Livestock Research for Rural Development 20 (1) 2008 Guide for preparation of papers LRRD News

Citation of this paper

Decline in available world resources; implications for livestock production systems in Asia

R A Leng

Emeritus Professor, University of New England,
Armidale, NSW, Australia

In the keynote speech at the first day of an oil depletion conference hosted by the Association for the Study of Peak Oil in Cork Sept 2007 former US Energy Secretary Dr James Schlesinger who was also Defence Secretary and CIA Director - claimed that the intellectual arguments over peak oil had been won, and that in effect ‘we are all peakists now’.


The world is faced with a global triple crisis: climate change, Peak Oil (the end of inexpensive energy) and global resource depletion. These are interrelated and interactive problems which makes the subject to be discussed in this paper extremely complex. The certainties are that there will be great changes to contend with in the future in order to produce and deliver food to maintain the present world population, let alone a balanced diet for everyone. At the present time there are roughly 1 billion people that are underfed and/or on imbalanced diets lacking essential micro nutrients that are provided by animal protein.

The primary resource depletion is that of fossil fuel energy since the world has been using more fossil energy than is being discovered and it appears that the reserves of oil that can be cheaply mined are now at peak production (half these resources have been combusted). As oil reserves are depleted it is predictable that, just as with any other commodity, prices will rise with increasing scarcity. World population expansion has been promoted by the availability of inexpensive oil, which has supported increased world food production by providing inexpensive inputs including fertilizers, insecticides, herbicides, traction power( lowering the need for labour and reducing the numbers of people in farming) and in places irrigation water. Inexpensive oil allowed food to be produced cheaply but this will change greatly as oil prices rise creating the potential for major disruptions in food availability.

Peak oil represents a massive change and will affect other resource availabilities. Agriculture has received inexpensive fertilizers on which high crop yields have been predicated including

The dependency of the industrialized countries on oil to drive agricultural production and the fact that most of these same countries cannot meet their own domestic requirements from local resources has seen a headlong development of alternative fuels including bioethanol produced from sugar cane and maize mainly in Brazil and the USA, respectively; and development of bio diesel from plant oils. The implications for world food stocks and prices are enormous, potentially creating major cereal food /feed grain shortages as land is diverted to fuel production. The expectation are that world cereal grain availability for livestock will be highly restricted and the case is made for the forage-fed ruminant as a major source of animal protein for the future. Herbivores in general are likely to be used more extensively with time, particularly the rabbit with its dual capabilities of high reproduction rates and the capacity to utilize efficiently forage resources produced locally.

 Biofuels production diverts land from food production to transportation energy and often the land is accessed from clearing of forests with often dramatic effects on biodiversity, erosion and the carbon balance of the land area.

Water is the other major resource required for agriculture, which has also been depleted. Fossil ground water (water created as the world cooled many millions of years ago) has been exploited using cheap fuel, but most fossil resources are now too deep to be economically mined for irrigation reducing some of the major areas of crop production (eg:  The U.S. Ogallala aquifer and the aquifer under the North China Plain). Many of the world’s aquifers that were normally replenished by rainfall have also been drawn down with periodic loss of irrigation potential   The advent of Peak Oil with ultimate high cost of fuel will clearly cause return of vast areas of highly productive irrigated crop land back to rain fed cropping, pasture  or desert  in the future with major loss of food productivity.

Soil erosion and fertilizer run off from cropping systems are also major concerns as the present day cereal crops only tap the nutrients in the top few inches of soil and even the prairies of USA which have been only cropped for about 100 years have depleted the top soil reserves with potential to decrease crop yields significantly. 

Global warming is now accepted as occurring and cannot be ignored in any discussion on future agriculture. Increasing sea levels will undoubtedly remove considerable areas of fertile delta and weather patterns will certainly change, leading to at times more intense drought and or flooding rains. Warming also carries with it the risk of decreased crop production as recent research has demonstrated that rice yields decrease by 10% for every o C rise in night time temperatures.

Each of the triple global crises has the potential to lower world crop production by direct or various flow on effects. It is suggested that we must now enter a stage in the world where grain-based animal production will become increasingly expensive as the competition for resources for food, feed and fuel, develops. The animal production industries based on herbivores will need extensive development exploiting a wide range of waste byproducts of agriculture or from land not dedicated to food or biofuels production.

Oil depletion, pressure to produce biofuels, soil fertility decline (including salinity and sodicity) the high cost of chemical fertilizers and the loss of arable land to erosion, non agricultural purposes (such as roads and houses), coupled with likely overall decreases in crop production from global warming, all appear to be interacting such that it will be difficult for many nations to feed themselves in the future. The developing countries seen by some as backward in agriculture may be the most capable of supporting themselves through the maintenance of small-scale farmer practices that integrate food and fuel production.

Key words: Grain, biofuels, peak oil, water, fertilizer, ground water, rivers, soil fertility, global warming, enteric methane, ruminants, pigs, poultry and rabbits


Crude oil, produced millions of years ago from decomposition of algal biomass grown in warm seas, was massively exploited in the early part of the 20th Century. The deposits were so large and distributed so widely that competition and volume of production kept them inexpensive. This inexpensive fuel provided the energy for tremendous developments in industry and agriculture in particular and allowed the world population and its wealth to grow at unprecedented rates. It also promoted world conflict, generally based on the acquisition of resources. Before there was abundant fossil fuel, world populations were constrained below 1 billion people and the population growth was slow and steady; but following the discovery of first coal, but more importantly oil, it has increased exponentially (Figure 1).


Figure 1.  World oil production has been the major resource supporting population growth.

Through time, and as sources of fossil energy were discovered and harnessed, their availability promoted massive mining of energy resources, creating world surpluses and extravagant, and somewhat illogical use of the inexpensive fuel,  including the phenomenal rise in transport energy that free trade demands, particularly the simultaneous trade of the same goods both  between countries and within countries (see Simms et al 2006).

Inexpensive oil in turn led to industrialization of food production, land clearing and cropping on a scale that had never been seen in the history of the planet. Fertilizers, extracted from natural sources or in the case of nitrogenous fertilizers, by the manufacture of ammonia from atmospheric nitrogen gas, became abundantly available and inexpensive. Intensive use of fertilizers increased crop yields and other crop inputs, including herbicides and insecticides allowed potentially high yielding crops to be successfully and inexpensively grown. This led to the Green Revolution which then supported a massive increase in the growth of the human population.

At the same time, the farmers of the world were inevitably exploiting soil fertility, with wind and water erosion reducing top soil and structure and depleting the nutrient status of land, but compensating for these loses by increased use of fertilizers. Run off from agriculture has resulted in considerable eutrophication of water bodies both fresh and salt water with the death of massive areas of many lakes and large areas of oceans (termed Dead zones). Water availability for agriculture is dwindling as ground water tables drop to levels that cannot be profitably pumped to the surface (Brown 2001) and major rivers are running dry from overuse of water by many industries and cities.

The massive increase in fuel availability, particularly for mining of the fossil fuels themselves and for other resources, transport and machinery use, electricity generation, fertilizer production, construction and synthesis of chemicals has caused a build up in both the atmosphere and water bodies, of carbon dioxide, methane and oxides of nitrogen that increase the retention of energy radiated from the sun and the infra red reradiated from the planet. This is altering the thermal load on the planet, leading to global weather and temperature instability usually referred to as global warming with profound effects for agriculture. Acidification of the seas by absorption of carbon dioxide will have profound effects on future marine production. Sea level rise from melting snows and ice appears to be an inevitable result of global warming which will massively reduce land areas of agricultural significance, particularly delta areas which are often the most fertile.

The food requirements and the resources to meet a projected human population of 8 billion people in the decade 2030-2040 appear to be unattainable. The resources required for this have been documented and extrapolated to the future by Vance (2001) and are shown in Table 1.

Table 1. Agriculture production and resource use, the recent past to the near future. Data derived from numerous sources by Vance (2001)





Food production (M tonnes)

1.8 × 109

3.5 × 109

5.5 × 109

Population (Billions)




Irrigated land (% of arable)




Cultivated land (ha)

1.3 × 109

1.5 × 109

1.8 × 109

Water-stressed countries




N fertilizer use (Tg)




P fertilizer use (Tg)




Any discussion and predictions of the effects of a decline in energy resources, and implications for world food, are extremely complex owing to the enormous interacting factors that are involved. The information in the literature is often confusing because of the political and economic misinformation that has to be handled. However it is not simply a matter of producing food, it is also relieving the ill health from essential nutrient deficiencies by balancing human diets. Animal products are a major source of essential micronutrients and essential amino acids that are often deficient in the diet of the poorest people.  By 2000, 1.0 billion people were chronically undernourished (consume fewer than 2,000 calories per day), 100 million pre-school children have a vitamin A deficiency, and 400 million women between the ages of 15 to 49 have an iron deficiency leading to anemia (Conway and Toenniessen 1999). The need for animal protein requires great attention as it effects the physical and intellectual development of young people (Waterlow 1998).    

Peak oil

The Hubbert Peak of oil resource exploitation

Prediction of oil availability and its use are dominated by principles originally proposed by  Dr M King Hubbert in 1956. Hubbert  introduced the concept that oil exploitation could be  described by a bell-shaped curve that indicated the early and late production rates from an oil field.

Following discovery of oil and the establishment of facilities to manage the wells, the rate of extraction is increased until a peak production is attained and then the extraction rate falls [this is known as the Hubbert Peak]. The peak extraction rate is always close to the mid point of depletion of the resource.

Peak oil was also foreseen in 1957 by Rear Admiral Hyman G Rickover who warned of the potential for the fossil fuel era to end rather abruptly with calamitous effects on food production( Rickover 1957). Many of his predictions are now happening.

Hubbert’s and Rickman’s predictions, if considered and acted upon could have prevented much of the conspicuous waste of fuel, particularly for transport, that now appears to draw nearer a calamitous time for future generations

The Hubbert Peak has become a reality in those oil fields [the vast majority] that have now passed their peak production and are depleting. Oil discoveries world wide, peaked in the mid 1960s and have declined since; the total world production of fossil fuel has probably already peaked or will within 3 to10 years (Figure 1). At the present time for every new barrel discovered the world is currently using 4 barrels. The reader is directed to the ASPO website for a reasoned  and unbiased discussion of  Peak oil.



Figure 2. Current forecast of future world oil production, including non-conventional oil, from the Association for the Study of Peak Oil, Released at Uppsala May 2002 First International Workshop on Oil Depletion, Uppsala University,  May 2002.

The reality of the Hubbert Peak concept appears to be now accepted by some politicians and  petroleum scientists (see quote at the head of this publication) and is being used to predict world oil supplies and their likely depletion rates (this is discussed in the books by Fleay 1996, Campbell 1997, Youngquist 1997,  Deffeyes 2001, Roberts 2004 and many others - see ASPO website). The pattern of reserves depletion for world fuels is validated by the pattern of depletion of some major oil provinces (eg: The North Sea Oil province, Figure 3)

Figure 3
. North Sea Oil has followed the pattern of exploitation precisely as predicted by Hubbert (1956)

The world has been using oil at a greater speed than the discovery rate (Figure 4).  The reserves of oil are fairly well documented and for this reason drilling activity has been curtailed to just a few areas. Despite highly sophisticated and accurate methodology for identifying the geological formations where oil and gas would have accumulated in the past, few fields and no new mega fields have been found.

Figure 4.
The difference in the rate of discovery of oil and the rate of oil use in the world

The other source of liquid fuels, the tar sands and heavy oils that are found in quantity [trillions of barrels] in Alberta, Canada and Venezuela have enormous  logistic and political problems as their extraction is costly in energy and water and  associated with considerable pollution issues. It appears that many analysts believe that the “ immense reserves” of non conventional oil from the Canadian tar sands, the Venezuelan Orinoco heavy oil deposits and various shale oil deposits, for example in Australia, will provide the short fall in oil into the foreseeable future . Shale oil is not oil but a kerogen that must be heated to very high temperature (pyrolysis) to make it flow and is unlikely to be mined in any quantity in the foreseeable future particularly since it requires large volumes of water in its extraction and is highly polluting  Youngquist (1998) states that “production of oil from oil shale has been attempted at various times for nearly 100 years. So far no venture has proved successful on a significantly large scale".

The non conventional oil and natural gas (methane) face severe extraction and transportation problems including lack of technological readiness, low energy content, high water requirements and in many cases a high fossil fuel cost in extraction, processing and marketing. Polar oil and deep sea oil have similar logistic problems that make them expensive sources.  Together with the increased carbon dioxide emissions and other pollutants it is highly improbable that these resources can come on stream quickly enough to compensate for the decline of conventional oil and the increased world requirement as the emerging countries demand their slice of the oil cake, particularly India and China.

Natural gas is often suggested as being an answer to oil scarcity, however to transport it any distance it needs to be compressed onto liquid form with a high energy cost. Liquid natural gas (LNG) is highly volatile and it has been estimated that approximately 9% of all gas escapes into the atmosphere between the extra sites of extraction and use. If this is true it would add significantly to global warming. Worldwide there are 17 production and export terminals, 41 import terminals and 141 LNG ships altogether handling approximately 120 million metric tons of LNG every year. These numbers are predicted to increase dramatically over the next decade due to the growing popularity of this “clean” fuel source.

Methane is a potent greenhouse gas absorbing some 20-23 times more energy than carbon dioxide, from infra red emissions reradiated from earth. Later in the discussion it is suggested that ruminants will need to substantially replace monogastric animals to provide animal products in the diets of people. However, their enteric methane production is a major draw back to this suggestion. World methane production is between 60-240 million tonnes, and ruminants contribute roughly 20% of this. However LNG seems set to be a major source of atmospheric methane.

Interacting factors effecting world agriculture

It is a logical conclusion that,  as fossil sources of energy are depleted, increasing world demand for fuel will inevitably force world fuel prices to rise (Campbell and Leherrere 1998), but with a saw-tooth pattern over time, as periodic recessions lower demand and price, allowing both to rise again thereafter (Campbell 2007). High oil prices have great implications for the cost of many of the essentials of life. Interacting factors also indicate that food availability and food prices will be compromised directly or indirectly by flow on effects of oil depletion (see Leng 2002, 2005), possibly the most important being the diversion of land from crop production to production of biofuels.

Industrial production of biofuels

The twin threats of peak oil and global warming have resulted in politically driven development of alternative liquid fuels resulting in massive development of industrialised production of fuel ethanol from sugar cane in Brazil, and maize in the USA. Both countries have huge importation costs for oil. The USA, while using 25% if the world’s oil production, imports 70% of its needs, making the country extremely vulnerable to world oil supply.  Biofuel production from cereal grain with competition for food and feed has massive implications for human health and welfare and livestock production world wide and particularly for developing countries (see Leng 2007).

Bioethanol manufacture using maize is growing at a great rate. It is not the intention here to focus on the net efficiency gains in transport fuel. However the amount of energy returned in ethanol from growing maize and processing the starches through to alcohol is hotly debated. The most scientific approach to the estimation of its net energy has been undertaken by two eminent scientists (Patzek and Pimental 2006; see also Pimental et al 1988, Patzek 2004, 2006, 2007) who are not committed to either a political party or an industry. Their research shows that there is a net energy loss when all the inputs and outputs are modeled. It is concluded that the establishment of subsidised ethanol industries in the USA is mainly motivated by fuel security reasons rather then to increase fuel availability. Others see a more sinister aspect and argue that the subsidized production of alcohol from maize grain in the USA is aimed at creating a world food monopoly for big business (see Carlson 2007) and that the triple challenge can only be handled by challenging corporate power (Vandana Shiva 2007) and removing the huge government subsidies paid to the industry (Carlson 2007).

It is difficult to comprehend the deliberate condemnation of millions of people to purgatory and starvation by a deliberate reduction in world food supplies; however, such a discussion goes beyond the scope of this paper.   

The Livestock Revolution coined by researchers from The International Food Policy Research Institute (Delgado et al 1999, 2002) was predicated on surplus world grain supplies and that the relative price of grain would not rise significantly in the next 50 years. It was theorised that grain, surplus to human requirements in most developed countries, would be exported to developing countries as the basis of an industrialised pig and poultry industry to meet their growing demand for meat. The major question here is whether the quantities of grain needed (Figure 5) will be available for this purpose and, if not, how can meat and milk be produced in significant quantities to meet the nutritional requirements for essential amino acids for people in developing countries.  

Figure 5. The trends in requirements for feed grain to meet the anticipated demand for meat by 2020 (Delgado et al 2002].

The industrial production of biofuels threatens to create major conflict over food for humans, feed for animals and feedstock for liquid fuels.  In 2006 about 17% of the US corn crop was converted to ethanol and supplied 2% of the nation’s needs of fuel for automobiles. The Earth Policy Institute predicts that ethanol production will claim 50 percent (or 140 million tonnes) of US grain in 2008, with 79 new ethanol distilleries due to come on line in the next two years. These new distilleries will double ethanol capacity at a time when world grain stocks are at their lowest level in 30 years and falling. By 2020, world alcohol production could remove conservatively 400 million tonnes of grain from world food - feed markets, either directly or by diversion of land from food crops to energy crops (Leng 2007). If maize was the sole source of the feedstock, President Bush's call for the USA to produce 35 billion gallons of renewable fuel by 2017 would require about 320 million tonnes of maize, more then the present annual production of maize in  the USA. The balance between maize exports and maize used for ethanol in the US indicates the extent of the potential effects on world food supplies (see Figure 6, from Earth Policy Institute [Brown 2007])

The US Congress recently enacted legislation  to compulsory blend  ethanol with gasoline and indicated that the target for ethanol production for this purpose should be 36 billion gallons by 2022, of which some 21 billion gallons to be produced from cellulosic biomass. The technology for the latter is almost totally untested and quite likely to require more fossil fuel in its manufacture then that in the ethanol produced (Patzek 2007).

Most countries of the world and even those that currently have chronic under and mal nutrition in their population are planning a biofuels program  (eg: in South Africa see Inevitably these programs, whatever the source of feedstock, will remove land from food production.

Figure 6. US grain for ethanol and for export (adapted from Earth Policy Institute 2007)

The world trade in all grains is around 240 million tones, of which around 80-90 million are exported from the USA. The acquisition of grain by the ethanol industry in the USA will thus have major impact on world grain availability and prices. Present world wheat and coarse grains reserves are about 280 million tonnes, down from 450 million tones in 6 years. However, world demand for grain is increasing. India in particular has emerged as a huge importer of grain this year having used up its 23 million tonnes stockpile in just 5 years to import 4 million tones in 2006.  China is also a net importer. World grain consumption has exceeded production in 5 of the last 6 years. Global per capita grain availability is also declining. (Figure 7).

Figure 7. World grain production and consumption has resulted in low world reserves (

Some of the grain reserves diverted to ethanol production will be offset by increased production from land that had been set aside in the USA and Europe when grain production was in surplus. This year USA appears to have planted 20% more land to maize but much of the land has been diverted from other crops such as cotton and soybeans.  Many countries,  particularly in South America (Brazil in particular) will clear forest land for cropping, which adds to global warming and ‘the new’ land quickly loses its initial high fertility. Following a short period of 2-10 years many of these highly fertile soils require substantial fertilizer application to support adequate yields of sugar cane and grain. Once the honeymoon period is over ethanol production costs must rise substantially.

Global warming and climate change are also likely to reduce crop yields

The huge industrialized ethanol industries that are developing are only compounding a number of other factors which are likely to reduce cereal grain yields. The most significant effects of climate change on agriculture arise through changes in climate patterns. Increasing temperatures in tropical countries can have a slowing effect on photosynthesis and hence plant growth.  For example, rice yields in Asia are declining by 10% for every ºC  rise in night-time temperatures (Peng et al 2004).

A recent paper (CGIAR 2007), that focused on the effects of increased temperatures on wheat production in the South Asia  Indo-Gangetic Plain, indicates a massive decrease in yields. This area produces 15% of total world wheat grain annually, about 90 million tonnes. CIMMYT researchers are reported to have suggested that under climatic conditions expected to prevail in 2050, the wheat mega-environment will shrink by just over half, mainly through shortening of the growth period as a result of heat stress early and late in the wheat growing season. This threatens the food security of about 200 million people.

 The predictions on climate change are for increasing rain in some areas but less rain in others, thus it appears that rainfall patterns will become more variable (Stern 2007) and storms more intense, which will lead to increasing crop failures. Conversely, warming will open up new land for grain production in the Northern Hemisphere but far away from the main centres of population. These lands will possibly be more attractive for biofuel crops.

Recent models of the effects of global warming suggest that the flow-on effects are likely to reduce world agricultural output by between 3 and 16%. However, the effects will not be spread evenly with productivity in tropical, developing countries likely to be reduced disproportionately by  9-21%.(Cline 2007) The spread of estimates is brought about by the uncertainty surrounding the benefits of  increased atmospheric carbon dioxide on plant growth (carbon fertilization).

Other resource depletions with implications for agriculture.

Over the last century, and particularly the early part of the 21st century, inexpensive energy enabled unprecedented growth in rates of extraction of many resources. Many of these resources appear now to be in depletion, as they begin to reach or have reached peak extraction rates. They will therefore become more expensive as availability is reduced.  Some resources will become expensive simply because the world’s reserves are being depleted, others because the mining, processing, delivery to the farm and application are dependent on the use of fossil energy that will become more expensive. The resource depletions that are likely to impact on crop yields are discussed below.


Water is the most potent resource for plant growth and without water, plant growth ceases. Two-thirds of the available fresh water are used for irrigation in agriculture (Revenga et al 1998) and water availability is a major factor limiting food production (Revenga et al 2000). The total amount of water withdrawn or extracted from freshwater systems has risen 35-fold in the past 300 years (Revenga et al 1998) and, since 1960, has increased by 20% per decade. Agriculture accounts for 70% of human water use. In addition, around the world, groundwater is also being withdrawn faster than it can be recharged; depleting a once renewable resource (Revenga et al 1998). Water use in many other industrialized processes is increasingly competing with water for agricultural purposes. The ethanol industry has a large appropriation of water and so has many industrial mining systems.

There is a growing body of opinion that water may ultimately limit world food production (Postel 1999). A number of significant rivers now do not reach their destination, either to the sea or to lakes,  because of water extraction and this is curtailing water use in food production (eg: the Murray-Darling river in Australia, the Amu Darya that feeds the dying Aral Sea, and the Ganges and Indus rivers which barely make it to their natural destination). The World Wild Life Fund recently released a major report concerning the many risks that the world’s river systems face selecting 10 major rivers of the world (Wong et al 2007).

Water flows are decreasing in rivers when unprecedented quantities of water are being added to river systems through melting ice due to global warming. However, with time, as the ice and snow reserves are reduced, river flows will decline further, probably non-synchronously with the need for irrigated crop production. Rain-fed agriculture will be affected mainly by changing weather patterns but these will  also influence river flows. Irrigated crop production accounts for an enormous proportion of the total world food production. In twenty years time, the Himalayan glaciers will have been reduced from 500,000 square kilometers to 100,000 square kilometers (see  Anthwal et al 2006, for a discussion on the rate of glacial melt). In the areas that are fed from these rivers, present rainfall occurs mainly in the winter and it is only the melting glaciers that supply water for irrigation and other purposes in the hot summer months placing over a billion people at risk.

Water tables are reported as dropping in nearly all countries (Brown 2005) as farmers over-use the aquifers that are replenished from rain. For example, the water table in the huge Ogallala aquifer occupies 174,000 square miles at shallow depths beneath parts of eight states of the United States. It used to be the source of irrigation for 13 million acres of land but this area is steadily reducing (down by 370,000 acres in 1992;  Postel 1992), owing to over-use for agriculture, returning the land to much lower producing systems based on rainfall.                                                             

The Ogallala Aquifer is being both depleted and polluted. Irrigation withdraws much groundwater, yet little of it is replaced by recharge. Since large-scale irrigation began in the 1940s, water levels have declined in parts more than 30 meters (100 feet). Depletion results in reduced irrigation in certain areas and increased energy cost in all areas as the depth to reach water increases. With the advent of expensive oil the depth from which it can be pumped has an economic limit.  The world's irrigated land was 48 million hectares in 1900 and about 220 million hectares in 1990. About 75% of all irrigated land is in the developing countries and around 60% of cereal grain is produced under irrigation. Irrigated land accounted for approximately 15% of the cultivated land but produced 36 percent of the world's food in 1990 (Jensen et al 1990). Using data from major aquifers in China, India, Saudi Arabia, North Africa, and the United States where water tables are dropping - in some places precipitously - Postel (1999) calculated the annual over pumping of aquifers at  160 billion tonnes. On the basis  that it takes 1,000 tonnes of water to produce 1 tonne of grain, Brown (2001) calculated  that a 160 billion tonne water deficit is equal to 160 million tonnes of grain that cannot be produced, or around 10% of total world grain production, but more importantly --  66% of the world’s currently traded grain.

With the enormous pressures coming onto land for food, feed and feedstock for biofuels, the world’s water deficit can only get worse. Expanding of the human population,  variously reported as rising by another 2 billion from 6.5 to 8.5 billion by 2025, is simply not sustainable.

Peak land availability and soil fertility

Over 5% of the world’s cropland is highly susceptible to erosion by wind and water and all land is subject to loss of soil in crop production with inevitable loss in fertility. Cereal crops in particular grow in the top few inches of soil where the nutrients are concentrated and loss of top soil leads to loss of productivity and /or an increased requirement for fertilizers. In addition to losing cropland to severe soil erosion, salination and desert expansion, the world is also losing cropland to many non farm uses, including construction of roads, houses and industrial buildings.

The enormous twentieth-century expansion in world food production pushed agriculture into highly vulnerable land in many countries and these will surely start to produce at reduced levels as off-take of commodities and erosion reduces productivity. The mining of highly fertile, newly cleared forest land is a case in question. When first cleared fertility is high but diminishes with time and the fertility can only be reclaimed with fertilizer use, leading to increased costs. This scenario appears to be playing out particularly in land cleared for sugar cane production for bioethanol in Brazil. Another serious effect of forest clearing is the removal of carbon sinks enhancing global warming. At the same time increasing temperatures are increasing the loss of a major carbon sink, the soil carbon which is more rapidly depleted as soil temperature increases (Carney et al 2007).

The conundrum is also made more complex if melting snow and ice influence sea levels. Most of the world’s most productive land is in delta areas that will flood or be inundated should sea levels rise as predicted by,  for instance, the Stern report (Stern 2007).


In industrialized countries, and increasingly in the emerging economies, crops grown for food, feed, biofuels or other commodities are produced with large inputs of oil for ploughing, direct drilling, seeding, cultivation, fertilizer application and the work of  harvesting and transport

The fertilizers used are mainly sources of N, P, K and S. These have been the catalysts that allowed crop yields to be increased, supported in part by the discovery of high yielding grain varieties that could take advantage of the improved nutrient availability in the soil. This resulted in the great leap forward in agricultural production that was termed the Green Revolution. However, fertilizer use will be constrained in the future depending on: i)  the cost of manufacture of nitrogenous fertilizers; ii) depletion of reserves of P, K and S; and iii) the cost of mining and delivery to the farm gate. Depletion of micronutrients (such as selenium, zinc, cobalt) and increasing cost of extraction are also becoming of major importance.

Nitrogen  is one of  the most abundant elements on Earth, and is the critical limiting element for growth of most plants due to its unavailability as salts in the soil (Smil 1999). Prior to 1930, the N cycle on Earth was in dynamic equilibrium (Frink et al1999). Grain crop yields until the 1930s were about 0.5 to 1.0 metric tonnes per hectare, with N supplied primarily from crop rotations and manures.  The advent of inexpensive energy allowed the production of ammonia based on the use of natural gas  Inexpensive fertilizers particularly ammonia and/or urea allowed large increases (up to 10 fold) in cereal grain production from high yielding grain varieties. This led to surplus world grain and massive investment in intensive animal production based on confinement of animals fed energy and protein-rich feeds.

N fertilizer manufacture is entirely dependent on the use of natural gas. The Haber -Bosch process of production uses 1% of all energy consumed by humans (Smith 2002) and its cost will follow fuel prices linearly. The availability of nitrates in soils is increased by leguminous plants that fix atmospheric nitrogen and this is probably the alternative source of nitrates when oil prices make artificial fertilizers too expensive. Phosphorous on the other hand is either not available in soil or unavailable because of extensive binding in the soil matrix. The growth of mycorrhizal fungi on and in plant roots dramatically increases the surface area of roots available for soil exploration of nutrients, particularly P, but also N (Marschner and Dell, 1994). Whilst these associated fungi  may increase  P uptake it is clearly difficult to find food crops with this attribute sufficiently developed and P is likely to be limiting in the future for food production. Growing crops remove soluble phosphates and other nutrients from the soil. Most of the world's farms do not have adequate amounts of phosphate for plant growth and plants that grow on P deficient soils are low in P and do not meet animal and human requirements for this element. It has been shown that P resources are limited and are being depleted (Steen 1998).

Just as with oil, human population growth was not possible until phosphorus deposits were found and inexpensive energy was available to extract, concentrate the ore into fertilizer, transport it to farms and add it to the soil. Future generations ultimately will face problems in obtaining enough phosphorus to exist. Recent studies have drawn analogies between Peak Oil and  Peak P (see Dery and Anderson 2007).

In the same way that Hubbert showed the production and depletion characteristics of fossil fuels, the characteristics of P fertilizer production and depletion (see IFIA 1997 for data on world P reserves) follow the same bell-shaped curve. Using what is now called Hubbert Linearization, which is used to fit a bell shaped curve to fossil fuel extraction and depletion, the same bell shaped prediction of reserve availability can be seen for P (Figures 8 and 9).


Figure 8: Actual production of rock phosphate


Figure 9: Fitting the Hubbert curve to the production of rock phosphate, showing likely dates of depletion

 It seems that Peak P was reached around 2000. Dery and Anderson (2007) go on to justify the use of this modeling by showing that deposits of phosphates on Nauru were depleted in precisely the same pattern and that the large deposits in the USA are being depleted similarly.

Peak P has immense implications for peak food production, with mounting problems with the cost and availability of phosphate fertilizers. Fortunately both P and N can be recycled and the conservation of nutrients within the farming system is still possible and will become what used to be considered a prime objective of agriculture,  that is the recycling of nutrients back to the soil. Whilst nutrient recycling within a farm can be effective, nutrients exported from the farm are less easily recycled. The problem is often that the food is consumed at some distance to the site of production and recycling then is costly in returning the nutrients to its origin because of water and fuel costs. It will be particularly expensive to do this from the huge point pollution sources in mega cities and from those that will arise, particularly in USA and Brazil, in the industrial production of alcohol. In fact, Giampietro et al (1997) observed that “large-scale production of ethanol fuel to supply 10% of the energy consumption of the USA (325 GJ per capita per year), will produce about 3.7 metric tonnes per capita per year of distiller's dark grains, the by-product of ethanol production from corn and sorghum. This quantity of byproduct is 37 times the commercial livestock feed used per capita per year in the USA. Hence, in large-scale biofuel production, by-products should be considered a serious waste disposal problem. In Brazil a medium ethanol  plant supplying the energy equivalent to that consumed by 40,000 people generates a pollution in the effluent water (BOD) equivalent to the sewage of a city of 2 million people(see Giampietro et al 2006).

Estimates of the world’s potash resources vary widely, but by all accounts resources are huge, ranging from about 160 to 250 billion tonnes as K2O. Canada’s potash resources are conservatively projected at 60 billion tonnes, while US resources are estimated at 6 billion tonnes... enough to produce at current levels for several thousand years (see Roberts and Stewart  2002). However, the reserves are concentrated in a few countries and cost of potash will rise with fuel costs. The reserves of sulphur remain almost indefinable. Bardi and  Pagani(2007) examined the world production of 57 minerals reported in the database of the United States Geological Survey (USGS). Eleven cases were found where production has clearly peaked and is now declining. Of these, selenium, phosphate rock and potash (contradicting earlier suggestions of ample amounts) were of immediate concern to agriculture.

The serious consequences of expensive fertilizer, particularly P and N are illustrated by the fact that half the N and P incorporated in world crops arises from fertilizers (see May 2007).

Human resources

Unbridled access to inexpensive oil was the catalyst for the massive increase in food production achieved throughout the world with the help of best scientific practices. Increased use of cheap oil for traction and availability of inexpensive inputs of fertilizers/herbicides, insecticides and water massively increased biomass production per unit of land area; this quickly reduced the numbers of people needed for food production particularly in the industrialized countries.  

It is clear that as numbers of people involved in agriculture were reduced the energy costs of food production were substantially increased. The point made here is that food production is expensive in terms of fossil fuel inputs. It was clearly shown in Cuba, when inexpensive fuel was shut off following the break up of the Soviet Union, that industrialised food production was the first casualty and there was an abrupt change to low input food production and total agrarian reform with a massive move of people into food production activities. The extinct animal traction industry was revived and over a short interval of time most traction was supplied by animal traction (over a period of less then 5 years 600,000 oxen had been deployed into agriculture) crop yields declined because of the lack of application of now expensive inputs such as fertilisers. Food production required more people mobilised into agriculture and a reduction in standard of living leading to attempted mass migration away from the resource deficient Island. The Cuban experience is possibly a model (although fairly extreme because of its rapid onset) of the effects of expensive oil on world food production.

The US is not alone and Western and Eastern Europe, Canada, Australia and the wealthy people in the developing countries have similar patterns of demographic change with increasing affluence. This in turn increases the ecological impact or ecological foot print. An ecological footprint is a resource management tool that measures how much land and water area the human population requires to produce the resources it consumes and to absorb its wastes under prevailing technology. It is clear that a nation’s or a person’s global ecological footprint increases disproportionately with increasing affluence.

The wealthiest nations and the wealthiest people have used (are using) the major proportion of the world’s fossil energy, which has largely been responsible for the damage to the atmosphere (an ecological debt). There is a just claim as to how this can be recompensed in the future (see Parsons [2007] for further development of this concept).

Table 2. Comparisons of developed and developing country consumption of commercial energy [1012 kcal] and the percent of the population engaged in agriculture [Pimentel 2001].


Solid fuel

Liquid fuel

Natural Gas

Hydro & nuclear energy

Total energy

Energy use per person[106 kcal]

% population in agriculture

United States
































Figure 10. Relationship between energy use intensity and proportion of the human population working in agriculture (Pimental 2001)

The question to be asked is a hard one. Will it be possible to move the numbers of people needed in agriculture from their preferred work and life style and will it be possible to train them to a new agriculture that will be less dependent on fossil energy? This is where those countries that have not industrialised their agriculture may be better prepared and therefore able to survive in a fossil fuel declining environment.

Concluding comments

The consensus, at a conference organised by the Association for the Study of Peak Oil in  Cork, Ireland (ASPO) in September 2007, was that oil production will peak in 2011 at below 100 million barrels per day and begin to decline thereafter. This time table is shorter than must experts believed and must surely change many of the attitudes of government to the growing potential degradation of human life.

The confluence of changes that appear to be occurring will have a multiplier effect on many factors. 

For people consuming cereal-based diets:

In the context of this presentation there will be major changes for the meat and milk producing industries with a greater emphasis on herbivores. Ruminants will continue to play a major role in meat production but the world cannot afford the enormous increment in enteric methane production if meat production from ruminants is achieved by increased numbers. The majority of the world’s ruminants are in developing countries The world’s population of ruminants is approximately 1.3 billion cattle, 0.14 billion Asian buffaloes and 1.6 billion goats and sheep. Globally, ruminant livestock produce about 80 million tonnes of methane annually, accounting for about 28% of global methane emissions from human-related activities.

The vast majority of ruminants in developing countries and a major proportion of the national herds of industrialized countries are supported on the by-products of agriculture or graze forages of intermittent or poor nutritional value.

In general, growth rates, milk production and reproductive rates in these systems are extremely low compared with the genetic potential of these animals (mostly about 10% and rarely exceeding 30%). Mostly cattle grow to maturity or slaughter weight over 4–5 years, cows produce their first calf at 4–5 years and then, on average, every two years..

Milk production on these feeding systems is often below 1000 litres/lactation. Cows may be kept largely to produce draught oxen and in some specialized systems they are kept for the production of dung (which is valued as a fuel) and a number of other minor purposes (eg:  as an investment, for recreation and for religious purposes). Slow growth, low milk yield and poor reproductive performance result in poor feed conversion and a large methane output relative to product output. (see Leng 1991). Treatment with alkali and supplementation of straw based diets reduce methane production (Figure 11). The vast majority of enteric methane is produced by animals that are constrained by diet to low production rates. This is clearly illustrated by the relation between cattle live weight gain and methane production per unit of gain (see Figure 12)

The benefits of high growth rates in reducing methane production per unit of meat production have been confirmed from direct  measures of methane output (Figure  12)   Provided growth rates (in cattle) are between 0.7 and 1 kg/day methane production  will be  minimised and these upper levels of growth are being achieved with cattle fed crop residues (see for example Dolberg and Finlayson 1995). In addition at these growth rates it is possible to produce quality meat for all the major markets of the world. Thus an answer to world meat shortages, when industrialised production systems become too expensive, is to develop ruminant production systems from crop by-products in industrialised countries and ensure a large input into research in the developing countries to achieve the levels of production at minimal cost to the environment and without increasing livestock numbers.


Figure 11. Alkali treatment (T) of rice straw (S) and supplementation with
bypass protein (SU) increases growth rate and thus reduces the methane
production by approximately 60% per unit of body weight gain
(Leng 1991, data on growth rate from Perdok and Leng 1990).

              Figure 12. The relationship between live weight gain (LWG) of cattle
and methane production per kg of gain (after.
Kurihara et al 1997,
Klieve. and Ouwerkerk 2007;
Howden and Reyenga  1999)

Over the past 20 years, ruminant nutrition has developed to the extent where efficient production of meat and milk [also wool and hair] is possible from forage resources such as crop and agro-industrial by products and biomass from fallow and waste lands (Leng 1990, 2004; Preston and Leng 1987). With improved nutrition the potential exists to double or even quadruple ruminant production without increasing their total numbers 

The world is not running out of fossil energy resources. It is entering a period of escalating prices because of oil and gas depletion and the costs of extraction of “difficult to get” sources of these fuels.  The appropriate future use of oil in agriculture will have to be rationalized and made as efficient as possible. It should  be used to catalyze new technologies.

Innovations are needed to facilitate and implement known technologies of:
Treating crop residues to improve digestibility
Supplementation to enhance efficient conversion to products
·        Recycling of manure (nutrients and refractory lignin and carbohydrate) back to the land.
·        Mechanization of crop residue processing with small inputs of energy thus removing the barrier of processing at the farm level which has restricted the introduction/application of these processes.

Farms will progressively have to evolve fuel generation locally and rationalize the distribution of farm outputs for food, feed and fuel. Home generated fuels such as biogas and producer gas will be critical inputs that will be used to catalyze overall production where human labour cannot meet the demand. This is discussed in more detail by Preston (2007).

Implicit in this is that production should be focused on minimizing methane production. Considerable research funding is presently under way to reduce enteric methane production by such approaches as inhibiting methanogen growth, immunization against methanogens, establishment of acetogens in the rumen that produce acetic acid from hydrogen and carbon dioxide (Klieve and Ouwerkerk. 2007). At the present time none of these has resulted in a major break through in controlling methanogenesis other then manipulation of nutrition or manipulation of the rumen to increase productivity (Leng 1991).

In the same way that arguments are developed to support future ruminant industries the supply of animal protein can be enhanced using the forage-fed rabbit (Lukefahr 2007; Leng 2006).  Their major attributes include ability to utilize cellulosic biomass efficiently, coupled to a high fertility with ability to breed every 6 weeks producing multiple offspring.


The Bottom Line

The bottom line is that present economic theories and policies have become outdated because they ignored the depletion of natural resources and the cost of environmental pollution. Governments should be urgently putting in place new economic policies based on ecological principles that will be advantageous to food production systems, particularly where these are environmentally friendly (from Leng 1994).

The arguments for a new paradigm in economics have recently been discussed by Hall and Klitgaard (2006) who state (sic) “that no resource can be viewed as truly sustainable at present rates of production, consumption and growth because all are subsidized by cheap petroleum” and that the value of a resource should be based on their EROI which stands for “energy return on investment”, and refers most explicitly to the ratio of energy delivered to society from one unit invested in getting that particular energy.

Ecological, bio-diverse, local agriculture is part of the solution to global warming and food scarcity. Under these conditions even the developed countries will recognize that priority must be given to ruminants and other herbivores that transform biomass into food resources with minimum jeopardy to the environment.


Anthwal A, Joshi V,  Sharma A  and Anthwal S 2006  Retreat of Himalayan Glaciers – Indicator of Climate Change. Nature and Science 4(4) 53-59

Brown L R 2001  Eco-Economy: Building an Economy for the Earth (NY: W.W. Norton& Co.,).   Earth Policy Institute

Brown LR  2005  Outgrowing the Earth: The Food Security Challenge (NY: W.W. Norton & Co., 2005).   Earth Policy Institute.

Brown LR 2007 Biofuels Blunder: Massive Diversion of U.S. Grain to Fuel Cars is Raising World Food Prices, Risking Political Instability.

Campbell  C J 1997  The Coming Oil Crisis. Multi–Science Publishing, Essex, UK.

Campbell C J and Leherrere J H 1998  The End of Cheap Oil. Scientific American March, 1998. Retrieved 2 January 1999 from

Carney K M,  Hungate B A, Drake BG and Megonigal J P 2007  Altered soil microbial community at elevated carbon dioxide leads to loss of soil carbon. Proceedings National Academy of Science Open Access article

Carlson C E 2007  Corn-to-Ethanol: US Agribusiness Magic Path to a World Food Monopoly. (sighted 1-10-07)

CGIAR Sighted 1/10/07) Global Climate Change: Can Agriculture Cope? global/climate.html  

Cline W 2007 Global warming and agriculture: Impact estimates by country ( )

Conway G and Toenniessen G 1999  Feeding the world in the twenty-first century. Nature Suppl 402: C55-C58

Delgado C L, Rosegrant M W and Meijer S 2002  Livestock to 2020.The Revolution Continúes. In World Brahman Congress, Rockhampton, Australia,  April 2002. 

Delgado C, Rosegrant M, Steinfeld H, Ehui S  and Courbois C 1999. Livestock to 2020; The Next Food  Revolution. Food, Agriculture,and the Environment Discussion Paper 28.International Food Policy Research  Institute. Washinton DC

Déry P and Anderson B 2007  Peak phosphorus: Energy Bulletin, Archived on 13 Aug 2007.

Dolberg F  and Finlayson P 1995  Treated straw for beef production in China.  World Animal Review  82, 14

Deffeyes  K S 2001  Hubberts Peak; The Impending World Shortage of Oil. Princetown University Press,New Jersey, USA.

Fleay B J 1995   Decline of the Age of Oil. Pluto Press, Annandale, NSW, Australia.

Frink C R, Waggoner P E and Ausubel S H 1999  Nitrogen fertilizer: retrospect and prospect. Proceedings National Academy of  Sciences.  USA 96: 1175-1180.

Giampietro M, Mayumi K and Ramos-Martin J 2006 Can biofuels replace fossil energy fuels? Multi-scale integrated analysis based on the concept of societal and ecosystem metabolism: Part 1 International Journal of Transdisciplinary Research Volume 1, No. 1, 2006 51-87

Giampietro M, Ulgiati S and Pimentel D 1997 “Feasibility of large-scale biofuel production: Does an enlargement of scale change the picture?” BioScience, 47(9): 587-600.

Howden S M and Reyenga  P  J 1999  Methane emissions from Australian livestock. In Meeting the Kyoto Target, Implications for the Australian Livestock Industries, Reyenga, P J and Howden S M, pp. 71-79).

Hubbert M K 1956  Nuclear Energy and Fossil Fuels. Proceedings American Petroleum Institute Drilling and Production Practices, pp. 7–25, Spring Meeting, San Antonio, Texas

IFIA 1997 International Fertilizer Industry Association. Annual report. In an Age of Falling Water Tables and Rising Temperatures (NY: W.W. Norton

Jensen M E, Rangeley W R and Dieleman P J 1990 Irrigation trends in world agriculture. In: Irrigation of Agricultural Crops. American Society of Agronomy, Madison, Wisconsin, pp. 31-67.

Klieve A V and Ouwerkerk D  2007 Comparative greenhouse gas emissions from herbivores, p. 487 – 500. In  Proceedings of the 7th International Symposium on the Nutrition of Herbivores (Beijing, China). Q X Meng, LP Ren and Z J  Cao (ed.) China Agricultural University Press, Beijing

Kurihara M, Shibata M, Nishida T, Purnomoadi A and Terada F 1997  Methane production and its dietary manipulation in ruminants. In Rumen microbes and digestive physiology in ruminants, Onodera, R., Itabashi, H., Ushida, K., Yano, H. and Sasaki, Y., pp. 199-208. Tokyo: Japan Scientific Societies Press)  as presented by Howden and Reyenga (1999) adapted from  Klieve, A.V. and D. Ouwerkerk. (2007)

Leng R A 1990 Factors effecting the utilisation of poor quality forages by ruminants particularly under tropical conditions  Nutrition Research Reviews  3, 277.

Leng  R A 1991 Improving ruminant production and reducing methane emissions from ruminants by strategic supplementation. A Report prepared for the Environmental Protection Agency of the U.S.A. EPA/400/1-91/004

Leng  R A 1994   Look at it this way. Outlook on Agriculture 23, 77{80.

Leng  R A  2002   Future directions of animal productionin a fossil fuel hungry world. Livestock Research for Rural Development, 14 (5 .

Leng  R A  2004   Requirements for protein meals for ruminant meat production. In: Protein Sources for theAnimal Feed Industry. Expert Consultation and Workshop, Bangkok, May 2002, pp. 225–254. FAO,Rome, Italy.

Leng R A 2005  Implications of the decline in world oil reserves for future world livestock production Recent Advances in Animal Nutrition in Australia, Volume 15 (2005) 95-106 pub university of New England, Armidale Australia

Leng R A 2007  Morality of Biofuels. Science Alert

Lukefahr S D 2007: Strategies for the development of small- and medium-scale rabbit farming in South-East Asia. Livestock Research for Rural Development. Volume 19, Article #138.

Marschner H and  Dell B 1994  Nutrient uptake in mycorrhizal symbiosis. Plant Soil 159: 89-102

Patzek  T  W  and Pimentel  D  2006  Thermodynamics of energy production from biomass, Critical Reviews in Plant Sciences 24(5–6): 329–364, Available at www.  .

Patzek  T  W  and Pimentel  D  2006  Thermodynamics of energy production from biomass, Critical Reviews in Plant Sciences 24(5–6): 329–364, Available at

Patzek  T  W  2004  Thermodynamics of the corn-ethanol biofuel cycle, Critical Reviews in Plant Sciences 23(6): 519–567, An updated web version is at

Patzek T W 2007  How can we outlive our way of life; Paper prepared for the 20th Round Table on Sustainable Development of Biofuels: Is the Cure Worse than the Disease? OECD Headquarters, Chˆateau de la Muette, Paris, 11-12. September  2007  

Peng  S , Huang J , Sheehy J E, Laza R C, Visperas R M , Zhong X, Centeno G S, Khush G S  and Cassman  K G 2004   Rice yields decline with higher night temperature from global warmingProc. Nat Acad  Sci  USA  101 ( 27 ), 9971-9975

Perdoc H B and Leng R A  1990 Effect of supplementation with protein meal on the growth of cattle given a basal diet of untreated or ammoniated rice straw. Asian –Australasian Journal of Animal Science 3, 269.

Pimentel  D 2001 Biomass Utilization,Limits of. In Encyclopedia of Physical Science and Technology. Third Edition Vol 2 pages 159.

Pimentel D, Warneke A F, Teel W S, Schab K A, Simcox N J, Ebert  D M, Baenisch  K D  and Aaron M R 1988  Food versus biomass fuel; Socio-economic and environmental impacts in the United States, Brazil, India and Kenya. Advances in Food Research 32 185-238

Postel S 1992  Last Oasis. Facing Water Scarcity .Publisher WW Norton, NY Earth Policy Institute

Postel S 1999  Pillar of sand:Can the miracle of irrigation last?Publisher WW Norton NY. Earth Policy Institute

Preston T R 2007 A carbon-negative model for production of feed and fuel from biomass; experiences in Cambodia and Colombia.

Preston T R and Leng R A 1987 Matching Livestock Systems to Available Resources in the Tropics and Sub Tropics. Penambul Books, Armidale, Australia

Roberts T L and Stewart W 2002 Inorganic Phosphorus and Potassium Production and Reserves Better Crops/Vol. 86 (2002, No. 2) pages 6-7$webindex/ADC8E71EF80F70D785256BDB004837F8/$file/02-2p06.pdf

Revenga  C, Murray  S, Abramovitz  J and Hammond A  1998  Watersheds of the World: Ecological Value and Vulnerability. World Resources Institute.Washington, DC.

Revenga  C  J,  Brunner  N,  Henninger  K,  Kassem  R and Payne  2000  Pilot Analysis of Global Ecosystems (PAGE): Freshwater Systems. World Resources Institute

Rickover G 1957  "Energy resources and our future" - remarks by Admiral Hyman Rickover delivered in 1957

Roberts P  2004   End of Oil. Bloomsbury Publishing,London,UK.

Smith  B E  2002 “Nitrogenase Reveals Its Inner Secrets”, Science, 6 September 2002: Vol. 297. no. 5587, pp. 1654 – 1655,

Smil V 1999  Nitrogen in crop production. Glob Biogeol Cycl 13: 647-662

Steen  I  1998  Phosphorus availability in the 21st century: Management of a non-renewable resource, Phosphorus & Potassium. British Sulphur Publishing, No. 217, 25-31.

Stern N 2007   Stern Review on the economics of climate change

Vandana Shiva, AlterNet. (Sighted October 1, 2007).

Vance P R 2001  Update on the state of nitrogen and phosphorus nutrition: Symbiotic nitrogen fixation and phosphorus acquisition: Plant nutrition in a world of declining renewable resources Plant Physiol, October 2001, Vol. 127, pp. 390-397

Waterlow J C 1998   with contributions by Tomkin A M & Grantham-McGregor. Protein-energy malnutrition. Edward Arnold, London

Wong  CM, Williams  CE, Pittock  J, Collier  U and P Schelle 2007 World’s top 10 rivers at risk. WWF International. Gland, Switzerland.

Youngquist  W 1997 Geodestinies National Book Company Portland Oregon

Youngquist  W 1998 Spending our great inheritance—Then what? Geotimes $#,[7] 24-27

Received 30 November 2007; Accepted 21 December 2007; Published 1 January 2008

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