Equation S1
BG =
å Roots ´ C ´
i
i
44gCO2 e
12gC
t
BG is the annualized difference in root growth and root mortality after t years of
production (7 for Crookston or 8 for Becker, Waseca, and Lamberton). Rootsi is root
biomass at depth interval i, and Ci is carbon concentration of root biomass at depth
interval i. Values were measured at the subplot level for each species mixtures/N
rate combination at all locations.
Equation S2
ETH = (((GLU + GAL + MAN)´172.82)+ ((XYL + ARA)´176.87))*0.00375
ETH is the theoretical ethanol yield based on the concentration of cell wall
carbohydrates GLU = glucose; GAL = galactose; MAN = mannose; XYL = xylose; ARA
= arabinose in g ka-1. Values were measured in 2008 at the subplot level for each
species mixtures/N rate combination at all locations.
Equation S3
t
åYLD ´ ETH ´
i
FFoffset =
i=1
0.66Lgas 31.7MJ gas 99.1gCO2 e 1kg
´
´
´
1LETH
1Lgas
1MJ gas
1000g
t
FFoffset is the average annual fossil fuel offset value of converting biomass into
cellulosic ethanol measured in kg CO2e ha-1 yr-1. FFoffset varies by year depending
on biomass yield (YLD). YLDi = biomass yield in year i (Mg ha-1) for t years, where t
is the number of years biomass was harvested (6 for Crookston or 7 for Becker,
Lamberton, and Waseca); ETH = ethanol potential in L Mg-1. Values were measured
at the subplot level for each species mixtures/N rate combination at all locations.
Equation S4
t
å(Nfert ´ 4.5kgCO e) + (
i
FI =
i=1
2
26kgCO2 e
15kgCO2 e
) + (YLDi ´
)
1haFi
1Mg
t
FI is the average annual sum of farm fossil fuel inputs during production in year i for
t years. FI is derived from three components; 1) fossil fuels used to create N
fertilizer (Nfert) during year i, 2) fossil fuels used to apply N fertilizer for each acre
applied during year i, and 3) fossil fuel used to cut and bale biomass (Yld) during
year i.
Nfert = nitrogen fertilizer rate applied in year i (kg ha-1); F = area fertilized in ha in
year i; Yld = biomass yield in Mg ha-1 in year i.; t = number of years biomass was
harvested from the system. Values were measured at the subplot level for each
species mixtures/N rate combination at all locations.
Equation S5
t
e(-0.5095+(0.0028´Nferti )+(0.1245´TEMPi ))kgN 2O - N
44kgN 2O
298kgCO2 e
´
´
å
1ha
28kgN 2O - N
1kgN 2O
N 2O = i=1
t
N2O is the average GHG emissions value of nitrous oxide emissions (measured in kg
CO2e ha-1 yr-1). N2O emissions are estimated as a function of N fertilizer rate (Nfert)
and the mean temp in January through April (TEMP) during year i for t years at each
location, where t equals the number of years in production after the seeding year.
Nfert = nitrogen fertilizer rate in kg ha-1; TEMP = mean temp in January through
April in degrees C.
Equation S6
t
åYLD ´ ETH ´
i
ECF =
i=1
67kgCO2 e
1lETH
t
ECFi is the average annual fossil fuel emission in CO2e from converting biomass to
cellulosic ethanol. YLD = biomass yield in Mg ha-1 during year i for t years; ETH =
ethanol potential in L Mg-1; t = number of years biomass was harvested and
converted to ethanol. Values were measured at the subplot level for each species
mixtures/N rate combination at all locations.
Equation S7
NetGHG = (BG + FFoffset)- FI - N2O - ECF
Net GHG mitigation potential is average annual sum of the C sinks minus GHG
emissions related to the maintenance of perennial bioenergy cropping systems.
Table S1. Plant species sown into species mixture treatments.
Treatment
Switchgrass
Grass mix
Grass/legume
12-species
High-diversity
Species sown
Common name1
Latin name
Functional
group
A
A
Switchgrass
Panicum virgatum L.
Grass
A, B, C, D
B
Big bluestem
Andropogon gerardii Vitman
Grass
A, B, C, D, I, J, K, L
A, B, C, D, I, J, K, L,
Q, R, S, T
C
Sorghastrum nutans L.
Elymus canadensis L. or Elymus
virginicus L.
Grass
D
Indiangrass
Canada wild rye or Virginia wild
rye
A through X
E
Little bluestem
Schizachyrium scoparium Michx.
Grass
F
Slender wheatgrass
Elymus trachycaulus Link
Grass
G
Sideoats grama
Virginia wild rye or Canada wild
rye
Bouteloua curtipendula Michx.
Elymus virginicus L. or Elymus
canadensis L.
Grass
Astragalus canadensis L.
Baptisia australis L. or Desmodium
canadense L.
Legume
J
Canada milkvetch
Wild blue indigo or showy tick
trefoil
K
Purple prairie clover
Dalea purpurea Vent.
Legume
Legume
Q
Partridge pea or pale pea
Showy tick trefoil or white
prairie clover
Roundheaded bushclover or
American vetch
Butterfly milkweed or purple
coneflower
Amorpha canescens Pursh
Lupinus perennis L. or Glycyrrhiza
lepidota Pursh
Chamaecrista fasciculate Michx. or
Lathyrus ochroleucus Hook.
Desmodium canadense L. or Dalea
candida Michx.
Lespedeza capitata Michx. or Vicia
Americana Muhl.
Asclepias tuberosa L. or Echinacea
purpurea L.
R
Maximillian sunflower
Helianthus maximiliani Schrad.
Forb
S
Stiff goldenrod
Solidago rigida L.
Forb
T
Yellow coneflower
Ratibida pinnata (Vent.) Barnhart
Forb
U
Rough blazing star or northern
Liatris aspera Michx. or Galium
Forb
H
I
L
Lead plant
Perennial lupine or American
M licorice
N
O
P
Grass
Grass
Legume
Legume
Legume
Legume
Legume
Forb
bedstraw
boreale L.
V
Wild bergamot
Forb
W
Cup plant or black eyed Susan
Monarda fistulosa L.
Silphium perfoliatum L. or Rudbeckia
hirta L.
X
Golden Alexander
Zizia aurea L.
Forb
Forb
First species within cell corresponds to that planted in southern locations (Becker, Lamberton, and Waseca), while second
species was an alternative for northern locations (Crookston).
1
Table S2. Average annual biomass yield (g m-2; SE) of 5 perennial grassland bioenergy crops with and without 67 kg N ha-1 at
4 locations in Minnesota from 2007 (Becker, Lamberton, and Waseca) or 2008 (Crookston) to 2013.
Becker
Crookston
Lamberton
Waseca
Species mixture
0 kg N ha
67 kg N ha
0 kg N ha
67 kg N ha
0 kg N ha
67 kg N ha
0 kg N ha
67 kg N ha
Switchgrass
340 (21.1)
467.2 (47.9)
443.8 (50.9)
690.6 (47.4)
866 (38.4)
994.3 (38.6)
653.7 (36.5)
901.5 (47.8)
Grass Polyculture
275 (19.9)
474.2 (39)
549.3 (31)
844 (65.2)
900.2 (41.9)
1027 (52.8)
366.5 (23.6)
651.5 (58.5)
Grass/Legume
287.5 (20.2)
479.9 (47)
553.8 (54.2)
545.8 (58.7)
637.3 (49.5)
524.1 (30.5)
554.3 (39.6)
707.4 (76.8)
12-species mix
201.6 (16.7)
263 (37.6)
406.4 (35.4)
488.9 (47.2)
567.5 (58.1)
593.9 (48.2)
503.3 (53)
663.1 (76.3)
High Diversity
208.3 (18)
315.9 (38.9)
483.7 (53.7)
519.3 (43.1)
540.6 (28.1)
493.1 (33)
444.1 (39.1)
500.6 (47.9)
Table S3. Average theoretical ethanol potential (l Mg-1; SE) from biomass of 5 perennial grassland bioenergy crops with and
without 67 kg N ha-1 at 4 locations in Minnesota. Value represent 90% carbohydrate conversion efficiency.
Becker
67 kg N ha
Lamberton
0 kg N ha
67 kg N ha
0 kg N ha
370 (30)
411 (1.4)
403 (5.2)
417 (1.8)
NA
NA
396 (2.9)
412 (3.3)
408 (2.3)
405 (2.3)
397 (1.8)
376 (4.1)
345 (18.2)
363 (5.8)
350 (6.2)
358 (10.7)
381 (10.8)
325 (13.1)
319 (1.9)
341 (4.5)
373 (5.5)
348 (3.6)
326 (2.6)
339 (11.5)
339 (5.5)
364 (5)
358 (7.7)
338 (5.2)
327 (11.4)
Species mixture
0 kg N ha
Switchgrass
417 (0.7)
415 (1.9)
402 (6.7)
Grass Polyculture
417 (0.9)
414 (2.3)
Grass/Legume
419 (0.7)
404 (9.1)
12-species mix
405 (3.2)
High Diversity
375 (31.1)
NA
392 (6.1)
0 kg N ha
Crookston
67 kg N ha
Waseca
67 kg N ha
Switchgrass
Grass mix
Grass/legume
12−species
High−diversity
0 kg
67 kg
(a)
(b)
Root Carbon (g kg-1)
40
30
20
10
0
0−30
30−60
60−90
0−30
30−60
60−90
Depth (cm)
Figure S1. Root carbon content (± 95% CIs) at three depth intervals for five native perennial bioenergy crop mixtures managed with
and without 67 kg N ha-1.
0 kg N ha-1
30
67 kg N ha-1
(a)
Becker
Crookston
Lamberton
Waseca
20
10
0
0 kg N ha-1
67 kg N ha-1
Root Biomass (Mg ha-1)
(b)
4
3
2
1
0
0 kg N ha-1
3
67 kg N ha-1
(c)
2
1
Sw
itc
hg
ra
ss
G
ra
ss
m
ix
G
ra
ss
/le
gu
m
12
e
−s
pe
ci
es
m
H
ix
ig
h−
di
ve
rs
ity
Sw
itc
hg
ra
ss
G
ra
ss
m
ix
G
ra
ss
/le
gu
m
12
e
−s
pe
ci
es
m
H
ix
ig
h−
di
ve
rs
ity
0
Treatment
Figure S2. Variation in root biomass (mean ± SE) within treatments and across
locations in depth intervals from 0-30 cm (a), 30-60 cm (b), and 60-90 cm (c). The
scale of the y-axes were adjusted for each depth interval to better highlight site-level
variation within each species mixture treatment.
67 kg
0 kg
Switchgrass
Grass mix
Grass/legume
12−species
High−diversity
Change in soil TOC (g kg-1)
4
0
−4
−8
0−15
15−30
30−45
0−15
45−60
15−30
30−45
45−60
Depth
Figure S3. Change in soil organic carbon (± 95% CIs) at three depth intervals for five
native perennial bioenergy crop mixtures managed with and without 67 kg N ha-1.