Sustainability and Environment: Impacts, Indicators and Trade-offs
Defining sustainability
Sustainability rests on three pillars - economic, environmental and social - and a system is only sustainable if all three hold over time. Candidates must name the main environmental impacts of agriculture: soil erosion by wind and water, salinity from rising water tables, nutrient runoff causing eutrophication, greenhouse gas emissions (methane from ruminants, nitrous oxide from nitrogen fertiliser), loss of biodiversity, and water use in irrigation districts.
Know the indicators used to judge performance: ground cover percentage, soil organic carbon, pH, salinity readings, nutrient balances, water-use efficiency and biodiversity counts. Ground cover is a strong proxy - bare soil erodes and sheds water, while cover protects structure and infiltration.
Traps to watch
- Treating sustainability as purely environmental. A practice that ruins farm profit fails the test too.
- Confusing renewable with unlimited. Groundwater recharges slowly; using it faster than recharge is mining.
- Assuming "organic" or "natural" automatically means sustainable - neither guarantees low erosion or low emissions.
- Overlooking off-site damage. Erosion on a paddock becomes sediment and nutrients in a river kilometres away.
Worked example
A paddock loses 8 t/ha of topsoil in a bare summer. Each tonne of topsoil holds roughly 1.5 kg of available nitrogen, so about 12 kg N/ha is lost - small in dollars, but the lost 15 mm of soil depth and reduced infiltration are the real cost. Retaining 70% ground cover typically cuts erosion sharply because raindrop energy is intercepted.
Rule of thumb
Judge a practice against all three pillars and ask whether the resource use rate exceeds the replenishment rate.