SACE Stage 2 Agricultural Production cheat sheet
SACE Stage 2 Agricultural Production · Keep the key ideas within reach.
Agricultural Production: Systems, Soil, Water and Livestock
Production systems are classified by enterprise mix and intensity: extensive grazing relies on natural pasture with low inputs per hectare, whereas intensive systems use confinement, irrigation, or supplementary feeding to raise output per unit area.
Soil texture is the proportional mix of sand, silt and clay; loam (roughly 40% sand, 40% silt, 20% clay) balances drainage, water-holding capacity and workability, making it the reference texture for crop suitability.
Soil pH controls nutrient availability: most field crops perform best at pH 5.5-7.5 (measured in water, CaCl2 readings run about 0.5-1.0 lower); aluminium toxicity becomes likely below pH 5.0 in many Australian soils.
Plant-available water is estimated as (field capacity minus permanent wilting point) multiplied by root-zone depth; a sandy soil may hold about 60-80 mm per metre of profile, a clay loam 150-200 mm per metre.
The limiting nutrient rule: yield is set by the nutrient or factor in shortest supply relative to crop demand, so applying a non-limiting nutrient raises cost without raising yield.
The nitrogen cycle steps in order are fixation, mineralisation (ammonification), nitrification, immobilisation, denitrification and leaching; legumes fix atmospheric N2 via rhizobia symbiosis, adding N to the following crop.
Crop rotation interrupts pest and disease cycles and balances nutrients; a cereal-legume rotation adds nitrogen and breaks cereal root-disease build-up, while continuous same-species cropping increases pathogen load and herbicide-resistance risk.
Ruminant nutrition is driven by rumen microbial fermentation of fibre; dietary crude protein is balanced against metabolisable energy, and a protein-to-energy imbalance limits intake and liveweight gain even when total feed is adequate.
Integrated pest management ranks controls as biological and cultural first, chemical last, and relies on economic thresholds and monitoring; rotating herbicide and insecticide modes of action slows resistance evolution.