Agricultural and Horticultural Science: production systems, environment and decisions
NCEA Level 3 Agricultural and Horticultural Science tests how production systems turn soil, plants, animals, technology and markets into products while managing environmental effects. Questions ask you to explain processes, compare systems and justify management decisions with evidence.
Core rules and concepts
- Soil is the base system: texture and structure control drainage and aeration; pH controls nutrient availability; cation exchange capacity and organic matter affect nutrient retention. Compaction and pugging reduce infiltration and increase runoff.
- Plant production: photosynthesis, water and nutrient uptake, phenology and canopy management determine yield and quality. Crop rotation, integrated pest management and irrigation scheduling reduce pest, disease and water risks.
- Animal production: feed supply and demand, metabolisable energy, digestibility, feed budgeting and stocking rate drive performance. Animal health, welfare and reproductive management set the limits.
- Environmental impact: nitrogen and phosphorus cycles link to leaching, runoff, eutrophication and greenhouse gases. Methane comes mainly from ruminant digestion; nitrous oxide comes mainly from urine and fertiliser nitrogen. Water use, biodiversity and soil carbon also matter.
- Economics and markets: gross margin, nutrient budgets, market specifications and supply-chain requirements determine whether a system is viable.
Worked example
A 100 ha block grows 12,000 kg DM/ha/yr, and 80% is harvestable. A ewe requires 550 kg DM/yr. Available feed = 12,000 × 0.80 = 9,600 kg DM/ha. Stocking rate = 9,600 ÷ 550 = 17.5 ewes/ha. At 20 ewes/ha, demand = 11,000 kg DM/ha, a 1,400 kg DM/ha deficit. The farmer must reduce stocking rate, buy supplement or raise pasture production; each option changes cost and environmental risk.
Traps that cost marks
Do not confuse leaching with runoff, or methane with nitrous oxide. Never quote a stocking rate without stating utilisation and feed assumptions. Do not treat environmental and economic effects separately when the question asks for a justified decision. Avoid claiming a system is sustainable without evidence about nutrient losses, water use or profitability. Link soil pH to nutrient availability rather than listing pH alone.