Methane and nitrous oxide emissions from the beef cattle feedlot manure management in Brazil: surveying, measuring and modeling

Abstract

Brazil is one of the world biggest beef producers, which around 10% of its production coming from feedlots. These feedlots have significatively grown in the last two decades in Brazil along with the environmental concerns regarding the greenhouse gas emissions (GHG) from agricultural systems, where the methane and nitrous oxide emissions from the animal manure management play important hole. However, there is no information regarding the impact and potential of mitigation options for the manure management in beef cattle feedlots in Brazil. Therefore, the aim of this work was to evaluate the GHG emissions (CH4 and N2O) from the manure management of the beef cattle feedlot in Brazil as well as potential alternatives for mitigation using the survey, field measurements and modeling approaches. In 2011 were surveyed feedlot properties which fed together almost 30% of the beef cattle fed in feedlots in 2010 (831,450 animal) in Brazil. Main findings showed the most representative manure management practice in 2010 consisted in removing manure from pens only at the end of the feeding period (~90 days) with subsequent storage in heaps (~75 days) before being applied to crop and pasture lands (~20 ton ha-1). Following the IPCC methodology, the manure management of these animals emitted 376.6 Gg CO2eq, out of which 69% were from direct sources (CH4 and N2O). However, limitations in this methodology in integrate emissions at farm-level prevented adequate GHG emissions evaluation as well as evaluating potential mitigation practices. Gas measurements made in a typical manure management in Brazil showed total emissions (CH4 + N2O) of 0.19 ±0.10 kg CO2eq per animal live weight gain (lwg-1), suggesting emissions may be about 5 times lower than the calculated using the IPCC methodology. Results provided by the Manure-DNDC model used in this work suggested increasing the frequency of the animal house cleaning and adopting no-tillage system for cultivating crop systems is the most efficient management for mitigating GHG emissions from manure (up to 75%). Examining the effect of an anaerobic digester (AD) through field measurements and literature values, results pointed out that direct GHG emission from manure management (0.14 ±0.06 kg of CO2eq lwg-1) may not drastically differ from the typically carried out in Brazil. However, the AD may indirectly promote an offset of 95% (±45%) of the direct emission through the replacement of mineral N-fertilizer and electricity with manure and biogas; therefore being an effective way for mitigating GHG emissions in beef cattle feedlot in Brazil. Since this work consists in one of the first assessments on the impact of the manure management of beef cattle feedlot in Brazil, more and continuous field measurements are required for decreasing uncertainties and improving estimates. We believe the results reported in this thesis provide useful information for improving the GHG emission balance of the manure management in beef cattle feedlots and the beef production in Brazil, as well as scientific perceptions for the design of future researches for strengthening the assessments.