Greenhouse Gas Balances of Livestock Manure during Storage and Field Application with and without Anaerobic Digestion.

Greenhouse gas balances of livestock manure during storage and field application with and without anaerobic digestion Khagendra R. Baral1 2*, Guillaume Jégo3, Barbara Amon4, Roland Bol5, Martin H. Chantigny3, Jørgen E. Olesen1 and Søren O. Petersen1 1Department of Agroecology, Aarhus University, Tjele, Denmark; 2International Maize and Wheat Improvement Center (CIMMYT), Kathmandu, Nepal 3Quebec Research & Development Centre, Agriculture and Agri-Food Canada, Québec, Canada; 4Leibniz Institute for Agricultural Engineering and Bioeconomy (ATB), Potsdam, Germany 5Institute of Bio- and Geosciences, Forschungszentrum Jülich GmbH, Jülich, Germany *Corresponding author. E-mail: k.baral@cgiar.org Abstract Livestock manure is increasingly used for anaerobic digestion (AD) to produce biogas which is considered as an alternative energy against natural fuel. The product of AD is rich in plant nutrients and often stored for agricultural use. Depending on the origin and management emission intensity of methane (CH4) and nitrous oxide (N2O) may vary during storage and after field application, and thus evaluation of GHG balances from various manures is essential to formulate appropriate emission mitigation practices. In this study, GHG balance was made by monitoring emissions from manure storage in a pilot-scale facility and after field application. The treatments were, (i) a manure-based digestate from the Maabjerg Bioenergy biogas plant (MBD); (ii) a mix of cattle slurry with digested and dewatered sewage sludge (CS+DDS); (iii) untreated cattle slurry (CS); and (iv) untreated pig slurry (PS). The manure storage experiment was conducted from June 2014 to April 2015, followed by field application and grown spring barley. During storage direct (CH4, N2O) and indirect (NH3) GHGs were measured continuously for 90 days and then measured once in a month. Cumulative emissions of CH4 were 0.5 to 3.6 kg CH4-C m-3, where 67 to 88% emitted during the first 90 d. In field only N2O was the source of GHG and cumulative emissions were 0.19 to 1.97 kg N2O-N ha-1. Taking 100 kg NH4+-N as a common basis, overall GHG balances for manure management chains were calculated that included digestion to field application. The GHG balance of MBD, CS+DDS, CS and PS were, respectively, +419, +5088, +5748 and +848 CO2eq, and dominated by CH4 emission during storage across manure management and field application. In this study, AD strategies reduced net GHG emissions by 10% (CS+DDS vs. CS) to 50% (MBD vs. PS) compared to the raw manure. Hence, carbon footprints can probably be minimized via application of AD during crop production, giving special attention to CH4 emissions during manure storage.