Global Pesticide Production 19451985

Source: Modified from Tilman, David, et al. 2001. "Forecasting Agriculturally Driven Global Environmental Change." Science 292-284.

Figure 2

Global Fertilizer Use 1960-2000

Figure 2

^^ World usage —— World usage excluding USSR

Source: Food and Agriculture Organization of the United Nations. (Accessed July 17, 2002).

Note that the apparent leveling of world fertilizer use since 1990 is a result of the collapse of the Soviet Union and subsequent decreases in Soviet fertilizer use. Fertilizer use for the rest of the world has continued to increase at unsustainable rates.

agricultural revolution spread to developing countries in a process referred to as the "green revolution."

This transformation has been tremendously successful at producing food. Global grain production doubled from 1945 to 1980. Today, more food is produced per person than ever before in earth's history. This success, however, has come with costs to the sustainability of agriculture and to biodiversity.

Over the next few decades humanity must develop forms of agriculture that can meet the needs of a growing population while minimizing our impact on the environment. To do so, agriculture must be done more sustainably by protecting soil fertility; must decrease dependence on fertilizers, pesticides, fossil fuels, and irrigation; and must integrate agricultural and natural areas so farms can be reservoirs and corridors of biodiversity.

Loss of Crop and Genetic Diversity Creates More Uniform Ecosystems Mechanization requires farms to have uniform crop types, structures, and management practices (for example, planting and harvesting dates). As a result, crop diversity has declined on most farms over the last century. For example, traditional farms, especially in the tropics, may include grains, root crops, vegetables, spices, medicinal plants, livestock, and trees for lumber, fruit, and firewood. In contrast, most modern farms are monocul-tures—that is, they have only one crop species planted over a large area. Farms with low crop diversity have poor "associated diversity" of species that were not assembled directly, such as insects, birds, and soil organisms.

The use of monocultures increases a farm's dependence on pesticides. Pests such as insects and pathogens (disease-causing organisms) can find their food sources more easily in monocultures than in diverse crop mixtures.

Monocultures also have lower populations of the natural enemies of pests, such as spiders, wasps, dragonflies, and predatory beetles.

The genetic diversity of crops has declined with industrial agriculture. Although hundreds of edible plant species have been important in traditional crop systems, today only three crops—rice, wheat, and corn—provide 60 percent of our plant-based diet worldwide. Diversity within crops also has declined because traditional varieties, or landraces, have been replaced by a few high-yielding varieties. This process is called genetic erosion. According to the Food and Agriculture Organization of the United Nations, 75 percent of crop diversity was lost during the twentieth century. Modern varieties have supplanted traditional varieties for 70 percent of the word's corn, 75 percent of Asian rice, and half of the wheat in Africa, Latin America, and Asia. In 1950, India had 30,000 wild varieties of rice, but by 2015 only 50 are expected to remain.

The loss of genetic diversity within crops is important for plant breeding. Much of the increased yield in modern crops is owed to the genetic diversity in traditional varieties. Landraces of many crops have provided the genes needed for pest and disease resistance, or to adapt crops to poor soils, drought, and cold temperatures. By losing landraces we are undermining our ability to adapt crops to future conditions, including climate change.

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