World Cropland Resources

More than 99% of human food comes from the terrestrial environment while less than 1% comes from the oceans and other aquatic ecosystems. Worldwide, there are a total of 13 billion hectares of land area on Earth. The percentages in use are cropland, 11%; pasture land, 27%; forest land, 32%; urban, 9%; and others 21%. Most of the remaining land area (21%) is considered unsuitable for crops, pasture, and/or forests. This is because the soil is too infertile or shallow to support plant growth, or the climate of the region is too cold, dry, steep, stony, or wet for agricultural use.

Per Capita Cropland

In 1960, when the world population numbered only 3 billion, approximately 0.5 ha of cropland per capita was available for food production. This area is considered optimum for the production of a diverse, healthy, nutritious diet of plant and animal products - similar to the typical diet of people living in the US and Europe.

Since then, as the human population has continued to increase and expand its diverse activities, including industry, transport systems, and urbanization, vital cropland has been covered and/or lost from agricultural production. Consider that each American requires 0.4 ha (1 acre) of land just for urbanization and highways.

China is an example of how rapid population growth is followed by major reductions in the availability of per capita cropland. The amount of available cropland is currently only 0.08 ha per capita. This relatively small amount of cropland provides the Chinese people primarily with a vegetarian diet. Chinese cropland is reported to be rapidly declining due to continued population growth, but also because of extreme soil erosion and land degradation.

Worldwide, as a result of population growth, the average available cropland per capita has diminished from 0.5 ha to less than 0.23 ha. This is less than half the amount needed to provide diverse food supplies similar to those enjoyed in the US and Europe. In the US, the average cropland per capita is now down to 0.5 ha, or the critical land area essential for food production.

The availability of cropland influences the kinds and amounts of foods produced. For example, about 1481kgyr~ per capita of agricultural products is produced to feed each American, while the Chinese food supply averages only 785 kgyr~ per capita. By all available measurements, the Chinese have reached or are exceeding the limits of their agricultural system. Currently, China imports large amounts of grain from the United States and other nations, and is expected to increase imports of grains in the near future. Furthermore, the Chinese reliance on large inputs of fossil-fuel-based fertilizers to compensate for shortages of arable land and their severely eroded soils, combined with their limited fresh water supply, suggests severe agricultural problems looming in the near future.

Loss of Cropland

Fertile topsoil is a precious agricultural resource. Once lost, topsoil renewal is extremely slow. In fact, it takes more than 500 years for 2.5 cm (1 inch) of topsoil to reform under agricultural conditions.

Along with the intrusion of humans and their activities throughout the Earth's land area, degradation of soil has emerged as a major global agricultural problem. Throughout the world current erosion rates are greater than ever before. Unwise practices, including improper land management, over use of soil, and the removal of biomass cover, leave exposed soil vulnerable to further erosion by wind and rainfall and contribute to the loss of fertile soil.

Under some arid conditions in India and with relatively strong winds, as much as 5600 tons per hectare per year (t ha~ yr~ ) of soil has been reported lost. Related to wind erosion, during the summer of 2001 the National Aeronautics and Space Administration photographed an enormous cloud of soil being blown from the African continent toward the South and North American continents (Figure 1).

Every year, soil erosion causes an estimated 10 million ha of world cropland to be abandoned and lost to production. In arid regions, where irrigation is necessary, another 10 million hayr-1 are critically damaged due to salinization, in large part as a result of poor irrigation and/or improper drainage methods.

Figure 1 NASA's Total Ozone Mapping Spectrometer primarily measures atmospheric ozone, but can also detect particulates in the air. The African dust cloud of 2001 is clearly visible in this Aerosol Index screen shot. Source: http//science.nasa.gov/headlines/y2001/ ast26jun%5F1.htm (accessed 31 May, 2007).

Figure 1 NASA's Total Ozone Mapping Spectrometer primarily measures atmospheric ozone, but can also detect particulates in the air. The African dust cloud of 2001 is clearly visible in this Aerosol Index screen shot. Source: http//science.nasa.gov/headlines/y2001/ ast26jun%5F1.htm (accessed 31 May, 2007).

Furthermore, people, especially in developing countries, have turned to the burning of crop residues for cooking and heating, and this practice exposes the soil to wind and rainfall energy that intensifies soil erosion as much as tenfold.

Soil erosion on cropland ranges from about 10tha~ yr-1 in the US to 401 ha-1 yr-1 in China. During the past 30 years, the rate of soil erosion throughout Africa has increased 20-fold.

Most of the additional cropland needed yearly to replace what is lost to erosion, is being taken from the world's forest areas. The urgent need to increase crop production accounts for more than 60% of the massive deforestation now occurring worldwide. Brazil is a classic example of massive deforestation caused by a desire for land to grow sugarcane for the expanding ethanol production program.

Granted, some crops can be grown under artificial conditions using hydroponic techniques, but the costs in terms of energy expenditure and dollars is approximately ten times that of conventional agriculture. Such systems are not affordable or energy sustainable for the future.

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