Agriculture & Feeding the World

You’ll be able to

Describe the trade-offs of the Green Revolution and industrial agriculture
Compare irrigation methods and explain how they lead to soil salinization
Calculate the percent change in crop yield from agricultural data

The Green Revolution and its trade-offs

The Green Revolution (mid-1900s) dramatically raised food production by introducing high-yield crop varieties, synthetic fertilizers, pesticides, irrigation, and mechanization. It fed billions but carried costs: heavy fertilizer and pesticide use pollutes water, monoculture (planting a single crop over a large area) increases vulnerability to pests and erodes genetic diversity, and fossil-fuel-powered machinery and fertilizer make industrial farming energy-intensive. The revolution traded higher yields for greater environmental impact and dependence on inputs.

Irrigation and the salinization problem

Irrigation lets farmers grow crops where rainfall is insufficient, but methods differ in efficiency. Flood and furrow irrigation are cheap but wasteful — much water evaporates or runs off. Drip irrigation delivers water directly to roots and is far more efficient. A major hazard of irrigation in dry climates is salinization: irrigation water carries dissolved salts, and when it evaporates from the soil surface it leaves the salts behind. Over years, salt accumulates until it becomes toxic to crops. Waterlogging — a rising water table drowning roots — is a related problem of over-irrigation.

Livestock, pests, and sustainable alternatives

Concentrated animal feeding operations (CAFOs) raise many animals in small spaces; they are efficient but generate huge volumes of manure that pollute water and require heavy antibiotic use. To fight crop pests, industrial farms rely on pesticides, but overuse breeds pesticide resistance (natural selection favors resistant pests) and kills beneficial insects. More sustainable methods include integrated pest management (IPM) — combining biological controls, crop rotation, and limited targeted pesticide use — plus contour plowing, terracing, and no-till farming to reduce soil erosion, and crop rotation to restore soil nitrogen.

Percent change in yield

percent change = [(new value − old value) / old value] × 100

A positive result is an increase, a negative result a decrease. Always divide by the ORIGINAL (old) value, not the new one.

Worked example

Before adopting Green Revolution methods, a farm produced 2 metric tons of wheat per hectare. Afterward it produced 6 metric tons per hectare. What was the percent increase in yield?

1.Identify old and new values: old = 2 t/ha, new = 6 t/ha.
2.Find the change: new − old = 6 − 2 = 4 t/ha.
3.Divide by the original value: 4 / 2 = 2.
4.Convert to a percent: 2 × 100 = 200%.

Answer: A 200% increase — the yield tripled. Note that tripling is a 200% increase, not 300%, because percent change measures the change relative to the original.

Checkpoint

A farmer in an arid region has irrigated the same field for 20 years using flood irrigation, and crop yields are now falling as a white crust builds up on the soil. What is the most likely cause?

Tip

Rank irrigation by efficiency: drip (most efficient, least evaporation) > spray/sprinkler > flood/furrow (least efficient, most evaporation and salinization risk). When a question asks how to reduce water waste or salinization, switching to drip irrigation is almost always a correct answer.

Checkpoint

Which is a major environmental drawback of planting a large monoculture of a single crop variety?

On the exam

For percent-change problems, the number-one error is dividing by the new value instead of the old. Anchor on "change ÷ original × 100." And remember: a doubling is +100%, a tripling is +200% — the increase is one less multiple than the factor of growth.

Answer the 2 checkpoints as you read.