Examining the Potential of Biochar in Post-Wildfire Rehabilitation
K.
1
Minatre ,
C.
2
Rhoades ,
D.
2
Pierson ,
M.
1
Cotrufo ,
& E.
1
Kelly
1Colorado
State University, 2USDA Forest Service, Rocky Mountain Research Station, Fort Collins, CO
Soil Science Society of America Annual Meeting, Long Beach California, 3 November 2015
Field Conditions
Greenhouse Soil and Tree Bioassay
Extractable NH4
2.0
-1
6.0
Soil pH (1:1 soil to DI water)
0 tons ha
2 tons ha-1
20 tons ha-1
1.5
1.0
0.5
0.0
y ne uly ust
il
r
a
M Ju
J ug
Ap
A
6
4
2
New Recruits
(< 6" Ht)
Advanced Regen
(> 6" Ht)
1000
500
7000
Subalpine Fir
6000
5000
4000
3000
2000
1000
0
1000
Aspen
Control 0 t ha-1
Biochar 20 t ha-1
Mulch
Mulch + Biochar 20 t ha-1
20
15
10
5
0
e
Jun
600
July
400
st
u
g
Au
ber
m
te
p
e
S
200
ut
C
nc
ut
U
ut
C
U
nc
ut
0
Study Overview
We investigated the potential of pine biochar to
contribute to reclamation of areas affected by high
severity wildfire and subsequent erosion on skeletal soils
in the Colorado Rockies. We compared biochar rates (0,
2, and 20 t ha-1) and wood mulch addition in a replicated
field study and complementary greenhouse trial.
Biochar
Feedstock: Blue-stained, lodgepole pine chips
8-10% moisture content
Pyrolysis: Biochar Engineering Corporation (BEC)
Step 1 O2-limited, 700-750 oC, < 1 minute
Step 2 O2-free, 400-550 oC, 10-15 minutes
Biochar Composition:
Moisture 1.1 %
Ash
9.4
pH
9.4
C
87.2
Surface Area 176
(m2/g)
N
0.4
Total Pore Vol. 0.105 (cc/g)
O
1.4
Characterization - D.W. Rutherford et al., USGS, Lakewood, CO
8
16
24
Biochar had no effect on soil
temperature (5 cm depth) in 6
study blocks, but char applied
alone and in combination with
wood
chip
mulch
both
consistently increased volumetric
soil moisture compared to
untreated soil (p < 0.01).
Biochar Leachate
Biochar
in DI
Change to
standard
solution
DOC
TDN
NH4-N
NO3-N
PO4-P
K
Mg
Ca
Na
mg L-1
10.4
0.4
0.1
0.3
1.8
5.9
3.9
10.1
0.8
Proportion
312.8
0.8
0.2
1.3
3.6
3.6
9.9
7.1
1.3
pH
ANC
EC
7.9
1586.2
209.2
Biochar reduced ammonium
and TDN concentrations.
Addition of 20 t ha-1 of biochar
significantly reduced 1 M KCl
extractable soil ammonium and
increased soil nitrate during most of
the 6 month greenhouse assay. In
contrast, the lower char addition had
few effect on the inorganic soil N
forms.
Soil pHw
5.8
5.6
5.4
5.2
1.0
0.5
0.0
0.30
8
Extractable NO3-
Gravimetric Water
0.25
0.20
0.15
6
4
2
0
0.10
-1
2 t ha-1
20 t ha-1
7
20 t
of blue stain biochar
increased P, Ca and K in greenhouse
soils compared to untreated and
the low biochar addition (p < 0.05).
1.5
5.0
Lodgepole Pine Height
P
Ca
K
Mg
CECeff
Biochar
Addition
------------------------mg/L-----------------------cmol kg-1
6.2
82.8
21.4
14.4
3.5
0 t ha-1
6.3
82.7
21.3
14.5
3.5
2 t ha-1
3.9
20 t ha-1
7.6* 91.7* 24.8* 15.5
Extractable NH4+
0 t ha-1
2 t ha-1
20 t ha-1
We compared the consistency of biochar effects under dry and wet
irrigation and with and without wood mulch. Over 24 weeks, 20 t ha-1
char significantly increased soil pH, gravimetric soil water, and nitrate and
decreased ammonium. The supplemental treatments altered soil
moisture in the absence of char or at the low application rate.
Conversely, the high rate of biochar generally masked the effects of both
irrigation and mulch.
Soil Cations and P
ha-1
2.0
0 t ha
Week
25
800
4
6
Height Increment (cm)
1500
Volumetric Soil Moisture (%)
Tree Density (t/Acre)
-
8
2
2000
0
Tree Density (t/Acre)
24
0
Lodgepole Pine
Tree Density (t/Acre)
16
Extractable NO3
-1
0
2500
Conifer colonization was scarce the first
2 yrs after the fire owing to combustion
of cones on beetle-killed pines. Tree
regeneration is limited to aspen sprouts.
Soil Nitrate(ug N g soil )
10
M
8
10
20
h
c
r
a
4
Gravimetric Moisture (g water g OD soil-1)
0 t ha-1
20 t ha-1
30
Burned
Unburned
2
40
Soil Temperature (Co)
Church’s Park Fire a 200-hectare area burned in October 2010,
is located in the Arapaho National Forest near Fraser Colorado
(2438-3200 m elevation). The area receives ~700 mm of
precipitation annually, 75% as snow. Forest vegetation consists
primarily of mountain pine bark beetle-killed lodgepole pine
(Pinus contorta) and aspen (Populus tremuloides). The burn sits
on gravelly, sandy-loam Alfisols derived from colluvium and
alluvium of granitic gneiss and schist parent material.
Wet - No Mulch
Wet - Mulch
Dry - No Mulch
Dry - Mulch
+
Soil Nitrate (ug N g soil-1)
-1
Soil Ammonium (ug N g soil )
2.5
Soil Ammonium (ug N g soil-1)
Field Study
High severity wildfires have significant, lasting impacts
on soils and forest watersheds. Nutrient and soil organic
matter losses and physical changes that influence plant
water availability can impede revegetation.
Land
managers commonly employ Burned Area Emergency
Response (BAER) treatments to counter immediate postfire soil loss, though these practices may also assist
recovery of soil productivity and speed revegetation.
Dry
Wet
5
4
3
2
1
0
0 ton 2 ton 20 ton
0 ton 2 ton 20 ton
Biochar increased tree seedling
growth under the dry watering
regime, but had no effect under
wet conditions.
In the dry
watering regime the 20 t ha-1 char
addition created soil moisture
equivalent to the wetter regime.
However, char did not elevate soil
moisture further when applied
under the wetter regime.
Key Findings & Potential Utility
Soil Moisture Blue-stain biochar added at 20 t ha-1 influenced soil moisture across a range of field moisture and conditions. This
rate of biochar also increased soil moisture and seedling growth in dry greenhouse soils. Under wet conditions, biochar did not
result in higher soil moisture or tree growth.
Soil Nutrients Blue-stain biochar both releases and retains soil nutrients and alters soil chemistry. The char added an equivalent of
5-10 kg Nitrate-N ha-1 to the 24 week greenhouse assay. It also adsorbed ~1 kg N ha-1 of ammonium.
Potential Utility These findings suggest that blue-stain biochar may assist with tree growth on xeric soils altered by high-severity
wildfire. Additional work is needed to determine if biochar provides an effective approach to general revegetation of burned and
otherwise disturbed ecosystems.
Acknowledgements
Funded by the US Forest Service R2 – BAER Program, USFS Rocky Mountain Research Station and Colorado State University.
Thanks to Jonah Levine (Biochar Solutions, Inc.), formerly of BEC.