The methods used to increase agricultural productivity, the environmental impacts of intensive farming, the differences between intensive and extensive and organic systems, and approaches to sustainable food production.

What this dot point is asking

AQA wants you to describe the methods used to raise agricultural productivity, explain the environmental impacts of intensive farming, compare intensive, extensive and organic systems, and explain approaches to sustainable food production. The command words that recur in this topic are Describe, Explain, Compare and Evaluate, so you must be able to do more than list techniques: you have to trace each technique through to its consequence.

Increasing agricultural productivity

Productivity, the yield of food per unit area of land per year, is raised by overcoming the natural factors that limit plant and animal growth.

Each lever works by relaxing a limiting factor. Liebig's law of the minimum is the underlying principle: yield is set by whichever resource is in shortest supply, so adding nitrogen only helps if nitrogen, not water or phosphorus, is the bottleneck. This is why farmers soil-test and apply balanced fertiliser rather than nitrogen alone.

Environmental impacts of intensive farming

Intensive farming maximises output per hectare with high inputs, but those inputs have downstream costs that AQA expects you to explain as cause-and-effect chains, not single words.

• Eutrophication. Soluble nitrate and phosphate from fertiliser run off into rivers and lakes. Algal blooms form, block light, then die and are decomposed by bacteria that consume dissolved oxygen, so fish and invertebrates suffocate. Nitrate also leaches into groundwater used for drinking.
• Soil degradation. Heavy machinery compacts soil; continuous cropping without rotation depletes organic matter and nutrients; bare soil between crops erodes by wind and water.
• Biodiversity loss. Monocultures and hedgerow removal destroy habitat and wildlife corridors, and broad-spectrum pesticides kill non-target species, including pollinators and the natural predators of pests.
• Pesticide problems. Persistent pesticides bioaccumulate up food chains (the classic example being organochlorines concentrating in birds of prey), and pests evolve resistance, prompting heavier doses.
• High energy use. Manufacturing nitrogen fertiliser by the Haber process, running machinery and transporting produce all consume fossil fuels, raising the carbon footprint of food.

Intensive, extensive and organic systems

The trade-off is central to exam answers. Intensive systems deliver the most food per hectare, which can spare other land from cultivation (the land-sparing argument), but they degrade the land they use. Extensive and organic systems are gentler per hectare but need more land per tonne of food (the land-sharing argument), so judging which is more sustainable depends on whether impact is measured per hectare or per unit of food produced.

Sustainable food production

Sustainable approaches aim to keep yields high while protecting soil, water and biodiversity for the future.

• Crop rotation alternates crop families, including a legume year that fixes nitrogen, to maintain fertility and break pest and disease cycles.
• Integrated pest management (IPM) combines biological control, resistant varieties, monitoring and minimal targeted pesticide use, cutting chemical inputs while controlling pests.
• Conservation farming uses reduced or zero tillage and cover crops to protect soil structure and reduce erosion, and retains hedgerows and field margins for wildlife.
• Precision agriculture uses GPS and sensors to apply fertiliser and water only where needed, reducing runoff and waste.