EPIBuilding a Sustainable Future
Outgrowing the Earth: The Food Security Challenge in an Age of Falling Water Tables and Rising Temperatures

Chapter 4. Raising the Earth’s Productivity: The Shrinking Backlog of Technology

Although the investment level in agricultural research, public and private, has not changed materially in recent years, the backlog of unused agricultural technology to raise land productivity is shrinking. In every farming community where yields have been rising rapidly, there comes a time when the rise slows and eventually levels off. For wheat growers in the United States and rice growers in Japan, for example, most of the available yield-raising technologies are already in use. Farmers in these countries are looking over the shoulders of agricultural researchers in their quest for new technologies to raise yields further. Unfortunately, they are not finding much.

From 1950 to 1990 the world’s grain farmers raised the productivity of their land by an unprecedented 2.1 percent a year, slightly faster than the 1.9 annual growth of world population during the same period. But from 1990 to 2000 this dropped to 1.2 percent per year, scarcely half as fast. (See Table 4–2.) As of mid-2004, it looks as though the annual rise in grain yields from 2000 to 2010 will drop to something like 0.7 percent, scarcely half that of the preceding decade and far behind world population growth. This loss of momentum in raising land productivity is due not only to the shrinking backlog of technology but also in some countries to the loss of irrigation water. 28

As noted earlier, yields vary widely among countries. This can be seen, for example, with the rice yields in Figure 4–4. Japan’s rice yields, already quite high by 1960, appear to have plateaued over the last decade. The sharp drop in 1994 was the result of an unusually cool, cloudy monsoon season when solar intensity was well below normal. 29

While India has doubled its rice yields over the last 40 years, they are still less than half those of China and Japan, and they have increased little over the last decade. This is partly because India’s proximity to the equator means that it does not have the long summer days of Japan and China, both temperate-zone countries. And since scarcely half of India’s rice production is irrigated, the remainder is entirely dependent on the vagaries of monsoon rainfall. 30

The big story has been the advance in rice yields in China since the economic reforms in 1978. Now that China’s rice yields are close to those of Japan’s, however, which are the highest in Asia, it will become progressively more difficult to raise them further. 31

Yields of wheat, the other principal food staple, also vary widely. U.S. wheat yields, though they fluctuate from year to year, have not increased much over the last two decades. (See Figure 4–5.) China’s, in contrast, rose rapidly after the 1978 economic reforms but have shown signs of plateauing in recent years. In France, with some of the highest wheat yields in the world, yields also appear to have plateaued over the last decade or so. 32

The corn yields in the world’s three largest corn producers vary widely. (See Figure 4–6.) For instance, Brazil’s are scarcely a third those of the United States. Much of China’s corn is grown as a second crop after winter wheat, which means it gets planted up to several weeks later than the maximum yield planting time. By the time the corn has germinated, day length is already beginning to shorten. 33

Figure 4–6 also shows how much corn production in the United States can fluctuate as a result of heat and drought. The two big drops, 1983 and 1988, were both associated with intense heat and drought. In both 2003 and 2004, exceptionally favorable weather helped boost yields well above the trend. 34

In addition to plateauing in agriculturally advanced countries such as Japan and South Korea, rice yields are also stagnating in several developing countries in Asia. In an analysis of yield trends and potentials, Kenneth Cassman and his colleagues at the University of Nebraska point out that in three of China’s major rice-producing provinces, which account for 35 percent of the country’s harvest, yields are stagnating. 35

In India, the world’s second largest rice producer after China, yields are leveling off in the Punjab, where wheat and rice are extensively double-cropped. Signs of rice yield plateaus are also appearing in Indonesia’s Central Java and in central Luzon, the largest island in the Philippines. 36

The Nebraska team further notes that there was no detectable yield gain in inbred rice varieties during the 37 years since the development of IR-8, an early prototype of the high-yielding rices from the 1960s, at IRRI. The only gains since then have come from hybrid rices, which China has led the way on. But these hybrids yield only 9 percent more than the much more widely grown inbred varieties. Half of China’s rice area is now planted to hybrids, but the area has not increased for many years, partly because hybrid rices are plagued by high seed cost and poor grain quality. 37

In 1990 IRRI launched a major research project to raise rice yields 25–50 percent by restructuring the rice plant. In the face of poor prospects for achieving this, the goal has now been scaled back to a rise of 5–10 percent. 38

In looking at the potential for raising wheat yields in developing countries, Cassman and colleagues note that wheat yields also appear to be stagnating in Mexico’s Yaqui Valley, the site of the international wheat-breeding effort that over the last 60 years produced the widely adapted versions of the high-yielding Japanese dwarf wheats that were at the heart of the Green Revolution. 39

In the Indian states of Punjab and Haryana, the country’s leading producers of irrigated wheat, yields are approaching those where the leveling off began in the Yaqui Valley. Since these two states account for 34 percent of India’s wheat harvest, reaching a plateau in yields here would substantially slow the rise in the national harvest trend. 40

For maize, the Nebraska team looked at the results of an irrigated maize yield competition for Nebraskan corn growers and noted the winning yield had not increased for 20 years. In other words, no varietal improvement or agronomic advances have enabled the contest winners to raise their yields. The Nebraska statewide average corn yield on all farms is continuing to rise on both irrigated and non-irrigated land, as is the yield of the contest winners on non-irrigated land. 41

Can genetic engineers restore a rapid worldwide rise in grainland productivity? This prospect is not promising simply because plant breeders using traditional techniques have largely exploited the genetic potential for increasing the share of photosynthate that goes into seed. Once this is pushed close to its limit, the remaining options tend to be relatively small, clustering around efforts to raise the plant’s tolerance of various stresses, such as drought or soil salinity. One major option left to scientists is to increase the efficiency of the process of photosynthesis itself—something that has thus far remained beyond their reach.

After 20 years of research, biotechnologists have yet to produce a single variety of wheat, rice, or corn that would dramatically raise yields above those of existing varieties. Thus far the focus in genetically engineered crops has been to develop herbicide tolerance, insect resistance, and disease resistance. Between 1987 and 2001, 70 percent of the applications for field releases of experimental genetically engineered varieties received by the USDA’s Animal and Plant Health Inspection Service, the regulatory agency for genetically modified crops, were in these three areas. Some 27 percent of the requested releases were for herbicide-tolerant varieties, principally soybeans. The second highest category, insect resistance, accounted for 25 percent of the total, including cotton varieties resistant to the boll weevil and corn varieties resistant to the corn borer. Crop varieties resistant to various diseases caused by viruses, fungi, or bacteria together accounted for 18 percent of new releases. 42

Some 6 percent of the requested releases had specific agronomic properties, such as drought resistance or salt tolerance, while 17 percent were focused on improving crop quality in some particular way. The latter category included crop strains that contained a specific trait such as higher protein quality in corn or higher oil content in soybeans. Not one of these varieties was bred to raise yields. To the extent that insect- and disease-resistant varieties provide better pest control than the use of pesticides, this could marginally increase crop output. But as a general matter, yield gains thus far from biotechnology are minimal to non-existent. 43

When genetic yield potential is close to the physiological limit, further advances in yields rely on exploiting the remaining unrealized potential in the use of basic inputs, such as fertilizer and irrigation, or on the fine-tuning of other agronomic practices, such as optimum planting densities or more effective pest controls. Beyond this, there will eventually come a point in each country, with each grain, when farmers will not be able to sustain the rise in yields.

USDA plant scientist Thomas R. Sinclair observes that advances in our understanding of plant physiology let scientists quantify crop yield potentials quite precisely. He notes that “except for a few options which allow small increases in the yield ceiling, the physiological limit to crop yields may well have been reached under experimental conditions.” For farmers who are using the highest-yielding varieties that plant breeders can provide, along with the agronomic inputs and practices needed to realize their genetic potential, there may be few options left to raise land productivity. 44

Reinforcing this view is the work cited earlier by Kenneth Cassman and colleagues that notes stagnation in raising the genetic yield potential of the major cereal crops—rice and maize, when average yields reach 80 percent of the genetic yield potential. Cassman points out that it is difficult to raise them further because “achieving 100 percent of the genetic yield potential requires perfect management in terms of varietal selection, plant density, planting date, nutrient management (neither deficiency or excess and perfect balance amongst all 16 essential nutrients), and in the control of weeds, insects, and diseases.” He notes that average farm yields tend to plateau at 80–85 percent of the genetic yield potential. 45

Most countries that have achieved a yield takeoff have managed at least to double if not triple or even quadruple grain yields. Among those that have quadrupled yields over the past half-century are the United States and China with corn; France, the United Kingdom, and Mexico with wheat; and China with rice. The bottom line is that all countries are drawing on a backlog of shrinking agricultural technology. And for some crops in some countries the backlog has largely disappeared. 46

The decelerating rise in grain yields since 1990 is not peculiar to individual grains or individual countries. It reflects a systemic difficulty in sustaining the gains that characterized the preceding four decades as yields of wheat, rice, and corn press against the ceiling ultimately imposed by the limits of photosynthetic efficiency. The efficiency of photosynthesis coupled with the area of land available to produce food defines the outer limit of how much food the earth can produce.

Table 4-2. World Grain Yield Per Hectare, 1950-2000, with Projection to 2010
Yield Per Hectare*
Annual Increase by Decade
* Yields for decadal years 1960 through 2000 are three-year averages.
** Projection of yield to 2010 by author.
Source: See endnote 28.


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28. Table 4–2 from USDA, op. cit. note 1; Worldwatch Institute, op. cit. note 1.

29. Figure 4–4 compiled from USDA, op. cit. note 1; monsoon weather from USDA, FAS, Grains: World Markets and Trade (Washington, DC: various years).

30. USDA, op. cit. note 1; USDA, op. cit. note 29.

31. USDA, op. cit. note 1.

32. Figure 4–5 compiled from ibid.; France from FAO, op. cit. note 13.

33. Figure 4–6 compiled from USDA, op. cit. note 1; information on China’s double cropping in W. Hunter Colby et al., Agricultural Statistics of the People’s Republic of China, 1949-1990 (Washington, DC: USDA, ERS, 1992), and in USDA, FAS, “Crop Calendar,” at www.fas.usda.gov/pecad/weather/Crop_calendar/crop_cal.pdf.

34. USDA, op. cit. note 1; U.S. weather from USDA, National Agricultural Statistics Service, “Weekly Weather and Crop Bulletin,” at jan.mannlib.cornell.edu/reports/nassr/field/ weather, and from NOAA/ USDA Joint Agricultural Weather Facility, “International Weather and Crop Summary,” updated weekly at www.usda.gov/agency/oce/waob/jawf/wwcb/inter.txt.

35. Kenneth G. Cassman et al., “Meeting Cereal Demand While Protecting Natural Resources and Improving Environmental Quality,” Annual Review of Environment and Resources, November 2003, p. 322.

36. Ibid.

37. Ibid., pp. 324–26.

38. Ibid., pp. 325–26.

39. Ibid., p. 328.

40. Ibid.

41. Ibid., pp. 327–29.

42. Sinclair, op. cit. note 5; Cassman et al., op. cit. note 35.

43. Sinclair, op. cit. note 5; Cassman et al., op. cit. note 35.

44. Sinclair, op. cit. note 5.

45. Kenneth Cassman, Professor and Head of Department of Agronomy and Horticulture, University of Nebraska, letter to author, 7 May 2004.

46. USDA, op. cit. note 1; FAO, op. cit. note 13.


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