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 gra.s.s 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 gra.s.s as a permanent crop on steeply sloping land and putting fields to pasture before they became exhausted. The gra.s.s 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 pa.s.sing 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 compet.i.tion 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 pa.s.sed 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 sh.e.l.ls 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 advertis.e.m.e.nts 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 l.u.s.t 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 s.e.xagenarian 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 pa.s.s 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 inst.i.tution 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 p.r.o.nounced than in the South.

Figure 14. Charles Lyell's ill.u.s.tration 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 a.s.sault 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.

Pa.s.sing 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. Pa.s.sing 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 a.s.sailed 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 inst.i.tution 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 pa.s.sage 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 unconst.i.tutional, 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 Const.i.tutional 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 gra.s.s 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 inst.i.tution 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 cla.s.s 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 anch.o.r.ed.

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 acc.u.mulation 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 gra.s.ses, 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 spa.r.s.e, 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 a.s.serts 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 acc.u.mulation 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.

DUST BLOW

One man cannot stop the dust from blowing but one man can start it.

FARM SECURITY ADMINISTRATION.

NORTHERN CANADA MESMERIZED ME THE FIRST TIME I flew over the pole from Seattle to London on a clear day. While the other pa.s.sengers enjoyed some Hollywood epic, I drank in the vast plain of bare rock and shallow lakes crawling by six miles below. For tens of millions of years before the onset of the glacial era, deep soil and weathered rock covered northern Canada. Redwood trees grew in the Arctic. Then, as the planet cooled into a glacial deep freeze about two and a half million years ago, rivers of ice began stripping northern Canada down to hard rock, dumping the ancient soil in Iowa, Ohio, and as far south as Missouri. High winds dropping off the great ice sheet blew the pulverized dirt around to shape Kansas, Nebraska, and the Dakotas. Today, these geologic dust bunnies produced by extreme erosion form the best agricultural lands on the planet.

Glaciers also stripped soils from northern Europe and Asia, redistributing thick blankets of finely ground dirt-loess-over more than a fifth of Earth's land surface. Mostly silt with some clay and a little sand, loess forms ideal agricultural soil. Sc.r.a.ped off the Arctic by glaciers and dropped in temperate lat.i.tudes by strong winds, the deep loess soils of the world's breadbaskets are incredibly fertile owing to a high proportion of fresh minerals. The absence of stones makes loess relatively easy to plow. But with little natural cohesion, loess erodes rapidly if stripped of vegetation and exposed to wind or rain.

Grazed by buffalo for at least two hundred thousand years, the Great Plains had a thick cover of tough gra.s.s that protected the fragile loess. Wandering across the plains the great herds manured the gra.s.slands, enriching the soil. Much of the bioma.s.s lay below ground in an extensive network of roots that supported the prairie gra.s.s. Traditional plows could not cut through the thick mat that held the plains together. So the first settlers simply kept heading West.

Then in 1838 John Deere and a partner invented a steel plow capable of turning up the prairie's thick turf. When he began selling his unstoppable plow, Deere set the stage for a humanitarian and ecological disaster because, once plowed, the loess of the semiarid plains simply blew away in dry years. Deere sold a thousand of his new plows in 1846. A few years later he was selling ten thousand a year. With a horse or an ox and a Deere plow a farmer could not only plow up the prairie sod, but farm more acreage. Capital began to replace labor as the limiting factor in farm production.

Another new labor-saving machine, Cyrus McCormick's mechanized harvester helped revolutionize farming and reconfigure the relation between American land, labor, and capital. The McCormick reaper consisted of a blade driven back and forth by gears as the contraption cut and stacked wheat while it advanced. McCormick began testing designs in 1831; by the i86os thousands of his machines were being a.s.sembled each year at his Chicago factory. With a Deere plow and a McCormick reaper a farmer could work far more land than his predecessors.

In the early 18oos American farms relied on methods familiar to Roman farmers, broadcasting seed by hand and walking behind plows pulled by horses or mules. The amount of labor available to a typical family limited the size of farms. Early in the twentieth century tractors replaced horses and mules. At the end of the First World War, there were about 85,000 tractors working on U.S. farms. Just two years later the number tripled to almost a quarter of a million. With steel plows and iron horses, a twentieth-century farmer could work fifteen times as much land as his nineteenth-century grandfather. Today, farmers can plow up eighty acres a day listening to the radio in the air-conditioned cab of a leviathan tractor unimaginable to John Deere, let alone a Roman farmer.

As they spread west, Deere's magical plows turned formerly undesirable land into a speculator's paradise. The Territory of Oklahoma (Indian territory, in Chocktaw) was set aside as a reservation for the Cherokee, Chickasaw, Choctaw, Creek, and Seminole nations in 1854. It did not take long before the Indians' practice of maintaining open prairie seemed a waste to land-hungry settlers. From 1878 to 1889 the U.S. Army forcibly ejected white settlers who encroached on Indian lands. Commercial interests and citizens eager to work the rich soil increasingly threatened treaty commitments made to people who just decades before had ceded their ancestral claim to the eastern seaboard in exchange for Oklahoma and the right to be left alone. Eventually bowing to public pressure, the government announced plans to open the territory to settlers in the spring of 1889.

From mid-March into April thousands of people flocked to Oklahoma's borders. Potential settlers were allowed to peruse Indian lands the day before the district opened. The land grab began at noon on April 22 (now celebrated as Earth Day) as the cavalry watched mobs race to stake out their turf. "Sooners" who had slipped by the border guards began filing papers to claim the best land for town sites and farms. By nightfall entire towns were staked out; many homesteads had multiple claimants. Within a week, Indian territory's more than fifty thousand new residents accounted for the majority of its population.

The following year, congressional aid prevented disaster when the settlers' first crops withered. The average rainfall of just ten inches a year could barely support the drought-adapted native gra.s.s, let alone crops. In contrast to prairie gra.s.s, which weathered dry years and held the rich loess soil in place, a sea of dead crops bared loose soil to high winds and thunderstorm runoff.

Recognizing the potential for an agricultural catastrophe, Grand Canyon explorer and director of the new U.S. Geological Survey Major John Wesley Powell recommended that settlers in the semiarid West be allowed to homestead twenty-five hundred acres of land, but be allotted water to irrigate just twenty acres. He thought this would both prevent overuse of water and conserve the region's fragile soils. Instead, Congress retained the allocation of one hundred and sixty acres of land to each homesteader wherever they settled. That much land could yield a fortune in California. On the plains, an industrious family could starve trying to farm twice as much.

Undeterred by nay-saying pessimists, land boosters advertised the unlimited agricultural potential of the plains, popularizing the notion that "rain follows the plow." It certainly helped their pitch that settlers started plowing the Great Plains during a wet spell. Between 1870 and 1900, American farmers brought as much virgin land into cultivation as they had in the previous two centuries. Mostly crops were good at first. Then the drought came.

The late nineteenth-century advent of widespread lending encouraged Oklahoma's new farmers to borrow liberally and pay off the interest on their loans by mining soil in aggressive production for export markets. Just over two decades after the Oklahoma land rush, farmers plowed up forty million acres of virgin prairie to cash in on high grain prices during the First World War. In the above-average rainfall of the early i9oos, millions of acres of prairie became amber fields of grain. Relatively few paused to consider what would happen should high winds accompany the next inevitable drought.

In 19o2 the twenty-second annual report of the U.S. Geological Survey concluded that the semiarid High Plains from Nebraska to Texas were fatally vulnerable to rapid erosion if plowed: "The High Plains, in short, are held by their sod." With rainfall too low to support crops consistently, grazing was the only long-term use for which the "hopelessly nonagricultural" region was well suited.' Once stripped of sod, the loess soil would not stay put under the high winds and pounding rains of the open prairie. The survey's findings were no match for land speculation and the high crop prices during the First World War. A century later, talk of returning the region to large-scale grazing as a buffalo commons echoes the survey's far-sighted advice.

Half of the potential farmland in the United States was under cultivation at the end of the nineteenth century. Even conservative textbooks held that static crop yields despite significant technological advances meant soil fertility was declining. Soil erosion was recognized as one of the most fundamental and important resource conservation problems facing the nation. Harvard University geology professor Nathaniel Southgate Shaler even warned that the rapid pace of soil destruction threatened to undermine civilization.

Protecting society's fundamental interest in the soil was not just the government's job, Shaler held, it was one of its primary purposes. "Soil is a kind of placenta that enables living beings to feed on the earth. In it the substances utterly unfit to nourish plants in the state in which they exist in the rocks are brought to the soluble shape whence they may be lifted into life. All this process depends on the adjustment of the rate of rock decay to that of... renewing soil." Shaler recognized that agricultural practices mined soil fertility by eroding soil faster than it formed. "The true aim ... of a conservative agriculture ... is to bring about and keep the balance between the processes of rock decay and erosion.... With rare exceptions, the fields of all countries have been made to bear their crops without the least reference to the interests of future generations." 2 Shaler considered those who abused land to be among the lowest of criminals.

Shaler understood how plowing altered the balance between soil production and erosion. "In its primitive state the soil is each year losing a portion of its nutrient material, but the rate at which the substances go away is generally not more rapid than the downward movement of the layer into the bed rock.... But when tillage is introduced, the inevitable tendency of the process is to increase the rate at which the soil is removed."3 Disturbance of such a balance led to predictable consequences.

Satisfied that modern evidence supported his ideas, Shaler concluded that soil erosion shaped ancient history throughout the Old World. Once the soil was lost, recovery lay beyond history's horizon. "Where subsoil as well as the truly fertile layer has been swept away the field may be regarded as lost to the uses of man, as much so, indeed, as if it had been sunk beneath the sea, for it will in most instances require thousands of years before the surface can be restored to its original estate."4 The six thousand square miles of fields by then abandoned to erosion in Virginia, Tennessee, and Kentucky testified to the American tendency to repeat Old World mistakes.

Although Shaler advised tilling down through the subsoil to break up decaying bedrock and speed soil creation, he argued that land sloping more than five degrees should be spared the plow. He predicted that fertilizers could replace rock weathering, but did not foresee how mechanized agriculture would further increase erosion rates on America's farmlands.

Nonetheless, soil erosion was becoming a national problem. In i9o9 the National Conservation Congress reported that almost eleven million acres of American farmland had been abandoned because of erosion damage. Four years later, the U.S. Department of Agriculture (USDA) estimated that annual topsoil loss from U.S. fields amounted to more than twice the quant.i.ty of earth moved to dig the Panama Ca.n.a.l. Three years after that, Agricultural Experiment Station researchers estimated that half the tillable land in Wisconsin suffered from soil erosion that adversely affected economic activity.

At the start of the First World War, the USDA's annual yearbook lamented the economic waste from soil erosion. Rain fell like "thousands of little hammers beating upon the soil" and ran off bare ground in rivulets that were slowly stealing the nation's future. "Under the original process of nature the soil was continually wearing away on the top, but more was forming, and the formation was somewhat more rapid than the removal. The layer of soil on hillsides represented the difference between the amount formed and that removed. After clearing, the rate of removal is greatly increased, but the rate of formation remains the same."5 Already more than three million acres of farmland had been ruined by erosion. Another eight million acres were too degraded to farm profitably.

Reclamation of all but the most severely damaged farmland was possible, and potentially even profitable, but it required new farming practices and att.i.tudes.

Many farmers when approached on the subject of erosion show interest and agree that the loss is great. They will say, "Why, yes, some of my fields are badly washed, but it doesn't pay to try to do anything with them." They expect reclamation, if it is ever accomplished, to be undertaken by the Government, and it is only with difficulty that they can be induced to make an attempt at stopping the ravages of erosion. It has been cheaper in the past to move to newer lands.

Soil loss occurred slowly enough that farmers saw the problem as someone else's concern. Besides, mechanization made it even easier to just plow more land than to worry about soil loss. Machines were expensive and needed to pay for themselves-dirt was cheap enough to ignore losing a little here and there, or even everywhere.

The wide-open plains presented an ideal place for tractors. The first locomotive-like tractors arrived around i9oo. By 1917 hundreds of companies were cranking out smaller, more practical models. Before abandoning the market to agricultural specialists like International Harvester and John Deere, Henry Ford invented a rear hitch that allowed tractors to pull plows, disks, sc.r.a.pers and other earth-moving equipment across farms. Armed with these marvelous machines, a farmer could work far more land than he had when trailing behind an ox or horse. He could also plow up the pasture to plant more crops.

The cost of the new machines added up to more than many small farms could afford. From i9io to ig2o the value of farm implements on a typical Kansas farm tripled. In the next decade costs tripled again as more farmers bought more tractors, trucks, and combines. When prices for grain were high, it was profitable to operate the machinery. When prices dropped, as they did after the First World War, many farmers were saddled with unmanageable debt. Farmers who stayed in business saw bigger machines working more land as the way to a secure future. Just as the English land enclosures of the seventeenth and eighteenth centuries had displaced poor peasants, the spread of tractors displaced those lacking the capital to join the party.