JCE Agriculture cheat sheet

Crop rotation with legumes fixes atmospheric nitrogen via Rhizobium symbiosis, typically adding 50–200 kg N/ha to the following cereal crop.

Seed germination requires adequate moisture, oxygen, and temperature above the base temperature for the species; below the base temperature, germination is zero regardless of other factors.

The law of limiting factors states that yield is constrained by the single most deficient growth resource, not by the sum of all resources.

Photosynthesis net assimilation is maximized at light saturation point; beyond it, additional light does not increase carbon fixation.

Planting density decision rule: increase density when expected emergence percentage is low or when the variety is short-statured with low tillering capacity.

Intercropping with a legume and a cereal increases land equivalent ratio (LER) above 1.0 when the species exploit different canopy layers or rooting depths.

Transplanting shock is reduced by hardening seedlings for 5–7 days before field setting and by irrigating immediately after transplanting.

The critical period for weed competition in most annual field crops occurs during the first 4–6 weeks after emergence; controlling weeds after this window gives minimal yield recovery.

Feed conversion ratio (FCR) = feed consumed ÷ liveweight gain; lower FCR indicates greater efficiency.

Ruminant digestion relies on microbial fermentation in the rumen; dietary crude protein below maintenance requirement causes negative nitrogen balance and weight loss.

The thermoneutral zone is the ambient temperature range where an animal maintains body temperature without extra energy expenditure; outside it, feed energy is diverted to thermoregulation.

Colostrum must be fed within the first 6–12 hours of birth because immunoglobulin absorption by the neonatal gut declines rapidly after 24 hours.

Inbreeding coefficient increases by 1/(2Ne) per generation where Ne is effective population size; small herds require planned outcrossing to avoid inbreeding depression.

Poultry layer production peaks at 90–95% hen-day egg production during the first laying cycle; a drop below 80% often signals inadequate calcium or lighting.

Body condition scoring (BCS) is a decision tool: cows below BCS 2.5 at calving have delayed estrus and lower conception rates.

Silage preservation depends on anaerobic fermentation producing lactic acid that lowers pH below 4.5, inhibiting spoilage organisms.

Soil texture triangle classifies soil by percentage of sand, silt, and clay; loam is roughly 40% sand, 40% silt, 20% clay.

Cation exchange capacity (CEC) measures the soil's ability to hold exchangeable cations; high-clay and high-organic-matter soils generally have higher CEC.

Soil pH below 5.5 reduces availability of phosphorus, molybdenum, and calcium; liming raises pH and is applied based on buffer pH or lime requirement tests.

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

The Universal Soil Loss Equation: A = R × K × LS × C × P, where A is predicted annual soil loss.

Contour plowing and terracing reduce the slope length factor (LS) and the cover factor (C), directly lowering erosion risk.

Available water capacity is the water held between field capacity and permanent wilting point; sandy soils hold less than clay loams.

Nitrogen immobilization occurs when soil C:N ratio exceeds about 30:1; adding high-carbon residues temporarily reduces plant-available nitrogen.

Tractor power take-off (PTO) standard speeds are 540 rpm and 1000 rpm; implement shafts and guards must match the PTO speed.

Draft requirement of a tillage implement increases with soil resistance, working width, and depth; draft = specific resistance × width × depth.

Wheel slip above 15–20% on a tractor indicates excessive ballast or load; slip below 8% indicates insufficient load for traction.

Three-point hitch categories (I, II, III) are determined by tractor power and determine implement pin and link dimensions.

A mower-conditioner combines cutting with crimping or crushing to speed forage drying; roll clearance and roll pressure control conditioning intensity.

Sprayer calibration: application rate (L/ha) = (nozzle output × number of nozzles × 600) ÷ (speed × swath width), with output in L/min, speed in km/h, width in m.

Gear selection rule: use lower gears for heavy draft loads to increase torque at the wheels; higher gears reduce fuel consumption on light loads.

Daily pre-operation checks on tractors include engine oil, coolant, tire pressure, and hydraulic fluid; failure to check hydraulic fluid can cause implement failure.

Roof pitch is expressed as rise over run; steeper pitches shed water faster but increase material and wind-load costs.

A pole barn derives structural support from embedded posts; post depth should extend below the frost line to prevent heaving.

Ventilation rate in livestock buildings is measured in air changes per hour; minimum winter rates prevent moisture buildup while limiting heat loss.

Concrete slab thickness for light farm equipment is typically 100–125 mm; heavier machinery requires 150 mm or more with reinforcement.

Electric fence energizers are rated in joules of stored energy; a rule of thumb is 1 joule per 1.6 km of fence under light weed load.

Woven wire fence height and mesh spacing are selected by animal species; sheep require smaller mesh than cattle to prevent head entrapment.

Snow load and wind load are the two dominant structural design loads for farm buildings; local building codes specify design values.

Grain storage structures require aeration fans sized to provide 0.1–0.5 m³/min per tonne, depending on grain type and moisture.

Gross margin = gross output (yield × price) − variable costs; fixed costs are excluded from gross margin calculations.

Break-even yield = total fixed costs ÷ (price per unit − variable cost per unit).

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

Depreciation methods: straight-line depreciation = (cost − salvage value) ÷ useful life; declining balance charges more in early years.

Opportunity cost is the value of the next best alternative forgone; it is included in economic profit but not accounting profit.

Farm records categories: physical records (yields, livestock numbers), financial records (receipts, payments), and supplementary records (inventory, labor).

Cash flow differs from profit: cash flow tracks timing of cash receipts and payments, while profit matches revenues to expenses in the accounting period.

Elasticity of demand for a farm product measures percentage change in quantity demanded per percentage change in price; inelastic demand means price changes cause proportionally smaller quantity changes.

Eutrophication of water bodies is driven by excess nitrogen and phosphorus; agriculture is a major non-point source via runoff and leaching.

Buffer strips along waterways trap sediment and nutrients; effectiveness increases with strip width and vegetation density.

Integrated pest management (IPM) uses economic threshold levels to time interventions, reducing pesticide load and resistance development.

Greenhouse gas sources in agriculture include enteric methane from ruminants, nitrous oxide from fertilized soils, and methane from flooded rice paddies.

Conservation tillage reduces soil erosion and fuel use but may increase reliance on herbicides for weed control.

Waterlogging and salinization are consequences of over-irrigation without adequate drainage; salinity is measured by electrical conductivity of the soil extract.

Agroforestry systems sequester carbon in woody biomass and improve soil organic matter while providing shade and wind protection.

Pesticide residues in soil and water are reduced by following label application rates, respecting pre-harvest intervals, and avoiding application before forecast rain.