NRES 497697

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NRES 497/697 Soil physical properties and
hydrology Soil Texture particle size Soil
Structure arrangement of soil particles Texture
Basic separation 2mm sieve lt
2mm gt2mm sand 0.05 - 2.0 mm gravel
2mm-8cm Silt 0.002 - 0.05 mm cobbles
8-25 cm Clay lt0.002 mm stones, boulders
gt25 cm channery (flat) 2mm - 38 cm See
Figure 4.2 for textural classification of lt 2mm
fraction.
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Figure 4.2 Soil textural triangle percentage of
clay and sand in t he main textural classes of
soils the remainder of each class is silt.
(Fisher and Binkley, 2000)

• Fine earth fraction (lt2mm)
• Loams are most fertile and have best water
  properties
• High clay has high bulk density, poor
  infiltration
• High sand has poor water holding, poor organic
  matter retention

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• Coarse Fragments (gt 2mm)
• Can enhance aeration, infiltration, and rooting
  in clay soils
• Usually contribute little to plant nutrition
  (dilute soil)
• Skeletal gt35 coarse fragments (gt2mm)

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• Soil Structure arrangement/aggregation of soil
  particles
• Major effect on aeration, infiltration in clay
  soils
• Affected by
• Surface chemistry
• Salts (especially Na)
• Oxide coatings
• Fungal hyphae and roots,
• Freezing and thawing
• Wetting and drying
• Soil organisms (especially earthworms).
• Soil texture
• Sandy soils no aggregation, "single grain"
  structure
• Loams and clays exhibit a wide variety of
  structural types.

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• Bulk Density and Porosity
• Bulk density (Db)
• Dry weight of soil per unit of volume (g cm-3)
• Range 0.2 (organic soils) to 1.9 (heavily
• compacted).
• Db gt 1.5 is compacted, problems with aeration,
  drainage, and root growth.

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Calculating pore volume
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• Soil temperature
• Specific heat amount of heat (calories) needed
  to raise 1 g of soil by 1 degree Celsius.
• Affected by
• Texture (specific heat of finer textured soils
  (e.g.,
• clays, clay loams) gt coarse textured soils (e.g.,
  sand)
• Organic matter (higher specific heat)
• Moisture content (specific heat of water is 1.0
• cal g-1, mineral soil is 0.2 cal g-1).

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• Soil temperature
• Heat conductance
• Increases with finer texture
• Lowers with increasing organic matter
• Increases with increasing water content
• Moist soils
• Cooler than dry soils (greater specific heat)
• Conduct heat more easily than dry soils
• Rain/irrigation can cool or warm soil quickly
• Subsoil temperatures fluctuate much less than
  surface soils because of buffering by upper soil
  layers (Figure 4.9).
• At deeper depths, soil temperature hovers near
  mean annual temperature.

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Soil temperature Subsoil temperatures fluctuate
much less than surface soils because of
buffering by upper soil layers At deeper depths,
soil temperature hovers near mean annual
temperature.
Figure 4.9 Daily temperature variations with
depth for (left) an unmulched and (right) mulched
clay soil where the litter mulch has a lower
thermal conductivity (Cochran, 1969). (Fisher and
Binkley, 2000).
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• Snow insulates soils because of its low thermal
  conductivity.
• Higher winter soil temperatures in northern
  locations or higher elevations because of thicker
  snow cover
• Deeper frost on southern than northern slopes
  (Table 4.3).

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• Snow insulates soils because of its low thermal
  conductivity.

Table 4.3. Snow and frost depths on north and
south slopes in Wisconsin (Sartz, 1973) (Fisher
and Binkley, 2000).
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Snow insulation affects decomposition rate in
Sierran Forests (Stark, 1973 Johnson, et al.,
unpubl data) Note lack of snow cover near tree
boles
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Treewell snow
Solar radiation on tree boles and rocks warms the
local environment so that snowmelt occurs earlier
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• Notice also litter buildup near tree boles
• Not all of this is due to greater litterfall!
• 80 of total annual litter decomposition takes
  place under snowpack (the rest of the year is too
  dry)
• Therefore, less snowpack means slower
  decomposition and more litter buildup

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• Soil Water Potential (? )
• ? ?????p ?g p
• ??? matric potential, attraction of water to
  soil solids
• p osmotic potential, attraction of water to
  solutes
• g gravitational potential
• p pressure potential
• Water is a polar molecule
• Slight negative charge at one end (oxygen)
• Slight positive charge at the other end
  (hydrogens)
• Cohesion attraction of water molecules to each
  other
• Adhesion attraction of water to other polar

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Matric Potential

• The matric potential (?) is due to capillary
  action, he attraction of water for the walls the
  capillary tube (adhesion) and the attraction of
  water to itself (cohesion)
• The height of rise of water in a capillary tube
  is determined
• by the diameter of the tube

Capillary rise formula r (k)
(1\h) Where r radius of tube h height of
rise k (T)(d)(g) 0.149 cm2
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Capillary Rise Formula
r (k) (1\h) Where r radius of tube h
height of rise k (T)(d)(g) 0.149 cm2
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Capillary Rise Formula
r (k) (1\h) Where r radius of tube h
height of rise k (T)(d)(g) 0.149 cm2
h
h
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Matric Potential Derivation of the capillary rise
formula
At equilibrium, when the water has risen to its
maximum height in the tube, the forces upward
equal the forces downward Forces up (T) (cos
?) (2pr) 1) T surface tension of
water (73 dynes cm-3) ?? the angle of the
meniscus (Figure 6) p pi r the radius of the
tube (cm) Forces down (g) (d) (p r2
h) 2) g force of gravity (981
dynes g-1) d density of water (1 g cm-3) p r2 h
volume of liquid in the tube Combining 1) and
2) (T) (cos ?) (2pr) (g) (d) (p r2 h)
3)
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Matric Potential Derivation of the capillary rise
formula
Rearranging, 2T (cos ?)
4) (g)(d)(h) When at
equilibrium, ????? and thus cos?? 1, so
equation 4 reduces to 2T
5) (g)(d)(h) S
ince T, g, and d are all constants, they can be
combined r (k)/h
6) where k (T)(d)(g) 0.149 cm2
r
r
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Matric Potential Derivation of the capillary rise
formula
Equation 6) is referred to as the capillary
rise formula. If we measure soil moisture
tension, we can calculate the size of the largest
pore which is filled with water h
(cm) kPa r (cm) 10 -1.5 0
.015 100 -15 0.0015 300
-30 0.0005 Field moisture
capacity 15,000 -1500 0.00001 Permanent
wilting percentage From equation 6), the pore
size distribution of a soil can be measured from
its moisture release curve.
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Soil water classification Gravitational water
is held at greater (less force) than -33 to -10
kPa. It will not stay in soil and will
leach. Field Moisture Capacity (FMC) Water
left after gravitational drainage after soaking
rain. Held at -33 (clays) to -10 (sands) kPa
(depending on soil type) or less (more strongly).
Permanent Wilting Percentage (PWP) Nominal
amount held at which plants can absorb no more.
Defined as -1500 kPa however, desert plants can
get water at up to -6000 kPa or less (tighter).
Water next to soil particles.
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Soil water classification Available Water
Capacity (AWC) Amount of water that could be
available to plants when soil is at FMC
FMC-PWP. Plant Available Water (PAW) Amount of
water in soil minus PWP (can be FMC or less,
typically). Note plants cannot depend on
gravitational water because is simply goes by too
fast.
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Soil Water Classification Capillary Water
Water held by small pores, and tension being
dependent on the pore size. (Show VG or diagram
of capillary rise and pore size). Water at FMC or
below, effectively is capillary
water. Saturation Percentage Water content at
complete saturation (under water all pores
filled).
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Soil Water Movement The movement of water in
soils has been modeled using Darcy's Law V
-k d? 6) dx d?
the difference in water potential between two
points dx the distance between the two points k
the hydraulic conductivity For saturated flow,
matric and osmotic potentials are ignored, and
only gravitational potential (dg) drives
flow d? dg Vs -ks d? 7)
dx
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Soil Water Movement

• k decreases to the fourth power of pore radius,
  and thus decreases rapidly with soil water
  content
• Whereas saturated flow is driven primarily by
  gravitational potential, unsaturated flow is
  driven primarily by matric potential.
• Water may move upward, like a wick, when
• the upper horizons are dry and water potential is
  negative than lower horizons.

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The Hydrologic Cycle
On an ecosystem scale, the water balance equation
is ?W P - (O U E) Where ?W storage in
the soil P precipitation O runoff U
deep drainage ET evapotranspiration
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The small watershed approach
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The hydrologic cycle

• Measurements
• P rain gauges
• O weirs, runoff collectors
• U weirs, flumes (where bedrock is impermeable)
  ?W TDR, tensiometers, neutron probe
• (assumed to be zero on an annual basis)
• ET by difference on a watershed scale

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The small watershed approach
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Hubbard Brook Watershed http//www.hubbardbrook.o
rg/yale/watersheds/w6/weir-stop/weirwork.htm
42
Flumes Flumes are used to measure flowrate
(discharge) in open channels.  They typically
have widths from a few cm to 15 m or so.  The
water depth in the approach section of flumes
typically can be between a few cm and about 2 m. 
Flumes, compared to weirs, have the advantage of
less head loss through the device, yet are more
complicated to construct and more difficult to
analyze. http//images.goo
gle.com/imgres?imgurlhttp//www.lmnoeng.com/Flume
s/FlumeDiagrams2.jpgimgrefurlhttp//www.lmnoeng.
com/Flumes/flumes.htmh335w547sz23hlenstar
t2um1tbnidGYlJFDdTi6jtZMtbnh81tbnw133pr
ev/images3Fq3Dflumes26svnum3D1026um3D126hl
3Den26rls3DRNWE,RNWE2004-41,RNWEen26sa3DN
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• Potential evpotranspiration (PET)
• Reflects the evaporation that would occur from an
  open pan of water
• Often less than actual ET (AET)because of low
  soil moisture.
• Estimated by
• Models using vapor pressure, wind,solar radiation
  and albedo (Penman)
• Empirical equations using temperature, day
  length, and latitude (Thornthwaite).

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The hydrologic cycle
Studies on both Hubbard Brook, NH and Walker
Branch, TN have shown that ET is relatively
constant from year to year
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The small watershed approach
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The small watershed approach
Walker Branch Watershed, TN (Johnson and Van
Hook, 1989
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The small watershed approach
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Jenny (1980) gives a good illustration of the
interplay between soil available water (W),
change in soil water (?W), PET, and AET.
Rules PET is satisfied first, if possible,
from P and AW. Thus 1) If PET lt P, then AET
PET and water is available for storage in soil
(to a max of FMC) and/or drainage to
groundwater. 2) If PET gt P but PET lt (P AW),
then PET AET, also because AW feeds PET. 3) If
PET gt (P AW), then AET P AW and AW is drawn
down 4) When AW 0 and PET gt AET, AET P 5)
When AW 0 and P 0, then AET 0
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Soil Chemistry

• Cation Exchange Capacity (CEC)
• The capacity of a soil to adsorb and exchange
  cations (positively charge ions, Ca2, Mg2, K,
  Na, NH4 , Al3, and H).

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Soil Chemistry

• Cation Exchange Capacity (CEC)
• Two types of the negative charge of soil colloids
• 1) Permanent charge CEC (in mineral clays)
• Isomorphous substitution of Al3 for Si4
  tetrahedra or Mg2 for Al3 octahedra
• Not affected by pH.
• 2) pH-dependent or variable charge CEC
• Due to mostly to dissociation of H from organics
  
• Some due to Fe, Al hyrous oxides (Al(OH)3
  Fe(OH)3 FeOOH) and allophane (Al2O3 . 2SiO2H2O)
• R-OH OH- --------gt R-O- H2O
• R organic matter or Fe, Al hydrous oxides
• pH must go (OH- is consumed) up for this to occur

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• Measurement of Cation Exchange Capacity (CEC)
  and Base Saturation (BS)
• CEC is measured by applying concentrated ammonium
  chloride (NH4Cl) or ammonium acetate (NH4OAc) to
  the sample to exchange all exchangeable cations
  with NH4 by mass action
• The extractant solution is analyzed for Ca2,
  Mg2, K, Na, and in some cases Al to
  determine what was on the exchanger.
• At that point, one measure of CEC can be made
  (see 1 below). Then the NH4 is displaced by
  another cation (typically Na or K ) by mass
  action, and NH4 is then measured to obtain
  another estimate of CEC.

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• Measurement of CEC and BS
• The usual assumption is that NH4 constitutes a
  negligible proportion of CEC.
• Exchangeable NH4 is often measured separately
  using concentrated KCl extractant.
• H (pH) is not measured on this extractant,
  either exchangeable H is measured another way.
• Some soil scientists argue that there is no
  exchangeable H on mineral soils all H that
  becomes absorbed onto clay minerals quickly
  enters the lattice structure and causes clay
  decomposition to hydrous oxides.

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• There are three ways to measure CEC (two from
  one method and one from another method)
• 1. Sum of cations Method
• The sum of Ca2, Mg2, K, Na, and Al after
  extraction with 1M NH4Cl (a neutral salt which
  does not buffer pH).
• CEC by sum of cations, CECsum, and is measured in
  the first extractant in Figure 1.
• In a pure clay system (no organic matter Fe, Al
  hydrous oxides, of allophane i.e., no
  pH-dependent CEC) this represents CEC and cations
  on the clay minerals (permanent charge CEC).

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• 2. Effective CEC (CECeff) at existing soil pH.
• This includes the permanent charge CEC plus that
  portion of pH-dependent CEC that is in effect at
  existing soil pH.
• It is determined from the second extractant in
  Figure 1, After the 1M NH4Cl extraction, the soil
  is washed with ethanol to remove soluble NH4 ,
  and then extracted with 1M NaCl to displace the
  exchangeable NH4.
• The extractant is analyzed for NH4 .

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• 3. Ammonium acetate CEC (CECOAc).
• This includes permanent charge CEC all
  pH-dependent CEC. Is is measured by extracting
  the soil with either ammonium acetate (NH4OAc,
  buffers pH at 7.0). (Figure 2).
• Then the same produre is followed as for the
  neutral salt CEC.
• Note exchangeable Al should be measured
  separately because Al precipitates as Al(OH)3 at
  high pH

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Base Saturation. Base Saturation (BS) is
defined as the sum of exchangeable base cations
(Ca2, Mg2, K, and Na) divided by CEC. It is
usually expressed as a percentage of CEC thus
Ca Mg K Na CEC
BS x 100
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• Base Saturation
• Since CEC can be measured in different ways, BS
  will vary with the method used, and must be
  specified.
• For a soil with a given amount of exchangeable
  bases, BS calculated from CECsum will be
  greater than that calculated from CECeff which
  will be greater than that calculated from CECtot
  because more of the potential acidity on the
  pH-dependen CEC is counted as CEC (i.e., CECsum lt
  CECeff lt CECtot).
• The example in the next figure shows how this
  might occur. In each case, the base cations are
  the same (6 cmolc kg-1) only the measure of CEC
  (the deminator) changes. (Note that BS BSCP -
  just a different notation for the same thing)

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• Note that BS BSCP - just a different notation
  for the same thing

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• Lyotropic series
• Ease of replacement by cations farther along the
  series (Bohn et al., 1985)
• Na gt K NH4 gt Mg2 gt Ca2 gt Al3
• Note The book expresses it the other way around
  (strength of displacement, not ease) on p. 101.

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Cation Exchange Equations Consider the
replacement of Ca2 on the exchange complex
(represented CaX) by Al3 CaX 2/3 Al3 ? 2/3
AlX Ca2
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Cation Exchange Equations Kerr approach to
selectivity coefficients is AlX2/3
Ca2 Ks ----------------------
CaX Al32/3 Products multiplied
together (each raised to the power of the number
of molecules in the reaction) over reactants
(also raised to the power of the number of
molecules)
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Cation Exchange Equations This can be
rearranged AlX2
Al32 ------------- Ks
--------------------
CaX3 Ca23 Both sides of the
equation were cubed to eliminate the fractional
powers.
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Cation Exchange Equations The ratio of
exchangeable aluminum to calcium on the soil
cation exchange sites will not change
substantially over short periods of time (the
pools are large) so making the left side a
constant, we have Al3 Kt Ca23/2 In
short, soil solution Al3 varies to the 3/2 power
of soil solution Ca2. By the same logic, soil
solution Ca2 varies by the square of soil
solution K
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Soil Chemistry

• Fe and Al hydrous oxides are amphoteric can take
  a positive, zero, or negative charge depending on
  pH
• The pH at which there is no charge is referred to
  as the point of zero charge.
• The zero point of charge on Fe,Al hydrous oxides
  and allophane is pH 8 - 9, so they usually act
  as anion exchangers

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Allophane and Fe/Al hydrous oxides are
amphoteric they can take on a , - or no charge,
depending on pH
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• Soil Acidity
• Both exchangeable Al3 and H contribute
• Al3 functions as an acid
• Al3 H2O ---------gt Al(OH)2 H
• Exchangeable H on clay minerals is short-lived,
  and is rapidly replaced by Al3 from within
  octahedral layers.
• Active acidity acidity immediately released
  into soil solution(soil pH
• Potential acidity includes all H pH-dependent
  CEC sites.
• Active acidity (pH)
• Potential, acidity (exch. Al3 H, ads.
  SO42-)
• Total acidity

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Soil Acidity

• Total acidity on solid phase gt 10,000 x that in
  soil solution
• The balance between the solid and solution phases
  depends on
• The salt concentration of the soil solution (pH
  is usually lower in salt than in water)
• The total quantity of acids present (often
  determined by organic matter content)
• The degree of dissociation of the soil acids
  (Binkley)
• The acid strength of the solid phase (Binkley)

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Natural sources of acid in soils 1.
Leaching a) Carbonic acid CO2 H2O
------------gt H2CO3 ---------gt HCO3- H X
K H ----------gt X H K
_________________________________________________
___________ CO2 H2O X K ------------gt X H
K HCO3- X exchange phase Base cation
(in this case, K) is leached with bicarbonate
and soil is acidified.
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• Natural sources of acid in soils
• 1. Leaching
• b) Organic acids
• R-OH ---------------------gt RO- H
• X K H ----------gt X H K
• __________________________________________________
  __________
• R-OH X K ------------gt X H K RO-
• Organic anions are usually not very mobile -
  adsorbed
• in B horizons.
• Organic acids also chelate insoluble cations like
  Fe
• and leach them (especially in Spodosols)

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Natural sources of acid in soils 1.
Leaching c) Nitrification and nitrate
leaching 2NH4 4O2 --------gt 2H 2NO3-
2H2O 2X K H ----------gt 2X H 2K
_________________________________________________
___________ 2NH4 4O2 2X K --------gt 2X H
2K 2NO3- A nitrate salt leaches from
the system and the soil is acidified.
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Natural sources of acid in soils 2.
Vegetation uptake Cations taken up in excess of
anions cause roots to release H
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• Natural sources of acid in soils
• 3. Humus Formation
• Adds to the potential acidity and pH-dependent
  CEC to soil
• Does not cause a reduction in exchangeable base
  cations as leaching and plant uptake do.

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Soil Chemistry

• Processes Mitigating Against Acidification
• Deep Rooting and Recycling by Vegetation
• Atmospheric Base Cation Inputs
• Soil Weathering
• Most important yet least understood mitigation
  processes
• Difficult to measure

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Soil Chemistry

• Effects of acidity on vegetation
• Nutrient availability with acidification
• Lower availability of Ca, Mg, and K (of course)
• Can lower P availability because of
• adsorption
• Greater availability of Fe
• Al effects
• Toxic to roots of some plants
• Required by other plants (e.g., tea) .
• Generalizations about the positive or
• negative effects of soil acidification are
  neither possible nor reasonable unless the
  species are identified.

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Anion adsorption and exchange in
soils Ortho-P gt SO42- gt Cl- NO3- Not
true anion exchange SO42- will not displace
Ortho-P Cl- and NO3- will not displace SO42-
Note Ortho-P PO43- H2PO42- HPO4-
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• Anion adsorption and exchange in soils
• Non-specific adsorption
• Exchange on positively charged Fe, Al
• hydrous oxide surfaces
• Highly pH-dependent
• Weak, involves NO3-, Cl-
• Specific adsorption
• Ligand exchange (with OH-)
• Strong, maybe fixes Ortho-P or even
• SO42-

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Ortho-P solubility is highly controlled by
precipitation as well as adsorption reactions in
soils
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As soils weather, the form of P changes
systematically
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• Oxidation and Reduction
• Oxidation the loss of electrons (O2 present)
• Reduction the gain of electrons (O2 absent)

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• Oxidation and Reduction
• Redox potential
• Can be expressed either as "Eh" or "pe pH".
• Eh voltage between a platinum electrode in the
• soil and the standard hydrogen electrode
• Low Eh reducing conditions
• High Eh oxidizing conditions
• Eh increases as pH decreases
• Thus, some prefer pe pH as a measure of
• redox potential
• Where pe -log of electron activity
• Eh (millivolts) 59.2 x pe

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Important oxidation-reduction reactions in
soils 1. Pyrite oxidation (mine
spoils) 4FeS2 15O2 8H2O -------gt 2Fe2O3
4O2 16H 8SO42- Thiobaccilus
thioxidans 2. Elemental S oxidation (used to
acidify soils) 2S 3O2 2H2O -------gt 2H
SO42- Thiobaccilus thi
oxidans 3. Sulfate reduction (anaerobic) SO42-
4H2 -------gt S2- 4H2O Desulfovibrio
desulfuricans
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Important oxidation-reduction reactions in
soils 4. Oxidation of ferrous iron (Fe2)
and manganese (Mn2) 2XFe2 1/2O2 5H2O
------gt 4XH 2Fe(OH)3 2XMn2 1/2O2 5H2O
------gt 4XH 2Mn(OH)3 X exchangeable
phase 5. Iron reduction This occurs in
submerged soils and makes iron more available to
plants. It raises pH. Fe(OH)3 e- H -----gt
Fe(OH)2 H2O
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• Important precipitation reactions in arid soils
• 1. Calcium carbonate
• This forms the caliche layer in arid soils
• Ca2 2HCO3- ----gt CaCO3(solid) H2O CO2(gas)
• 2. Gypsum
• Ca2 SO42- -----gt CaSO4(solid)
• Gypsum is more soluble than calcite
• Thus, there is typically a layer of gypsum under
  the layer of caliche (calcite) in undisturbed
  prairie soils.
• 3. Ca-phosphates (already discussed)

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Soil Solution Chemistry

• Major soil solution anions
• Chloride sea salt
• Sulfate sea salt, atmospheric deposition, pyrite
• Bicarbonate soil CO2
• Nitrate nitrification, from air pollution,
  fertilizer, N
• fixation (only important in some cases)
• Ortho-P not important in moles L-1, but
  important
• nutrient

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Soil Solution Chemistry

• Major soil solution cations
• Sodium sea salt, minerals (not exchanger)
• Potassium minerals, exchanger
• Calcium minerals, exchanger
• Magnesium minerals, exchanger
• Aluminum only in acid soils exchanger

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Soil Solution Chemistry

• Si released with mineral weathering, but is
  neutral as silicic acid
• For example, the weathering of albite releases
  aluminum ions and silicic acid
• NaAlSi3O8 6H20 2 H ? Na Al(OH)2
  3Si(OH)4 2 H20

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NRES 497/697 Case Study No 2 Do conifers acidify
soils? 1 Feb 2008 Base cation (especially Ca)
concentrations in foliage and litterfall in
deciduous species is often two to three fold
greater than in conifers. For this reason, and
because conifer litter often produces a mor
rather than a mull forest floor, and because
conifers are often associated with organic acid
generation which causes podzolization,
conventional wisdom for many years in forest
soils is that conifers strip base cations from
soils and acidify them whereas deciduous species
increase base status because they enrich the soil
with high-base litter. Below are data sets from
studies by Alban (1982) and Turner and Kelly
(1977) comparing litter and soils in adjacent
stands of conifers and deciduous species. Keep
in mind that Ca is the major exchangeable base
cation. References Alban, D.H. 1982. Nutrient
accumulation by aspen, spruce, and pine on soil
properties. Soil Sci. Soc. Amer. J 46
853-861. Turner, J., and J. Kelly. 1977. Soil
chemical properties under naturally regenerated
Eucalyptus spp. and planted Douglas-fir. Aust.
For. Res. 7 163-172.
103

• Case Study 2
• Class segment
• 1 February 2008
• Names____________________________________________
  __________________________________
• Alban (1982)
• Plantations of different species were established
  on two soils in Minnesota in 1933-34, sampled in
  1972-74. Results from one soil are shown in Table
  1 and Figure 2. (results from the other soil were
  similar). Note pH of the O horizons in the aspen
  and white spruce stands ranged from 5.5 to 6.5,
  whereas that from the two pine stands ranged from
  4.5 to 5.5
• Questions
• Did the conifers acidify the forest floor (O
  horizons)? Why or why not?
• Did the conifers acidify the soil? Why or why
  not?
• How did forest floor Ca content and pH affect
  the mineral soil Ca content and pH? Why?
• Did aspen increase soil pH and base status? Why
  or why not?
• What role, if any, has organic matter played in
  causing soil acidification?
• What caused the difference in soils between white
  spruce and pine? (All were conifers)
• Do conifers acidify soils? If so, how do they do
  it and in which horizons do they do it?

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Table 1. Litterfall, forest floor, and soil data
from Alban (1982)
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L, F, and H are the organic horizons (now
referred to as the O horizons) L litter layer
(now designated as the Oi horizon) F
fermentation zone (now designated as the Oe
horizon) and H the humus layer (now designated
as the Oa horizon). RP Red pine JP Jack
pine WS white spruce QA quaking aspen