Sugarcane

Abstract

This chapter is a review about sugarcane, one of the most important energy crops. It will describe some aspects of the production system, like varieties, pests and diseases, nutrients requirements, mechanical harvest, residue management and water use. After, sugarcane products and co-products are presented, followed by an energy balance of the production of sugarcane ethanol in Brazil. To finish, an analysis of the land use changes in sugarcane areas is made. About varieties, in the last years, beyond traditional cross breeding, molecular marker techniques and genetic engineering have also been used in genetic improvement programmes. Current improvement faces new challenges, where the objective is to use all parts of the plant that are not normally used to produce energy, as straw, leaves, and the residues and not only the juice extracted in grinding. As a result of these genetic programmes the sugarcane sector is a model in the gain of production (tons per hectare; litres per ton) and in the employment of technologies that reduce the use of chemical defensives, as, for instance, the biological control of pests. Those programs were successful in introducing materials resistant or tolerant to the main pests and diseases that affect sugarcane. In addition, it is expected that the use of transgenic cultivars will result in a greater reduction in the use of defensives, though environmental impacts should be better defined. In spite of the success, new pests and diseases, like Telchin licus licus and orange rust, have appeared, posing new challenges. Sugar cane cultivation culture is considered relatively efficient in using nutrients – the mean dose of mineral fertilizer used is 408 kg/ha, similar to that of several other crops with much smaller productions of biomass per area. One important aspect for this rational use of fertilizers is nutrient recycling, common in sugarcane agroindustry, by returning solid and liquid residues, such as filter cakes, ashes, straw, and, especially, vinasse. Also, the biological nitrogen fixation (BNF) has an important role in the nitrogenous nutrition of sugarcane in Brazil, and in the world. In the industry, rational water use has been adopted. The industry requirement for water has dropped from 5 m3 per ton to 1.83 m3 per ton of sugarcane; reaching 1.23 m3 of water per ton. Mills with the best management practices replace only 500 litres of water in the industrial system, with a recycling rate of 96.67 %. The sugarcane production system and the processing of its main products, sugar and alcohol, generates a significant number of co-products that have high added value. In addition to vinasse and filter cake, the bagasse is the co-product most used in the agroindustrial system of sugarcane. It is mainly used to produce energy. Basically all the thermal energy, and about 95% of the electric energy, is produced at the mill with co-generation systems using the bagasse. The estimation of the total fossil energy used in the field operations is 12329.7 MJ ha−1 year−1. Considering that one litre of ethanol produces 21.45 MJ of energy in the combustion, one hectare of sugarcane currently producing an average 6510 L of ethanol could generate 139639.0 MJ of energy, approximately 11 times the fossil energy invested in the agricultural operations. In addition to the energy balance, analysis of the process of land use change must be made. Studies recently conducted show that, in Brazil, sugarcane production is localized and expanding in areas that have been designated for agricultural production since long ago. The projections indicated that sugarcane expansion will continue in those areas. This means that there is no sugarcane expansion in the agricultural frontier. An Agroecological Zoning analysis for Sugarcane showed that the country has about 64.7 million hectares of land that is suitable for the expansion of sugarcane cultivation. And, to supply the market for the conditions in the year 2020, the additional area needed for the production of sugarcane will be of approximately 5.1M ha. Also, it is expected for the year 2020 that there will be a net reduction of approximately 100 kg CO2 eq m−3 of ethanol, in the emissions associated with the land use change in Brazil. Combining these facts, it is observed that sugarcane expansion in Brazil has a great chance of being conducted in a way that is less harmful to the environment, with land use changes that allow for a smaller emission of greenhouse gases and greater sustainability of the adopted production systems.