Towards a representative assessment of methane and nitrous oxide emissions and mitigation options from manure management of beef cattle feedlots in Brazil

Abstract

We conducted an inventory to estimate methane (CH4) and nitrous oxide (N2O) emissions from beef cattle feedlot manure in Brazil for the year of 2010. The aim was to determine (CH4) and (N2O) emissions from beef cattle feedlot manure in Brazil using the IPCC United Nations Intergovernmental Panel on Climate Change approach and present a framework that structures priority research for decreasing uncertainties and assessing mitigation scenarios. The analysis consisted of the use of specific farm-scale activity data applied to the 2006 (IPCC) guideline equations for animal manure management updated with specific parameters for Brazil conditions. Uncertainties were assessed by error-propagation technique. The results indicated that 376.6 GgCO2eq were emitted from the manure management of beef cattle feedlots in Brazil in 2010. Nitrous oxide accounted for 61 % of total emissions, out of which 69 % came from direct emissions. Uncertainties were high, comprising −30 to +80 %. Solid storage-heap and field application were the largest sources of greenhouse gas (GHG) emissions (81 % of total emissions) and held most of the variance in uncertainties. Although, due to limitations in the IPCC methodology for integrating GHG emissions at farm-scale, we could not account for emissions occurring from different lengths of time in each manure management compartment prior to field application. As a consequence, this GHG inventory lacks consistence. The use of more robust methodologies such as process-based models are recommended for improvements, however they are currently unavailable because there is a lack of key data for Brazil conditions for validating those models. Our literature revision shows that the most effective research for raising those data would track emissions from manure: generated from male Nellore (Bos Indicus) cattle fed for 90 days with a high-energy diet, removed only at the end of feeding period and held in heaps over 60 days before being applied to maize (Zea mays L.) cropping fields under clay soil. The proposed research and methodology approaches described in this work is required to establish a manure management emission assessment that will become more responsive to the changing practices on Brazilian beef cattle feedlots and, consequently, permitting implication of mitigation scenarios to be ascertained.