JCE Agriculture flashcards

32 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 or meq/100g. High clay and organic matter content generally increases CEC and nutrient retention.

Field capacity

The water content remaining in soil after excess water has drained by gravity, typically measured 2–3 days after saturation. It represents the upper limit of plant-available water.

Permanent wilting point

The soil water content at which plants can no longer extract water and remain wilted even in a humid atmosphere. It marks the lower limit of plant-available water.

Soil texture triangle

A triangular diagram used to classify soil into textural classes based on the percentages of sand, silt, and clay. Each class has distinct water-holding and drainage properties.

Universal Soil Loss Equation

A model predicting average annual soil erosion: A = R × K × LS × C × P, where factors represent rainfall erosivity, soil erodibility, slope length and steepness, cover management, and support practice.

Crop rotation

The practice of growing different crops in sequence on the same land. It disrupts pest and disease cycles, improves soil structure, and legume phases add nitrogen.

Land equivalent ratio

The ratio of land area needed in sole cropping to the area needed in intercropping to produce the same yield. A value above 1.0 indicates an intercropping advantage.

Law of limiting factors

The principle that crop yield is controlled by the growth factor in shortest supply, not by the total of all factors. Correcting the most deficient factor gives the greatest response.

Critical weed-free period

The crop growth stage during which weed competition causes the greatest yield loss, typically the first 4–6 weeks after emergence in annual field crops.

Seed germination requirements

Viable seed requires adequate moisture, oxygen, and a temperature above the species base temperature. Below the base temperature, germination does not occur regardless of other conditions.

Feed conversion ratio

The ratio of feed consumed to liveweight gain, calculated as feed intake divided by weight gain. A lower FCR indicates more efficient feed utilization.

Thermoneutral zone

The ambient temperature range in which an animal maintains normal body temperature without extra energy for heating or cooling. Outside this zone, feed energy is diverted from production.

Colostrum

The first milk produced after birth, rich in immunoglobulins. Neonatal animals must consume it within 6–12 hours because gut absorption of antibodies declines rapidly after 24 hours.

Body condition score

A subjective assessment of fat and muscle cover, usually on a 1–5 or 1–9 scale. Low scores at calving are associated with delayed estrus and poor conception rates.

Silage fermentation

Anaerobic microbial conversion of sugars to lactic acid, lowering pH below about 4.5. This acidic, oxygen-free environment inhibits spoilage organisms and preserves forage.

Rumen fermentation

Microbial breakdown of feed in the rumen producing volatile fatty acids, microbial protein, and gases. Dietary crude protein below maintenance requirement causes negative nitrogen balance.

Power take-off speed

The standard rotational speed of a tractor PTO shaft, typically 540 rpm or 1000 rpm. Implement shafts and guards must be matched to the tractor PTO speed.

Wheel slip

The difference between theoretical and actual travel distance of a driven wheel, expressed as a percentage. Slip above 15–20% indicates excessive load or insufficient ballast.

Three-point hitch categories

Standardized hitch classes I, II, and III determined by tractor power, specifying pin and link dimensions. The category must match between tractor and implement.

Sprayer calibration formula

Application rate in L/ha equals (nozzle output in L/min × number of nozzles × 600) divided by (speed in km/h × swath width in m).

Draft requirement

The force needed to pull a tillage implement, calculated as specific soil resistance multiplied by working width and depth. Draft increases with speed, depth, and soil moisture.

Frost line depth

The maximum depth to which soil freezes in winter. Building posts and foundations should extend below this depth to prevent frost heaving.

Air changes per hour

The number of times the total air volume of a livestock building is replaced in one hour. Minimum winter rates control moisture while limiting heat loss.

Electric fence energizer rating

The stored energy of an energizer measured in joules. A rule of thumb is one joule per 1.6 km of fence under light weed load.

Roof pitch

The ratio of vertical rise to horizontal run of a roof. Steeper pitches shed water faster but increase material and wind-load costs.

Snow and wind loads

The two dominant structural design loads for farm buildings. Local building codes specify design values that determine structural member sizing.

Gross margin

Gross output (yield × price) minus variable costs. Fixed costs are excluded, allowing comparison of enterprise profitability per unit area or per head.

Break-even yield

The yield at which total revenue equals total costs, calculated as total fixed costs divided by (price per unit minus variable cost per unit).

Partial budget analysis

A method comparing added returns and reduced costs against added costs and reduced returns to evaluate a proposed change in farm operations.

Straight-line depreciation

An accounting method that allocates an asset's cost evenly over its useful life: (cost − salvage value) divided by useful life in years.

Eutrophication

Nutrient enrichment of water bodies, mainly by nitrogen and phosphorus, causing algal blooms and oxygen depletion. Agriculture is a major non-point source via runoff and leaching.

Integrated pest management

A pest control strategy using economic threshold levels to time interventions, combining biological, cultural, and chemical methods to reduce pesticide use and resistance.