Chapter 1 The Indispensable Dirt

Chapter 1 charts the remarkable soil systems that sustain much of terrestrial life. I spoke to several experts whose views on this subject are included in the book. I offer the following published sources by way of further background.

Page 27. I cite an estimate that one-third of farmed soil has been degraded since the mid-20th century. This figure taken from: Oldeman L.R. (1992). Global Extent of Soil Degradation. ISRIC Bi-Annual Report 1991-1992. The figure in question is found on page 33. The full paper can be seen on-line at:

Page 30. I point out how the organic matter in soil can enable it to hold much more water than when the organic content is lower. For a source on this subject see: Dick, W.A. et al. (2004): Developing and maintaining soil organic matter levels. In: Managing Soil Quality Challenges in Modern Agriculture. (Eds. P. Schjonning, S. Elmholt & B.T. Christensen). CABI Publishing, Wallingford. pp.103-120.

Page 31. On the diversity and mass of bacteria dwelling in soil, see for example: Ritz K. (2003) Underview: origins and consequences of belowground biodiversity. In: BES Soil Biodiversity and Ecosystem Function, Bardgett et al. (eds.), Lancaster, U.K.
See also: Bardgett, R. (ed.). (2005). The biology of soil: A community and ecosystem approach. Oxford. This publication can be found on-line at:

Page 32. On the question of soil carbon storage, I cite a figure of some 10 billion tonnes being stored in UK soils. For the source of this number see: Milner, R. & Brown, T. A. (1997). Carbon in the vegetation and soils of Great Britain. Journal of Environmental Management. Vol. 49. 413-433. This paper can be found on-line at:

Page 32. Regarding the estimate that there is more carbon in the soils of the English uplands than trees in the UK and France put together, see: HM Government, (2006). Climate Change: The UK programme 2006. HMG. The number in question can be found on page 102. This resource can be found on-line at:

Page 33.   I cite a figure from the Environment Agency on how one hectare of soil can filter enough water to supply 1000 people. This comes from the Agency’s Corporate Strategy 2010-2015 and can be found on-line at: The same figure can also be found in a DEFRA strategy document: DEFRA, (2009). Soil strategy for England: supporting evidence paper. DEFRA. This is available at

Page 34. On the estimated loss of 1.6 billion tonnes of soil from the Yellow River catchment, see the website of the Ministry of Water Resources the People’s Republic of China:

Page 34. The estimate that about one third of farmed soils have become degraded since the mid-twentieth century can be sourced from:  page 33 of Global Extent of Soil Degradation, L.R. Oldeman, ISRIC Bi-Annual Report 1991-1992 the full paper can be seen on-line at

Page 35. For a source on the rate of peat loss in Eastern England, see: Hodge, C.A.H. et al. (1984). Soils and their use in Eastern England. Soil Survey of England and Wales Bulletin No.13. Harpenden. And for a source on the estimate that the exposed lowland peatlands of England are releasing about six millions tonnes of carbon per year, see: Thompson, D. (2008). Carbon Management by Land and Marine Managers. Natural England Research Reports, Number 026. This report may be found on-line via the Natural England website.

Page 35. For a source on the rate of soil loss in different parts of the world, see a 2006 study by Cornell: Pimentel, D. (2006). Soil Erosion: A Food and Environmental Threat. Environment, Development and Sustainability. Vol. 8 (1) 119-137. This paper can be found on-line at:

Page 37. For more on how soil loss has led to the historical collapse of civilisations and societies, including those mentioned on page 37, see: Diamond, J.M. (2005). Collapse: How Societies Choose to Fail or Succeed. Penguin. ISBN-10: 0143117009; ISBN-13: 978-0143117001.

Pages 37 and 39. On page 37 I refer to the area of cropland and pasture created between 1985 and 2005 and give an estimate of the area of the land surface that is now cultivated. On page 39 I mention the increase in food production achieved since 1960. These figures were taken from the Millennium Ecosystem Assessment. This vast study is presented in several volumes, but an overview can be found in: Millennium Ecosystem Assessment, 2005. Ecosystems and Human Well-being: Synthesis. Island Press, Washington, DC. The synthesis report can be found at:

Page 38. I mention the estimate from FAO that demand for food will increase by 70 per cent by 2050. A way into the background behind that figure can be found at the FAO website here:

Page 38. The estimate that some 56 million hectares of land was acquired by bodies outside the countries concerned comes from a World Bank report: Deininger, K. (2011). Rising Global Interest in Farmland: can it yield sustainable and equitable benefits? World Bank, Washington DC. This report can be accessed on-line at:

Page 40. On the long-term loss of soil organic matter caused by cultivation, and what might be done to reverse that trend, this review provides a helpful way into the literature: Liu, X. et al. (2006). Effects of agricultural management on soil organic matter and carbon transformation – a review. Plant soil environ., 52(12): 531–543. Find this paper on-line at:

Page 41. For further background on perennial grain-producing plants, see: Glover, J.D. (2005). The necessity and possibility of perennial grain production systems. Renewable Agriculture and Food Systems. Vol. 20(1). 1-4. This piece can be found on-line at:;jsessionid=D02C09F5EE08F3AE5FFDC89489524B76.journals?fromPage=online&aid=688096

Page 41. For more information on the world of the Agroforestry Research Trust, see their website at:

Page 43. For a powerful impression of both the historical level of erosion on the Loess Plateau in China, and how restoration work has succeeded in restoring its productivity, see this inspiring and informative video:

Page 44. For a little more on how sustainable farming in Kenya has helped to improve incomes, carbon storage and food production, this World Bank article on the Triple Win of Climate-Smart Agriculture put into Practice is worth reading. It provides ways into other sources too:,,contentMDK:22842518~menuPK:64885113~pagePK:7278667~piPK:64911824~theSitePK:5929282,00.html

Page 45. The estimate that it is possible (by 2030) to sequester each year some 5.5 billion tonnes of carbon in soil originates in an assessment from the Intergovernmental Panel on Climate Change. This report from Deutsche Bank puts the figure into a more comprehensive context. The 5.5 number is at the bottom of page 16. Deutsche Bank Research (2011). Mitigating climate change through agriculture: An untapped potential. Deutsche Bank Research, Frankfurt. You may find this report on-line via:

Page 47. Further details on the grazing experiments that have helped to restore pasture at Dimbangombe in Zimbabwe can be found at: 

Page 48. More on Richard Branson’s Earth Challenge can be found at: