BSCS Officer General Exam cheat sheet

Soil texture classes follow the USDA textural triangle: sand, silt, and clay percentages sum to 100; the class name is read from the intersection of the three axes.

Stokes' law governs sedimentation analysis: particles settle at a velocity proportional to the square of particle diameter, so sand settles first, then silt, then clay.

Soil bulk density = oven-dry mass / total volume; particle density of most mineral soils is about 2.65 g/cm3, so porosity = 1 - (bulk density / 2.65).

Five soil-forming factors (Jenny): climate, organisms, relief, parent material, and time; CLORPT is the mnemonic.

Cation exchange capacity is expressed in cmol(+)/kg (numerically equal to meq/100 g); it increases with clay content and organic matter and with 2:1 rather than 1:1 clay minerals.

Base saturation = (sum of exchangeable Ca, Mg, K, Na / CEC) x 100; it is used as a proxy for soil fertility and pH-related lime need.

Soil pH is measured in a 1:1 or 1:2.5 soil-water suspension; a shift of one pH unit is a tenfold change in hydrogen ion activity.

Master horizons: O (organic), A (mineral topsoil), E (eluvial), B (illuvial/subsoil), C (weathered parent material), R (bedrock).

Essential macronutrients: N, P, K, Ca, Mg, S; micronutrients: Fe, Mn, Zn, Cu, B, Mo, Cl, Ni; C, H, O come from air and water.

Liebig's law of the minimum: yield is limited by the nutrient in shortest supply relative to crop need, not by the most abundant one.

Fertilizer grade N-P2O5-K2O: to convert P2O5 to elemental P multiply by 0.44; to convert K2O to elemental K multiply by 0.83.

Nutrient requirement (kg/ha) = (target yield x nutrient concentration in tissue) adjusted for soil supply and recovery efficiency; recovery efficiency for N is typically 30-60%.

Nitrogen fixation by legumes requires adequate Mo, Fe, and Co and a pH near 6.0-7.0; Rhizobium inoculation is warranted where the host-specific strain is absent.

Critical soil pH: below about 5.5, Al and Mn toxicity limit roots; lime requirement rises with clay content and organic matter buffer capacity.

Mobile nutrients (N, K, Mg) show deficiency first in older leaves; immobile nutrients (Fe, Ca, B) show it first in young leaves.

Split application of N and placement (banding, incorporation) reduce volatilization and leaching losses compared with broadcast surface urea.

Crop growth rate = (biomass at time 2 - biomass at time 1) / (time interval x ground area); net assimilation rate is growth rate per unit leaf area.

Harvest index = economic yield / total biological yield; it quantifies partitioning of assimilate to the harvested organ.

C3 plants (rice, wheat, soybean) use RuBisCO and photorespire at high temperature; C4 plants (maize, sugarcane, sorghum) use PEP carboxylase and have higher water-use efficiency.

Crop rotation interrupts pest and disease cycles and diversifies root depth and nutrient uptake; monoculture raises soil-borne pathogen pressure.

Leaf area index (LAI) of about 3-5 optimizes light interception in most field crops; beyond that, self-shading reduces marginal gain.

Growing degree days (GDD) = sum of [(Tmax + Tmin)/2 - Tbase] for each day with the value floored at zero; used to predict phenology and maturity.

Intercropping and relay cropping raise land equivalent ratio (LER) above 1.0 when component crops use resources complementarily.

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

Universal Soil Loss Equation: A = R x K x LS x C x P; A is soil loss, R rainfall erosivity, K soil erodibility, LS slope length-steepness, C cover management, P support practice.

Contour farming, terracing, and strip cropping reduce the LS and P factors; maintaining cover reduces C toward zero.

Terracing converts long slopes into short segments; bench terraces suit slopes above about 15-20% where annual cropping continues.

Grassed waterways and check dams handle concentrated flow; contour practices alone do not control gully erosion.

Conservation tillage leaves at least 30% residue cover after planting; no-till leaves the most and reduces sheet erosion sharply.

Wind erosion control: shelterbelts, surface residue, roughness, and strip width reduction; erodible fraction rises as soil surface dries and crusts break down.

Runoff coefficient is the fraction of rainfall converted to surface flow; it increases with slope, soil compaction, and impervious cover.

Land capability classes I-VIII: I-IV are arable with increasing limitations; V-VII are suited to pasture, forestry, or wildlife; VIII is unsuitable for production.

USDA Soil Taxonomy orders: Gelisols, Histosols, Spodosols, Andisols, Oxisols, Vertisols, Aridisols, Ultisols, Mollisols, Alfisols, Inceptisols, Entisols.

Diagnostic horizons drive classification: mollic (thick dark surface), argillic (clay accumulation), oxic (highly weathered), spodic (organic-metal accumulation), cambic (weak alteration).

Soil series is the lowest category in Soil Taxonomy; a series is defined by a unique combination of horizons and properties within a family.

Soil survey map units carry a symbol and a named component; inclusions and inclusions' proportions are described in the map unit description.

Land suitability evaluation compares land qualities (slope, drainage, depth, fertility) against crop requirements and yields S1 to N classes.

Soil test correlation and calibration relate extractable nutrient levels to crop response; critical levels separate responsive from non-responsive soils.

A soil profile description records horizon depth, color (Munsell), texture, structure, consistence, and boundary; these data feed both classification and interpretation.

Hydrologic soil groups A-D rank infiltration and runoff potential; group A has low runoff potential, group D high.

IPM hierarchy: prevention (resistant varieties, sanitation, rotation), monitoring (scouting, thresholds), then biological, cultural, mechanical, and chemical controls as last resort.

Economic threshold is the pest density at which control prevents the pest from reaching the economic injury level; EIL is the density causing economic loss.

Action threshold = EIL adjusted for control efficacy, cost, and crop value; thresholds are pest- and crop-stage-specific.

Insecticide resistance management: rotate among modes of action (IRAC groups) and avoid repeated applications of one group within a season.

Fungicide resistance: protectant fungicides (multi-site) face lower resistance risk than single-site systemic fungicides; FRAC groups guide rotation.

Herbicide mode-of-action groups (HRAC) should be rotated and tank-mixed to delay resistant weed biotypes.

Biological control agents include parasitoids, predators, and microbials (Bt, Trichoderma); their efficacy depends on pesticide selectivity and timing.

Quarantine and phytosanitary measures prevent introduction of exotic pests; early detection and rapid response limit establishment.

Seed germination requires viable embryo, adequate moisture, suitable temperature, and for many species light or dark cues; dormancy must be broken first.

Seed viability testing: tetrazolium (TZ) test stains living tissue red; standard germination test measures normal seedlings under controlled conditions.

Seed vigor tests (accelerated aging, cold test, electrical conductivity) predict field emergence beyond what germination percentage alone reveals.

Pure live seed (PLS) = purity % x germination %; seeding rates are adjusted by dividing desired pure live seed by PLS fraction.

Heritability (H2) = genetic variance / phenotypic variance; high heritability traits (e.g., maturity) respond well to simple selection.

Marker-assisted selection uses DNA markers linked to traits; it speeds backcrossing and pyramiding of major genes.

Transgenic traits require regulatory approval, stewardship, and refuge or resistance-management plans; gene flow to wild relatives is a biosafety concern.

Mutation breeding, hybridization, and doubled-haploid production are non-transgenic routes to genetic gain; seed certification tracks varietal purity.

Soil remediation options: excavation and landfill, soil washing, thermal desorption, bioremediation, phytoremediation, and stabilization/solidification.

Phytoremediation categories: phytoextraction (metals into harvestable biomass), phytostabilization (immobilize in root zone), rhizodegradation (root-zone microbes degrade organics).

Heavy metal bioavailability depends on pH, organic matter, and redox; liming reduces Cd, Pb, and Zn mobility in acid soils.

Nitrate leaching risk rises with N rate above crop requirement, high rainfall, and coarse texture; cover crops and split N reduce it.

Eutrophication is driven by P and N loading to surface water; P is often the limiting nutrient in freshwater.

Soil organic carbon is built by residue input, reduced tillage, and cover crops; it is lost by erosion, tillage, and bare fallow.

Sustainable systems balance productivity, profitability, and resource conservation; indicators include soil organic matter, erosion rate, nutrient balance, and biodiversity.

Composting requires a carbon-to-nitrogen ratio near 25-30:1, moisture around 50-60%, and aeration to reach thermophilic temperatures that kill pathogens.

Gross margin = gross income - variable costs; it ranks enterprises before fixed costs are allocated.

Break-even yield = total fixed costs / (price per unit - variable cost per unit); break-even price is the inverse calculation.

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

Depreciation (straight-line) = (purchase cost - salvage value) / useful life; it is a fixed cost in enterprise budgets.

Farm records fall into production, financial, and physical categories; cash flow, income statement, and balance sheet are the core financial statements.

Extension adoption curve: innovators, early adopters, early majority, late majority, laggards; diffusion accelerates once opinion leaders adopt.

Demonstration plots, field days, and farmer field schools are participatory extension methods; mass media reaches many but changes behavior slowly.

Price elasticity of demand = % change in quantity demanded / % change in price; staple foods are typically inelastic, so supply shifts move prices sharply.

Professional codes require competence within one's scope, honesty in reporting, confidentiality, and avoidance of conflicts of interest.

Conflict of interest exists when a private interest could influence, or appear to influence, official judgment; disclosure and recusal are the standard responses.

Regulatory decisions require due process: notice, opportunity to be heard, reasons for decisions, and a route of appeal.

Data integrity rules: record raw data, retain it for the prescribed period, and report results without selective omission.

Plagiarism and misattribution violate research ethics; authorship requires substantive contribution and approval of the final manuscript.

Public officers must avoid accepting gifts or favors that could reasonably be seen as influencing official action.

Environmental and pesticide regulations require registration, label compliance, and reporting of adverse effects; label directions are legally binding.

Administrative practice: document decisions, keep an audit trail, and follow delegation of authority; undocumented verbal approvals are not defensible.