VII. Some Facts and Figures related to Sustainability of Agriculture

Table of Contents

• Facts and Figures
  • GROWTH IN DEMAND
  • STATE OF THE RESOURCE: SOIL
  • STATE OF THE RESOURCE: WATER
  • STATE OF THE RESOURCE: BIODIVERSITY
  • STATE OF THE RESOURCE: THE GENETIC BASE
  • LANDSCAPE MOSAICS: an example of an ecosystem
    level approach
• Cited Literature and Links

GROWTH IN DEMAND

Food supply must increase 28% over 1998 production by 2020, and 58% by 2050. just to keep pace with projected population growth (Table 1):

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Some facts and figures related to soil erosion (Pimental et al., 1995)

• Globally, approx. 12 x 10⁶ ha of arable land are destroyed and abandoned annually because of nonsustainable farming practices.
• Soil erosion rates are highest in Asia, Africa and South America (avg. 30-40 t ha^-1 year^-1; and lowest in the US and Europe (avg. ca. 17 t ha^-1 year^-1).
• Rates in US and Europe still greatly exceed the average rate of conversion of parent material into soil (ca. 1 t ha^-1 year^-1) .
• Erosion rates in undisturbed forests range from 0.004 to 0.05 t ha^-1 year^-1.
• Moderately eroded soils absorb 7-44% less rainfall than the original soil.
• A ton of fertile topsoil contains 1-6 kg N, 1-3 kg P, 2-30 kg K.
• Soil removed by wind or water is 1.3 to 5 times richer in organic matter than soil left behind.
• A loss of 17 t ha^-1 year^-1 corresponds on average to a loss of 75 mm water, 2 tons of organic matter and 15 kg available N each year, and loss of 1.4 mm depth of soil.
• The implementation of appropriate soil and water conservation practices has the potential to reduce erosion rates from 2 to 1000-fold and water loss from 1.3 to 21.7 fold (Tables 3, 4) .

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STATE OF THE RESOURCE: WATER

"Humanity now uses 26 percent of total terrestrial evapotranspiration and 54 percent of runoff that is geographically and temporally available. Increased use of evapotranspiration will confer minimal benefits globally because most land suitable for rain-fed agriculture is already in production. New dam construction could increase accessible runoff by about 10 percent over the next 30 years, whereas population is projected to increase by more than 45 percent during that period" (Postel et al., 1996).

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Pimentel et al. (1992) note that only 3.2% of world land area is now protected by national parks, and that most biological diversity exists in human-managed ecosystems; thus protection of biological diversity in these systems is vital to overall preservation of biodiversity; and to agriculture itself; they note, for example:

• "An estimated $20 billion is spent annually in the world for pesticides. Yet, parasites and predators existing in natural ecosystems are providing an estimated 5-10 times this amount of the pest control" .
• An estimated $50 billion worth of nitrogen is provided by biological N2 fixation.
• In the US alone, 40 crops, valued at approx. $30 billion are absolutely dependent on insect pollinators. Allen-Wardell et al. (1998) document sharp declines in managed honeybee populations in recent years, and note that this greatly increases our reliance on wild pollinators.

Amongst the measures Pimetel et al. (1992) cite as prompting biological diversity are:

• conservation of crop residues on soil surface
• cover cropping
• intercroppiing
• use of shelterbelts and hedgerows
• maintaining high organic matter in soils
• effective recycling of livestock manure
• moderate stocking of pastures
• agroforestry
• biological control (vs chemical control) of pests

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STATE OF THE RESOURCE: THE GENETIC BASE

From FAO, 1995, 1996:

Since 1900, about 75% of genetic diversity of agricultural crops has been lost; some specific examples:

• In China, 10,000 wheat varieties were in use in 1949, and only 1000 by the 1970s.
• In the US, of the 7098 apple varieties documented as in use between 1804 and 1904, approx. 86% have been lost; 95% of cabbage, 91% of field maize and 81% of tomato varieties also apparently no longer exist .
• In India, there will soon be only 30-50 rice varieties over an area where once 30,000 once flourished.
• Half of the animal breeds that existed in Europe at the start of the present century are now extinct, and one-quarter of the livestock breeds of the world are now at high risk of loss (see LIVESTOCK genetic diversity) .

A wide variety of strategies are being advocated and pursued to conserve and increase genetic diversity, including Genetic Engineering.

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LANDSCAPE MOSAICS: an example of an ecosystems level approach to resolving some of the negative impacts of agriculture (Ryszkowski, 1995).

"Intensification and simplification of agriculture in many parts of Europe has triggered many secondary effects, including increasing vulnerability to flooding, groundwater pollution and impoverishment of biota. Long-term research in the West Poland Lowland suggests that a mosaic landscape structure of small cultivated fields, shelterbelts, meadows and small ponds enhances water shortage, controls groundwater chemistry and helps maintain biological diversity."

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VII. Cited Literature & Links

• Allen-Wardell, G et al. (21 co-authors). 1998. The potential consequences of pollinator declines on the conservation of biodiversity and stability of food crop yields. Conservation Biology 12: 8-17.
• FAO. 1995. Dimensions of need. An Atlas of Food and Agriculture. FAO, Rome.
• FAO. 1996. Sixth World Food Survey. FAO, Rome
• FAO. 1996. Report on the State of the World's Plant Genetic Resources for Food and Agriculture. FAO, Rome. Dal. Lib. SB 123.3 R46
• Pimentel, D. et al. (8 co-authors). 1992. Conserving biological diversity in agricultural forestry systems. BioScience 42: 354-362.
• Pimentel, D. et al. (10 co-authors). 1995. Environmental and economic costs of soil erosion and conservation benefits. Science 267: 1117-1123
• Postel, S.L., G.C. Daily, and P.R. Erlich. 1996. Human appropriation of renewable fresh water. Science 271: 785-788.
• Ryszkowski, L. 1995. Managing ecosystems services in agricultural landscapes. Nature and Resources 31(3): 27-63
• Syers, J.K. 1997. Managing soils for long-term productivity. Philosophical Transactions of the Royal Society of London 352: 1011-1021.
• US CENSUS BUREAU: TOTAL MIDYEAR POPULATION FOR THE WORLD 1950-2050
  (http://www.census.gov/ipc/www/worldpop.html) U.S. Bureau of the Census, Auth. (2000, November 5; Viewed 30 Jan. 2001)