Agricultural and Horticultural Science (Level 2): Management Decisions in Plant and Animal Production
Agricultural and Horticultural Science (Level 2)
This domain tests how well you explain, not just describe, the management decisions used in plant and animal production in Aotearoa New Zealand. Examiners want biology and soil science linked to a management action, a measurable outcome, and a reason it matters for profit, animal welfare or the environment.
Core rules and concepts
- Soil texture (the sand, silt and clay proportions) controls structure, drainage and plant-available water. Clay soils hold more nutrients because of higher cation exchange capacity, but drain slowly and are prone to pugging.
- Pasture grows best around pH 5.8–6.5. Lime raises pH and reduces aluminium toxicity; nitrogen fertiliser supplies N but does not change pH and acidifies soil slowly.
- Macronutrients are N, P, K, S, Ca and Mg. Nitrate leaches to groundwater, while phosphorus moves with eroded sediment and drives eutrophication of waterways.
- Sexual propagation (seed) gives genetic variation and is used in breeding. Asexual propagation (cuttings, grafting, budding, division, tissue culture) gives true-to-type, uniform plants and earlier maturity, but transmits viruses and creates no new variation.
- Feed conversion ratio (FCR) = kg feed eaten ÷ kg liveweight gain; a lower FCR is better. Stocking rate must be matched to pasture growth, leaving a grazed residual of roughly 1,200–1,500 kg DM/ha so regrowth is rapid.
- Market requirements shape practice: product must meet quality grade, supply timing, traceability and food-safety standards, so management is modified to hit specification, not just to maximise yield.
Worked example
A 20 ha block grows 12,000 kg DM/ha/yr. Total feed = 20 × 12,000 = 240,000 kg DM. A ewe needs 550 kg DM/yr. If utilisation is 70% (30% lost to trampling, senescence and residual cover), usable feed = 168,000 kg DM. Carrying capacity = 168,000 ÷ 550 = 305 ewes.
Traps
- Dividing pasture yield by stock demand and forgetting utilisation - this overstates carrying capacity.
- Inverting FCR, or treating a high FCR as efficient.
- Confusing lime (raises pH) with nitrogen fertiliser (drives growth).
- Claiming “maximum stocking rate = maximum profit” without considering feed supply and animal health limits.
- Saying asexual propagation increases variation - it does the opposite.