CPAg flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Growing Degree Days
- Sum of daily mean temperature above a crop-specific base temperature, with upper and lower caps applied, used to predict crop and pest development timing.
- Crop coefficient Kc
- Ratio of crop evapotranspiration to reference evapotranspiration, varying by crop and growth stage; ETc equals ET0 multiplied by Kc.
- Liebig's Law of the Minimum
- Yield is constrained by the single most limiting growth factor rather than by the total supply of all resources, so correcting that factor raises yield most.
- CEC
- Cation exchange capacity, the quantity of exchangeable cations a soil can hold per unit mass, usually expressed in cmol charge per kilogram; it buffers nutrient supply.
- Soil texture classes
- Sand, silt, and clay proportions determine texture class; sand particles are 2.0 to 0.05 mm, silt 0.05 to 0.002 mm, and clay below 0.002 mm.
- Bulk density
- Oven-dry soil mass divided by total soil volume including pore space; high values indicate compaction that can restrict root growth and water movement.
- Available water capacity
- Difference between field capacity and permanent wilting point; the water a soil can store and release to plants, largest in silt loam textures.
- Nitrification
- Microbial oxidation of ammonium to nitrite and then nitrate under aerobic conditions, producing nitrate that is mobile and vulnerable to leaching and denitrification.
- P2O5 to elemental P
- Phosphorus fertilizer grades are expressed as P2O5; multiply P2O5 by 0.44 to obtain elemental phosphorus, and K2O by 0.83 for elemental potassium.
- Economic threshold
- Pest population density at which the cost of control equals the value of the crop loss that control would prevent, justifying treatment.
- Disease triangle
- Concept requiring a susceptible host, a virulent pathogen, and a favorable environment simultaneously for disease to develop; removing one component prevents epidemic.
- HRAC Group 2
- ALS-inhibitor herbicides; repeated use selects target-site and metabolic resistance in many weed species, so rotation with other modes of action is needed.
- FRAC Group 11
- QoI or strobilurin fungicides acting at the cytochrome bc1 complex; the G143A target-site mutation confers high resistance risk in several pathogens.
- IRAC Group 4A
- Neonicotinoid insecticides acting on nicotinic acetylcholine receptors; they are systemic and important for resistance management because of cross-resistance within the group.
- Degree-day biofix
- Starting date or event, often first moth catch or planting, from which heat units are accumulated to predict pest or crop stage.
- Seed lot purity
- Proportion of seed by weight that is the desired species; used with germination percentage to calculate pure live seed and adjust seeding rates.
- Pure live seed
- Product of germination percentage and purity percentage; dividing desired viable seeds by pure live seed gives the actual bulk seeding rate.
- Corn black layer
- Dark abscission layer at the kernel base marking physiological maturity, typically near 30 to 35 percent grain moisture before field drying.
- Safe grain storage moisture
- Moisture content below which mold growth is limited in stored grain, roughly 14 percent for corn and wheat at moderate temperatures.
- No-till system
- Planting directly into undisturbed residue; it reduces erosion and builds surface organic matter but stratifies phosphorus and potassium near the soil surface.
- Cover crop function
- Crop grown between cash crops to reduce erosion and nitrate leaching, add organic matter, suppress weeds, or fix nitrogen depending on species.
- Double cropping
- Producing two crops in the same field in one year, feasible only where the growing season is long enough for both to mature.
- Fertilizer grade notation
- Convention expressing percent nitrogen, available P2O5, and soluble K2O in that order, for example 46-0-0 for urea and 18-46-0 for DAP.
- Fertilizer product calculation
- Divide the required nutrient rate by the nutrient fraction in the product to obtain the mass of fertilizer product needed per hectare.
- Nutrient removal calculation
- Harvested yield multiplied by nutrient concentration in the harvested portion, used to estimate maintenance fertilizer rates that prevent soil depletion.
- Sprayer output formula
- Litres per hectare equals nozzle flow in litres per minute times 600, divided by the product of speed in km/h and nozzle spacing in metres.
- Bushel yield conversion
- Corn bushels per acre multiplied by 62.77 gives kilograms per hectare; wheat and soybean bushels per acre multiplied by 67.25 give kilograms per hectare.
- Critical soil test level
- Soil nutrient concentration below which a crop response to added fertilizer is likely; above it, maintenance rates based on removal suffice.
- Soil sampling depth
- Consistent coring depth, typically 0 to 15 or 0 to 20 centimetres, needed so soil test values can be compared across years.
- Tissue sufficiency range
- Concentration range of a nutrient in plant tissue sampled at a defined growth stage that indicates adequate nutrition without deficiency or excess.
- Crop rotation benefit
- Alternating crop species interrupts pest and disease life cycles, diversifies weed control, and often raises yield beyond the monoculture baseline.
- Soil organic matter carbon
- Organic matter contains roughly 58 percent carbon by mass; increasing it improves aggregation, water retention, and nutrient reserves in the topsoil.