soil properties and horizons lecture

What is a horizon (topsoil) composed of?

Decomposed dark organic matter called humus

Thick indicates

helps hold water & nutrients

Dark brown/black

rich in nitrogen and organic matter

Gray, yellow, or red topsoils need

nitrogen enrichment

Do B&C horizons have inorganic matter or organic matter?

linorganic matter, sand, silt, clay, and gravel

sand

high drainage, largest particles, lots of air, low water holding ability

silt

particles larger than clay, but smaller than sand, drains slowly

Clay

smallest particles, poor drainage

Loam

best soul, mostly humus, 40-40-20 (sand, silt, clay), good infiltration (downward movement of water)

Porosity

describes how quickly the soil drains

how is the texture of the soil is determined?

by the percentages of sand, silt, and clay

The finer the texture:

the more difficult a soil is to work or till

the greater the water holding capacity

the slower water will enter and move through the soil profile'

more difficult plant root penetration

the more readily surface soil will crust

the more nutrient rich the soil

Gritty

has a lot of sand

sticky

has a lot of clay; retains a lot of water

smooth

soil is silt laden

Crumbly/spongy

soil is heavily loam, holds water; good growth & permeability

What is soil porosity affected by?

Soil texture

porosity in soil determines

soil permeability

Clay is bad for agriculture but is good for

holding water, it is terrible for the roots

Cation exchange capacity (CEC) is

the ability of soil to absorb and release cations

Acids

flush out nutrients from the soil, aluminum and hydrogen

Base saturation

the measure of the proportion of soil bases to soil acids; percentage

Soil Bases

generally promote plant growth and are essential

Calcium, magnesium, and potassium