An Unintentional Experiment in
Soil Genesis:
the Lysimeter Soils at the San
Dimas Experimental Forest
Soil Genesis Studies
S = f (cl,o,r,p,t)
S:
cl:
o:
r:
p:
t:
soil formation
climate
organisms
relief
parent material
time
Hans
Jenny
Soil Genesis Study: Biosequence
S = f (organisms)cl,r,p,t
Vegetation monocultures
Soil Genesis Study: Biosequence
S = f (organisms)cl,r,p,t
Confined
lysimeters
1987
Unconfined
lysimeters
17 m x 24 m
Soil Genesis Study: Biosequence
S = f (organisms)cl,r,p,t
cl:
r:
p:
t:
o:
mesic, xeric (MAP = 710 mm)
toeslope (5% slope, south facing)
diorite-derived material
time 0 = 1946
Quercus dumosa (“oak”) or
Pinus coulteri (“pine”)
1934
5.3 m x 5.3 m x 2.1 m
1937
~1937
~1937
1937
Lysimeter fill material (“p”)
Samples archived in 1937
Fine sandy loam
7.5 YR 4/4 moist
San Dimas Lysimeters Chronology
1934
Construction begins
1937
Lysimeters filled
1946
Wildland species planted; Time = 0 yrs
1987
Soils sampled for Graham (1991,
1995), Tice (1995), Ulrey (1995),
Quideau (1998);
Time = 41 yrs
1996
Soils sampled for Johnson-Maynard
(2002, 2004), Quideau (2000,2001,
2003); Time = 50 yrs
1940
1946: Time = 0
1987: Time = 41 years
1987
Oi
Oe
A
Oi
A
BAt
AC
Bt
OAK
PINE
Typic Xerorthent
Horizon
Depth (cm)
Oi
7-0
A
0 – 7.5
AC
C
Horizon
Depth (cm)
Oi to Oe
10 - 0
10 YR 3/3
A
0-1
10 YR 4/3
7.5 - 20
7.5 YR 4/4
BAt
1 – 10
7.5 YR 4/4
20 - 65
7.5 YR 4/4
Bt
10 – 20
7.5 YR 4/4
C
35 - 65
7.5 YR 4/4
Parent Material
Moist Color
Typic Haploxeralf
7.5 YR 4/4
Moist Color
7.5 YR 4/4
Oi
Oe
A
Oi
A
BAt
AC
Bt
OAK
300 earthworms m-2
PINE
no earthworms
Oi
Oe
A
Oi
A
BAt
AC
Bt
OAK
300 earthworms
m-2
PINE
no earthworms
Oi
Oe
A
Oi
A
BAt
AC
OAK
OC,
g kg-1
Depth,
cm
Bt
PINE
Oi
Oe
A
Oi
A
BAt
AC
OAK
Clay,
%
Bt
PINE
A
A
Bt
Depth, cm
AC
C
C
Initial Conclusions
• Biotic factor determines direction and rate of
soil formation
• Biotic factor = plants + animals
• Earthworms impact:
– Clay distribution
– Biocycling
– Clay mineralogy
– Organic matter decomposition
Lysimeter fill
material
archived 1937
1987: Time = 41 years
• Soils sampled in 1937.
• Litter and A horizon material sampled in
1987.
• 14C content measured in the 1937 and 1987
samples by Accelerator Mass Spectrometry.
14CO
2
“Bomb” 14C is used as a tracer for organic carbon
cycling as long as pre-1960’s archived soils exist
Measured litter fall (g m-2 yr-1) 1997-1998
225
135
Oi
Oe
A
Oi
A
BAt
AC
OAK
Bt
PINE
Measured litter fall (g m-2 yr-1) 1997-1998
225
135
Oi
226
A
12.7
BAt
AC
OAK
Oi
Oe
A
Bt
PINE
Estimated carbon inputs from leaves and roots
into soil A horizon (g m-2 yr-1 )
No earthworms
300 earthworms m-2
OAK
1.8
Oi
12.5
A
1.9 – 3.7 Oi
33 Oe
A
25
AC
Bt
BAt
PINE
Estimated turnover rates of organic C (years)
Conclusion:
“…the model results demonstrate distinctly
different SOM dynamics under different tree
species which implies that similar differences
exist among shrubs and herbs”
San Dimas Lysimeters Soils Research
Paul Zinke
Hutch Wood
Bob Graham
Oliver Chadwick
Kathy Rose
Jodi Johnson-Maynard
April Ulery
Sylvie Quideau
Paul Hendrix
Louise Egerton-Warburton
Paul Sternberg
Pete Shouse
Jack Jobes
Xiahong Feng
• USFS Pacific Southwest Experiment Station
Mike Oxford, Pete Wohlgemuth, Dave Larson
• National Science Foundation
• Kearney Foundation of Soil Science
• National Commision on Science for Sustainable Forestry
OAK
pH
Depth,
cm
PINE