Understanding processes determining soil carbon balances under perennial bioenergy crops CARBO-BIOCROP

Lead Research Organisation: Rothamsted Research
Department Name: Sustainable Soils and Grassland Systems

Abstract

In contrast to annual food crops, evidence suggests that biofuels from perennial bioenergy crops have a positive greenhouse gas (GHG) mitigation potential. However, the magnitude of this benefit has been recently questioned, since long-term and indirect effects may considerably reduce any GHG savings generated by the cropping system. Indeed, impacts on soil C have been identified as the weak link in life-cycle analysis of net carbon-equivalent benefit presented by bioenergy. Changes in rates of nitrous oxide (N2O) and methane (CH4) emission are relevant too since they have a large GHG warming potential, but these changes are mostly unquantified for perennial bioenergy cropping systems. Although several soil carbon and trace-gas models have been developed for agricultural and conventional forest systems these have not been parameterized and validated for transition of land-use to perennial bioenergy crops. To predict the changes in SOC that will occur one to three decades after establishing biomass crops, we need to establish (a) differences in turnover dynamics and fluxes of carbon under key biomass crops in terms of amount, quality and placement of carbon into the soil from the plant, and (b) mechanisms to overcome short-term loss of pre-existing soil carbon during transition (c) quantitative, process-based modeling approaches that are predictive, to explore future scenarios for optimum soil carbon management. The overarching aim of this project is to provide improved understanding of fundamental soil processes resulting in changes of soil carbon stocks and pools as a result of land conversion from arable/grassland to land-based renewables. The project focuses on impacts of land use change specifically to perennial bioenergy crops (fast growing SRC trees and grasses) where there is currently a significant knowledge gap. This project will generate new evidence to improve current understanding on how soil carbon processes, sequestration and emission, are affected by the introduction of perennial energy crops. The soil carbon balance is key to informing the debate on whether using these crops for bioenergy and biofuels will result in significant carbon savings compared to land use for food crops and the use of fossil fuels for heat, power and liquid fuels. In the long-term (beyond the life of this project), this will enable dynamic, spatially explicit modeling of GHG (C equivalents, abbreviated here as C) mitigation potential of land-based bioenergy systems across different climates and soil types of the UK. We wish to develop 'Carbon Opportunity Maps' for the UK. The work of the project will be undertaken in three workpackages dealing with data synthesis (WP1), experimental data collection (WP2) and modeling (WP3). Throughout the project we will use leverage of other resources including two flagship sites at Brattleby and Aberystwyth, where commercial-scale plantations are established and where several long-term measuring and monitoring activities are underway funded from elsewhere. Similarly, the modeling resources from within the project are extensive and funded from other sources that will be levered against the work here. They included DNDC, JULES, ROTH C and on-going modeling approaches for miscanthus and SRC. Outputs will include a new database of synthesized data for soil carbon under bioenergy crops. We will have tested and calibrated process-based models that are capable of simulating the dynamics of soil organic carbon, carbon sequestration and greenhouse gas emissions for perennial bioenergy crops in the UK. We will provide increased fundamental understanding of soil processes occurring under bioenergy cropping systems including the role of mycorrhizal associations and the effectiveness of biochar as a potential to optimize soil carbon and plant growth. We will develop capacity for future 'carbon opportunity' mapping.

Publications


10 25 50
 
Description We conducted an extensive review of the existing literature concerning the carbon capture and retention under perennial energy crops (published in Bioenergy Research). This is an important contribution to the systems' understanding in terms of differences between woody and herbaceous/grass crops for energy.
We designed and compiled a data base for the consortium and most importantly, we used the insight derived from the data for a new model to predict the long-term carbon stock change in the soil. Our conclusion from our analyses is that previous models overestimated the net carbon enrichment by a factor of two and that sequestration rates under current Miscanthus or willow-SRC yields (10 t/ha/yr) are about 0.5 t/ha annually.
We are in the process of recalibrating our model for carbon sequestration under Miscanthus, based on carbon isotope data for a series of long-term experiments. It seems that the sequestration rate declines with time and depends on initial state and management intensity
Exploitation Route Once the model has been published the approach can be tested against new data
The crop growth and soil carbon model need to be fully integrated to capture the interactions.
Sectors Agriculture, Food and Drink,Environment
 
Description The project has finished in Dec 2014 but results are being used in other projects, e.g. ELUM project, funded by the ETI and Bioenergy Value Chain Optimization, funded by EPSRC. Further progress was possible in the "Integrating Carbon Systems" part of Rothamsted's ISP "Cropping Carbon" The articles have been downloaded many times already and entered the Citation Index in the first year after publication.
First Year Of Impact 2015
Sector Agriculture, Food and Drink,Energy,Environment
Impact Types Economic,Policy & public services
 
Description Biomass Value Chain Modelling
Amount £148,000 (GBP)
Organisation Energy Technologies Institute (ETI) 
Sector Public
Country United Kingdom of Great Britain & Northern Ireland (UK)
Start 01/2011 
End 12/2012
 
Title CarboBioCrop Database 
Description The data base is an ACCESS-based tool that allows you to search and input data of carbon capture (yield, production), input to the soil system and retention of carbon in the soil system under diverse perennial and annual/arable biomass/bioenergy crops. 
Type Of Material Database/Collection of data 
Year Produced 2012 
Provided To Others? Yes  
Impact The database was supplied to the Carbo-Biocrop consortium and is a search tool to be used in model calibration and evaluation. It is being used internally and had the potential of being used externally (e.g. ETI funded ELUM project), however, there was no interest, probably due to IP issues. 
 
Title RothC-PEC 
Description RothC-PEC or RothC_E (expanded) is a new form of the Rothamsted Carbon Model which allows to differentiate the carbon inputs to the system and soil by their longevity and turnover rate (1/Mean Residence Time). 
Type Of Material Computer model/algorithm 
Provided To Others? No  
Impact Once this model has been published (draft presented at the EGU-SSSA Conference in Bari/Italy in September 2014 this model allows a much better analysis of the impact of perennial energy crops on the carbon balance of the soil/production system 
 
Description Cropping carbon and carbon retention in soils 
Organisation Biotechnology and Biological Sciences Research Council (BBSRC)
Department Rothamsted Research
Country United Kingdom of Great Britain & Northern Ireland (UK) 
Sector Academic/University 
PI Contribution Due to "long-term" and continuation of newly established experiments for energy crops, Miscanthus and willow-SRC we were able to draw upon new data/samples for the validation of the newly developed models. The collaboration with the off-site (North Wyke) and local colleagues enabled us to develop some synergies between experimental evidence and modelling as well as synthesizing a large body of literature.
Collaborator Contribution Colleague A Gregory contributed considerably to the literature review and organised the sample inventory and laboratory work, which we had started initially to develop ourselves due to the lack of adequate data for the modelling exercise.
Impact New soil data sets from EMI-trial, BSBEC trial, excellent management and yield history joint publication on experimental evidence and review (pending revision) and drafted modelling paper(s)
Start Year 2012
 
Description ETI-Bioenergy Research Focus 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? Yes
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact These discussions shaped two major research project of national (UK) importance

We subsequently competed and contributed to two project proposals which eventually got continued in an on-going EPSRC-funded project (Bioenergy value chain optimization, led by Imperial College)
Year(s) Of Engagement Activity 2010,2011
 
Description Roots to the Future 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Participants in your research and patient groups
Results and Impact We were invited to submit our paper to a special issue of Annals of Botany but it turned out to be premature analysis of the results and it sparked a whole series of analyses and discussion; now finally accepted in Agriculture, Ecosystems and Environment

We implemented some contacts with researchers in Brazil and Italy and the result was an invitation to be lead author of a chapter of a special issue that compared US and EU approaches to resources for Bioenergy and the Bioeconomy (see publication for Bio-fpr, corresponding author for article which was finally led by Li )
Year(s) Of Engagement Activity 2012