Due to new possibilities for using sugarcane (Saccharum spp.) trash for electricity generation, and the production of 2 nd generation ethanol and others chemicals, the interest for its recovery has increased. However, the question of how much trash can be removed from sugarcane field still needs to be clarified. This study evaluated the amount of dry matter, nutrients content, structural compounds and efficiency of the enzymatic hydrolysis of the hydrothermal pretreated materials for tops and dry leaves in samples from sugarcane varieties. Tops and dry leaves present differences in nutrients content and moisture. Therefore, the amount of trash to be collected should not be simply based on percentages, but also should take into account the different fractions of the crop residues. For instance, around 80 % of N, P and K were derived from tops. Therein, the environmental indicators of the entire chain of sugarcane could be benefited because more nutrients would be recycled and less mineral fertilizers might be used for sugarcane production if tops are left on the field. Further, the tops have seven times more moisture than dry leaves and higher amounts of extractives (organic compounds of low molecular weight). Moreover, as the result of yield obtained in the pretreatment steps for dry leaves were superior to the tops and the glucose yields obtained in the enzymatic hydrolysis step were similar, it can be predicted that for second generation ethanol production, it is more viable to recover parts of the dry leaves fraction, leaving the tops on the field.

No abstract

Sugarcane straw, consisting of green tops and dry leaves, can be maintained on fields to improve soil quality, or harvested for bioenergy production. The optimum option between these two uses is still uncertain and requires further study. This study, conducted across three crop cycles, provides an assessment of the moisture, nutrients, ash, extractives, cellulose, hemicelluloses, and lignin contents of four sugarcane varieties across seven regions of south‐central Brazil. Suitability of the straw fractions for nutrient recycling, bioelectricity, and second‐generation ethanol production were also evaluated. Results showed that the sugarcane straw yield (dry mass) was 14.0 Mg ha−1, and the ratio of dry straw/fresh stalk was 12%. The composition of green tops and dry leaves differed consistently across varieties, sites, and crop cycles. Dry leaves represented 60% of the straw, but green tops contained about 70% of the total N, P, and K content. Therefore, green tops recycled up to four times more nutrients than dry leaves. Green tops also had six times higher moisture and greater chlorine content which decreased the mill process efficiency. In turn, dry leaves had higher lignin, cellulose, and hemicelluloses content, greater heating value (higher: 17.3 MJ kg−1; lower: 15.6 MJ kg−1) and tended to be a better second‐generation ethanol production feedstock. Overall, the results show that it is preferable to use dry leaves for bioenergy production while leaving green tops on the field for nutrient recycling. This study pointed out that more efficient methods for separating these fractions in the field need to be developed. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd