Soil properties Flashcards
What direct effect does color have on behavior or use of soil?
Soil warming in spring (the darker the soil the faster it warms)
Importance of soil color
Provides valuable clues to the nature of other soil properties (as well as classification)
Hue
Designates the color (number on top of page)
Value
designates the lightness of color (number on side of page)
Chroma
Distinguishes pure hue from a gray shade (number on bottom of page)
Main factors influence on soil color
- Water content
- Organic matter
- Oxidation state of iron and manganese/Magnisum
Black - Dark Brown (10Yr 2/1)
High organic matter
Reds and yellows
Ferric Iron (Fe^3+) oxides and hydroxides
Hematite
red (intense weathering) (5R 3/6)
Goethite
Yellowish brown (10YR 8/6)
Limonite
Yellow (humid environments)
Ferrihydrite
dark red (2.5 YR 3/6)
Gray and Bluish
Reduced iron compounds and poorly drained soils
Black (10YR 2/1) (Little Organic material)
Manganese Oxides
Greenish
Glauconite
White/Gray (10YR 6/1)
Quartz and silicate minterals
Whites (10YR 8/2)
Carbonate accumulation calcites, and soluble salts
How does chemical reduction affect soil color and under what conditions does it occur?
ferric iron oxides to mobile ferrous iron
results in gray colored soils
Why is texture considered a “basic soil property”?
does not change
Relationship between particle size and surface area
Larger particle = lower surface area
What does soil surface area influence in the soil?
Water holding capacity, chemical reactions, soil cohesion, cation exchange capacity, ability to support microorganisms
Teton dam
Failure to pay attention to soil properties. Seepage of water into an area with poor sealing like sand or silt.
Aggregates
Sand, silt, and clay particles when they are not independent of each other
Microaggreates
Comprised of smaller particles (2-250 micrometers)
Macroaggregates
larger (.25-5mm) comprised of microaggregates
Peds
Large-scale structure evident when observing soil profile
Granular
-spherical aggregates
-loosely packed together
-typically high in organic matter
-very porous
-often observed in A horizons
-susceptible to rapid changes
Blocky
-irregular and cubelike
-molded by shape of surrounding blocks
-common in B horizon in humid regions
(angular and sub angular)
prismlike
-pillarlike
-up to 150mm
-swelling clays
-b horizon
-arid regions
(columnar and prismatic)
platy
-thin sheets
-caused by soil forming process or PM
-compaction
-lower porosity
Block density
mass of a unit volume of dry soil
factors that affect bulk density
-texture
-Organic matter
-type of material
-compaction
What bulk density inhibits root growth
above 1.6 g/cm^3
Equation for bulk density
Db= mass soil/bulk soil volume
What typically has the greatest bulk density?
Sand
Least amount of bulk density
clay
Particle density
Mass per unit volume of soil solids
Factors that affect particle density
-type of mineral present
-organic matter content
Average particle density in mineral soils
2.65
Exceptions for average particle density
soils with high O.M
Very sandy or clayey soils
Particle density equation
Dp= mass soil/volume of soil solids
Benefits of tillage
-break large clods into aggregates
-incorporate organic material
-kills weeds
disadvantages of tillage
-accelerate decomposition of OM
-compaction
Plow pans
Dense zones immediately below plow layer (increases bulk density and restricts root growth)
Ways to reduce compaction
-decrease tillage
-use wider wheels
-minimize operations on wet soils
- use rotations with deep-rooting crops
Porosity
the total volume percentage of the bulk density that is not occupied by soil particles (air and water and plant)
pore space equation
% pore space= 100- (Db/Dp * 100)
Macropores
-Allow rapid movement of water/air into or through soil
-large enough to accommodate plant roots and small organisms
micropores
-do not allow air movement
-usually filled with water in field soils
-water movement through micropores is slow
-some pores are too small for bacteria
when is pore size more important than total pore volume
soil drainage and aeration
effect of cultivation on pore space
reduces pore space and pore size
Soil aggregates
many soil particles held in a single mass or cluster, such as a clod, crumb, block or prism
Primary mechanism of soil particles being held together
held together by clay or organic matter
psuedosand
clay and iron oxides held together forming a stable aggregate
What if a more weakly charged ion such as sodium (Na+ or K+) is present with few divalent or trivalent ions?
-clays will not stick together
-not good for plant production
-common in arid regions
Earthworms form _____ after ingesting soils
casts
what form sticky networks to bind particles together?
Plant root hairs and fungal hyphae
Microorganisms create
organic glues
Soil tilth
the physical condition of soil in relation to plant growth
Soil tilth is influenced by
- aggregate formation and stability
-bulk density and pore space
-soil moisture
-soil texture
Soil crusting
develop when sealed over soil surface dries out after rainfall or irrigation
proctor test
simple way to evaluate how compact you can get a soil and what content you want
