NZ Scholarship Agricultural and Horticultural Science cheat sheet

Production system components: inputs (seed, fertiliser, water, labour, capital), throughputs (photosynthesis, digestion, growth), outputs (yield, profit, waste), and feedbacks (soil fertility, herd health, cash flow) - map every case study onto this model before analysing it.

Yield gap = potential yield (climate- and cultivar-limited) minus actual yield (limited by water, nutrients, pests, management); explaining a gap requires ranking limiting factors, not listing them.

Economic thresholds: act against a pest only when the cost of control is less than the value of yield lost; threshold density depends on crop value, pest damage rate, and control efficacy.

Sustainability is assessed across four pillars - economic viability, environmental integrity, social acceptability, and intergenerational equity; a practice that improves one pillar while degrading another is not automatically sustainable.

Water quality indicators: nitrate-N (drinking water guideline 11.3 mg/L as N), phosphorus (freshwater ecological guideline 0.01–0.033 mg/L DRP), E. coli, turbidity, and dissolved oxygen; agricultural impacts are diffuse and cumulative, so regulation targets land use rather than point discharges.

Nutrient budgets compare inputs (fertiliser, feed, fixation, deposition) with outputs (produce, leaching, runoff, volatilisation, denitrification); a surplus indicates accumulation or loss risk, a deficit indicates mining of soil capital.

Life cycle assessment stages: goal and scope, inventory, impact assessment, interpretation; functional unit choice (per kg milk, per hectare, per kg N leached) changes the ranking of systems.

Decision frameworks: SWOT identifies position, cost-benefit compares options in money, and multi-criteria analysis weights incommensurable objectives (profit, emissions, animal welfare) when no single metric dominates.

New Zealand context: pasture-based systems rely on clover fixation and urine patch N cycling; the main contaminant pathways are nitrate leaching from urine patches and sediment and P loss via surface runoff and bank erosion.

Soil texture triangle: sand, silt and clay proportions determine water-holding capacity, aeration, and nutrient retention; clay holds more water and cations but has lower infiltration and is prone to compaction when wet.

Cation exchange capacity (CEC) rises with clay and organic matter; base saturation and pH determine availability of nutrients - P is most available at pH 6.0–6.5, and micronutrients such as Mn and B become limiting at high pH.

Liebig's law of the minimum: growth is set by the scarcest resource; adding a non-limiting nutrient gives no yield response, which is why soil tests target the limiting factor first.

Photosynthesis drivers: light interception (leaf area index, canopy architecture, row spacing), CO2, temperature, water, and N (Rubisco); dry matter production is approximately the product of intercepted radiation and radiation use efficiency.

Crop rotation benefits: breaking pest and disease cycles, restoring N (legumes), improving soil structure, and diversifying income; monoculture raises the risk of soil-borne pathogens and herbicide-resistant weeds.

Integrated pest management hierarchy: prevention (resistant cultivars, hygiene, habitat), monitoring and thresholds, biological control, then chemical control as a last resort, with resistance management through mode-of-action rotation.

Animal production: feed conversion efficiency, metabolisable energy intake, stocking rate, and reproductive rate drive profitability; stocking rate interacts with pasture residual and body condition, so overstocking reduces per-head performance.

Horticultural quality attributes: soluble solids (Brix), firmness, colour, size grade, and shelf life; pre-harvest factors such as crop load, light exposure, and water deficit influence post-harvest storage life.

Post-harvest chain: harvest maturity, cooling rate, controlled atmosphere (low O2, elevated CO2), ethylene management, and cold chain integrity; each break in the chain shortens shelf life and increases waste.