Monday, August 04, 2014

Soil Erosion, Climate Change and Global Food Security: Challenges and Strategies. Part 9.

This is the ninth (and final) part of a much longer article published in the journal Science Progress, and which may be found here:

24. How many people can the Earth support?

It is claimed78 that “a population density of 6─10 people per acre might be supported through permaculture, and in excess of the number that our current cereal-based food economy can sustain”. Since our ability to grow cereals, in the quantity we do, depends on industrialised agriculture, with its considerable inputs of oil- and gas-based fuels, fertilizers and pesticides, the practice is not sustainable and so the comparison is not strictly valid. We are then left with the question of how many people might be supported by the earth, if permaculture methods were widely introduced. If we assume the lower limit, this means that 15 people can be fed per hectare. Thus, to feed the human population of 7 billion, we would need 467 million hectares of land, or 4.7 million km2. Since we have 150 million km2 of dry land, and around 14 million km2 of arable land, it would appear there is no problem in sustaining the present global population, and that supporting even 9 billion by 2050, or 12 billion by 2100, is feasible. Toby Hemenway, regarded as one of the gurus of permaculture, is less optimistic, and believes that the maximum carrying capacity of the Earth is nearer 2 billion.79 [This is also the number arrived at by Pimentel et al.80, on the basis of the limited resources of energy, water and food available to us, and it seems most likely that it is failing supplies of these key inputs, particularly freshwater, that will reduce and finally limit our population. One is reminded of the “four horsemen of the apocalypse”: pestilence, war, famine and death, each rider being perceivable in a guise of resource shortages. Since the consequence of consumption is pollution, this too must prove a determinant to the numbers of humans that can live sustainably on “Spaceship Earth”, as the visionary Buckminster Fuller termed81 our existence].

Other permaculturists are far more sanguine than Hemenway about what might be achieved, in terms of sustaining the global population, and point out that predictions of food shortages are based on limits of the resources that are necessary for modern agriculture, whereas permaculture is based on the interacting and holistic mechanisms of nature, where nothing is wasted and everything is recycled, all elements being returned to the ecosystem, by death, and from which new life can flourish. David Blume claims to have fed up to 450 people on two acres (0.8 ha) of land for 9 years, by the end of which the soil contained 22% SOM, with a CEC of >25 (a measure of its humus content). This amounts to ca 18 m2/person, which might be understood to imply that the current world population of 7 billion could be fed on just 120,000 km2 of land. The key to this success is polyculture, which benefits from the growth of mycorrhizal fungi and less solar saturation82. Blume has described this technique as “restorative agriculture”, and he believes that there is, correspondingly, no immediate limit to the number that can be fed on Planet Earth, and that ethanol fuel, produced on the local scale could meet all our energy needs – including electricity production – and obviate the need for crude oil. Hemenway has spoken83 on the subject of: “How Permaculture Can Save Humanity and the Earth, but Not Civilization,” which may initially sound like an oxymoron. It is in fact a rather more subtle proposition, to the effect that while permaculture cannot sustain the present global economy and global civilization with a population of 7 billion people, it might support a lesser number of up to 2 billion, but, of necessity, its practices mean living in small communities. Thus, the civilization that permaculture could sustain is a globe of villages, not the global village. The principles of permaculture are central to the growing community-based Transition Towns movement59.


As we have seen, the subject of land degradation is complex. A significant part of this complexity lies in establishing a clear link between the degree of degradation – principally from soil erosion – and declining crop yields, since the latter can be masked by the application of fertilizers to improve soil productivity, even in cases where the soil has been significantly degraded. Irrigation is a key factor too. Most determinations of the extent of land degradation (e.g. GLASOD) have been made on the basis of “expert judgement” and perceptions, as opposed to direct measurements of this multifactorial phenomenon. More recently, satellite-based remote sensing measurements have been used to provide some overview of the global situation. Globally, the amount of biomass was measured to increase by 3.8% during the years 1981─2003, which is thought due to the fertilization effect of rising atmospheric CO2 concentration. However, 24% of the global land area suffered some degree of degradation over the same period. Hence, there are regions of “greening” while elsewhere, “browning” has occurred. It appears that while long-term trends in NDVI derivatives are only broad indicators of land degradation, taken as a proxy, the NDVI/NPP trend is able to yield a benchmark that is globally consistent and to illuminate regions in which biologically significant changes are occurring. Thus attention may be directed to where investigation and action at the ground level is required, i.e. to potential “hot spots” of land degradation and/or erosion.

The term “sustainable agriculture” has been described as an oxymoron, on the basis that by its very nature, agriculture is ultimately unsustainable84. It is not simply the degradation of the soil, or the loss of biodiversity that are at issue, but that the external energy inputs amount to perhaps ten times that actually consumed in the food itself. In the absence of a cheap and plentiful supply of crude oil (and the fuels, pesticides and herbicides that are derived from it), cheap natural gas (from which nitrogen fertilizers are made), and mined phosphate rock (used to make phosphorus fertilizers and mined using machinery powered by fuels refined from crude oil), the present industrialized global agricultural mechanism would be impossible, and it is only through the latter that the global human population has risen to its present number. Projections about future population numbers tacitly assume that these inputs will prevail into the future, when all evidence is that the age of cheap oil and gas is drawing to a close. It is very likely that the present system of large-scale industrialized agriculture will not survive, and humans will return to growing food on smaller areas, including the adoption of urban permaculture, as happened in Cuba when its bestowals of cheap fuels, and other agricultural inputs (pesticides, herbicides, fertilizers) from the Former Soviet Union were curtailed by the collapse of Communism2.While in principle, a permaculture approach can be applied on all scales (from the small plot to the full field), it cannot be adopted as a substitute for industrialized modern monoculture crop production since it is implicitly holistic. Accordingly it is not possible to separate our growing of food from other aspects of community, and so to adopt the design principles of permaculture for our food production, we must adapt all other lifestyle elements as an underpinning and simultaneous part of the process.

As fuel prices rise, and actual shortages of fuel ensue, long-distance mass transportation of food will no longer be economic or feasible, further driving food production at the local level, as a means to achieve food security and community resilience. The loss of soil organic matter (SOM) is a critical factor both in soil erosion and in the loss of soil productivity, the latter from the loss of soil (depth) per se, and a decline in the structure, level of nutrients and hence the innate fertility of the soil. Thus, by increasing the SOC, the structure of the soil is improved, which increases its holding capacity for water, and allows better drainage, hence there is more groundwater and less flooding, while droughts are mitigated. The agricultural productivity of the soil is heightened, enlarging crop yields, and soil erosion is attenuated, especially if the ground is also covered by mulching or with cover crops. Degraded lands may be restored in their production through increasing their SOC content, giving better soil, and water quality. The improved soil structure leads to a better retention of water and nutrients, and smaller inputs onto the farm of oil-based fuels, fertilizers, pesticides and herbicides, while biodiversity is enhanced. The term “biodiversity” does not only refer to what is visible above the ground, but also to the roots systems of plants, and their accompanying fungal rhizosphere which is an essential part of the soil food web. The importance of rebuilding the soil food web2 – the ecosystem of microbes, and visible creatures that dwell in soil – is central to maintaining food production in perpetuity, i.e. achieving a system that is truly sustainable.

The Chikukwa project shows that by using low tech methods, even highly degraded land, with severely eroded soil can be brought back to life - and with very little money, but a good design. This is not a quick-fix strategy, and has taken over two decades to come to achieve; however, it is a sustainable landscape, which is the more important element. In part it may appear that the case for catastrophic land degradation through soil erosion, and an according threat to the survival of humanity has been overstated, although the rising human population will increase demand inexorably for what the soil can provide. It must be stressed, that the productivity of much agricultural land is maintained only through those inputs, of oil and natural gas (from which fuels, pesticides, herbicides and fertilizers are sourced), and irrigation water, which are vital organs of current industrial food production. Therefore, on grounds of stabilising the climate, preserving the environment, and ensuring the robustness of the global food supply, maintaining and building good soil, in particular improving its SOM content and hence its structure, is highly desirable. In particular, those regions of the world that are significantly degraded are unlikely to support an appreciable population increase (e.g. Africa, whose population is predicted70 to grow from its present1.1 billion to 4.2 billion by 2100) in which case a die-off or mass migration might be expected, if population limitations are not included in future plans to achieve sustainability and food security.

The latter figure should be placed in the context of a total70 world population of almost 11 billion by 2100, nearly 40% of which would therefore be African. It is more likely, however, that a constraint on the size of future populations will be imposed by an insufficiency of oil, gas and therefore food, to sustain the growing multitude. Indeed, rather than the number of humans on Earth increasing throughout the present century and probably beyond, there are various analyses which indicate instead that the population will peak at some stage before 2100. It is probable that industrial populations will soon peak85, with the developing nations following suit around 40 years later as they try to emulate their current industrial counterparts. The population of Europe has been estimated85 to peak in 2025, with the world population peaking at around 8.5 billion around the year 2050. However, a critical loss in the global oil (and hence, food) supply could precipitate a more immediate and rapid decline in human numbers.



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Captions to figures.

Figure 1. Vertical structure of a typical soil. Mediterranean red soil. A, represents soil; B, represents laterite, a regolith; C, represents saprolite, a less-weathered regolith; the bottom-most layer represents bedrock. Credit Carlosblh.

Figure 2. A soil texture diagram- soil types according to their clay, silt and sand composition, as used by the USDA, redrawn from the USDA webpage: Credit Mikenorton.

Figure 3. Iron rich red soil near Paint Pots mineral springs in Kootenay National Park, British Columbia, Canada. Credit Marek Ślusarczyk.

Figure 4. The soil food web. Credit USDA.

Figure 5. A hillside covered in rills and gullies due to erosion processes caused by rainfall. Credit: Ivar Leidus.

Figure 6. Normalized Difference Vegetation Index (NDVI) from November 1, 2007, to December 1, 2007, during autumn in the Northern Hemisphere. Food, fuel, and shelter: vegetation is one of the most important requirements for human populations around the world. Satellites monitor how “green” different parts of the planet are and how that greenness changes over time. These observations can help scientists understand the influence of natural cycles, such as drought and pest outbreaks, on vegetation, as well as human influences, such as land-clearing and global warming. Credit: NASA.

Figure 7. Global soil regions. Source: U.S. Department of Agriculture.

Figure 8. Fertility of world’s soils.

Figure 9. Left - a nutrient-poor oxisol; right - an oxisol transformed into fertile terra preta. Credit: Bruno Glaser.

Figure 10. Subsurface waters. Source U.S.G.S.

Figure 11. Replenishment of aquifers by infiltration. Source: U.S.G.S.

Figure 12. Natural and artificial recharge of groundwater. Source: U.S.G.S.

Figure 13. A browse image of the water-level-change contours data set for the High Plains aquifer, 1980 to 1995. Credit: McGuire, Virginia L. and Sharpe, Jennifer B. '''Source''': United States Geological Survey[

Figure 14. This shot shows how the Chikukwa lands looked in the early nineties,
bare hillsides and soil erosion, with the consequence in poor nutrition. Credit: Terry Leahy

Figure 15. This picture shows a small section of the Chikukwa clan lands as they are now. The houses nestled among orchards, the bunds with vetiver grass in the
cropping fields and the extensive woodlots are all typical of this design strategy. Credit: Terry Leahy


Jessica said...

A good way to combat erosion and harmful sediments is using quality inlet filters. Thanks for the post!

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techno said...

useful information of erosion control and how can we prevent it.
nice and unique article keep sharing this type of informative updates
soil erosion definition

samuel woods said...

lack of importance and knowledge of farming leads people to convert farmland into residential and commercial place.
It causes heavy damage to soil and converts it into soil erosion

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Alicia climent said...

Soil erosion is the displacement of the upper layer of soil, the agents of soil erosion are the same as the agents of all types of erosion: water, wind, ice, or gravity. Running water is the leading cause of soil erosion because water is abundant and has a lot of power. The wind is also a leading cause of soil erosion because wind can pick up soil and blow it far away.