In the spring the National Academy of Sciences (NAS) published a report titled Agricultural Production Efficiency which concluded that the rate of increase in yields (production per acre) of most crops in the United States may slow in the foreseeable future. The conclusion, if valid, could have profound implications for U.S. farmers and consumers as well as for the hundreds of millions of the poor and hungry around the world. For the trends in crop yields in the United States could largely determine whether the world's food supply will be abundant or scarce.
The United States is the grain and soybean supplier of the world. From the end of World War II until 1972 the growth of American capacity to produce and export these and other food commodities assured U.S. consumers an increasing food supply at declining real prices and made an important contribution to the supplies of other countries, including the most needy. This expansion of U.S. capacity was achieved primarily by substituting capital—machinery, fertilizers, pesticides, improved seed varieties, and managerial skills—for labor and land. So rapid was this substitution that employment in agriculture declined by more than 50 percent during the years between 1950-72, and harvested land fell from 337 million acres to 290 million acres while output continued to increase. The increase in yields of grains was particularly impressive, with those for wheat doubling while corn yields were rising by almost 160 percent. These rate increases were among the highest in the history of world agriculture.
The rise in world demand. The academy's pessimistic assessment of the future growth of yields in the United States is especially significant because, according to recent projections of the U.S. Department of Agriculture (USDA) foreign demand for U.S. grains and soybeans may rise sharply over the next decade. Even if past rates of increase in yields were maintained, the response to rising demand might entail higher costs of production because of higher energy costs. American agriculture is very energy intensive, and energy costs are rising. However, the rise in production costs will be more pronounced if the increase in yields slows appreciably.
Slower yield increases would also imply an increase in cultivated land to meet the growth in food demand. Studies done at the USDA suggest that expanding the cultivated area much beyond 1974-75 levels would encounter rising costs of land development and considerably greater exposure to erosion. More fundamentally, however, slower growth of yields with current technology would probably imply declining increments of production per unit of all farm inputs. The result would be rising average costs of production unless the rate of fall in prices of inputs were to exceed the rate of decline in productivity growth. This seems unlikely.
The NAS analysis. The academy's conclusion about the growth of yields in the United States is based on three considerations: (1) evidence that the current technology may be encountering diminishing returns; (2) the social constraints being placed on the use of this technology, primarily to reduce environmental damage; and (3) the likelihood that no economically attractive alternative technologies, or significant modifications in existing technologies, will become widely available in the next decade.
The most striking evidence for diminishing returns is the flattening slope of the curve relating fertilizer use to crop yields. The NAS report includes a graph showing that since the mid-1960s there have been smaller increases in crop yields per pound of fertilizer applied to the fields. Fertilizer, of course, is not the only input contributing to output. However, a more comprehensive measure calculated by the USDA relating total farm output to all inputs shows a similar pattern. Between 1950 and 1960 output per unit of input rose at an average annual rate of 2.5 percent. From 1960 to 1971 the annual rate of increase slowed to 1.5 percent.
As shown in the accompanying table, recent experience with yields for the principal grains and soybeans shows not merely slower increases but actual declines over the span of the past four years.
Although the marked fall in 1974 was an aberration reflecting extraordinarily bad weather, it is noteworthy that the recovery of yields for all three crops in 1975, generally considered an excellent growing year, still left them below the previous peaks.
The experience of the 1970s so far does not prove that yields of corn, wheat, and soybeans have permanently leveled off, or have begun to decline. The failure of yields to recover in 1975 probably is owed in part to the fall fertilizer consumption and to the lower productivity of land brought under cultivation since 1972. Nonetheless, the experience reflected in the table is sobering, and gives added strength to the conclusion that a slowing of yields may be in the offing.
The NAS report considered the impact of constraints on agricultural technology that may limit future increases in yields. Some of these are general, such as the limited supplies of capital, labor, land, and water for which agriculture must compete with other sectors of the economy. Other constraints are more specific to agriculture, particularly those placed on the use of fertilizers and pesticides in the interest of environmental protection. Since fertilizers and pesticides were responsible for an important part of the extraordinary increases in yields from the early 1950s on, restrictions on their use could seriously limit the remaining yield potential of current technology.
For fertilizers, these restrictions so far are more latent than real, judging from the NAS report. Restrictions on pesticide use, however, already have been imposed. Use of DDT, except in special circumstances, was banned some years ago, and, in 1974 and 1975, the Environmental Protection Agency (EPA) also suspended use of other persistent insecticides—aldrin, dieldrin, heptachlor, and chlordane. Total consumption of these materials in the production of grains and soybeans was small, and the EPA rulings against them included the judgment that their suspension would not have a major impact on crop production. The NAS report does not address this issue but focuses instead on a subtle—but perhaps in the long run more significant—aspect of pesticide regulation. This is the argument that the regulations increase research and development costs to such an extent that they will seriously limit introduction of new pest control materials. According to the NAS report, only larger companies can finance the costly tests needed to get a new chemical cleared, and fewer of them are finding the effort economically worthwhile.
Looking ahead. Turning to the outlook for improved technology the NAS report concludes "that duplication of twentieth-century spectacular productivity breakthroughs may not be repeated." The technology which yielded these massive gains in productivity—genetic manipulation and hybridization, improved cultivation practices such as planting and pruning for maximum leaf area, elimination of severe weed competition, improved insect control, and increased use of fertilizer and farm machinery—may have about run its course. Consequently it is doubtful that improvements in this technology will yield advances comparable to those achieved over the last several decades.
The report therefore turns to consideration of new technologies that are now in various stages of development for controlling pests and increasing yields. Alternatives to pesticides receive considerable attention. The report is optimistic about the eventual payoff from techniques employing insect hormones and pheromones to control insect pests. Hormones can be used to upset insect growth patterns and pheromones to interfere with the insect communication systems required for sexual attraction. According to the NAS report, these techniques have worked in a number of field tests, but nothing is said about when they may become economically attractive on a wide scale. Nor does the report see any significant help from another alternative, breeding plants for increased resistance to pests. In summarizing the alternatives to chemical pesticides, the report asserts that "In spite of much progress in the area of biological pest control, and in spite of the development of many pest resistant varieties, there is no convincing evidence that chemical pesticides can be replaced in the foreseeable future."
Crop growth depends fundamentally on photosynthesis, the still imperfectly understood process by which water and carbon dioxide, energized by sunlight, are converted to plant food. The process is grossly inefficient. Only a very small proportion of the sun's energy reaching the plant is converted to stored energy. Some plants—such as sugarcane, corn, and sorghum—are more efficient than others—such as wheat and soybeans. The NAS report considers research now underway to improve photosynthetic efficiency of the second group, primarily by enriching the carbon dioxide content of the atmosphere in which these plants grow. This is relatively easy in greenhouses, but for field crops no economically efficient technique has yet been developed.
Another new technology of great potential importance is increased biological nitrogen fixation by legumes, of which the soybean is by far the most important. Root nodules of these plants carry bacteria which have the capacity to capture (that is, to "fix") nitrogen from the air, making it available to the plant. The NAS report asserts that carbon dioxide enrichment of the atmosphere in which the plants grow greatly increases their nitrogen-fixing capacity. If this technique could be successfully applied at the field level, soybean yields might be doubled. Since soybeans are second only to corn in acreage under cultivation in the United States, accelerating the growth of soybean yields would significantly ease both the economic and environmental pressures exerted by the nation's agricultural sector. The report does not estimate, however, when this technological breakthrough might occur.
The report considers two other frontier technologies that may in time produce higher yields. One would build on a recent scientific discovery that permits growing of entire plants from single cells. This technique could greatly increase productivity by shortening the generation cycle for plants. Development of the technique still confronts unsolved scientific problems, and no economically promising plants have been produced. The other technology relies on chemical compounds to regulate plant growth, for example, to speed germination and to stimulate the growth of seedlings. The report asserts that compounds controlling crop maturity, thus increasing yields and reducing losses from failure to reach maturity, could have a dramatic economic impact in the foreseeable future. Already such compounds are being used on sugarcane, and several others are in the experimental product stage.
The NAS review of alternatives to existing agricultural technologies suggests, on balance, that while a number show high promise, few, if any, are close enough to economic feasibility to substitute for, or to supplement, existing technologies on a large scale in the near future. This, and the projection that the yield potential of existing technologies may be approaching exhaustion, leads one to conclude that the rate of increase in yields may slow.
The report's message is not that the best days of American agriculture are over. It is, however, a powerful argument against the complacent notion that "technology" will somehow automatically rescue the world from the constraints of resource scarcity. The report drives home the point that technology is not an abstract, autonomous process but the application by people of specific materials and knowledge to the solution of specific problems. The particular combination of these elements produced spectacular results for American agriculture for more than twenty years after World War II. Now the evidence suggests that new combinations may be needed and that new knowledge and materials must be developed to cope with new problems.
A version of this article appeared in print in the Winter 1976 issue of Resources magazine.
