Crop intensification may also be a prime culprit in yield stagnation, especially for rice. Today, it is common for farmers to produce two or even three rice crops per year where only one or two were grown in the past. This is possible because some new rice varieties mature more quickly than traditional varieties, in addition to yielding more grain per plant. For example, the rice known as IR-8, one of the early “miracle rice” varieties introduced in 1966 by plant breeders at the International Rice Research Institute (IRRI) in the Philippines, ripens 20 to 30 days ahead of unimproved varieties . Yet the extra crops that the newer varieties allow can place a heavy strain on soils, particularly those used in paddy rice production, where the growing medium is under water for long periods. It is not yet clear how much this strain erodes yields in the long term .
Yields of other staples more commonly grown outside the developed world have also declined. Sorghum and millet rate fifth and seventh, respectively, in production among the world’s grains. They and a handful of other crops are crucial staples in many regions, especially in Africa and Asia, where drought is commonplace and the populations are among the world’s poorest .
In recent years, world sorghum and millet production has increased, but only because the cultivated area has grown. Even so, yields per hectare have remained flat or have even declined in places where production has expanded into more marginal areas. Improved varieties of millet and sorghum exist, but, in general, poor, small-scale farmers commonly achieve only about one fifth of the genetic potential of millet and sorghum because they cannot afford fertilizers, good weed control, timely planting, and the other crop management techniques that these crops require. Yields might decline even further in the future because many small-scale millet and sorghum producers have been shortening their fallow periods in an attempt to increase production levels-a strategy that may eventually lead to declining soil fertility .
|Yields vary widely|
|World average, highest, and lowest yields of cereal crops, 1990-96 mean value (metric tons per hectare)
|World Average Yield||2.7|
|Highest Yields (Netherlands)||8.8|
|Lowest Yield (Botswana)||0.35|
Source: Food and Agriculture Organization of the United Nations (FAO), FAOSTAT Statistical Database (FAO, Rome, 1997).
For other crops as well, an enormous gap exists between the yields actually achieved on real-world farms and those theoretically possible. For wheat, for example, the average global yield is less than 2 metric tons per hectare. The record yield is said to be 14 metric tons per hectare, and as many as 21 metric tons may be possible . There is also a wide variation in yields from country to country. (See Yields Vary Widely.)
How can the world’s farmers take advantage of this genetic potential? Both biotechnology and traditional plant breeding techniques still hold great promise for yield increases. For example, scientists at IRRI are currently using both strategies to improve older rice varieties by tailoring them to take advantage of specific local environments. They are also working on an entirely new “super rice” that in trials has achieved up to 25 percent higher yields than current varieties, although this new strain will not be ready for introduction for another 5 years or so .
The need for such improvements is urgent. Some projections suggest that roughly 50 percent more people will become rice consumers during the next 25 years, requiring a major increase in rice production .This increase will, by necessity, have to be achieved with less land, less water, and less labor .
References and notes
6. Agnes C. Rola and Prabhu L. Pingali, Pesticides, Rice Productivity, and Farmers’ Health (International Rice Research Institute and World Resources Institute, Los Ba<@241>os, Philippines, and Washington, D.C., 1993), p. 21.
7. Osamu Ito, International Rice Research Institute, July 10, 1997 (personal communication).
8. International Crops Research Institute for the Semi-Arid Tropics and Food and Agriculture Organization of the United Nations, The World Sorghum and Millet Economies: Facts, Trends, and Outlook (International Crops Research Institute for the Semi-Arid Tropics, Andhra Pradesh, India, 1996), p. 1.
9. Op. cit. 2.
10. Nurul Islam, ed., Population and Food in the Early Twenty-First Century: Meeting Future Food Demand of an Increasing Population (International Food Policy Research Institute, Washington, D.C., 1995), pp. 208-209.
11. Mark Rosegrant and Robert Livernash, “Growing More Food, Doing Less Damage,” Environment, Vol. 38, No. 7 (1996), p. 30.
12. Op. cit. 7.
13. Op. cit. 7.