CHAPTER 1 ~ SUSTAINABILITY OF THE OUTPUTS OF THE WORLD'S CROPLANDS ~
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 website.
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Section [A] ~ ELEMENTS OF NON-SUSTAINABILITY ~
Part [A1] ~ Overview ~
The broader issue of the sustainability of the productivity of soils and croplands revolves around a variety of issues. The main ones are:
In theory, most of these degradation mechanisms can be corrected in a matter of years or decades by fallowing, although bare-land fallowing usually results in serious soil erosion. In practice, however, all of these mechanisms reflect ever-increasing pressures on the land, typically a result of population growth, so fallowing becomes increasingly unaffordable, and as a result fallow periods worldwide tend to shrink over time. This adds an increasing element of non-sustainability to the productivity of the world's croplands. The net result of the above degradation mechanisms is a loss of roughly 100,000 km2 of irrigated and non-irrigated croplands per year - a loss rate that can, in theory, be compensated for (for about 1.5 centuries) by developing as-yet undeveloped arable lands (lands declared arable by analyses involving aerial photography). In practice however there are considerable doubts as to whether this land actually exists in usable form. (See Section [D] .) Much evidence suggests that it does not. There are questions as to how much of this undeveloped arable land is actually:
Data on the above cropland- and soil degradation mechanisms are provided in this Chapter 1 and in Chapter 4 of this sustainability study. Lots of additional data are provided in the document "Topsoil Loss - Causes, Effects and Implications: A Global Perspective" and "Irrigated Lands Degradation: A Global Perspective" found elsewhere on this website.
Losses of croplands and their soils through urbanization, degradation-induced abandonment, salinization and waterlogging are global phenomena, but they are more common in developing nations. New croplands are increasingly being created in regions of low precipitation and therefore have soils with low organic matter content. Such croplands have low productivities due both to low precipitation rates and low soil organic matter contents. They also have low resistance to wind erosion due to low soil organic matter contents, and they also face high risks of prolonged droughts. The short-lived US "dust bowl" in the 1930s and the former Soviet Union's "Great Lands" project in 1954-1962 (96G2) are among the more colossal examples. If there were plenty of undeveloped arable lands as some contend, why would anyone invest in such low profitability -high-risk ventures as semi-arid croplands? These lands should remain as grasslands where the possibilities for sustainable production are higher, though by no means assured. (See Chapter 3) The trend toward creating croplands in increasingly dry climates explain the rapid rates of increase (in number and magnitude) of both intercontinental dust storms and expanding deserts. Data on the increasing frequency and magnitude of these events is found in this document and in "Topsoil Loss: Causes, Effects and Implications - A Global Perspective" on this website.
New croplands, particularly in developing nations, are also increasingly being created on thin, rocky soils on steep hillsides where sustainability is rarely achieved, and abandonment is probable within a matter of a few decades. The driving forces for this trend are (1) population growth, (2) the lack of better quality undeveloped arable land, and (3) conversion of labor-intensive agriculture to capital-intensive agriculture (which require far less labor per unit area of land). The most common result of abandonment is the migration of ex-farmers to huge rings of wretched slums that surround most of the large urban areas of the developing world. There they usually join the rapidly growing "informal" economy where their survival is a challenge and where their world is one of growing social, political, and economic instability. These instabilities make the financial capital needed to correct the agricultural problems less safe and less available - causing further rounds of even greater instabilities and financial capital scarcity. Remember that most developing nations derive typically on the order of 70% of their GDP from agriculture, so the rural-urban migrations alluded to here represent a human migration of truly epic proportions. All this could hardly be understood if the supply of undeveloped arable land were even a fraction of the huge area that is alleged to exist. The non-sustainable agriculture, mass migrations, wretchedness, hunger, hope-deprivation, informal economies, and social-, political- and economic instabilities could all be largely eliminated with a modest investment in family planning. (See Ref. (06S1) and (07S1) on this website.)
Part [A2] ~ Sustainability Problems in Africa's Croplands - Some Case Studies ~
[A2a] ~Cropland Sustainability Problems in Sub-Saharan Africa,
[A2b] ~Cropland Mismanagement Problems in Ethiopia,
[A2c] ~Cropland Productivity vs. Human Population in Rwanda,
[A2d] ~Sustainability Issues in Burkina Faso,
[A2e] ~Cropland Sustainability in Zimbabwe
Consider:
Considerations (3) through (8) are easily traced back to Considerations (1) and (2) above. Thus the sustainability of Africa's food- and wood-production systems is almost certainly the world's worst. One must be careful, however, not to conclude that Africa is necessarily over-populated. If Africa's population growth rates (NOT population) could be reduced, Considerations (3) through (7) would be far simpler to deal with as a result of financial capital becoming far less scarce (06S1). One should also not be too quick to conclude that Africa's problems are simply a matter of an intellectually inferior populace and a bunch of dumb farmers. Before doing that, read the remainder of this Part [A2]. In fact, there is at least one region of Sub-Saharan Africa where cultures, farmers and agricultural practices are on a level comparable to those in Northern Europe - and superior to essentially everyone else. (See "Sustainability Issues in Burkina Faso" below.)
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Sub-Part [A2a] ~ Cropland Sustainability Problems in Sub-Saharan Africa ~
Sub-Saharan Africa provides an insightful case study for any analysis of the undeveloped potential of inorganic (chemical) fertilizer. African soils are, by geology and by climate (tropical), poor in terms of both organic matter and chemical nutrients. Yet, in the 1990s, inorganic fertilizer consumption in China was 240 kg./ ha/ year, 110 in India, but about 8 in Sub-Saharan Africa. Some Sub-Saharan African cropland soils have nutrient losses exceeding 60 kg/ ha/ year of nitrogen, phosphorus and potassium (02F1). So the region would appear to be a prime candidate for increasing inorganic fertilizer consumption. Inorganic fertilizer prices in Sub-Saharan Africa are 6 times greater than in Asia, the EU and North America. (On the basis of hours of labor required to purchase a tonne of inorganic fertilizer, the cost to Africans is 60 times that in the EU.) Infrastructure (mainly roads) is the cause of much of the price problem. An entrepreneur in Central Africa pays more than 3 times what his Chinese counterpart pays to transport a container a given distance (06W1). Much of Africa has less than 10% of the road density of India or China (02F1) and road quality is low. These infrastructure problems result from a shortage of financial capital that are due to Sub-Saharan Africa's high population growth rates (2.5%/ year - second-highest in the world) and the cost of infrastructure expansion required to accommodate this population growth (06S2).
Sub-Saharan African farm soils are also poor in organic matter, but farmers cannot raise much livestock (manure source) because of population pressures on the land. Also, instead of putting manure and crop residues into cropland soils, Africans must burn them for fuel and cooking - yet another consequence of population pressures on the land (02F1). The importance of soil organic matter in determining the fertility and numerous other characteristics of soil is described in Section [B5] of this chapter. For these reasons, low organic matter contents worsen the economics of inorganic (chemical) fertilizer consumption and irrigation (02F1).
So, in theory, there is much untapped potential for inorganic (chemical) fertilizers in Sub-Saharan Africa. However the reason it remains untapped is high population growth rates that require huge amounts of financial capital to fund the infrastructure growth required to accommodate population growth. The financial capital needed for building the roads that could make imported chemical fertilizer affordable is but one of many unfilled needs for financial capital. According to Norman E. Borlaug of Green Revolution fame, Africa's grain productivity could be doubled or tripled in three years (02K1). 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). These people ignore the fact that the chemical fertilizer required for this is simply impossible to afford until population growth rates drop, creating the financial capital needed to build better transportation infrastructure. Africa's present food deficit, plus its expected population doubling over the next 3-4 decades, demands at least a tripling of grain production. One third of the 590 million people in Sub-Saharan Africa are chronically under-nourished. Foreign food donations, even today, cover only 20% of Africa's food deficits (02K1). The rapidly increasing price of grain due to increases in fossil fuel prices and reallocation of land to crops for ethanol are dramatically increasing the price Africans must pay for food imports. The World Bank has warned of possible food riots in Africa. Sub-Saharan Africa's ever-growing external debt and extreme shortage of financial capital for solving infrastructure problems suggest that comments by Borlaug, Higgins and Kassam (and even the FAO's projections (03B3) out to 2030 of a 61% increase in food production) on Sub-Saharan Africa's future grain production are likely to remain wishful thinking until more fundamental problems are solved. If chemical fertilizer prices in the US were to rise by a factor of 60 to be comparable to the situation in Africa, it seems highly likely that US consumption of chemical fertilizers (with their low marginal productivities) would drop significantly in order to rebalance marginal costs against marginal productivities. Also hunger in the US would probably increase significantly.
Go to this Chapter's Table of Contents ~ Go to Top of Part [A2] ~
Sub-Part [A2b] ~ Cropland Mismanagement Problems in Ethiopia (03T1) ~
Admittedly, Ethiopia is an environmental basket case in terms of soil erosion, overgrazing and deforestation. Rapid population growth and declining rainfall also add to Ethiopia's increasingly frequent bouts of hunger and starvation. But even then, Ethiopia offers an example of the extreme economic hardship that can result from bad advice from international lenders. (For other examples see Ref. (06S2).) These external influences encouraged huge increases in food production through the use of genetically improved grains, while discouraging or ignoring government activities (subsidies, tariffs, infrastructure, finance, market development, etc.) in all the other aspects of the overall agricultural system. High population growth rates also left Ethiopia starved for the financial capital needed for overall agricultural system development, in particular transportation infrastructure. As a result, in good crop years, local crop prices collapse due to infrastructural inadequacies. Farmers are then unable to cover production costs and are unable to borrow, so they go bankrupt. In drought years, farmers meet the same fate due to crop failures. The result has been huge areas of croplands lying idle while millions of Ethiopians starve. Countries like Viet Nam and China lavished government attention on their total agriculture systems (contrary to the fundamental rules of globalization that oppose subsidies) and so avoided Ethiopia's fate (06S2).
Ethiopia's food- and cropland problems are compounded by the fact that its rains comes out of the west, across the southern edge of the Sahara Desert where there has been much overgrazing. Since rain falls and is re-evaporated about five times on its way east across Africa from the Atlantic Ocean, the decreasing vegetation ground cover reduced the amount of re-evaporation, hence the declining rainfalls and increased hunger and armed conflict in Ethiopia, Sudan and the surrounding area. (In Sudan, immediately west of Ethiopia, an estimated 50 to 200 km southward shift of the boundary between semi-desert and desert has occurred since rainfall- and vegetation records were first kept in the 1930s (07U1).)
Go to this Chapter's Table of Contents ~ Go to Top of Part [A2]
Sub-Part [A2c] ~ Cropland Productivity vs. Human Population in Rwanda ~
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 with far better soils, far more chemical- and organic 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 on highly erodible, rocky hillsides. Rwandans could not afford fertilizer imports for reasons described above (02F1). 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).
No Rwandan government leadership, no matter how competent, could possibly have done anything under such circumstances to eliminate these genocides. Cornucopians usually argue that the developing world's problems are purely a matter of bad government. In reality, bad government is not a cause of the developing world's other more fundamental problems, but is a consequence of them (06S1). Rwanda's problems are clearly beyond problems of population growth and are clearly a simple matter of overpopulation: 0.07 acre/ capita of low-grade tropical soil with much of it on rocky hillsides could probably not feed Rwanda's population regardless of how sophisticated the agriculture was. The resultant social, economic and political instabilities and lack of infrastructure could not attract foreign direct investment needed for a manufacturing economy. Nations like Korea, Japan, Taiwan, Hong Kong and Singapore were probably staring down the same potential problems some decades ago. This caused them to invest heavily in family planning programs. This enabled them to generate the financial capital needed to create human capital and infrastructure, which in turn produced a manufacturing economy that enabled them to import or manufacture chemical fertilizers, develop irrigation systems, pursue the Green Revolution, import large quantities of food and wood, and export manufactured goods of a high level of technological sophistication. Why Rwanda chose not to pursue the same course of action is not known. However it is known that the predominant religion in Rwanda opposes modern means of contraception.
Go to this Chapter's Table of Contents ~ Go to top of Part [A2]
Sub-Part [A2d] ~ Sustainability Issues in Burkina Faso ~
SUSTAINABLE AGRICULTURE IN BURKINA FASO: A BY-PRODUCT OF AN AMAZING CULTURE ~
Their Final Decades? or a Recovery Model for the Rest of Africa?
A fascinating document (01M2) has reported results of four decades of research on the productivity of soils in Burkina Faso located in the Sahel region of West Africa. The purpose was to see how productivities change with time (1960-1998 - during which time the human population more than doubled). This research was an attempt to check numerous studies that suggested that soils in the Sahel region, and in sub-Saharan Africa as a whole, were degrading over time, soil organic matter was being depleted, and soil nutrients were being "mined." It was found that Burkina Faso's soil productivities actually increased during those four-decades, almost as rapidly as the population increased, despite a slight gradual decline in rainfall during the four-decade span of the research. Also, agricultural productivity per unit of cultivated area mainly correlated with long-term average rainfall (environment) and was barely related to rural population density (pressure on resources) or to animal traction (technology). Another research effort attempted to determine how soil chemistry changed during a three-decade span (a period during which the population nearly tripled in the region where the soil chemistry was measured). In 14 of the 20 comparison pairs, no significant degradation in soil chemistry was observed. Additional research was undertaken to compare soil chemistries in two areas in which population densities were much different (13/ km2 vs. 50/ km2). No significant differences were found in terms of organic matter, total nitrogen, total phosphorous and available potassium. This too suggests that local land management practices are sustainable. Another research effort examined how soil fertility (organic matter, Nitrogen, Phosphorous, and Potassium) varied from intensely cultivated fields to uncultivated areas. It was found that organic matter changed very little, while N, P, and K generally decreased as one went from the intensely cultivated fields to the less-intensely cultivated fields to the uncultivated fields. This too suggests that human pressures on the land have not degraded Burkina Faso's cropland and hence that local cropland management practices are sustainable, contrary to what appears to be the case throughout the rest of Africa.
These results at first seem hard to understand, since numerous studies found that Africa's food production per capita has been decreasing in sub-Saharan Africa since the early 1970s and cropland soils tend to be degrading. Sub-Saharan Africa's consumption of chemical fertilizer is a tiny fraction of that anywhere else in the world (for reasons described elsewhere in this review of sustainability issues) (This is also the case in Burkina Faso except in the rice and maize fields producing for export - fields not involved in the above-mentioned research.) Also livestock manure and crop residues in much of sub-Saharan Africa must frequently be used for heating and cooking given the lack of fossil fuels and wood. Thus one can easily compute that sub-Saharan African farmers are "mining" soil nutrients. The authors of the study described here (01M2) drew the conclusions from their research that: (A) there is little supporting evidence of alleged widespread degradation of crop- and fallow land in Burkina Faso. This calls into question the widespread belief that low external inputs practices used by West African farmers are leading to region-wide land degradation processes, and (B) the skills of Sahelian farmers have been significantly under-estimated.
What is needed now is some way of rationalizing the huge differences between the results given above and the all-too-common observations of serious land degradation problems throughout sub-Saharan Africa. The notion expressed by the authors of the above study that the numerous experts involved in the other African land studies were a bit sloppy seems likely to be widely rejected without efforts to rationalize the differences. This rationalization is done below. It was aided by the analyses of Burkina Faso's culture and environment that were made by the authors of the above-mentioned study (01M2). (Mazzucato is an anthropologist and an economist; Niemiejer is an environmental geographer.) Burkina Faso is apparently an exporter of rice and maize. The rest of West Africa must import 40% of its rice needs. Because of the tripling of rice prices on the world market over the past few years there is danger of food riots in West Africa, according to the World Bank. (See Sub-Part [A4a] below.) Africa as a whole is a net importer of food. It is also dependent on food aid to a significant degree, meaning that it cannot afford to pay for all the food needed to avoid the hunger that is common throughout sub-Saharan Africa.
This suggests that human pressures on Burkina Faso's agriculture are significantly less than that in sub-Saharan Africa as a whole. This also suggests that human pressures on the land have not yet reached the point at which the all-too-common practices of sacrificing sustainability on the altar of near-term expediency have begun. Rainfall in Burkina Faso is about 80 cm./ year (01M2), meaning that Burkina Faso is somewhat more humid than the rest of the Sahel and West Africa. Farmers have shown excellent skills at water management, using stone bunds, grass strips, living hedges, mulching, selective clearing, and adapted plant spacings. Such sustainability-promoting practices would typically have been sacrificed on the altar of near-term productivity had human pressures on the land been intense. Deforestation in Burkina Faso is on-going at a significant rate, but it apparently has not yet reached the point where livestock manure and crop residues must be used for cooking rather than to fertilize croplands. Rates of cropland fallowing appear to still be quite reasonable, suggesting that human pressures on the land are not yet extreme. Livestock populations appear to increase in parallel with the rapid growth of human populations (doubling every four decades) and appear to be well managed. Obviously the rates of deforestation and livestock growth cannot continue indefinitely. At some point, the ability of the people to replenish the organic matter and other soil nutrients will diminish; soil chemistries will decline as human populations continue to grow, and the end of sustainability will have begun.
The obvious next question is to inquire why Burkina Faso has relatively low human pressures on the land relative to most or all of the rest of sub-Saharan Africa. After all, many parts of Africa receive far more rain than Burkina Faso, and yet their agriculture is badly degraded. One answer is that Burkina Faso's farmers demonstrate an extremely high level of knowledge and skill, as the Mazzucato-Niemiejer paper (01M2) show quite clearly, easily on a par with northern Europe. They would put American, Canadian and Australian farmers to shame. But the huge difference in the levels of education between Burkina Faso and the developed world makes the small difference in agricultural knowledge and skills baffling. (Some facets of Burkina Faso's culture suggest almost a primitive culture.) Obviously explaining Burkina Faso's success purely in terms of agricultural excellence begs the question. The real answer comes from a close inspection of the second half of the Mazzucato-Niemiejer paper that gets into the amazing culture of the Burkina Faso civilization. This culture might have been common in Africa in the period preceding the start of Africa's agricultural death spirals (declines of sustainability into a state characterized by hunger, wretchedness and armed conflict) that now engulf so many African nations. Burkina Faso's culture probably only persists because their agricultural death spiral has not yet begun, though it probably will begin in a matter of a few decades as the human population continues to double every four decades, deforestation becomes complete, and livestock populations can no longer keep up with human numbers (making it impossible for farmers to maintain the soil organic matter content in their croplands).
Burkina Faso is claimed to be one of the world's 14 poorest nations in terms of GDP. However the economy is mainly agricultural, and much production does not pass through any marketplace where it can be counted, so Burkina Faso is probably better off than GDP data would suggest. Burkina Faso uses a mix of currency and gifts as mediums of exchange, suggesting a quasi-primitive culture. There are no economic "safety nets;" no one gets anything for nothing. However, as a result of six types of brilliantly conceived "social networks," risks so common in agricultural economies are reduced to an absolute minimum. The "social networks" also make the utilization of labor, capital, land and other natural resources very efficient. This efficiency provides time for farmers to engage in labor-intensive soil- and water-conservation projects (that are common and well done), and to engage in commerce, allowing them to diversify their livelihoods, further reducing agriculture-related risks. Increased land-utilization efficiency enables them to extend fallow periods, which intense population pressures usually cause to be shortened. It is a capitalistic society, but as such it would have to be considered significantly more economically efficient than the capitalistic societies of the developed world. The key feature of social networks is the ability to avoid, in numerous ways, the "poverty trap" by reducing all manner of risks to an absolute minimum. When a farmer encounters a few years of bad weather, or other problems, a common tendency, worldwide, is to sacrifice agricultural sustainability on the altar of current production maximization. This can often lead to positive feedbacks that ultimately produce collapse into a situation marked by hunger; increasingly desperate struggles for survival needs, and then armed conflict. Risk minimization thus prolongs the lifetime of an economy based on sustainable agriculture. This probably explains why Burkina Faso has, so far, done better than African nations generally.
The role of Burkina Faso's central government appears to be minimal. Local governments are the source of leadership. This makes the concept of "social networks" viable. There is clearly an element of precariousness in the Burkina Faso culture. Reducing that precariousness by strengthening the central government would probably ruin everything. The "social networks" could not possibly survive in an environment of rapidly declining, non-sustainable agriculture, and a mix of hunger and armed conflicts so common in Africa. The loss of these networks would precipitate an even faster rate of decline. Globally there is a tendency to view African cultures as inherently inferior to those found elsewhere in the world. Could Africa's population growth rate and human stress upon the land be cut significantly, Burkina Faso's culture might be replicated, and the seeming inferiority of African culture would probably be seen as nothing more than an artifact of the inherent poverty of Africa's tropical soils. Africa's farmers might then be seen as second to none. The details surrounding the fascinating Burkina Faso culture, the effects of this culture on Burkina Faso's agriculture (and vice-versa), and their sustainability-oriented agricultural practices are too numerous to include here. Those interested should study the Mazzucato-Niemeijer paper (01M2). The second half of that paper contains the anthropological aspects of the interplay between culture and agriculture.
It is interesting to note that, in the FAO projection of global food productivity during the period 1998 to 2030 (03N1), the Mazzucato-Niemeijer paper was cited as evidence that the world's problems with agricultural land degradation are significantly over-rated. The unique situation that characterizes Burkina Faso as described above would suggest, however, that the lack of cropland soil degradation there is far from typical of the situation characterizing the remainder of the developing world or even of Africa.
Go to this Chapter's Table of Contents ~ Go to Top of Part [A2]
Sub-Part [A2e] ~ Cropland Sustainability in Zimbabwe ~
In the creation of Zimbabwe, white farmers initially got all the level, bottom-land farmlands, while black Africans got the steep, rocky hillsides to farm - where extreme erosion rates on low-grade, highly erodible, thin soils limit cropland lifetimes and force migration to the slums surrounding the urban areas where survival is a real challenge. This created a highly non-sustainable food-production system, at least for black Zimbabweans living on subsistence earnings and unable to afford to bid for food in the world marketplace. Considering Zimbabwe's high population growth rate, the bloody conflicts over croplands in recent years were easily predictable. And it is far from clear that any government, however capable, could have prevented the bloodletting. The result of this bloodshed was the takeover of previously white-owned farms by blacks that lacked the technical expertise and access to capital to manage such farms. The result was widespread famine in Zimbabwe -and social, economic, and political turmoil. A nearly identical problem occurred in the post-World-War-II Philippines. But it lead, in the 1980s, to groups like the Marxist New People's Army that threatened US interests (00N1). If there is so much potential (undeveloped) cropland in Africa or the Philippines as some would suggest, why are environmentally marginalized farmers unable to find anything other than steep, rocky, erosion-prone hillsides? All the wretchedness, bloodletting, and bad government could probably have been prevented by some proactive "brother's keeper" aid offering contraceptives and family-planning services.
Part [A3] ~ Could Chemical Fertilizers contribute significantly more to Global Cropland Productivity? ~
[A3a] ~ Marginal Productivities of Chemical Fertilizers in Developed Nations
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[A3b] ~ Marginal Productivities of Chemical Fertilizers in Developing Nations
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[A3c] ~ Side Effects of Chemical Fertilizers on Soil Properties
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[A3d] ~ Side Effects of Chemical Fertilizers on Other Elements of the Global Food Production System
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[A3e] ~ Side Effects of Chemical Fertilizers on Human Health
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Early in the 20th century Haber (in Germany) developed the basic process for converting the nitrogen in ammonia to an organic form that plants can use. World War II delayed the industrial-scale development of the process until the late 1940s, when low-cost "chemical" (inorganic) fertilizers were able to replace animal manure, crop residues and assorted organic waste products. The use of chemical fertilizers expanded 600% during the first 30 post-WWII years. It was the single most important factor in cropland productivity growth, and it made possible the "Green Revolution." It also enhanced the economics of irrigation sufficiently to cause the rapid creation of large-scale irrigation projects. These three developments were largely responsible for the doubling or tripling of the global rate of production of food and some organic fibers during the last four decades of the 20th century. One-third of the global increase in cereal production during the 1970s and 1980s has been attributed to increases in chemical fertilizer consumption (03B3). (This is not even counting the role of chemical fertilizers in the Green Revolution and in the development of large-scale irrigation projects.) It could also be argued that if Haber's process had been developed earlier (and the US had supplied Germany with the necessary ammonia), most or all of the economic wretchedness and social-, political- and military tumult of the first half of the 20th century might have been avoided. That half-century was, after all, a period when contraceptives and abortion were usually outlawed, population growth was rapid, and agricultural productivity was low, a dangerous mix according to environmental determinism theory.
One should not infer, however, that global cropland productivity can increase indefinitely simply by consuming ever-increasing amounts of chemical fertilizers. Neither should one infer that the "Green Revolution" and/or large-scale expansion of irrigation could continue indefinitely. The main reasons for the limitations of chemical fertilizers are:
Sub-Part [A3a] ~ Marginal Productivities of Chemical Fertilizers in Developed Nations ~
In the mid-19th century, Justus von Liebig formulated his "Law of the Minimum" (76J1) that states that plant growth is limited by the availability of whatever nutrient is scarcest. In other words, the marginal productivity of any plant requirement (water, sunlight, nutrients) decreases with increasing dose of that requirement. This explains, for example, why chemical fertilizer is more effective in an irrigation system than elsewhere. The marginal productivity of chemical fertilizer in the developed world is now a fraction of what it was some decades ago (91B1) (Ref. 71 of (97B3)). US farmers have discovered that there are optimal levels beyond which further applications of fertilizer are not cost-effective, and so are using less fertilizer in the mid-1990s than in the early 1980s. This trend is now also evident in Western Europe and in Japan (Ref. 71 of Ref. (97B3)). Some data on declining marginal productivities are given below.
Chemical fertilizer consumption dropped 23% during 1988-98 (98P2) due to elimination of fertilizer subsidies in India, China and the former USSR (94B4). If the marginal productivity of chemical fertilizers had been able to cover their marginal costs, it seems unlikely that elimination of government subsidies would have resulted in reduced consumption, or that subsidies would have been deemed necessary in the first place. This would suggest that the marginal productivity of chemical fertilizers had fallen in these nations to the point where it was not worth the unsubsidized price. As the price of chemical feed stocks (mainly natural gas), a key ingredient of chemical fertilizer, increases, the point of zero marginal economic return will come at lower doses of chemical fertilizer, and as food prices increase, the point of zero marginal economic return will come at higher doses of chemical fertilizer. This explains why farmers in some regions of sub-Saharan Africa use little or no chemical fertilizer. The price, in units of labor required to purchase a tonne of chemical fertilizer is on the order of 60 times the corresponding price in the EU. (See Part [A2] above.)
Sub-Part [A3b] ~ Marginal Productivities of Chemical Fertilizers in Developing Nations ~
If the marginal productivity of chemical fertilizers has fallen to, or nearly to, the point of zero marginal returns in the developed world, one must not extend this conclusion to the developing world without closer examination. Chemical fertilizer consumption per unit area of cropland in 1997 in developed countries was about 40% more than in developing countries (00W1). But the heavy usage of chemical fertilizers in the developed world comes, in no small part, from heavy European subsidies for chemical fertilizer consumption (98D1). Also, much of the consumption of chemical fertilizer is closely tied to use on "Green Revolution" crops. These were developed especially to make them amenable to higher doses of chemical fertilizer. In the developing world "Green Revolution" crops are limited to high base-status soil areas of tropical Asia and tropical America (18% of the tropics, and areas that are already intensively exploited (75S1)). So, even under optimal conditions, chemical fertilizer consumption per unit area of cropland in developing nations must be inherently less than in the developed world. Thus it should not be inferred that lower fertilizer consumption in developing nations means there is lots of potential for increasing fertilizer consumption in developing nations.
For all of the above reasons, the remaining justifiable potential for increasing chemical fertilizer consumption in the developing world must be well below 40%. Whatever the remaining justifiable percentage increase in inorganic fertilizer consumption in the developing world is, the percentage increase in food/ wood production to be expected from this extra fertilizer must be far less. This simply reflects the law of diminishing marginal returns and von Liebig's "Law of the Minimum." The conclusion from all of this is that it is far from clear that the developing world has a lot more potential for adding more chemical fertilizer. The exception to this is sub-Saharan Africa. They use extremely little chemical fertilizer (for reasons in Part [A2] above). Therefore they have lots of potential for increasing chemical fertilizer consumption. The problem is that they can't afford it. (See above.)
Sub-Part [A3c] ~ Side Effects of Chemical Fertilizers on Soil Properties ~
Some previously unanticipated (and damaging) side effects of chemical fertilizers are now being more broadly recognized. These show that simply adding more and more chemical fertilizer to cropland under conditions of low marginal productivity and increasing feed stock prices is increasingly unlikely to be economically justifiable, and could easily prove to be counterproductive.
Results similar to those found in Ref. (99U2) (See above) have been found in far more extensive studies (07K1). It is often perceived that chemical nitrogen fertilizers sequester soil organic carbon by increasing the input of crop residues. This perception is shown to be false, and the opposite is found to be true. After 40 years of synthetic (chemical) fertilization in which inputs of fertilizer nitrogen exceed grain (crop) nitrogen removal by 60 to 190%, a net decline occurred in soil organic carbon despite large amounts of residual organic carbon being incorporated into the soil (07K1). These findings implicate chemical (fertilizer) nitrogen in promoting the decomposition of crop residues and soil organic matter. The results are consistent with data from numerous cropping experiments involving synthetic nitrogen fertilization in the US Corn Belt and elsewhere (07K1).
Despite the use of forage legumes, many Midwestern US soils had suffered serious declines in both nitrogen content and soil organic matter by 1950, except in cases involving regular applications of manure. There are good reasons for being concerned that these declines could adversely affect both agricultural productivity and sustainability of cropland productivity because soil organic matter plays a key role in maintaining soil aggregation and aeration, hydraulic conductivity, water availability, cation-exchange, buffer capacity, and the supply of mineralizable nutrients (07K1). Numerous 15N-tracer studies have found that the nitrogen found in grain (crops) originates largely from soil nitrogen (the nitrogen stored in soil organic matter) rather than from the nitrogen supplied by chemical fertilizers (07K1). This means that the positive effects of chemical nitrogen fertilizers must ultimately be totally counteracted by the effects of chemical nitrogen fertilizers in reducing soil organic matter. (See Part [B5] for more details on soil organic matter.)
Sub-Part [A3d] ~ Side effects of chemical fertilizers on other elements of the global food production system ~
The common practice of applying chemical fertilizer nitrogen in ever increasing excesses relative to crop (grain) nitrogen also carries serious implications for atmospheric CO2 enrichment because soils represent the Earth's major surface-carbon reservoir. Mineralization of soil organic carbon to produce atmospheric CO2 is speeded up by chemical fertilizers, and this does double damage: (1) depleting soil organic matter and (2) increasing atmospheric CO2. Also, application of chemical fertilizers beyond crop nitrogen requirements contributes to anthropogenic production of N2O, a potent greenhouse gas, and a gas with adverse implications for stratospheric ozone. In addition, excessive chemical fertilizer nitrogen promotes NO3- pollution of surface water and ground water (07K1). Excessive chemical fertilizer nitrogen applications can be reduced or eliminated by extensive use of forage legumes and applications of livestock manure (as is done in "mixed agriculture" in Europe and Wisconsin) (07K1). ("Mixed agriculture" commonly refers to farms that produce both livestock and crops. This form of agriculture is most commonly practiced on smaller farms and is probably the most sustainable form of agriculture.)
Sub-Part [A3e] ~ Side effects of chemical fertilizers on human health ~
Excess chemical fertilizer runoffs also produce high concentrations of nitrates in surface- and ground water supplies that harm human health (cancer, "blue-baby" syndrome and other illnesses) (99U2). Note that both organic and chemical fertilizers contribute to nitrates in surface- and groundwater supplies. Thus is why nitrate levels in surface and ground waters in large areas of the EU often approach or exceed legal limits (50 ppm) based on health considerations (03N1). Since the 1970s extensive leaching of nitrate from soils into surface water and groundwater has become an issue in almost all industrial countries Ref.(OECD, 2001a) of Ref. (01O1).
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Part [A4] ~ Could Genetically Modified Plants Contribute Significantly More to Global Cropland Productivity?
[A4a] ~ Basic Issues
~
[A4b] ~ Could "New Rice for Africa" (Nericas) put life back into the dormant "Green Revolution?"
Sub-Part [A4a] ~ Basic Issues ~
The question here is whether more improvements in the genetic makeup of cereal grains (like those that occurred during the "Green Revolution") could make up for the soil productivity losses resulting from all those degradation processes listed at the top of this section - or even do anything more than maintain what we already have? Below are arguments that suggest that the answer is No.
Plant breeders have never been able to fundamentally alter the basic process of photosynthesis itself, i.e. to produce more plant mass without added water, fertilizer, etc. (97B3). Instead, the "Green Revolution" contributed to global food production by increasing the "Harvest Index," the fraction of plant photosynthate devoted to seed development (i.e. grain - roughly 80% of the food people eat). The "Harvest Index" for originally domesticated wheats was around 20%. The "Green Revolution" increased the Harvest Index for wheat, rice and corn to over 50%. Scientists see a physiological upper limit to the "Harvest Index" of around 60% (97B3) (93E1) or less (99M1). This suggests that further major improvements to global food supplies via genetic improvements are unlikely. This belief is supported by the fact that, after over 20 years of research, bio-technologists have not produced a single high-yield variety of wheat, rice or corn (97B3). Maximum rice yields have been the same for 30 years. Still, official projections from the World Bank, FAO, and IFPRI assume agricultural researchers can repeat the Green Revolution (99M1). This would require a Harvest Index of over 100% - far beyond the theoretical limit.
Weighing against whatever small potential for genetic improvements still exist are the negative side effects that are likely to decrease the probability of future genetic improvements. The number of varieties of food grains in common use is shrinking as a result of planting ever fewer genetically improved grain species. Reducing biodiversity increases vulnerability to pests. Also, farmers are now planting huge monocultures instead of practicing strip-cropping and crop rotation. This gives pests an even greater advantage. Since 1900, 75% of the genetic diversity of domestic agricultural crops has been lost (98H1). Without constant infusions of new genes, geneticists cannot continue to improve crops. Cultivars need to be reinvigorated about every decade in order to protect them against genetically improved pests that keep adapting by a process of natural selection to the changing genetic make-up of crops (98H1). The most effective way to do this is to interbreed domestic varieties with wild ones (98H1). This may be one reason why, despite major increases in pesticide-use in recent decades (both in terms of tonnage and in toxicity per ton), losses to pests have not decreased. (See Part [A5] ) Other reasons include an ever-increasing rate of introduction of exotic pest species as (a result of globalization of the world's economies), monocropping, and other ill-advised agricultural practices that largely reflect growing population pressures upon the land. The overall trend in genetics research for the past several decades appears to be away from high-yield species. The focus is shifting to damage control - developing new plant species with improved pest-resistances to replace previously developed plant species that have lost, or are losing, their resistance to genetically improved pests that keep evolving through natural selection.
The "genetically modified" crops one hears about during the past decade or two are almost entirely developments to increase pest resistance. These "modifications" were developed to counteract the genetic adaptations of pests to enable them to consume those "pest-resistant" plant species developed a decade or so earlier. So all that present-day "genetically modified" plants do is to keep one step ahead of "genetically modified" pests. Losses to pests have not decreased for some decades (See Part [A5] .) This suggests that expecting significant improvements in productivity from "genetically modified" plants is likely to produce nothing but disappointment. The objective now is to hang onto current productivities rather than advance the "Harvest Index" - the approach taken in the 1940s and 1950s when all those "miracle strains" of cereal grains were developed. There is no reason to believe this will ever change.
If we cannot develop genetically improved cereal grains of the sorts we developed back in the "Green Revolution" days of the 1940s and 1950s, perhaps we can expand the range of existing genetically improved cereal grains. Below we argue that this, too, is unlikely in all but a few instances.
Some undeveloped potential for genetic improvements to increase cereal grain productivity lies in the fact that not all grain crops now growing in developing nations are genetically improved. Across all developing countries, modern rice varieties were being grown on 74% of the planted area in 1991, modern wheat on 74% in 1994 ((98M2), p. 220 and about 70% of the world's corn in the early 1990s (00R1). Overall, it was estimated that 40% of all farmers in the developing world were using Green Revolution seeds by the early 1990s, with the greatest use found in Asia, followed by Latin America (00R1). Today's numbers would be expected to be significantly higher. However, 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 tropical soils) are already intensively exploited and have been so for some decades (75S1). It would seem therefore, that high-yielding, fertilizer-responsive crop varieties are planted on nearly croplands that are suitable (91B1).
Also note that the basic concept behind the "Green Revolution" is to make plants better able to utilize chemical fertilizers and organic fertilizers. In Africa, very little chemical fertilizer or organic fertilizer is used, so the Green Revolution is barely applicable to Africa. The reason why chemical fertilizers are so little used in Africa is because they cost 60 times more than they cost in the European Union (in units of hours of labor per tonne of chemical fertilizer). This is due mainly to the fact that Africa has a very poor transportation infrastructure. This, in turn, is due to Africa's high population growth rates, placing huge financial demands on the infrastructure growth needed to accommodate that population growth. In a region where the median earning is less that $2/ person/ day (00S1), this makes financial capital extremely scarce, thus Africa's bad transportation infrastructure (in terms of both miles of roads and quality of roads.) The reason why so little organic fertilizer is used on Africa's croplands is that the manure from livestock and crop residues must be used as fuel for cooking food, since fossil fuels are such an expensive luxury. The result of all this is that Africa's farmers are "mining" the nutrients like nitrogen, potassium and phosphorous from their cropland soils. This is certain to diminish the productivity of Africa's croplands over time. So if any small increases do occur in the extent of utilization of genetically improved crops, these increases are likely to be counteracted by the increasing poverty of Africa's soils - soils that were of very low quality even long before Man set foot in Africa. (Australia's soils are also very poor because they are very old, i.e. there weren't any ice ages or volcanic activity to renew them.)
The miracle that has fed us for a whole generation now was the "Green Revolution:" higher-yielding crops that enabled us to almost triple world food production between 1950-90 while increasing the area of farmland by no more than 10%. The global population more than doubled in that time, so we now live on less than half the land per person than our grandparents needed. That one-time miracle is over. Since the beginning of the 1990s, crop yields (per unit area) have essentially stopped rising (06D1).
Thus the question of whether the "Green Revolution" has yet to peak, has peaked, or has become counter-productive at its margins remains open. But it seems clear that the era of rapid productivity growth via genetic improvements is over, and has been over for at least several decades. The "Harvest Index" has hit up against its theoretical limit, or has come very close to it. To improve yields (production per unit area) in order to accommodate the 50% population growth expected by 2050 and compensate for the loss of croplands to urbanization, erosion, salinization, water-logging and other forms of degradation (total: about 0.1 million km2 out of a total global cropland inventory of about 15 million km2), (an)other process(es) will have to be found.
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Sub-Part [A4b] ~ Does "New Rice for Africa" (Nericas) put life back into the dormant "Green Revolution?"
In the late 1990s a new rice hybrid was bred to grow in the uplands of West Africa. It produces 50% more grain per unit area of cropland, matures 30-50 days earlier, has superior weed competitiveness, greater tolerance to soil acidity and iron toxicity, and has enhanced disease-, pest-, and drought-resistance (Ref. 36 of (03R1)). The website of the Africa Rice Center where the rice was developed does not verify the 50% productivity-enhancement figure. The new rice apparently does not increase the harvest index. Nor does it make the rice better able to make use of chemical fertilizers like the usual "Green Revolution" rice species do. Its claim to higher productivity is apparently a result of all the other improvements mentioned above. The increased pest resistance part of this productivity enhancement is only good for about a decade until genetically modified pests come along. Sub-Saharan Africa currently imports 40% of its rice needs, and rice demand doubles every 9 years or so. Taking the 50% productivity enhancement at its face value, the "New Rice for Africa" can handle only about 5 years of demand-growth before Sub-Saharan Africa is back to where it started. Clearly the development of "New Rice for Africa" is an impressive advancement. However it is also apparent that it will not have anywhere near the results that were achieved by the "Green Revolution" rice species of the 1940s and 1950s. It does not break through the theoretical "Harvest Index" barrier. The world's rice reserves are now (June 2007) at their lowest level since 1983-84. Also, rice prices are expected to double in the next few years, setting the stage for widespread food riots in West Africa (according to a warning from the World Bank (Ref. 36 of (03R1)). Nericas might postpone these food riots for a few years, but in the final analysis, this is all that Nericas has to offer.
The same problem that has plagued all of sub-Saharan Africa for decades - the lack of financial capital (07D1) - has severely limited the benefits Africans are able to derive from Nericas relative to its potential. High population growth rates create huge demands on capital to create the additional infrastructure that population growth demands. As a result:
Even a decade after Nericas was developed, it has spread to only 5% of the croplands of West Africa where it would be of value (07D1). This creates the added problem of Nericas cross-breeding with the more common types of rice each year, thereby reducing rice yields. To make matters worse, developed world aid for developing world agriculture has dropped over the past two decades (07D1).
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Part [A5] ~ Could More and Better Pesticides Sustainably Enhance Global Food Productivity? ~
In theory, one might postulate that the degradation in the world's cropland soils and the declining inventories of cropland soils could be compensated for by increasing the tonnage and potency of pesticides, thereby providing some semblance of sustainability to the world's food/ wood production systems. Unfortunately the available data indicate that this is not possible. It also seems unlikely that it will ever be possible. Some details of this reality are given below.
The share of harvest lost to pests remains largely the same as in 1950, despite much greater rates of application of pesticides and much more toxic pesticides (98Y1).
During 1945-89 in the US, insecticide applications increased 10-fold, but pre-harvest crop losses to insects nearly doubled (from 7% to 13% of the harvest in 1989) (96G1). This loss is probably in addition to the global post-harvest loss of over 20% of harvested food because of spoilage, spillage, and losses to rodents and insects (96G1). Mono-cropping, reductions in both strip cropping and crop rotation practices explains part of the higher rate of losses to pests (96G1). The decreasing genetic diversity of crops (a result of the "Green Revolution)" also aids pests and necessitates increased usage of pesticides. Ever-increasing rates of introduction of exotic pest species, a product of globalization, also tends to counteract the effects of increased pesticide use and toxicity. Also, the pesticides that are developed tend to be "non-specific" meaning that they often kill non-target organisms, including the natural enemies of targeted pests. Because of the disruption of natural enemies of pests, there have been resurgences of existing pests and outbreaks of new ones (03B4).
The overall focus in plant genetics research appears to have moved away from developing new, high productivity "miracle" (genetically enhanced) strains of cereal grains. The new focus appears to be that of developing new plant species with improved pest-resistances to replace previously developed plant species that are losing their resistance to genetically enhanced pests that keep evolving through natural selection. So far, genetically enhanced pests are winning or holding their own in the race with genetically enhanced plants. It is not clear that this will ever change, especially with all the help they keep getting from the ill-advised agricultural practices, the ever increasing rates of importation of exotic pest species, and the non-specificity of pesticides described above. Almost all economically significant pests are now resistant to at least one chemical pesticide (03B4).
The trend toward monoculture does not just promote crop losses to pests. It also causes yields 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).
If all of the above weren't frightening enough, it must be pointed out that as the potency (toxicity per ton) of pesticides increase, they also become more toxic to humans as well. Also, humans have a distinct disadvantage relative to smaller pests. Smaller pests can be genetically enhanced via natural selection in something on the order of a decade (about the same time as that required to develop an improved pesticide or a new pest-resistant plant specie). Humans, on the other hand require a vastly longer time to be genetically enhanced via natural selection. Much research has been done on the effects of residual pesticides on human health. As a result, government agencies have placed restrictions on the amount of residual pesticides that various food products can contain. But there are other ways that pesticide residues can make their way into human blood streams and livers. One other way is for agricultural workers and gardeners to come into direct physical contact with pesticides residing on plant surfaces. One effect on agricultural workers and gardeners is described below.
A study followed the health of 143,000 people since 1982 tried to pick out the factors that lead to diseases. People regularly exposed to pesticides were found to have a 70% higher incidence of Parkinson's disease. Gardeners who used such chemicals were as much at risk as farm workers. The findings support the idea that exposure to pesticides is a risk factor for Parkinson's disease (a brain disease that afflicts about 150,000 Britons, with nearly 10,000 new cases a year). Scientists have suspected a link between pesticides and Parkinson's since 1983 when Californian drug addicts were diagnosed with the disease after taking impure drugs. Since then, epidemiological studies have hinted at links but few studies have been large enough to extract meaningful data. The latest research is big enough to get around that problem but it raises new questions, especially as to which pesticide(s) might be causing this effect. In Britain 31,000 tons of pesticides are applied to gardens and farms each year. Many pesticides are designed to be toxic to pests' nervous systems, so a link between pesticides and Parkinson's disease in humans should not be surprising ("US: Study Reveals Pesticides Link to Parkinson's," The Times (6/25/06)). As application rates of pesticides continue to increase, and as pesticide potencies continue to increase, the effects of pesticides on human health can hardly do anything but increase also.
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Part [A6] ~ Could Some as-yet-Unknown Development(s) Contribute Significantly to Global Cropland Productivity? ~
Plants need water, nutrients, good genes and light for survival - little else. The water issue is within the irrigation issue. The nutrients issue is within the fertilizer issue. The genes issue is within the "green revolution" issue. All these issues have been analyzed above or elsewhere in this document and have all been found to offer little potential for contributing significantly to global cropland productivity on a scale needed to accommodate the 50% increase in global population by 2050 and also counteract the numerous degradation processes that threaten current productivities. Only light remains as a potential, not-yet-addressed source of food/ wood-productivity improvements. But this is not a variable that can be subject to much manipulation. Replacing the sun by electric light bulbs, as in hydroponics, is capable of producing only the most expensive foods (some fruits and vegetables, but not grains - 80% of human food supplies) and then only under excellent growing conditions. The notion of adding significantly to the total amount of light falling on 16 million km2 of croplands seems unrealistic, especially if we also have to create excellent growing conditions on all those millions of km2. Any argument that contends that a yet-to-be-developed technology could sustainably increase food supplies should begin by defining the unmet plant need that the new process is likely to serve. Since no un-addressed plant needs remain, it seems unlikely that other as-yet-unknown processes await development. A few possibilities, however remote, for developments that might contribute significantly to the productivity of the world's tropical croplands are described below.
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Part [A7] ~ Could typically low-fertility tropical soils be significantly increased on a large scale? ~
[A7a] ~Fundamental Problems, [A7b] ~Tropical Soil Chemistry, [A7c] ~The Cerrado Strategy, [A7d]~ "Terra-Preta" Soils ~
Sub-Part [A7a] ~ Fundamental Problems ~
Tropical soils are quite fertile in a closed cycle environment. For most tropical soils, that fertility resides in the plant life growing on these soils and in the decaying leaves, stems, branches, trunks, roots and fruit of dead plants. When you convert most tropical system to open-cycle environments, e.g. by harvesting fruits and vegetables, or removing grazing animals (e. g. beef cattle) or cutting and removing timber, soil fertilities degrade to a small fraction of what they were as closed systems. Fortunes have been lost by people trying to convert large plots of tropical land into croplands with fertilities similar to those in temperate climates. Garden plots of tropical shifting cultivators must be abandoned (fallowed) after several years of use and left unused (operated as a closed system) for several decades to allow soil fertilities to be restored. Most tropical grazing lands used for raising beef cattle etc. degrade to extremely low fertilities after 7-10 years and must then be fallowed, probably for several decades. This author does not know how long it takes for soil fertilities in forest plantations to degrade to very low values. It doubtlessly depends on the length of the timber-harvest cycle. Available data are weak.
Sub-Part [A7b] ~ Tropical Soil Chemistry ~
The basic problem is that the organic matter contents of most tropical soils are roughly a third of what they are in most temperate soils. (Organic matter contents of semi-arid or arid temperate soils are also very low - and so are their fertilities.) The useful forms of key soil nutrients (nitrogen, phosphorous, potassium, calcium, magnesium and other elements) are to be found associated with the soil organic matter. So with less soil organic matter these key nutrients get leached out into surface waters and ground waters draining the soil. Soil organic matter also increases the water-holding capacity of soils, increases their tilth, and provides numerous other benefits. (See Part [B5] for details.) The basic chemistry seems to be that there are two competing fundamental chemical reactions going on. One is the reaction of the organic matter of, say, a dead leaf with minerals, e.g. clay, to form organo-mineral complexes that are stable and long-lasting. The other chemical reaction is the "mineralization" of the organic matter in the dead leaf, e. g. carbon combining with oxygen to form CO2 that then leaves the soil, and potassium forming some non-organo-mineral compound that then leaches into the groundwater or surface water. The first of these two reactions makes the soil more fertile as a result of all those stable organo-metallic compounds remaining in the soil. The second chemical reaction contributes nothing to soil fertility since the reaction products leave the soil and go into the air, surface water, or ground water. Apparently the second chemical reaction occurs at a faster rate than the first chemical reaction at higher temperatures (typical of tropical climates), and at a slower rate at lower temperatures (typical of temperate climates). This apparently explains the high fertility of most temperate soils, and the low fertility of most tropical soils.
Sub-Part [A7c] ~ The Cerrado Strategy ~
Some developments over the past few decades in central Brazil have offered a glimmer of hope that a way to make tropical soils fertile might be found (07O1). Brazil's Cerrado region is a vast tropical savannah (semi-arid grassland) that covers 23% of Brazil in central Brazil. It was always thought that Cerrado soils were of low fertility typical of tropical soils. However, by rotating soybeans (a nitrogen-fixing legume) with other crops, and by adding lots of chemical fertilizers (plus limestone to reduce the soil's high acidity), crop yields can be greatly increased. E.g. rice yields were 740 kg./ha in 1974 vs. 2500 kg./ha in 2007. Corn yields have tripled in the Cerrado's richest soils. Soybeans add nitrogen and organic matter (via crop residues) to the soil, and the soybean crop residues apparently hold the nitrogen and perhaps other key nutrients in place, reducing the rate at which they are leached or mineralized out of the soil. Now the Cerrado yields soybeans, corn, sorghum, cotton, rice, beans and fresh produce. Sugar is limited to 10% of the area to avoid damaging the soil. (30% of Brazil's automobile fuel currently comes from sugar-cane-based ethanol.) Various genetically modified soybean species were developed by the Brazilian government to be compatible with the tropical heat and the low humidity of the Cerrado. Brazil has historically been a major exporter of only coffee and sugar. Today it is a world leader in sales of soy, beef, and orange juice (Of these, only soy is attributable to the Cerrado.) Grain output has doubled in one decade. Brazil's agriculture industry now accounts for 90% of Brazil's trade surplus of more than $40 billion/ year. There are drawbacks however. Native fruits that depended on acid soils have vanished from large areas. The Cerrado's sandy clay soil still has a low capability for holding organic wastes (typical behavior of tropical soils), so animal waste and chemical wastes wind up polluting water sources rather than enhancing soil fertilities (07O1). Many tropical soils also have a variety of serious problems with soil chemistry, so it is not clear how widely applicable the Cerrado strategy is, or whether it is sustainable over a many-decade time frame. This development is not applicable to sub-Saharan Africa because inadequate transportation infrastructure there makes chemical fertilizers too expensive. (Brazil has had an active family-planning program, so population growth rates are down significantly, so financial capital is more available for transportation infrastructure.)
Sub-Part [A7d] ~ "Terra Preta" Soils ~
A recent development with more potential than the Cerrado strategy for raising the productivity of tropical soils is being studied in Brazil (06G1). Throughout Amazonia have been found numerous patches, roughly 50 acres (20 ha) in size, of very fertile soil (called "terra preta" by people who extract the soil and sell it). These fertile patches are surrounded by typically infertile tropical soils. These fertile patches contain large amounts of charred wood ("char-wood"), nearly to the point of being charcoal. These bits of "char-wood" date back as far as 7000 years before the present. Food scraps, bones of small animals, and human excrement, had provided organic matter in these fertile soils. The charred wood buried in the soil probably came from cooking fires. Charcoal is extremely porous material full of tiny pores with lots of internal surface area. The current theory is that this huge amount of surface area provided locations for the formation of organo-mineral complexes. These are what is needed to keep soil organic matter and the nutrients in it from being mineralized (e.g. converted to CO2) or leached out of the soil into the groundwater. (Many soil clays have atomic-scale tunnels that serve the same purpose.) Research is now under way to find ways of creating 21st century copies of terra preta cheaply and in large quantities covering sizeable areas of land (06G1). Since all the ingredients are readily available, and labor is plentiful, the potential exists for significant changes in the fertility of tropical soils. Tropical grassland soils, where wood is scarce, such as the Cerrado, could not be converted to terra preta.
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Section [B] ~ BASIC DATA ~ [B1]~ Non-Categorized, [B2]~ Hunger- and Food Supply Issues, [B3]~ Fertilizer Issues, [B4]~ Cumulative Cropland Losses and Cropland Loss Rates, [B5]~ Organic Matter Issues,
Part [B1] ~ Non-Categorized Data ~
It has been estimated that, today, 83% of the world's free-ice lands are impacted, directly or indirectly, by humans (02S3). The area of ice-free land in the world is about 131 million km2. 83% of 131 is 109 million km2. But only about 90 million km2 are reasonably biologically productive. So this is saying that human impacts extend over the entire world's reasonably productive land - and then some.
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 high erodibility and low productivity.
Cropland Area Under No-Till in 1998-99, km2 (01D1).
|
US |
193,000 |
|
Brazil |
112,000 |
|
Argentina |
73,000 |
|
Canada |
41,000 |
|
Australia |
10,000 |
|
Paraguay |
8,000 |
|
Mexico |
5,000 |
|
Bolivia |
2,000 |
|
Others |
1,100 |
|
Total |
455,000 |
For perspective, total global cropland area is about 15,000,000 km2 so only about 3% of global cropland areas were under No-till during 1998-99.
During the 36-year period when world average grain yields more than doubled from 140 tonnes/ km2 in 1961/63 to 305 in 1997/99 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. 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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Part [B2] ~ Hunger- and Food Supply Issues ~
Net cereal imports by developing countries will almost triple over the next 30 years while net meat imports might increase by a factor of almost five (03B1). (Note that the US, normally the world's largest exporter of foods, was a net importer of food in 2004.)
Although China, along with the US, is one of the world's leading grain producers, It is expected that by 2025-30, China "will need to import 175-200 million tons [of grain]", an amount equal to the entire world's current grain exports (02W2). (Note that China recently [~2005] switched from being a grain exporter to being a grain importer.) Spreading deserts, urbanization of agricultural lands, declining soil organic matter contents and growing population help to explain China's need to increase imports.
If the Chinese were to consume seafood at the Japanese per-capita rate, China would need the entire world's wild fish catch (95B2). (See below.) It should be noted however that only about 20% of the Chinese population participated in the global economy, and even this percentage is dependent on the willingness of the US to incur massive trade deficits and a willingness to prop up the US economy with massive internal borrowing (budget deficits) - both processes that are unsustainable.
Raising per-capita beef consumption in China to that in the US would require 49 million additional tons of beef per year. If that came from cattle in feedlots, American style, it would require 343 million tons of grain per year - an amount equal to the entire US grain harvest (data from Economic Research Service, USDA, Washington DC). (See statement above about the non-sustainability of China's current prosperity.)
The number of chronically hungry people in the world is set to fall from 776 million now to 440 million in 2030, says the UN FAO. The FAO concludes that global grain production will have to rise by 1.2%/ year to meet the demand for food and feed. This is 17% higher that the 1990s average. The FAO report says the area of land under crops can increase by 20% by 2030, even with a slower rate of deforestation worldwide. But it concedes that the bulk of the production increases - up to 80% - must come from boosting yields per hectare. The FAO rejects the conclusions of other analysts, such as Lester Brown of the Earth Policy Institute in Washington, that such yield increases are unlikely. These analysts fear that the halving in the annual growth rate of grain production since the 1980s is a sign that land, water and the biological potential of crops to turn fertilizer into grain is reaching a maximum. The FAO says yield increases have slowed because of a fall in demand caused by slowing population growth - and the inability of people without money to turn their need for grain into market demand (03F1).
On 5/11/07, the US Department of Agriculture (USDA) released its first projections of world grain supply and demand for the coming crop year: 2007/08. The USDA predicts that world grain supplies will plunge to a 53-day supply, their lowest level in the 47-year period for which data exists. The USDA projects global grain supplies will drop to their lowest levels on record. Further, it is likely that, outside of wartime, global grain supplies have not been this low in a century, perhaps longer. Most important, 2007/08 will mark the seventh year out of the past 8 in which global grain production has fallen short of demand. This consistent shortfall has cut supplies from a 115-day supply in 1999/2000 to the current level of 53 days. The world is consistently failing to produce as much grain as it uses. The current low supply levels are not the result of a transient weather event or an isolated production problem: low supplies are the result of a persistent draw-down trend (07Q1).
UNICEF's 1998 State of the World's Children reports that malnutrition in some parts of the world has decreased, but the overall number of malnourished children is on the rise. At least 50% of all children under age 5 in South Asia (mainly India), and 33% of those in sub-Saharan Africa are malnourished (98P1).
Over 7.3 million people die from hunger annually. (BBC http://www.bbc.co.uk/worldservice/oneplanet/live.ram (1/5/00))
About 18 million people/ year, mostly children, die from starvation, malnutrition, and related causes (97H1).
In recent years, Canada, Australia, the EU and Russia have all imposed constraints on food exports (06D1)
Worldwide, an estimated 2 billion people, disproportionately women and girls, suffer from malnutrition and dietary deficiencies (97H1). (The majority of these suffer from dietary deficiencies.)
The 49 LDCs (Least-Developed Countries) agricultural trade deficit has increased so rapidly that, by the end of the 1990s, agricultural imports were more than twice as high as agricultural exports (Figure 9.2 of Ref. (03S3)). These are the countries that can least afford trade deficits since these must often be financed with loans from external sources.
In developing countries, demand for food has been growing faster than food production, so net imports increased from 39 million tonnes in the mid-1970s to 103 million tonnes in 1997/99 (Figure 3.7 of Ref. (03A1)). Aggregate self-sufficiency (percentage of consumption covered by production) in these countries declined from 96 to 91%. If we exclude the three major developing cereal exporters (Argentina, Thailand and Viet Nam) net imports of the other developing countries increased from 51 to 134 million tonnes and self-sufficiency fell from 93% to 88% (03A1).
The World Bank (00W3) stated: "On balance, we do not see compelling reasons why real commodity prices should rise during the early part of the 21st century, while we see reasons why they should continue to decline. The World Bank obviously did not foresee the development of biofuels manufactured from corn, nor did they foresee the major economic expansions in China and India that raised [and will probably continue to raise] global prices and demands for oil, food, minerals and other commodities. Such prices make it increasingly difficult for developing nations to afford to import food and make food riots and large-scale hunger increasingly likely.
The FAO contends that historical evidence suggests that the growth of the productive potential of global agriculture has so far been more than sufficient to meet the growth of effective demand. This is what the long-term term decline in the real price of food suggests (03A1) (Figure 3.1 of Ref. (00W3)). The fallacies in this view are discussed at length in Section [D] of the previous (introductory) chapter of this document. The long-term decline in real food prices (40% between 1961 and around 2000) occurred during a period of huge increases in consumption of chemical fertilizers, the development and rapid increase in use of genetically improved strains of cereal grains, and the rapid expansion of large-scale irrigation. Today's environment is completely different as should be clear from Section [A] of this chapter and there is no reason for believing that the future will see any sort of return to the environment of the second half of the 20th century. See Section [D] of the previous (introductory) chapter for further analyses. The FAO uses these declining food prices to conclude that, in practice, world agriculture has been operating in a demand-constrained environment (03A1). This may very well be true if one takes the date from 1960 to 2000 when three massive changes were underway in agriculture - changes that cannot continue much longer (See Section [A] above).
The FAO further notes that the "demand-constrained environment" has coexisted with hundreds of millions (800-900 million) of the world population not having enough food. The FAO then notes that the situation of un-met demand coexisting with actual or potential plenty is not specific to food and agriculture. It is found in other sectors as well, such as housing, sanitation and health services (03A1). The FAO's contention that the lack of food is conceptually similar to the lack of housing, sanitation and health services needs to be examined more carefully. Housing, sanitation and health services are all very capital-intensive components of the basic infrastructure of an economy. Developing nations virtually all suffer an extreme scarcity of financial capital as a result of the extremely high costs of the infrastructure growth needed to accommodate the high population growth rates found throughout the developing world. Agriculture in developing nations is not, or need not be, capital intensive. All that is required is land, labor and some seeds - all items of very low capital intensity so long as excess (unused) arable land is readily available. The FAO contends that undeveloped arable land exists in plentiful supply. If this contention were true there would be no reason for those hundreds of millions of people to not have enough food. There would also be no need for farmers to raise their crops and livestock on steep low-grade land where sustainable agriculture is difficult if not impossible. There would also be no need for farmers to raise crops and livestock on semi-arid lands where risks of wind erosion and long-tern drought are very high. There would also be no need for farmers to migrate in huge numbers to the wretched slums ringing essentially all major urban areas of the developing world where they must become part of the "informal" economy where just survival is a major challenge. The FAO needs to admit that the lack of food is fundamentally different from the lack of housing, sanitation and health care - or it needs to admit that undeveloped arable land is nowhere near as plentiful as the FAO believes it to be. They cannot have it both ways.
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Part [B3]
Part [B4]~ Cumulative cropland losses and cropland loss rates ~
The global rate of irrigated land loss to salination and waterlogging is 20-30,000 km2/ year (94K3).
The global cropland urbanization rate: 20-40,000 km2/ year (92P2), (94K3).
Russia's semi-arid croplands are being 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)).
Wind erosion removes 15,000 km2/ year of semi-arid croplands from production in the former Soviet Union. A much larger area in the former Soviet Union is damaged to some degree each year (89S3).
In Himachal Pradesh, Uttar Pradesh, Assain, Jarumu and Kashmir in India, tens of thousands of km2 have no more soil covering the rocky substrata (75E1).
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 40,000 km2 (87U1).
Erosion associated with shifting cultivation has denuded 27,000 km2 east of Bihar, India (96G2).
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.)
In northern Ethiopia, "stone deserts" have replaced nearly 40,000 km2 of what once were fertile farmlands ((88J1), p. 9).
Nigeria was losing 500 km2 of cropland to desertification per year in 2001(announcement by Nigeria's Minister of Environment (January 2001)).
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)).
Mexico abandons 1036 km2 of farmland to desertification per year (94S4).
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).
Over the last 20 years, 50% of Mongolia's wheat land has been abandoned, and wheat yields have also 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.
China loses 1200 km2/ year of farmland and pastureland to drifting sand dunes (86W4). The spread of deserts in China is widely attributed to deforestation and overgrazing.
Oxford-based expert Norman Myers says Morocco, Tunisia and Libya are each losing over 1000 km2 of productive land a year to desertification (05L2).
NOTE: The document "Topsoil Loss - Causes, Effects and Implications: A Global Perspective" contains much more data similar to the data given above.
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Part [B5] ~ Soil Organic Matter Issues ~
Soil organic matter plays numerous important roles in determining the productivity of cropland soils ((66K1), p. 228):
Organic Matter in the Upper 50 cm. of Topsoil Relates Closely to Corn Yields (Ref. 23 of Ref. (83S1)), i.e.:
|
Organic Matter (tonnes/ km2) |
4000 |
5000 |
7000 |
9000 |
11,000 |
|
Corn Yield (tonnes/ km2/ year) |
160 |
260 |
300 |
340 |
400 |
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.
Go to Table of Contents of this Chapter ~ Go to top of this Section [B] (Basic Data) ~
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
Note: The data below is a sampling of a far larger set of data to be found in "Topsoil Loss - Causes, Effects and Implications: A Global Perspective," Edition 7 (July 2007) in this same website.
Part [C1] ~ Global ~
Percent of the arable land expected to degrade to non-arable status by 2025 (04H1)
|
Africa |
67% |
|
Asia |
33% |
|
South America |
20% |
Much of this land is probably in semi-arid regions where productivities tend to be low, organic matter contents are low, and hence resistance to water- and wind erosion is also low.
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 habit