Problem Soils and Problem Situations

1
Problem Soils and Problem Situations
2
1) Depleted Matrices in A and E Horizons
3
Depleted Matrix
4
Depleted matrix has lost Fe by reduction,
and as a result its matrix color has a
value of 4 or more, and
chroma 2 or less.Colors show mineral
grains are clean or free of Fe coatings.
5
These colors can also occur in A and E
horizons where reduction has not
occurred.Mineral grains were cleaned by
processes other than Fe reduction.
6
Soil Particles cleaned by Organic acids
moving through horizon. Eluviation Abrasi
on by wind and rainfall
7
Rain
Leaves
A
Organic acids Dissolve Fe And leach it downward
E
Bhs
Fe precipitates
8
E horizon Leached by Organic acids
Fe accumulates In Bhs horizon
9
Eluviation -- water moving downward through
soil carries particles out of one layer into
another layer.
10
Eluviation
Rain
A
Clay and Fe moved into Bt
E
Clay coats along cracks
Bt
11
Abrasion by wind or rainfall
Rain
Wind
Fe coatings coat grains
Clean grains
12
E horizon Formed by abrasion
13
Hydric Soil
Not Hydric
Black matrix
A
A
Lt. Black
Gray matrix
E
Gray
E
Red Fe masses
Bt
Brown
Bg
Gray matrix
14
Summary

• In A and E horizons a depleted matrix must have
• 2 or more redox concentrations regardless of
  value or chroma.
• This mean abundances must be described as common
  or many.
• Few does not count because it is less than 2.

15
Depleted matrix In E horizon, Fe
concentrations present
16
No depleted Matrix, no concentrations in E
within 10 in. (25 cm)
17
2) Measuring depths from the Soil
Surface
18
Soil DepthDepth is normally measured
from the mineral soil surface when no O
horizons are present.
19
O horizons are layers composed of organic
material.
20
Oa horizon at surface (muck)
21
When O horizons are present, the soil
surface is the top of the layer showing
at enough decomposition to make a muck.
22
Loose leaves not part of indicator. Must be
removed.
23
Loose leaves (Oi and Oe horizons) and branches
dont count as soil and are scraped off
before measuring depth.
24
3) Variation in Horizon DepthsBoundaries
between soil layers are usually wavy.They move
up and down in the horizon direction.
25
Horizon boundary varies over short distance
26
Depths to indictors are specified and must
be met exactly.If an indicator must begin
within 25 cm (10 in.) and it starts at 25
cm, then the indicator is not met.
27
Be sure to dig one or more holes to
verify the depths, and account for horizon
variation.
28
4) Using indicators when a soil contains
both sandy horizons and loamy horizons.
29
Some soils contain sandy horizons and loamy
horizons over loamy or clayey ones.Each
horizon will use different sets of
indicators.
30
Example

• 0 to 3 in., 10YR 3/1, loamy sand, 75
  of sand grains coated
  (meets S9, thin dark surface)
• 3 to 13 in., 2.5Y 6/1, sandy loam, 5
  10YR 5/8 Fe masses
• (meets F3, depleted matrix)

31
5) Combining Thin Layers of Indicators

• Some soil have thin horizons which meet
  indicators on basis of color, but are not
  thick enough to fully meet a
  single indicator.

32
When two thin layers are present, and
both contain features to meet an indicator,
but not the same indicator, then ...
33
1) Add the thicknesses of both layers
together, and 2) Consider an indicator
met if the combined thickness meets or
exceeds the thickness requirements of both
indicators.
34
ExampleA, 0 to 3 in., 10YR 3/1, sandy
loam, 10 distinct Fe masses, (too thin for F6,
Redox Dark Surface)
35
E, 3 to 8 in., 10YR 4/2, sandy loam, 5
distinct Fe masses, (too thin for F3, Depleted
Matrix)Bt, 8 to 15 in., 10YR 4/3, clay, (no
indicator)
36
Solution

• Combine the thicknesses of the A and E
  horizons -- 3 in. 5
  in. 8 in.

37
Because indicator F6 requires a thickness of 4
in., and indicator F3 requires 6 in., the
combined thickness of 8 in. exceeds the
requirements of both indicators.The soil is
hydric and meets combination of indicators F3/F6.
38
Justification

• Hydric soils are those that were anaerobic in the
  upper 12 in.
• If thin layers of two indicators each show the
  soil was anaerobic, then combining them also
  shows the soil was anaerobic.

39
6) Applying Fill to Hydric Soil

• Applying fill to a hydric soil may or may
  not change whether a soil is hydric.
• Interpretations vary between USDA and COE.
• This discussion does not imply that applying
  fill to hydric soil is legal.

40
USDA

• Fill is considered part of soil.
• If it has indicators then it is a hydric soil,
  otherwise it is not hydric.
• Note that depths are measured from the top of
  the fill.

41
Corps of Engineers

• Fill is not considered part of soil.
• Hydric soil below fill is considered hydric.
• Depths for indicators begin at the original soil
  surface, not that of the fill.

42
This fill may have to be removed.
43
7) High Chroma Layers
Hydric Soil Concept
Black (10YR 3/1)
A
Gray (10YR 5/1)
E
Gray (10YR 5/1)
Btg
44
All soil layers have chromas lt2.

• This concept suggests soil is anaerobic to
  surface for some period in most years.

45
Soil layers with chromas gt 2 may not be
anaerobic in majority of
upper 12 in.
46
If layers above indicators have chromas gt2,
then soil is hydric only if layers with
chromas gt2 are lt6 in. thick.
USDA
47
Example

• A 0 - 2in., 10YR 4/3, sandy loam, no Fe
  masses
• E 2 - 7 in., 10YR 5/3, sandy loam, no Fe
  masses
• Btg 7 - 20 in., 10YR 5/2, sandy clay, 5
  distinct Fe masses.

48
Comments

• Soil is not considered hydric.
• Soil has a depleted matrix, (in Btg)
  but this does not count here.
• Above the Btg, soil layers have chromas gt2.

49
Comments

• Corps of Engineers does not
• accept this rule.
• High chroma layers over
• indicators do not negate
• indicator.

50
Summary

• USDA and COE interpretations
• differ in two areas
• USDA considers fill part of soil and
• indicators in fill are diagnostic.
• 2. USDA policy negates indicators if
• High chroma soil overlies them.
• COE accepts neither interpretation.