AP® Human Geography review sheet from Aim for Five (aimforfive.com/geo/units/5/5-5)
Unit 5 · Topic 5.5
5.5 The Green Revolution
The Green Revolution spread high-yield seeds, chemical fertilizers, pesticides, irrigation and machinery from the 1940s through the 1960s, starting in Mexico and reaching India, Pakistan and much of Asia. It sharply raised harvests and helped feed fast-growing populations, but it also brought environmental damage, unequal benefits and much less success in sub-Saharan Africa.
Key terms
- Green Revolution
- high-yield varieties
- chemical fertilizer
- pesticides
- irrigation
- Norman Borlaug
What the Green Revolution was
The Green Revolution was a package of farming technology spread to lower-income countries in the mid-1900s. Many geographers treat it as part of the Third Agricultural Revolution, which also includes later biotechnology like GMOs (5.11). The package had four main parts:
- High-yield varieties (HYVs): new strains of wheat and rice bred to produce much more grain per plant. Many were semi-dwarf, with short, sturdy stems that didn't fall over under heavy heads of grain.
- Chemical fertilizers, which the new seeds needed to reach their high yields.
- Pesticides and herbicides to protect crops.
- Irrigation and machinery, such as tube wells and tractors, to supply steady water and work more land.
Where and when it spread
It began in Mexico in the 1940s, where a program supported by the Rockefeller Foundation and the Mexican government worked on wheat. Plant scientist Norman Borlaug developed disease-resistant, semi-dwarf wheat there and later won the Nobel Peace Prize (1970).
In the mid-1960s, Borlaug's wheat reached India and Pakistan, which were facing food shortages. At the International Rice Research Institute in the Philippines, scientists released IR8, a high-yield rice, in 1966. The term Green Revolution was coined in 1968. India's wheat harvest roughly doubled within about seven years, with the biggest gains in irrigated states like Punjab.
Benefits
- Much higher yields on the same land, which helped prevent widespread famine as populations grew. This challenged Malthus's prediction that food couldn't keep up with population (2.6).
- More food at lower prices for many people in South and East Asia and Latin America.
- Less pressure to clear new land, because existing fields produced more.
Costs and criticisms
- Water: heavy irrigation drained groundwater. In Punjab, India, water tables have fallen sharply.
- Chemicals: fertilizer and pesticide runoff polluted rivers and wells, and overuse damaged soils.
- Less diversity: farmers replaced many local crop varieties with a few HYVs, which reduced genetic diversity and made crops more vulnerable to new pests.
- Unequal benefits: the package cost money, so farmers with more land, water and credit gained the most. Some small farmers fell into debt or sold their land, and machines replaced farm workers, adding to rural-to-urban migration.
- Diet changes: the focus on wheat and rice sometimes pushed out pulses and millets that added nutrition.
Why sub-Saharan Africa saw less success
The early Green Revolution focused on wheat and rice grown with irrigation. Much of sub-Saharan Africa relies on rain-fed farming and on crops like sorghum, millet, cassava and yams that got less research attention. Africa's environments are also very varied, and many farmers lacked roads, credit and affordable fertilizer. More recent programs have tried to bring improved seeds to African farmers, with mixed results.
Worked examples
Try each one yourself first, then open the solution.
- Example 1
Explaining a negative consequence at a named scale
Explain one environmental consequence of the Green Revolution in South Asia.
Show the solutionHide the solution
- Step 1: Name a specific input: irrigation from tube wells.
- Step 2: Explain the process: high-yield rice and wheat need a lot of water, so farmers pumped groundwater faster than rain refilled it.
- Step 3: Give the result at a named scale: falling water tables in Punjab threaten future farming in that region.
Answer: Model answer: High-yield wheat and rice need steady water, so farmers in Punjab, India, drilled tube wells and pumped groundwater faster than rainfall could replace it. As a result, the region's water table has dropped sharply, which raises pumping costs and threatens farming there in the future.
Common mistakes
- Calling the Green Revolution organic or environmentally friendly because of its name. It relied on chemical fertilizers, pesticides and heavy irrigation.
- Saying it ended hunger. It raised food production, but hunger depends on access and income too, and benefits were uneven.
- Saying the Green Revolution involved GMOs. Its seeds came from conventional crossbreeding; genetic engineering came later.
On the exam
- Many questions ask for one positive and one negative consequence. Pair each with a specific place, like Punjab or Mexico.
- Be ready to explain why the Green Revolution worked less well in sub-Saharan Africa.
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Check yourself
4 questions on 5.5 The Green Revolution. Pick an answer to see if you got it, and why.
After droughts in 1965 and 1966 cut harvests, India imported high-yield, semi-dwarf wheat varieties first bred in Mexico. The seeds were planted widely in the state of Punjab, where canals and wells already supplied irrigation water, and farmers paired them with chemical fertilizer.
Wheat harvests rose sharply within a few years, and India's need for grain imports fell. Later, however, problems appeared. Water tables under Punjab dropped as farmers pumped more groundwater, and spending on fertilizer, pesticides and fuel for pumps kept climbing. Farmers with little land or no irrigation often gained less.
Secondary-style passage written for this practice set
Which condition described in the passage helped the new wheat varieties succeed in Punjab?
Which statement best describes the Green Revolution in Punjab at different scales?
Which factor best explains why the Green Revolution had less success in most of sub-Saharan Africa than in South Asia?
The Green Revolution relied most heavily on which combination of inputs?
0 of 4 answered