This is the ninth (and final) part of a much longer article published in the journal Science Progress, and which may be found here: http://stl.publisher.ingentaconnect.com/content/stl/sciprg/2014/00000097/00000002/art00001
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.
(2) Rhodes, C.J. (2012) Feeding and healing the world: through regenerative agriculture and permaculture. Sci. Prog., 95(4), 345-446.
(3) Bai, Z.G. et al. (2008) Proxy assessment of land degradation. Soil Use and Management. 24, 223-234.
(4) Bai, Z.G. et al. (2008) Global assessment of land degradation and
improvement 1. Identification by remote sensing. Report 2008/01, ISRIC, Wageningen.
(5) Adams, C.R. and Eswaran, H. (2000) Global land resources in the context of food and environmental security. In: Gawande SP, editor. Advances in Land Resources Management for the 20th Century. New Delhi: Soil Conservation Society of India, 35-50.
(6) UNEP (2008) Africa: atlas of our changing environment. Division of early warning and assessment (DEWA) United Nations Environment Programme (UNEP). Nairobi 00100, Kenya.
(7) Snel, M.and Bot, A. (2003) Draft paper: suggested indicators for land degradation assessment of drylands. FAO, Rome.
(8) Agro-ecological zoning and GIS application in Asia with special emphasis on land degradation assessment in drylands (LADA). Proceedings of a Regional Workshop, Bangkok, Thailand10–14 November 2003. FAO, internet website: ftp://ftp.fao.org/agl/agll/docs/misc38e.pdf, accessed July 1, 2008.
(9) Dobie, P. (2001) Poverty and the drylands. United Nations Development Programme, Dryland Development Centre. Nairobi, Kenya.
(10) Kapalanga, T.S. A review of land degradation assessment methods. http://www.unulrt.is/static/fellows/document/taimi-1-.pdf
(11) Eswaran, H., Lal, R. And Reich, P.F. Land degradation: an overview. http://soils.usda.gov/use/worldsoils/papers/land-degradation-overview.html
(13) Stocking, M. (2001) A handbook for the field assessment of land degradation. Earthscan Publications U.K.
(14) Rhodes, C.J. (2008) The oil question: nature and prognosis. Sci Prog. 91(4), 317-375.
(15) Rhodes, C.J. (2013) Peak phosphorus – peak food? The need to close the phosphorus cycle. Sci Prog. 96(4), 109-152.
(16) Blanco, H. and Lal. R. (2010) Tillage erosion. principles of soil conservation and management. New York: Springer. ISBN 978-90-481-8529-0.
(17) Committee on 21st Century Systems Agriculture. Toward Sustainable Agricultural Systems in the 21st Century. National Academies Press; 2010 ISBN 978-0-309-14896-2.
(18) Nîr D. M. (1983) A geomorphological agent: an introduction to anthropic geomorphology. New York: Springer. p. 121–122. ISBN 978-90-277-1401-5.
(19) Intergovernmental Panel on Climate Change (IPCC) (1995). Second Assessment Synthesis of Scientific-Technical Information relevant to interpreting Article 2 of the UN Framework Convention on Climate Change, p. 5.
(20) Pruski, F. F. and Nearing, M..A. (2002) Runoff and soil loss responses to changes in precipitation: a computer simulation study. J. Soil Water Conserv. 57(1), 7–16.
(21) Lane, L.J., Shirley, E.D. and Singh, V.P. (1988) Modeling erosion on hillslopes. In: M.G. Anderson , editor. Modeling Geomorphological Systems. New York: John Wiley, p.287-308
(22) Kinnell, P.I.A. (2010) Event soil loss, runoff and the universal soil loss equation family of models. J. Hydrol. 385(1-4), 384-397.
(23) Nearing, M.A. (2000) Measurements and models of soil erosion rates. Science. 290, 1300-1301.
(24) Wischmeier, W.H., C.B. Johnson, and B.V. Cross (1971) A soil erodibility nomograph for farmland and construction sites. J. Soil Water Conserv. 26, 189-193.
(25) Pimentel, D. et al. (1995) Environmental and economic costs of soil erosion and conservation benefits. Science. 267, 1117-1123.
(26) Boardman, J. J. (1998) An average soil erosion rate for Europe: myth or reality? Soil and Water Conserv. 53(1), 46-50.
(27) Arden-Clarke. C. and Evans, R. (1993) Soil erosion and conservation in the United Kingdom. In: Pimentel D, editor. World soil erosion and conservation. Cambridge: Cambridge University Press, p.192-215.
(28) Evans, R. (1995) Some methods of directly assessing water erosion of cultivated land – a comparison of measurements made on plots and in fields. Prog. Phys. Geog. 19(1), 115-129.
(29) Ryszkowski, L. (1993) Soil erosion and conservation in Poland. In: Pimentel D, editor. World soil erosion and conservation. Cambridge: Cambridge University Press, p. 217-232.
(30) Crosson, P. (1995) Soil erosion estimates and costs. Science. 269, 461-463.
(31) Lal, R. (1990) Soil erosion and land degradation: the global risks. In: Lal R. and Stewart, S.A., editors. Soil degradation, New York: Springer-Verlag, p132.
(32) Brown, L. (1984) In: Norton WW, eitor. State of the world 1984. New York: Worldwatch Institute.
(33) Pimentel, D. et al. (1995) Science. 269, 264-465.
(34) Oldeman. L., Hakkeing. R. and Sombroeck, W. (1990) World map of the status of human-induced soil degradation: an explanatory note. International soil and reference information center, Wageningen. Nairobi Kenya: The Netherlands, and United Nations programme.
(35) Trimble, S.W. and Crosson, P. (2000) U.S. soil-erosion rates – myth and reality. Science. 289, 248-250.
(36) Cerdan, O. et al. (2012) Geomorphology, 122, 167-177.
(37) Parsons. A.J. et al. (2004) A conceptual model for determining soil erosion by water. Earth Surf. Process. 29, 1293-1302.
(39) Dregne, H.E. and Chou, N.T. (1994) Global desertification dimensions and costs. In: Dregne, H.E., editor. Degradation and restoration of arid lands. Lubbock: Texas Technical University.
(40) Eswaran, H. and Reich, P.F. (1998) Desertification: a global assessment and risks to sustainability. Proc. 16thInt. Cong. Soil Sci. Montpellier: France.
(41) Sonneveld, B.G.J.S. and Dent, D.L. (2009) How good is GLASOD? J. Env. Management. 90, 274-283.
(42) Montgomery, D.R. (2007) Soil erosion and agricultural sustainability. PNAS. 33, 13268-13272.
(43) Stocking. M. (2003) Erosion and crop yield. Encycloped. Soil. Sci. New York: Marcel Dekker Inc. p. 1-3.
(44) Bakker, M.M., Govers, G. and Rounsevell, M.D.A. (2004) The crop productivity-erosion relationship: an analysis based on experimental work. Catena. 7, 55-76.
(45) Bakker, M.M. et al. (2007) The effect of soil erosion on Europe’s crop yields. Ecosystems. 10(7),1209 – 1219.
(46) Bakker, M.M. et al. (2005) Soil erosion as a driver of land use change. Agricul. Ecosyst. Env. 1005, 467-481.
(47) Bakker, M.M. et al. (2008) The response of soil erosion and sediment export to land-use change in four areas of Europe. Geomorphology. 98, 213-226.
(48) Sattari, S.Z. et al. (2012) Residual soil phosphorus as the missing piece in the global phosphorus puzzle. PNAS. 109(16), 6348-6353.
(49) Veneklaas. E.J. et al. (2012) New Phytologist. 195, 306-320.
(52) Baker, J.M. (2007) Tillage and soil carbon sequestration – what do we really know? Agricul. Ecosyst. Env. 118, 1-5.
(54) Gattinger, A. et al. (2012) Enhanced top soil carbon stocks under organic farming. PNAS. 109(44), 18226-18231
(55) Leifeld, J. et al. (2013) Organic farming gives no climate change benefit through soil carbon sequestration. PNAS Early Edition. http://www.pnas.org/content/early/2013/02/20/1220724110.full.pdf
(56) Gattinger, A. et al. (2013) Reply to Leifeld et al.: Enhanced top soil carbon stocks under organic farming is not equated with climate change mitigation. PNAS Early Edition. http://www.pnas.org/content/early/2013/02/20/1221886110.full.pdf
(58) Lal, R. (2011) Management to mitigate and adapt to climate change. J. Soil Water Conserv. 66, 276-285.
(59) Hopkins R. (2008) The transition handbook – from oil dependency to local resilience. Totnes, U.K.: Green Books Ltd.
(60) Ekebafe, M.O., Ekebafe, L.O. and Maliki, M. (2013) Utilisation of biochar and superabsorbent polymers for soil amendment. Sci. Prog. 96, 85-84.
(61) Petersen, J.B., Neves, E. and Heckenberger. M.J. (2001) Gift from the Past: Terra Preta and Prehistoric Amerindian Occupation in Amazonia.In: McEwan C et al. eds. Unknown Amazon: Culture and Nature in Ancient Brazil. London: British Museum Press, p. 86-105.
(62) Lehmann. J. et al. (2011) Biochar effects on soil biota – a review. Soil Biol. and Biochem. 43, 1812-1836.
(63) Fischer, D. and Glaser, B. (2012) Synergisms between compost and biochar for sustainable soil amelioration. In: Sunil K, Barti A, editors. Management of Organic Waste. Chapter 10. Open Access: Intech, p. 167-198. http://cdn.intechweb.org/pdfs/27163.pdf
(65) Yang, H. et al. (2004) Land and water requirements of biofuel and implications for food supply and the environment in China. Energy Policy, 37(5), 1876–1885.
(66) S. Khan, M.A. and Hanjra, J. M. (2009) Water management and crop production for food security in China: a review. Agricultural Water Management, 96, 349-360.
(67) L.Reijnders, http://scitizen.com/stories/future-energies/2009/04/Biofuels-and-water/
(72) Aiken, R.M. et al. (2013) Replacing Fallow with Continuous Cropping Reduces Crop Water Productivity of Semiarid Wheat. Agron. J. 105(1), 199-207.
(75) Mollison, B. and Jeeves, A. (1988) Permaculture: A Designers’ Manual. Tasmania: Tagari Publications. ISBN 978-0908228010.
(76) Holmgren, D. (2011) Permaculture: Principles and Pathways Beyond Sustainability. East Meon: Permanent Publications. ISBN 978-1856230520
(81) Buckminster Fuller, R. (2008) Operating Manual for Spaceship Earth. Lars Muller. ISBN 978-3037781265
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. http://upload.wikimedia.org/wikipedia/commons/d/d3/Estructura-suelo.jpg
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: http://soils.usda.gov/education/resources/lessons/texture/. Credit Mikenorton. http://upload.wikimedia.org/wikipedia/commons/8/80/SoilTexture_USDA.png
Figure 3. Iron rich red soil near Paint Pots mineral springs in Kootenay National Park, British Columbia, Canada. Credit Marek Ślusarczyk. http://upload.wikimedia.org/wikipedia/commons/7/75/Kootenay_National_Park_-_Paint_Pots_1.jpg
Figure 4. The soil food web. Credit USDA. http://upload.wikimedia.org/wikipedia/commons/8/89/Soil_food_webUSDA.jpg
Figure 5. A hillside covered in rills and gullies due to erosion processes caused by rainfall. Credit: Ivar Leidus. http://upload.wikimedia.org/wikipedia/commons/7/7b/Rummu_aherainem%C3%A4gi2.jpg
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. http://upload.wikimedia.org/wikipedia/commons/a/a9/Globalndvi_tmo_200711_lrg.jpg
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. http://upload.wikimedia.org/wikipedia/commons/b/bf/Terra_Preta.jpg
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[http://water.usgs.gov/GI http://upload.wikimedia.org/wikipedia/commons/f/f7/Ogallala_changes_in_feet_1980-1995_USGS.gif
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 www.gifteconomy.org.au
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 www.gifteconomy.org.au