WESTWARD HOE - Dirt: The Erosion of Civilizations - David R. Montgomery

Dirt: The Erosion of Civilizations - David R. Montgomery (2007)


Since the achievement of our independence, he is the greatest Patriot, who stops the most gullies.


SEVERAL YEARS AGO, ON A BREAKNECK research trip down rough dirt roads through a recently deforested part of the lower Amazon, I saw how topsoil loss could cripple a region's economy and impoverish its people. I was there to study caves created over a hundred million years as water slowly dissolved iron-rich rocks that lay beneath soils resembling weathered frying pans. Walking through an iron cave impressed upon my imagination how long it must have taken for dripping water to carve them. Just as striking on this trip were the signs of catastrophic soil loss after forest clearing. Yet what really amazed me was how this human and ecological catastrophe-in-themaking did not change people's behavior, and how the modern story of the lower Amazon paralleled the colonial history of the United States.

Standing on the edge of the Carajas Plateau, I straddled the skeletal remains of an ancient landscape and another still being born. Beside me, high above the surrounding lowlands, I could see landslides chewing away at the scraps of the ancient plateau. On all sides of this jungle-covered mesa, erosion was stripping off a hundred million years' worth of rotted rock along with the deepest soil I'd ever seen.

Since the time of the dinosaurs, water dripping through the equatorial jungle and leaching into the ground has created a deep zone of weathered rock extending hundreds of feet down to the base of the plateau. After South America split off from Africa, the resulting escarpment swept inland eating into the ancient uplands from the side. Standing on the cliff at the edge of the plateau-a small remnant of the original land surface-I admired the wake of new rolling lowlands that fell away toward the Atlantic Ocean.

The Carajas Plateau is made up of banded iron-almost pure iron ore deposited by an anoxic sea long before Earth's oxygen-rich atmosphere evolved. Buried deep in the earth's crust and eventually pushed back to the surface to weather slowly, the iron-rich rock gradually lost nutrients and impurities to seeping water, leaving behind a deeply weathered iron crust.

Aluminum and iron ore can form naturally through this slow weathering process. Over geologic time, the ample rainfall and hot temperatures of the tropics can concentrate aluminum and iron as chemical weathering leaches away almost everything else from the original rock. Although it may take a hundred million years, it is far more cost-effective to let geologic processes do the work than to industrially concentrate the stuff. Given time, this process can make a commercially viable ore-as long as weathering outpaces erosion. If erosion occurs too rapidly, the weathered material disappears long before it could become concentrated enough to be worth mining.

On top of the Carajas Plateau, a gigantic pit opened a window into the earth, extending hundreds of feet to the base of the deep red weathered rock. Huge, three-story-tall trucks crawled up the terraced walls, dragging tons of dirt along the road that snaked up from the bottom. Viewed from the far side, the hundred-foot-tall trees left standing on the rim of the pit looked like a fringe of mold. Gazing at this bizarre sight in the midday sun, I realized how the thin film of soil and vegetation covering Earth's surface resembles a coating of lichen on a boulder.

Speeding off the plateau, we dropped down to the young rolling hills made of rock that once lay beneath the now-eroded highlands. As we drove through virgin rainforest, road cuts exposed soil one to several feet thick on the dissected slopes leading down to the deforested lowland. Leaving the jungle, we saw bare slopes that provided stark evidence that topsoil erosion following forest clearing led to abandoned farms. Around villages on the forest's edge, squatters farmed freshly cleared tracts. Weathered rock exposed along the road poked out of what had until recently been soilcovered slopes. The story was transparently simple. Soon after forest clearing, the soil eroded away and people moved deeper into the jungle to clear new fields.

A few miles in from the forest edge, family farms and small villages gave way to cattle ranches. As subsistence farmers pushed farther into the forest, ranchers took over abandoned farms. Cows can graze land with soil too poor to grow crops, but it takes a lot of ground to support them. Largescale cattle grazing prevents the forest from regrowing, causing further erosion and sending frontier communities farther and farther into the jungle in an endless push for fresh land. The vicious cycle is plainly laid out for all to see.

Instead of clearing small patches of forest for short periods, immigrants to the Amazon are clearing large areas all at once, and then accelerating erosion through overgrazing, sucking the life from the land. The modern cycle of forest clearing, peasant farming, and cattle ranching strips off topsoil and nearly destroys the capacity to recover soil fertility. The result is that the land sustains fewer people. When they run out of productive soil, they move on. The modern Amazon experience reads a lot more like the history of North America than we tend to acknowledge. Yet the parallel is as clear as it is fundamental.

Between forty million and one hundred million people lived in the Americas when Columbus "discovered" the New World-some four million to ten million called North America home. Native Americans along the East Coast practiced active landscape management but not sedentary agriculture. Early colonists described a patchwork of small clearings and the natives' habit of moving their fields every few years, much like early Europeans or Amazonians. While there is emerging evidence of substantial local soil erosion from native agriculture, soil degradation and erosion began to transform eastern North America under the new arrivals' more settled style of land use.

Intensive cultivation of corn quickly exhausted New England's nutrientpoor glacial soils. Within decades, colonists began burning the forest to make ash fertilizer for their fields. With more people crowded into less space, New Englanders ran out of fresh farmland faster than their neighbors in the South. Early travelers complained about the stench from fields where farmers used salmon as fertilizer. And in the South, tobacco dominated the slave-based economies of Virginia and Maryland and soil exhaustion dominated the economics of tobacco cultivation. Once individual family farms coalesced into slave-worked tobacco plantations, the region became trapped in an insatiable socioeconomic system that fed on fresh land.

Historian Avery Craven saw colonial soil degradation as part of an inevitable cycle of frontier colonization. "Men may, because of ignorance or habit, ruin their soils, but more often economic or social conditions, entirely outside their control lead or force them to a treatment of their lands that can end only in ruin."' Craven thought frontier communities generally exhausted their soil because of the economic imperative to grow the highest value crop. The tobacco economy that ruled colonial Virginia and Maryland was exactly what Craven had in mind.

In 16o6 James I granted the Virginia Company a charter to establish an English settlement in North America. Founded by a group of London investors, the company expected their New World franchise to return healthy profits. Under the leadership of Captain John Smith, on May 14, 1607, the first load of colonists landed along the banks of the James River sixty miles up Chesapeake Bay. Hostile natives, disease, and famine killed two-thirds of the original settlers before Smith returned to England in 1609.

Desperately searching for ways to survive, let alone earn a profit, the Jamestown colonists tried making silk, then glass; harvesting timber; growing sassafras; and even making beer. Nothing worked until tobacco provided a profitable export that propped up the colony.

Sir Walter Raleigh is often credited with introducing tobacco to England in 1586. Whether or not that dubious honor is actually his, Spanish explorers brought both leaf and seeds back from the West Indies. Smoking became immensely popular and the English developed quite a taste for Spanish tobacco grown with slave labor in the Caribbean. Sold at a premium to London merchants, tobacco offered just what the Jamestown colonists needed to keep their colony afloat.

Unfortunately, England's new smokers did not like Virginian tobacco. With an eye toward competing in the London market colonist John Rolfe (perhaps better remembered as Pocahontas's husband) experimented with planting Caribbean tobacco. Satisfied that the stuff "smoked pleasant, sweete and strong," Rolfe and his compatriots shipped their first crop to England. It was a hit in London's markets, comparing favorably with premium Spanish tobacco.

Soon everybody was planting tobacco. Twenty thousand pounds were sent to England in 1617. Twice as much set sail in the next shipment. Captain Smith praised Virginia's "lusty soyle" and the colonial economy quickly became dependent upon tobacco exports. On September 30, 1619, colonist John Pory wrote to Sir Dudley Carleton that things were finally turning around. "All our riches for the present doe consiste in Tobacco, wherein one man by his owne labour hath in one yeare raised to himselfe to the value of zoo sterling and another by the meanes of sixe Servants hath cleared at one crop a thousand pound English."2 Within a decade, one and a half million pounds of Virginian tobacco reached English markets each year.

Americas colonial economy was off and running. Within a century, annual exports to Britain soared a thousandfold to more than twenty million pounds. Tobacco so dominated colonial economics that it served as an alternative currency. The stinking weed saved the faltering colony, but growing it triggered severe soil degradation and erosion that pushed colonists ever inland.

Colonial tobacco was a clean-tilled crop. Farmers heaped up a pile of dirt around each plant with a hoe or a light one-horse plow. This left the soil exposed to rainfall and vulnerable to erosion during summer storms that hit before the plants leafed out. Despite the obvious toll on the land, tobacco had a singular attraction. It fetched more than six times the price of any other crop, and could survive the long (and expensive) journey across the Atlantic. Most other crops rotted on the way or could not sell for enough to pay for the trip.

Colonial economics left little incentive to plant a variety of crops when tobacco yielded by far the greatest returns. So Virginians grew just enough food for their families and devoted their energy to growing tobacco for European markets. New land was constantly being cleared and old land abandoned because a farmer could count on only three or four highly profitable tobacco crops from newly cleared land. Tobacco strips more than ten times the nitrogen and more than thirty times the phosphorous from the soil than do typical food crops. After five years of tobacco cultivation the ground was too depleted in nutrients to grow much of anything. With plenty of fresh land to the west, tobacco farmers just kept on clearing new fields. Stripped bare of vegetation, what soil remained on the abandoned fields washed into gullies during intense summer rains. Virginia became a factory for turning topsoil into tobacco.

King James saw the tobacco business as an attractive way to raise revenue. In 16i9 the Virginia Company agreed to pay the Crown one shilling per pound on its shipments to England in exchange for restrictions on Spanish tobacco imports and on tobacco growing in England-a monopoly on the popular new drug. Just two years later, new regulations mandated that all tobacco exported from the colonies be sent to England. In 1677 the royal treasury pocketed £ioo,ooo from import duties on Virginian tobacco and another £50,000 from Maryland tobacco. Virginia returned more to the royal pocketbook than any other colony; more than four times the revenue from the East Indies.

Not surprisingly, colonial governments piled on to use tobacco to raise revenue. Once hooked on the new source of cash, they quickly squashed attempts to stem reliance on tobacco. When Virginians requested a temporary ban on tobacco growing in 1662, they were unsubtly told never to make such a request again. The secretaries for the colony of Maryland tried to ensure that colonists did not "turn their thoughts to anything but the Culture of Tobacco."3

The short-lived fertility of the land under tobacco cultivation encouraged rapid expansion of agricultural settlements. Abandoning fields that no longer produced adequate returns, Virginia planters first requested permission to clear new land farther from the coast in 1619. Five years later, planters at Paspaheigh sought permission from the colonial court to move to new land, even though fifteen years before their governor had pronounced their lands excellent for growing grain. Little more than two decades later, tobacco farmers along the Charles River petitioned the governor for access to virgin lands because their fields "had become barren from cultivation." Seventeenth-century Virginians complained about the extreme loss of soil during storms; it was hard to overlook the destructive gullies chewing up the countryside. Moving inland, planters encountered soils even more susceptible to erosion than those along the coast and in the major river valleys. Pushing south as well, by 1653 tobacco farmers were clearing new fields in North Carolina's coastal plain where there was still plenty of fresh land.

As soil fertility declined along the coast, farmers moved inland. The potential for access to the rich lands beyond the mountains motivated Virginians during the French and Indian War. Colonial farmers were enraged at mother England when the peace treaty of 1763 effectively closed the western lands to immediate settlement. Lingering resentment over debilitating tobacco taxes and perceived obstructions to westward expansion helped fuel dissatisfaction with British rule.

Colonial agriculture remained focused on tobacco in the South despite depressed prices stemming from oversupply and the requirement that the whole crop be shipped to England. By the middle of the eighteenth century, government duties accounted for about 8o percent of the sale price of tobacco; the planter's share had dropped to less than 1o percent. Anger over perceived inequities in the regulation, sale, and export of tobacco simmered until the Revolutionary War.

Particularly in the South, the ready availability of new lands meant that farmers neglected crop rotation and the use of manure to replenish soils. Published in 1727, The Present State of Virginia blamed the rapid decline in soil fertility on failure to manure the fields. "So it is at present that Tobacco swallows up all other Things, every thing else is neglected.... By that time the Stumps are rotten, the Ground is worn out; and having fresh Land enough ... they take but little Care to recruit the old Fields with Dung."4 Moving on to fresh ground was easier than collecting and spreading manure-as long as there was plenty of land for the taking.

Other contemporary observers also noted that tobacco consumed the full attention of planters. In a 1729 letter to Charles Lord Baltimore, Benedict Leonard Calvert concisely summarized the influence of tobacco on colonial agriculture. "In Virginia and Maryland Tobacco is our Staple, is our All and Indeed leaves no room for anything Else."5 Tobacco reigned as undisputed king of the southern colonies.

The need for continual access to fresh land encouraged the establishment of large estates. Low prices in the glutted tobacco market of the late seventeenth century created opportunities to consolidate large holdings when small farmers went out of business. Just as in Rome two thousand years before, and in the Amazon almost three centuries later, abandoned family farms ended up in the hands of plantation owners.

In New England, some colonists began experimenting with soil improvement. Connecticut minister, doctor, and farmer Jared Eliot published the first of his Essays Upon Field Husbandry in 1748 reporting the results of experiments on how to prevent or reverse soil degradation. Riding on horseback to call on his parishioners and patients, Eliot noticed that the muddy water running off bare hillsides carried away fertile soil. He saw how deposition of mud washed from the hills enriched valley bottom soils and how loss of the topsoil ruined upland fields. Eliot recommended spreading manure and growing clover for improving poor soils. He endorsed marl (fossil sea shells) and saltpeter (potassium nitrate) as excellent fertilizers almost equal to good dung. Bare soil left exposed on sloping ground was particularly vulnerable to washing away in the rain. Sound as it was, few colonial farmers heeded Eliot's advice, particularly in the South where new land was still readily obtained.

Benjamin Franklin was among those who bought Eliot's essays and began experimenting with how to improve his land. Writing to Eliot in 1749 he confided his concern about how difficult it would be to convince American farmers to embrace soil husbandry. "Sir: I perused your two Essays on Field Husbandry, and think the public may be much benefited by them; but, if the farmers in your neighborhood are as unwilling to leave the beaten road of their ancestors as they are near me, it will be difficult to persuade them to attempt any improvement."6 Eliot likened farmers who did not return manure and crop wastes to the fields to a man who withdrew money from the bank without ever making a deposit. I imagine that Franklin concurred.

Commentary on the depleted state of colonial soils was routine by the end of the eighteenth century. Writing during the Revolutionary War, Alexander Hewatt described farmers in the Carolinas as focused on shortterm yields and paying little attention to the condition of their land.

Like farmers often moving from place to place, the principal study with the planters is the art of making the largest profit for the present time, and if this end is obtained, it gives them little concern how much the land may be exhausted.... The richness of the soil, and the vast quantity of lands, have deceived many.... This will not be the case much longer, for lands will become scarce, and time and experience, by unfolding the nature of the soil ... will teach them ... to alter [their] careless manner of cultivation.?

Hewatt was not alone in his bleak assessment of American agriculture.

Many Europeans who traveled through the southern states in the late 170os expressed surprise at the general failure to use manure as a soil amendment. Exiled French revolutionary Jacques-Pierre Brissot de Warville toured the newly independent United States in 1788 and wondered at the ruinous style of agriculture. "Though tobacco exhausts the land to a prodigious degree, the proprietors take no pains to restore its vigour; they take what the soil will give, and abandon it when it gives no longer. They like better to clear new lands, than to regenerate old. Yet these abandoned lands would still be fertile, if they were properly manured and cultivated."8 Careless waste of good land perplexed European observers accustomed to cheap labor and a shortage of fertile land.

At the close of the eighteenth century, newly arrived settler John Craven found Virginia's Albemarle County so degraded by poor farming practices that the inhabitants faced the simple choice of emigrating or improving the soil. Writing to the Farmer's Register years later, Craven recalled the sad state of the land. "At that time the whole face of the country presented a scene of desolation that baffles description-farm after farm had been worn out, and washed and gullied, so that scarcely an acre could be found in a place fit for cultivation.... The whole of the virgin soil was washed and carried off from the ridges into the valleys."9 Visiting Virginia and Maryland the following year, in i8oo, a baffled William Strickland declared that he could not see how the inhabitants scratched a living from their fields.

In 1793 Unitarian minister Harry Toulmin left Lancashire for America to report to his congregation on the suitability of the new country for emigration. Land hunger and the rising price of food in Britain increased pressure to leave for America, particularly for those living on fixed incomes and low wages in the industrializing economy. In addition, many Unitarians and others sympathetic to the progressive ideals of the American and French revolutions abandoned their homeland for the New World when the new French Republic declared war on England.

Finding agricultural prospects poor along the Atlantic seaboard, Toulmin procured letters of introduction from James Madison and Thomas Jefferson to John Breckinridge, who had quit a Virginia congressional seat to emigrate to Kentucky. Toulmin's letters and journals provide a vivid description of Kentucky's soils at the time of first settlement. Reporting on the agricultural potential of Mason County in northern Kentucky, Toulmin described the gently undulating country as well endowed with rich soil. "The soil is in general rich loam. In the first-rate land (of which there are some million of acres in this county) it is black. The richest and blackest mold continues to about the depth of five or six inches. Then succeeds a lighter colored, friable mold which extends about fifteen inches farther. When dry it will blow away with the wind."10 Testimony such as Toulmin's helped draw people west from the coast. It also proved far more prophetic than he could have imagined.

About the time of the American Revolution, some of the founding fathers began to worry about the impact of mining the soil on the country's future. George Washington and Thomas Jefferson were among the first to warn of the destructive nature of colonial agriculture. Ideological rivals, these prosperous Virginia plantation owners shared concern over the long-term effects of American farming practices.

After the Revolution, Washington did not hide his scorn for the shortsighted practices of his neighbors. "The system of agriculture, (if the epithet of system can be applied to it) which is in use in this part of the United States, is as unproductive to the practitioners as it is ruinous to the landholders."" Washington blamed the widespread practice of growing tobacco for wearing out the land. He saw how poor agricultural practices fueled the desire to wrest the greatest return from the ground in the shortest time-and vice versa. In a 1796 letter to Alexander Hamilton, Washington predicted that soil exhaustion would push the young country inland. "It must be obvious to every man, who considers the agriculture of this country ... how miserably defective we are in the management of [our lands] .... A few years more of increased sterility will drive the Inhabitants of the Atlantic States westward for support; whereas if they were taught how to improve the old, instead of going in pursuit of new and productive soils, they would make these acres which now scarcely yield them any thing, turn out beneficial to themselves." 12

Washington's interest in progressive agriculture began long before the Revolution. As early as 1760, he used marl (crushed limestone), manure, and gypsum as fertilizers and plowed crops of grass, peas, and buckwheat back into his fields. He built barns for cattle in order to harvest manure, and instructed reluctant plantation managers to spread the waste from livestock pens onto the fields. He experimented with crop rotations before finally settling on a system that involved interspersing grains with potatoes and clover or other grasses. Washington also experimented with deep plowing to reduce runoff and retard erosion. He filled gullies with old fence posts, trash, and straw before covering them with dirt and manure and then planting them with crops.

Perhaps most radical, however, was Washington's realization that soil improvement was next to impossible on large estates. Dividing his land into smaller tracts, he instructed his overseers and tenants to promote soil improvement. Washington's efforts focused on preventing soil erosion, saving and using manure as fertilizer, and specifying cover crops to include in rotations.

Returning to Mount Vernon after the Revolution, Washington wrote English agriculturalist Arthur Young for advice on improving his lands. Young embraced Washington as a "brother farmer" and agreed to provide the American president with any assistance desired.

In 1791 Young asked Washington to describe agricultural conditions in northern Virginia and Maryland. Washington's reply indicates that the old practices that encouraged soil erosion and exhaustion remained widespread. In particular, the practice of growing steadily falling yields of tobacco, followed by as much corn as the exhausted land could produce, continued to reduce soil fertility. With limited pasture and livestock, few farmers used manure to prolong or restore soil fertility. Washington explained that American farmers had a strong incentive to get the most out of their laborers regardless of the effect on their soil; workers cost four times the value of the land they could work. He also reported a growing tendency to abandon tobacco in favor of wheat, even though wheat yields were barely comparable to medieval European yields. American agriculture was wearing down the New World.

Thomas Jefferson too worried that Americans were squandering the productive capacity of their land. Where Washington blamed ignorance of proper farming methods, Jefferson saw greed. "The indifferent state of [agriculture] among us does not proceed from a want of knowledge merely; it is from our having such quantities of land to waste as we please. In Europe the object is to make the most of their land, labor being abundant; here it is to make the most of our labor, land being abundant. "13 When a perplexed Arthur Young questioned how a man could produce five thousand bushels ofwheat on a farm with cattle worth only £150, Jefferson reminded him that "manure does not enter into this because we can buy an acre of new land cheaper than we can manure an old one." 14 Better short-term returns were to be had by mining soil than by adopting European-style husbandry. In Jefferson's view, failure to care for the land was the curse of American agriculture.

The relationship between eighteenth-century plantation owners and their poorer neighbors bolsters Jefferson's argument. Wealthy landowners generally exhausted their land growing tobacco, used their slaves to clear new fields, and then sold their old fields to farmers lacking the means and the slaves to clear and work a tobacco plantation. Plantation owners often bought food from neighboring farms to feed their own families. Cotton and tobacco so dominated agriculture that before the Civil War the South was a net importer of grains, vegetables, and farm animals.

In the spring of 1793 Jefferson's son-in-law Colonel T. M. Randolph started plowing horizontally along hillslope contours rather than straight downhill. Skeptical at first, Jefferson himself became a convert when Randolph developed a hillside plow fifteen years later. Thereafter a vocal proponent of contour plowing, Jefferson testified that formerly erosive rains no longer carved deep gullies across his fields. Randolph's invention won him a prize from the Albemarle County Agricultural Society in 1822. Together with his famous father-in-law, Randolph popularized contour plowing through an extensive network of correspondents.

In one such letter, written to C. W. Peale in 1813, Jefferson extolled the virtues of the new practice.

Our country is hilly and we have been in the habit of ploughing in straight rows whether up and down hill, in oblique lines, or however they lead; and our soil was all rapidly running into the rivers. We now plough horizontally, following the curvatures of the hills and hollows, on the dead level, however crooked the lines may be. Every furrow then acts as a reservoir to receive and retain the waters, all of which go to the benefit of the growing plant, instead of running off into the streams. In a farm horizontally and deeply ploughed, scarcely an ounce of soil is carried off from it. 15

But the new approach had to be employed with care. Even if pitched slightly down slope, furrows would still collect runoff and guide incipient streams into gullies. Though contour plowing caught on, many considered the effort needed to do it, let alone do it right, too much bother. In the i83os Randolph's son described how the "new" practices of deep plowing, fertilizing with gypsum, and rotating corn with clover or grass would soon eclipse his father's contribution in the fight to reclaim worn out lands.

Early in the nineteenth century, Americans began to recognize the need to safeguard and restore soil fertility. Some farmers began plowing deeper and adding animal and vegetable manures to their fields. In particular, agriculturalist John Taylor argued that soil conservation and improvement were necessary to sustain southern agriculture. "Apparent to the most superficial observer, is, that our land has diminished in fertility.... I have known many farms for above forty years, and ... all of them have been greatly impoverished." Forecasting the future of the South, Taylor predicted "our agricultural progress, to be a progress of emigration,"16 unless soil improvement became the region's agricultural philosophy. By the i82os, the need for aggressive efforts to improve the soil was widely recognized throughout the South.

Taylor's French contemporary Felix de Beauj our characterized American farmers as nomads continually on the move. He marveled at their general reluctance to use manure to restore soil fertility. "The Americans appear to be ignorant that with water manure is every where made; and that with manure and water, there is not an inch of ground that cannot be made fertile. The land for this reason is there soon exhausted, and ... the farmers of the United States resemble a people of shepherds, from their great inclination to wander from one place to the other." 17 Such descriptions abound in early nineteenth-century accounts of the South.

Rural newspapers across the country carried the remarks of retired president James Madison on the front page when he addressed Virginia's Albe marle County Agricultural Society in May 1818. Madison cautioned that the nation's westward expansion did not necessarily mean progress. Building a nation with a future required caring for and improving the land. Neglect of manure, working the land too hard by cultivating it continuously, and plowing straight up and down hills would rob land of its fertility. Madison cautioned that agricultural expansion be moderated; improving the soil was not just an alternative to heading farther west, it was the only option over the long run.

The ideas of Pennsylvania farmer John Lorain, whose book Nature and Reason Harmonized in the Practice of Husbandry was published after his death in 1825, maintained that erosion was beneficial under natural vegetation because soil gained as much as it lost. Valley bottoms were enriched by soil eroded from hillsides where weathering produced new soil that replaced the eroded material. Farmers changed the system so that erosion from improvident use of the plow and exposure of bare soil to rain impoverished both the soil and the people working the land.

Lorain suggested using grass as a permanent crop on steeply sloping land and putting fields to pasture before they became exhausted. The grass cover would prevent erosion by intercepting and absorbing the impact of rainfall and keep the ground porous enough for precipitation to sink into the ground, instead of running off over the surface. The key to preventing erosion and maintaining soil fertility was to incorporate as much vegetable and animal matter into the soil as possible. An advocate of inexpensive erosion control measures that even poor farmers could adopt, he maintained that careful attention to plowing along contours and preventing surface runoff from gathering into destructive gullies could conserve the soil.

Lorain also saw the tenant system as a major obstacle to soil conservation. The novel efforts of gentleman farmers like Washington and Jefferson discouraged small farmers who could not afford the expense. Instead, tenants with no vested interest in the land wasted the soil, and ignored potentially beneficial conservation measures. His solution was to free his slaves and mandate soil improvement as a condition of all leases. Lorain ridiculed the idea held by many farmers that they could find, somewhere, a soil that was inexhaustible. "When the Pacific Ocean puts a stop to their progress, it is possible they will be convinced, that no such soil exists.""

Many other contemporary observers who examined the question of soil exhaustion concluded that lack of manure was to blame for rapid exhaustion of the region's soil. Using slaves to grow livestock fodder was far less profitable than applying their labor toward cultivating cotton or tobacco. Although it was known that a well-manured field would produce two to three times the harvest of unmanured fields, Southerners left their cattle to graze in the woods year round. On most plantations, virtually no effort was made to gather dung and spread it on the fields; numerous historical accounts refer to the sad state of southern cattle.

An article in the October 11, 1827, edition of the Georgia Courier quoted a letter from a traveler passing through Georgia who noted that the exhausted land provided common motivation for a steady stream of westbound emigrants. "I now left Augusta; and overtook hordes of cotton planters from North Carolina, South Carolina, and Georgia, with large groups of negroes, bound for Alabama, Mississippi, and Louisiana; `where the cotton land is not worn out.""9 The South was heading West.

By the i82os slavery was becoming less economically viable along the eastern seaboard. John Taylor noted that many plantation owners refused to abandon even marginally profitable tobacco cultivation because to do so would have left them without winter work for their slaves. As much land lay abandoned in North Carolina as was being farmed. Low prices for tobacco and cotton, owing to competition from farms working fresh soils to the west, kept profits low on the depleted Piedmont and coastal lands. Slaves began to be a burden to their masters. On March 24, 1827, the Niles Register complained about the situation. "Most of our intelligent planters regard the cultivation of tobacco in Maryland as no longer profitable and would almost universally abandon it if they knew what to do with their slaves."20

Emigrant planters continued their destructive ways in the new western lands to which their old habits had driven them. Writing to Farmer's Register in August 1833, one Alabama resident expressed dismay at continuing the cycle. "I have not much hope of seeing improvement in the agriculture of this state. Our planters are guilty of the same profligate system of destroying lands that has characterized their progenitors of Georgia, the Carolinas, and Virginia, immemorially. They wage unmitigated war both against the forest and the soil-carrying destruction before them, and leaving poverty behind." 2' There was no debate about the connection between abused land and depressed economies in nineteenth-century America. A nation of farmers could read the signs for themselves.

As the editor of the Cultivator, Jesse Buel was the most articulate representative of conservative farmers who embraced agricultural improvement rather than westward emigration. Born in Connecticut two years after the opening salvos of the Revolution, Buel apprenticed to a printer and then purchased a farm in the 182os. A decade later he began championing manure as the key to rural prosperity, believing that land judiciously managed need not wear out. In his view, it was a farmer's duty to treat the land as a trust to be passed on unimpaired to posterity.

Buel's views were shared by German and Dutch farmers who immigrated to Pennsylvania, bringing progressive European agricultural practices that contrasted with typical colonial practices. They organized their modest farms around giant barns where cows turned fodder crops into milk and manure. Unlike most American farmers, they treated dirt like gold. Their land prospered, yielding bountiful harvests that astounded visitors from the South where publication of Edmund Ruffin's Essay on Calcareous Manures in 1832 initiated a revolution in American agriculture.

Better known to history as an early agitator for southern independence, Ruffin believed in the power of agrochemistry to restore soil fertility-and the South. Ruffin inherited a rundown family plantation in i8io at the age of sixteen. Struggling to turn a profit from fields already farmed for a century and a half, he adopted the deep plowing, crop rotation, and grazing exclusion advocated by agricultural reformer John Taylor. Unimpressed with the results and almost ready to join the exodus westward, Ruffin tried applying marl to his land.

The results were dramatic. Plowing crushed fossil shells into his fields raised corn yields by almost half. Ruffin began adding marl to more of his land and almost doubled his wheat crop. Concluding that Virginia's soils were too acidic to sustain cultivation, Ruffin reasoned that adding calcium carbonate to neutralize the acid would enable manure to sustain soil fertility. His essay received widespread attention and favorable reviews in leading agricultural journals.

Following Ruffin's example, Virginia's farmers began increasing their harvests. Propelled to prominence in southern society, Ruffin began publishing Farmer's Register, a monthly journal devoted to the improvement of agriculture. The newspaper carried no advertisements and featured practical articles written by farmers. Within a few years Ruffin had more than a thousand subscribers. Eager to compete with the new cotton kingdom emerging out West, South Carolina's newly elected governor James Hammond hired Ruffin to locate and map the state's marl beds in 1842. Ten years later Ruffin accepted the presidency of the newly formed Virginia Agricultural Society.

Well known, highly regarded, and with a lust for public attention, Ruffin turned his attention to advocating southern independence in the 185os. Seeing secession as the only option, he argued that slave labor had sustained advanced civilizations like ancient Greece and Rome. Upon learning of Lincoln's election, Ruffin hastened to attend the convention that adopted the ordinance of secession. When the sexagenarian was awarded the distinction of firing the first shot at Fort Sumter in April 1861, he had already helped start an agrochemical revolution by demonstrating that manipulating soil chemistry could enhance agricultural productivity.

Ruffin thought that soils were composed of three major types of earths. Siliceous earths were the rock minerals that allowed water to pass freely and were thus the key to a well-drained soil. Aluminous earths (clays) absorbed and retained water, creating networks of cracks and fissures that served as miniature reservoirs. Calcareous earths could neutralize acidic soils. Ruffin thought that soil fertility lay in the upper few inches of a soil where organic material mixed with the three earths. Productive agricultural soils were those composed of the right combination of siliceous, aluminous, and calcareous earths.

Ruffin recognized that topsoil erosion squandered soil fertility. "The washing away of three or four inches in depth, exposes a sterile subsoil ... which continues thenceforth bare of all vegetation." as He also agreed with agricultural authorities that manure could help revive the South. But he thought that the ability of manure to enrich soil depended on a soil's natural fertility. Manure would not improve harvests from acidic soils without first neutralizing the acid. Ruffin did not believe that calcareous earth fertilized plants directly; supplemented by calcareous earth, manure could unleash masked fertility and transform barren ground back into fertile fields.

Ruffin further saw that the institution of slavery made the South dependent on expanding the market for slaves born on plantations. He believed that surplus slaves had to be exported unless agricultural productivity could be increased enough to feed a growing population. Ruffin's views on agricultural reform and politics collided with the reality of the Civil War. He committed suicide shortly after Lee surrendered.

The problem of soil exhaustion was not restricted to the South. By the 1840s, addresses to agricultural societies in Kentucky and Tennessee warned that the new states were rapidly emulating Maryland and Virginia in squandering their productive soils. By the advent of mechanized agriculture in the mid-nineteenth century, per-acre wheat yields in New York were just half of those from colonial days despite advances in farming methods. Still, the more diversified northern economy made the effects of soil depletion on northern states less pronounced than in the South.

Figure 14. Charles Lyell's illustration of a gully near Milledgeville, Georgia, in the 1840s (Lyell 1849, fig. 7).

In the i84os British geologist Charles Lyell toured the antebellum South, stopping to investigate deep gullies gouged into the recently cleared fields of Alabama and Georgia. Primarily interested in the gullies as a way to peer down into the deeply weathered rocks beneath the soil, Lyell noted the rapidity with which the overlying soil eroded after forest clearing. Across the region, the consistent lack of evidence for prior episodes of gully for mation implied a fundamental change in the landscape. "I infer, from the rapidity of the denudation caused here by running water after the clearing or removal of wood, that this country has been always covered with a dense forest, from the remote time when it first emerged from the sea."23 Lyell saw that clearing the rolling hills for agriculture had altered an age-old balance. The land was literally falling apart.

One gully in particular attracted Lyell's attention. Three and a half miles west of Milledgeville on the road to Macon, it began forming in the 182os, when forest clearing exposed the ground to direct assault by the elements. Monstrous three-foot-deep cracks opened up in the clay-rich soil during the summer. The cracks gathered rainwater and concentrated erosive runoff, incising a deep canyon. By Lyell's visit in 1846, the gully had grown into a chasm more than fifty feet deep, almost two hundred feet wide, and three hundred yards long. Similar gullies up to eighty feet deep had consumed recently cleared fields in Alabama. Lyell considered the rash of gullies a serious threat to southern agriculture. The soil was washing away much faster than it could possibly be produced.

Passing through an area of low rolling hills on the road to Montgomery, Lyell marveled over the stumps of huge fir trees in a recent clearing. Curious as to how many years it would take to regrow such a forest, he measured the diameter of stumps and counted their annual growth rings. The smallest spanned almost two and a half feet in diameter with a hundred and twenty annual rings; the largest was four feet in diameter and had three hundred and twenty rings. Lyell was confident that such venerable trees could never regrow in the altered landscape. "From the time taken to acquire the above dimensions, we may confidently infer that no such trees will be seen by posterity, after the clearing of the country, except where they may happen to be protected for ornamental purposes."24 Tobacco, cotton, and corn were replacing the forest of immense trees that had covered the landscape for ages. Bare and exposed, the virgin soil bled off the landscape with every new storm.

In addition to impressive gullies, Lyell ran into families abandoning their farms and moving to Texas or Arkansas. Passing thousands of people migrating westward, Lyell reported that those he met kept asking, "Are you moving?" After showing the eminent geologist some fossils, one elderly gentleman offered to sell Lyell his entire estate. Lyell pressed him as to why he was so eager to sell the land he had cleared himself and lived on for twenty years. The man replied: "I hope to feel more at home in Texas, for all my old neighbours have gone there."25

Traveling through much of the South by canoe, Lyell watched the rivers along the way, describing how dramatically accelerated soil erosion following forest clearing and cultivation were obvious to anyone paying attention. Special training in geology was not needed to read the signs of catastrophic erosion. People he met along Georgia's Alatamaha River told him that the river had flowed clean even during floods until the land upriver was cleared for planting. As late as 1841, local residents could determine the source of floodwaters from individual storms because the deforested branch of the river ran red with mud, while the still forested branch flowed crystal clear even during big storms. By the time of Lyell's visit the formerly clear branch also flowed muddy after Native Americans were driven out and the land was cleared for agriculture.

The toll of contemporary agricultural methods on soil and society was no secret. The report of the commissioner of patents for 1849 attempted to tally up the cost to the country.

One thousand millions of dollars, judiciously expended, will hardly restore the one hundred million acres of partially exhausted lands in the Union to that richness of mould, and strength of fertility for permanent cropping, which they possessed in their primitive state.... Lands that, seventy years ago, produced from twenty-five to thirty-five bushels of wheat in the State of New York, now yield only from six to nine bushels per acre; and in all the old planting States, the results of exhaustion are still more extensive and still more disastrous.26

Since falling crop yields were apparent throughout the original states, how to protect soil fertility presented a fundamental challenge. "There appears to be no government that realizes its duty `to promote the public welfare' by ... impressing upon them the obligation which every cultivator of the soil owes to posterity, not to leave the earth in a less fruitful condition than he found it."27 Before the start of the Civil War, agricultural periodicals throughout the country assailed the twin evils ofsoil erosion and exhaustion. As the shortage of fresh land became acute, pleas to adopt soil conservation and improvement techniques became increasingly common.

The immediate causes of soil exhaustion in the antebellum South were not mysterious. Foremost among these were continuous planting without crop rotation, inadequate provision for livestock to provide manure, and improvident tilling straight up and down sloping hillsides that left bare soil exposed to rainfall. But there were underlying social causes that drove these destructive practices.

There can be no doubt that the desire for the greatest short-term returns drove plantation agriculture. Land was cheap and abundant. Moving farther inland every few years, a planter could enjoy the benefits of perpetually farming virgin ground-as long as there was new ground to be had. Clearing new fields was cheap compared to carefully plowing, terracing, and manuring used land. Still, finding virgin land required uprooting and relocating the family and all its possessions, including slaves, to newly opened states in the West. Given the high cost of moving-both socially and financially-what kept such practices alive in the face of overwhelming evidence they were ruining the land?

For one thing, the large plantations' owners-those most likely to recognize the problem of soil exhaustion-did not work their own land. Just as two thousand years before in ancient Rome, absentee ownership encouraged soil-wasting practices. Overseers and tenant farmers paid with a percentage of the crop were more concerned about maximizing each year's harvest than protecting the landowner's investment by maintaining soil fertility. Time invested in plowing along contours, repairing nascent gullies, or delivering manure to the fields reduced their immediate income. Overseers who rarely remained on the same ground for more than a year skimmed off a farm's fertility as quickly as possible.

Another fundamental obstacle to agricultural reform was that the institution of slavery was incompatible with methods for reversing soil degradation. In a way, the intensity of soil erosion in the antebellum South helped trigger the Civil War. While we're all taught that the Civil War was fought over slavery, what we don't learn is that the tobacco and cotton monocultures that characterized the southern economy required slave labor to turn a profit. More than a cultural convention, slavery was essential to the underpinnings of southern wealth. It was not simply that the South was agricultural; much of the North was too. Slavery was critical to the exportoriented, cash-crop monoculture common throughout the South.

Of course, any comprehensive explanation for the Civil War must address a complex set of conditions and events that predated the outbreak of hostilities. The main reasons for the Civil War are usually given as controversy over tariffs and the establishment of a central bank, abolitionist agitation both in Congress and the North in general, and passage of fugitive slave laws. Obviously, efforts to outlaw slavery arose from its ongoing practice in the South. But the most volatile issue of the period preceding the Civil War was the question of slavery's status in the new western states.

Tensions came to a head after the Supreme Court's infamous 1857 Dred Scott decision that slaves were not citizens and therefore lacked standing to sue for their freedom. Five of the nine Supreme Court justices came from slave-holding families. Pro-slavery presidents from southern states had appointed seven. The decision declared the 1820 Missouri Compromise unconstitutional, holding that the federal government had no authority to restrict slavery in the new territories. Southerners hailed an apparent vindication of their views.

Outraged northern abolitionists embraced the upstart Republican Party and after much politicking nominated long-shot candidate Abraham Lincoln for president on a platform that held slavery should spread no farther. The Democrats fragmented when Northerners endorsed Stephen Douglas and Southerners broke ranks to nominate Vice President John Breckin- ridge of Kentucky. The Constitutional Union Party composed of diehard Whigs from the border states nominated John Bell of Tennessee.

Fragmented opposition was just what Lincoln needed. In an election split along geographical lines, the southern states went for Breckinridge. The border states of Kentucky, Virginia, and Tennessee voted for Bell. Douglas carried Missouri and New Jersey. Lincoln won just 40 percent of the popular vote, but carried a majority of electoral votes-all the northern states plus the new states of California and Oregon.

With Lincoln in the White House, war became increasingly likely. Northern perspectives leading up to the war are easy to grasp. Abolitionists considered slavery immoral. Many Northerners regarded legalized slavery as inconceivable in a nation based on the precept that all men are created equal. Still, even though Northerners overwhelmingly desired immediate abolition, most were pragmatically content to prevent slavery's expansion into the new territories.

Southern perspectives as war loomed were more complicated, equally pragmatic, and less flexible. Most Southerners believed that Lincoln's election spelled the end of slavery-or at least the end of its expansion to the West. Many were angry over northern interference in their way of life and intrusion into what they considered affairs of their property. Some were incensed about perceived insults to southern honor. But given that Lincoln's election only meant limitation-outright abolition stayed off the table until the war-and that less than a quarter of Southerners actually owned slaves, why did this issue generate enough political friction to blow the country apart?

As is often the case, insight comes if we follow the money. The economic significance of limiting slavery's expansion lies in the central role of soil exhaustion in shaping plantation agriculture and the southern economy.

Most parents of teenagers know that involuntary labor rarely produces quality results. It is hardly surprising that even the best slaves generally do not exhibit initiative, care, and skill. Instead, slaves generally want to maintain competence sufficient to avoid corporal punishment. They cannot be fired from their job and have no incentive to do it well. The very nature of servitude discourages creative expression or expertise at work.

Agriculture tailored to fit the needs of the land requires close attention to detail and flexibility in running a farm. Absentee landlords, hired overseers, and forced labor do not. Furthermore, an adversarial labor system maintained by force necessarily concentrates workers in one place. Singlecrop plantation farming thus lent itself well to the rules and routine procedures of slave labor. At the same time, slaves were most profitable when following a simple routine year after year.

Until the 1790s plantations worked by slave labor grew virtually nothing but tobacco. Slave labor became less economical as southern plantations began raising a greater diversity of crops and kept more livestock at the end of the eighteenth century. Many in the South thought that slavery would fade into economic oblivion until the rise of cotton breathed new life into the slave trade. Cotton was almost as hard on the land and relied even more on slave labor than did tobacco.

Slave labor virtually required single-crop farming that left the ground bare and vulnerable to erosion for much of the year. Reliance on a single crop precluded both crop rotation and developing a stable source of manure. If nothing but tobacco or cotton were grown, livestock could not be supported because of the need for grain and grass to feed the animals. Once established, slavery made monoculture an economic necessity-and vice versa. In the half century leading up to the Civil War, southern agriculture's reliance on slave labor precluded the widespread adoption of soilconserving methods, virtually guaranteeing soil exhaustion.

In contrast to the South, New England's agriculture was more diversified from the start because no lucrative export crop grew there. The fact that slavery did not persist into the late eighteenth century in the northern states may have less to do with abstract ideals of universal freedom and human dignity than the simple reality that tobacco could not grow that far north. Without the continued dominance of large-scale monoculture, slavery might have died out in the South not long after it did in the North.

But this still doesn't explain the vitriolic southern opposition to Lincoln's proposed territorial limitation on the spread of slavery. After all, slavery in the South was not itself directly at issue in the election of i86o. Consider that slaves moved west along with their owners. At the time of the first national census in 1790, Maryland, Virginia, and the Carolinas held 92 percent of all the slaves in the South. Two decades later, after a ban on importing more slaves, the coastal states still held 75 percent of the South's slaves. By the 183os and 1840s many of the slaveholders in the Atlantic states were breeding slaves for western markets. For plantation owners who stayed behind to work exhausted fields, the slave trade became an economic lifeboat. In 1836, more than one hundred thousand slaves were shipped out of Virginia. One contemporary source estimated that in the late 1850s slave breeding was the largest source of prosperity in Georgia. Census data for i86o suggest that the value of slaves directly accounted for almost half the value of all personal property in the South, including land. By the start of the Civil War, almost 70 percent of the slaves in the South toiled west of Georgia.

Whether Missouri, Texas, and California would become slave states was a make-or-break issue for plantation owners moving west. The laborintensive plantation economy of the South required conscripted labor. And for all practical purposes, the rapid soil erosion and soil exhaustion produced by slave-based agriculture condemned the institution of slavery to continuous expansion or collapse. So if slavery was banned in the West, slaves would lose their value-wiping out half of the South's wealth. Lincoln's election threatened slave owners with financial ruin.

Plantation owners knew that new states could create new markets for slaves and their offspring. It was widely expected that allowing slaveholding in Texas would double the value of slaves. The territorial expansion of slavery was a trigger issue for the Civil War because of its immense economic importance to the landed class of the South. While moral issues were hotly debated, friction between the states ignited only after election of a president committed to limiting slavery's expansion.

Whether or not you believe this argument, you don't need to take it on faith that colonial agriculture caused extensive erosion on the eastern seaboard. You can read the evidence for it in the dirt. Soil profiles and valley bottom sediments allow reconstructing the intensity, timing, and extent of colonial soil erosion in eastern North America. Instead of the thick, black topsoil described by the earliest arrivals from Europe, the modern A horizons are thin and clayey. In some places the topsoil is miss ing entirely, exposing subsoil at the ground surface. Some formerly cultivated parts of the Piedmont have even lost all of their soil, leaving weathered rock exposed at the surface. Soil erosion accelerated by at least a factor of ten under European land use in the colonial era.

Figure 15. Map of the Piedmont region of the southeastern United States showing the net depth of topsoil eroded from colonial times to i98o (modified from Meade i98z, 241, fig. 4).

Evidence for colonial-era soil erosion is apparent all along the eastern seaboard. Estimates of the average depth of soil erosion in the Piedmont range from three inches to more than a foot since colonial forest clearing. Truncated upland soils missing the top of their A horizon indicate four to eight inches of topsoil loss since colonial farmers began migrating inland. Soils of the southern Piedmont from Virginia to Alabama lost an average of seven inches. Upland soils across two-thirds of the Georgia Piedmont lost between three and eight inches. A century and a half of agriculture in the Carolina Piedmont stripped off six inches to a foot of topsoil. Accelerated erosion was particularly bad under colonial land use, and the problem remains significant today. Sediment yields from forested and agricultural lands in the eastern United States show that agricultural lands still lose soil four times faster than forested land.

Figure 16. North Carolina gully system circa 1911 (Glenn 1911, pl. iiib).

The social and economic impacts of colonial soil erosion were not limited to the farmers who kept moving to find new land to grow tobacco. Just as in ancient Greece and Rome, coastal ports became choked with sediment. Most colonial port towns were located as far inland as possible to minimize overland transport of tobacco. These locations, however, bore the brunt of accelerated soil erosion when material stripped from hillsides reached the estuaries. Half a century of upstream farming converted many open-water ports to mud flats. John Taylor noted that silt washed from hillsides by upland farming buried the bottomlands, filling in coastal rivers and streams and plugging estuaries. At a time when rivers were the nation's highways, the sediments washed from hillsides into rivers and ports were everybody's problem.

Maryland's colonial ports of Joppa Town and Elk Ridge, located on opposite sides of Baltimore, were abandoned after they could no longer accommodate ocean-going vessels. Established by an act of the Maryland legislature in 1707, Joppa Town rapidly grew to become the most important seaport in the colony. The largest oceangoing merchant ships loaded at its wharf until clearing of the uplands started a cycle of erosion that began filling in the bay. By 1768, the county seat was moved to Baltimore where the harbor was unaffected by sedimentation. In the 1940s the remnants of the old wharf stood behind a hundred feet of tree-covered land that extended out past where tall ships once anchored.

The head of Chesapeake Bay shoaled by at least two and a half feet between 1846 and 1938 with deposition of dirt from the surrounding farmlands. The bay also filled with sediment at the head of navigation on the Potomac. A decade after Georgetown was established in 1751, the town built a public wharf extending sixty feet out into deep water. In 1755 a British fleet of heavy warships moored in the river above Georgetown but by 1804 sediment had filled in the main shipping channel.

Arguments over the cause complicated decades of congressional debate over what to do about silting up of the Potomac. By 1837 the river was less than three feet deep above Long Bridge; some blamed construction of the bridge while others blamed the Georgetown causeway. Leading a survey of bridges across the Potomac in 1857, engineer Alfred Rives recognized the true cause as rapid erosion from the extensively plowed hillsides of the surrounding country. Today the Lincoln Memorial sits on ground where ships sailed in the eighteenth century, and Indian missionary Father Andrew White's 1634 description of a crystal-clear Potomac River reads like fiction. "This is the sweetest and greatest river I have seene, so that the Thames is but a little finger to it. There are noe marshes or swampes about it, but solid firme ground.... The soyle ... is excellent ... commonly a blacke mould above, and a foot within ground of a readish colour.... It abounds with delicate springs which are our best drinke."28

Sedimentation rates in the Furnace Bay tributary of Chesapeake Bay, just east of the mouth of the Susquehanna River increased almost twentyfold after European settlement. At Otter Point Creek, Maryland, the sedimentation rate in a tidal freshwater delta in upper Chesapeake Bay increased by a factor of six after 1730, and then again by another factor of six by the mid- 18oos. The rate of sediment accumulation in a bog at Flat Laurel Gap in the Blue Ridge Mountains of North Carolina remained relatively steady for more than three thousand years and then increased four- to fivefold when land clearance reached the crest of the range around i88o.

Slavery wasn't the only reason that erosion was a bigger problem in the South than in the North. Bare fields were particularly vulnerable to erosion in the South because rainfall intensities could reach up to one and a half inches per hour and the frozen ground and snow cover in the North allowed for little erosion during winter storms. In addition, the South's topography is carved into rougher slopes than the gentle contours of glacier-sculpted New England.

Erosion continued to degrade the South after the Civil War. After surveying regional erosion problems in the southern Appalachians from 1904 to 1907 for the U.S. Geological Survey, Leonidas Chalmers Glenn described farming practices little changed from colonial days.

When first cleared, the land is usually planted in corn for about two or three years, is then for two or three years put in small grain ... and then back into corn for several years. Unless it is well cared for the land has by this time become poor, for it has lost its original humus. The soil has become less porous and less able to absorb the rainfall and erosion begins. Means are rarely taken to prevent or check this erosion, so it increases rapidly and the field is soon abandoned and a new one cleared.... Many fields are worn out and abandoned before the trees girdled in its clearing have all fallen. Then new grounds are usually cleared beside the abandoned field and the same destructive process is repeated.

It took a few hundred years, but agricultural clearing was finally reaching into the remotest uplands of the region in a process much like what happened in Greece, Italy, and France. "In some places it was found that the entire surface wore away slowly, each heavy rain removing a thin layer or sheet of material, so that the fertile soil layer gradually wore thin and poor and the field was at last abandoned as worn out.... Sheet-wash erosion is so slow and gradual that some farmers fail to recognize it and believe that their soils have deteriorated through exhaustion of the fertility, whereas they have slowly and almost imperceptibly worn away to the subsoil."29

By the early i9oos more than five million acres of formerly cultivated land in the South lay idle because of the detrimental effects of soil erosion.

When the government began to support aggressive soil conservation efforts in the 1930s, the new U.S. Soil Conservation Service did not offer up radical new ideas. "Most of the erosion-control practices in use at the present time, such as the use of legumes and grasses, deep plowing, contour plowing and hillside ditching, the prototype of modern terracing, were either developed by the Virginia farmers or became known to them during the first half of the nineteenth century."30 Actually, most of these techniques, or similar practices, had been used in Europe for centuries and were known in Roman times. If these ideas were so good and had been around for so long why did they take so long to become widely adopted? While Thomas Jefferson and George Washington might disagree on both the reason and the cure, the lessons of the Old World and colonial America remain on the sidelines as a similar story unfolds in the Amazon basin, where the Brazilian government has a long history of encouraging peasants to clear rainforest in order to pacify demands for land reform.

Figure 17. Eroded land on tenant farm, Walker County, Alabama, February 1937 (Library of Congress, LC-USF346-o25121-D).

Ironically, the Amazon itself holds clues to a solution. Archaeologists recently discovered areas with incredibly fertile black soil not far from the Carajas Plateau. This rich dirt, called terra preta, may cover as much as a tenth ofAmazonia. Not only did this distinctly untropical soil sustain large settlements for several thousand years, but intensive habitation produced it. Faced with trying to make a living from nutrient-poor soils, Amazonians improved their soil through intensive composting and soil husbandry.

Found on low hills overlooking rivers, terra preta is full of broken ceramics and organic debris with a high charcoal content and evidence of concentrated nutrient recycling from excrement, organic waste, fish, and animal bones. Abundant burial urns suggest that the human population recycled itself too. The oldest deposits are more than two thousand years old. Practices that built terra preta soils spread upriver over a span of about a thousand years and worked well enough for sedentary people to prosper in an environment that had previously supported a sparse, highly mobile population.

Typically one to two feet thick, deposits of terra preta can reach more than six feet deep. In contrast to the typical slash-and-burn agriculture of tropical regions, Amazonians stirred charcoal into the soil and then used their fields as composting grounds. With almost twice the organic matter as adjacent soils, terra preta better retains nutrients and has more soil microorganisms. Some soil ecologists believe that Amazonians added soil rich in microorganisms to initiate the composting process, as a baker adds yeast to make bread.

Radiocarbon dating of terra preta at Acutuba near the confluence of the Amazon and the Rio Negro showed that the site was occupied for almost two thousand years, from when the black soils began forming about 360 BC until at least AD 1440. When Francisco de Orellana traveled up the Amazon River in 1542 he found large settlements no more than "a crossbow shot" from each other. His conquistadors fled from the throngs of people that swarmed the river at a large site near the mouth of the Tapajos River where terra preta covering several square miles could have supported several hundred thousand people.

Geographer William Denevan argues that slash-and-burn agriculture in which farmers move their plots every two to four years is a relatively recent development in the Amazon. He asserts that the difficulty of clearing huge hardwood trees with stone tools rendered frequent clearing of new fields impractical. Instead, he believes that Amazonians practiced intensive agroforestry that included understory and tree crops that together protected the fields from erosion, allowing rich black earth to build up through time.

Much like a villagewide compost heap, terra preta soils are thought to build up from mixing ash from fires and decomposing garbage into the soil. Similar darkening and enrichment of the soil has been noted around villages in the jungle of northeastern Thailand. Native communities often kept fires burning at all times and terra preta deposits appear lens shaped, suggesting accumulation within, rather than around villages. Relatively high phosphorus and calcium content of terra preta also suggests contributions from ash, fish and animal bones, and urine. Estimated to have grown by an inch in twenty-five years, six feet of terra preta could build up after several thousand years of continuous occupation. Today, terra preta is dug up and sold by the ton to spread on yards in urbanizing parts of Brazil.

Whether catastrophically rapid or drawn out over centuries, accelerated soil erosion devastates human populations that rely on the soil for their living. Everything else-culture, art, and science-depends upon adequate agricultural production. Obscured in prosperous times, such connections become starkly apparent when agriculture falters. Recently, the problem of environmental refugees fleeing the effects ofsoil erosion began to rival political emigration as the world's foremost humanitarian problem. Although usually portrayed as natural disasters, crop failures and famines often owe as much to land abuse as to natural calamities.