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Chapter 4. Raising the Earth’s Productivity: Trends and Contrasts
Throughout most of history, rises in farmland productivity were so slow as to be imperceptible within a given generation. When Japan succeeded in launching a sustained rise in rice yields in the 1880s, it became the first country to achieve a “takeoff” in grain yield per hectare. But it was not until World War II that other industrial countries, including the United States and the countries of Europe, also initiated steady rises in cropland productivity. 4
Plant breeding programs in Japan that gave the world the dwarf rices and wheats and the U.S. programs that yielded hybrid corn were at the center of the revolutionary rises in land productivity. By the mid-1960s, developing countries such as India were also beginning to raise yields. Using a combination of price incentives and a modified version of Japan’s high-yielding dwarf wheats that were developed at the International Maize and Wheat Improvement Center in Mexico, India doubled its wheat crop between 1965 and 1972. This was the fastest doubling of a grain harvest in a major country on record. Other countries, including Pakistan and Turkey, also moved quickly to raise wheat yields, although China’s big jump in grain yields did not come until after the economic reforms of 1978. 5
Early success in adapting the high-yielding dwarf wheats in Mexico led to an intense effort to adapt Japan’s dwarf rices to tropical and subtropical growing conditions throughout Asia. Indeed, the International Rice Research Institute (IRRI) in the Philippines was founded in 1960 by the Rockefeller and Ford Foundations specifically for this purpose. 6
The record rise in world grainland productivity since 1950 had three sources—genetic advances, agronomic improvements, and synergies between the two. The genetic contribution to raising yields has come largely from increasing the share of the plant’s photosynthetic product (the photosynthate) going to seed. Shifting as much photosynthate as possible from the leaves, stems, and roots to the seed helps to maximize yields. For example, the originally domesticated wheats devoted roughly 20 percent of their photosynthate to the development of seeds. Through plant breeding, it has been possible to raise this share—known as the “harvest index”—in today’s wheat, rice, and corn to more than 50 percent. Given the essential requirements of the roots, stems, and leaves, the theoretical limit of the share going to seed is 60 percent. 7
The key to this shift was the incorporation of the dwarf gene into both rice and wheat varieties by the Japanese during the late nineteenth century. Traditional wheat and rice varieties had tall straw because their wild ancestors needed to compete with other plants for sunlight. But once farmers began controlling weeds, growing tall was a waste of the plant’s metabolic energy. As plant breeders shortened wheat and rice plants, reducing stem length, they reduced the share of photosynthate going into the straw and increased the portion going into seed. L. T. Evans, a prominent Australian agricultural scientist, observes that in the high-yielding dwarf wheats the gain in grain yield is roughly equal to the loss in straw weight from the dwarfing. 8
With corn, varieties grown in the tropics were reduced in height from an average of nearly three meters to less than two. But Don Duvick, for many years the director of research at the Pioneer Hybrid seed company, observes that with the hybrids used in the U.S. Corn Belt, the key to higher yields is the ability of varieties to “withstand the stress of higher plant densities while still making the same amount of grain per plant.” Growing more plants per hectare benefited from reorienting the horizontally inclined leaves of traditional strains that droop somewhat, making them more upright and thereby reducing the amount of self-shading. 9
Although plant breeders have greatly increased the share of the photosynthate going to the seed, they have not been able to fundamentally improve the efficiency of photosynthesis—the process plants use to convert solar energy into biochemical energy. The amount of photosynthate produced from a given leaf area by today’s crops remains unchanged from that of their wild ancestors. 10
On the agronomic front, raising land productivity has depended on expanding irrigation, using more fertilizer, and controlling diseases, insects, and weeds. All these tactics help plants realize their genetic potential more fully. 11
Other factors affecting yields include solar intensity and day length, natural conditions over which farmers have little control. Japan, for example, has developed a highly productive rice culture, one based on the precise spacing of rice plants in carefully tended rows. Yet rice yields in Spain, California, and Australia are consistently 20–30 percent higher. The reason is simple. These locations have an abundance of bright sunlight, whereas in Japan rice is necessarily grown during the monsoon season, when there is extensive cloud cover. 12
Day length can also make a huge difference. To begin with, there are no high yields of any cereals—wheat, rice, or corn—in the equatorial regions. High yields come with the long growing days of summer in the higher latitudes. The world’s highest wheat yields are found in Western Europe. 13
Western Europe occupies a northerly latitude comparable to that of Canada and Russia, but the warmth from the Gulf Stream makes its winters mild, enabling the region to grow winter wheat. This wheat, planted in the fall, becomes well established and reaches several inches in height before winter dormancy begins. When early spring comes, it immediately begins to grow again. This enables wheat in Western Europe to mature during the summer, with days that are particularly long at that latitude. Thus four environmental conditions—moderate winters, inherently fertile soils, reliable rainfall, and long summer days—combine to give the region wheat yields that reach 6–8 tons per hectare. 14
The difference in wheat yields among leading producers worldwide is explained more by soil moisture variations than by any other variable. Table 4–1 illustrates this point well. Kazakhstan, a country with low rainfall, averages 1.1 tons of wheat per hectare. France, the major wheat-growing country in Western Europe, harvests 6.8 tons per hectare—six times as much. 15
Mexico’s wheat yields are nearly double those of the United States primarily because virtually all of Mexico’s wheat is irrigated, whereas the U.S. crop is largely rain-fed and grown in low rainfall regions. Similarly with India and Australia: in 1950, the yield in each country was roughly 1 ton of wheat per hectare. Today India gets 2.7 tons per hectare, while Australia gets only 1.7 tons. The reason is not that India’s farmers are much more capable than farmers in Australia but rather that they can irrigate their wheat and can thus also efficiently use more fertilizer. 16
|Table 4-1. Wheat Yield Per Hectare in Key Producing Countries, 2002*|
|* Yield for 2002 is the average of 2001 through 2003.
Source: See endnote 15.
4. World grain production data from ibid.; 1880s Japan data from “Grain Yields in Japan and India” (USDA, ERS), cited in Lester R. Brown, Increasing World Food Output: Problems and Prospects, Foreign Agricultural Economic Report No. 25 (Washington, DC: USDA, ERS, 1965), pp. 13–14.
5. Dwarf wheats and rice information from Thomas R. Sinclair, “Limits to Crop Yield?” in American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Physiology and Determination of Crop Yield (Madison, WI: 1994), pp. 509–32; India grain production data from USDA, op. cit. note 1.
6. Dwarf wheats and rice information from Sinclair, op. cit. note 5; IRRI data from www.irri.org, viewed 9 September 2004.
7. Percent photosynthate to seed from L. T. Evans, Crop Evolution, Adaptation and Yield (Cambridge: Cambridge University Press, 1993), pp. 242–44; theoretical upper limit from Thomas R. Sinclair, “Options for Sustaining and Increasing the Limiting Yield-Plateaus of Grain Crops,” paper prepared for the 1998 Symposium on World Food Security, Kyoto, Japan (Washington, DC: USDA Agricultural Research Service, September 1998), p. 14.
8. Evans, op. cit. note 7.
9. Donald N. Duvick, Affiliate Professor of Plant Breeding, Iowa State University, letter to author, 14 March 1997.
10. Evans, op. cit. note 7; Sinclair, op. cit. note 7.
11. Sinclair, op. cit. note 7.
12. USDA, op. cit. note 1; USDA, Foreign Agricultural Service (FAS), Grains: World Markets and Trade (Washington, DC: various years).
13. USDA, op. cit. note 1; U.N. Food and Agriculture Organization (FAO), FAOSTATStatisticsDatabase, at apps.fao.org, updated 24 May 2004.
14. USDA, op. cit. note 1; USDA, FAS, World Agricultural Production (Washington, DC, various years), at www.fas.usda.gov/wap_arc.html.
15. Table 4–1 from USDA, op. cit. note 1, with France from FAO, op. cit. note 13.
16. USDA, op. cit. note 1.
Copyright © 2004 Earth Policy Institute