Assessing methods to attribute soil greenhouse gas emissions to a crop in life cycle assessment of cropping systems

Citation

P Goglio, W Smith, B Grant, R Desjardins, D Worth, A Williams, P Burgess. 2016. Assessing methods to attribute soil greenhouse gas emissions to a crop in life cycle assessment of cropping systems. 10th International Conference on Life Cycle Assessment of Food 2016. http://www.lcafood2016.org/wp-content/uploads/2016/10/LCA2016_BookOfAbstracts.pdf#149

Plain language summary

There is an increased demand for a reduction in greenhouse gas emissions. Life cycle analysis has been widely applied to agricultural systems for assessing these emissions. However, no consensus has been found regarding the time period over which to estimate and apply the greenhouse gas emissions in agricultural Life cycle analysis. In this study we compare methods of attribution (year period, planting to planting, harvest to harvest) and assess advantages and disadvantages of each method. Soil carbon dioxide and nitrous oxide emissions were estimated over 28 years using an agricultural model for 4 different management practices (conventional till, no-till, inclusion of legumes in rotation, and residue removal). Model results were used to estimate global warming potential on a hectare basis. Results showed no significant differences among methods when considering the full cropping system, however large differences were found on a year basis. Larger differences among methods were found for the cropping system where residues remained on the field. A long term period is suggested to assess the global warming potential of cropping systems which reduces the importance of which type of method (time period) should be used for applying greenhouse gas emissions in life cycle analysis.

Abstract

There is an increased demand for a reduction in greenhouse gas (GHG) emissions and LCA has been widely applied to agricultural systems to assess GHG. However, no consensus has been found on how to attribute soil GHG emissions in agricultural LCA. In this study, the objectives were: (i) to compare methods of attribution (year period, planting to planting, harvest to harvest), and (ii) to assess advantages and disadvantages of each method when used to attribute CO2 and N2O emissions to a crop in the LCA of cropping system with no winter crops. Soil CO2 and N2O emissions were estimated over 28 years using the biogeochemical DNDC model for 4 different scenarios based on a field experiment in Manitoba, Canada. Model results were used in the Crop.LCA tool to estimate global warming potential (GWP) on ha basis. Results showed no significant differences among methods when considering the full cropping system, however large differences were found on a year basis. Inter-annual variability was found to be higher than the difference across methods. Larger differences among methods were found for the cropping system where residues remained on the field. Thus a multimethod approach is suggested together with a long term LCA assessment to assess this system. However, the choice of methods to employ is a compromise between accuracy and applicability with regards to the LCA objectives.

Publication date

2016-11-01