Impact of mechanization and previous burning reduction on GHG emissions of sugarcane harvesting operations in Brazil

Ethanol production from sugarcane under Brazilian conditions has resulted in positive economic, energetic and environmental indicators, primarily due to a high agro-industrial yield, recycling of by-products and bagasse utilization for power generation. Following the trends of improvement in the overall processes and increasing environmental constraints, the extensive use of labor and previous burning in sugarcane harvesting has been progressively replaced by mechanical harvesting without the need for burning.Currently, this operation is performed in three ways: manual harvesting with previous burning, mechanical harvesting with previous burning, and mechanical harvesting of green sugarcane. Generally, the main reason for use of previous burning in sugarcane fields is the elimination of straw to facilitate manual cutting. However, studies indicate emissions of greenhouse gases (GHGs) and, mainly, other pollutants. associated with this practice. In Brazil, specific environmental laws and protocols have established a progressive reduction in previous burning aimed at total elimination in the next decade. In addition, an increase in the use of mechanical harvesting due to high productivity compared with manual cutting has been observed. In this context, this study has estimated the specific GHG emissions (tonCO₂ₑq/ha) in sugarcane harvesting as a function of the simultaneous reduction of previous burning and increase in the use of mechanization.The estimates were applied to the sugarcane harvesting area of the São Paulo State, which is responsible for approximately half of Brazilian production. Considering the period between 1990 and 2009, the GHG emissions from sugarcane fields were estimated considering the shares of areas with mechanical harvesting and previous burning use, agricultural yield, diesel consumption by machinery, and straw/stalk ratio. The estimation was carried out using two approaches: an estimation that considered only the share of areas with harvesting practices, and a complete estimation, in which all parameters were accounted for over the years. In a Business as Usual scenario (BAU), the specific GHG emissions progressed from 1.015 to 0.633tonCO₂ₑq/ha using the first approach, and from 1.053 to 0.639tonCO₂ₑq/ha with the second. The reduction represented a change of 37.6% and 39.3% in the last 20years, respectively. The progressive decrease in previous burning was determining factor for this observation, responsible for an average of 80% of total emissions from harvesting operations. Two additional Reference Scenarios were considered: the sugarcane was manually harvested in the first scenario and mechanically harvested in the second. When compared with the BAU scenario, the average reduction of GHG emissions was 17.4% and 26.7%, respectively.