HSC Agriculture cheat sheet

Photosynthesis: 6CO2 + 6H2O + light energy -> C6H12O6 + 6O2; gross primary production minus respiration equals net dry matter accumulation.

Law of the minimum: yield is limited by the single most deficient growth factor (water, nitrogen, light), not by the sum of all inputs.

Dry matter digestibility of pasture declines as herbage matures; leaf-to-stem ratio is the key driver of feed quality in grazing systems.

Critical soil pH for most field crops is 5.5-6.5 (CaCl2); below this, aluminium toxicity and phosphorus lock-up reduce root growth.

C3 plants (wheat, rice) photorespire above ~25 C; C4 plants (maize, sorghum, sugarcane) concentrate CO2 and maintain higher water-use efficiency.

Seed germination requires viable embryo, adequate moisture, temperature above base temperature, and oxygen; dormancy is broken by stratification, scarification, or light.

Crop rotation interrupts pest and disease cycles and balances nitrogen: legumes fix atmospheric N2 via rhizobia symbiosis, cereals deplete it.

Growing degree days (GDD) = sum of daily ((Tmax+Tmin)/2 - Tbase); used to predict phenology, maturity, and pest emergence timing.

Dry matter intake (DMI) in ruminants is roughly 2.5-4% of body weight per day; higher for high-quality forage, lower for low-digestibility roughage.

Rumen fermentation yields volatile fatty acids: acetate from fibre, propionate from starch, butyrate from sugars; acetate-to-propionate ratio shifts with diet.

Protein requirement is expressed as metabolisable protein or crude protein; rumen-degradable protein feeds microbes, undegradable protein bypasses to the small intestine.

Pregnancy diagnosis in cattle: ultrasound from ~28-30 days, rectal palpation from ~35-45 days; gestation averages 283 days in cattle, 147 days in sheep.

Feed conversion ratio (FCR) = feed consumed / liveweight gain; lower FCR means more efficient conversion of feed into animal product.

Heat stress: cattle pant above ~25-30 C; respiration rate, water intake, and reduced feed intake signal thermal load, lowering milk yield.

Body condition score (1-5 or 1-8 scale) is a management tool linking nutrition to fertility; extremes delay return to oestrus and reduce conception rates.

Colostrum must be fed within the first 6-12 hours of life; gut absorption of immunoglobulins declines rapidly after birth.

Gross margin = gross income - variable costs; fixed costs (depreciation, rates, permanent labour) are excluded and compared separately across enterprises.

Return on assets = farm operating profit / total assets; measures efficiency of capital use independent of how the farm is financed.

Break-even yield or price = total costs / (area or output); used to identify the minimum output needed before the enterprise is profitable.

Cash flow differs from profit: it tracks timing of receipts and payments; seasonal enterprises often need overdraft finance before income arrives.

Depreciation allocates the cost of an asset over its useful life; it is a non-cash fixed cost but affects taxable income and replacement planning.

Whole-farm planning balances land capability, labour, machinery capacity, and risk; diversification spreads price and climate risk across enterprises.

Water-use efficiency in irrigation = yield or gross value per megalitre applied; scheduling by evapotranspiration replacement avoids deep drainage and salinity.

Soil testing every 2-3 years guides fertiliser decisions; nutrient budgeting compares inputs (fertiliser, fixation, manure) with removals in product.

Elective options typically include farm product study, agribusiness, sustainable agriculture, or experimental design; each applies the core production and management principles.

In a valid experiment, only one variable is deliberately changed (independent), all others held constant (controlled), and the response is measured (dependent).

Replication and randomisation reduce the effect of uncontrolled variation; a control treatment provides the baseline for comparison.

A hypothesis is a testable prediction stated before the experiment; results either support or fail to support it, never 'prove' it.

Marketing chains: gross return to the farm gate is the retail price minus all downstream costs (processing, transport, retail margin).

Value adding (grading, packaging, processing, provenance claims) raises unit price but requires capital and market access; assess by marginal return.

Sustainability indicators include soil organic carbon, ground cover, biodiversity, nutrient balance, and profitability over time, not single metrics.

Risk management tools: diversification, forward contracts, crop insurance, and enterprise mix reduce the variance of farm income.