Impact of the intensification of beef production in Brazil on greenhouse gas emissions

The objective of this study was to investigate the impact of increasing pasture productivity using fertilizers, forage legumes, supplements and concentrates, on the emissions of greenhouse gases (GHGs) in five scenarios for beef production with Nellore cattle in the Cerrado region of Brazil. A life cycle analysis (LCA) approach, from birth of calves to mature animals ready for slaughter at the farm gate, was utilized using both the Tier 1 and Tier 2 methodologies of the Intergovernmental Panel on Climate Change and the results were expressed in carbon dioxide equivalents per kg of carcass produced. The first four scenarios were based solely on cattle production on pasture, ranging from degraded Brachiaria pastures with minimal management, through to a mixed legume/Brachiaria pasture reformed every five years with P and K fertilizers and lime and an improved N fertilized (150 kg N/ha per year) pasture of Guinea grass (Panicum maximum). The most intensive scenario was also based on a fertilized Guinea grass pasture but with a 75 day finishing period in confinement with total mixed ration. To compare scenarios a herd based on 400 cows was utilized. Across the scenarios from 1 to 5 the increase in digestibility promoted a reduction in the forage intake for animal weight gain and a concomitant reduction in methane emissions per herd. For the estimation of nitrous oxide emissions from animal excreta using Tier 2, emission factors from a study in the Cerrado region were utilized which postulated lower emission from dung than from urine and much lower emissions in the long dry season in this region. Fossil carbon dioxide emissions from direct use of fuel and energy were also included in the LCA along with that necessary for the production of fertilizers, supplements and feeds. The greatest impact of intensification of the beef production systems was in the reduction of the area necessary for carcass production from 320 to 45 square meters per kg carcass. Carcass production increased from 43 to 65 Mg per herd across the scenarios from 1 to 5, and total emissions per kg carcass were estimated by Tier 2 methodology to be reduced from 53.7 to 27.9 kg carbon dioxide equivalents. GHG emissions per kg carcass were slightly lower for the mixed grass legume scenario (3), although this was partly due to the lack of data on emissions of nitrous oxide from legume residues. Another large source of uncertainty for the confection of such LCAs was the lack of data for enteric methane emissions from cattle grazing tropical forages