Food production and sustainability

What limits food production?

Food production means growing crops and rearing animals to feed people. We measure how well a farm is doing using yield: the mass of crop (or amount of produce) obtained from a given area or animal.

Yield is usually given in tonnes per hectare (t/ha). One hectare (ha) is about the size of a Gaelic football pitch.

Many factors can lower yield:

• Weather: too much rain causes waterlogging and disease; drought or frost damages plants. A wet harvest can ruin a cereal crop.

• Soil: poor, acidic or compacted soil has fewer minerals (nitrates, phosphates) for plants to take up.

• Pests and diseases: insects, slugs, fungi and viruses eat or damage crops and animals. Potato blight is a famous example.

• Competition: weeds compete with crops for light, water and minerals.

• Animal health and feed: a poor diet or illness reduces milk and meat output.

Fertilisers, pesticides and eutrophication

Farmers add inputs to raise yield.

A fertiliser is a substance added to soil to supply minerals such as nitrates, phosphates and potassium. Plants need these to grow. Fertiliser can be natural (slurry, manure, compost) or artificial (made in factories).

A pesticide is a chemical that kills organisms harming crops: insecticides (insects), herbicides (weeds) and fungicides (fungi).

Eutrophication

When rain washes excess nitrates and phosphates off fields into a lake, the water becomes over-rich in minerals. This is eutrophication.

The steps are:

1. Nitrate-rich run-off enters the lake.

2. Algae grow rapidly on the surface (an algal bloom).

3. The bloom blocks light, so plants below die.

4. Bacteria decompose the dead material and use up dissolved oxygen.

5. Fish and other animals suffocate.

To reduce it: apply less fertiliser and at the right time (not before heavy rain), leave grass or hedgerow buffer strips beside rivers, and fence livestock away from water.

Energy, diet and food chains

Why does beef need so much more land and water than wheat? The answer is in the food chain.

Energy enters a food chain from the Sun and is captured by producers (grass, wheat) in photosynthesis. At each step up to the next trophic level, only about 10% of the energy is passed on. The rest is lost as heat from respiration, in movement, and in waste and uneaten parts.

Eating plants directly (wheat, vegetables) takes energy from the first level. Eating meat adds another level, so far more crop energy, land and water are used per person fed. This is why 1 kg of beef needs about 15,000 litres of water while 1 kg of wheat needs about 1,500.

A family could cut its water footprint by replacing some beef meals with bean, lentil or chicken dishes, since the data show plant foods use far less water per kilogram.

Breeding, farming methods and feeding the world

Selective breeding

Selective breeding is choosing parents with useful features and breeding them together, repeating over many generations.

1. Selection: pick the best animals or plants (for example cows with high milk yield).

2. Breeding: cross the chosen individuals.

3. Repetition: choose the best offspring and breed again, generation after generation.

Irish dairy cows now produce far more milk than in 1980 because of this. The downside is reduced genetic variation: the animals are very alike. If a new disease appears, there may be no resistant individuals, so the whole herd could be at risk.

Intensive and organic farming

A monoculture is growing one crop over a large area. Pests spread easily, so more pesticide is used, which kills insects and the birds that feed on them: biodiversity falls. Crop rotation (changing the crop each year) breaks pest cycles and, when a legume such as clover or beans is included, adds nitrates to the soil, so yields can improve.

What is sustainable?

Sustainable food production meets today's needs without damaging the environment or reducing the ability of future generations to produce food. A farmer can be more sustainable by using crop rotation, planting hedgerows, using less fertiliser, or reducing water use.

Feeding 9.7 billion

To raise production without using much more land:

• Improved varieties through selective breeding or genetic modification (GM).

• Better farm management: precision fertiliser use, better storage to cut waste.

• Reducing food waste and eating more plant-based foods.

Every strategy raises questions. GM crops can raise yield and disease resistance, but people worry about effects on wild species, who owns the seeds, and whether small farmers can afford them. When you evaluate, give evidence on both sides and say what the data cannot tell you (for example, a study of two farms may not show long-term results).

Back to the start: feeding 9.7 billion people is possible only if we raise yields, cut waste and protect the land, water and wildlife that food production depends on.

Summary

• Yield = harvest ÷ area (t/ha). Weather, soil, pests, weeds and animal health limit it.

• Fertilisers add minerals and pesticides protect crops, but run-off causes eutrophication: algal bloom, oxygen loss, fish deaths.

• Only about 10% of energy passes to the next trophic level, so plant foods use less land and water than meat.

• Selective breeding (selection, breeding, repetition) raises output but reduces genetic variation and increases disease risk.

• Sustainable production meets present needs without harming the environment or future production; evaluate methods with evidence and note the limits of the data.

• Percentage change = (change ÷ original) × 100.