LC Ag Science cheat sheet

Independent variable is the factor deliberately changed; dependent variable is the measured response; controlled variables are held constant to prevent confounding.

A hypothesis must be falsifiable and testable: state a predicted relationship between variables, not a general statement of interest.

Replication reduces the effect of random variation; randomisation of treatments to plots or animals controls systematic bias such as soil gradients or pen position.

A control group receives no treatment or a standard treatment so the effect of the factor under test can be isolated.

Precision describes repeatability of measurements (low random error); accuracy describes closeness to the true value (low systematic error).

Calculate percentage error as (measured value − true value) ÷ true value × 100; report the mean plus a measure of spread such as standard deviation or standard error.

Correlation between two variables does not establish causation; a plausible mechanism and a controlled experiment are required.

Significant figures and units must match the resolution of the instrument used, e.g. a balance reading to 0.01 g is reported to two decimal places.

In agricultural trials, guard rows and discard rows reduce edge effects from neighbouring plots, light, and spray drift.

Soil formation is driven by climate, parent material, organisms, relief/topography, and time (CLORPT); climate and parent material dominate in most systems.

Soil texture is the proportion of sand (2.0–0.05 mm), silt (0.05–0.002 mm), and clay (<0.002 mm); texture class is read from a texture triangle.

Soil structure is the arrangement of particles into aggregates; good structure gives stable crumbs with continuous macropores for air and drainage.

Bulk density = oven-dry soil mass ÷ total volume; compaction raises bulk density and reduces porosity and root penetration.

Cation exchange capacity (CEC) is the sum of exchangeable cations held on clay and humus surfaces, expressed in cmol(+)/kg; higher clay and organic matter give higher CEC.

pH affects nutrient availability: phosphorus is least available at extremes, and micronutrients such as iron and manganese become less available as pH rises above about 7.

Nitrogen cycling includes mineralisation, nitrification, immobilisation, denitrification, and volatilisation; legume symbiosis fixes atmospheric N2 into plant-available forms.

Soil biological activity (bacteria, fungi, earthworms, mycorrhizae) drives organic matter decomposition and nutrient turnover; mycorrhizae extend root access to phosphorus and water.

Photosynthesis converts CO2 and water to carbohydrate using light energy in chloroplasts; net growth depends on gross photosynthesis minus respiration losses.

Transpiration pulls water through xylem from roots to leaves; stomata balance CO2 uptake against water loss and close under water stress.

Phloem transports assimilates from source leaves to sink organs such as grain, fruit, and roots.

Plant hormones: auxins control cell elongation and apical dominance, gibberellins promote stem elongation and germination, cytokinins promote cell division, ethylene ripens fruit, abscisic acid closes stomata.

Monocot and dicot differences: monocots have one cotyledon, parallel veins, and fibrous roots; dicots have two cotyledons, net veins, and a taproot.

Ruminant digestion relies on microbial fermentation in the rumen to break down cellulose into volatile fatty acids; non-ruminants rely more on enzymatic digestion in the small intestine.

Animal breeding uses heritability and selection differential: response to selection = heritability × selection differential, so traits with low heritability respond slowly.

Homeostasis in farm animals regulates body temperature, blood glucose, and water balance; heat stress reduces feed intake and fertility.

Seed germination requires adequate moisture, oxygen, and a suitable temperature; sowing depth must balance moisture supply against emergence energy.

Sowing rate = target plant population ÷ (germination % × establishment %), adjusted for thousand-grain weight and expected field losses.

Liebig's law of the minimum: yield is limited by the scarcest essential nutrient, so adding other nutrients will not raise yield until that deficiency is corrected.

The nitrogen cycle in cropping includes legume fixation, fertiliser application, leaching, and gaseous loss; split applications reduce leaching risk.

Integrated pest management ranks tactics: cultural, biological, and physical controls first; chemical control is used only when thresholds are exceeded.

Economic threshold is the pest population at which the value of crop loss equals the cost of control; below it, spraying does not pay.

Harvest timing depends on maturity indices such as grain moisture, dry matter content, or firmness; too-early harvest reduces yield and quality.

Post-harvest losses arise from respiration, moisture, temperature, and pests; cooling and drying reduce respiration and spoilage.

A ration must supply energy, protein, minerals, vitamins, and water in proportions matched to the animal's age, weight, and production stage.

Feed conversion ratio = feed consumed ÷ liveweight gain; a lower value indicates more efficient conversion.

Protein quality depends on essential amino acid balance; limiting amino acids such as lysine and methionine cap growth in monogastrics.

Breeding tools include selection index, estimated breeding value (EBV), and crossbreeding to exploit heterosis; EBV predicts genetic merit, not phenotype.

Inbreeding raises homozygosity and can expose recessive defects; outcrossing restores vigour, and a minimum effective population size protects genetic diversity.

Disease control combines biosecurity, vaccination, quarantine, and hygiene; antibiotics must be used prudently to limit antimicrobial resistance.

The five freedoms cover freedom from hunger and thirst, discomfort, pain/injury/disease, fear and distress, and freedom to express normal behaviour.

Stress indicators in livestock include cortisol levels, heart rate, and behavioural changes; chronic stress lowers growth and immune function.

Nutrient budgeting compares inputs (fertiliser, feed, fixation) with outputs (produce, leaching, volatilisation) to identify surplus and loss pathways.

Eutrophication results from excess nitrogen and phosphorus entering water; it causes algal blooms, oxygen depletion, and fish kills.

Greenhouse gas sources on farm include enteric methane, manure management, fertiliser nitrous oxide, and fuel; mitigation options include improved efficiency and feed additives.

Soil erosion is controlled by maintaining ground cover, contour farming, reduced tillage, and buffer strips along watercourses.

Water-use efficiency = marketable yield ÷ water applied; irrigation scheduling based on soil moisture or evapotranspiration improves it.

Biodiversity on farmland is supported by field margins, hedgerows, crop rotation, and reduced pesticide use; these also support pollinators and natural enemies.

Carbon sequestration in soil depends on organic matter inputs, reduced tillage, and residue retention; gains are finite and reversible.

Life cycle assessment quantifies environmental impact per unit of product across production, processing, transport, and waste stages.

Gross margin = gross output (sales plus valuation changes) − variable costs; fixed costs are excluded because they do not change with enterprise scale.

Profit = total revenue − total costs (variable plus fixed); a positive gross margin does not guarantee profit if fixed costs are high.

Break-even yield = total costs ÷ price per unit; break-even price = total costs ÷ expected yield.

Partial budget analysis compares extra costs and reduced returns against extra returns and reduced costs to evaluate a change.

Opportunity cost is the value of the next best alternative forgone; it is central to enterprise choice and resource allocation.

Price elasticity of demand measures responsiveness of quantity demanded to price; staple foods are generally inelastic, so price swings hit farm income hard.

Supply chain stages run from input supply through production, processing, distribution, retail, and consumption; each stage adds value and cost.

Risk management tools include diversification, forward contracts, insurance, and storage; each trades potential gain for reduced variability.

A practical investigation must state an aim, a testable hypothesis, and a clear independent, dependent, and controlled variable set.

Method must be reproducible: record equipment, quantities, timings, and environmental conditions so another candidate could repeat it.

Risk assessment identifies hazards, who is at risk, and control measures; agricultural hazards include machinery, chemicals, livestock, and zoonoses.

Data tables need column headings with units and the correct number of decimal places; raw data are recorded before any averaging.

Graphs use the independent variable on the x-axis and the dependent variable on the y-axis, with labelled axes, units, and a fitted trend line where appropriate.

Evaluate validity (does the method test the hypothesis?), reliability (would repeats give the same result?), and precision (instrument resolution).

Conclusions must be justified by the data and linked to agricultural science theory; unexplained anomalies are identified and commented on rather than deleted.

Ethical and welfare considerations include animal handling protocols, humane endpoints, and consent for farm data, and must be documented in the plan.