More crop per drop: Most of the world's water is used to grow food. Saving water in food production systems matters more than any other saving.
The points to remember
- Farming uses about 70% of the freshwater taken from rivers, lakes and aquifers.
- So saving water on farms saves far more than saving it at home.
- The aim: more crop per drop, the same food from less water.
- Five ways: drip irrigation, greenhouses, aquaponics, drought-resistant crops, less meat.
Remember it as: Drip it, roof it, loop it, swap it, eat less meat.
Real example: around Almería in southern Spain, about 31,000 hectares of plastic greenhouses grow vegetables for Europe in a place with less than 350 mm of rain a year. Most of their water comes from aquifers, and one of them was declared over-used in 2004.
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Old-style flood irrigation loses much of its water to evaporation and run-off. Drip irrigation puts the water where the plant needs it.
Watering more wisely
- Drip irrigation: pipes with small holes drip water onto each plant's roots.
- Little water evaporates or runs off, so most of it reaches the crop.
- Water at night or in the cool morning, so less evaporates.
- Mulch and cover crops shade the soil; terracing stops water running off slopes.
- Limits: drip systems cost money to buy and need clean water so the holes do not block.
Real example: as Almería's aquifers fell, its greenhouse farmers changed to drip irrigation and hydroponics, so each tomato needs less water.
Not just 'irrigation': 'Use irrigation' does not answer a question about saving water: irrigation can waste it. Name the method, such as drip irrigation, and say why less water is lost.
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A greenhouse is a building of glass or plastic. Its roof can catch rain, and its closed space lets farmers collect water and use it again. Aquaponics goes further: nothing is thrown away.
Greenhouses and aquaponics
- Greenhouses keep the air moist, so plants lose less water than in open fields.
- Rain falling on the roof is harvested into tanks or ponds and used to water the crop.
- Water that drains from the roots is collected, cleaned and recycled.
- Aquaponics: fish waste feeds the plants, and the plants clean the water for the fish.
- The same water goes round again and again; only a little is topped up.
Real example: in Almería, many greenhouses now grow vegetables in hydroponics with the drainage water collected and reused, instead of letting it soak into the ground.
Some plants need much less water than others. Plant breeders, and sometimes genetic modification, produce drought-resistant crops.
Choosing crops
- Drought-resistant crops grow with less water: farms need less irrigation.
- They raise yields in dry years and let farmers use dry land that grew little before.
- Salt-tolerant crops can use salty water or soils.
- Swap thirsty crops such as cotton or rice for ones that need less, such as oats or millet.
- Limits: seeds can cost more, GM varieties have low genetic diversity, and few kinds exist.
Strengths
- Less irrigation water needed
- Higher yields in dry years
- Dry land can be farmed
Limits
- Seeds can cost more
- GM varieties: low genetic diversity
- Few kinds are available yet
Real example: from the 1960s, rivers feeding the Aral Sea in Central Asia were used to irrigate cotton, a very thirsty crop. The sea shrank to a small part of its old size: the cost of growing the wrong crop in a dry place.
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Animals eat crops, and those crops need water. So the more meat a country produces, the more water its food system uses. Switching to vegetarian food production saves water.
Less meat, less water
- Animals eat crops that need water, so meat needs far more water than plant food.
- 1 kg of beef needs about 15,400 litres; 1 kg of chicken about 4,300.
- Producing more plant food and less meat means less water for the same people.
- Switching from beef to chicken also saves water, even without going vegetarian.
- Limits: people's culture, taste and income, and farmers' jobs, make change slow.
Real example: beef needs about 15,400 litres of water per kilogram and chicken about 4,300, so beef needs almost four times as much water as the same amount of chicken.
Use the numbers: Quote two figures and compare them: 'beef needs about 15,400 litres per kilogram, nearly four times as much as chicken'.
How this comes up: Paper 2, Section A: identify two strategies to grow crops where water is scarce [2].
Farmers in southern Spain grow tomatoes and peppers in an area where more than 40% of the renewable water supply is already taken each year.
Identify two strategies that could be used to grow crops in areas of high water stress.
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