Carbon Cycling in Perennial Biofuel Management Systems
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Carbon Cycling in Perennial Biofuel Management Systems Tracy M. Wilson and Jason G. Warren Graduate Student, Associate Professor, Department of Plant and Soil Sciences, Oklahoma State University, Stillwater, OK Acknowledgements Introduction Increasing demand for clean, renewable and sustainable fuel sources has stimulated interest in cellulosic biofuels Cellulosic biofuels can offset CO 2 emissions Perennial biofuel feedstocks may also sequester C in soil However, few efforts have been made to assess the impact of species selection and harvest frequency on soil C sequestration in perennial biofuel feedstock production systems We thank Austin Hudson and Andrew Whitaker for research and technical support and the Oklahoma Bioenergy Center for financial support. Experiment 1 In Exp. 1 there were no interactions for yield between harvest frequency and grass species, therefore data is pooled by species (Fig.1) and harvest frequency (Fig. 2). Harvest frequency was only significant in 2009, when the single harvest produced more yield, biomass C, residue and residue C (Fig. 2). In 2009 yields were low due to low rainfall in May and June (Fig. 3), therefore no significant differences were observed among species (Fig. 1). However, the carbon mass harvested from switchgrass was significantly greater that that in the eastern gammagrass. In 2010, miscanthus provided significantly greater yields than the remaining species. The same trend was seen in biomass C harvested (Fig. 1). Despite these differences in yield and residue, soil carbon was not affected by treatment (Table 1). Methods In the spring of 2009, management was reestablished in a small plot study (originally initiated in to provide long-term monitoring of SOC sequestration Established on a Kirkland silt loam at the Oklahoma State University, Agronomy Farm in Stillwater, OK Experimental design is a randomized complete block design with 6 treatments and 4 replicates, each plot is 3m by 6m Treatments include 3 species: ‘Alamo’ switchgrass (Panicum virgatum) , miscanthus (Miscanthus spp.) and eastern gammagrass (Tripsacum dactyloides) The harvest frequency treatments were: Single harvest at the end of the growing season (Oct-Nov.) Split harvest treatment- harvested at mid season (Aug.) and again at the end of the growing season Yields were harvested from a 1m by 6m area of each plot Residue in each plot was taken from a 0.35m 2 area. Biomass and residue subsamples were dried at 60°C for dry weight determination. Both biomass and residue were analyzed for total C and N. The second experiment (Exp. 2) was established in June 2006 to evaluate the impact of switchgrass variety selection on biomass yield. These plots are harvested annually after the growing season Soils were collected in early spring time with a hydraulic probe to a depth of 80 cm and section into 0-10, 10-20, 20-40, and 40-80 cm. Soils were analyzed for bulk density, total C, inorganic C, and organic carbon by their difference. Figure 2: The differences in yield between single harvest treatments and split harvest treatments in 2009. Means followed by different letters are significantly different at the 0.05 probability level. Cumulative Biomass Yield Biomass C Harvested Residue Mass Residue C 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 a a a a b b b b 2009 Single Harvest Split Harvest Kg ha-1 Cumulative Biomass Yield Biomass C Harvested Residue Mass Residue C 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 a a b b a ab a a a b a a 2009 Switchgrass Miscanthus E.Gammagrass Kg ha-1 Results and Discussion Figure 1: The differences in mean yield between species in 2009 and 2010. Means followed by different letters are significantly different at the 0.05 probability level. Cumulative Biomass Yield Biomass C Harvested Residue Mass Residue C 0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 b b a a a a a a b b a a 2010 Kg ha-1 Conclusions Significant differences found between harvest frequency in 2009 but not in 2010 indicate there is an interaction between harvest frequency and environmental conditions during the growing season. The data also indicated that miscanthus can outperform switchgrass and E. gammagrass under favorable conditions but that switchgrass assimilates the most carbon of the three species under low yield conditions. Soil Carbon was not affected by species or harvest frequency, which may be explained by the lack of yield differences in the years prior to soil collection. Exp. 2 suggests that soil carbon is generally proportional to yield. However, this did not hold true for 3 varieties, indicating that additional mechanisms also influence soil carbon storage. These mechanisms may include differences in the distribution of organic carbon inputs or differences in soil respiration under these 3 varieties compared to the varieties under which soil carbon appears to have accumulated. Species Harvest Frequency ------------------Spring 2009------------------ ------------------Spring 2010------------------ 0- 10cm† 0-20cm 0-40cm 0-80cm 0-10cm 0-20cm 0-40cm 0-80cm ----------------------------------------------------Mg ha - 1 ---------------------------------------------------- Contrast Comparisons of Species Switchgrass 17a‡ 28a 47a 65a 17a 29a 46a 64a Miscanthus 18a 29a 47a 67a 17a 28a 46a 64a E. Gammagrass 18a 29a 47a 62a 16a 27a 44a 62a Contrast Comparisons of Harvest Frequency Single 18a 29a 46a 64a 17a 28a 45a 62a Split 18a 29a 47a 67a 17a 28a 46a 65a † The cumulative carbon mass is the carbon measured in each segment from the soil surface to the indicated depth. ‡ No significant interactions between species and harvest frequency were observed therefore contrast analysis were use for comparisons. Means followed by different letters are significantly different at the 0.05 probability level. Table 1: Cumulative soil organic carbon content in soils under each species and each harvest frequency treatment. 3.00 5.00 7.00 9.00 11.00 13.00 15.00 17.00 19.00 13.0 13.5 14.0 14.5 15.0 15.5 16.0 16.5 17.0 17.5 f(x) = 0.113177049398976 x + 15.0783434408133 R² = 0.976933851465731 2009 Yield (Mg ha-1) Carbon mass in surface 10cm (Mg ha-1) Cave-in- Rock (Upland) NSU 95-2001- 1 (Upland) Blackwell (Upland) Alamo (Lowland) NL 93-2 (Lowland) NSL 2001-1 (Lowland) Kanlow (Lowland) NL 94-2001-1 (Lowland) SL 93-2001-1 (Lowland) Figure 3: Exp. 2. The relationship between the 2009 mean yield and soil C mass (0-10cm) in soils collected in spring 2010. (The alleys in this experiment contained 15 Mg C ha -1 .) Objectives The objective of this research is to evaluate the impact of species selection, harvest frequency, switchgrass variety on soil carbon sequestration under perennial biofuel feedstock production systems. Experiment 2 Differences in soil carbon mass below 10 cm were not observed among varieties (data not shown). Exp. 2 showed that soil carbon mass in the surface 10 cm was proportional to the previous growing season yields (Fig. 3). Soil carbon was also proportional to the 3 year average yields for these varieties, yet this relationship was weaker (R 2 =0.8884) than the relationship shown in Fig. 3. Soil carbon under 3 varieties did not show this relationship. The average carbon mass in soils under these varieties was 14.9 Mg C ha -1 , which is similar to that found in the alleys (alleys were chemically fallowed for the duration of the experiment).
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Carbon Cycling in Perennial Biofuel Management Systems. Methods. Tracy M. Wilson and Jason G. Warren Graduate Student, Associate Professor, Department of Plant and Soil Sciences, Oklahoma State University, Stillwater, OK . - PowerPoint PPT Presentation
Transcript of Carbon Cycling in Perennial Biofuel Management Systems
Carbon Cycling in Perennial Biofuel Management Systems
Tracy M. Wilson and Jason G. Warren Graduate Student, Associate Professor, Department of Plant and Soil Sciences,
Oklahoma State University, Stillwater, OK
Acknowledgements
IntroductionIncreasing demand for clean, renewable and sustainable fuel sources has stimulated interest in cellulosic biofuelsCellulosic biofuels can offset CO2 emissionsPerennial biofuel feedstocks may also sequester C in soilHowever, few efforts have been made to assess the impact of species selection and harvest frequency on soil C sequestration in perennial biofuel feedstock production systems
We thank Austin Hudson and Andrew Whitaker for research and technical support and the Oklahoma Bioenergy Center for financial support.
Experiment 1In Exp. 1 there were no interactions for yield between harvest frequency and grass species, therefore data is pooled by species (Fig.1) and harvest frequency (Fig. 2). Harvest frequency was only significant in 2009, when the single harvest produced more yield, biomass C, residue and residue C (Fig. 2). In 2009 yields were low due to low rainfall in May and June (Fig. 3), therefore no significant differences were observed among species (Fig. 1). However, the carbon mass harvested from switchgrass was significantly greater that that in the eastern gammagrass.In 2010, miscanthus provided significantly greater yields than the remaining species. The same trend was seen in biomass C harvested (Fig. 1). Despite these differences in yield and residue, soil carbon was not affected by treatment (Table 1).
MethodsIn the spring of 2009, management was reestablished in a small plot study (originally initiated in to provide long-term monitoring of SOC sequestration Established on a Kirkland silt loam at the Oklahoma State University, Agronomy Farm in Stillwater, OKExperimental design is a randomized complete block design with 6 treatments and 4 replicates, each plot is 3m by 6mTreatments include 3 species:
‘Alamo’ switchgrass (Panicum virgatum) , miscanthus (Miscanthus spp.) and eastern gammagrass (Tripsacum dactyloides)
The harvest frequency treatments were: Single harvest at the end of the growing season (Oct-Nov.) Split harvest treatment- harvested at mid season (Aug.) and again at the end of the growing season
Yields were harvested from a 1m by 6m area of each plotResidue in each plot was taken from a 0.35m2 area.Biomass and residue subsamples were dried at 60°C for dry weight determination.Both biomass and residue were analyzed for total C and N.The second experiment (Exp. 2) was established in June 2006 to evaluate the impact of switchgrass variety selection on biomass yield. These plots are harvested annually after the growing seasonSoils were collected in early spring time with a hydraulic probe to a depth of 80 cm and section into 0-10, 10-20, 20-40, and 40-80 cm. Soils were analyzed for bulk density, total C, inorganic C, and organic carbon by their difference.
Figure 2: The differences in yield between single harvest treatments and split harvest treatments in 2009. Means followed by different letters are significantly different at the 0.05 probability level.
Cumulative Biomass Yield
Biomass C Harvested
Residue Mass Residue C0500
100015002000250030003500400045005000
a
a
a
a
b
b
b
b
2009 Single HarvestSplit Harvest
Kg h
a-1
Cumulative Biomass Yield Biomass C Harvested Residue Mass Residue C0100020003000400050006000700080009000
10000
a
ab
b
a
ab
a
a
a
b
a
a
2009 Switchgrass
Miscanthus
E.Gammagrass
Kg h
a-1
Results and Discussion
Figure 1: The differences in mean yield between species in 2009 and 2010. Means followed by different letters are significantly different at the 0.05 probability level.
Cumulative Biomass Yield
Biomass C Harvested
Residue Mass Residue C0100020003000400050006000700080009000
10000
b
ba
a
a
aa
a
b
b
a
a
2010
Kg h
a-1
ConclusionsSignificant differences found between harvest frequency in 2009 but not in 2010 indicate there is an interaction between harvest frequency and environmental conditions during the growing season.The data also indicated that miscanthus can outperform switchgrass and E. gammagrass under favorable conditions but that switchgrass assimilates the most carbon of the three species under low yield conditions. Soil Carbon was not affected by species or harvest frequency, which may be explained by the lack of yield differences in the years prior to soil collection. Exp. 2 suggests that soil carbon is generally proportional to yield. However, this did not hold true for 3 varieties, indicating that additional mechanisms also influence soil carbon storage.
These mechanisms may include differences in the distribution of organic carbon inputs or differences in soil respiration under these 3 varieties compared to the varieties under which soil carbon appears to have accumulated.
Species Harvest Frequency ------------------Spring 2009------------------ ------------------Spring
2010------------------0-
10cm†0-20cm 0-40cm 0-80cm 0-10cm 0-20cm 0-40cm 0-80cm
----------------------------------------------------Mg ha-1---------------------------------------------------- Contrast Comparisons of Species
Switchgrass 17a‡ 28a 47a 65a 17a 29a 46a 64aMiscanthus 18a 29a 47a 67a 17a 28a 46a 64a
E. Gammagrass 18a 29a 47a 62a 16a 27a 44a 62a
Contrast Comparisons of Harvest FrequencySingle 18a 29a 46a 64a 17a 28a 45a 62aSplit 18a 29a 47a 67a 17a 28a 46a 65a
† The cumulative carbon mass is the carbon measured in each segment from the soil surface to the indicated depth.‡ No significant interactions between species and harvest frequency were observed therefore contrast analysis were use for comparisons. Means followed by different letters are significantly different at the 0.05 probability level.
Table 1: Cumulative soil organic carbon content in soils under each species and each harvest frequency treatment.
3.00 5.00 7.00 9.00 11.00 13.00 15.00 17.00 19.0013.013.514.014.515.015.516.016.517.017.5
f(x) = 0.113177049398976 x + 15.0783434408133R² = 0.976933851465731
2009 Yield (Mg ha-1)
Carb
on m
ass
in s
urfa
ce
10cm
(M
g ha
-1) Cave-in-Rock
(Upland)NSU 95-2001-
1(Upland)
Blackwell(Upland)
Alamo(Lowland)
NL 93-2(Lowland)
NSL 2001-1(Lowland)
Kanlow(Lowland)
NL 94-2001-1(Lowland)
SL 93-2001-1(Lowland)
Figure 3: Exp. 2. The relationship between the 2009 mean yield and soil C mass (0-10cm) in soils collected in spring 2010. (The alleys in this experiment contained 15 Mg C ha-1.)
ObjectivesThe objective of this research is to evaluate the impact of species selection, harvest frequency, switchgrass variety on soil carbon sequestration under perennial biofuel feedstock production systems.
Experiment 2Differences in soil carbon mass below 10 cm were not observed among varieties (data not shown).Exp. 2 showed that soil carbon mass in the surface 10 cm was proportional to the previous growing season yields (Fig. 3).
Soil carbon was also proportional to the 3 year average yields for these varieties, yet this relationship was weaker (R2=0.8884) than the relationship shown in Fig. 3.
Soil carbon under 3 varieties did not show this relationship. The average carbon mass in soils under these varieties was 14.9 Mg C ha-1, which is similar to that found in the alleys (alleys were chemically fallowed for the duration of the experiment).
