Forest Soils & Site Productivity
Soil Organic Matter
and
Organisms
1
2
3
Soil Carbon
Inputs – Outputs = Residual
• Inputs: ?
plants (litterfall, roots, exudates), microorganisms,
animals, atmosphere (dust, wind, ppt, etc), erosion
deposition, humans (mulching, biosolids, etc), ???
• Outputs: ?
leaching, decomposition/respiration
(microbes/invertebrates, etc), uptake, erosion, fires,
humans (plowing, bulldozing, digging, harvesting, etc),
???
4
5
Organic Matter
• Surface residues/Forest Floor/O horizons
– Not universally considered as part of SOM but
as O horizon it may be included as OM of the
soil.
• Soil Organic Matter (SOM). Component of
the <2 mm fraction.
6
A Soil Profile
in Iceland
7
Larix sibirica
8
Betula
pubescens
9
Pinus contorta
10
Iceland research study, 2000
Betula pubescens
(Mg/ha)
Trees
Foliage
Living branches
Dead branches
Stem wood
Stem bark
Basal sprouts
Total aboveground tree
Understory
Forbs
Woody understory
Monocots
Moss
Equisetum
Fungi
Total understory
2.9
16.0
1.0
28.8
7.3
3.1
59.3
Larix sibirica
(Mg/ha)
2.4
14.5
13.9
65.7
12.7
b
b
a
b
a
Pinus contorta
(Mg/ha)
b
b
c
c
c
.
c
19.5
30.3
9.9
82.4
10.8
a
a
b
a
b
108.5 b
0.2 a
0.3 a
0.5 a
2.8 a
0.1ab
<0.1 a
3.9 a
0.3 a
0.0 a
0.6 a
1.6 b
0.6 a
0.1 a
3.1ab
Total aboveground biomass
63.1 c
112.2 b
154.5 a
Roots
Coarse (>5 mm diam.)
Fine (<5 mm diam.)
Total roots
30.0 c
9.0 a
39.0 c
48.9 b
11.2 a
60.1 b
77.7 a
9.0 a
86.7 a
Total vegetation biomass
102.2 c
172.3 b
241.2 a
153.0 a
0.1
0.0
0.1
1.4
<0.1
<0.1
1.6
a
b
b
b
b
a
b
11
Forest type
Location
(Latitude)
Age
(years)
Forest
Floor
(Mg/ha)
Betula pubescent
Larix sibirica
Pinus contorta
Abies amabilis
Abies amabilis
Pseudotsuga menziensii
Betula papyrifera
P.contorta/L.occidentalis
Pinus elliotti
Lowland Dipterocarp
Iceland (64N)
Iceland (64N)
Iceland (64N)
Washington (47N)
Washington (47N)
Oregon (44N)
Alaska (64N)
Washington (47N)
Florida (30N)
Malaysia (3N)
60-65
47-52
43-45
23
180
450
50
65-70
27
mature
52
55
71
48
150
51
69
14
33
13
Soil
Ecosystem
organic
total
matter
(Mg/ha)
(Mg/ha)
268
421
261
489
280
592
220
428
273
1248
113
1249
280
491
48
301
111
207
90
483
12
Leachates from Larch,
Birch, and Lodgepole Pine
Ecosystems
4
3
2.5
Larix 99
Betula 99
Pinus 99
2
1.5
1
0.5
Oct
12
10
Larix 99
8
Larix 98
Betula 99
6
Betula 98
4
Pinus 99
2
Pinus 98
10/06/99
09/06/99
08/06/99
07/06/99
06/06/99
0
05/06/99
Sodium (mg/L)
Sep
10/6/1999
Aug
9/6/1999
July
8/6/1999
May June
7/6/1999
6/6/1999
0
5/6/1999
Nitrate (mg/L)
3.5
13
Pseudotsuga menziesii
Soil Organic Matter
(Mg/ha)
250
200
150
High site quality
Low site quality
100
50
0
stand
age - 0
10 yrs
40 yrs
70 yrs 150 yrs
14
Some Organic Compounds
in the Soil
1. Carbohydrates
–
–
–
–
a) sugars – pentoses & hexoses (eg, glucose –
C6H12O6)
b) starches – glucose chains
c) hemicellulose – polysaccharides, H20 insoluble
d) cellulose – glucose long-chain polymers (most
abundant in plant)
15
Some Organic Compounds
in the Soil
2. Proteins – small C-chains, combination of amino
acids – C, H, N & some O & S
3. Lignin – complex polymer of aromatic nature
4. Fats, oils, waxes, resins – complex
carbohydrates, H20 insoluble
5. Chitin – polysaccharide exoskeletons of insects
& also in walls of many fungi
6. Humus – amorphous, dark colored, colloidal
organic material
16
17
18
Mechanisms of
Soil Organic Matter Stabilization
19
Predicted Organic Matter fractions and turnover times in the
unmanured plot of the Broadbalk experiment, Rothamsted.
Annual input of C = 1.2 Mg ha-1.
Fraction
Amt of Carbon
(Mg ha-1)
0.1
Turnover time
(years)
0.2
Resistant plant tissue
0.6
3.3
Microbial biomass
0.3
2.4
Physically protected OM
13.6
71
Chemically stabilized OM
14.6
2900
Readily decomposed plant
tissue
20
SOM - where in the SOIL????
Depth
(cm)
1
2
%Carbon
3
4
5
6
0
10
20
30
40
50
60
21
Aridisol
Alfisol
Mollisol
Spodosol
Soil
Order
??
22
Aridisol
Alfisol
Mollisol
Spodosol Mollisol
plowed
23