Comparing first- and second-generation bioethanol by-products from sugarcane: Impact on soil carbon and nitrogen dynamics

Abstract The first- and second-generation bioethanol by-products (bagasse and fermentation by-product, respectively) have different biochemical characteristics relating to carbon (C) and nitrogen (N) due to their production processes. To examine the impacts of fermentation by-product and bagasse on soil C and N dynamics, a 120 day laboratory incubation experiment was conducted by applying these amendments in soil at an equal carbon application rate (2.2 g C kg−1 soil). There was a significant increase in overall cumulative CO2-C production from amended soil compared to the control soil, though the loss was greatest in bagasse amended soil. However, δ13C-CO2 measurements suggested that fermentation by-product addition suppressed native soil C mineralization and prompted strong negative C priming (−57%). In contrast, bagasse amendment maintained similar native soil C mineralization to control soil. Decreased microbial biomass turnover time appears to be the major driving force for increased CO2-C production and soil C loss following bioethanol by-product amendments. Increased mineral N production indicated net N mineralization after fermentation by-product addition, while addition of bagasse resulted in lower N availability and N immobilization. Overall, results suggested that fermentation by-product application is advantageous in maintaining native soil C stock and N mineralization compared to bagasse. Thus, in a sustainable second-generation bioethanol production system, bagasse may be used for second-generation bioethanol production and the cogenerated by-product could be used as an amendment to improve soil C stock and N availability.