Agricultural Solutions to the Demands of the Growing Population

Most artificial fertilisers are NPK fertilisers, which supply nitrate (N), phosphate (P) and potassium (K) ions. Natural fertilisers such as manure and compost supply the same minerals more slowly.

Nitrate is used to make amino acids and so proteins, phosphate is needed for DNA and cell membranes, and potassium helps the enzymes of photosynthesis and respiration to work. A shortage of any of them stunts growth and lowers the yield.

Fertilisers make crops grow faster and larger, so more food comes from the same field, and the same crop can be grown year after year on the same land.

Fertilisers cost money, and rain washes the extra minerals into rivers and lakes, where they cause eutrophication and pollute drinking water.

Insecticides kill insects that eat crops, herbicides kill weeds that compete with the crop for light, water and minerals, and fungicides kill fungi that cause diseases such as blight and mildew.

Crops lose less to pests, weeds and disease, so the yield and the quality of the harvest are higher, and the pesticides act quickly and are easy to use.

Many pesticides kill harmless insects as well, including bees and other pollinators, and so reduce biodiversity and the pollination of crops.

Some pesticides are not broken down and build up in the bodies of animals along a food chain. The pesticide DDT made the shells of birds of prey thin and weak, and their numbers fell.

A pest that survives the spray passes on its resistance, so a pesticide may stop working over time and a new one has to be found.

The roots are held in a solution of water with all of the mineral ions the plant needs, and a pump bubbles air through it so that the roots get oxygen for respiration. The plants are held up by a support, and light is provided by the sun or by lamps.

The farmer can set the exact amount of each mineral, the pH, the temperature and the light for every crop, so each plant gets exactly what it needs.

Yields are high, crops can be grown all year round and in places with poor soil or no space, such as cities and deserts, and less water is used because it is recycled. There are no soil pests and fewer diseases.

The equipment, the lighting and the pumps are expensive to set up and to run, and the farmer needs skill. A power failure or an infection can ruin the whole crop, because every plant shares the same solution.

The farmer releases an animal that eats the pest. Ladybirds and their larvae eat aphids, and in greenhouses predatory mites are released to eat red spider mites.

Parasitic wasps lay their eggs in pests such as whitefly or caterpillars, and the wasp larvae feed on the host and kill it.

A bacterium called Bacillus thuringiensis, sprayed on a crop, makes caterpillars ill and kill them. Insects that eat only one weed can be released to control it.

There are no chemical residues, it does not kill most other species, pests do not become resistant to it as quickly, and it can be sustainable because the control organism reproduces.

It works slowly and does not completely remove the pest, the control species may not survive or may eat other organisms, and it can be expensive to buy and release the organisms.

A gene from the bacterium Bacillus thuringiensis (the Bt gene) makes maize and cotton produce a protein that kills caterpillars that eat them, so the farmer sprays less pesticide.

Crops can be given resistance to a herbicide, to drought, or extra vitamins such as vitamin A in golden rice.

Yields rise and losses to pests fall, so more food is produced from the same land.

The seed is expensive, and some people are concerned about the effects on other organisms and on human health. The details are covered in the lessons on genetic engineering.