SOCR 240 EXAM 2

soil texture refers to

particle size and distribution of the soil

how do we assign soil texture class?

soil texture triangle

sieves

separate sand sized particles into subclasses

hydrometer method

when suspended in water, soil particles fall at a rate proportional to the square of the particles diameter

what is a hydrometer

a float like device that estimates the suspension density at a series of elapsed times in settling process.

D=

diameter of particle

g=

acceleration due to gravity

Pp=

density of particle

Pl=

density of liquid

***η***

viscosity of a liquid

hue

dominant wavelength (red, yellow, etc)

value

lightness or darkness of color. lower number, darker soil

chroma

purity or grayness of color

what are some causes of soil color difference?

humus content, silicon dioxide, salts, oxides, reduced iron

mottling is

a contrasting or blotchy color pattern within the dominant soil color.

structure in soil science is simple

organization of soil particles

name some soil properties influenced by strucure

soil stability against erosional forces, water holding capacity, aeration and gas diffusion, infiltration of water and percolation of water through soil, root penetration

in general, how can soil structure be improved and why?

addition of organic material. it binds mineral particles to stable aggregates

name some tools we talked about in lecture

flex cultivator, tandem desk, springtooth harrow, 3x bed prep, no till grain drill, deep ripper, range pitter

Pp

particle density

how do you calculate particle density

mass of particle divided by volume of particle

Pb

bulk density

how do calculate bulk density?

mass of dry soil solids divided by volume of soil(solid plus pores)

what is Pp

the density of quartz, 2.65 g/cm cubed

how do you calculate porosity

volume of soil pores over volume of soil

typically, sands are

dominated by large pores but have less total porosity than clays

walking on soil would

increase density, lower porosity

tilling soil would

decrease density, increase porosity

θg

gravimetric water content

how do you find the gravimetric water content

mass of water / mass of soil solids

θv

volumetric water content

how do you find θv?

volume of water/ volume of soil

v=

m/d

calculating back and forth between θv and θg is made easy using what

Pb

dielectric system

name the 6 important properties of water

unsymmetrical molecules, dipole nature results in electrostatic attraction, ideal chemical solvent, adhesion/cohesion, osmotic pressure, capillary rise

osmotic pressure

water has net attraction to solution of a higher solute concentration and results in water pressure difference

biological membranes in soil have cell walls and water may enter or exit due to

solute concentration differences

cohesion

attraction of a substance to a like molecule

adhesion

attraction between unlike substances

when attraction forces to surface exceed surface tension

liquid wets surface

capillarity

attraction of water to mineral surfaces and the cohesive properties of H20, h20 rises against gravity into pores, more so smaller pores

water if not dripping out in relation to air

has negative pressure

water moves in response to

energy gradients

water wants to move to areas with

salt

if water potential of a root is less than the water potential of the soil

then the water move into the root

what 3 factors influence soil color

om content, water content, presence of oxidation states of FE/MN in minerals

when soils are wet they

have lower value and are darker

gravitational potential head

distance above or below a reference line you establish

if you are in unsaturated soil, the matric potential is

negative

if you are in saturated soil, water pressure head is

positive

the majority of water taken up by the plant is lost to

the atmosphere in transpirational stream

field capacity - wilting point

PAW

θs

saturated water point - volumetric water content

OM does what in regards to soil strucure

holds onto water and improves structure

soil color aeration

dark soils absorb more heat than light

soil water content aeration

wetter soil, more energy to evap and satifsy heat cap of water

heat capacity

energy required to change temperature of unit volume of substance by 1 degree

thermal conductivity

a measure of ease of heat flow for a given temp gradient across a substance

aggregation increases _ which reduces _

porosity, thermal conductivity

thermal conductivity increases as what goes up

bulk density

aeration

movement of gas from above ground atmosphere into soil. movement is typically by diffusion in response to concentration gradients, but can also be by mass movement of air

gas concentration gradients are created by what

production or consumption of gas in soil

what is a key determinate in gas movement

soil water content

does o2 diffuse better in wet or dry soil

dry

o2 consumption with aggregates can lead to

anoxic conditions within the aggregate

infiltration

movement of water into soil across upper boundary

runoff

lateral surface flow of non infiltrated water

percolation

movement of water through soil profile

permeability

ease of gas and water flow through soil

what are some factors affecting soil permeability

organic material, texture, hardpans/compacted layers

flow =

transmission coefficient x driving force

what is driving force

how hard it is being pushed through the system

transmission coefficient for water

K, hydraulic conductivity

transmission coefficient for heat

λ, thermal conductivity

transmission coefficient for gas

Dg, gas diffusion coefficient

driving force for water

\

darcys law

flow (vol/time) x cross sectional area of flow x

heat flow equation

gas flux equation

suspension

lift of small particles in air

saltation

bouncing of particles along surface

surface creep

rolling of particles along surface

what are the factors involved in surface resistance to wind erosion

amount of foliar cover, size/distance of inter canopy gaps, vegetative height, soil prop like water content texture and physical cover

effects of wind erosion

reduces soil fertility, degrades air quality, dust deposits in unwanted areas

haboob

intense dust storm

conservation tillage

recognition that plant residue left on soil surface were critical in protecting soil from erosion led to new ways of tilling soil