Agricultural Science, Ecology and Sustainability
This domain tests whether you can explain farming as an ecological process and judge which practices can continue without degrading the resource base.
Ecosystem concepts
A farm is an ecosystem: producers (crops, pasture), consumers (livestock, pests), decomposers (soil organisms) and a physical environment. Energy flows one way and is lost as heat at each transfer, roughly 90% per step, so food chains are short and meat production needs more land than grain. Nutrients cycle: nitrogen fixation, mineralisation, nitrification, leaching and denitrification; carbon returns to the atmosphere through respiration and burning.
Sustainable practice
Conservation agriculture combines minimum tillage, permanent soil cover and rotation. Agroforestry adds trees for shade, fodder, fuel and nitrogen. Integrated pest management uses resistant varieties, rotation, natural enemies and thresholds before chemicals. Others: water harvesting, mulching, composting, terracing, buffer strips, organic farming and controlled grazing to prevent overstocking beyond carrying capacity.
Worked example
A pasture fixes 50,000 kJ of energy per m² per year in grass tissue. If 10% passes to grazing cattle, cattle store 5,000 kJ; if humans eat the beef and transfer 10% again, only 500 kJ reaches us. That roughly hundred-fold loss over two steps explains why a grain-based diet feeds more people per hectare than a beef-based one, and why food chains in farm ecosystems rarely exceed four or five links.
Traps that cost marks
The 10% figure is an average, not a law. 'Organic' does not mean pest-free or automatically sustainable. Burning crop residues loses nitrogen and organic matter. Monoculture reduces biodiversity and natural enemies. Overstocking is measured against carrying capacity, not against how much feed you can buy.