Quantifying the reduction of greenhouse gas emissions as a result of composting dairy and beef cattle manure E. Pattey, M. K. Trzcinski and R.L. Desjardins Agriculture and Agri-Food Canada, Research Branch, Ottawa Animal Production & Manure Management Network Meeting London, Canada, 08 March 2006
INTRODUCTION Greenhouse gas emissions from the agricultural sector can be reduced through implementation of improved management practices. For example, the choice of manure storage method should be based on environmental decision criteria, as well as production capacity. In this study, greenhouse gas emissions from three methods of storing dairy and beef cattle manure were compared during the summer period.
MATERIAL and METHODS GHG emissions were measured from three different methods of manure storage: slurry (S), stockpile (P), and compost (C). Overall, the slurry was mostly anaerobic (except the crust that formed at the surface), the compost was mainly aerobic, and the stockpile was in between. The emissions from three replicates of each storage type were monitored for 14 weeks for the dairy cattle manure and for 11 weeks for the beef cattle manure.
The emissions of CH 4, N 2 O and CO 2 from manure stored as slurry, stockpile, and compost were measured using a flow- through closed chamber Each manure storage bin, made of a wood frame, was 1.00 m deep, 1.22 m wide and 2.13 m long (internal dimensions)
Methane Emissions during Storage
Nitrous Oxide Emissions during Storage
Carbon Dioxide Emissions during Storage
Carbon Dioxide Emissions during Storage Because ruminant manure carbon originates from autotrophic fixation which is released as CO 2 to the atmosphere over a relatively short period of time, manure CO 2 emissions are not considered to contribute to global warming and are not included in the calculation of manure storage contribution to GHG emissions. CO 2 emissions were measured concomitantly to CH 4, N 2 O emissions for monitoring the aerobic decomposition and for evaluating if the enclosure was tightly installed over the bin.
GHG Emissions in CO 2 -eq over 3-month summer storage period for dairy cattle summer storage period for (g g CO 2 -eq kg -1 DM using GWP CH4 = 23 GWP N2O = 296) Compost Stockpile Slurry Slurry(5 months) CO 2 399 444 208 231 CH 4 35 182 367 570 N 2 O 172 119 30 30 CH 4 +N 2 O 207 301 397 600
GHG Emissions in CO 2 -eq over 3-month summer storage period for beef cattle summer storage period for (g g CO 2 -eq kg -1 DM using GWP CH4 = 23 GWP N2O = 296) Compost Stockpile Slurry Slurry(5 months) CO 2 342 358 141 157 CH 4 3 66 225 349 N 2 O 48 10 5 5 CH 4 +N 2 O 51 76 230 354
Annual GHG Emissions in CO 2 -eq hd -1 during dairy & beef cattle manure storage (t t CO 2 -eq hd -1-1 yr -1 ) Dairy Cattle Compost Stockpile Slurry Beef Cattle Compost Stockpile Slurry CH 4 0.080 0.416 1.301 0.003 0.067 0.357 N 2 O 0.393 0.272 0.068 0.049 0.010 0.005 Assuming an increase of 10% in emissions beyond the sampling period
Actual & potential annual GHG Emissions for relevant dairy & beef cattle manure storage systems in Canada (Tg CO 2 -eq yr -1 in Canada) Dairy Cattle Beef Cattle Compost Stockpile SlurryCompost Stockpile Slurry Actual 0.411 0.672 0.182 0.090 Potential 0.515 0.749 1.489 0.136 0.201 0.941 Potential refers to total Canadian GHG emissions by fully adopting a given storage system
Potential Reduction of Canadian GHG Emissions by adopting a given manure storage systems for dairy & beef cattle (Tg CO 2 -eq yr -1 in Canada) Dairy Cattle Beef Cattle Compost Stockpile SlurryCompost Stockpile Slurry Actual 0.411 0.672 0.182 0.090 Potential 0.515 0.749 1.489 0.136 0.201 0.941 eduction -0.568-0.334-0.136-0.071 The extrapolation does not account for possible variations in weather conditions and manure composition across Canada.
Management recommendations A reduction of 0.70 Tg CO 2 -eq yr -1 could be achieved by composting all the cattle manure stored as slurry and stockpile in Canada, using the passively aerated windrow system. Composting would generate minor additional costs (i.e. the perforated pipes) if the technique used in this study is adopted since no mechanical aeration is required. Another mitigation option could be to collect and burn the CH 4 emitted from the existing slurry facilities. In this case a reduction of 0.76 Tg CO 2 -eq yr-1 could be achieved. If all the produced cattle manure stored in facilities relevant to the experiment was stored as slurry and CH 4 collected and burned, then a reduction of 1.08 Tg CO 2 -eq yr -1 could be achieved. Collecting and using CH 4 on farm involve additional costs that can be offset to some extend by the energy saving.
Impact for Canada Based on the 6% GHG reduction commitment by 2008-2012 in the Kyoto protocol, it is anticipated that the Canadian agricultural sector will need to reduce GHG emissions by about 7.75 Tg CO 2 -eq yr -1 (Boehm et al. 2004). If one assumes full adoption of the proposed mitigation options, the cattle manure storage practice might contribute by itself about 9-14% of the objective. Moreover, manure stored as slurry could also be applied to fields as fertilizer prior to crop growth to avoid the increase in temperature during the summer, which would reduce GHG emissions.
New CH 4 Emissions Factors For North-America under cool conditions the new CH 4 emission factors : For dairy cattle manure 45.2 kg CH 4 hd -1 yr -1 (old: 36 kg CH 4 hd -1 yr -1 ) For beef cattle manure 2.7 kg CH 4 hd -1 yr -1 (old: 1 kg CH 4 hd -1 yr -1 ) By using the proportion of manure storage practices relevant to Canada the emission factors become 35.8 kg CH 4 hd -1 yr -1 for dairy cattle manure and 4.1 kg CH 4 hd -1 yr -1 for beef cattle manure. This estimation shows how sensitive are the emission factors to the allocation of the manure storage practices proportion.