Dirt_ The Erosion of Civilizations Part 8

From 1970 to 1990 the total number of hungry people fell by 16 percent, a decrease typically credited to the green revolution. However, the largest drop occurred in communist China, beyond the reach of the green revolu tion. The number of hungry Chinese fell by more than 50 percent, from more than 400 million to under zoo million. Excluding China, the number of hungry people increased by more than io percent. The effectiveness of the land redistribution of the Chinese Revolution at reducing hunger shows the importance of economic and cultural factors in fighting hunger. However we view Malthusian ideas, population growth remains criticaloutside of China, increased population more than compensated for the tremendous growth in agricultural production during the green revolution.

Another key reason why the green revolution did not end world hunger is that increased crop yields depended on intensive fertilizer applications that the poorest farmers could not afford. Higher yields can be more profitable to farmers who can afford the new methods, but only if crop prices cover increased costs for fertilizers, pesticides, and machinery. In third world countries the price of outlays for fertilizers and pesticides increased faster than green revolution crop yields. If the poor can't afford to buy food, increased harvests won't feed them.

More ominously, the green revolution's new seeds increased third-world dependence on fertilizers and petroleum. In India agricultural output per ton of fertilizer fell by two-thirds while fertilizer use increased sixfold. In West Java a two-thirds jump in outlays for fertilizer and pesticides swallowed up profits from the resulting one-quarter increase in crop yields in the i98os. Across Asia fertilizer use grew three to forty times faster than rice yields. Since the i98os falling Asian crop yields are thought to reflect soil degradation from increasingly intensive irrigation and fertilizer use.

Without cheap fertilizers-and the cheap oil used to make them-this productivity can't be sustained. As oil prices continue climbing this century, this cycle may stall with disastrous consequences. We burned more than a trillion barrels of oil over the past two decades. That's eighty million barrels a day-enough to stack to the moon and back two thousand times. Making oil requires a specific series of geologic accidents over inconceivable amounts of time. First, organic-rich sediment needs to be buried faster than it can decay. Then the stuff needs to get pushed miles down into the earth's crust to be cooked slowly. Buried too deep or cooked too fast and the organic molecules burn off; trapped too shallow or not for long enough and the muck never turns into oil. Finally, an impermeable layer needs to seal the oil in a porous layer of rock from which it can be recovered. Then somebody has to find it and get it out of the ground. It takes millions of years to produce a barrel of oil; we use millions of barrels a day. There is no question that we will run out of oil-the only question is when.

Estimates for when petroleum production will peak range from before 2020 to about 2040. Since such estimates do not include political or environmental constraints, some experts believe that the peak in world oil production is already at hand. Indeed, world demand just rose above world supply for the first time. Exactly when we run out will depend on the political evolution of the Middle East, but regardless of the details oil production is projected to drop to less than io percent of current production by the end of the century. At present, agriculture consumes 30 percent of our oil use. As supplies dwindle, oil and natural gas will become too valuable to use for fertilizer production. Petroleum-based industrial agriculture will end sometime later this century.

Not surprisingly, agribusiness portrays pesticide and fertilizer intensive agriculture as necessary to feed the world's poor. Even though almost a billion people go hungry each day, industrial agriculture may not be the answer. Over the past five thousand years population kept pace with the ability to feed people. Simply increasing food production has not worked so far, and it won't if population growth keeps up. The UN Food and Agriculture Organization reports that farmers already grow enough to provide 3,500 calories a day to every person on the planet. Per capita food production since the i96os has increased faster than the world's population. World hunger persists because of unequal access to food, a social problem of distribution and economics rather than inadequate agricultural capacity.

One reason for the extent of world hunger is that industrialized agriculture displaced rural farmers, forcing them to join the urban poor who cannot afford an adequate diet. In many countries, much of the traditional farmland was converted from subsistence farms to plantations growing high-value export crops. Without access to land to grow their own food, the urban poor all too often lack the money to buy enough food even if it is available.

The USDA estimates that about half the fertilizer used each year in the United States simply replaces soil nutrients lost by topsoil erosion. This puts us in the odd position of consuming fossil fuels-geologically one of the rarest and most useful resources ever discovered-to provide a subst.i.tute for dirt-the cheapest and most widely available agricultural input imaginable.

Traditional rotations of gra.s.s, clover, or alfalfa were used to replace soil organic matter lost to continuous cultivation. In temperate regions, half the soil organic matter commonly disappears after a few decades of plowing. In tropical soils, such losses can occur in under a decade. By contrast, experiments at Rothamsted from 1843 to 1975 showed that plots treated with farmyard manure for more than a hundred years nearly tripled in soil nitrogen content whereas nearly all the nitrogen added in chemical fertilizers was lost from the soil-either exported in crops or dissolved in runoff.

More recently, a fifteen-year study of the productivity of maize and soybean agriculture conducted at the Rodale Inst.i.tute in Kutztown, Pennsylvania showed no significant differences in crop yields where legumes or manure were used instead of synthetic fertilizers and pesticides. The soil carbon content for manured plots and those with a legume rotation respectively increased to three to five times that of conventional plots. Organic and conventional cropping systems produced similar profits, but industrial farming depleted soil fertility. The ancient practice of including legumes in crop rotations helped retain soil fertility. Manuring actually increased soil fertility.

This is really not so mysterious. Most gardeners know that healthy soil means healthy plants that, in turn, help maintain healthy soil. I've watched this process in our own yard as my wife doused our lot with soil soup brewed in our garage and secondhand coffee grounds liberated from behind our neighborhood coffee shop. I marvel at how we are using organic material imported from the tropics, where there are too few nutrients in the soil in the first place, to help rebuild the soil on a lot that once had a thick forest soil. Now, five years into this experiment, the soil in our yard has a surface layer of rich organic matter, stays moist long after it rains, and is full of coffee-colored worms.

Our caffeinated worms have been busy since we hired a guy with a small bulldozer to rip out the ragged, eighty-two-year-old turf lawn our house came with and reseed the yard with a mix of four different kinds of plants, two gra.s.ses and two forbs-one with little white flowers and the other with little red flowers. The flowers are a nice upgrade from our old lawn and we don't have to water it. Better still, the combination of four plants that grow and bloom at different times keeps out weeds.

Our eco-lawn may be advertised as low maintenance, but we still have to mow it. So we just cut the gra.s.s and leave it to rot where it falls. Within a week all the cuttings are gone-dragged down into worm burrows. Now I can dig a hole in the lawn and find big fat worms where there used to be nothing but dry dirt. After just a few years, the ground around the edges of the lawn stands a quarter of an inch higher than the patio surface built at the same time we seeded the eco-lawn. The worms are pumping up the yard-plowing it, churning it, and pushing carbon down into the ground-turning our dirt into soil. Recycling organic matter literally put life back in our yard. Adjusted for scale, the same principles could work for farms.

About the same time that mechanization transformed conventional agriculture, the modern organic farming movement began to coalesce around the ideas of Sir Albert Howard and Edward Faulkner. These two gentlemen with very different backgrounds came to the same conclusion: retaining soil organic matter was the key to sustaining high intensity farming. Howard developed a method to compost at the scale of large agricultural plantations, whereas Faulkner devised methods to plant without plowing to preserve a surface layer of organic matter.

At the close of the 193os Howard began to preach the benefits of maintaining soil organic matter as crucial for sustaining agricultural productivity. He feared that increasing reliance on mineral fertilizers was replacing soil husbandry and destroying soil health. Based on decades of experience on plantations in India, Howard advocated incorporating large-scale composting into industrial agriculture to restore and maintain soil fertility.

In Howard's view, farming should emulate nature, the supreme farmer. Natural systems provide a blueprint for preserving the soil-the first condition of any permanent system of agriculture. "Mother earth never attempts to farm without live stock; she always raises mixed crops; great pains are taken to preserve the soil and to prevent erosion; the mixed vegetable and animal wastes are converted into humus; there is no waste; the processes of growth and the processes of decay balance one another."10 Constant cycling of organic matter through the soil coupled with weathering of the subsoil could sustain soil fertility. Preservation of humus was the key to sustaining agriculture.

Howard felt that soil was an ecological system in which microbes provided a living bridge between soil humus and living plants. Maintaining humus was essential for breaking down organic and mineral matter needed to feed plants; soil-dwelling microorganisms that decompose organic matter lack chlorophyll and draw their energy from soil humus. Soil organic matter was essential for the back half of the cycle of life in which the breakdown of expired life fueled the growth of new life.

In the i92os at the Inst.i.tute of Plant Industry in Indore, India, Howard developed a system to incorporate composting into plantation agriculture. His process mixed plant and animal wastes to favor the growth of microorganisms, which he considered tiny livestock that enriched the soil by breaking organic matter into its const.i.tuent elements. Field trials of Howard's methods in the tropics were extremely successful. As word of his increased crop yields and soil-building methods spread, plantations in India, Africa, and Central America began adopting his approach.

Howard saw intensive organic farming as how to undo the damage industrial farming inflicted on the world's soils. He thought that many plant and animal diseases arose from reliance on artificial fertilizers that disrupted the complex biology of native soils. Reestablishing organic-rich topsoil through intensive composting would reduce, if not eliminate, the need for pesticides and fertilizers while increasing the health and resilience of crops.

After the First World War, Howard saw munitions factories begin manufacturing cheap fertilizers advertised as containing everything various crops needed. He worried that adopting fertilizers as standard practice on factory farms would emphasize maximizing profits at the expense of soil health. "The restoration and maintenance of soil fertility has become a universal problem.... The slow poisoning of the life of the soil by artificial manures is one of the greatest calamities which has befallen agriculture and mankind."li The Second World War derailed adoption of Howard's ideas. After the war the companies that supplied the world's armies turned to pumping out fertilizer, this time cheap enough to eclipse soil husbandry.

In the middle of the Second World War, Edward Faulkner published Plowman's Folly in which he argued that plowing-long considered the most basic act of farming-was counterproductive. Enrolled in courses on soil management and farm machinery decades earlier at the University of Kentucky, Faulkner had annoyed his professors by asking what was the point of tearing apart the soil for planting instead of incorporating crops into the organic layer at the ground surface where plants naturally germinate. Despite the usual reasons offered for plowing-preparing the seedbed, incorporating crop residues and manure or fertilizers into the soil, and allowing the soil to dry out and warm up in spring-his instructors sheepishly admitted that they knew of no clear scientific reasons for why the first step in the agricultural process was actually necessary. After twenty-five years working as a county agricultural agent in Kentucky and Ohio, Faulkner eventually concluded that plowing created more problems than it solved.

Challenging agronomists to reconsider the necessity of plowing, he argued that the key to growing abundant crops was maintaining an adequate surface layer of organic material to prevent erosive runoff and maintain soil nutrients. This was heresy. "We have equipped our farmers with a greater tonnage of machinery per man than any other nation. Our agricultural population has proceeded to use that machinery to the end of destroying the soil in less time than any other people has been known to do in recorded history." 12 Faulkner also considered reliance on mineral fertilizers unnecessary and unsustainable.

Like most heretics', Faulkner's unconventional beliefs were grounded in experience. He inadvertently discovered in his backyard garden that he could greatly increase crop yields by not tilling when he began growing corn in soil he considered better suited for making bricks. From 1930 to 1937 he introduced organic matter into his backyard plot by digging a trench with a shovel and mixing in leaves at the bottom of the trench to emulate the standard practice of plowing under last year's crop stubble. Like conventional plowing, this buried the organic-rich surface material to a depth of six or eight inches. In the fall of 1937 he tried something different. He mixed the leaves into the surface of the soil.

The next year his soil was transformed. Previously he had been able to grow only parsnips in the stiff clay soil; now the soil texture was granular. It could be raked like sand. In addition to parsnips, he harvested fine crops of carrots, lettuce, and peas-without fertilizer and with minimal watering. All he did was keep the weeds down.

When the Soil Conservation Service staff were unimpressed with his backyard experiment, Faulkner took up the challenge and leased a field for a full-scale demonstration. Instead of plowing before planting, he disked the standing plants into the surface of the soil, leaving the ground littered with chopped-up weeds. Skeptical neighbors forecast a poor harvest for the careless amateur. Surprised and impressed when Faulkner's crop exceeded their own, they were unsure what to think about his mysterious success without plowing, fertilizers, or pesticides.

After several years of repeated success on his leased field, Faulkner began to advocate rebuilding surface layers of organic material. He was confident that with the right approach and machinery, farmers could recreate good soil wherever it had existed naturally. "Men have come to feel ... that centuries are necessary for the development of a productive soil. The satisfying truth is that a man with a team or a tractor and a good disk harrow can mix into the soil, in a matter of hours, sufficient organic material to accomplish results equal to what is accomplished by nature in decades." What farmers needed to do was stop tilling the soil and begin incorporating organic matter back into the ground. "Everywhere about us is evidence that the undisturbed surface of the earth produces a healthier growth than that portion now being farmed.... The net effect of fertilizing the land, then, is not to increase the possible crop yield, but to decrease the devastating effects of plowing."13 Like Howard, Faulkner believed that reestablishing healthy soil would reduce, if not eliminate, crop pests and diseases.

Soil organic matter is essential for sustaining soil fertility not so much as a direct source of nutrients but by supporting soil ecosystems that help promote the release and uptake of nutrients. Organic matter helps retain moisture, improves soil structure, helps liberate nutrients from clays, and is itself a source of plant nutrients. Loss of soil organic matter reduces crop yields by lowering the activity of soil biota, thereby slowing nutrient recycling.

Different soils in different climates can sustain agriculture without supplemental fertilization for different periods of time. Organic-rich soil of the Canadian Great Plains can be cultivated for more than fifty years before losing half its soil carbon, whereas Amazon rainforest soils can lose all agricultural potential in under five years. A twenty-four-year fertilization experiment in northwestern China found that soil fertility declined under chemical fertilizers unless coupled to addition of straw and manure.

Nowhere is the debate over the appropriate application of technology more polarized than in the field of biotechnology. Downplaying notions of population control and land reform, industry advocates push the idea that genetic engineering will solve world hunger. Despite altruistic rhetoric, genetic engineering companies design sterile crops to ensure that farmerslarge agribusinesses and subsistence farmers alike-must keep on buying their proprietary seeds. There was a time when prudent farmers kept their best seed stock for next year's crop. Now they get sued for doing so.

Despite the dramatically increased yields promised by industry, a study by the former director of the National Academy of Sciences' Board on Agriculture found that genetically modified soybean seeds produced smaller harvests than natural seeds when he a.n.a.lyzed more than eight thousand field trials. A USDA study found no overall reduction in pesticide use a.s.sociated with genetically engineered crops, even though increased pest resistance is touted as a major advantage of crop engineering. Whereas the promise of greatly increased crop yields from genetic engineering has proven elusive, some fear that genetically modified genes that convey sterility could cross to nonproprietary crops, with catastrophic results.

Given the significant real and potential drawbacks of bioengineering and agrochemistry, alternative approaches deserve a closer look. Over the long run, intensive organic farming and other nonconventional methods may prove our best hope for maintaining food production in the face of population growth and continuing loss of agricultural land. In principle, intensive organic methods could even replace fertilizer-intensive agriculture once cheap fossil fuels are history.

Here is the crux of Wes Jackson's argument that tilling the soil has been an ecological catastrophe. A genetics professor before he resigned to become president of the Land Inst.i.tute in Salina, Kansas, Jackson says he is not advocating a return to the bow and arrow. He just questions the view that plowing the soil is irrefutably wholesome, pointedly suggesting that the plow destroyed more options for future generations than did the sword and that-with rare exceptions-plow-based agriculture hasn't proven sustainable. He estimates that in the next two decades severe soil erosion will destroy 20 percent of the natural agricultural potential of our planet to grow crops without fertilizer or irrigation.

Yet Jackson is neither doomsayer nor Luddite. In person he sounds more like a farmer than an environmental extremist. Instead of despair, he calls for agricultural methods based on emulating natural systems rather than controlling, or replacing them. In promoting natural systems agriculture, Jackson is the latest prophet for Xenophon's philosophy of adapting agriculture to the land rather than vice versa.

Drawing on experience in the American farm belt, Jackson seeks to develop an agricultural system based on imitating native prairie ecosystems. Unlike annual crops raised on bare, plowed ground, the roots of native perennials hold the soil together through drenching rainstorms. Native prairies contain both warm-season and cold-season gra.s.ses, as well as legumes and composites. Some of the plants do better in wet years, some thrive in dry years. The combination helps keep out weeds and invasive species because plants cover the ground all year-just like our eco-lawn.

As ecologists know, diversity conveys resilience-and resilience, Jackson says, can help keep agriculture sustainable. Hence he advocates growing a combination of crops year-round to shield the ground from the rain's erosive impact. Monocultures generally leave the ground bare in the spring, exposing vulnerable soil to erosion for months before crops get big enough to block incoming rain. Storms. .h.i.tting before crops leaf out cause two to ten times the erosion of storms later in the year when the ground lies shielded beneath crops. Under monoculture, one good storm at the wrong time can send erosion racing decades ahead of soil production.

The beneficial effects of Jackson's system are evident at the Land Inst.i.tute. Research there has shown that a perennial polyculture can manage pests, provide all its own nitrogen, and produce a greater per-acre crop yield than monocultures. Although the specifics of Jackson's approach were designed for the prairies, his methods could be adapted to other regions by using species mixtures appropriate to the local environment. Understandably, pesticide, fertilizer, and biotechnology companies are not very excited about Jackson's low-tech approach. But Jackson is not a lone voice in the wilderness; over the past few decades many farmers have adopted methods like those advocated by Faulkner and Howard.

Whatever we call it, today's organic farming combines conservationminded methods with technology but does not use synthetic pesticides and fertilizers. Instead, organic farming relies on enhancing and building soil fertility by growing diversified crops, adding animal manure and green compost, and using natural pest control and crop rotation. Still, for a farm to survive in a market economy it must be profitable.

Long-term studies show that organic farming increases both energy efficiency and economic returns. Increasingly, the question appears not to be whether we can afford to go organic. Over the long run, we simply can't afford not to, despite what agribusiness interests will argue. We can greatly improve conventional farming practices from both environmental and economic perspectives by adopting elements of organic technologies. Oddly, our government subsidizes conventional farming practices, whereas the market places a premium on organic produce. A number of recent studies report that organic farming methods not only retain soil fertility in the long term, but can prove cost effective in the short term.

In 1974, under the leadership of ecologist Barry Commoner, the Center for the Biology of Natural Systems at Washington University in St. Louis began comparing the performance of organic and conventional farms in the Midwest. Pairing fourteen organic farms with conventional farms of similar size, operated with a similar crop-livestock system on similar soils, the two-year study found that organic farms produced about the same income per acre as did conventional farms. Although the study's preliminary results surprised skeptical agricultural experts, many subsequent studies confirmed that substantially lower production costs more than offset slightly smaller harvests from organic farms. Industrial agrochemistry is a societal convention and not an economic imperative.

Subsequent studies also showed that crop yields are not substantially lower under organic agricultural systems. Just as important is the demonstration that modern agriculture need not deplete the soil. Rothamsted, the estate where John Lawes proved the fertilizing effects of chemical fer tilizers, hosts the longest ongoing comparison of organic and conventional agriculture-a century and a half-placing manure-based organic farming and chemical fertilizer-based farming side by side. Wheat yields from conventionally fertilized and organic plots were within 2 percent of each other, but the soil quality measured in terms of carbon and nitrogen levels improved over time in the organic plots.

A twenty-two-year study by the Rodale Inst.i.tute on a Pennsylvania farm compared the inputs and production from conventional and organic plots. Average crop yields were comparable under normal rainfall, but the average corn yields in the organic plots were about a third higher during the driest five years. Energy inputs were about a third lower, and labor costs about a third higher in the organic plots. Overall, organic plots were more profitable than the conventional plots because total costs were about 15 percent lower, and organic produce sold at a premium. Over the twodecade-long experiment, soil carbon and nitrogen contents increased in the organic plots.

In the mid-i98os, researchers led by Washington State University's John Reganold compared the state of the soil, erosion rates, and wheat yields from two farms near Spokane in eastern Washington. One farm had been managed without the use of commercial fertilizers since first plowed in i9o9. The adjoining farm was first plowed in 1908 and commercial fertilizer was regularly applied after 1948.

Surprisingly, there was little difference in the net harvest between the farms. From 1982 to 1986 wheat yields from the organic farm were about the average for two neighboring conventional farms. Net output from the organic farm was less than that of the conventional farm only because the organic farmer left his field fallow every third year to grow a crop of green manure (usually alfalfa). Lower expenses for fertilizer and pesticides compensated him for the lower net yield. More important, the productivity of his farm did not decline over time.

Reganold's team found that the topsoil on the organic farm was about six inches thicker than the soil of the conventional farm. The organic farm's soil had greater moisture-holding capacity and more biologically available nitrogen and pota.s.sium. Soil on the organic farm also contained many more microbes than the conventional farm's soil. Topsoil on the organic farm had more than half again as much organic matter as topsoil on the conventional farm.

The organic fields not only eroded slower than the soil replacement rates estimated by the Soil Conservation Service, the organic farm was building soil. In contrast, the conventionally farmed field shed more than six inches of topsoil between 1948 and 1985. Direct measurements of sediment yield confirmed a fourfold difference in soil loss between the two farms.

The bottom line was simple. The organic farm retained its fertility despite intensive agriculture. Soil on the conventional farm-and by implication most neighboring farms-gradually lost productive capacity as the soil thinned. With fifty more years of conventional farming, the region's topsoil will be gone. Harvests from the region are projected to drop by half once topsoil erosion leaves conventional farmers plowing the clayey subsoil. To sustain crop production, technologically driven increases in crop yields will have to double just to stay even.

European researchers also report that organic farms are more efficient and less detrimental to soil fertility. A twenty-one-year comparison of crop yields and soil fertility showed that organic plots yielded about zo percent less than plots cultivated using pesticide-and-fertilizer-intensive methods. However, the organic plots used a third to half the input of fertilizer and energy and virtually no pesticides. In addition, the organic plots harbored far more pest-eating organisms and supported greater overall biological activity. In the organic plots, the bioma.s.s of earthworms was up to three times higher and the total length of plant roots colonized by beneficial soil mycorrhizae was 40 percent greater. Organic farming methods not only increased soil fertility, profits from organic farms were comparable to those of conventional farms. Commercially viable, organic farming need not remain an alternative philosophy.

Other recent studies support this view. A comparison of neighboring farms using organic and conventional methods on identical soils in New Zealand found the organic farms had better soil quality, higher soil organic matter, and more earthworms-and were as financially viable per hectare. A comparison of apple orchards in Washington State found similar crop yields between conventional and organic farming systems. The five-year study found that organic methods not only used less energy, maintained higher soil quality, and produced sweeter apples, they proved more profitable than conventional methods. An orchard grown under conventional methods that became profitable in about fifteen years would show profits within a decade under organic methods.

While the organic sector is the fastest-growing segment of the U.S. food market, many currently profitable conventional farming methods would become uneconomical if their true costs were incorporated into market pricing. Direct financial subsidies, and failure to include costs of depleting soil fertility and exporting pollutants, continue to encourage practices that degrade the land. In particular, the economics and practicalities of largescale farming often foster topsoil loss and compensate with fertilizers and soil amendments. Organic farming uses fewer chemicals and-for that very reason-receives fewer research dollars per acre of production. At this point, individuals seeking healthier food contribute more to agricultural reform than do governments responsible for maintaining long-term agricultural capacity.

Over the past decade American farm subsidies averaged more than $io billion annually. Although subsidy programs were originally intended to support struggling family farms and ensure a stable food supply, by the i96os farm subsidies actively encouraged larger farms and more intensive methods of crop production focused on growing single crops. U.S. commodity programs that favor wheat, corn, and cotton create incentives for farmers to buy up more land and plant only those crops. In the 197os and i98os, subsidies represented almost a third of U.S. farm income. A tenth of the agricultural producers (coincidentally, the largest farms) now receive two-thirds of the subsidies. Critics of the subsidy program, including Nebraska Republican senator Chuck Hagel, maintain that it favors large corporate farms and does little for family farms. Good public policy would use public funds to encourage soil stewardship-and family farms, they argue-instead of encouraging large-scale monoculture.

Organic agriculture is starting to lose its status as a fringe movement as farmers relearn that maintaining soil health is essential for sustaining high crop yields. A growing shift away from agrochemical methods coincides with the renewed popularity of methods to improve the soil. Today, a middle ground is evolving in which nitrogen-fixing crops grow between row crops and as cover in the off-season, and nitrate fertilizer and pesticide are used at far lower levels than on conventional farms.

The challenge facing modern agriculture is how to merge traditional agricultural knowledge with modern understanding of soil ecology to promote and sustain the intensive agriculture needed to feed the world-how to maintain an industrial society without industrial agriculture. While the use of synthetic fertilizers is not likely to be abandoned any time soon, maintaining the increased crop yields achieved over the past half century will require widespread adoption of agricultural practices that do not further diminish soil organic matter and biological activity, as well as the soil itself.

Soil conservation methods can help prevent land degradation and improve crop yields. Simple steps to retain soil productivity include straw mulching, which can triple the ma.s.s of soil biota, and application of manure, which can increase the abundance of earthworms and soil microorganisms fivefold. Depending on the particular crop and circ.u.mstances, a dollar invested in soil conservation can produce as much as three dollars' worth of increased crop yields. In addition, every dollar invested in soil and water conservation can save five to ten times that amount in costs a.s.sociated with dredging rivers, building levees, and flood control in downstream areas. Although it is hard to rally and sustain political support for treating dirt like gold, American farmers are rapidly becoming world leaders in soil conservation. Because it is prohibitively expensive to put soil back on the fields once it leaves, the best, and most cost-effective strategy lies in keeping soil on the fields in the first place.

For centuries the plow defined the universal symbol of agriculture. But farmers are increasingly abandoning the plow in favor of long-shunned notill methods and less aggressive conservation tillage-a catchall term for practices that leave at least 30 percent of the soil surface covered with crop residue. Changes in farming practices over the past several decades are revolutionizing modern agriculture, much as mechanization did a century ago-only this time, the new way of doing things conserves soil.

The idea of no-till farming is to capture the benefits of plowing without leaving soils bare and vulnerable to erosion. Instead of using a plow to turn the soil and open the ground, today's no-till farmers use disks to mix organic debris into the soil surface and chisel plows to push seeds into the ground through the organic matter leftover from prior crops, minimizing direct disturbance of the soil. Crop residue left at the ground surface acts as mulch, helping to retain moisture and r.e.t.a.r.d erosion, mimicking the natural conditions under which productive soils formed in the first place.

In the r96os almost all U.S. cropland was plowed, but over the past thirty years adoption of no-till methods has grown rapidly among North American farmers. Conservation tillage and no-till techniques were used on 33 percent of Canadian farms in r99i, and on 6o percent of Canadian croplands by 2ooi. Over the same period conservation tillage grew from about 25 percent to more than 33 percent of U.S. cropland, with i8 percent managed with no-till methods. By 2004, conservation tillage was practiced on about 41 percent of U.S. farmland, and no-till methods were used on 23 percent. If this rate continues, no-till methods would be adopted on the majority of American farms in little more than a decade. Still, only about 5 percent of the world's farmland is worked with no-till methods. What happens on the rest may well shape the course of civilization.

No-till farming is very effective at reducing soil erosion; leaving the ground covered with organic debris can bring soil erosion rates down close to soil production rates-with little to no loss in crop yields. In the late 1970s, one of the first tests of the effect of no-till methods in Indiana reported a more than 75 percent reduction in soil erosion from cornfields. More recently, researchers at the University of Tennessee found that no-till farming reduced soil erosion by more than 9o percent over conventional tobacco cultivation. Comparison of soil loss from cotton fields in northern Alabama found that no-till plots averaged two to nine times less soil loss than conventional-till plots. One study in Kentucky reported that no-till methods decreased soil erosion by an astounding 98 percent. While the effect on erosion rates depends on a number of local factors, such as the type of soil and the crop, in general a io percent increase in ground surface cover reduces erosion by 20 percent, such that leaving 30 percent of the ground covered reduces erosion by more than 50 percent.

Lower erosion rates alone do not explain the rapid rise in no-till agriculture's popularity. No-till methods have been adopted primarily because of economic benefits to farmers. The Food Security Acts of 1985 and 199o required farmers to adopt soil conservation plans based on conservation tillage for highly erodible land as a condition for partic.i.p.ating in popular USDA programs (like farm subsidies). But conservation tillage has proven to be so cost-effective that it also is being widely adopted on less erodible fields. Not plowing can cut fuel use by half, enough to more than offset income lost to reduced crop yields, translating into higher profits. It also increases soil quality, organic matter, and biota; even earthworm populations are higher under no-till methods. Although adopting no-till practices can initially result in increased herbicide and pesticide use, the need declines as soil biota rebound. Growing experience in combining no-till methods with the use of cover crops, green manures, and biological pest management suggests that these so-called alternative methods offer practical complements to no-till methods. Farmers are adopting no-till methods because they can both save money and invest in their future, as increasing soil organic matter means more fertile fields-and eventually lower outlays for fertilizer. The lower cost of low-till methods is fueling growing interest even among large farming operations.

No-till agriculture has another advantage; it could provide one of the few relatively rapid responses to help hold off global warming. When soil is plowed and exposed to the air, oxidation of organic matter releases carbon dioxide gas. No-till agriculture has the potential to increase the organic matter content of the top few inches of soil by about i percent a decade. This may sound like a small number, but over twenty to thirty years that can add up to io tons of carbon per acre. As agriculture mechanized over the past century and a half, U.S. soils are estimated to have lost about 4 billion metric tons of carbon into the atmosphere. Worldwide, about 78 billion metric tons of carbon once held as soil organic matter have been lost to the atmosphere. A third of the total carbon dioxide buildup in the atmosphere since the industrial revolution has come not from fossil fuels but from degradation of soil organic matter.

Improvement of agricultural soils presents an opportunity to sequester large amounts of carbon dioxide to slow global warming-and help feed a growing population. If every farmer in the United States were to adopt notill practices and plant cover crops, American agriculture could squirrel away as much as 300 million tons of carbon in the soil each year, turning farms into net carbon sinks, rather than sources of greenhouse gases. While this would not solve the problem of global warming-the soil can hold only so much carbon-increasing soil carbon would help buy time to deal with the root of the problem. Adoption of no-till practices on the world's 1.5 billion hectares of cultivated land has been estimated to be capable of absorbing more than 9o percent of global carbon emissions for the several decades it would take to rebuild soil organic matter. A more realistic scenario estimates the total carbon sequestration potential for the world's cropland as roughly 25 percent of current carbon emissions. Moreover, more carbon in the soil would help reduce demand for fertilizers and would lead to less erosion, and therefore further slow carbon emissions, all while increasing soil fertility.

The attraction of no-till methods is immense, but obstacles remain to their universal adoption. And they don't work well everywhere. No-till methods work best in well-drained sandy and silty soils; they do not work well in poorly drained heavy clay soils that can become compacted unless tilled. Slow-to-change att.i.tudes and perceptions among farmers are primary factors limiting their wider adoption in the United States; the lag in adoption of no-till methods in Africa and Asia additionally reflects lack of financial resources and governmental support. In particular, small-scale farmers often lack access to specialized seed drills to plant through crop residues. Many subsistence farmers use the residue from the previous year's crops as fuel or animal fodder. These challenges are substantial, but they are well worth tackling. Reinvesting in nature's capital by rebuilding organic-rich soils may well hold the key to humanity's future.

It is no secret that if agriculture doesn't become sustainable nothing else will; even so, some still treat our soil like dirt-and sometimes worse. The eastern Washington town of Quincy is an unlikely place to uncover one of our nation's dirtiest secrets. But in the early 199os the town's mayor clued Seattle Times reporter Duff Wilson in to how toxic waste was being recycled into fertilizer and sprayed on croplands. Patty Martin was an unusual candidate for a whistle blower, a conservative housewife and former pro basketball player who won a virtually uncontested race for mayor of her small farming community. When Martin's const.i.tuents began complaining about mysteriously withered crops and crop dusters spraying fertilizer out on the open prairie for no apparent reason, she learned that Cenex, a fertilizer-specialty division of the Land O'Lakes Company (yes, the b.u.t.ter people), was shipping toxic waste to her town, mixing it with other chemicals in a big concrete pond near the train station, and then selling the concoction as cheap, low-grade fertilizer.

It was a great scheme. Industrial polluters needing to dispose of toxic waste avoided the high cost of legitimate dumps. (Anyone who puts something into a registered toxic waste dump owns it forever.) But mixing the same stuff into cheap fertilizer and spreading it on vacant land-or selling it to farmers-makes the problem, and the liability, disappear. So trains pulled in and out of Quincy in the middle of the night and the pond went up and down with no records of what went in or out of it. Sometimes Cenex sold the new-fangled fertilizer to unsuspecting farmers. Sometimes the company paid farmers to use it just to get rid of the stuff.

Martin discovered that state officials allowed recycling waste rich in heavy metals into fertilizer without telling farmers about all those extra "nutrients." Whether or not something was considered hazardous depended not so much on what the stuff was as on what one intended to do with it. Approached about the practice of selling toxic waste as fertilizer, staff at the state department of agriculture admitted they thought it was a good idea, kind of like recycling.

Curiously enough, the toxic fertilizer began killing crops. Unless they are eroded away, heavy metals stick around in the soil for thousands of years. And if they build up enough in the soil, they are taken up by plants-like crops.

Why would a company like Cenex be mixing up a toxic brew and selling it as low-grade fertilizer? Try the oldest reason around-money. Company memos reveal that they saved $170,ooo a year by calling their rinse pond waste a product and spraying it on farmer's fields. The legal case ended in 1995 when the company agreed to plead guilty to using pesticide for an unapproved purpose and pay a $io,ooo fine. Now I don't particularly like to gamble, but even I'd take my savings to Vegas anytime with a guaranteed 17 to I payout.

After the Cenex case, other farmers in the area began to wonder whether bad fertilizer had been the cause of their failing crops. One told Martin's friend Dennis DeYoung about a fertilizer tank that Cenex delivered to his farm and forgot about years earlier. Dennis scooped out some of the dried residue from the abandoned tank and sent it off to a soil-testing lab in Idaho. The lab found lots of a.r.s.enic, lead, t.i.tanium, and chromium-not exactly premium plant food. The lab also reported high lead and a.r.s.enic concentrations in peas, beans, and potatoes DeYoung sent in from crops fertilized by Cenex products. Samples of potatoes another friend of DeYoung's sent in were found to have ten times the allowable concentration of lead.

Washington wasn't the only place where toxic waste was being recla.s.sified as fertilizer. Between 1984 and 1992, an Oregon subsidiary of ALCOA (the Aluminum Company of America) recycled more than two hundred thousand tons of smelter waste into fertilizer. ALCOA saved two million dollars a year turning waste into a product marketed as a road de-icer during the winter and plant food in the summer. Companies all across America were saving millions of dollars a year selling industrial waste instead of paying to send it to toxic waste dumps. By the late 199os, eight major U.S. companies converted 120 million pounds of hazardous waste into fertilizer each year.

Strangely, n.o.body involved seemed too anxious to talk about the toxic waste-into-fertilizer industry. They didn't have to worry. No rules prevented mixing hazardous waste into fertilizer, and then into the soil. No one appeared too concerned about such blatant disregard of the importance of healthy soil. Never mind that, as seems obvious, farms are about the last place we should use as a dumping ground for heavy metals.

The way we treat our agricultural soils, whether as locally adapted ecosystems, chemical warehouses, or toxic dumps, will shape humanity's options in the next century. Europe broke free from the ancient struggle to provide enough food to keep up with a growing population by coming to control a disproportionate share of the world's resources. The United States escaped the same cycle by expanding westward. Now with a shrinking base of arable land, and facing the end of cheap oil, the world needs new models for how to feed everybody. Island societies provide one place to look; some consumed their future and descended into brutal compet.i.tion for arable land, others managed to sustain peaceful communities. The key difference appears to be how social systems adapted to the reality of sustaining agricultural productivity without access to fresh land-in other words, how people treated their soil.

ISLANDS IN TIME

When our soils are gone, we too, must go unless we find some way to feed on raw rock.

THOMAS C. CHAMBERLAIN.

ON HIS WAY TO INDONESIA AND THE SPICE ISLANDS, a Dutch admiral discovered a small volcanic island in a remote part of the Pacific Ocean on Easter Sunday 1722. Shocked by apparent cannibalism among the natives, Jakob Roggeveen and his crew barely paused and sailed on across the Pacific. Never attractive for colonization or trade because of its meager resource base, Easter Island was left alone until the Spanish annexed it half a century later. The most interesting thing about the place was a curious collection of hundreds of colossal stone heads littered across the island.

Easter Island presented a world-cla.s.s puzzle to Europeans who wondered how a few stranded cannibals could have erected all those ma.s.sive heads. The question mystified visitors until archaeologists pieced together the environmental history of the island to learn how a sophisticated society descended into barbarism. Today Easter Island's story provides a striking historical parable of how environmental degradation can destroy a society.

The tale is not one of catastrophic collapse but of decay occurring over generations as people destroyed their resource base. Easter Island's native civilization did not disappear overnight. It eroded away as environmental degradation reduced the number of people the island could support to fewer than those living there already. Hardly cataclysmic, the outcome was devastating nonetheless.

Pollen preserved in lake sediments records an extensive forest cover when a few dozen people colonized Easter Island. The conventional story is that Polynesians arrived in the fifth century and over the next thousand years cleared the forest for agriculture, fuel, and canoes as the population grew to almost ten thousand in the fifteenth century. Then, within a century of the peak in population, a timber shortage began forcing people to live in caves. Although recent rea.n.a.lysis of radiocarbon dating suggests colonization may have occurred centuries later, pollen and charcoal from sediment cores indicate the island retained some forest cover through the seventeenth century. The island was virtually treeless by the time the first Europeans arrived. By then the last trees lay out of reach, sheltered at the bottom of the island's deepest extinct volcano.

Soil erosion accelerated once forest clearing laid the land bare. Crop yields began to fall. Fishing became more difficult after the loss of the native palms whose fibers had been used to make nets. As access to food decreased, the islanders built defensive stone enclosures for their chickens-the last food source on the island not directly affected by loss of trees and topsoil. Without the ability to make canoes, they were trapped, reduced to perpetual warfare over a diminishing resource base that ultimately came to include themselves as their society unraveled.

Rapa Nui (the native inhabitants' name for Easter Island) is located at the same lat.i.tude as central Florida, but in the Southern Hemisphere. Continually swept by warm Pacific winds, the island consists of three ancient volcanoes occupying less than fifty square miles-a tropical paradise more than a thousand miles from the nearest inhabitable land. Such isolation meant that the island supported few native plants and animals when wayward Polynesians landed after paddling across the Pacific Ocean. The native flora and fauna offered so little to eat that the new arrivals' diet was based on chickens and sweet potatoes they brought with them. Sweet potato cultivation took little effort in the island's hot, humid environment, leaving the islanders with enough free time to develop a complex society centered on carving and erecting gigantic stone heads.

The monstrous statues were carved at a quarry, transported across the island, and then capped by a ma.s.sive topknot of red stone from a different quarry. The purpose of the statues remains a mystery; how the islanders did it was as much of a mystery for many years. That they transported their immense statues without mechanical devices and using only human power perplexed Europeans viewing the treeless landscape.

When asked how the great stone statues had been transported, the few remaining islanders did not know how their ancestors had done it. They simply replied that the statues walked across the island. For centuries the bare landscape fueled the mystery of the heads. No one, including the sculptors' descendants, imagined that the great stone statues were rolled on logs-it seemed just as likely that they had walked across the island on their own.

Many of the statues were left either unfinished or abandoned near their quarry, implying that their sculptors ignored the impending timber shortage until the very end. As timber became scarce, compet.i.tion for status and prestige continued to motivate the drive to erect statues. Even though the Easter Islanders knew they were isolated on a world they could walk around in a day or two, cultural imperatives apparently overcame any concern about running out of trees.

European contact finished off what was left of the native culture. In the 1850s most of the island's remaining able-bodied men, including the king and his son, were enslaved and shipped off to Peruvian guano mines. Years later, the fifteen surviving abductees repatriated to their island introduced smallpox to a population with no immunity. Soon thereafter the island's population dropped to just one hundred and eleven, unraveling any remaining cultural continuity.

The story of how Easter Islanders committed ecological suicide is preserved in the island's soil. Derived from weathered volcanic bedrock, thin poorly developed soil, in places only a few inches thick, blankets most of the island. Just as in other subtropical regions, the thin topsoil held most of the available nutrients. Soil fertility declined rapidly once vegetation clearing allowed runoff to carry away the topsoil. After that only a small part of the island remained cultivatable.

Distinctively abbreviated subsoil exposed at the ground surface testifies to erosion of the island's most productive soil. Exposures at the foot of hillslopes reveal that a layer of material brought down from higher on the slopes covers the eroded remnants of the older original soil. These truncated soil profiles are studded with telltale casts of the roots of the now extinct Easter Island palm.

The relationship of soil horizons to archaeological sites reveals that most of the soil erosion occurred after construction of stone dwellings (ahus) a.s.sociated with the rise of agriculture on the island. These dwellings were built directly on top of the native soil, and younger deposits of material washed off the slopes now bury the ahus'foundations. So the erosion that stripped topsoil from the slopes happened after the ahus were built.

Radiocarbon dating of the slope-wash deposits and soil profiles exposed by erosion, in road cuts, or in hand-dug soil pits record that the top of the island's original soil eroded off between about AD 1200 and 165o. Apparently, vegetation clearing for agriculture triggered widespread erosion of the A horizon upon which soil fertility depended. Easter Island's society faded soon after its topsoil disappeared, less than a century before Admiral Roggeveen's unplanned visit.

A detailed study of the soils on the Poike Peninsula revealed a direct link between changing agricultural practices and soil erosion on Easter Island. Remnants of the original soil still standing on a few tiny hills, flat-topped sc.r.a.ps of the original ground surface, attest to widespread erosion of the native topsoil. Downhill from these remnant soil pedestals, hundreds of thin layers of dirt, each less than half an inch thick, were deposited on top of a cultivated soil studded with the roots of the endemic palm tree. A halfinch thick layer of charcoal immediately above the buried soil attests to extensive forest clearing after a long history of cultivating plots interspersed among the palm trees.

Initial agricultural plots in planting pits dug between the trees protected the ground from strong winds and heavy rainfall, and shielded crops from the tropical sun. Radiocarbon dating of the charcoal layer and material obtained from the overlying layers of sediment indicate that the soil eroded off the upper slopes, and buried the lower slopes, between AD 1280 and 1400. The numerous individual layers of sediment deposited on the lower slopes show that the soil was stripped off storm-by-storm a fraction of an inch at a time. These observations tell the story of how after centuries of little erosion from fields tucked beneath a forest canopy, the forest of the Poike Peninsula was burned and cleared for more intensive agriculture that exposed the soil to accelerated erosion. Agriculture ceased before AD 1500, after just a century or two in which the soil slowly disappeared as runoff from each storm removed just a little more dirt.

The island's birds disappeared too. More than twenty species of seabirds inhabited Easter Island when Polynesians arrived. Just two species survived until historic times. Nesting in the island's closed canopy native forest, these birds fertilized the soil with their guano, bringing marine nutrients ash.o.r.e to enrich naturally poor volcanic soils. Wiping out the island's native birds eliminated a key source of soil fertility, contributing to the decline of the soil and perhaps even the failure of the forest to regenerate. I doubt the Easter Islanders had any idea that eating all the birds could undermine their ability to grow sweet potatoes.

The story of Easter Island is by no means unique. Catastrophic erosion followed forest clearing by Polynesian farmers on many other-but by no means all-Pacific Islands. Among the last places colonized on earth, South Pacific islands provide relatively simple settings to study the evolution of human societies because they had no land vertebrates before people imported their own fauna of chickens, pigs, dogs, and rats.

The islands of Mangaia and Tikopia provide stark contrasts in human adaptation to the realities of a finite resource base. Sharing many common traits and similar environmental histories until well after people arrived, these societies addressed declining resource abundance in very different ways. As worked out by UC Berkeley anthropologist Patrick Kirch, their stories show how transgenerational trends shaped the fate of entire societies.

Mangaia occupies just twenty square miles-a small dot of land in the South Pacific twenty-one and a half degrees south of the equator. Visited by Captain James Cook in 1777, Mangaia looks like a medieval walled fortress rising from the sea. The deeply weathered basaltic hills of the island's interior climb more than five hundred feet above sea level, surrounded by a gray coral reef lifted out of the ocean. A hundred thousand years ago, growth of the nearby volcanic island of Rarotonga warped Earth's crust enough to pop Mangaia and its fringing reef up out of the sea. Streams flowing off the island's core run into this half-mile-wide wall of razor-sharp coral that rises half the island's height. There they drop their sediment load and sink into caves running down to the island's narrow beach. Radiocarbon-dated sediment cores recovered from the base of the island's interior cliffs tell the story of Mangaia's last seven thousand years.

Covered by forest for five thousand years before Polynesians arrived about 500 BC, Mangaia eroded slowly enough to build up a thick soil in the island's volcanic core. Kirch's sediment cores record sweeping changes between 400 Bc and AD 400, when a rapid increase in the abundance of microscopic charcoal particles records the expansion of slash-and-burn agriculture. Charcoal is virtually absent from sediment older than 2,400 years; dirt deposited less than 2,000 years ago contains millions of tiny carbon fragments per cubic inch of dirt. In the sediment cores, sharp increases in the abundance of iron and aluminum oxides, along with decreased phosphorus content, show that erosion of a thin, nutrient-rich layer of topsoil rapidly exposed nutrient-poor subsoil. The native forest depended on recycling nutrients that the weathered bedrock could not readily resup ply. So topsoil loss r.e.t.a.r.ded forest regeneration. Well adapted to grow on the nutrient-poor subsoil, ferns and scrub vegetation useless for human subsistence now cover more than a quarter of the island.

By about AD I2oo the pattern of shifting slash-and-burn agriculture had stripped so much topsoil from cultivated slopes that Mangaian agriculture shifted to reliance on labor-intensive irrigation of taro fields in the alluvial valley bottoms. Occupying just a few percent of the island's surface area, these fertile bottomlands became strategic objectives in perpetual intertribal warfare. Control of the last fertile soil defined political and military power on the island as population centers grew around these productive oases.

Polynesian colonization changed the ecological makeup of the island, and not only in terms of the soil. Between AD 1000 and 1650 guanoproducing fruit bats vanished as the islanders killed off more than half the native bird species. Historical accounts and changes in the abundance and variety of bones in prehistoric deposits indicate that by the time of Cook's visit Mangaians had eaten all their pigs and dogs, and probably all their chickens too. The Mangaian diet began to change radically-and not for the better.

After most protein sources were gone, charred rat bones became prevalent in deposits excavated from prehistoric rock shelters. Early nineteenthcentury missionary John Williams wrote that rats were a favorite staple on Mangaia. "The natives said they were exceedingly 'sweet and good'; indeed a common expression with them, when speaking of any thing delicious, was, 'It is as sweet as a rat."" Charred, fractured, and gnawed human bones appear in excavated rock shelter deposits around AD 1500, attesting to intense compet.i.tion for resources just a few hundred years before European contact. Chronic warfare, rule by force, and a culture of terror characterized the end state of precontact Mangaian society.