test #2 Flashcards
pores
air pockets in soil
soil structure
how soil particles stick together to form peds
categorized by: type & grade
structureless soil peds
Massive and single grain (sand/sand-sized)
extremes in terms of effects on permeability
neither present great conditions for crop use
Structure grade
determines soil quality
says how strongly the ped is held together
four grades: strong, moderate, weak, structureless
good structure=
good aeration because of more pore space
organic matter
important for forming soil structure
effective depth
soil evaluation criteria relative to structure
is the zone which plant roots can easily grow (the deeper the effective depth the better)
limitations of effective depth/barriers for root growth are caused by
massive soils, dense soil structure, poor internal drainage, abrupt texture changes between horizons, gravely and large sands
components of soil
45% minerals, 5% organic matter, 50% air and water
soil particles
sand silt clay
sand
.05-2mm, round shape, gritty, adds porosity, reduces water holding capacity
silt
.002-.05mm, round shape, smooth, not sticky, moderate porosity, helps water holding capacity
clay
less than .002mm, flat or platy, sticky, bad for porosity,(fit together tightly because they are so small), locks in water/makes it unavailable for plants use
relationships of soil and water/soil quality
defined by two principals:
permeability
water holding capacity
permeaility
the rate which water moves though soil
depends on texture, structure, organic matter (porosity)
porosity
pores in the soil are created by: roots and other organic matter (i.e. decaying substances)
animals (worms and rodents)
soil particle size and ‘fit’
rapid permeability rate
texture: sands and silts
structure: strong/well defined
porosity: porous
slow permeability rate
texture: clays
structure: weak and massive
porosity: not porous
water holding capacity
the quantity of water retained by soil particles
depends mainly on texture
improved by organic matter
high water holding capacity
texture: silts, loams and clays
organic matter: present
low water holding capacity
texture: sands
organic matter: absent
soil water
available water
unavailable water
saturated soils
available water
free for plants use
unavilable water
held too tightly by clay particles
saturated soil
have exces water that will run off increasing erosion concerns
