Hutton Seminar Series: Biological N2 fixation inputs and greenhouse gas emissions from Brazilian agriculture

The anthropogenic greenhouse gas (GHG) emissions in Brazil were until recently dominated by those derived from deforestation (LULUCF), principally biomass burning in the Amazon region. However, since 2004 such emissions have been greatly reduced such that at the 2010 inventory compared to that of 2005 estimates of total GHG emissions were reduced from 2,730 Tg to 1,260 Tg CO2eq, a reduction of 54% in 5 years. This reduction in the LULUCF sector has brought into focus the large emissions in the agriculture sector, which is now the largest, somewhat more than those from LULUCF and the energy generation/transport sectors. Within the agriculture sector, only emissions of nitrous oxide and methane are counted. The largest single emission, which constitutes approximately 60% of all the agriculture sector emissions, is enteric methane from Brazil's national herd of approximately 200 million cattle. There is an ongoing effort in Brazil to estimate these emissions more accurately as in contrast to almost all other countries the almost all cattle are raised exclusively on low quality tropical forage grass. The influence of the introduction of N2-fixing legumes into these swards is under study. Nitrous oxide emissions result principally (70%) from dung and urine deposited in pastures or from manure management, followed by those from N fertilizer application (mainly on cereals and sugar cane) and decomposition of harvest residues. Despite the huge area dedicated to soybean and its high N accumulation (a mean of 220 kg N ha-1) from BNF, emissions of N2O are modest, being only derived from crop residues. In the future, as energy generation becomes dominated by solar and wind sources (the latter is already responsible for 8% of our electricity generation), and even the advent of electric- or hydrogen-powered vehicles, Brazil´s GHG emissions will be dominated by the agricultural sector, assuming that the efforts to further decrease deforestation are effective.

Born in Birmingham, England, UK, Dr Robert Boddey obtained a BSc at Leeds University (UK) in Agricultural Chemistry (1972-1975) before moving to the University of the West Indies, St Augustine, Trinidad and Tobago for a PhD entitled “Biological nitrogen fixation associated with the wetland rice crop”. Bob then worked as a consultant with Dra Johanna Döbereiner at the Embrapa Soil Biology unit (now known as Embrapa Agrobiologia), Seropédica, Rio de Janeiro State, Brazil, and has remained there until today, being contracted permanently by Embrapa in 1986. His work originally was concentrated on using and improving different methods (both with the stable isotope ¹⁵N and also non-isotopic methods) to quantify biological nitrogen fixation (BNF) associated with forage grasses, sugarcane and rice as well as grain, tree and forage legumes. More recently the work has expanded to evaluation of the sustainability of different agro-ecosystems (e.g. grazed pastures, soybean-based crop rotations under direct drill or conventional tillage, sugar cane) using long term experiments, stable isotopes (¹³C and ¹⁵N) and studies on nutrient cycling. This led his team to work on carbon “sequestration” and N₂O emissions from various agroecosystems and the importance, or otherwise, of biofuels as a strategy to mitigate CO₂ emissions.

Dr Boddey's work at present is concentrated on the impact of the introduction of forage legumes, as opposed to N fertilizer applications, on greenhouse gas emissions in tropical pastures. He has published over 150 papers in refereed journals (Google Scholar h = 60), and a further 90 or so full length articles in Conference proceedings or as Book Chapters. He was awarded “Embrapa Researcher of the Year” in 2010, and is regularly invited as a guest speaker at international conferences on BNF, biofuels, carbon sequestration and greenhouse gas emissions (and their mitigation).