Agronomic, economic, and environmental assessment of site-specific fertilizer management of Brazilian sugarcane fields

Precision agriculture (PA) is an essential tool for site-specific management of soil fertility in sugarcane fields. However, the complexity of the cropping system, limitations on data handling, availability of adequate equipment and the lack of appropriate decision support systems limit the adoption of PA by the sugarcane industry. The objective of this study was to verify the potential economic, environmental and yield gains provided by the site-specific management of soil fertility in the sugarcane industry. A field experiment was conducted over four years, using conventional soil analysis, yield monitor data and variable rate application of lime, nitrogen (N), potassium (K) and phosphorus (P). After two years of variable rate application of fertilizer, available phosphorus (P) content was better distributed, stable, and sufficient to meet crop needs. Maps of potassium (K) rates changed each year, and K content reduced over the years, demonstrating that plant uptake of K was higher than applied. Results showed that applying fertilizer according to the spatial variability of soil can produce better economic and environmental gains, despite the similar average yield (∼80 Mg ha¯¹ year¯¹) when compared with a field managed according to mill procedures. Maps of yield and soil fertility are a powerful tool for sugarcane management, providing useful information about nutritional requirements based on spatial variation of soil fertility. The economic-environmental assessment performed in this study showed that the site-specific management provides improved soil fertility and sustainability indicators, contributing to higher profitability and low environmental impacts

Assessment of sugarcane trash for agronomic and energy purposes in Brazil

Due to new possibilities for using sugarcane (Saccharum spp.) trash for electricity generation, and the production of 2nd 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.70530531