exam 2 (lectures 6-11)

bulk density

density of soil with pores and solids

bulk density formula

mass of dry soil/volume of soil with solids and pores

particle density

density of soil with only solids

particle density formula

mass of dry soil/volume of solids

porosity

space between particles

macropores

space between soil aggregates, in coarse soils, better for drainage

micropores

space between particles, in fine soils, better for holding water

porosity formula

(1-bulk density/particle density)*100

biopores

organisms creating pores

effect of compaction

decreases total porosity, increases fine particles, decreases macropores, increases micropores, increases bulk density

compaction from tillage

loosens surface soil but compacts underlying soil

porosity management techniques

proper tillage, incorporate organic matter (lower bulk density), increase surface area of weight loads

importance of soil aeration

effects nutrient availability, carbon cycle, and provides oxygen to organisms

key to soil aeration

macroporosity

mass flow

pressure forcing gas to move

diffusion

movement of gas from high to low concentration, eventually reaching equilibrium

diffusion coefficient

rate of gas transport

what increases the diffusion coefficient

sand, soil structure

what decreases the diffusion coefficient

soil compaction, increased water

temperature

average kinetic energy of particles in a substance

radiation heat

electromagnetic waves

shortwave

visible high energy from the sun

longwave

infrared low energy from the earth

convection

physical movement of air

conduction

collisions between atoms in solids, liquids, gases

optimal soil temperature for most organisms

10 to 35 degrees celsius

soil heating factors

albedo, aspect, soil cover, soil moisture

albedo

ability of a surface to reflect sunlight

heat capacity

ability of a substance to store heat

thermal conductivity

ability of a medium to transmit heat

soils with high thermal conductivity

compact, wet, fine particles

increases in soil temperature lead to

increased plant growth and microbial activity

mulch

soil cover leading to lower albedo

water content

wet soils stay cooler

porosity

mineral rich and compacted soils have higher thermal conductivity

clear plastic mulch

permits and traps light, increases soil temperature

black plastic mulch

absorbs light, increases soil temperature slightly less than clear mulch

infiltration

water entering the soil

percolation

movement of water through soil

properties of water

density lower as a solid than liquid, only natural substance found in all three states

water as universal solvent

dissolves most substances due to polarity

cohesion

attraction of water to other water molecules

adhesion

attraction of water to other substances

capillary movement

movement of water through tubes

capillary movement relationship

as height rises, radius decreases

gravimetric water content

(mass of wet soil-mass of dry soil)/mass of dry soil * 100

volumetric water content

volume of water/volume of soil * 100

bulk density relationship with water content

volumetric water content = gravimetric water content * bulk density

soil water potential

difference in energy level between water

matric potential

water bound to soil surfaces, lowering energy

osmotic potential

water bound to salts

graviational potential

water that flows

hydrostatic potential

movement of water in the saturated zone below the water table

capillary water

plant available water held in fine pores

hygroscopic water

unavailable water tightly held by adhesive forces in small micropores

available water holding capacity

amount of plant available water after free drainage

field capacity

water held against the force of gravity

permanent wilting percentage

amount of water where plants can no longer extract water

awhc equation

awhc=fc-pwp

texture with best awhc

medium texture soils like silt and loams

saturated flow

all pores are filled with water, water moves through macropores, driving force is graviational potential

saturated hydraulic conductivty

size and configuration of soil pores

unsaturated flow

the larger pores are empty, water moves through micropores, driving force is matric potential

vapor movement

water vapor movement in dry soils

darcy’s law

quantity of water per unit of time that flows through a column of saturated soil