Soil Density and Porosity

There is a ________ relationship between bulk density and porosity

inverse

Define macropores

Large pores, water drains rapidly through them due to the force of gravity.

Define mesopores

Medium-sized pores. Holds plant-available water. Held tighter than the force of gravity but not so tight that plants can’t extract the water.

Micropores

Small pores, tend to retain water so tightly, its unavailable to plants.

Bulk Density equation

Mass of oven dry soil (g)/ volume of soil (cm³)

Core is 500m³ and weighs 650 g when oven dried. Find bulk density

650g/ 500 cm³ = 1.3 g/ cm³

Bt has a ______ bulk density than the O horizon

higher

Sand has a _______ bulk density than clay. Clay has ______ porosity then sand

higher, higher

Particle Density equation

mass of oven dry soil (g)/ volume of particles (cm³)

always greater than bulk density

Porosity equation:

volume of pores (cm³)/ volume of soil (cm³)

or  

saturated soil weight (g)- oven dry soil weight (g)/soil volume 

soil core: 500

650 g when dry

when saturated is 900

900 g-650 g/ 500 cm³ = 50%