manure-crop cycle was adapted for urban life. In New York, soil collectors cleared privies during the night and loaded barrels of human waste onto barges heading for Long Island, where farmers bought the valuable human faeces. Farmers piled composted manure onto fields to grow vegetables which then sailed back across Long Island Sound to be sold to New Yorkers. That closed, organic cycle worked pretty well until the mid-19th century, when cities grew so large that the collectors couldn’t keep up. Women held their skirts up to wade across streets of horse and pig manure. Leaking cesspools drained into private wells. People got sick from faecal bacteria.

Worried about murderous dirty water, city managers hooked up specially built drainpipes that tunnelled human waste into rivers. As American cities grew, underground arteries pumping faeces invisibly sutured together the muck of urban areas to surrounding rural landscapes. Urban sewer systems unquestionably improved people’s health, but they precipitated an enormous scientific experiment gone wrong. Algae in rivers and lakes fed on phosphorus and nitrogen from faeces. The algae multiplied to turn clear water into floating green lawns. As the algae died and sank to the bottom, bacteria used oxygen to decompose it. As oxygen levels dropped, fish suffocated.

People understood that sewer lines severed the nutrient chain between humans and crops. Newspaper editor and abolitionist Horace Greeley called the practice of tossing away good faecal matter to choke up local waterways “inexplicable stupidity”. As local farmland lost fertility, urbanites relied on food from farther and farther away.

Soil and conquest

But there was always more land to be had for cash crops. In the 19th century, European and American adventurers headed abroad looking for riches, as their forefathers had done. This time, they sought to mine new ground for nutrients to feed growing urban populations at home. Unfortunately, most good agricultural land was already under the till. Around the world – from Russia to Poland, India to South Africa, New Zealand to Japan – leaders and colonisers pushed into marginal land at their peripheries. The new imperialism of the 19th century drained much of the world’s lingering portions of accessible fertile land. The rate of ploughing under virgin territory outpaced even unprecedented population growth.

Settlers did not go easy on the land. They cut down forests and ripped through grasslands, sent topsoil sliding downhill and over riverbanks to create new geological features such as huge, artificial canyons, land-filled lakes and elevated rivers. Forests were chopped down, meaning that far less rain fell on the plains. Rain and wind swept unobstructed across disturbed ground, sending earth skyward. Famines caused by man-made droughts and soil erosion convulsed the Russian Empire, China and British India at the turn of the 20th century.

Thinkers in the 19th century obsessed over degraded soils. Rosa Luxemburg spoke of the theft of earth right out from under workers’ feet. Karl Marx determined that all original sources of wealth grew from the soil first and workers second. Marx ended his life reading about soil science and fretting over the “metabolic rift”: the failure of farmers to return nutrients to the ground they have worked. Charles Darwin in his dotage became fascinated with the soil-building properties of earthworms. Early 20th-century conservationists often wrote about “desertification”. Nothing short of a miracle, they worried, would halt the tip toward soil exhaustion that threatened to turn all of Earth into a vast desert.

And then Alexander von Humboldt sneezed. Travelling in South America, the Prussian polymath noticed Peruvians unloading baskets of a dusty substance that made his nose twitch. He learned it was guano, the faeces of birds that had fed on fish and landed on coastal rocks to relieve themselves. Humboldt brought a scoop of guano home and chemists found it was rich in nitrogen, potassium and phosphate – just the nutrients that plants on famished ground need. Experiments showed that crops flourished in guano-rich soils. Soon, everyone wanted it.

By mid-century, the quest for nitrogen sources led to a new round of colonisation. The US passed the Guano Islands Act in 1856. They raced Great Britain, Peru, Ecuador and Chile to poke their flag down on every rocky, bird-shit-coated outcropping they could find. British leaders took hold of Namibian guano. In 1879, Peru and Bolivia went to war against Chile for access to Chilean-owned mines of sodium nitrate, a guano substitute. The name of the disputed mineral “Chilean saltpetre” tells you who won that war. But there was never enough. Farmers ran through the original supply of Peruvian guano in just a few decades. Prices for Chilean saltpetre rose.

Watching world populations multiply while soils grew exhausted, pundits predicted calamity. German thinkers worried especially. If Germany had a conflict with a superior naval power (say Great Britain), they would be cut off from Chilean nitrate imports. Germany was addicted to imported nitrates for both fertiliser and explosives. For a century, German scientists tried to “fix” nitrogen in the air to a form they could use, a simple task which plants cooperating with microbes do reflexively.

Organic farming and the nitrogen glut

It took 100 years before the German chemist Fritz Haber devised a high-energy method using heat and pressure to combine atmospheric nitrogen with hydrogen to form ammonia or nitric acid. The engineer Karl Bosch scaled up Haber’s invention. Bosch drew up blueprints for the Oppau ammonia factory in 1909, the same year that 1,000 people met in Budapest for the first international conference on soil science. The attendees had no idea that the Haber-Bosch process, an invention whose impact on human history rivals the steam engine and the splitting of the atom, would flip the ratio of nitrogen on earth from scarcity to glut.

But before that happened, the unlucky convergence of the Haber-Bosch process with the First World War diverted the technology from food to war. In the spring of 1915, a blockade severed Germany from Chilean nitrates just as barrels of nitric acid rolled off the line to make explosives. After the war, the soil problem intensified – but the Haber-Bosch process had made commercial nitrogen cheap, curbing the desire for recycled human waste.

Around this time, Albert Howard, an English botanist stationed in India, became the modern proponent of “organic farming”, a new term for old practices. His basic tenet held that farms should close the cycle of nutrients from soils to crops and back again. Some contemporaries took this idea further. The Indian botanist Jagadis Chandra Bose and the Austrian Goethe scholar Rudolf Steiner saw a “vital force” in soils. Bose speculated there existed no break “in the life processes that characterised the animate and inanimate world”. Steiner thought a farm should be treated as a living organism. Soils, like plants and animals, were alive, Steiner taught his disciples.

Many scientists rejected Steiner as unscientific and mystical (his followers meditated over seeds and filled cow horns with manure to bury in autumn when the moon was on the wane). But what Bose and Steiner called “vital” conveyed the insight that scientists increasingly understand today: that microbial life under our feet works in concert with insects, worms, plant roots and fungal arteries to create a living world of creativity and mastery, one which scientists are just beginning to grasp.

For 50 years, the insights of these early soil activists were sidelined. In 1941, when Americans went to war again, the US War Department subsidised ammonia plants to produce explosives. By 1943, they produced more than needed. Companies sold the surplus to farmers.

After the war, marketers promoted a new thought – not only could nitrogen fertilisers restore depleted soils, they could increase crop yields too. More food per acre could feed growing global populations. Agronomists in the US encouraged farmers to pack in ammonia. They developed hybrid seeds that could handle this tsunami of nitrogen, which sickens many plants. Farmers who used to save their own seeds and manage their own nutrient cycles got hooked into buying hybrid seeds, commercial fertiliser, pesticides, herbicides and heavy machinery to distribute it. These technologies were expensive, polluting and produced less nutritious food. But they turned farmers into voracious, dependable consumers.

Americans exported this new green revolution abroad. Soviets picked it up and spread the model to their satellite states. China, devastated by famine in the 1950s, jumped on board the inorganic nitrogen train. As farmers poured nitrogen onto their fields, dearth flipped to excess. Nitrates and nitrites that flowed into water sources reached tap water and poured into the bodies of commercial animals and humans. Excess nitrogen turned babies blue and transformed clear ponds into glistening green lozenges. We don’t yet know the full health costs of that excess nitrogen in the food cycle. We do know the impact on the planet’s health. The Worldwatch Institute estimates that up to 51 per cent of greenhouse gas emissions comes from the agricultural supply chain; a good portion of that from excess fertiliser run-off that feeds microbes that produce nitrous oxide.

Small farmers who could not finance large agricultural inputs lost out to big farmers who bought up ever larger portions of the territorial pie. Agribusiness leaders argue they can’t feed a projected nine billion people without industrial agriculture. We can’t live without it; we have trouble living with it.

Then the pandemic hit. Supply chains collapsed. In the US, where I live, guards halted migrant farm workers at the border. Farmers destroyed produce they could not harvest or distribute. Grocery store shelves thinned out and lots of people turned to their gardens. We had trouble finding seeds in the spring of 2020.

Bacterial resurrection

As we scrapped over rocky ground, I doubted we had enough nutrients for our crops to thrive. I’d read a study about a successful and affordable supplement called Bloom, made by the DC waste treatment plant. This plant adhered to the general concepts that the British agronomist Gilbert Fowler engineered in 1915. Using high temperatures and pressure in an oxygen-free environment, the plant cooks Washington sludge and produces a fertiliser which April Thompson, the plant’s marketing director, told me is clean enough to be labelled organic (though it is not). Unlike most American cities of its size, DC waste water has little industrial waste, which makes Bloom cleaner than the usual “biosolid”.

I suggested to Wesley that we use it to enrich our crops. Wesley wasn’t so sure. A lot of things end up in our drains – cleaning fluids, condoms, oil runoff. Human waste, Wesley pointed out, has come a long way since the more biologically innocent night soil days of the 19th century. My view was that since farmers today use Bloom and other “biosolids” as fertiliser for our food, we might as well know what is in it. People may not realise that what they flush down the toilet returns on their dinner plates.

A dump truck left us a huge pile of smouldering Bloom cut with wood mulch. It smelled like a barn (or maybe worse). I plunged my shovel in. Steam floated up, wafting humid, sauna-thick air. Millions of bacteria in the pile were working away, getting heated up as they dined and burped carbon. Even through my glove, the pile was hot to touch. For days, we carted the compost to perennial plant beds. Bloom did the job we needed, covering eroded ground of gravel and clay. That was good, but as fine particles coated my throat, I began to feel I’d like a bit more social distance from my community’s faecal matter.

Thankfully, microbes can mutate as quickly as every 20 minutes, fast-forwarding to adapt to their micro-local environments. In really dirty locations, some work like military mine-sappers, learning how to digest the most toxic pollutants in urban environments such as arsenic, solvents, inorganic fertilisers and coal tar.

After planting, we stepped back and watched. The plants fertilised by Bloom grew swiftly at first, but, as the heat and drought of high summer rolled in, the soils dried up fast and a hard crust formed on the surface. We had to chop the ground to pry it open and water more. In the beds, fat worms slunk around; insects scurried, roots grew wildly and our plants flourished. A whole little farm on a quarter acre of public land in a crowded city.

I was struck by how easy it was to regenerate the soil (albeit on a microscale). As our plants grew, they created plant material that we mulched back into the ground. As organic matter piled up, it drew worms and microbes that set to work breaking it down. The beds turned dark brown, springy; they lifted from the earth. It was the kind of resurrection that doesn’t require faith in miracles.

This article is from the New Humanist summer 2021 edition. Subscribe today.