BSCS Officer General Exam flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Cation exchange capacity

The total quantity of exchangeable cations a soil can hold, expressed in cmol(+)/kg. It rises with clay and organic matter content and governs nutrient retention and lime requirement.

Soil textural triangle

A USDA diagram that converts percentages of sand, silt, and clay into a textural class name. The three percentages must sum to 100 before plotting.

Jenny's soil-forming factors

Climate, organisms, relief, parent material, and time. These five factors together determine the properties of a soil at any given location.

Bulk density

Oven-dry soil mass divided by total soil volume, including pore space. Values near 1.3 g/cm3 indicate good structure; compaction raises them and lowers porosity.

Liebig's law of the minimum

Crop yield is limited by the essential nutrient in shortest supply relative to plant need. Supplying other nutrients cannot compensate for that single deficiency.

Fertilizer grade conversion

Fertilizer labels report N, P2O5, and K2O. Multiply P2O5 by 0.44 to get elemental P, and multiply K2O by 0.83 to get elemental K.

Mobile versus immobile nutrients

Mobile nutrients such as nitrogen and potassium show deficiency first in older leaves because the plant redistributes them. Immobile nutrients such as iron and boron show it first in young leaves.

Base saturation

The percentage of the cation exchange capacity occupied by exchangeable calcium, magnesium, potassium, and sodium. It is used as an indicator of soil fertility and lime need.

Harvest index

The ratio of economic yield to total biological yield. It measures how efficiently a crop partitions assimilate into the harvested organ rather than into stems and leaves.

Growing degree days

A heat accumulation index summing daily mean temperature above a crop-specific base temperature. It predicts emergence, flowering, and maturity timing better than calendar days.

Leaf area index

Total leaf area per unit ground area. Most field crops reach near-maximum light interception at an index of roughly three to five.

Land equivalent ratio

The sum of the relative yields of intercrops grown together compared with their sole-crop yields. A ratio above one indicates an intercropping advantage.

Universal Soil Loss Equation

A = R x K x LS x C x P. It estimates long-term average annual soil loss from sheet and rill erosion as a product of rainfall, soil, slope, cover, and practice factors.

Conservation tillage

Any tillage system that leaves at least 30 percent of the soil surface covered by crop residue after planting. It reduces sheet and rill erosion and conserves moisture.

Land capability classes

Eight classes ranked by limitations for agricultural use. Classes I to IV are arable; V to VII suit pasture, forestry, or wildlife; VIII is unsuitable for production.

Runoff coefficient

The fraction of rainfall that becomes surface runoff rather than infiltrating or evaporating. It increases with slope steepness, soil compaction, and impervious surface cover.

Soil series

The lowest category in USDA Soil Taxonomy. A series is a group of soils with a unique combination of horizons and properties within a soil family.

Diagnostic horizon

A soil horizon with specific properties used to classify a profile, such as a mollic, argillic, oxic, spodic, or cambic horizon.

Hydrologic soil group

A classification from A to D ranking soils by runoff potential and infiltration rate. Group A soils have low runoff potential; group D soils have high runoff potential.

Economic injury level

The pest population density at which the cost of control equals the value of crop loss avoided. It sets the basis for economic thresholds used in scouting decisions.

Integrated pest management

A decision framework combining resistant varieties, sanitation, monitoring, biological and cultural controls, and judicious chemicals. Chemical control is used only when monitoring shows thresholds are exceeded.

Mode-of-action rotation

Alternating pesticides with different target-site mechanisms, tracked by IRAC, FRAC, or HRAC groups, to delay the evolution of resistant pest, pathogen, or weed populations.

Economic threshold

The pest density at which control action should be taken to prevent the population from reaching the economic injury level. It is lower than the injury level.

Pure live seed

The product of percentage purity and percentage germination, expressed as a fraction. Seeding rates are divided by this fraction to deliver the intended number of viable seeds.

Tetrazolium viability test

A rapid seed viability test in which living embryos reduce tetrazolium salt to a red compound. Stained tissue indicates respiration and therefore viable seed.

Heritability

The proportion of total phenotypic variance attributable to genetic variance. Traits with high heritability respond rapidly to selection in breeding programs.

Phytoextraction

A remediation technique in which metal-accumulating plants take up contaminants into harvestable shoots. Repeated harvests gradually remove metals from the soil.

Eutrophication

Excess nitrogen and phosphorus enrichment of surface water that triggers algal blooms and oxygen depletion. Phosphorus is usually the limiting nutrient in freshwater systems.

Compost C:N ratio

The carbon-to-nitrogen ratio of composting feedstock, ideally near 25 to 30 to 1. Proper ratio, moisture, and aeration drive thermophilic decomposition and pathogen kill.

Gross margin

Gross income from an enterprise minus its variable costs. It allows comparison of enterprises before fixed costs such as land, machinery, and overhead are allocated.

Partial budget

A farm management tool listing added returns and reduced costs against added costs and reduced returns. The net balance shows whether a proposed change is profitable.

Extension adoption curve

A model describing adoption of innovations over time by innovators, early adopters, early majority, late majority, and laggards. Diffusion accelerates once opinion leaders adopt.

Conflict of interest

A situation in which a private interest could influence, or appear to influence, official judgment. Standard responses are disclosure and recusal from the decision.