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Healthy Plowing

Carbon retained in the soil is expected to increase with the mechanization of sugar cane harvesting

Eduardo CesarSugar cane fields: being tested for environmental impactEduardo Cesar

Mechanized sugar cane harvesting is expected to increase the amount of carbon in the soil because it covers the soil with straw which slowly decomposes, in contrast with the manual harvesting process, which is based on the burning of leaves to facilitate the cutting. Likewise, converting degraded pasture land into sugar cane fields is also expected to increase the amount of carbon in the soil, says Marcelo Galdos, a researcher at the University of São Paulo/USP’s Centro de Energia Nuclear na Agricultura/Cena, Center of Nuclear Energy in Agriculture. Galdos headed the analysis of the carbon flow in sugar cane fields in Brazil, Australia and South Africa. The results were published in May in two scientific journals, the Soil Science Society of America Journal and Plant and Soil. This topic was also discussed on June 16 at the workshop on the Social, Economic, Environmental and Land Use Impacts organized by FAPESP as part FAPESP’s Programa de Pesquisa em Bioenergia, Bioenergy Research Program/Bioen.

“We have to use conservation agriculture, transferring the carbon gas (CO2) from the air to the plants and to the soil”, says Carlos Clemente Cerri, a professor at Cena who acted as the advisor for these two projects. Researchers from the USA’s Colorado State University and from South Africa’s Sugar Cane Research Institute participated in the two projects. “The manually harvested sugar cane, which includes burning the leaves, reduces the stock of carbon in the soil; when the leaves are not burned, the amount of carbon in the soil increases”, Cerri stated. He added that mechanized harvesting can cause the soil to retain up to three tons of carbon in three years, “a significant result that can be deducted from the greenhouse gas emissions generated by the production of ethanol”.

No consensus has been reached yet in regard to these values. “We haven’t found any major benefits by leaving the straw on the soil”, said Urquiaga, a researcher at the Empresa Brasileira de Pesquisa Agropecuária/Embrapa Agrobiologia, Agricultural Research Center. He obtained more modest results – a mere 300 kilograms of carbon per hectare in the course of the sixteen years during which he kept track of sugar cane fields in the State of Pernambuco that had been harvested with and without burning. “We cannot restrict ourselves to worrying only about the carbon; we have to reflect on the dynamics of organic material and the role of nitrogen”, he said. “If things were different, all we would have to do would be to bury the sugar cane bagasse to transfer the carbon to the soil.” In his opinion, the amount of carbon retained in the soil depends on the residues, the level of degradation (more seriously degraded soil retains more carbon than the well-preserved soil does) and the soil’s capacity to accumulate carbon. “At the beginning, the soil accumulates large quantities, and later it accumulates less”, he pointed out.

During the day’s discussions, the researchers agreed that converging methodologies need to be established to obtain more extensive and accurate information on the impact of sugar cane ethanol production and possible effects on the reduction of greenhouse gases such as carbon, which cause global warming. “Calculating the impact and environmental benefits depends on knowledge of the impact on the use of soil which is still not clear”, said Isaías de Carvalho Macedo, from the Núcleo Interdisciplinar de Planejamento Estratégico/Nipe, Strategic Planning Center at the State University of /Unicamp. Carlos Henrique de Brito Cruz, scientific director of FAPESP, encouraged the researchers to conduct studies whose findings would be published in international journals. In general, “results remain hidden in Portuguese-language publications. We need to have more international exposure in this respect”. In his opinion, one of the upcoming challenges is “to produce globally competitive science”, by increasing the number of scientists and the scientific competency in this field, to maintain the leadership of ethanol production technology.

“Brazil is at the forefront in this respect, and has the experience, but this leadership position is not guaranteed”, said Marcos Jank, a professor at USP’s School of Economics, Administration and Accounting/FEA) and president of the União da Indústria de Cana-de-açúcar/Unica, Sugar Cane Industry Trade Association. “The next step depends on investments and planning. I have seen a lot of duplication, lack of integration and lack of planning”, he pointed out, adding that he has met with directors of foreign companies with budgets amounting to approximately US$ 50 million for new product development, such as sugar cane-based hydrocarbons. Research institutes are also investing heavily in this field. Last May, the Energy Biosciences Institute, a public-private consortium comprised of two US universities and an energy company, announced the first 49 research projects for which US$ 20 million have been allocated of the US$500 million reserved for research in this field in the next ten years. Evan Delucia, from the University of Illinois, was one of the speakers at the workshop. The University of Illinois is one of the partners of the Energy Biosciences Institute. At the FAPESP event, Delucia described the research studies on ethanol taking place in the United States on other plants, for example, corn.

Deforestation. In Brazil, sugar cane plantations are still associated with deforestation, a problem that Jank tried to minimize at the event. In early June, former US president Bill Clinton praised Brazil’s sugar cane ethanol at a world ethanol summit held in São Paulo. He said that this ethanol could avoid greenhouse gas emissions, but pointed out that the emissions from deforestation, especially in the Amazon Region, are still very high. Two weeks later, Jank stated that: “Sugar cane does not cause deforesting, because sugar cane is being planted on pasture land.”

In one of the chapters of the Sugarcane ethanol – Contributions to climate change mitigation and the environment, by Peter Zuurbier and Jos van de Vooren, a team coordinated by André Meloni Nassar, general director of the Instituto de Estudos do Comércio e Negociações/Ícone institute and one of the coordinators of the projects taking place at Bioen, observed that the sugar cane fields are not encroaching upon the country’s agricultural frontiers and do not directly pressure the native vegetation in any region of the country. According to Jank, it is actually the pasture lands that take over the spaces previously taken up by forests and other kinds of natural vegetation. “The problem is indirect deforestation, which is still not being accurately measured”.

“It is not enough to be a fuel”, said Heitor Cantarella, coordinator of Bioen’s agronomy and land use work group and a researcher at the Instituto Agronômico de Campinas, Agronomy Institute. “Ethanol needs to pass sustainability tests and prove that it is environmentally acceptable”. Glaucia Mendes Souza, coordinator of the Bioen, said that one of the objectives of the research program and the meetings with experts is to define the regions that need more attention and investments. Launched in July 2008, Bioen’s initial investments total R$ 73 million for research on sugar cane varieties, production processes of ethanol and other by-products, and the social, economic and environmental impact of the use and production of biofuels.

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