The Green Revolution: what it changed and what it cost

The problem it answered

In the early 1960s, many experts expected famine across South Asia and elsewhere. Populations were growing fast, most good land was already farmed, and traditional cereal yields were low: around a tonne of grain per hectare was common for wheat and rice in much of the developing world.

The obvious fix, more fertiliser, did not work with the varieties of the time. Traditional tall wheats and rices respond to nitrogen by growing taller and leafier. Their weak stems then bend and collapse (lodging) before harvest, and much of the extra growth goes into straw rather than grain. Yield hit a ceiling.

The science: semi-dwarf varieties

The breakthrough was dwarfing genes, which shorten the stem without shrinking the ear or panicle.

• Wheat. The semi-dwarfing genes (now known as Rht-B1b and Rht-D1b) came from a Japanese variety, Norin 10, brought to the United States after 1945. Breeders there and, above all, Norman Borlaug's programme in Mexico crossed them into adapted wheats. Borlaug's team, at what became CIMMYT (the International Maize and Wheat Improvement Center), also bred for wide adaptation and insensitivity to day length by alternating generations between two Mexican locations at different latitudes and seasons, a method called shuttle breeding.
• Rice. At IRRI (the International Rice Research Institute, founded in the Philippines in 1960), a cross between the Indonesian variety Peta and the Taiwanese semi-dwarf Dee-geo-woo-gen produced IR8 in 1966, the first of the modern semi-dwarf rices. Its dwarfing gene is sd1.

These varieties shared a set of traits that made them responsive to inputs:

• Short, stiff straw, so they could carry heavy grain under high nitrogen without lodging.
• A higher harvest index: a larger share of the plant's dry matter went into grain.
• Erect leaves (in rice), letting light into a dense canopy.
• Insensitivity to photoperiod, so they could be sown in different seasons and latitudes and, with irrigation, allow two or even three crops a year.
• Earlier maturity in many cases, which also made multiple cropping possible.

A package, not a seed

The new varieties alone yielded little more than the old ones without inputs. Their advantage appeared when they were grown with:

• Fertiliser, especially nitrogen, now affordable thanks to cheap ammonia manufacture.
• Reliable water: canal irrigation and, increasingly, privately owned tube wells pumping groundwater.
• Crop protection, because dense, uniform, well-fed stands also suited pests and diseases.
• Policy: public investment in research and extension, rural credit, input subsidies, roads and markets, and guaranteed or stabilised grain prices that made the investment safe for farmers.

The phrase "Green Revolution" was coined in 1968 by William Gaud of the United States aid agency, contrasting it with violent "red" revolutions. Borlaug received the Nobel Peace Prize in 1970.

What it achieved

• Yields. Between the early 1960s and 2000, average cereal yields in developing countries roughly doubled to tripled, and total cereal production more than doubled while population roughly doubled. Wheat in South Asia and Mexico and rice in South and South-East Asia led the way; maize yields rose later, with hybrids.
• Food prices and hunger. Real prices of staple grains fell for decades, a large benefit for poor consumers, who spend most of their income on food. Widely predicted famines did not happen.
• Land sparing. Studies estimate that without the yield gains, many millions of hectares more forest and grassland would have had to be cleared to grow the same food.
• Economic growth. Higher farm incomes and cheaper food supported rural non-farm employment and wider growth in several Asian economies.

What it cost, and its limits

The record is not one-sided, and examiners expect the costs.

• Water. Tube-well irrigation on cheap or subsidised power has lowered water tables in several intensively irrigated regions of Asia and the Middle East, threatening the systems the revolution built. Canal irrigation without drainage caused waterlogging and salinity.
• Soils and nutrients. Intensive cereal–cereal rotations with mostly nitrogen fertiliser depleted other nutrients; zinc and sulphur deficiencies emerged, organic matter fell in some systems, and yield growth slowed even with more fertiliser ("fatigue" of intensive systems).
• Pests. Heavy and sometimes indiscriminate insecticide use killed natural enemies and caused pest resurgence; the brown planthopper outbreaks in tropical Asian rice in the 1970s are the classic case, and they helped launch integrated pest management.
• Diversity. Uniform modern varieties replaced many traditional landraces (genetic erosion), and the shift to wheat and rice displaced pulses, millets and other crops from fields and diets, with effects on nutrition.
• Equity. Early adopters were often larger farmers with irrigation and access to credit, and benefits concentrated in favourable, irrigated regions. Later evidence showed that small farmers adopted widely too, and that landless labourers gained from more work and cheaper food; but rainfed and marginal areas were largely bypassed.
• Environment. Fertiliser losses contributed to nitrate in groundwater, eutrophication and nitrous oxide emissions.

Why it largely bypassed sub-Saharan Africa

African farming relied on many crops (maize, sorghum, millets, cassava, yams, pulses) rather than irrigated wheat and rice; most farming was rainfed on diverse, often nutrient-poor soils; and roads, fertiliser supply, credit and markets were weaker. Gains came later and more slowly, notably with improved maize, cassava and rice varieties, and a "Green Revolution for Africa" has been a policy goal since the 2000s with mixed results.

The legacy

Today's debate is about how to keep raising yields while repairing the costs: more efficient nitrogen and water use, diversified rotations including pulses and millets, biofortified varieties, integrated pest management, conservation agriculture, and better support for rainfed farming. These ideas are sometimes grouped as an "evergreen revolution" or sustainable intensification: higher productivity from the same land with less environmental harm.

Questions people ask

Sources

1. Evenson, R. E. and Gollin, D. "Assessing the impact of the Green Revolution, 1960 to 2000." Science 300, 758–762 (2003).
2. Pingali, P. L. "Green Revolution: impacts, limits, and the path ahead." Proceedings of the National Academy of Sciences 109, 12302–12308 (2012).
3. Hedden, P. "The genes of the Green Revolution." Trends in Genetics 19, 5–9 (2003).
4. Stevenson, J. R., Villoria, N., Byerlee, D., Kelley, T. and Maredia, M. "Green Revolution research saved an estimated 18 to 27 million hectares from being brought into agricultural production." PNAS 110, 8363–8368 (2013).
5. Hazell, P. B. R. The Asian Green Revolution. IFPRI Discussion Paper 00911, International Food Policy Research Institute, 2009.

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