Praxis Agriculture flashcards
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32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Cation exchange capacity
- The total negative charge on soil particles that holds exchangeable cations such as calcium, magnesium, and potassium. Higher clay and organic matter content raises CEC and improves nutrient retention.
- Liebig's law of the minimum
- The principle that crop yield is limited by the single most deficient essential resource, not by total resources. Supplying other nutrients beyond sufficiency does not increase yield.
- Growing degree days
- A heat accumulation measure calculated by averaging daily maximum and minimum temperatures, subtracting a crop-specific base temperature, and summing over the season to predict crop development.
- Rhizobium nitrogen fixation
- A symbiotic relationship in which bacteria in legume root nodules convert atmospheric nitrogen gas into ammonia the plant can use. Rotation with legumes reduces synthetic nitrogen needs.
- Soil pH and nutrient availability
- Soil pH near 6.0 to 6.8 maximizes availability of most nutrients. Phosphorus becomes less available in strongly acid soils and in alkaline soils.
- C3 versus C4 plants
- C4 plants such as corn and sorghum fix carbon into four-carbon compounds and are more water-use efficient in heat. C3 plants include wheat, soybeans, and most cool-season crops.
- Essential macronutrients
- Nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur are required by plants in relatively large amounts. Their deficiency or excess directly limits growth and yield.
- Rumen fermentation
- Microbes in the rumen ferment fibrous feed into volatile fatty acids that supply most ruminant energy. Rumen pH near 6.0 to 6.8 supports fiber digestion.
- Crude protein calculation
- Crude protein equals percent nitrogen multiplied by 6.25, because protein averages about 16 percent nitrogen. Feed analysis uses this conversion to express protein content.
- Colostrum and passive immunity
- The antibody-rich first milk that newborns must consume soon after birth. The gut absorbs maternal antibodies only briefly before closure, so delayed feeding leaves young vulnerable.
- Beef cattle gestation length
- Beef cattle gestation averages about 283 days, roughly nine months. Breeding and calving dates are planned backward from this interval.
- Swine gestation length
- Swine gestation averages about 114 days, remembered as three months, three weeks, and three days. Farrowing schedules and weaning timing depend on this interval.
- Monogastric digestion limits
- Swine and poultry have simple stomachs and cannot efficiently digest large amounts of fiber. Their diets rely more on starch and protein concentrates than ruminant diets.
- Metabolic body weight
- Maintenance energy requirements scale with body weight raised to the power 0.75. This means larger animals need less feed per unit of body weight than smaller animals.
- Estrous cycle length
- The interval between heat periods in cattle and sheep averages about 21 days and about 21 days in swine. Accurate detection determines breeding and conception timing.
- Break-even yield
- Total production costs divided by the price received per unit. It shows the yield required to cover all costs at a given price.
- Marginal value product
- The added revenue from one more unit of input, calculated as marginal product times output price. Profit is maximized when it equals marginal input cost.
- Partial budget analysis
- A decision tool comparing added returns and reduced costs against added costs and reduced returns for a proposed change. A positive net difference favors the change.
- Short-run shutdown rule
- A farm should keep producing in the short run if price exceeds average variable cost, even when price is below average total cost. Fixed costs are sunk.
- Straight-line depreciation
- An annual non-cash expense equal to purchase cost minus salvage value, divided by useful life in years. It spreads machinery or building cost over its service life.
- Balance sheet versus income statement
- A balance sheet lists assets, liabilities, and net worth at one point in time. An income statement reports revenues and expenses over a period.
- Economic threshold
- The pest population density at which control should be applied to prevent the population from reaching the economic injury level. It drives scouting-based spray decisions.
- Economic injury level
- The lowest pest population that causes crop loss equal to the cost of control. It sits at or above the economic threshold and reflects pest damage and control cost.
- Herbicide site-of-action rotation
- Repeated use of one herbicide mode of action selects resistant weeds. Rotating among effective site-of-action groups and using non-chemical tactics slows resistance.
- Restricted-entry interval
- The legally required waiting period after a pesticide application before workers may enter the treated area without protective equipment. It appears on the pesticide label.
- Disease triangle
- A plant disease requires a susceptible host, a virulent pathogen, and a favorable environment. Breaking any one leg prevents epidemic development.
- Bacillus thuringiensis
- A soil bacterium used as a biological insecticide. Its proteins are toxic to caterpillars and some beetle larvae after ingestion and are considered low-risk to many beneficials.
- Tractor rollover protection
- Rollover protective structures with seat belts prevent operator deaths in overturns. Raising the center of gravity or narrowing the wheelbase increases rollover risk.
- Power take-off speed
- Tractor PTO shafts operate at standard speeds of 540 or 1000 revolutions per minute. Shields must stay in place because entanglement causes severe injury.
- Ohm's law
- Voltage equals current in amperes multiplied by resistance in ohms. Electrical power in watts equals volts times amps, useful for sizing farm electrical equipment.
- Grain bin engulfment hazard
- Flowing grain can trap and submerge a person within seconds. Never enter a bin without lockout, harness, observer, and ventilation, and test for toxic gases.
- 4R nutrient stewardship
- Applying fertilizer using the right source, right rate, right time, and right place. It improves nutrient use efficiency and reduces losses to water and air.