Food security: what limits yield and what it costs to raise it
Crop yield can be limited by pests, diseases, water or nutrients. Raising yield can use more water or harm soil, rivers and wildlife. Food security also depends on whether people can obtain safe, nutritious food.
What a learner can do afterwards
- Identify threats to harvests and explain how climate change can increase some risks
- Explain why feeding human-edible crops to animals usually leaves less food energy for people than eating those crops directly
- Evaluate one intensive farming method by what it gains and what it costs
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Food security means everyone can reliably obtain enough safe, nutritious food. A large harvest does not give everyone access if food is unaffordable or cannot reach them. Pests, diseases, drought, floods and soil damage can reduce harvests. Climate change can increase heat stress and change drought or heavy-rain risks. Warmer winters can let some crop pests survive. People with fewer resources may find it harder to cope.
Plants store sunlight energy in food. Animals use food energy for respiration and release heat. Energy in uneaten or undigested material can pass to decomposers. Only some feed energy becomes new tissue. In calculations here, assume 10% becomes edible animal tissue. Ten percent is one tenth, found by dividing by 10. Real efficiencies vary. Compare food energy before human digestion.
A harvest has 4000 energy units in grain people can eat. At 10% transfer, edible animal tissue holds 4000 ÷ 10 = 400 units. The difference is 4000 - 400 = 3600 units. Eating the edible grain directly avoids the transfer through animals, which releases heat and leaves energy in waste or inedible parts. Grass and some by-products are not human food, so this comparison does not fit every farm.
Fertiliser can raise yield when mineral nutrients limit growth. Dissolved nutrients can enter rivers and contribute to eutrophication, as in the previous topic. Irrigation supplies water when water limits growth. Pumping groundwater faster than it is replaced can lower the water table. Choose a method that addresses the crop's limit, then compare its yield gain with its money, water and environmental costs.
Pesticides can protect yield by reducing pest damage. Some pests already resist a pesticide. If they survive spraying and reproduce, repeated use can make resistance more common. Pesticides can also harm non-target organisms, including species exposed through polluted water. To evaluate a pesticide, compare the crop damage it prevents with its cost, resistance risk and possible harm to other species.
Food security needs reliable access to safe, nutritious food. Compare crop and animal food using stated assumptions, and judge farming methods by both yield gains and costs.
Lesson, questions and study cards written for this dataset. Energy-flow textbook records were consulted for scientific background; no source passages or illustrations are reproduced.
Readings and study cards written for this dataset. Videos credit Brent Loken and Birke Baehr. Their publishers' reuse terms have not been verified.
More to read
Compare the food people could eat
Before comparing two food routes, check what the animals eat. Grain suitable for people offers a direct food alternative. Grass that people cannot eat does not offer the same alternative.
Suppose edible grain contains 5000 energy units. If a stated model transfers 10% into edible animal tissue, that tissue contains 5000 ÷ 10 = 500 units. The difference between the two food totals is 4500 units. These figures describe food before people eat it, not the energy absorbed during human digestion.
The other energy has not vanished. Animals use energy in respiration and release heat. Undigested material and uneaten feed can supply decomposers. Energy stored in animal parts that people do not eat is also outside the edible-food total.
Ten percent is an assumption for this calculation. Different animals and farming systems have different efficiencies. Feeding livestock grass or by-products people cannot eat also changes the comparison. Food-energy totals explain part of the production question, but they do not establish whether a diet contains all the nutrients people need.
Match the method to the crop's limit
A crop short of mineral nutrients may respond to fertiliser. The same treatment may do little when the main problem is lack of water. Irrigation supplies water, but it does not remove every pest or disease. To choose a method, first identify what is holding growth or harvest yield back.
Fertiliser can increase yield, while dissolved nutrients carried into rivers can contribute to eutrophication. Extra nutrients may support algal growth. Decomposers breaking down dead organisms respire and can lower the dissolved oxygen available to fish.
Pesticides can prevent crop damage. Some pests already resist a particular pesticide. If they survive spraying and reproduce, repeated use can make resistance more common. Other species may also be harmed by exposure, including exposure through polluted water.
Irrigation can help a water-limited crop. Its water source matters: pumping groundwater faster than it is replaced can lower the water table.
Compare the food gained with the money, water and environmental costs. Yield per hectare means the amount harvested from each hectare of land. A higher yield per hectare shows a production gain, but it does not describe every cost.
Food must reach people
Food security means everyone can reliably obtain enough safe, nutritious food. Harvest size alone cannot show whether that happens. Food may be available for sale but unaffordable to some households. A disrupted delivery route can also leave food out of reach.
Growing enough food still matters. Pests and diseases can damage crops, while drought, floods and soil damage can reduce harvests. Climate change can increase heat stress and change drought or heavy-rain risks. Warmer winters can allow some crop pests to survive. The effects depend on the crop, pest and region.
A proposed response needs to match the problem. Irrigation may help where water limits growth. Pest control may reduce damage where pests limit the harvest. Neither response alone makes food affordable or restores a delivery route.
When judging a plan, explain which problem it addresses and how it could help. Then consider its costs and who can obtain the resulting food. More food energy harvested does not by itself show that everyone has access to a safe diet with the nutrients they need.
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