MSCE Agriculture cheat sheet

C3 plants fix CO2 via RuBisCO into 3-phosphoglycerate; C4 plants use PEP carboxylase in mesophyll and bundle-sheath cells, raising water-use efficiency and photorespiration resistance in high temperature.

Photosynthetically active radiation (PAR) spans 400-700 nm; only about 1-2% of incident solar energy is converted to net biomass, and crop growth rate peaks near leaf area index 4-6 in cereals.

Cardinal temperatures: below the minimum no germination, between minimum and optimum germination rises, above the optimum it falls, and above the maximum no germination occurs.

Law of the minimum: yield is limited by the single most deficient growth factor; Liebig's barrel analogy means correcting other factors cannot raise yield until that limiting factor is removed.

Seed rate (kg/ha) = (target plant population per m2 x 1000-grain weight in g) / (germination % x field establishment % x 100).

Growing degree days (GDD) = sum over days of [(Tmax + Tmin)/2 - Tbase]; maize commonly uses Tbase 10 C, wheat 0 C, and rice 10 C.

Crop rotation with a legume interrupts cereal pest cycles and adds biologically fixed N; cereals following legumes typically gain 20-40 kg N/ha equivalent.

Harvest index = economic yield / total biological yield; modern wheat and rice cultivars reach 0.4-0.5 versus roughly 0.3 in older tall types.

Vernalization is cold exposure that induces flowering in winter cereals; photoperiod response then determines heading date, and both must be satisfied for timely anthesis.

Monogastric digestion relies on enzymatic hydrolysis in the stomach and small intestine; ruminants ferment fibre in the rumen with microbes before enzymatic digestion, allowing use of roughage.

Rumen pH 6.0-7.0 supports cellulolytic bacteria; a drop below about 5.5 signals subacute ruminal acidosis and depresses fibre digestion and milk fat.

Maintenance energy requirement scales with metabolic body weight (W^0.75); energy above maintenance drives growth, milk, or reproduction, and feed conversion ratio = feed intake / gain.

Crude protein = total N x 6.25; rumen-degradable protein feeds microbes while rumen-undegradable (bypass) protein supplies amino acids directly to the small intestine.

Breeding value and selection response: annual genetic gain = (selection intensity x accuracy x genetic SD) / generation interval, so shortening generation interval accelerates progress.

Inbreeding coefficient rises by 1/(2Ne) per generation; effective population size Ne below 50 raises inbreeding depression and loss of genetic variation.

Colostrum must be fed within the first 6 hours of life because gut absorption of maternal antibodies (passive immunity) declines sharply after 24 hours.

Oestrus cycle length is about 21 days in cattle, 17 days in sheep, and 21 days in pigs; gestation is approximately 283 days cattle, 150 days sheep, 114 days pigs.

Soil texture classes follow the USDA triangle; separates are sand 2.0-0.05 mm, silt 0.05-0.002 mm, and clay below 0.002 mm, with clay controlling water holding and cation exchange.

Cation exchange capacity (CEC) in cmol(+)/kg: sandy soils 1-5, loams 10-20, and clay or organic soils above 25; high CEC buffers pH and nutrient leaching.

Base saturation = (exchangeable bases / CEC) x 100; values above about 80% indicate fertile, near-neutral soils, while low values indicate acidity.

Soil pH below 5.5 releases toxic Al3+ and Mn2+, fixing phosphorus; liming raises pH and the lime requirement rises with clay content and organic matter.

Bulk density = oven-dry soil mass / total volume; values above about 1.6 g/cm3 in loams restrict root growth through compaction.

Available water capacity is water held between field capacity (about -33 kPa) and permanent wilting point (about -1500 kPa); sandy soils hold less than clay loams.

Nitrogen cycle steps are fixation, mineralization (ammonification), nitrification, immobilization, denitrification, and volatilization; waterlogged soils favour denitrification losses.

Universal soil loss equation: A = R x K x LS x C x P, where R is rainfall erosivity, K soil erodibility, LS slope length and steepness, C cover, and P support practice.

Gross margin = gross output (yield x price) minus variable costs; fixed costs are excluded because they do not change with the enterprise in the short run.

Break-even yield = total fixed costs / (price per unit - variable cost per unit); break-even price = total cost / expected yield.

Partial budget format: added returns plus reduced costs versus added costs plus reduced returns; the net change decides whether a proposed change is profitable.

Law of diminishing returns: marginal product falls as a variable input increases with others fixed; profit is maximized where marginal value product equals marginal factor cost.

Benefit-cost ratio, net present value, and internal rate of return are the standard investment appraisal tools; NPV above zero and IRR above the discount rate indicate acceptance.

Elasticity of demand = % change in quantity demanded / % change in price; demand for staple food is inelastic (below 1) while luxury foods are elastic.

Depreciation straight-line = (purchase cost - salvage value) / useful life; this annual charge is a fixed cost affecting machinery ownership decisions.

Farm records fall into physical (yields, stock numbers) and financial (cash book, balance sheet, income statement) categories; enterprise accounts allocate shared costs by area or herd size.

Draft of a tillage implement rises with soil strength, depth, and speed; draught force scales roughly with width and depth, and deeper tillage increases power requirement disproportionately.

Drawbar power (kW) = draft force (kN) x forward speed (m/s); tractor power selection must cover draft plus rolling resistance plus slip losses.

Wheel slip above about 15% wastes fuel and damages soil; ballasting and correct tyre inflation reduce slip and improve traction efficiency.

Field capacity (ha/h) = (implement working width in m x speed in km/h) / 10; field efficiency = theoretical time / actual field time, typically 70-85% for tillage.

Sprinkler and drip irrigation: application rate must not exceed soil infiltration rate; drip achieves 90% or higher efficiency versus 60-75% for surface furrow.

Moisture content wet basis = (water mass / total wet mass) x 100; dry basis = (water mass / dry matter mass) x 100; safe storage of grain is generally below 13-14% wet basis.

Grain drying rate depends on air temperature, humidity, and airflow; over-drying causes cracking and weight loss, so drying should stop at the safe storage moisture.

Machine economics: total annual cost = fixed costs (depreciation, interest, insurance, housing) plus variable costs (fuel, repairs, labour); timeliness losses count when operations are delayed.

Integrated pest management hierarchy: prevention, monitoring and thresholds, then biological, cultural, mechanical, and chemical control as the last resort.

Economic threshold is pest density at which control action prevents the pest from reaching the economic injury level; scouting determines when the threshold is crossed.

Disease triangle requires a susceptible host, virulent pathogen, and favourable environment; the disease tetrahedron adds a human or vector factor.

Koch's postulates confirm a pathogen: isolate it from diseased tissue, culture it, inoculate a healthy host to reproduce symptoms, then re-isolate the same organism.

Fungicide resistance management rotates modes of action (FRAC groups); systemic single-site fungicides carry higher resistance risk than multi-site protectants.

Pesticide label signal words reflect acute toxicity: Danger (highly toxic), Warning (moderately toxic), Caution (slightly toxic); pre-harvest interval must be observed.

Notifiable livestock diseases include foot-and-mouth disease, African swine fever, and avian influenza; suspicion requires immediate reporting and movement restriction.

Vaccination principles: live vaccines mimic natural infection and give strong immunity but risk in pregnant or immunosuppressed animals; killed vaccines are safer but need boosters.

Extension is a non-formal education process transferring technology and facilitating farmer learning; adoption follows awareness, interest, evaluation, trial, and adoption stages.

Rogers' adopter categories: innovators (about 2.5%), early adopters (13.5%), early majority (34%), late majority (34%), and laggards (16%).

Diffusion of innovations depends on relative advantage, compatibility, complexity, trialability, and observability; higher complexity slows adoption.

Extension methods: individual (farm visits, office calls), group (demonstrations, field days, farmer field schools), and mass media (radio, leaflets, SMS).

Farmer field school is a participatory, season-long learning approach where farmers observe and experiment in their own fields, building decision-making capacity.

Training and visit (T&V) system uses scheduled fortnightly visits by subject-matter specialists to train frontline agents; participatory approaches replaced it in many systems.

Agricultural extension linkage: research generates technology, extension disseminates it, and farmers provide feedback; weak research-extension-farmer linkage causes low adoption.

Monitoring and evaluation: monitoring tracks inputs and activities continuously; evaluation assesses outcomes and impact at intervals against baseline indicators.

Greenhouse gases from agriculture: methane from enteric fermentation and flooded rice, nitrous oxide from fertilizer and manure; N2O has about 265 times the global warming potential of CO2.

Conservation agriculture has three principles: minimum soil disturbance, permanent soil cover, and crop rotation or diversification.

Agroforestry combines trees with crops or livestock; benefits include shade, windbreak, soil fertility, and carbon sequestration, but competition for water and light must be managed.

Erosion control measures: contour ploughing, terracing, grass strips, check dams, and mulching; cover crops reduce raindrop impact and runoff velocity.

Integrated nutrient management balances organic sources (manure, compost, legumes) with mineral fertilizer to match crop demand and minimize nutrient losses.

Water quality risk from agriculture includes nitrate leaching and phosphate runoff causing eutrophication; buffer strips along watercourses intercept nutrients.

Biodiversity in farmland is supported by field margins, hedgerows, and reduced tillage; monoculture and pesticide overuse reduce natural enemy populations.

Climate-smart agriculture aims at three outcomes simultaneously: increased productivity, enhanced resilience, and reduced greenhouse gas emissions per unit of output.