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1. chinaXiv:201605.00546 [pdf]

Environmental costs and benefits of growing Miscanthus for bioenergy in the UK

Jon P. McCalmont; Astley Hastings; Niall P. McNamara; Goetz M. Richter; Paul Robson; Iain S. Donnison; John Clifton-Brown
Subjects: Biology >> Botany >> Plant ecology, plant geography

Planting the perennial biomass crop Miscanthus in the UK could offset 2–13 Mt oil eq. yr−1, contributing up to 10% of current energy use. Policymakers need assurance that upscaling Miscanthus production can be performed sustainably without negatively impacting essential food production or the wider environment. This study reviews a large body of Miscanthus relevant literature into concise summary statements. Perennial Miscanthus has energy output/input ratios 10 times higher (47.3 ± 2.2) than annual crops used for energy (4.7 ± 0.2 to 5.5 ± 0.2), and the total carbon cost of energy production (1.12 g CO2-C eq. MJ−1) is 20–30 times lower than fossil fuels. Planting on former arable land generally increases soil organic carbon (SOC) with Miscanthus sequestering 0.7–2.2 Mg C4-C ha−1 yr−1. Cultivation on grassland can cause a disturbance loss of SOC which is likely to be recovered during the lifetime of the crop and is potentially mitigated by fossil fuel offset. N2O emissions can be five times lower under unfertilized Miscanthus than annual crops and up to 100 times lower than intensive pasture. Nitrogen fertilizer is generally unnecessary except in low fertility soils. Herbicide is essential during the establishment years after which natural weed suppression by shading is sufficient. Pesticides are unnecessary. Water-use efficiency is high (e.g. 5.5–9.2 g aerial DM (kg H2O)−1, but high biomass productivity means increased water demand compared to cereal crops. The perennial nature and belowground biomass improves soil structure, increases water-holding capacity (up by 100–150 mm), and reduces run-off and erosion. Overwinter ripening increases landscape structural resources for wildlife. Reduced management intensity promotes earthworm diversity and abundance although poor litter palatability may reduce individual biomass. Chemical leaching into field boundaries is lower than comparable agriculture, improving soil and water habitat quality.

submitted time 2016-05-04 Hits8632Downloads889 Comment 0

2. chinaXiv:201605.00540 [pdf]

Evaluation of the ECOSSE model for simulating soil organic carbon under Miscanthus and short rotation coppice‐willow crops in Britain

Marta Dondini; Mark Richards; Mark Pogson; Edward O. Jones; Rebecca L. Rowe; Aidan M. Keith; Niall P. McNamara; Joanne U. Smith; Pete Smith
Subjects: Biology >> Botany >> Plant ecology, plant geography

In this paper, we focus on the impact on soil organic carbon (SOC) of two dedicated energy crops: perennial grass Miscanthus x Giganteus (Miscanthus) and short rotation coppice (SRC)-willow. The amount of SOC sequestered in the soil is a function of site-specific factors including soil texture, management practices, initial SOC levels and climate; for these reasons, both losses and gains in SOC were observed in previous Miscanthus and SRC-willow studies. The ECOSSE model was developed to simulate soil C dynamics and greenhouse gas emissions in mineral and organic soils. The performance of ECOSSE has already been tested at site level to simulate the impacts of land-use change to short rotation forestry (SRF) on SOC. However, it has not been extensively evaluated under other bioenergy plantations, such as Miscanthus and SRC-willow. Twenty-nine locations in the United Kingdom, comprising 19 paired transitions to SRC-willow and 20 paired transitions to Miscanthus, were selected to evaluate the performance of ECOSSE in predicting SOC and SOC change from conventional systems (arable and grassland) to these selected bioenergy crops. The results of the present work revealed a strong correlation between modelled and measured SOC and SOC change after transition to Miscanthus and SRC-willow plantations, at two soil depths (0–30 and 0–100 cm), as well as the absence of significant bias in the model. Moreover, model error was within (i.e. not significantly larger than) the measurement error. The high degrees of association and coincidence with measured SOC under Miscanthus and SRC-willow plantations in the United Kingdom, provide confidence in using this process-based model for quantitatively predicting the impacts of future land use on SOC, at site level as well as at national level.

submitted time 2016-05-04 Hits7533Downloads557 Comment 0

3. chinaXiv:201605.00538 [pdf]

Simulation of greenhouse gases following land‐use change to bioenergy crops using the ECOSSE model: a comparison between site measurements and model predictions

Marta Dondini; Mark I. A. Richards; Mark Pogson; Jon McCalmont; Julia Drewer; Rachel Marshall; Ross Morrison; Sirwan Yamulki; Zoe M. Harris; Giorgio Alberti; Lukas Siebicke; Gail Taylor; Mike Perks; Jon Finch; Niall P. McNamara; Joanne U. Smith; Pete Smith
Subjects: Biology >> Botany >> Plant ecology, plant geography

This article evaluates the suitability of the ECOSSE model to estimate soil greenhouse gas (GHG) fluxes from short rotation coppice willow (SRC-Willow), short rotation forestry (SRF-Scots Pine) and Miscanthus after land-use change from conventional systems (grassland and arable). We simulate heterotrophic respiration (Rh), nitrous oxide (N2O) and methane (CH4) fluxes at four paired sites in the UK and compare them to estimates of Rh derived from the ecosystem respiration estimated from eddy covariance (EC) and Rh estimated from chamber (IRGA) measurements, as well as direct measurements of N2O and CH4 fluxes. Significant association between modelled and EC-derived Rh was found under Miscanthus, with correlation coefficient (r) ranging between 0.54 and 0.70. Association between IRGA-derived Rh and modelled outputs was statistically significant at the Aberystwyth site (= 0.64), but not significant at the Lincolnshire site (= 0.29). At all SRC-Willow sites, significant association was found between modelled and measurement-derived Rh (0.44 ≤  0.77); significant error was found only for the EC-derived Rh at the Lincolnshire site. Significant association and no significant error were also found for SRF-Scots Pine and perennial grass. For the arable fields, the modelled CO2 correlated well just with the IRGA-derived Rh at one site (= 0.75). No bias in the model was found at any site, regardless of the measurement type used for the model evaluation. Across all land uses, fluxes of CH4 and N2O were shown to represent a small proportion of the total GHG balance; these fluxes have been modelled adequately on a monthly time-step. This study provides confidence in using ECOSSE for predicting the impacts of future land use on GHG balance, at site level as well as at national level.

submitted time 2016-05-04 Hits791Downloads429 Comment 0

4. chinaXiv:201605.00530 [pdf]

Initial soil C and land‐use history determine soil C sequestration under perennial bioenergy crops

Rebecca L. Rowe; Aidan M. Keith; Dafydd Elias; Marta Dondini; Pete Smith; Jonathan Oxley; Niall P. McNamara
Subjects: Biology >> Botany >> Plant ecology, plant geography

In the UK and other temperate regions, short rotation coppice (SRC) and Miscanthus x giganteus (Miscanthus) are two of the leading ‘second-generation’ bioenergy crops. Grown specifically as a low-carbon (C) fossil fuel replacement, calculations of the climate mitigation provided by these bioenergy crops rely on accurate data. There are concerns that uncertainty about impacts on soil C stocks of transitions from current agricultural land use to these bioenergy crops could lead to either an under- or overestimate of their climate mitigation potential. Here, for locations across mainland Great Britain (GB), a paired-site approach and a combination of 30-cm- and 1-m-deep soil sampling were used to quantify impacts of bioenergy land-use transitions on soil C stocks in 41 commercial land-use transitions; 12 arable to SRC, 9 grasslands to SRC, 11 arable to Miscanthus and 9 grasslands to Miscanthus. Mean soil C stocks were lower under both bioenergy crops than under the grassland controls but only significant at 0–30 cm. Mean soil C stocks at 0–30 cm were 33.55 ± 7.52 Mg C ha−1 and 26.83 ± 8.08 Mg C ha−1 lower under SRC (P = 0.004) and Miscanthus plantations (P = 0.001), respectively. Differences between bioenergy crops and arable controls were not significant in either the 30-cm or 1-m soil cores and smaller than for transitions from grassland. No correlation was detected between change in soil C stock and bioenergy crop age (time since establishment) or soil texture. Change in soil C stock was, however, negatively correlated with the soil C stock in the original land use. We suggest, therefore, that selection of sites for bioenergy crop establishment with lower soil C stocks, most often under arable land use, is the most likely to result in increased soil C stocks.

submitted time 2016-05-04 Hits724Downloads412 Comment 0

5. chinaXiv:201605.00510 [pdf]

An interyear comparison of CO2 flux and carbon budget at a commercial‐scale land‐use transition from semi‐improved grassland to Miscanthus x giganteus

Jon P. McCalmont; Niall P. McNamara; Iain S. Donnison; Kerrie Farrar; John C. Clifton-Brown
Subjects: Biology >> Botany >> Plant ecology, plant geography

A 6-ha field at Aberystwyth, UK, was converted in 2012 from semi-improved grassland to Miscanthus x giganteus for biomass production; results from transition to the end of the first 3 years are presented here. An eddy covariance sensor mast was established from year one with a second mast added from year two, improving coverage and providing replicated measurements of CO2 exchange between the ecosystem and atmosphere. Using a simple mass balance approach, above-ground and below-ground biomass production are combined with partitioned CO2 fluxes to estimate short-term carbon deltas across individual years. Years one and two both ended with the site as a net source of carbon following cultivation disturbances, cumulative NEE by the end of year two was 138.57 ± 16.91 g C m−2. The site became a cumulative net sink for carbon by the end of June in the third growing season and remained so for the rest of that year; NEE by the end of year three was −616.52 ± 39.39 g C m−2. Carbon gains were primarily found in biomass pools, and SOC losses were limited to years one (−1.43 Mg C ha−1 yr−1) and two (−3.75 Mg C ha−1 yr−1). Year three saw recoupment of soil carbon at 0.74 Mg C ha−1 yr−1 with a further estimate of 0.78 Mg C ha−1 incorporated through litter inputs over the 3 years, suggesting a net loss of SOC at 3.7 Mg ha−1 from a 0- to 30-cm baseline of 78.61 ± 3.28 Mg ha−1, down 4.7%. Assuming this sequestration rate as a minimum would suggest replacement of cultivation losses of SOC by year 8 of a potential 15- to 20-year crop. Potential coal replacement per hectare of harvest over the three-year study would offset 6–8 Mg of carbon emission, more than double the SOC losses.

submitted time 2016-05-04 Hits637Downloads349 Comment 0

6. chinaXiv:201605.00502 [pdf]

High‐resolution spatial modelling of greenhouse gas emissions from land‐use change to energy crops in the United Kingdom

Mark Richards; Mark Pogson; Marta Dondini; Edward O. Jones; Astley Hastings; Dagmar N. Henner; Matthew J. Tallis; Eric Casella; Robert W. Matthews; Paul A. Henshall; Suzanne Milner; Gail Taylor; Niall P. McNamara; Jo U. Smith; Pete Smith
Subjects: Biology >> Botany >> Plant ecology, plant geography

We implemented a spatial application of a previously evaluated model of soil GHG emissions, ECOSSE, in the United Kingdom to examine the impacts to 2050 of land-use transitions from existing land use, rotational cropland, permanent grassland or woodland, to six bioenergy crops; three ‘first-generation’ energy crops: oilseed rape, wheat and sugar beet, and three ‘second-generation’ energy crops: Miscanthus, short rotation coppice willow (SRC) and short rotation forestry poplar (SRF). Conversion of rotational crops to Miscanthus, SRC and SRF and conversion of permanent grass to SRF show beneficial changes in soil GHG balance over a significant area. Conversion of permanent grass to Miscanthus, permanent grass to SRF and forest to SRF shows detrimental changes in soil GHG balance over a significant area. Conversion of permanent grass to wheat, oilseed rape, sugar beet and SRC and all conversions from forest show large detrimental changes in soil GHG balance over most of the United Kingdom, largely due to moving from uncultivated soil to regular cultivation. Differences in net GHG emissions between climate scenarios to 2050 were not significant. Overall, SRF offers the greatest beneficial impact on soil GHG balance. These results provide one criterion for selection of bioenergy crops and do not consider GHG emission increases/decreases resulting from displaced food production, bio-physical factors (e.g. the energy density of the crop) and socio-economic factors (e.g. expenditure on harvesting equipment). Given that the soil GHG balance is dominated by change in soil organic carbon (SOC) with the difference among Miscanthus, SRC and SRF largely determined by yield, a target for management of perennial energy crops is to achieve the best possible yield using the most appropriate energy crop and cultivar for the local situation.

submitted time 2016-05-04 Hits861Downloads486 Comment 0

7. chinaXiv:201605.00500 [pdf]

Land‐use change to bioenergy: grassland to short rotation coppice willow has an improved carbon balance

Zoe M. Harris; Giorgio Alberti; Maud Viger; Joe R. Jenkins; Rebecca Rowe; Niall P. McNamara; Gail Taylor
Subjects: Biology >> Botany >> Plant ecology, plant geography

The effect of a transition from grassland to second-generation (2G) bioenergy on soil carbon and greenhouse gas (GHG) balance is uncertain, with limited empirical data on which to validate landscape-scale models, sustainability criteria and energy policies. Here, we quantified soil carbon, soil GHG emissions and whole ecosystem carbon balance for short rotation coppice (SRC) bioenergy willow and a paired grassland site, both planted at commercial scale. We quantified the carbon balance for a 2-year period and captured the effects of a commercial harvest in the SRC willow at the end of the first cycle. Soil fluxes of nitrous oxide (N2O) and methane (CH4) did not contribute significantly to the GHG balance of these land uses. Soil respiration was lower in SRC willow (912 ± 42 g C m−2 yr−1) than in grassland (1522 ± 39 g C m−2 yr−1). Net ecosystem exchange (NEE) reflected this with the grassland a net source of carbon with mean NEE of 119 ± 10 g C m−2 yr−1 and SRC willow a net sink, −620 ± 18 g C m−2 yr−1. When carbon removed from the ecosystem in harvested products was considered (Net Biome Productivity), SRC willow remained a net sink (221 ± 66 g C m−2 yr−1). Despite the SRC willow site being a net sink for carbon, soil carbon stocks (0–30 cm) were higher under the grassland. There was a larger NEE and increase in ecosystem respiration in the SRC willow after harvest; however, the site still remained a carbon sink. Our results indicate that once established, significant carbon savings are likely in SRC willow compared with the minimally managed grassland at this site. Although these observed impacts may be site and management dependent, they provide evidence that land-use transition to 2G bioenergy has potential to provide a significant improvement on the ecosystem service of climate regulation relative to grassland systems.

submitted time 2016-05-04 Hits602Downloads324 Comment 0

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