Agriculture — AQA A-Level Environmental Science

Agriculture covers the manipulation of environmental factors and ecological processes to optimise the production of biomass for human consumption and raw materials. It explores the control of abiotic parameters such as water, nutrients, temperature, and photoperiod, alongside biotic controls including pest management and genetic selection.

This topic forms a core pillar of applied environmental science by contrasting intensive agrochemical systems with sustainable, agroecological practices. Mastering this unit requires understanding how modern agricultural practices perturb natural biogeochemical cycles, deplete soil organic carbon, and drive biodiversity loss, while evaluating technologies that mitigate these pressures.

• →Agroecosystems vs Natural Ecosystems: Agroecosystems maintain early successional stages (plagioclimax), feature drastically reduced species diversity, open nutrient cycles requiring artificial replenishment, and low ecological stability.
• →Energy Ratios: Energetic efficiency calculated by comparing edible energy yield to direct (labour, diesel) and indirect (fertilisers, pesticides, machinery fabrication) artificial energy inputs.
• →Soil Degradation and Conservation: Mechanisms of water and wind erosion, salinisation, and compaction, countered by mitigation practices such as contour ploughing, terracing, cover crops, and minimum-tillage.
• →Pest Control Strategies: Comparison of synthetic persistent pesticides (bioaccumulation and biomagnification risks) versus Integrated Pest Management (IPM), biological control agents, and cultural practices.
• →Genetic Resources: Selective breeding, GM technology, and the conservation of Crop Wild Relatives (CWRs) in seed banks (e.g. Svalbard Global Seed Vault) to maintain genetic diversity against pathogens and climate stress.

• Identifies agriculture as deliberate control of food webs rather than simple collection of wild organisms.
• Explains that photosynthesis captures light energy and that this energy is transferred along food chains to the harvested product.
• States that energy is lost at each trophic transfer, largely through respiration, so shortening or simplifying food chains diverts more energy to human food.
• Describes control of abiotic factors such as light, water, temperature, soil nutrients or pH to raise photosynthetic output.
• Describes control of biotic factors such as pests, weeds, disease or competing grazers to reduce losses of the crop.
• Links a named management practice to the mechanism by which it increases the proportion of photosynthetic energy reaching human food.

• 💡Anchor every answer in the energy-flow idea: state where the energy comes from, where it is lost and how management reduces the loss.
• 💡Separate abiotic controls from biotic controls explicitly, then give one concrete example of each.
• 💡Use precise terms such as photosynthetic energy, trophic transfer, respiration and biomass rather than vague words like growth.
• 💡When a question asks about maximising production, name the factor controlled and the mechanism by which yield rises.
• 💡Use precise soil science terminology: Distinguish between sand, silt, and clay in terms of pore space, aeration, water holding capacity, and cation exchange capacity (CEC).
• 💡Whenever evaluating an agricultural intervention, balance the argument across yield, economic viability, ecosystem services, and carbon/energy footprints.
• 💡Memorise specific case study examples, such as the use of Encarsia formosa wasps to control glasshouse whiteflies, or the impact of the Haber-Bosch process on global nitrogen fluxes.

• Describes agriculture only as growing plants and ignores the control of food webs; correct this by explaining how removing pests or competitors redirects energy to the crop.
• Claims that energy is destroyed in food chains; correct this by stating that energy is lost as heat through respiration at each transfer.
• Lists abiotic and biotic factors without linking them to production; correct this by naming the mechanism, such as added nutrients raising photosynthetic rate.
• Treats maximising production as having no environmental cost; correct this by noting that intensive control can affect biodiversity, pollution and energy use.
• Assuming organic farming produces zero environmental impacts: Organic systems eliminate synthetic chemicals, but often yield lower outputs per hectare, meaning greater land conversion and habitat clearance may be required to produce equivalent food volumes.
• Confusing biomagnification with bioaccumulation: Bioaccumulation is the progressive build-up of a non-biodegradable substance within an individual organism over time; biomagnification is the escalating concentration of that chemical across successive trophic levels in a food web.
• Believing GM crops are inherently hazardous to native biodiversity: GM traits can reduce pesticide applications (e.g. Bt toxin cotton) or enhance drought tolerance, though non-target ecological impacts and gene transfer to wild relatives remain legitimate evaluation points.

1. 1Day 1-3: Review abiotic control techniques (irrigation, aeroponics, glasshouses, liming) and calculate energy ratios for diverse farming models.
2. 2Day 4-6: Master pest control mechanics: chemical classes (organochlorines, organophosphates, pyrethroids, neonicotinoids) versus biological controls and IPM schemes.
3. 3Day 7-9: Study soil degradation types (wind/water erosion, salinisation) and memorise corresponding engineering and cultural conservation practices.
4. 4Day 10-12: Complete timed past paper 6-mark and 9-mark evaluation questions focusing on sustainability transitions (e.g. agroforestry, precision farming).
5. 5Day 13-14: Test memory retention using active recall cards focused on definitions, formulas, and environmental legislations.

• 📋Calculation questions: Determining energy ratios, percentage change in crop yield, or application rates of nutrients.
• 📋Data analysis and graphical interpretation: Assessing pesticide resistance development, soil loss curves under different management regimes, or leaching rates.
• 📋Structured 6-mark or 9-mark extended responses: Evaluating agricultural practices such as GM technology, livestock vs arable efficiency, or agrochemical versus biological pest controls.