Sugarcane burning in the State of Sao Paulo, Brazil
December 2008
Photography and words by: Dr Peter Wells
Burning the sugarcane crop prior to harvesting is a traditional practice, which is adopted in order to facilitative manual cutting of the cane. Without the practice of burning, the crop is too dense and the leaves are too aggressive to allow a reasonably rapid rate of cutting.
Not surprisingly, the practice is also controversial. Not only is it wasteful, with up to 30% of the energy content of the crop being lost, it is also environmentally malign. The burning process of course releases a significant quantity of carbon dioxide into the atmosphere, hence negating some of the carbon benefits of sugarcane-derived ethanol compared with petrol. Burning also causes local air quality problems, with black soot released into the atmosphere and subsequently falling as a gentle ‘rain’ upon the surrounding towns and countryside.
The State of Sao Paulo has in place an ‘Agroenvironmental Protocol’ under which there will be a phased reduction in burning of the sugarcane prior to harvesting. In land suitable for mechanisation, it is anticipated that all burning will be eliminated by 2014. This ruling applies to land with fields above a critical threshold size, and having slopes of less than 12 degrees.
The burning process is carried out by a specialist crew of ten to fifteen workers. Only an area big enough for harvesting the next day is burned, the fields having already been arranged into suitable blocks bounded by wide firebreaks and access lanes.
The burning crew includes a water tender able to direct high-pressure water at any outbreaks of unwanted fire. In essence, it is the dry leaves (straw) of the cane that is burnt, leaving the main stems intact.
As the fire burns inwards to the centre of the block, a cloud of steam and black soot is released, with large amounts of small particles of cane leaf thrown up into the air. The roar of the inrushing air is augmented by the crackling and snapping of the cane, until in an instant the fire burns itself out, the noise stops, and all that is left is a few pockets of smouldering embers to be extinguished by the crew.
