Download Soil Taxonomy and Soil Geography

Quiz 3 - Answers
1.) T
F
Conservation tillage refers to methods of preparing the soil for planting that are more likely to
disturb or move soil than conventional tillage.
2.) T F One thing soil color helps to identify is the moisture regime of a soil.
3.) a. What textural class is a soil with 10% clay and 60% sand?
sandy loam
(1)
(1)
(4)
b. What % silt would this soil have?
30% silt
c. Can you change a soil’s textural class by adding organic matter?
No
d. Why or why not?
Soil texture is a property referring only to the mineral particles;
therefore organic matter plays no part in determining a soil’s textural
class.
4.)
What is the % pore space of a typical mineral soil having a Db of 1.05 Mg/m3?
60.4% pore space
5.)
(2)
What did you learn about bulk density from the Sharratt article?
Some possible answers: In areas of compaction, bulk density can
be higher. Bulk density did not account for a thinner A horizon. The
effects of compaction causing greater bulk density can last for 100 yrs.
(2)
• http://nature.berkeley.edu/classes/espm-120/
Photo of Soil Profile
Classification = Typic Haplohumult
REVIEW:
Processes of Soil Formation
CO2 flux
•Additions
OM additions, OM
–Organic C
transformations,
weathering
–Dust
•Removals
–CO2
–Weathering products
•Transfers
–Clay
–Organic matter
–Carbonate
•Transformations
–Plants to SOM
–Primary silicates to
secondary silicates,
carbonates
Clay transfers
Clay and
carbonate
transfers
Leaching
Soil Horizon Nomenclature
•Based on interpretation of dominant soil forming processes affecting
that horizons
–Names based on presumed changes relative to parent material
(t=0)
•Universal with some variance
•Originated by Russians in 19th Century
Master Horizon Nomenclature
Master Horizons
O
Definition and Examples of Lower Case Modifiers
Layers domi nated by org anic ma tter. State of decomposition
determines type: highly (Oa), moderately (Oe), or slightly (Oi)1
decomposed.
A
Mineral horizons that have formed at the surfa ce of the mineral
portion o f the soil or below an O ho rizon. Show one o f the following:
(1) an accumulation o f hum ifi ed organic ma tter closely mixed with
minerals or (2)properties result ing from cultivation, pa sturing, o r
other huma n-caused disturbance (Ap)
E
Mineral horizons in which the main feature is loss of sil icate clay,
iron, a luminu m, or some combination o f these, leaving a
concentration of sand and s il t particles
B
Horiz ons formed below A, E, or O horizons. Show on e or more of the
following : (1) illuvial2 concentration of silicate clay (Bt), iron (Bs),
humus (Bh), carbonates (Bk), gypsu m (By), or silica (Bq) alone or in
combination; (2) removal of carbonates (Bw); (3) residual
concentration of ox ides (Bo); (4) coating s of sesquioxid es3 that make
horizon h igher in chroma or redder in hu e (Bw); (5) brittleness (Bx);
or (6) gleying 4 (Bg).
C
Horiz ons little aff ected by p edogen ic processes. May in clude soft
sedimentary ma terial (C) or partiall y weathered bedrock (Cr)
R
Strongly indu rated5 bedrock
W
Water layers within or und erlying so il
(1) The symbols in parentheses illustrate the appropriate lower case modifiers used to
describe specific features of master horizons.
(2) The term illuvial refers to material transported into a horizon from layers above it.
(3) The term sesquioxide refers to accumulations of secondary iron and/or aluminum
oxides.
(4) Gleying is a process of reduction (caused by prolonged high water content and low
oxygen concentrations) that result in soil colors characterized by low chromas and
gray or blueish chromas.
(5) The term indurated means strongly consolidated and impenetrable to plant roots
Example
A
Bt
Btqm
BC
Master
Horizon
Subdivisions
Lower Case
Modifiers of
Master
Horizons
a
b
c
d
e
f
g
h
i
j
k
m
n
o
p
q
r
s
ss
t
v
w
x
y
z
Definitions (relative to soil parent material)
Highly de composed organic ma tter (O horizon).
Buried soil horizon
Concretions o r nodules of rion, aluminum, mangan ese or titaniu m.
Non-cemented, root restric ting n atural or hum an made (plow layers,
etc.) root restrictive la yers.
Interme diate decomposit ion o f organic ma tter (O horizon).
Indication o f presence of permafr ost
Strong g leying p resent in form of reduction o r loss of Fe and resulting
color change s.
Accumu la tion o f illuvial complexes of organic ma tter which coat sand
and s ilt partic les.
Sli ght ly decomposed organic matter (O horiz on).
Presence of ja rosite (iron sulfat e mi neral) due to oxidation o f pyrite in
previou sly reduced soils.
Accumu la tion o f calcium carbonate due to pedogenic processes.
Nearly continou sly ceme nted ho rizons (by va rious p edogenic
minerals)
Accumu la tion o f exchange able sodiu m
Residual a ccumulation o f oxides due to long-term chemical
weathering.
Horiz on a lt ered by hum an related activitie s
Accumu la tion o f sil ica (as opal)
Partially weathered bedrock
Illuv ia l accumulation o f sesquiox ides
Presence of fe atures (call ed slic kensides) caused by expansion and
contraction o f high c lay soils
Accumu la tion o f sil icate cla y by w eathering and/or ill uvi ation
Presence of pli nthit e (ir on rich, reddish so il ma terial)
Indicates init ial developme nt o f oxidized (or other) colors and/o r soil
structure
Indicates horizon o f high firm ness and b rittleness
Accumu la tion o f gypsu m
Accumu la tion o f salts more soluble than gyp sum (e.g. N a2CO3, etc.)
Chapter 3:
Soil Classification
“It is embarrassing not to be able to agree on what soil
is. In this the pedologists are not alone. Biologists
cannot agree on a definition of life and philosophers on
philosophy.”
-Hans Jenny
from The Soil Resource: Origin and Behavior
Classification
• Pedon: the smallest volume that can be called “a soil”
• Polypedon: two or more contiguous pedons, also called “soil
individual”
• Landscape: region, tract of land
Figure 3.1
Classification
• Genetic horizon: soil layers resulting from soil-forming
processes (pg. 73)
– presence or absence help classify soil
• Diagnostic horizon: soil layers having specific soil
characteristics indicative of certain classes of soils
– at surface: “epipedon”
– below surface: “diagnostic subsurface horizon”
Figure 3.4