Physical Properties Part 2

two types of density measured in soils

particle density (ps)

bulk density (pb)

what is the soil particle density a ratio of

soil mass (oven dried) / volume of solids

does soil particle density account for pore space

NO

what is particle density mainly influenced by

density of soil minerals (< 2 mm)

what is range for soil particle density

2.60 to 2.75 g/cm3

what is the assumed value for soil particle density when not calculated

2.65 g/cm3

what is soil particle density not affected by variation in

parameters that alter volume of pores in soil

what are some soil factors that do not effect soil particle density

compaction, loss of structure, tillage

is soil particle density or soil bulk density always greater for the same soil

soil particle density

what is the ratio of soil bulk density between

soil mass (oven dried) / total soil volume (pores and solids)

what is the relationship between soil bulk density and total volume

soil bulk density increases = total volume decreases

what does soil bulk density reflect

amount of pore space in soil

what are four factors affecting soil bulk density

1. SOM content

2. soil structure

3. soil texture

4. compaction

OM density is ______

low (ranges from 0.9 to 1.4)

what does high SOM content cause in soil bulk density

1. direct reduction in bulk density

2. indirection reduction in bulk density

how does a high SOM content have direct and indirect reductions in soil bulk density

direct - OM has lower density than most mineral solids

indirect - OM promotes granular structure = increases pore space

how does soil structure affect soil bulk density

often increases in volume of pores = decreasing soil bulk density

what is the best structure for reducing soil bulk density

granular structure (high volume of pores)

what structures increase soil bulk density

columnar and platy

how does soil texture affect soil bulk density

non compacted soils high in sand have slightly higher soil bulk density than soils high in clay

do non compacted soils high in clay or sand have higher soil bulk density

sand

despite higher soil bulk density, sandy soils are not as _____ as clayey soils

restricting to root growth

why are sandy soils not as restricting to root growth compared to clayey soils

sandy soils have larger pore size than clayey soils

ideal bulk densities for soils depend on ______

texture

what is the ideal bulk densities for root growth

1.00 to 1.70 g/cm3

compare the ideal soil bulk density for fine/medium textured soils? coarse textured soils?

fine and medium - 1.20

coarse - 1.50

what are the root restricting bulk densities for clay texture class? loamy sand texture class?

clay texture class => 1.45

loamy sand texture class - >= 1.80

bulk soil density most affects root growth in _____ than ____ soils

dry and moist

what helps seed emergence in crusted soils

irrigation

what is the main cause of compaction

heavy vehicle traffic and improper tillage

what does compaction cause

subsoil compaction (hard pan forms below A horizon)

how can plow pan and traffic pan be corrected

by subsoiling operation

what are six effects of soil compaction

1. reduces soil pore volume = increases bulk density

2. reduces water retention and drainage

3. increases runoff and erosion

4. damages soil structure

5. reduces plant yield

6. reduces earthworm numbers (microbes)

what is porosity

the amount of pore space in soils

what is porosity influenced by

soil texture and structure

what is the ideal soil pore space

50% of soil volume half filled with water

what is total porosity a ratio between

volume of pore space (liquid + air) / total soil volume (dry soil)

what is the equation for total porosity

Pb = oven dry mass of soil / total volume (pore and solids)

Ps = mass dry soil / volume of solids

what are factors that affect soil porosity

any factor affecting bulk density also affects porosity

what is the relationship between bulk density and porosity

as bulk density increases = decrease in porosity

what two things can be used to evaluate the compactness of soil

porosity and bulk density

if pore spaces are limited what are plant roost limited in

access to air, water and nutrients

soil compaction does what to pore size and space

decreases size and space

macropores are _____ mm

> 0.08

what type of pores are most effective in translocation of air and water

macropores

what is water holding capacity

soil capacity to store water against gravity

what primarily controls water holding capacity

soil texture and OM

what is available water holding capacity

portion of water stored in soil that can be used by the plant roots

is all water stored in soils available to plants

NO

what is true of a soil with good tilth

• well aggregated

• has good infiltration, drainage, water holding capacity

what is the consistence of tilth

friable to very friable

what is soil tilth

physical condition of soil, which influences ease of tillage, seedbed preparation, seedling emergence and root growth