Soil Properties 4.3

Particle Size, Texture, & Porosity

geologic portion of soil = 3 particles

• sand>silt>clay

Soil Texture

% sand/slit/clay in soil

• always = 100% ; 40-40-20 (loam)

Sand

0.05-2mm

• b/c sand is bigger, it has bigger pores

• more sand in soil = more porous/higher porosity (easier for water and air to enter)

Silt

.002-0.05mm

• middle ground

Clay

< .002

• b/c sand is smaller, it has smallerpores

• less sand in soil = less porous/lower porosity (harder for water and air to enter)

Soil Texture Chart

1. start w/ sand % (bottom)

2. move where sand meets silt

3. straight to clay

4. add to 100% always

• blue circle; 30-20-50

• pink circle; 40-40-20

Porosity

space of pores within soil (> sand = > porosity)

Permeability

ease at which water drains through soil

• positive relationship between permeability and porosity

H2O Holding Capacity

how well water is retained by soil

• more porous = lower H2O capacity

• inverse relationship between porosity/permeability and H2O Holding Capacity

Effects on Fertility

• if soil is too sandy (permeable), water drains too quickly for roots and dries out

• clay - heavy soil doesn’t let H2O drain to roots: water logs (suffocating)

• ideal soil is loam; balances porosity or drainage w/ H2O HC

Nutrients

N, P, K+, Ca+, NA+

Increase Nutrient Factors

organic matter, humus, decomposer activity, clay, bases (calc-carb, limestone)

Decrease Nutrient Factors

acids leach positive charge nutrients, > precip/irri leach, > farming depletion, top soil erosion

Water/H2O

needs to hold water, not too much

Increase Water Factors

aeriated soil (bio activity), organic matter, clay %, root structure (esp native)

Decrease Water Factors

compacts soil, topsoil, sand %, root loss

Texture

• what it tells you; % sand, silt, clay - % porous and permeable

• how to test it; let soil settle in water, measure 3 layers

Permeability

• what it tells you; ease at which water drains - > = dry, < = roots have no water or drown

• how to test it; time H2O drains through soil column

pH

• what it tells you; how acidic (<) or basic/alkaline (>) in soils - < = < nutrient activity

• how to test it; pH strip, H+ ion concentration, litmus

Color

• what it tells you; dark = more humus, nutrients, and moisture

• how to test it; compare w/ soil color chart

Nutrient %

• what it tells you; > = > plant growth, < indicates acidic soil/depletion

• how to test it; measure NH 4+, NO 3-, PO4 3-