CHAPTER 1 ~ SOIL LOSS OVERVIEW ~
Edition 9, March 2010

~ TABLE OF CONTENTS ~
[A]~
Soil Politics, [B]~Soil Inventory, [C]~Soil Carrying-Capacity, [D]~Potential Cropland, [E]~Potential for Cropland Productivity Improvements, [F]~Topsoil Loss/ Cropland Degradation, [G]~Urbanization-Related Soil Loss, [H]~Erosion Costs, [I]~Grazing Land Erosion, [J]~Positive Feedbacks, [K]~Progress in Soil Conservation, [L]~Some Soil-Related Trends, [M]~Some Good News, ~

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NOTE: The notation (su1) means that the data is used in the document analyzing the sustainability of the productivity of the world's food, fiber and water supply systems. (See elsewhere in this website.)

Soils are an incredibly complex, intimate, and symbiotic relationship between the mineral world and the living (organic) world. Organic matter, tightly bound to minerals in soils, gives soils much of their fertility, erosion resistance, and water-holding capacity. Soil minerals stabilize soil organic matter for centuries, preventing it from being mineralized (converted back to CO2) in the normal few months, years or decades. The nuances of soil chemistry determine whether a given part of the globe can support advanced civilizations. (Some of it cannot.) The physics, chemistry and anthropogenics of soil build-up, loss and degradation determine how long a given civilization will last in a progressive mode. They also determine how much cropland a nation can have on a sustainable basis, and this largely determines that nation's human carrying capacity.

The physics of soil erosion are also incredibly complex and poorly understood. Erosion is usually thought of as a slow, unrelenting process. In reality it occurs mainly in spurts. In most rivers, 40-60% of total sediment load is discharged during 1% of the time, and 85-95% of sediment-discharge happens during 10% of the time. Erosion fluctuates extremely space-wise also. In regions of the globe where population pressures on the land are extreme, river beds can rise by 10-30 cm/ year, whereas the rest of the world's rivers see only about one cm/ year rise. (Historically the rate of riverbed rise is zero [or less] - Playfair's Law.) Also, erosion sediments don't always wind up in streams, rivers and oceans. Roughly half of the world's erosion sediments now wind up on lower slopes, flood plains, etc., and barely 5-10% now make it to oceans. (Historically, essentially 100% of erosion sediments wind up in oceans - Playfair's Law.)

It was the ability of farmers to emerge from an agrarian society by producing surplus food that created the religious, educational, industrial, cultural and philosophical components of human civilization (probably in that order). So when the price of food (see Section 10-E-i) rises to demand essentially all of human earning-power, these trappings of modern civilization must then vanish. Though this may seem remote, be aware that demand for food is highly inelastic: a small surplus produces plummeting prices, while minor shortages produce explosive price increases.

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SECTION [A]~ Soil Politics ~
Public attitudes toward, and the politics of, soil and soil conservation vary markedly about the world. In the Third World, steep land is used more frequently for cultivated crops, and pressure grows to expand production on to even more marginal lands. In such environments, soil-conservation practices are generally expensive. They are also felt to be non-affordable because they reduce short-term productivity, and thereby cause hunger and political instability. This assures an ever-downward spiral into ever-increasing degrees of human wretchedness that can be postponed only briefly by exporting sufficient labor-proxies to the First World to be able to import First-World food. This strategy should fail fairly soon, since the US (world's foremost exporter of food) exports (net) only 12% of its food production, and the US population grows 1%/ year. Around 2005, the US was a net importer of food.

In most of the First World, contempt for soil could hardly be greater. Economists assure us that, in most cases, soil conservation is not economically justifiable. They recommend, in essence, putting the money saved by not conserving soil into a bank and then, when the soil is gone, we simply live off the interest. Some analysts say we should focus on soil productivity instead of soil depth, knowing full well that the highly non-linear relation between the two quantities gives wildly optimistic and erroneous projections of future soil productivity. Some politicians ignore massive compilations of data and argue that the scale of human activity is so dwarfed by the scale of natural phenomena that natural resource conservation of any kind is a pointless exercise in morality. Others argue that an endless series of technological fixes will keep us out of trouble - ignoring the trouble the human race is already in, and the limits of past fixes.

The 1935 act establishing the US Soil Conservation Service provided that, in return for furnishing technical and financial assistance on private lands, states were required to enact and enforce laws imposing permanent restrictions on the use of erosive lands. But instead, state laws that were passed made passage and enforcement of controls on the use of erosive lands difficult. Few, if any, instances are recalled in which the regulatory powers granted to state conservation districts have actually been used to conserve soil for long-term public benefit. Thus, one of the basic intents of national conservation policy, local controls on use-of-land problems, has been lost. There is little by way of laws requiring US farmers to control soil erosion. Most if not all agricultural soil-erosion legislation takes the form of government subsidies to encourage soil conservation. Americans have spoken clearly on the issue of soil conservation: "Erosion controls will be achieved by voluntary means or not at all". In Australia, laws contain considerable coercive authority for achieving soil conservation goals. These laws are generally ineffective because they are not enforced. As in the US, continuing conflict exists between public interest and private rights.

It gets worse. The Reagan administration proposed (1984) to abolish the SCS (a small toothless agency mainly engaged in data-gathering, hand-wringing and subsidy-dispensing). Reagan also appointed a politically oriented head to replace a technically oriented head - the first time a political person headed the SCS in its history. The argument of the time was to let US soil erosion proceed to the point where it got so bad that topsoil depths are reduced to the depth of root zones (about 6 inches) and then farmers will feel compelled, on their own, to conserve soil (a perilous argument devoid of supporting evidence and over-balanced by compelling counter-arguments). In 1980, Anson R. Bertrand, senior USDA official said (of the USA) "The economic pressures to generate export earnings, to strengthen the balance of payments and thus the dollar - has been transmitted more or less directly to our natural resource base. As a result, soil erosion today can be described as epidemic in proportions". Since that time, the federal Conservation Reserve Program and increasing use of conservation tillage have reduced US soil erosion significantly.

Northern and Western Europe provides a marked contrast to the US and Australia. After feudalism and communal agriculture disappeared in Europe, crop rotation, manuring, liming, and other soil-building procedures became common. Since then land-use patterns in the region have been highly conservative of soil fertility. Had that not happened, Europe would have long-since become one of the more wretched parts of the Third World. It is tempting to conclude that it is culture, not politics that determine soil-management policies, but this conclusion should probably await a review of the relative roles of money in the politics of various regions of the First World.

SECTION [B]~ Soil Inventory ~
The Earth's land area is about 149 million km2, but only 85-90 million of that is reasonably biologically productive (117 million km2 are "vegetated"). 15 million km2 serve as croplands. 2.5 million km2 serve as irrigated cropland, and this could hardly be expanded by more than 50%. Typical soils are about 11 inches deep, and weigh about 400,000 tonnes/km2 (t/km2). This suggests a total cropland topsoil inventory of 6000 Gt. This is based on 1970s data at the high end of the range of measurements. Just correcting for topsoil losses since then (See below) would give an inventory of about 4000 Gt. Another recent estimate gives 3600 Gt. But when topsoil depths drop below about 6 inches (a typical depth of the root zone of crops), productivity drops off sharply. The most optimistic estimate for the rate of topsoil formation from sub-soil in croplands is 1"/3 decades (11000 tonnes/ km2/ decade). The most optimistic rate of formation of topsoil from sub-soil on grasslands and forestlands is about a tenth of that - as is the rate of weathering on bedrock to form sub-soil. Averaging all the estimates of soil formation rates would give numbers only a half or a third of these.

It is against these numbers that you should weigh the statistics in this document on soil erosion and largely irreversible cropland degradation, abandonment, urbanization (See Chapter 6 of this document.) waterlogging and salinization (See the document on irrigation in this website). After you understand the physical aspects of topsoil degradation you can start thinking about the nearly-as-serious problems of chemical degradation-organic matter loss, the growing tendencies toward monocultures, etc.

Statistics in this document on soil erosion come from two types of physical measurements-direct measurements of erosion phenomena, and measurements of sediment flows into rivers, oceans, river bottoms and dam backwaters. Both types of physical measurements have drawbacks, but seeking out consistency between these two can give a clearer picture of what is going on.

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SECTION [C]~ Soil Carrying-Capacity ~
For perspective, the world's 6.6 billion people use 15 million km2 of cropland; 367 people/ km2 of cropland. About half of all cropland produces grain, and 37% of the world's grain production goes to feed livestock, poultry or fish (1997). Cereal grains provide half of the world's protein and calories. (Others say grains make up 80% of the world's food supply, but this seems doubtful.)

The human carrying capacity of a given area of cropland soils varies by easily a factor of several hundred depending on location and water-input. It is convenient and useful to evaluate carrying capacity in terms of grain-producing cropland. Neglecting protein needs and focusing on energy needs, the average human requires less than 2500 kcal/ day (0.7kg. of grain/ day) (0.256 tonnes/ year) (0.16 tonnes/ year is the minimum needed for survival.) In the US Midwest, the average corn harvest is over 4000 bushels/ km2/ year (over 600 tonnes of edible substance/ km2/ year). I.e. 1 km2 of high quality farmland under US conditions can support 600/0.256= 2400 people (actually 1900 because over 20% of harvested food never makes to the dinner table because of spoilage, spillage, and losses to rodents and insects). Note however that Midwestern US soils are far better than average, even for temperate soils, so this 1900 figure should be taken as the far upper end of the temperate-cropland range. Tropical (0 degrees latitude) croplands are about 30% as productive as temperate croplands at 40o latitude. Much tropical soil is far less productive. (Most areas of tropical rain forest are underlain by soils classified as infertile. The bulk of the nutrients are found in the plant life or in the soil surface litter, so if these are removed, a 20-30-year fallow period is required for nutrients to be bought up from below by deep-rooted plants.) For example, when tropical rainforest is used for shifting cultivation, the carrying capacity of the land is about 10 people/km2 (probably less if used as grazing land). Note that the 1980 population-density of shifting cultivators on tropical rainforest was about 16 people/ km2 and the average fallow period was only a small fraction of the 20-30 years required for restoration of fertility.

Irrigated croplands produce about 4 times as much per unit area as non-irrigated cropland in terms of weight. This is why the world's 2.7 million km2 of irrigated land provide about 40% of the world's cropland productivity. In dollar-value terms they produce about 6.6 times as much food as non-irrigated croplands, since irrigated croplands are used for more expensive crops. Grazing lands produce animal protein and therefore have a carrying capacity on only 10-20% of what would be the case if humans could (would) eat and digest forage at the same efficiency as grazing animals. This is one reason why grazing lands produce only 18% as much food (in $-value terms) as non-irrigated croplands. The other reason is that grazing lands are typically more arid than croplands.

All these numbers provide lots of blue smoke and mirrors for whatever political agenda you may have. Allude to Midwestern US croplands to show that the world could support five times its present population (assuming everyone became a vegetarian). Allude to the shifting cultivators of the tropics to show that the Earth can't support, sustainably, more than 3% of its 1990 population.

SECTION [D]~ Potential Cropland ~
Various estimates have been made of the Earth's inventory of potentially arable (cultivatable) land, and these typically estimate that global cropland area could potentially double. However the notion of an extra 15 million km2 of land just sitting around waiting for someone to come along with a plow is naive at best. A more useful (but far less common) analysis is to determine the land area that is not now cropland, but which could be cropped on a sustainable basis. The sustainability requirement reduces the amount of potential and unused cropland down to about 10-20% of existing cropland inventory. Canada is typical. In theory Canada could double its cropland, but almost none of this extra land could be cropped sustainably. Much of Canada's cropland has lost half of its organic matter, and fallow periods have dropped, so it is hard to imagine farmers putting up with all this with unused good cropland just sitting there. Much current cropland also lacks the attribute of sustainability, so a more refined analysis of global sustainable cropland inventory would probably come up with a number somewhat less than current inventory. In any case the current rate of cropland abandonment, salinization and urbanization would, in a few decades, equal the area of potential but unused sustainable cropland. Could growing population pressures on the land change cropland-management practices so that some of the inventory of non-sustainable cropland could be relabeled as sustainable? Probably not. Cropland degradation rates tend to increase as pressures on cropland to produce are increased. Thus Adam Smith's law tends to work in reverse, and this is due to many costs not being internalized, resulting in numerous positive feedbacks. For all practical purposes, the option of feeding a growing global population by expanding global cropland area no longer exists. A more detailed analysis of the amount of undeveloped arable land, worldwide, is given in the document on sustainability in this website.

SECTION [E]~ Potential for Cropland Productivity Improvements ~
From the start of agriculture to 1950, most food supply doublings came from expansion of the area under cultivation and area being grazed. Since 1950, these doublings have come mainly from chemical fertilizers, large-scale irrigation systems, and improvements in plant genetics. All three of these mechanisms now show clear signs of saturation or decline.

The extra crop production per increment of fertilizer-application has dropped to roughly 20% of what it was a few decades ago. (Well-established laws of plant growth predicted this limit long before the fact.) This makes the economics of increased fertilizer-use iffy in most nations. This fact, plus the fact that government subsidies for fertilizer consumption have been disappearing, have resulted in global fertilizer consumption falling from its 1989 peak of 146 million tonnes/ year (1995 consumption: 122 million tons/ year). (US farmers are using less fertilizer in the mid-1990s than in the early 1980s.) Regional variations in fertilizer consumption are extreme and illuminating, e.g. 70 tonnes/ km2/ year in the Netherlands where crop subsidies are high; over 20 tonnes/ km2/ year in Japan where land is scarce; 10 tonnes/ km2/ year in the US, and under 3 tonnes/ km2/ year in most developing countries where chemical fertilizer is relatively expensive. In sub-Saharan Africa, the cost of chemical fertilizer is about 60 times (on an hours-of-labor per tonne of fertilizer-basis) that in Europe. The reason is that the transportation infrastructure is so poor that transportation costs are much higher than in Europe.

Annual appearances of new irrigated area have dropped from about 3% of inventory (1955-78) to 1% since 1978. The rate decreases as government subsidies dwindle. They dwindle because developing nations have an accumulated external debt of over $3 trillion. But salinization-caused abandonment of irrigation systems now wipes out irrigated land at about 1%/ year. This rate can only increase due to the time lag for salinization to set in, and the newness of most of the world's irrigation systems. Reallocation of irrigation water to urban use wipes out an added estimated 0.25% of irrigation systems annually (See companion document in this website on irrigation). So irrigation is probably now in decline, not growth. The world's dams that support the world's massive irrigation system are now filling with erosion sediments about as fast as dams can be built. Estimates of how fast the world's 6000 km3 of dam-backwater volumes are filling with sediments vary from 1% to about 0.4%/ year. The most recent estimates of potential (not yet used) irrigation land give a value of about 50% of current inventory of about 2.5 million km2, but with water being reallocated to urban uses, this potential will probably never be realized.

Improved plant genetics only increase the fraction of plant biomass devoted to seeds (grain)-not the rate of photosynthesis. Scientists estimate that the originally domesticated wheat devoted roughly 20% of their photosynthate to the development of seeds. Today's wheat, rice and corn devote over 50% as a result of the "green revolution". The physiological limit is believed to be about 60% at most. Plant breeders have not been able to fundamentally alter the basic process of photosynthesis itself, i.e. to produce more plant mass without added water, fertilizer, etc. After 20 years of research, bio-technologists have not produced a single high-yield variety of wheat, rice or corn. The IRRI reported (1990) that, during the past 5 years, growth in rice yield has virtually ceased. Others note that the genetic yield potential of rice has not increased significantly since the release of high-yielding varieties in 1966, though small improvements continue to be made. High-yielding, fertilizer-responsive crop varieties are now planted on nearly all suitable land, so the potential for expanding the land area devoted to high-yield grains is limited. Most high-yield seed varieties of wheat, corn and rice are inapplicable for large areas of the developing world because of adverse soil conditions such as build-up of salts, iron- or aluminum excesses, or high acidity. The spread of the Green Revolution is limited to high base-status soil areas of tropical Asia and tropical America. High base-status soils (18% of the tropics) are already intensively exploited.

Since these three mechanisms address all the controllable factors influencing plant productivity (nutrients, water, genetics), there is reason to believe that future food-supply doublings will be harder to come by. Furthermore two of these new systems entail Faustian bargains (conversion of sustainable systems to non-sustainable ones), suggesting, not a leveling-off or a steady-state, but ultimately a decline, even after human-population growth falls to zero.

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SECTION [F]~ Topsoil Loss/Cropland Degradation ~
From a global viewpoint, the crescent from Korea to the Middle East has the world's highest soil-erosion rates - roughly 5000 tonnes/ km2/ year. Excluding the US and Europe, soil erosion rates are next-highest in the rest of the world - roughly 3000 tonnes/ km2/ year. In the US and Europe erosion rates are the lowest (1700 tonnes/ km2/ year). Erosion rates are dropping in the US due to a combination of the Conservation Reserve Program and the expansion of "conservation-tillage" agriculture. Not all the First World is in good shape: soil erosion has been called Australia's most serious problem. Some analysts have concluded that topsoil losses in developing countries average 3000 tonnes/ km2/ year. Others have generalized that erosion rates in developing countries are roughly twice the corresponding US rates.

Regional averages can hide a deeper understanding of the problem however. At least as important are erosion rates on the marginal lands that farmers are expanding into, driven by population pressures and the need to abandon cropland that has become too gullied to be cropped. Reports of losses exceeding 10,000 tonnes/ km2/ year are common for individual plots, especially on sloping terrain, in many developing countries. Gully erosion (a prelude to cropland abandonment) is characterized by erosion rates of roughly 40,000 tonnes/ km2/ year - a rate that eliminates all topsoil in roughly a decade.

It is also useful to examine erosion rates on non-croplands to gain perspective. Below are some useful rough numbers.

Some Typical Erosion Rates on Non-Croplands
Land Use- - - - - - - -|Erosion|Soil
- - - - - - - - - - - -| ~ Rate|formation rate*
Furrow-Irrigated Row Crop| 450 |1100
Grass~ ~ ~ ~ ~ ~ ~ ~ ~ ~ | ~60 | 100
Grassy Pasture ~ ~ ~ ~ ~ | 400 | 100
Forest Land (Undisturbed)|0.4-5| 100
Forest (Recently Logged) |10000| 100
* (tonnes / km2/ year)

Perhaps the world's worst trouble spot terms of the human effects of erosion is Africa which is plagued by a combination of some of the world's worst soils, the fastest population-growth rate of any continent in history, and wide-spread soil erosion and desertification. Per-capita grain production peaked in Africa in 1967 (The world peaked in 1984), and has declined 1%/ year ever since. In 1984, 140 of 531 million Africans were fed with imported grain (much of it paid for with borrowed money). Madagascar, one of the world's most eroded countries, is plagued by slash-and-burn rice agriculture on steep hillsides. Asians have been more adept than Africans at building dams and irrigation systems and exporting manufactured goods to pay for expanded food imports. Africans are paying for their inability to keep up with their population growth in the form of numerous civil wars and growing anarchy, making them even less capable of expanding irrigation systems and exports - a downward spiral with little hope (other than declining human fertility) of a turn-around.

Other regions are also showing signs of impending disasters. The southern portion of the former USSR has been seriously damaged by many centuries of erosion. Half of Russia's arable land is now unusable for farming. The extremely high rate of wind-erosion (suggesting desperate measures to grow crops on excessively arid land), the high rate of gully-erosion and the high rate of agricultural-land abandonment all suggest that the USSR has no more sustainable croplands in reserve. (1000 km2 of USSR croplands are lost to gullies yearly, and the USSR abandoned roughly 10,000 km2/ year since 1977.)

Wind erosion in Canada's prairie region accounts for twice as much soil loss as water erosion, suggesting desperate measures to expand cropland into arid lands that shouldn't be cropped, or that need more fallow-time than it is being given. (Globally, wind erosion rates are only about 30-35% of water-erosion rates, and fallow periods in Canada's prairie provinces are falling.) The loss of about half the organic matter from Canada's prairie croplands over the past half-century or so also predicts decreasing cropland productivity, increased soil erosion, and the lack of sustainable cropland reserves.

The US, though now in relatively good shape, has had serious problems in the past. About 405,000 km2 of US farmlands are badly gullied. Around 1939, 39% of US dams were expected to be filled with erosion sediments within 5 decades. Cotton monocultures in the south used to cause erosion rates of about 7200 tonnes/ km2/ year until much of the cropland was abandoned and later converted to pulpwood plantations. Americans should not feel so secure, however, until they see how the globalization of the food supply system plays out. (World trade doubles in real terms about once every two decades.)

Numerous parameters suggest serious and imminent problems for Mexican agriculture. Thus far 40% of Mexico's topsoil has been lost.

Topsoil loss should not just be characterized in terms of tonnes per unit area per year but also in the rate of abandonment of croplands that have become so gullied that they have become unusable. Various estimates have been made. One gives a current global loss rate of 50,000 km2/ year of arable land to wind- and water erosion, salinization, sodication, and desertification. Another gives a rate of cropland loss through degradation during 1945-90 of 20,000 km2/ year and a current cropland loss rate through degradation of 50-100,000 km2/ year. This would suggest that the cropland-abandonment rate doubles about every two decades. The rate of abandonment of irrigated land through salinization alone is estimated to be on the order of 20-25,000 km2/ year (about 1% of inventory). It is useful to attempt to translate these losses into a topsoil-mass loss rate. If 20,000 km2/ year of irrigated land are abandoned and if the remaining 30-80,000 km2 are gullied croplands with only 25% of their topsoil remaining, and if non-eroded cropland contains 400,000 tonnes/ km2 of topsoil, cropland abandonment translates to a topsoil loss rate of about 9 Gt./ year from salinization and 10 from gully erosion.

Various estimates have also been made of the global rate of topsoil loss. Fournier (1960) measured sediment-accumulation in numerous small catchments about the globe and obtained a global soil-erosion rate value of 58 Gt./ year. Schumm (1963) estimated 41 Gt./ year based on data from 30-square-mile US catchments, and 20.5 Gt./ year based on data from 1500-sq.mi. US catchments. Extrapolating these data to small catchments would give a global erosion rate of about 61 Gt./ year. Both Fournier's and Schumm's values consider only water erosion. A more recent estimate is 75 Gt./ year, but this includes both wind and water, so this estimate is quite compatible with the other two values. Brown and Wolf (1985) estimated a gross global erosion rate of 37 Gt./ year, but the sediment-delivery ratio used in the calculation seems much too low relative to measured values. The bulk (2/3+) of global topsoil-erosion loss is from croplands, so these studies suggest a global cropland-topsoil loss via water-erosion of on the order of 40 Gt./ year. All these studies neglected cropland topsoil losses to urbanization (14 Gt./ year; see below), salinization (9 Gt./ year), abandonment of worn-out (gullied) cropland (10 Gt./ year) and wind erosion (12 Gt./ year). These four additional losses, considering only croplands, would give an additional 48 Gt./ year, for a gross loss rate for cropland topsoil of 88 Gt./ year. The rate of topsoil formation on croplands is about 17 Gt./ year, giving a net cropland topsoil loss rate of 71 Gt./ year. This should be compared to the global inventory of cropland topsoil (noted above) on the order of 4000 Gt. (Nearly one third of the world's arable land has been lost by erosion in the past 4 decades.)

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SECTION [G]~ Urbanization-Related Soil Loss ~
Soil resources are also lost through urban developments of croplands, grazing lands and forestlands. Of these, cropland loss is by far the most important. To give an idea of the relative impact of erosion-losses and urbanization-losses, a 1995 report by David Pimemtel at annual meeting of the AAAS, said that the US loses 4000 km2/ year of agricultural land to urban developments, and 8000 to erosion and salinization. A literature review and analysis of urbanization-related soil losses is given in Chapter 6 of this document. The analysis found that the global urban land inventory (4.745 million km2) grows 2.7%/ year, i.e. 128,000 km2/ year. This can be proportioned among non-irrigated croplands (35,100 km2/ year -0.23%/ year), grazing-land (27,270 km2/ year - 0.081%/ year), and closed forest land (25,110 km2/ year - 0.084%/ year). Other land categories (mainly non-croplands within cropland mosaics, open woodlands and non-grazed grasslands) lose the remaining 40,520 km2/ year.

SECTION [H]~ Erosion Costs ~
Total cost of on-site- (farm) and off-site damages (such as health costs, dredging waterways and water treatment (but neglecting damage to aquatic life) from agricultural erosion is roughly $400 billion/ year (global). This places no value on the lost soil itself. Placing a modest value on topsoil ($25/ tonne) would increase total costs to over $2 trillion/ year.

SECTION [I]~ Grazing Land Erosion ~
Information on erosion from grazing lands is perplexing. Grazing lands cover about 56 million km2 (compared to 15 million km2 of croplands. The average grazing area is overgrazed by a factor of 1.7-2.0, implying significant soil loss. If one examines data on the sediment load carried by rivers draining grazing lands, these loads are found to be about twice those for rivers draining croplands (on a per-unit-area-of-drainage-basin basis) (US data). But organic-matter contents of grazing-land sediments are significantly lower than for croplands. Also, the extremely limited data on pasture (grassland) erosion rates suggest lower erosion rates than for croplands. In a companion document on grazing lands, it is theorized that most erosion sediments from grazing lands are sub-soil from gully erosion. Gullies are common on grazing lands, and gullies do not impede grazing nearly as much as they impede cultivation of croplands. The growth of gullies implies a loss of topsoil also, but it is quite possible that studies of grassland erosion avoided gullied land to avoid complications in data-interpretation (thereby making the data far less meaningful). Extremely low-grade (arid) grazing lands show high erosion rates, and studies of grassland erosion may have avoided these areas also. High erosion rates on near-deserts must have an anthropogenic origin or otherwise they would have long-since been eroded to bedrock. Thus, one must conclude that grazing-land erosion is a long way from being quantified. Note that the bulk of gullies in the arid regions of the western US formed during and after the massive over-grazing of the late 19th century and the early 20th century.

SECTION [J]~ Positive Feedbacks ~
What is even worse, positive feedbacks (instabilities) seem to dominate all cropland-, grassland-, forest- and aquatic life-support systems. In the past, rising fish prices would cause greater investment in fish trawlers. Today that approach only hastens the decline of fisheries. Rising grain prices would encourage greater investment in irrigation wells. Today that approach only hastens the depletion of aquifers.

These positive feedbacks are probably the main reason why nearly all ancient civilizations never achieved a steady state near their state of furthest advancement. Instead they lasted in a progressive mode for no more than about 50 generations before they collapsed. (The few that lasted far longer were the ones that were based in broad alluvial river valleys where annual floods replenished the soil.) (Section (3-F)).

Virtually all positive feedbacks in cropland-, grassland-, fishery- and forests systems stem from one source: the human perception that the earth must be responsive to human needs and numbers, rather than the recognition that human needs and numbers must be responsive to the intrinsic, sustainable capacity of the earth to produce food and fiber. Some examples of positive feedbacks:

All this suggests that human civilization rests on a mass of fundamental instabilities related mainly to pushing croplands and grasslands too hard. Forest management and fishery management are also characterized by numerous positive feedbacks.

So today, land-productivity-enhancement processes (described above) are saturating, while land-degradation processes are accelerating via numerous positive-feedback loops. Without fundamental changes, the outcome of all this is certain. Future food production is likely to come more from farming marginal land, usually with steeper, drier slopes, where erosion rates are often one- to two orders of magnitude higher than rates on flat, moist, well-drained bottom lands.

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SECTION [K]~ Progress in Soil Conservation ~
In the US, major advances have been made in several aspects of soil conservation. The U.S. Dept. of Agriculture's Conservation Reserve Program (CRP) has taken much of the nation's most highly erosive croplands out of production (by paying farmers to do so). In 4 years the CRP reduced erosion on its land from 21 to 2 tons/ acre/ year. Excess topsoil loss has been cut from 1.6 to 1.0 Gt./ year. As of 1990, the natural resource benefits from the CRP are estimated at $9.6 billion ($213/ acre). (Farmers receive $48.60/ acre/ year in annual rental payments.) The US spends $1.7 billion/ year in the CRP to save 584 million tons of soil/ year, i.e. $2.91/ ton. Other analyses give $2.10/ ton of topsoil saved. If and when the CRP reaches its enrollment target of 40-45 million acres, it will produce a net program benefit of $3.4 to $11 billion and save 0.73 Gt. of topsoil/ year. Over 60% of topsoil savings on U.S. croplands since 1985 are credited to the CRP. Conservation practices of all kinds contributed to a 25% reduction in US soil erosion during 1982-1992.

Another major advance in soil conservation has been the spread of "conservation tillage" cropland management techniques. These greatly reduce soil erosion and reduce farming costs and conserve water (which increases yields). These techniques have been adopted widely in the US. Over 400,000 km2 world-wide are planted under "conservation tillage". Soil erosion rates can be reduced by 80-90%. (Soil conservation is considered be farmers as an incidental benefit, not the cause for adoption of these measures.)

SECTION [L]~ Some Soil-Related Trends ~
As population pressures on the land grow, people tend to seek out short-term ways of increasing production - even at the cost of long-term production.

One such practice is to increase the use of monoculture. When monoculture is practiced, yields tend to decrease with time regardless of how much fertilizer is applied. A steady annual presence of a particular root system favors a few organisms - bacteria, fungi, nematodes - that are potagenic to plant roots. Changing to a different crop alters the circumstances, and all but the most unspecialized pathogens are unable to thrive in the absence of their usual host. Monocultures also increase losses to pests, and this necessitates increased use of pesticides. Insecticide applications increased 10-fold in the US during 1945-89, but crop losses to insects nearly doubled (from 7% to 13% of the harvest). Mono-cropping explains part of the higher losses. Insect species resistant to common pesticides numbered only 182 in 1965, but number over 900 in 1996. Global pesticide use increased from 1.3 million tonnes/ year in 1970 to 2.9 million tonnes/ year in 1990, and the rate of pesticide application has been increasing by 10%/ year.

Another such practice is the tendency to use animal dung for fuel rather than fertilizer. This reduces the organic matter of the soil, making it less fertile and more erosion-prone. Within 50 years of the introduction of moldboard plowing on the US Great Plains in the 19th century, 60% of the soil's organic matter was washed or blown away. About the same numbers apply to Canada's three prairie provinces. Some say that organic matter losses from soils due to soil erosion are much less than losses due to oxidation. The organic matter problem is made even worse by erosion. Soils removed by either wind- or water erosion are commonly 1.3-5 times richer in organic matter than the soils left behind. The reason for this is that erosive agents (water or wind) pick up lightweight organic matter in preference to denser soil particles.

Another such practice is the tendency to cultivate increasingly arid lands (often grazing lands) in order to replace croplands that have been abandoned due to misuse. (Croplands should receive at least 25 inches of precipitation per year.). The result is increasing wind erosion and less production per unit of input. On low-stress regions such as the US, wind accounts for only 25% as much US soil erosion as water-induced erosion. On a global average, wind-erosion rates are 30-35% of water-erosion rates. On Canada's prairie provinces, the climate is arid, and wind-erosion losses are two times the losses due to water-erosion.

Another such practice is to increase the number of crops grown per year on each plot of cropland. Soils used to yield 2-3 crops/ year rapidly run out of nutrients, while bugs living there thrive.

A far more serious trend is the increase in the pressures on cropland to produce - a major cause of cropland degradation. Until recently, the world had three reserves against a poor harvest:

  1. Cropland idled under farm programs in the First World,
  2. Surplus stocks of grain in storage, and
  3. 40% of the grain harvest that is fed to livestock, poultry and fish.

As of 1997, reserves (1) and (2) have largely disappeared. As food reserves dwindle and as the communist threat diminishes, the willingness of the First World to provide food aid to the Third World drops.

Some recent food-aid figures (in millions of tons/ year)
Year - - - - - |1993 |1996 |1998
Global ~ ~ ~ ~ |16.8 | 7.5 | 6.5
US Contribution|10.0+| 4.0-| ???

Some trends in food production
Trend - - - - - - - - - - - -|Period |Growth|Period |Growth
Per-capita Grain Production~ |1950-84|+ 40% |1984-93|-12%
Per-capita Seafood Production|1950-88|+126% |1988-93| ~9%
Per-capita Beef/ Mutton Prod.|1950-72|+ 36% |1972-93|-13%
Per-capita Meat Production ~ |1950-80|+ 58% |1980-93| +7%
Grain-Land Productivity~ ~ ~ |1950-90|+ 80% |1990-95| +5%
Grain Harvest~ ~ ~ ~ ~ ~ ~ ~ |1950-90|+120% |1990-96| +6%
Food Aid (Global)~ ~ ~ ~ ~ ~ |- - - -|- - - |1993-98|-61%

Though malnutrition is diminishing, the situation remains unsettling. Below are some statistics on the extent of malnutrition: (fewer people suffer from hunger.)

SECTION [M]~ Some Good News ~
Since around 2001, scientists from around the world have been trying to reproduce a development (by ancient Amazonians some 7000 years ago but never transmitted to modern man) for permanently improving the fertility of tropical soils by a factor of 2-3. Brazilians now sell these ancient soils called "terra preta" (Portuguese for "dark earth"). The ancient soil stores far greater amounts of carbon in the soil permanently, thus the far greater fertility. Besides offering the possibility of eliminating tropical world hunger (until population growth catches up) terra preta is the only physically and economically viable way of eliminating and reversing global warming. More information is found in a document titled "Terra Preta . . ." in this website.

Go to the Home Page of this entire website ~
Go to the Table of Contents of this document on soils and croplands degradation ~
Go to the Reference List of this document ~ 
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