Note: The data found below represent a sampling of a far larger collection of data compiled in "Topsoil Loss - Causes, Effects and Implications: A Global Perspective," found on this same website.

U. S. Department of Agriculture plant scientist Thomas R. Sinclair observes that advances in plant physiology now let scientists quantify crop-yield potentials quite precisely. The physiological limits of such metabolic processes as transpiration, respiration, and photosynthesis are well known. He notes, "except for a few options which allow small increases in yield ceilings, the physiological limit to crop yields may well have been reached under experimental conditions." In these situations, national or local, where farmers are using the highest-yielding varieties that plant breeders can provide, and the agronomic inputs and practices needed to realize fully their genetic potential, there are few options left for dramatically raising land productivity (94S3) (98B3).

Scientists estimate that the originally domesticated wheats devoted roughly 20% of their photosynthate to the development of seeds (grains - what humans eat). (20% was therefore the original "Harvest Index") Today's genetically improved wheat, rice and corn devote over 50%. The physiological limit to the Harvest Index is believed to be about 60% (Ref. 68 of Ref. (97B3)). 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. (97B3). After 20 years of research, bio-technologists have not produced a single new high-yield variety of wheat, rice or corn (97B3). The part of the Green Revolution involving development of "miracle" strains of cereal grains has been over for some decades now (since around 1960). Current efforts appear to focus on developing new strains that can withstand genetically improved pests that prior miracle strains are no longer immune to. Thus the goal of the Green Revolution has changed from doubling the number of people an acre of cropland can feed to being able to feed the same number of people as in the previous year. The rate of evolution of genetically improved breeds of pests appears, so far, to be similar to the rate of evolution of new cereal strains. Whether this balance can continue as the gene pools of the world's wheats, rices and corns continue to shrink remains an open question. The UNFAO estimates that, since 1900, about 75% of the world's genetic diversity of domestic agricultural crops has been lost. Without constant infusions of new genes from the wild, geneticists cannot continue to improve domestic crops. Cultivars need to be reinvigorated every 5-15 years in order to give them greater protection against diseases and insects. The most effective way to do this is to interbreed domestic varieties with wild ones (98H1).

Plant breeders at CIMMYT and IRRI increased the "harvest index" - the percentage of the plant's mass that is grain - to about 50%, almost double the previous figure (Science (8/22/97) p.1038) (99M1). However most plant breeders see little scope in wheat and rice for increasing the harvest index beyond the present value of about 50% (Statement by Roger Austin, an agricultural consultant in Cambridge, England) (99M1). Not everyone is as cautious. With varying degrees of caution, official projections from the World Bank, FAO, and IFPRI assume agricultural researchers can repeat the Green Revolution. But plant breeders note "Those maximum rice yields have been the same for 30 years. We're plateauing out in biomass." (Statement by Robert S. Loomis, agronomist at University of California, Davis.) (99M1). Repeating the Green Revolution would appear to require increasing the harvest index to 1.0 - a physical absurdity.

Effective soil conservation technologies (e.g. no-till) have spread since the 1930s, especially in North America and Europe. However, in global terms, the past 60 years have bought human-induced soil erosion and destruction of soil ecosystems to unprecedented levels (04M1) (02M1).

On a global scale, and on a historical time frame, soil erosion occurred in three main waves (04M1).

Most high-yield seed varieties of wheat, corn and rice developed by Borlaug et al during the "Green Revolution" 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 (82B1). 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 (75S1). Large increases in the rates of application of chemical fertilizers tend to increase soil acidity and deplete soil organic matter. The effects of this are described in detail in Part [B5] and Part [A3].

Dregne and Chou (Ref. 18 of Ref. (97C1)) estimate the value of production of irrigated cropland at $62,500/ km²/ year, $9,500/ km²/ year for rain-fed cropland, and $1,750/ km²/ year for rangelands. Irrigated croplands produce about 60% of the world's crops (in dollar terms). All this gives a good perspective on the effect of water on cropland productivity.

Worldwide soil degradation mechanisms and their relative effects on soil degradation are water 56%; wind 28%; chemical degradation 12%, physical degradation 4% (90O2). Over time, croplands are expanding into semi-arid lands, more typically used as grazing lands. So the wind portion of the worldwide soil degradation mechanisms can be expected to increase over time. The rapid increase in the frequency and severity of dust storms originating in both East Asia (particularly China) and Africa tends to bear this out.

In 1998, 16% of US cropland was no-till, according to the Conservation Technology Information Center. In 2004, preliminary data shows that percentage at 22.5% (Pittsburgh Post Gazette (11/08/04)).

Low-till Agriculture Growth in South Asia: 30 km² in 1998-99, 1000 km² in 2000-2001 and may rise to 40,000 km² by 2004. The technique cuts herbicide usage by 50%, water consumption by 30-50% and significantly improves yields ("New Farming Techniques Could 'Cut Food Crises in South Asia'", Financial Times (London) (10/3/01)).

Over 100 million acres (405,000 km²) (2.7%) of the world's cropland were planted under "conservation tillage" in the mid-1990s (Howard G. Buffett, Wall Street Journal (5/22/97)). No-till farming has helped reduce US water erosion by over 40% since 1982 (04K1). The Conservation Reserve Program in the US has reduced this figure significantly further. The shift away from the moldboard plow (to no-till methods) has also increased soil organic matter and has led to a looser, less erodible soil that retains more water for crops (99A2).

McGregor et al found that, on a highly erodible soil in Mississippi, erosion was reduced from 1750 tonnes/ km²/ year to 180 tonnes/ km²/ year after a no-tillage system was used (Ref. 10 of Ref. (80P1)). Triplett et al (Ref. 8 of Ref. (80P1)) found that a no-tillage system reduced soil erosion by as much as 50-fold. Many similar studies are noted in Ref. (80P1).

In a Nebraska study, soil erosion averaged 763 tonnes/ km²/ year with "till-planting", compared with an erosion rate of 2400 tonnes/ km²/ year for a plow/ disk/ harrow system (p. 151 of Ref. (76P2)).

Typical soil loss on conventionally cropped fields of the Palouse Region (8,000 km²) of the US is 5600 tonnes/ km²/ year. Minimum tillage can reduce this to 1100 (82O1). (Soil in the Palouse Region (mainly Idaho) is mainly loess (wind-deposited) soil with low organic matter and hence they are high erodible and have low productivity.)

Cropland Area Under No-Till in 1998-1999, km² (01D1).

During the 36-year period when world average grain yields more than doubled from 140 tonnes/ km² in 1961-1963 to 305 in 1997-1999 and the overall cropping intensity probably increased by some 5 percentage points, the amount of arable land required to produce any given amount of grain declined by 56%. This decline exceeded the above-mentioned 40% fall in the arable land per person that occurred during the same period (03B3).

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 (90A1).

Soils pushed to yield 2-3 crops/ year rapidly run out of nutrients, while bugs (pests) living in such environments thrive. Even on the IRRI's 2.52-km² model farm, crop yields show long-term declines (91U1). (IRRI is the International Rice Research Institute.)

Birds, bats, bees and other species that pollinate North American plant life are losing population. Some 75% of all flowering plants depend on pollinators for fertilization. (Other pollinators include butterflies and wild bees.) (06E1). American honeybees, which pollinate more than 90 domestic commercial crops have declined by 30% in the last 20 years. Pesticides and introduced parasites, such as the varrora mite, have hurt honeybee population (06E1). Bats, which carry pollen to a variety of crops, have declined as cave vandalism and development destroyed some of their key cave roosts (06E1).

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Soils in China are low in organic matter because 60% of crop residues are typically removed from fields and used for forage or fuel (95B2) (Ref. 41 of (95P1)). About 90% of crop residues are removed and burned for fuel in Bangladesh (95P1). This would suggest that a similar percentage of manure is also burned for fuel.

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Section [C] ~ HUMAN PRESSURES ON THE LAND: NON-SUSTAINABLE CROPLAND PRODUCTIVITY ~ [C1]~Global, [C2]~Central Asia, [C3]~Asian Sub-Continent, [C4]~Southeast Asia, [C5]~Sub-Saharan Africa, [C6]~Latin America, [C7]~Australia and Oceania, [C8]~Far East, [C9]~North America, [C10]~Middle East and North Africa

Percent of the arable land expected to degrade to non-arable status by 2025 (04H1)

Deforestation and soil erosion were factors in almost every civilization collapse studied by Jared Diamond in his book (04D1). For example, deforestation in what is now eastern Turkey created the massive soil erosion and hence the river sediments that ruined the irrigation systems in the Tigris-Euphrates Valley.

Soil degradation has affected 67% of the world's agricultural (crop?) lands in the last 5 decades. (00U3). "Agricultural" sometimes include grazing lands and sometimes not. Grazing lands tend to degrade faster than croplands because semi-arid and arid soils tend to have low organic matter contents and thus are more erosion-prone. Also, erosion gullies destroy the usefulness of croplands, but not grazing lands. Also most of the productivity of grazing lands is found in the riparian habitats (only a few percent of the total area) and cattle tend to congregate there and destroy these areas quickly.

The UNEP Global assessment of soil degradation survey reveals that over 3 billion acres (12 million km²) of land (11% of the earth's vegetated surface) have been seriously degraded since 1945. Some 2/3 of these degraded lands are in Asia and Africa (92M3). These data are of minimal value because it does not distinguish between cropland and grazing land. The size of the degraded area is about 75% of the global area of croplands, so clearly other land classes are involved. Because of the extreme difference in the economic productivities of croplands and grazing lands, the above statement has little value. (The economic productivity of irrigated croplands, rain-fed croplands, and grazing lands vary as 35.8: 5.4: 1.0.)

Destructive agricultural practices (on croplands?) account for 28% of global land degradation. Over-grazing accounts for another 35%. (World Resources Institute Press Release (3/24/92)). Presumably the total land area is assumed to be the ice-free area. Presumably the degraded cropland figure includes irrigated lands that have been abandoned due to salinization or waterlogging.

Nearly 40% of the world's agricultural land is seriously degraded, according to scientists at the International Food Policy Research Institute (IFPRI). Evidence compiled by IFPRI suggests that soil degradation has already had significant impacts on the productivity of 16% of the world's agricultural (crop?) land (00L1).

Some 100,000 km² of the world's cropland is being eroded and abandoned each year throughout the world. (99P2) (Ref. 7 of Ref. (97P3)) This number probably includes irrigated cropland salinization and urbanization of cropland.

Globally, desertification claims 60,000 km²/ year irreversibly, and 200,000 km²/ year reversibly (Ref. 8 of Ref. (88J1)).

Some 60,000 km²/ year of land becomes so severely degraded that it loses its productive capacity and becomes wasteland (Ref. 11 of Ref. (91B2)). (This probably includes both cropland and grazing lands.)

* The Urban Development datum is from Ref. (00W1). A partial allocation among regions is given in Table FG.5.
Source: Ref. (90O1) (See Ref. (92N1), Table 4)

Human-Induced Soil Degradation between 1945-1990 (Oldeman et al. (1990) and WRI (1992) in Ref. (96N1))
Degradation is in units of millions of km²/ % of vegetated land.

A global map showing degree of desertification of arid lands from Dregne's Book "Cropland Degradation" (from a 1991 UN study) (97G1) (Areas are in units of 1000 km²)

Globally, 1.6 million km² of hillside land were identified as "severely eroded" in 1989 (96G2).

If the most severe degradation (that which leads to abandonment) continues at its 1945-1990 rate, 470,000 km² will be lost by 2020 (Ref. 53 of (96G2)). (1945-1990 losses were 860,000 km² (Ref. 44 of Ref. (96G2)).) (Current cropland loss rate from degradation severe enough to pull land from production = 50-100,000 km²/ year (Ref. 44 of Ref. (96G2)).)

The UNEP GLASOD study concluded that, globally, 2.95 million km² are so degraded that restoration to full productivity is beyond the normal means of a farmer, but could be restored with major investments. 9.1 million km² are moderately degraded to the point that original biotic functions are partly destroyed, and agricultural productivity is greatly reduced (92N1). Urbanized lands (about 4.75 million km² (00W1)) should be added to this list.

A study by Oldeman et al (Ref. 15 of Ref. (97C1)) calculated that of the world's 87.35 million km² of croplands, grasslands and forestlands:

• 19.65 million (22%) were degraded to some extent;
• 33% of this 22% were degraded lightly,
• 46% of the 22% were degraded moderately,
• 20% of the 22% were degraded strongly, and
• 1% of the 22% was degraded severely (See Ref. (97C1)).
• 77% were judged not degraded at all ***.
• Wind and water were believed to account for 85% of the degradation.
• Chemical degradation (loss of soil nutrients and salinization) and physical degradation (compaction of soil by heavy farm machinery and cattle) accounted for the remainder (97C1).

Soil degradation induced by human activity, globally, since 1945: 20 million km² - 17% of the Earth's vegetated land (UNEP study). Of these 20 million km², 38% are lightly degraded - full potential for recovery; 46% are moderately degraded - restorable only through considerable financial and technical investment; 15% are severely degraded -no agricultural utility under local management systems and reclaimable only with major international assistance; 0.5% are extremely degraded - incapable of supporting agriculture and irreclaimable (95D3). These degraded lands occupy 20% of Asia's vegetated lands, 22% of Africa's and 23% of Europe's. Direct causes: overgrazing (35%), deforestation (30%), other agricultural activities (28%), over-exploitation for fuel wood (7%), and bio-industrial activities (1%) (95D3).

Status of Global Dry-land* Degradation as of 1983-1984 (89P2)
(Col. 2= Area at least moderately degraded (in millions of km²))
(Col. 3= Total global area of that land category (in millions of km²))
(Col. 4= Area deteriorating to zero net economic return (in millions of km²/ year))

Agronomist H. Dregne's Classification of Cropland Erosion (90B2) (goes with the table below)

Distribution of Cropland Among Dregne's Categories (90B2) (Figures are in percent, and totals in each row add up to 100%)

An assessment by International Soil and Reference Information Centre (ISRIC) found that, of the 115 million km² of vegetated land on Earth (17%) is degraded, largely through erosion, and 16% can no longer support crops. The main causes, according to the survey, were deforestation and agricultural practices such as overgrazing (04K1). Other analysts contend that the global area of reasonably biologically productive land is on the order of 90 million km² - not 115 million. (See Section 2 of the Soil Degradation Review) Also, about 4.75 million of that 90 million km² is now urbanized.

Soil erosion rates are highest in Asia, Africa and South America (3000-4000 tonnes/ km²/ year), and lowest in the US and Europe (1700 tonnes/ km²/ year) (Ref. 16 of Ref. (95P1)). This probably reflects the difference in population pressures on the land, resulting in cropping on steeper slopes, shorter fallow periods, etc.

Over 100,000 km² of cropland (global) are degraded and lost annually due to wind- and water erosion. (David and Marcia Pimentel, Population Press (4/4/00)). This figure includes salinization and urbanization - at least according to some sources - see below.

Soil erosion and other forms of land degradation now rob the world of 50-70,000 km²/ year of farming (arable?) land (98H1).

Worldwide, soil erosion has caused abandonment of 4.3 million km² of arable land during the last 4 decades (110,000 km²/ year) (90U1), (90U2). (The 4.3 million km² estimated to have been abandoned during a 4-decade period is supported by the World Resources Institute's estimate that cropland is lost by erosion at a rate of 100,000 km²/ year.)

Globally, At least 100,000 km²/ year of cropland are lost to degradation (92P2). The breakdown is 50-70,000 km²/ year to soil erosion, 20-40,000 km²/ year to urbanization, and 20-30,000 km²/ year to salinization and waterlogging for a total of 90-140,000 km²/ year (94K3).

Since WWII, as many as 89,000 km² of the world's lands have been so ruined by over-grazing, deforestation, and unstable agricultural practices that they are impossible to reclaim. Another 12 million km² are considered "seriously degraded." These could be restored, but only at great cost (92U2).

Globally, more than 770,000 km² of land is salt-affected by secondary salinization: 20% of irrigated land, and about 2% of dryland agricultural land (FAO, AGL, 2000 data) (06S1). The area of irrigated cropland is about 23% of the area of dryland agricultural cropland.

The global rate of irrigated land loss to salinization and waterlogging is 20-30,000 km²/ year (94K3).

The global cropland urbanization rate: 20-40,000 km²/ year (92P2), (94K3).

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The Institute for Soil Management estimates that Kazakhstan's grain land area will be reduced by over 25% when the rapidly eroding portion of its grain land is abandoned (97B2). Grain land in Kazakhstan is forecasted to stabilize at 130-160,000 km² - 50-67% of the 1980s peak area (97G1). This was probably part of the former Soviet Union's "Great Lands" debacle in 1954-1962 (96G2).

Some 27% of the former Soviet Union's land area is used for agriculture. No more than 2/3 of this land is considered arable (89S3).
The USSR's harvested grain area was 1.23 million km² in 1977; 0.94 million km² in 1994 (95B1).
USSR summer fallow: 170-180,000 km² (in the late 1960s and early 1970s) (84B2).
USSR summer fallow: 120,000 km² (in the mid-1970s) (84B2).
Drops in area fallowed probably reflect increased human pressures on the land.

Farming in the former Soviet Union has been extended into highly marginal rainfall areas. This is evidence that the prospects for expanding the former Soviet Union's cropland base were not good, even in the 1970s (p. 34 of Ref. (78B2)).

Russian croplands are abandoned at a rate of 5000 km²/ year because they are so severely wind-eroded that they are no longer worth farming (p. 18 of Ref. (84B3)). This is a result of cropping typically semi-arid lands that should have been left as grazing lands.

Wind erosion removes 15,000 km²/ year of cropland from production in the former Soviet Union (89S3). A much larger area in the former Soviet Union is damaged to some degree each year (89S3).

Some 26,000 km² (72% of Kazakhstan's wind-eroded cropland) have suffered severe erosion (93M2). Conversion of grazing land to cropland, and removal of straw from fields for use as fodder have severely diminished soil fertility and humus content (4.1% down to 2.9% in the past 22 years (a loss of 4500 tonnes/ km²)) (93M2).

In Kazakhstan (the largest grain producer in central Asia), the Institute of Soil Management projects a loss of 30% of grain-land because of severe soil erosion (97B3).

Excess topsoil loss from the former Soviet Union's croplands is nearly 2.1 Gt./ year (84B2). Ref. (85B3), p. 19, gives an erosion rate of 2.3 Gt./ year. 5000 km² of Russian croplands are abandoned annually because they are so severely wind-eroded that they are no longer worth farming ((84B3), p. 18) (84B2).

Nearly 50% of the 6.1 million km² of cultivated land in the former Soviet Union is imperiled by erosion and other ills. About 1.6 million km² are saline, 1.1 million km² are eroded, 0.25 million km² are waterlogged or swampy, 13% more are rocky, hilly or over-grown ((78B2), p. 34).

Pravda (newspaper) reports that the Soviet Union is suffering from a catastrophic decline in soil fertility (90B2). 1000 km² of (the former) Soviet Union's croplands are lost to gullies yearly. 1.52 million km² (2/3 of arable land) has lost fertility as a result of water erosion and wind erosion (90B2).

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In India's Rajasthan, 30% of the (semi) arid land was being cultivated in 1951, and 60% was being cultivated in 1971, mainly at the expense of grazing lands and traditional long-fallow periods (FAO data) (86G2) (86G3). This usually results in severe wind erosion sooner or later - recall the "dust-bowl" in Oklahoma and surrounding states during the 1930s and the "Great Lands" fiasco in the Soviet Union in 1954-1962 (96G2).

Crop yields in Nepal have declined 22-30% due largely to erosion (91N2).

For the past 6 years Bhutan (South Central Asia) (Asian Sub-Continent) has been losing about 1000 acres (4 km²) of paddy growing (crop) land annually to development (urbanization) activities, natural disasters and regeneration of forests. Bhutan has only 71,832 acres (291 km²) of such wetlands out of which 23,132 acres (94 km²) were lying fallow according to renewable natural resources 2003 statistics. ("Maintaining food security", Kuensel Online, (3/2/05)).

In the lower Himalayas, the land has lost its capacity for any productive purpose according to ecologist P. R. Ramakrishnan of Jawaharlal Neru University (04K1).

In Himachal Pradesh, Uttar Pradesh, Assain, Jarumu and Kashmir in India, tens of thousands of km² have no more soil covering the exposed rocky substrata (75E1).

In the Deccan's "black soil" region of India, soil erosion rates are 4000-10,000 tonnes/ km²/ year ((86P1), Ref. 5).

India's wastelands - areas affected seriously by salinity, alkalinity, wind- and water erosion - cover one million km², of which 420,000 km² are still being cultivated. Ravines in India have swallowed a total of 40,000 km² (87U1).

Erosion associated with shifting cultivation has denuded 27,000 km² east of Bihar, India (96G2).

In the Annapurna region (in central Nepal), erosion rates on grazing land and croplands are 2000-5000 tonnes/ km²/ year (Ref. 51 of Ref. (95D1)).

In Nepal, soil erosion rates in hills and mountains are 2000-5000 tonnes/ km²/ year in agriculture fields, and 20,000 tonnes/ km²/ year in some highly degraded watersheds (92C2). Crop yields in these watersheds declined by 8-21% during 1970-1995 (03N1).

Some 38% of Nepal's eastern hills consist of fields abandoned due to soil erosion (85J1). Abandonment of cropland usually reflects gully erosion. This is usually permanent for croplands - but not grazing lands.

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Part [C4] ~ Southeast Asia ~[C4a]~Philippines, [C4b]~Indonesia, [C4c]~Malaysia, [C4d]~Thailand,

In Southeast Asia, increasing population pressures on the land have extended the use of steep hill slopes particularly for maize production. This has led to a significant increase in erosion on lands with slopes of greater than 20% (91H5) (03N1).

In the Philippines, hillside agriculture accounted for 10% of all agricultural lands in 1960, but 30% in 1987 (94A1). Presumably "agricultural" here refers only to croplands, not grazing lands.

In Zamboanga del Sur Province of the Philippines, farmers testify to an 80% decline in corn yield over 15 years. Cumulative soil loss has been up to 1meter depth over boulders and core stones (85O2).

Slopes of over 50% are being cultivated on a continuous basis in Java in Indonesia (90H2). China limits the slope of croplands to 28%.

In Java and Bali (in Indonesia), 400,000 km² are badly eroded as a result of deforestation (84G1).

In Sarawak (Indonesia), soil loss from logged areas was over 10,000 tonnes/ km²/ year, vs. about 10 tonnes/ km²/ year from primary forest (96G3) (a negligible rate). Much of Indonesia's logging is done illegally. (See Forest Lands Degradation Review in this website.)

Indonesia's main island (Java) must be one of the most eroded places in Asia, if not the world. Indonesia's government classifies more than 10,000 km² (8% of croplands) as critically eroded (85U1) (Ref. 56 of Ref. (92D1)). The land is said to be so badly degraded that it already is, or soon will be, unable to sustain even subsistence agriculture. Some small fields are losing 5 cm. of soil/ year (150,000 tonnes/ km²/ year) (92D1) (85U1).

In Java's uplands of Indonesia, the eroded part of croplands expands by 1-2%/ year, and covers about one third of the total cultivated area (96M1).

In Malaysia's Cameron Highlands, most cultivated areas are on slopes of 18-70% (91H4). Malaysia has severe soil erosion even though terracing is common (91H4). Even China limits the slope of croplands to 28%.

Erosion in Thailand is blamed for an average yield decline of 50% for corn and upland rice (Ref. 2 of Ref. (92D1).

Estimated (USLE) erosion rates run as high as 100,000 tonnes/ km²/ year on steep deforested land where intensive subsistence agriculture is practiced in Thailand. Deforestation and erosion both appear to be even worse in the Karat Plateau of Northeastern Thailand (Ref. 17 of Ref. (92D1)).

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Part [C5] ~ Sub-Saharan Africa ~[C5a]~In General, [C5b]~Rwanda, [C5c]~Zimbabwe, [C5d]~Kenya, [C5e]~Nigeria, [C5f]~Ethiopia, [C5g]~Tanzania, [C5h]~Madagascar

The fallow system in the West African Sahel region was used to preserve soil fertility. That system has almost disappeared. Farmers in some regions now cultivate their land year-around, and with low levels of fertilization, causing the soils to quickly lose their productivity (07N1). In essence the West African Sahel is subjecting its croplands to "nutrient mining." The eastern part of Burkina Faso in the Sahel continues to maintain its cropland soil fertility (01M2).

In 2002 a UN team found: "Agriculture in Lesotho faces a catastrophic future; crop production is declining and could cease altogether over large tracts of the country if steps are not taken to reverse soil erosion, degradation, and the decline in soil fertility." Nearly 50% of children under five in Lesotho are stunted physically. Many are too weak to walk to school (07B1)." Sub Saharan African farmers use very little fertilizer, either organic (manures) or chemical (due to high cost caused by poor transportation infrastructure).

The large and growing numbers of livestock and the cultivation of the lowland's more marginal lands have accelerated land degradation in the Pangani River basin of Tanzania (07M1).

African soils are, by nature extremely poor. They are very low in both organic matter and nutrients. Farmers in Sub-Saharan Africa once used fallow periods to replenish soil nutrients, but population pressures made this option unaffordable, so they have been essentially mining soil nutrients for some decades (02F1). Also the lack of fossil fuel and high prices of chemical fertilizers (6 times the price in the EU) forced farmers to use animal dung as fuel, depriving cropland soils of organic matter.

About 20% of Africa's cropland area is seriously degraded (00L1).

Desert + cumulative desertified land in Africa = 7.42 million km² (25% of Africa) (Ref. 38 of Ref. (88L1)). Others estimate that as much as 65% of Africa is prone to some degree of desertification (Refs. 6, 7, 69 of Ref. (88L1)).

In the early 1960s, fertilizer use in Sub-Saharan Africa was about 500 kg./ km²/ year, compared to 10 in India and China. In the 1990s, China was using 240 kg. / km²/ year and India about 110, but Sub-Saharan Africa was using about 8. But in a number of Sub-Saharan African countries, nutrient losses exceed 6 tonnes/ km²/ year of nitrogen, phosphorus and potassium (NPK) (02F1). (This is called "nutrient-mining.")

In Europe, urea costs about US$90/ tonne. Shipping it to a port in Kenya or Mozambique raises the price to about US$120/ tonne. Getting it into the African interior raises the price to $500/ tonne in eastern Uganda, and $770 in Malawi. These rates are 6 times greater than prices in Asia, Europe and North America. Infrastructure is the cause of much of the problem. Much of Africa has less than 10% of the road density of India. India has 1004 km. of paved road per million people, China has 803; Ghana has 494; Uganda has 94; Ethiopia has 66 (02F1). Taxes on imported fertilizer worsen the situation (02F1). Organic soil amendments lack some nutrients such as phosphorus. Manures have only 2% nitrogen (02F1). Sub-Saharan African farm soils are poor in organic matter, making them less fertile and more erosion-prone, but farmers cannot raise livestock (an organic matter [manure] source) because of population pressures on the land. Also, instead of putting manure and crop residue in soils, people burn them for fuel because they cannot afford to import oil (02F1).

Higgins and Kassam (Ref. 20 of Ref. (90L1)) estimated that soils of tropical Africa, if properly used, and at low levels of inputs, could feed 3 times the 1975 African population, and 1.5 times the estimated population in 2000. At intermediate levels of input, Africa could feed 5 times the population projected for 2000 (90L1). Norman Borlaugh (father of the Green Revolution) has made similar statements.

Crop yields hover around 1 tonne/ km² in many parts of sub-Saharan Africa, compared to 6-7 tons per km² common in rain-fed systems in the US and Europe (04M1). Sub-Saharan Africa uses very little chemical fertilizer because it is so expensive - about 60 times more on the basis of hours of labor to purchase a ton of chemical fertilizer - in large part due to inadequate transportation infrastructure. As a result, African farmers are unsustainably mining the nitrogen, phosphorous and potassium from their cropland soils. Animal dung is commonly used as fuel for cooking (a substitute for oil that Africans cannot afford) so it cannot be used as fertilizer either.

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The latest (1994) of several genocides in Rwanda claimed over 900,000(?) people - 14% of Rwanda's population, the overwhelming majority of them Tutsis, but in northwestern Rwanda at least 5% of the residents were slaughtered even though there were no Tutsis. Rwanda contained 2040 people per square mile, twice the population density of the Netherlands (a nation that has far better soils, far more fertilizer and far greater ability to import food). The average Rwandan farmer worked 0.07 acre of land with agricultural practices not far removed from those of the Stone Age. By 1990, 40% of Rwanda's population was living on less than 1600 calories per day - famine level. A team of Belgian economists concluded that the outbreak of fighting "provided a unique opportunity to settle scores or reshuffle land properties, even among Hutus". It is not rare to hear Rwandans argue that the war was necessary to wipe out an excess population and bring numbers in line with the available land resources (04D1).

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Some 80% of Zimbabwe's population lives in communal farming areas, while the rest live in large commercial farming areas and cities (92T1). Ten years after independence from Rhodesia, Zimbabwe's 4200 white-owned commercial farms occupied the best lands, while 750,000 black farmers remained tied to the poor, rocky soils of the officially designated "communal lands" (90B3). Communal lands comprise 42% of Zimbabwe. 75% of communal lands are dry, hilly, isolated and of value mainly for grazing - not crops (90B3).

Topsoil erosion of "communal" (black-owned) lands (42% of Zimbabwe) = 4090 tonnes/ km²/ year (90B3).

The National Environment Secretariat (NES) says 483,830 km², 85% of Kenya's land area of 569,137 km², is experiencing some form of desertification. The NES says 19.3% of Kenya is severely affected by degradation, and 9.4% is moderately affected (91D2).

In the early 1960s, an American research team and a top-level soil conservation advisor reported: "Even to the casual visitor to Ethiopia, the extent of soil erosion seen in many parts of the country will leave a lasting impression of desolation and impending disaster". In southern Ethiopia's Gamu Highlands, agricultural system was observed to be in a state of collapse around 1968 (Ref. 26 of Ref. (75E1)).

In northern Ethiopia, "stone deserts" have replaced nearly 40,000 km² of what once were fertile farmlands ((88J1), p. 9).

Five million acres (20,000 km²) of former, or current, cropland in Ethiopia's highlands have reached the point of no return (Ref. 16 of Ref. (90D1)).

Ethiopia, a mountainous country with highly erodible soils on steeply sloping land, is losing an estimated 1 billion tons of topsoil a year, washed away by rain (07B1).

In Ethiopia's Wollo Highlands, at present erosion rates, 18% of farmland will be useless for crops by 2010 (87M2).

Nigeria was losing 500 km² of cropland to desertification per year in 2001(Announcement by Nigeria's Minister of Environment, January 2001).

About 20-50% of soils in (croplands of) one watershed in northern Nigeria are seriously gullied (77L2).

In Tanzania's Kondoa Province, nearly 1500 km² are so badly damaged by gully erosion that they cannot be rehabilitated (Ref. 13 of Ref. (87E2)). Gully erosion is mainly harmful to cropland, less so to grazing lands.

Madagascar is often called the most eroded country in the world. Slash-and-burn rice agriculture on steep forested hillsides ("tavy") is partly to blame - as is cattle raising using procedures that produce large-scale gullying ("lavaka") (89U4).

Madagascar's rivers run red with the soil of the central highlands (apparently a result of "tavy" agriculture that converts tropical rainforest to rice fields, destroying soil fertility and erosion resistance) (07R1).

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Almost 75% of the cropland in Central America is seriously degraded (00L1).

Some 20% of Mexico's croplands are on steep slopes (Ref. 16 of Ref. (97R1)).

More than 50% of all Mexico's farmers' farms are on highly erodible slopes (97R3).

Grain area in Mexico declined 10% during the 1980s -attributed to abandonment of degraded farmland, and to cropland conversion to non-farm uses such as urban developments (Ref. 15 of (88B4)).

Expansion in the 20th century of irrigation in northwest Mexico has been plagued by serious salinity problems. In Yaque Valley, 400 km² were damaged by salt, and 150 km² had to be retired from production by the mid-1960s. In the Colorado Delta, 80% of arable land was affected by salinity, and 14% of arable was too saline for cultivation by 1965 (p. 127 of Ref. (76E1)).

Mexico abandons 1036 km² of farmland to desertification per year (94S4).

An official report indicates that 40% of Mexico's topsoil has been lost - a 30% reduction in agricultural productivity (Ref. 17 of Ref. (92B2)).

Grain area in Mexico declined by 10% during the 1980s. This was attributed to abandonment of degraded farmland, and to cropland conversion to non-farm (typically urban) uses (Ref. 15 of Ref. (88B4)).

As much as 75% of the cultivated land in Venezuela's highlands is on slopes greater than 25% (77L1).

A third of Haiti's land is now virtually useless, and 40% of Haiti's population is mal-nourished ((88J1), p. 15) (89J1).

The UN Development Program has labeled "rapid and increasing erosion" as Haiti's principal problem. Land tenure forces peasants onto steep slopes where cultivation is a futile, temporary proposition ((76E1), p. 169).

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Problems with dryland salinity in Australia affect 25,000 km². About 170,000 km² of Australia's 300,000 km² (of dryland cropland) are likely to be destroyed by salinity by 2050, based on current trends (01B1) (02C1). If so, Australia will cease to be one of the world's 5 major net food exporters.

About 35% of Australia is affected by some form of land degradation (90D2). About 324,000 km² of Australia are affected by natural and human-induced dryland salting (90D2). Australia is a very arid land (on average) with old, poor soils; i.e. no ice-ages and no volcanoes.

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Part [C8] ~ Far East ~ [C8a]~In General, [C8b]~China,

Over the last 20 years, 50% of Mongolia's wheat land has been abandoned, and wheat yields have fallen by 50%, shrinking the harvest by 75%. Mongolia is almost 3 times the size of France with a population of 2.6 million, and now imports nearly 60% of its wheat (07B1). Mongolia's permanent and arable cropland area is about 15,700 km². So estimate the lost (abandoned) wheat land at about 5000 km².

The spread of deserts in China in recent years has been so rapid that as many as 20,000 villages have been abandoned (04D1). The spread of deserts in China has been widely attributed to deforestation and overgrazing.

In China, plowing excesses became common in several provinces as agriculture pushed northward and westward into the pastoral zone (typically semi-arid) between 1987 and 1996. Inner Mongolia's cultivated area increased by 11,000 km², (22%), during this period. Other provinces that expanded their cultivated area into semi-arid lands by 3% or more during this 9-year span include Heilongjiang, Hunan, Tibet (Xizang), Qinghai, and Xinjiang. Severe wind erosion of soil on this newly plowed land made it clear that its only sustainable use was controlled grazing (07B1).

China loses 1200 km²/ year of farm and pasture land to drifting sand dunes (86W2) (86W4). (China's total land area is 9,327,420 km² and its agricultural area is 1,539,560 km².) The spread of deserts in China is widely attributed to deforestation and overgrazing.

China had 5 major dust storms during the 1950s; 23 in the 1990s and 20 during 2001-2002 (03U1) (Chinese Meteorological Agency data).

From 2002 to 2004, China went from being essentially self-sufficient in wheat to being the world's largest importer of wheat. China's wheat harvest peaked at 123 million tons in 1997 and fell to 90 million tons in 2004 (05B3). The reduction since 1997 was probably due to the conversion of croplands to urban lands and possibly to the conversion to aquaculture (fish ponds).

Some 24,000 Chinese villages have either been abandoned or have had their farm economies seriously impaired by invading deserts. In the arid northern half of China where most of China's wheat is grown, tens of thousands of wells go dry each year. These trends, combined with weak grain prices that lower planting incentives, shrank the harvest from its peak of 123 million tons in 1997 to 86 million tons in 2003 (04B1).

In addition to the land already converted to desert, 900,000 km² of China show a clear "tendency toward desertification." This land is mostly rangeland (i.e. semi-arid), but includes some cropland (01Q1).

During the 1950s, 1960s and 1970s, the average rate of desert spread in China was 1560 km²/ year. During the 1980s this expanded to 2100 km²/ year, and to 2460 km²/ year in the 1990s (Wang Tao, "In Brief, Lhasa Dust Storm", China Daily (1/29/02)).

During 1994-1999, China's desertified land area grew by 52,500 km². Deserts now cover more than 25% of China's 9,327,420 km² of total land area (02L1).

Frequency of dust storms in Inner Mongolia: 1950-1959 - 5: 1960-1969 - 8: 1970-1979 - 13: 1980-1989 - 14: 1990-1999 - 23: 2000-2009 - 100 (projected, based on 20 storms during 2000 and 2001) (01C1).

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Crop production on over 1 million acres in Idaho is probably reduced by 10% over what it would be if there were no erosion (85C8). This statement might be referring to the Palouse region with its loess (wind-blown) soils with inherently low organic matter content, and hence inherently low productivity.

Nearly 50% of US corn land is grown continuously as a monoculture (94G2).

During 1948-1984 the soil organic matter content of 10 sites in western Kansas declined by an average of 19% (86L1). Organic matter levels are now 50-60% of original levels in prairie soils of Canada, and 60-70% of original levels in croplands under hay-rotations in central and eastern Canada (Refs. 5, 7 of Ref. (86D1)).

Canada's Prairie Province soils were naturally high in organic matter. They have lost 45% of their original organic matter content since cultivation began at the turn of the 20^th Century (84S2). Land in fallow is particularly vulnerable to soil erosion and salinization when it lays bare. Introduced in the early 1900s in Canada's prairie provinces, the excessive tillage associated with summer fallow has contributed substantially to reduced organic-matter levels, reduced soil-tilth, nitrogen loss, and less-efficient crop-use of available water (Ref. 7 of Ref. (87M1)).

Salinization in Canada's Prairie Provinces (wheat-growing area) affects 22,000 km². In addition, 1000 km² of Canada's irrigated land suffer the effects of salinization. These salt-affected areas are expanding at a rate of 10%/ year. Crop yields have been reduced by 10-75% (50% on average) due to salinization (84S2).

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In the Sistan basin of Afghanistan and Iran, more than 100 villages have been abandoned because of windblown dust (03E1).

In the summer of 1996, the government of Jordan, suffering from higher prices of imported wheat and a growing fiscal deficit, was forced to eliminate its bread subsidy. The resultant riots lasted several days and threatened to bring down the government (Ref. 9 of Ref. (97B3)). Egypt is also known to have a significant bread subsidy - paid by the US as part of the Mideast Peace agreement.

Oxford-based expert Norman Myers says Morocco, Tunisia and Libya are each losing over 1000 km² of productive land a year to desertification (05L2).

Disorganized and poorly managed mechanized rain-fed agriculture on 65,000 km² of Sudan have led to large-scale deforestation and severe land degradation (07U1). (The combination of rapid population growth and environmental degradation of all types is believed to have created the desperate struggles over resources and the consequent armed conflicts in the Sudan in recent years (07U1).)

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Before 1960 the major contribution to increasing global food supplies came from cultivating more previously unused but arable land. Since 1960 increasing crop yields (tonnes/ unit area) has been the predominant contributor to increasing food supplies (99Y1) (98E1). However even today, all projections of future food productivity include an increase in cereal harvest area of about 25,000 km²/ year and an increase in total cultivated area of about 42,000 km²/ year (99Y1). These projections are supported by estimates of arable land area capable of being cultivated but not yet cultivated that are sometimes as high as twice the area of croplands currently under cultivation. Globally the total cropland area under cultivation is 15 million km² (96S5). This figure can be broken down into 5.4 million km² for the developed world and 9.6 million km² (03A2) for the developing world. Developing countries are claimed to have 28 million km² of land with a potential for rain-fed agriculture at yields above a "minimum acceptable level." This suggests an undeveloped arable land area in developing nations of about 18 million km² (03A2). A large fraction of the world's urbanized land (4.75 million km²) are probably situated on undeveloped arable land. Most of the developing world's undeveloped arable land is concentrated in a few countries in South America and sub-Saharan Africa (03A2). In addition, a good part of the undeveloped arable land in developing nations is under forest (03A2). Brazil has 27% of the world's arable land that is not being used as cropland, and that land is largely rainforest (99Y1). All this suggests a major error in the estimates of undeveloped arable land area in the developing world. The population of shifting cultivators in the world's tropical rainforest is far larger than the carrying capacity of that rainforest. (See Section [G] below.) So even though only a small fraction of the world's tropical rainforest is actually under cultivation at any point in time, it has to be considered as fully utilized in terms of its use by shifting cultivators.

Young (99Y1) has done much research that casts considerable doubts on notion that such a huge arable area lies idle, waiting for someone to come along with a plow. The fact that all of the numerous projections of future annual increases in cropland area are such a tiny fraction of the estimates of total arable, but unused, cropland provides tacit admission that Young is probably correct. Young also points out that the total area of cereal-producing croplands in the LDCs (less-developed countries) peaked in 1996 at 4.45 million km² (out of a total area of arable land of 7.49 million km²) and by 2002 had fallen to 4.27 million km². For the low-income food-deficient countries (LIFDCs) the total area of cereal-producing cropland peaked in 1998 at 3.45 million km² (out of a total area of arable land of 5.4 million km²) and by 2002 had fallen to 3.29 million km² (See www.land-resources.com). Five major studies analyzed by Young estimated that the amount of arable land in the developing world (excluding China) not being cultivated was 16.7 to 19.0 million km² (about twice the presently cultivated area in the developing world [excluding China]).

Young personally visited 30 developing world countries to try to find the arable land that are not yet cultivated that studies keep estimating. Below are some of the inconsistencies that Young found (99Y1).

• Cultivation is often extended onto steep slopes, frequently without adequate soil conservation and thus not sustainable. Some examples from the Sections above are: (1) cropland slopes steeper than 50% in Java (90H2), (2) croplands on slopes between 18% and 70% in Malaysia's Cameron Highlands (91H4), (3) 20% of Mexico's cropland area is on "steep" slopes (97R1), (4) In Venezuela's highlands, 75% of cultivated lands are on slopes in excess of 25% (77L1).
• Cultivation has become increasingly common in semi-arid zones with high risks of drought and wind-erosion, and often in conflict with former pastoral use. (Conflicts between farmers and pastoralists are common throughout sub-Saharan Africa, Rwanda being a prime example (07M1) (07R1).)
• Large regions of both Asia and Africa are being cropped continuously, with no fallow periods or other soil rest periods. This has resulted in declining crop yields.
• Nutrient cycling studies show chronic negative balances, i.e. nutrient removals in harvesting exceeding natural inputs and nutrient inputs via fertilizers. This is especially common in sub-Saharan Africa.
• Land degradation is often found to be widely attributed to unsustainable land use, often initiated by a cycle of land shortage, poverty and land degradation.
• Average farm size in some areas has fallen substantially below one hectare. This is commonly a result of farms being subdivided among several children. If there were substantial areas of undeveloped arable land this would probably not have happened,
• Illegal cultivation of forest reserves, national parks and other protected areas is commonly observed.
• Independently of famines caused by natural disasters or civil conflict, chronic under-nutrition is widespread.

• In Jamaica, where 49% of arable land is allegedly not being used as cropland, smallholders have been forced to cultivate very steeply sloping land in the interior (99Y1).
• In Kenya where 50% of arable land is alleged to not be used as cropland, farms are becoming too small to support a family, and cultivation has been expanding into semi-arid zones where the risks of drought and wind erosion are high (99Y1). (Conflicts between farmers and pastoralists are common throughout sub-Saharan Africa (07M1) (07R1).)
• In Malaysia, 47% of arable land is supposedly not being used as cropland, but the non-cropped arable land is under tropical rainforest. There is widespread agreement that it should stay that way. (15 countries in the world are home to 72% of arable land that is not being used as cropland; seven of these countries have large areas of rainforest.) (Brazil has 27% of the world's arable land that is not being used as cropland, and that land is largely rainforest.) (99Y1) (See Section [G] of this document for data on human populations far in excess of the carrying capacity of the land in tropical rainforests being used for shifting cultivation.)
• Malawi is said to have 55% of its arable land not being used as cropland. But in 1958-1962, the most fertile regions were all100% cultivated, for the most part continuously. On the poorer soils, some land remained under rotational fallows and the population was 3 million. By 1973, with a population of 5 million, all sustainably usable land was taken up, and cultivation extended up the hill slopes and down into the scarp lands of the Rift Valley. In 1999, the population exceeded 10 million, and it is inconceivable that any arable land might not be used as cropland. Field observations confirmed this (99Y1).
• In Ethiopia where 57% of the arable land is said to not be used as croplands, there is widespread cultivation on steep slopes with concomitant severe erosion (99Y1).
• In Madagascar, where 90% of its arable land is said to not be used as croplands, the government is having great difficulty in preventing clearance of its protected areas (99Y1).

In the above nations the alleged large amounts of arable lands that are not being used as croplands are clearly totally inconsistent with the facts on the ground. It is quite apparent that estimates of undeveloped arable land are grossly in excess of what detailed measurements would find. Below are some possible sources of the error (99Y1).

The FAO estimates that 930,000 km² are available for agricultural expansion in developing nations (excluding China) during 1990-2010 (mostly in sub-Saharan Africa and Latin America) (Ref. 69 of (96G2)). But cropland is lost to degradation at a rate of about 100,000 km²/ year (0.7%/ year) (92P2) (50-70,000 lost to soil erosion, 20-40,000 to urbanization, and 20-30,000 to salinization and waterlogging) (94K3). So the land available for agricultural expansion over two decades is scarcely adequate to cover, for one decade, the rate of cropland abandonment. The problems with the above-mentioned claim are that nearly all of this "potential" cropland (a) cannot be cropped sustainably, or (b) is of low productivity and/or (c) is presently serving vital roles as urban lands, grazing lands, forest lands and wetlands. Global harvested area of annual crops grows by only 0.3%/ year (00W2) to 0.5%/ year (Table AF.2 in Ref. (00W1)), so cropland area per-capita has been shrinking. (The developing world's population growth rate is about 1.3%/ year). Other data noted above (www.land-resources.com) says that the area planted to cereals in less developed countries peaked in the 1990s and has been declining since then. This further supports the contention that the world's cropland area in use is close to, or in excess of, the land area capable of being cropped sustainably. Alexandratos (95A2) found that over 70% of the land with rain-fed crop production potential in sub-Saharan Africa and Latin America suffers from one or more soil- and terrain constraints.

One possible location of undeveloped arable land is Argentina. The evidence is that Argentina, mostly as a result of cropland expansion, increased wheat production by 68% in 1996 and maize production by 48% in 1997 and another 25% in 1998. These increases followed price rises in the immediately preceding years (03B4). Whether the land that was put into production was suited to sustainable agriculture is not know.

Developing countries (still) have over 3 million km² of natural wetlands that are potentially suitable for crop production (03N1). It would be a mistake however to regard these 3 million km² as a component of the world's undeveloped arable land since they serve important rolls in flood prevention and aquifer recharge. For example, in central China, 5000 km² of wetlands have been reclaimed for crop production since 1950, contributing to a reduction of floodwater storage capacity of 50 billion m³. There is strong evidence that wetland conversion to cropland is responsible for about two-thirds of this loss in storage capacity, and thus for about two thirds of the US$20 billion flood damage in 1998. Similar links have been established for the severe 1993 floods in the US (03N1). In some Sahelian countries of Africa, wetlands are potentially important contributors to food security (86J1) and might be considered as potential undeveloped arable land. However past experience in inland valleys of the Sahelian belt suggest that conversion of wetlands to agricultural use has been of doubtful benefit despite huge international investments. Many irrigation schemes have failed through mismanagement and inadequate infrastructure maintenance, civil unrest and weak market development. Soils in Africa's Sahelian belt are potentially productive only after constraints are overcome, e.g. acid sulphate-, aluminum- and iron-toxicity and waterlogging (86J1). An analysis by Buringh (89B8) tends to support the views and work of Young. Buringh contends that "Today, virtually all of the productive land on this planet is being exploited by agriculture. What remains unused is too steep, too wet, too dry or lacking in soil nutrients (89B8)."

Canada is said to be using only half of its arable lands (84S2). But all of its unused arable lands are low-grade, low-productivity lands that could not be cropped without high erosion rates - or are grazed or urbanized (78B2). Croplands on Canada's semi-arid plains have lost half of their organic matter over the past six or so decades (Refs. 5, 7 of Ref. (86D1)), reducing productivity, water retention, tilth and erosion resistance. Also, Canada has felt compelled to reduce cropland fallow periods (92U1) (Wall Street Journal (5/1/96)), increasing the rates of erosion and salinization (84S2). Why would Canada's plains farmers choose to endure these problems with their current soils if all they had to do is buy some idle land and plow it?

Australia's soils are geologically old (no ice-ages and no volcanoes), poor, shallow, and have long-term, serious, erosion- and salinity problems. Salinity is increasing in the area that provides 40% of Australia's agricultural value. The area degraded by salinity could triple over the next five decades (Australia's "State of the Environment, 2001" (March, 2002)). Australia's food exports support about 50 million people - 8 month's growth of the world's population. Land degradation, population growth, and serious global-warming-driven droughts are likely to cause these exports to shrink significantly, or to vanish over the next generation.

Russia would appear to be the ultimate in land-richness, but arable wealth is another matter. During 1954-1962 the former Soviet Union embarked on a massive "Great Lands" program, converting 300,000 km² of semi-arid grazing land to semi-arid croplands. The results were predictable - windstorms wiped out all the increased productivity and then some. The program was declared a disaster and abandoned (96G2). If Russia has large tracts of idle but arable land, why did it not develop these, rather than resort to a desperate scheme with predictably disastrous results? And why are 13% of Russia's croplands on rocky hillsides (78B2)? Might a dose of free market economics have eliminated these problems? Russia's grain lands productivity in the mid-1980s was on a par with Canada's (90B2). Both have similar climates, and Canada has newer, less eroded soils. About 27% of the former Soviet Union's land area is used for agriculture. No more than 2/3 of this land is arable (89S3). This could hardly be the case if there were significant areas of undeveloped arable land.

The US is also believed to have lots of undeveloped cropland now masquerading as urban lands, grazing lands and forestlands. But in 1972, when bad weather conditions prevailed, grain prices doubled over the following few years (98D1) and much of these idle, potential croplands were pressed into use. The results were huge increases in erosion. The Cropland Reserve Program, during the past few decades, took most of this non-sustainable cropland back out of production (96G2). This withdrawal (about 47,000 square miles during 1982-1997) achieved huge reductions in net US soil loss. If large tracts of potential, but good, cropland are waiting for a plow, why was it necessary to put extremely marginal lands to the plow and risk disaster? The US Great Plains (a semi-arid wheat-growing area) are suffering the same ills as their Canadian neighbors - loss of about half of their organic matter and some salinity problems. What is so worrisome is that these US- and Canadian plains are the world's largest and second-largest sources of exportable wheat. A large fraction of the rest of the world depends on wheat imports from the US and Canada. As these North American grain lands degrade, and as China's net grain exports change to large net grain imports, and as more food crops are used to produce biofuels to replace oil, major problems are likely to erupt worldwide - problems that would probably not have happened if there were large areas of undeveloped arable land.

In recent years, Canada, Australia, the EU and Russia have imposed constraints on food exports (06D1).

According to US Department of Agriculture Economic Research Service estimates released 11/22/04, 2005 will be the first year in nearly 50 that the US will not turn an agricultural trade surplus (04G1).

Globally, 4.6 million of the world's 12.3 million km² of rain-fed croplands are classified as dry lands (97C1). Most, if not all, of these dry lands should probably be used as grazing lands to avoid high wind-erosion rates, the risk of dust bowls and extreme droughts. If the world is awash in potential croplands waiting for the plow, why has so much low-productivity, economically marginal land been pressed into service as croplands? And why would so much financial capital, effort, and government subsidies be invested in irrigation?

In Zimbabwe (90B3), the Philippines (00N1) and probably throughout the developing world, farmers producing for local markets have been marginalized into cropping steep, erodible hillsides of low-grade land with no hopes of producing sustainably. The results were predictable - bloodshed and political unrest. If there were large tracts of unused but good-quality potential cropland in these developing nations, why were all these environmentally marginalized farmers unable to find them? In the Philippines, hillside agriculture accounted for 10% of all agricultural lands in 1960, but 30% in 1987 (94A1). It is increasingly doubtful, then, that the Philippines have plenty of undeveloped arable land of sufficient quality as to enable agriculture to be practiced on it sustainably.

In Bangladesh, landlessness among rural households rose from 35% in 1960 to 53% in the early 1990s (97U1). This is not what one would expect if there were cropland-grade lands sitting idle.

The 3-4 major genocides in Rwanda in the past few decades can probably be explained by its cropland supply situation. Fifty percent of all farming there took place on hillsides by the mid-1980s (Ref. 16 of (97R1)). By the mid-1990s, Rwanda had less than 0.03 ha/ person of grain land, mostly on steep slopes (95D2). This is about a third of that in Bangladesh. This is totally inadequate, especially considering Africa's typically poor soils. The latest (1994) of several genocides in Rwanda claimed over 900,000 people -- 14% of Rwanda's population. The overwhelming majority of them were Tutsis, but in northwestern Rwanda at least 5% of the residents were slaughtered even though there were no Tutsis. Rwanda contained 2040 people per square mile, twice the population density of the Netherlands (a nation that has far better soils, far more fertilizer, and far greater ability to import food). The average Rwandan farmer worked 0.07 acre of land with agricultural practices not far removed from those of the Stone Age. Much of this cropland is highly erodible, rocky hillsides. Rwandans could not afford chemical fertilizer. The price is six times greater than in the EU and 60 times greater on an hours-of-labor-per-tonne-of-chemical-fertilizer basis. By 1990, 40% of Rwanda's population was living on less than 1600 calories per day - famine level. A team of Belgian economists concluded that the outbreak of fighting "provided a unique opportunity to settle scores or reshuffle land properties, even among Hutus". It is not rare to hear Rwandans argue that the war was necessary to wipe out an excess population and bring numbers in line with the available land resources (04D1). Conflicts between cropland farmers and livestock grazing farmers (the difference distinguishing Tutsis from Hutus) are common throughout much of sub-Saharan Africa (07M1) (07R1).

In South America, holders of large land tracts are being overwhelmed by hordes of wretched landless people seeking ways of survival (04C1). This is totally inconsistent with the view that vast areas of undeveloped arable lands exist throughout South America. If they did exist, these landless hordes would surely have found them and converted them into croplands.

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Context
In the global marketplace, per-capita food supplies increased by 24%, and real food prices fell 40% between 1961 and the late 1990s, even as the world population increased by 100% from 3 to 6 billion (00W2). The commonly asked (and crucial) question is what happens during the next roughly five decades as the world population is forecasted to increases by an additional 50% to about 9 billion (99U5) and then stabilizes at around this figure, possibly falling thereafter. The tendency of forecasters of future cereal (essentially food) production is to try to mainly extrapolate the results of the previous 40 years. It will be seen below that this extrapolation procedure has little logical basis and is dangerously deceptive. This is primarily because the three processes responsible for the above-mentioned results of the previous four decades all have fundamental limitations, and all three processes are at or close to these limitations now. Below we critique some of these projections, pointing out some faults. It is interesting to note that all of these projections of cereal production parallel, quite closely, the forecasted growth of the world's population. This is because the past 4+ decades have been characterized by demand-driven food production rather than supply-driven production. It is far from clear that this situation will characterize the next 4+ decades. The projections focus mainly on analyses of production growth and virtually ignore the sustainability issues involved.

To be fair, all of the forecasts known to this author took place before it was widely known that the glaciers coming off the Himalayan Mountains, Andes Mountains, Rocky Mountains of North America and Europe's Alps are shrinking, if not vanishing. This is a worldwide process that some attribute to global warming. Half the world's population depends on rivers starting from mountain glaciers as their freshwater source. Himalayan glaciers alone feed 7 major Asian rivers (mainly in the Asian sub-continent, i.e. South Asia), ensuring year-round water supplies for two billion people (05U2). Shrinking glaciers, threaten the uniformity of the flows of these major rivers, and hence threaten the already over-stretched water supplies and irrigation systems that these two billion people depend upon. Retreating glaciers in the Andes Mountains, the Rocky Mountains, the Alps and the Himalayan Mountains probably account for the bulk of the three billion people of the world whose water supplies are being placed at risk as a result of retreating glacier. Also all of these forecasts took place before the huge increase in demand for (and price of) biofuel raw materials (corn, sugar, palm oil and soybeans) and hence the land these plants grow on. Also all of these forecasts took place before the huge growth in demand for (and price of) all sorts of commodities that the rapid economic growth of India and China called for. So perhaps the optimism expressed in these forecasts should not be criticized too harshly.

The Dyson Forecast
One interesting analysis of the prospects for feeding humanity out to 2025 (predicted global population: 8 billion) was done by Dyson (98D1). A zero increase in cropland area is assumed. Most other forecasters assume small increases in cropland area despite the fact that the commonly accepted view is that the amount of arable land that is not used for cropland is similar in magnitude to the current inventory of cropland now in use. An analysis of this issue is given in Section [D] above. Dyson's primary error appears to be that cropland cereal yield (tonnes per unit area per year) are essentially extrapolated from yield data between 1961-1998, a period during which cropland yields doubled due to greatly increased consumption of chemical fertilizers, rapid expansion of large-scale irrigation, and the "Green Revolution." As noted in Sections [A3] through [A6] in this document and in Chapter 4 on irrigation issues, it is unlikely that any of these strategies will be anywhere near as productive in first quarter of the 21^st century as during 1961-1998.

• Marginal productivities of inorganic (chemical) fertilizers have dropped by at least 50% at application rates typical of developed nations and China (89B5) (91B1) (82W1). This declining marginal productivity (saturation effect) is a natural consequence of Justus von Liebig's "law of the minimum" that states that plant growth is limited by the availability of whatever plant need is scarcest (76J1). This explains, for example, why fertilizer is more effective in an irrigation system than elsewhere. It is not known whether Dyson considered this saturation effect when he stated that a doubling of the rate of chemical fertilizer application is needed by 2025. If not, a lot more fertilizer than a doubling would be required.
  Doubling the rate of consumption of chemical fertilizers would carry high risks of damaging temperate soil chemistries, surface waters and ground waters. (See Part [A3] for details.) This is especially true in a world where the supply of organic fertilizer (manure) (needed to compensate for some, but not all, of the harmful effects of chemical fertilizers) is either negligible or shrinking (such as the US). Much of the developing world must use manure and crop residues for cooking, and the newer portion of the developed world is getting away from mixed agriculture [raising both livestock and crops] and increasingly raising livestock in feedlots or in CAFOs [concentrated animal feeding operations] making it expensive to haul manure to croplands. This is especially true in the vast North American plains that grow much of the world's wheat exports, and where soil organic matter content has dropped 50% in the past century and where salinization is becoming a problem (84S2) as is also the case in Australia's wheat fields.
  Since the 1970s, extensive leaching of fertilizer-produced nitrate from soils into surface water and groundwater has become an issue in almost all industrial countries (01O1). In large areas of the EU, for example, nitrate concentrations are near to, or exceed, the maximum permitted concentration of 50 mg per liter or 50 ppm (parts per million) (03N1). This nitrate poses serious risks to human health (99U2). It also contributes to eutrophication of rivers, lakes and coastal waters, endangering fisheries. Substituting organic fertilizer for chemical fertilizer does not improve the nitrate situation. In an environment where fertilizer application rates are already pushing against the limits posed by legal constraints on nitrate contents in surface and ground water, it seems doubtful that a doubling of fertilizer application rates could be tolerated. Since the early 1990s an increasing number of countries have been introducing economic measures in the form of pollution taxes on chemical fertilizers (03N1). (See more details in Part [A3] above.)
  In sub-Saharan Africa, fertilizer application rates are extremely low, so the above-mention problems do not exist there. But these low rates reflect the fact that the cost of chemical fertilizers in Africa is about 60 times that in the EU (in labor units). Telling Africans that they should double their rates of chemical fertilizer applications seems unlikely to produce the desired result. They have known that for decades. (See Part [A2a] above for an analysis of this problem, and the solution,)
• Per-capita irrigation expansion rates are now small fractions of what they were during 1961-1998 for numerous reasons that would suggest that the trend will continue well into the future. Also there are good reasons for believing that major reallocations of irrigation water to urban uses will occur at an increasing rate in the decades to come. Furthermore, this will come at a time of (a) increasing rates of shrinkage of aquifers, (b) increasing rates of abandonment of irrigation systems due to salinization and water-logging, and (c) rapid increases in the staggering external debt of developing nations, making the financing of irrigation systems increasingly difficult and (d) rapidly shrinking dam backwater capacity per capita as a result of sedimentation of dam backwaters, population growth, and reduced rates of dam construction due to lack of suitable sites and staggering external debts of developing nations. In addition, the glacier problem noted above is likely to shrink, rather than increase, irrigated area. (See Chapter 4 on irrigation and freshwater supply issues.). In addition, the politics of irrigation are especially discouraging. Governments worldwide heavily subsidize water supplies for irrigation systems. Typically on the order of 80-90% of the cost of supplying water is government-funded. The result is that only about 1% of the world's irrigation systems use drip irrigation or micro-irrigation. The net result is massive amounts of water being wasted, and far greater problems with salinization of irrigated lands - salinization that would not have occurred had the irrigation been done by drip- or micro-irrigation.
• The Green Revolution is now approaching close to its theoretical upper limits. The miracle strains of grains that were developed in the 1950s increased "harvest indices" from around 0.2 to around 0.5 (close to the theoretical limit of 0.55-0.6). The "Green Revolution" has been over for some decades. Today's genetic manipulations are aimed only at developing resistance to genetically improved pests that threaten the previous editions of miracle strains of grain. It is far from clear that this post-green-revolution genetic manipulations will be able to stay ahead of genetic improvements in pests that occur by natural selection.
• Ever-increasing tonnages and potencies-per-ton of pesticides have never been able to reduce crop losses to pests. Pesticides are, however, now posing ever-increasing risks to human health. Unfortunately natural selection processes in humans don't work nearly as well as on pests. This is because sexual maturity is reached over a much shorter time frame in pests than in humans.

The FAO Analysis of 2003
The most serious model of world food trends with an estimate of future trends from 1998 out to 2030 was published by the FAO (03B1). It updated its 1995 forecast (95A2). It too uses extrapolations of past trends to predict future trends, and ignores dozens of sustainability constraints described in this document. It produces the same basic conclusions as Dyson's analysis, i.e. that the world's food needs out to 2030 could be met. The 2003 model's estimate of future trends notes that, in the 32-years from 1997/99-2030, the world could increase annual production of cereals (including rice in milled form) by nearly another billion tonnes (03A1) i.e. by roughly 50%. This statement was made in 2003 when there was no awareness of (1) the huge increases in demand for (and prices of) commodities of all categories required by India and China to fuel their economic expansion, (2) the major increases in demand for (and prices of) grain, sugar, palm oil and soy beans for use in production of "biofuels" and (3) the global-scale shrinkage of the worlds glaciers that put the supplies of continuously flowing freshwater of three billion people at risk. So any revised forecast is virtually certain to require a cereal production growth during these 32 years of well over 50% to match food production with human needs.

The FAO projection also expects irrigation water withdrawals in developing nations to grow by 14% during 1998 to 2030 from 2128 km³/ year to 2420 km³/ year. It also expects developing nations to increase harvested irrigated area during 1998 to 2030 by 400,000 km², from 2.02 million km² to 2.42 million km². (Table 4.8 in Ref. (03B1)). The percentage difference between projected harvest-area growth and irrigation-water withdrawal growth is explained by an anticipated increase in average irrigation-water-use-efficiency from 38% to 42%. Why irrigation-water-use efficiency should be expected to increase when irrigation water supplies are so heavily subsidized virtually worldwide was not made clear. The FAO's projected expansion of irrigated land by 400,000 km² (during 1998-2030) is assumed to be an increase in net terms. This means that it assumes that losses of existing irrigated land resulting from, e.g., water shortages or degradation because of salinization, will be compensated through rehabilitation or substitution by new areas for those lost. This seems far-fetched. In this authors extensive review of the global literature on irrigated land degradation I have never encountered any document referring to any rehabilitation of abandoned irrigation systems. Irrigation systems that are destroyed by salinization and waterlogging apparently remain abandoned essentially forever. This is probably because the water needed to rehabilitate the land does not produce any near-term crops. Regions where irrigated land is abandoned would appear to be regions that cannot afford to expend water without expecting immediate returns in terms of food production. The various estimates in the literature of the global rate of irrigated land abandoned give on the order of 10,000 to 20,000 km²/ year, i.e. 320,000 to 640,000 km² in a 32-year period. Such an abandonment rate would essentially negate the FAO's anticipated irrigated area growth of 400,000 km² during the 32 years from 1998 to 2030.

• In the late 1990s, at least 400 million people lived in regions with severe water shortages. By 2050, this number is expected to be 4 billion. Thus large-scale reallocations of irrigation water to municipal- and industrial uses are virtually certain in coming decades. (Urban consumption of water is growing several times faster that human population growth, and urban users have the political and economic power to reallocate irrigation water to urban uses.)
• Irrigation is the primary reason why so many of the world's major rivers no longer reach the oceans during at least parts of the year. It is also the primary reason why the number of lakes and the sizes of inland seas are shrinking so rapidly, and why the number of endangered lakes is now so large as to pose a threat to up to one billion people (01A1).
• The International Water Management Institute (a CGIAR laboratory in Sri Lanka) projects that by 2025 as many as 39 countries - including northern China, eastern India, and much of Africa - will be forced to reduce irrigation rather than expand it due to a lack of water.
• The FAO (in a different document) said that two-thirds of the world's population could be threatened by water shortages by 2025. Today 1.2 billion people live in areas with insufficient water. An additional 0.5 billion could soon face shortages.
• The Director General of International Irrigation Management Institute believes that annual losses in irrigated areas (typically abandonment due to salinization, waterlogging, or water reallocation to urban areas) may now exceed annual gains.
• Bangladesh's Inland Water Transport Authority says 80% of Bangladesh's 235 rivers are drying up.
• The number of Indian villages without any water source increased from 750 in 1985 to 65,000 in 1996.
• By 2025, water scarcity is expected to cause annual global losses of 350 million metric tons of food production - slightly more than the entire current US grain crop.

Intensification and yield growth are subject to limits for reasons of plant physiology and because of environmental stresses associated with intensification (01M1) (03B4).

The "arable land expansion" envisioned by the FAO appears to be referring mainly to converting additional areas tropical rainforests to croplands. The projected area involved is 1.2 million km² (from 9.56 million km² in 1998 to 10.76 million km² in 2030) (03B3). The bulk of this projected expansion is expected to take place in sub-Saharan Africa (600,000 km²), Latin America (410,000 km²) and East Asia, excluding China (140,000 km²). This can now be done on low-productivity tropical soils by producing legume crops such as soybeans in rotation with other crops using large doses of chemical fertilizers and limestone. (See Section [A7c] on Brazil's Cerrado.) (Chemical fertilizer consumption in developing countries is projected to increase from 85 million tonnes in 1997/99 to 120 million tonnes in 2030. This translates to a global increase from 138 to 188 million tonnes in 2030. Chemical fertilizer use intensity in developing countries is projected to grow from 89 kg/ ha in 1997/99 to 111 kg/ ha in 2030) There are grave concerns worldwide over losing the remainder of the world's tropical forests to the production of soybeans for export to China and to the production of soy- and palm-oil-based biofuels. The world's tropical rainforests are already badly over-populated with shifting cultivators. (See Section [G].) Also illegal timber harvesting is already taking a heavy toll on the world's tropical rainforests. It is far from clear that sacrificing the world's wood productivity in order to achieve greater food productivity or biofuels productivity is a sound long-term strategy. In many parts of the developing world, urban people pay a significant fraction of their meager incomes to purchase wood or charcoal hauled in from distant forests. Section [D] gives a compelling case for the contention that the world's supply of undeveloped arable land is far smaller than aerial surveys would indicate. Perhaps the reason why tropical rainforests probable are the main source of undeveloped arable land is that tropical soils are usually extremely low in productivity, and only recently has it been found that the combination of rotating legume crops with other crops in combination with lots of chemical fertilizer and lime are able to greatly increase cropland productivities. The FAO's strategy of using "intensification of crop production in the form of higher yields" to achieve greater food productivity in the developing world probably also refers to the tropical rainforest strategy just described. If the strategy refers to increased consumption of chemical fertilizer elsewhere in the developing world, one would have to question why this has not already been done in order to reduce the financial burden of agricultural trade deficits. In Sub-Saharan Africa there are compelling reasons why this has not already been done, and probably will not be done until some more fundamental issues are addressed. (See Section [A2]) As the global price of natural gas increases, and as the "informal" economy becomes an ever-larger fraction of the developing world's overall economy, it would seem more likely that the developing world's consumption of chemical fertilizer will decrease rather than increase in the next few decades out to 2030.

The IFPRI's IMPACT model
Another model of world food trends was done by the International Food Policy Research Institute (IFPRI) (03R1). Its "IMPACT" model (02R1). It predicted that, between 1997 and 2050, cereal production would increase by 71% and production of meats would increase by 131% (03R1). The IMPACT model is based essentially of extrapolating existing trends from around 1960 to the 1990s when chemical fertilizer consumption was expanding rapidly, the development of large irrigation systems was expanding rapidly, and the "Green Revolution" was producing huge increases in grain-land productivity. None of these three processes are occurring today and all three processes are at, or approaching, their limits as described elsewhere in this document. So, again, it is not clear that it is legitimate to extrapolate these three trends for another five decades.

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• Shifting cultivation can support 10 people/ km² (84G1) (World Bank data).
• Another source suggests that, though conditions vary widely, shifting cultivation can only support about 7 people/ km² (76E1).
• Another source contends that shifting cultivation can support 5-10 people/ km² with a 20-year fallow period (Ref. 4 of Ref. (84P1)).
• Shifting cultivation in tropical rainforest can be stable (1-3 years of cultivation followed by 10-30 years of fallow) only for population densities of under 8 people/ km² (Ref. 14 of Ref. (82B1)).

Limitations of this nature could explain the demise of the ancient Mayan empire in Central America (56B2). Ref. 10 of Ref. (84G1) describes a successful procedure for using poor tropical soils for agriculture, but heavy, skilled applications of (chemical) fertilizer and high crop prices are required. In recent years it has been found that legume crops, such as soybeans, can be grown on poor soils of tropical rainforests with heavy applications of chemical fertilizers, particularly in Brazil. The net result of this is liable to be a huge reduction in the global biomass inventory and growing scarcity of tropical wood supplies.

• Shifting cultivation cycles in Madagascar have been reduced from an average of 15 years to 3 years (89K2).
• The average shifting-cultivation cycle in Bangladesh has decreased from 10 years to 3 years (80R1).
• The average fallow period for shifting cultivation in India is 4.3-5.9 years (91J1).
• Shifting cultivation in some tropical rainforest areas of Sarawak in Malaysia has fallow periods as short as 3 years (91H4).

• After removal of rainforest forest cover in western Nigeria, maize yields drop from 500 to 150 tonnes/ km²/ year after 2 years of cropping, and drop to 50 tonnes/ km²/ year after 4 years (Refs. 24, 37 of Ref. (88L1)).

A carrying capacity of 10 people/ km² implies a carrying capacity of the 3 million km² of land under shifting cultivation of 30 million people. (Other data indicate a tropical rainforest area affected by shifting cultivation of 94,700 km² (FAO, 1981 Landsat data) (Area burned annually is much less.) (91J1).) Compare this to the 1980 population of shifting cultivators of 250 million (80U3). (The population 27 years later could easily be double that.) If all tropical forestland with poor soil (90% of 17.6 million km² of open- plus closed forest) were devoted to shifting cultivation, the carrying capacity of this land would be 158 million people. This is 63% of the 1980 population of shifting cultivators, and a far smaller percentage of today's population of shifting cultivators. Eventually the combination of falling productivity, population growth, and conversions of tropical forest to grazing lands and forest plantations forces ever increasing numbers of shifting cultivators to migrate to the slums ringing most large urban areas in tropical climates. There is clearly nothing that is sustainable in the modern-day process of shifting cultivation. In theory, shifting cultivation can be perfectly sustainable. The problem is not with the theory but with the ever-growing populations of people imposing ever-increasing pressures on the land to produce. Ever-increasing degrees of urbanization in the developing world probably will not help, since the overwhelming bulk of these farmers-turned-city-people will be joining the "informal" economy in which just survival is a real challenge (08S1).

An ominous new threat to tropical rainforests and to the shifting cultivators who live there is the increasing use of "biofuels." The oil palm is a highly efficient producer of vegetable oil. An acre of oil palm yields as much palm oil as 8 acres of soybeans, the main rival for oil palm. Rapeseed (canola oil) is a distant third (in productivity per acre). Only sugar cane comes close to rivaling oil palms in terms of calories of human food per acre. Palm oil prices jumped 70% in 2007. As a result, vast areas of tropical rainforests are being converted to oil palm plantations and to soybean farms (08B1).

It is interesting to note that, in spite of the obvious importance of the above issues to the developing world, no developing country has in place a national monitoring system for soil quality, so researchers must use a variety of crude and approximate procedures for evaluating the time- and spatial-dependence of soil quality (99S2).

For some reason cornucopian writers (67K1) (81S3) (87W4) (01L1) (98D1) (03B2) remain oblivious to all of these issues and have even persuaded the public at large to see global agriculture in the same way as they see it. Ultimately, if not currently, there is a price to be paid for all of this denial and self-delusion.

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