PRC ABE flashcards

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

Gravimetric water content

Mass of water in a soil sample divided by the oven-dry mass of the soil, determined by drying at 105 degrees Celsius to constant mass.

Field capacity

The water content remaining in a soil after free drainage has essentially stopped, commonly associated with a matric potential near minus 10 to minus 33 kilopascals.

Permanent wilting point

The soil water content at which plants can no longer extract water, conventionally taken at a matric potential of about minus 1500 kilopascals.

Available water capacity

The difference between field capacity and permanent wilting point multiplied by the effective root-zone depth, giving the water volume available to crops.

Darcy's law

The flow rate through porous media equals negative saturated conductivity times the hydraulic head gradient; in unsaturated soil, conductivity becomes a function of matric potential.

Universal Soil Loss Equation

A = R times K times LS times C times P, where the factors represent rainfall erosivity, soil erodibility, slope length and steepness, cover management, and support practice.

Manning's equation

Open-channel velocity equals one over Manning's roughness n times hydraulic radius to the two-thirds power times slope to the one-half power.

Crop evapotranspiration

ETc equals the crop coefficient Kc multiplied by reference evapotranspiration ETo, representing water use by a specific crop at a given growth stage.

Tractive efficiency

The ratio of drawbar power produced at the hitch to power delivered to the drive wheels; it decreases as wheel slip and rolling resistance increase.

Drawbar power

Power available at the tractor hitch, calculated as drawbar pull multiplied by forward speed; it is lower than PTO power because of traction losses.

Wheel slip percentage

The difference between theoretical travel speed under no load and actual travel speed, divided by theoretical speed and expressed as a percentage.

Sprayer application rate

Litres per hectare equals nozzle flow per minute times 600, divided by the product of nozzle spacing in metres and travel speed in kilometres per hour.

Variable-rate application

A precision agriculture practice that adjusts seed, fertilizer, or chemical rates across a field according to prescription maps derived from yield and soil data.

Field capacity of machinery

The area a machine can cover per hour, calculated as implement width in metres times speed in kilometres per hour divided by ten, times field efficiency.

Livestock ventilation rate

The volume of air exchanged per animal per hour, set to control moisture and gases in winter and heat in summer; it rises with ambient temperature.

Greenhouse energy balance

Solar gain plus supplemental heat equals transmission losses through the glazing plus ventilation losses plus latent heat consumed by crop evapotranspiration.

Janssen equation

A relation for pressures in silos and bins that accounts for wall friction, causing vertical and lateral pressures to approach limiting values rather than increasing linearly with depth.

Manure storage sizing

Storage volume is based on animal population, storage period, wash water, and precipitation, plus allowances for sludge accumulation and freeboard.

Rational Method

Peak runoff equals a runoff coefficient times rainfall intensity times drainage area; it is applied to small catchments where storage effects are minor.

Watershed water balance

Precipitation equals evapotranspiration plus streamflow plus change in storage plus groundwater recharge, accounting for all water movement in a catchment.

Riparian buffer

A vegetated strip along a watercourse that traps sediment and nutrients; effectiveness depends on width, slope, vegetation type, and whether flow is sheet or concentrated.

Composting C:N ratio

The carbon-to-nitrogen ratio of composting feedstock, ideally near 25 to 30 to 1, together with moisture and oxygen levels that support thermophilic microbial activity.

D-value

The time required at a specified temperature to reduce a microbial population by 90 percent, used to design thermal processes in food engineering.

z-value

The temperature change in degrees Celsius that causes a tenfold change in the D-value of a microorganism, describing how lethality depends on temperature.

Water activity

The ratio of vapor pressure of water in a food to that of pure water at the same temperature; microbial growth is generally inhibited below about 0.6.

Log-mean temperature difference

The driving temperature difference used to size heat exchangers, calculated from the inlet and outlet temperature differences of the two fluid streams.

Differential leveling

A surveying method in which elevation difference equals backsight minus foresight, and height of instrument equals known elevation plus backsight.

Traverse angular closure

For a closed polygon with n sides, the sum of interior angles should equal (n minus 2) times 180 degrees; the residual is the angular misclosure.

Contour interval

The constant vertical distance between adjacent contour lines on a topographic map; closer spacing indicates steeper slope.

Capital recovery factor

A factor that converts a present sum into equal annual payments, equal to i(1+i)^n divided by (1+i)^n minus 1.

Net present value

The sum of all project cash flows discounted to the present at a chosen rate; a positive value indicates an economically acceptable project.

Internal rate of return

The discount rate at which a project's net present value equals zero; the project is acceptable when this rate exceeds the minimum attractive rate of return.