News
Environmental equation
August 12, 2009
By Fábio de Castro, in Atibaia, Brazil
FAPESP News – Reducing emissions of the greenhouse gases that cause global warming is one of the main goals behind the international effort to replace fossil fuels with clean energy sources, such as ethanol made from sugarcane. But the fertilizers needed to produce biofuels could play a role in those emissions.
The role of fertilizers in emissions will need to be carefully studied in order to understand the environmental impact of sugarcane plantations, believes Heitor Cantarella, a researcher and specialist in soil fertility and fertilization at the Agronomy Institute, in the city of Campinas, Brazil.
Cantarella participated Tuesday (Aug. 11) in the workshop “Biofuel Technologies and their Implications for Land and Water Use”, held in the city of Atibaia through August 12th. The event is sponsored by the FAPESP Program for Research on Bioenergy (BIOEN) and by the Biotechnology for Bioethanol sector of the National Institute of Science and Technology.
Agreementing to Cantarella, one of the leaders of the BIOEN Program, the nitrogen contained in fertilizers used in the cultivation of sugarcane plays a significant role in greenhouse emissions.
“When we use sugarcane to make biofuel, we need to evaluate its impact on the emissions balance. Nitrogen comes into the equation because after it enters the soil microbiological reactions cause the emission of small quantities of nitrous oxide, an important greenhouse gas,” Cantarella told FAPESP News.
The greenhouse effect produced by each molecule of nitrous oxide is almost 300 times greater than for each molecule of carbon dioxide, agreementing to Cantarella. The Intergovernmental Panel on Climate Change, or IPCC, notes that approximately 1% of nitrogen fertilizers used on fields ends up in the atmosphere in the form of nitrous oxide.
“But it’s important to remember that the IPCC’s numbers are very general. There are few studies of nitrous oxide and sugarcane cultivation. We need to measure, under normal growing conditions, what is the real contribution of nitrogen fertilizers,” he said.
Cantarella says that in the case of sugarcane, the fact that fertilizers are added during a relatively dry period of the year means the conditions are, at least theoretically, not very favorable for the production of nitrous oxide in the soil. But a lack of studies prevents any precise analysis. “This is something that needs to be evaluated in practice,” he said.
Sugarcane cultivation is still expanding in São Paulo, a trend that is expected to continue. “Despite the expansion, from an environmental point of view the problem of nitrous oxide emissions isn’t too serious. However, it becomes critically important when we calculate the environmental impact of a crop that is intended to mitigate greenhouse gas emissions,” he says.
The use of fertilizers on sugarcane plantations is generally efficient, agreementing to Cantarella, who is also president of the Council of Trustees of the Foundation to Support Agricultural Research. Even with the same amount of fertilizer used on other crops, cane yields much more biomass.
“Even so, the large extent of sugarcane plantations means they account for 13% to 17% of all the fertilizer used in Brazilian agriculture,” he said.
New challenges
Recent technological changes are the biggest obstacle to efficient fertilizer use in the state’s sugarcane fields. “With the increase of areas using mechanized harvesting, we have a large quantity of straw being left on the ground. That interferes with the incorporation of fertilizers, which are often left exposed. And one of the main nitrogen fertilizers used on the sugarcane crop, urea, is susceptible to large losses due to volatilization,” Cantarella explained.
One possible solution to the problem, he said, would be to use a different source of nitrogen instead of urea. “But such alternatives are more expensive and less readily available,” he said.
Other possible solutions include mechanical incorporation of fertilizer into the soil and additives that can reduce losses. “We still don’t have a practical and economical solution that’s widely used. It’s a challenge we need to face,” he said.
Also requiring more study, Cantarella said, is the role bacteria plays in the fixation of atmospheric nitrogen. Biological fixation of nitrogen by bacteria associated with cane plantations could reduce the need for fertilizers, which would lead to major environmental and economic savings.
“But the magnitude of that kind of fixation isn’t well understood. The numbers in the literature vary pretty widely. Our challenge is to determine what the contribution is and see if we can improve it—either by adding more efficient microorganisms or by choosing sugarcane varieties that respond better,” he said.
Media Contacts
Fernando Cunha, FAPESP (www.fapesp.br)/ (+55) 11 3838-4151
São Paulo Research Foundation – FAPESP – is an independent public foundation with the mission to foster research and the scientific and technological development of the State of São Paulo, Brazil. This is achieved through the support of research projects carried out in higher education and research institutions, in all fields of knowledge.