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Ethanol derived from sugarcane (Saccharum officinarum) could replace a substantial amount of fossil fuel in Brazil, provided the greenhouse gas (GHG) budget is balanced. Green harvest systems have significantly increased the potential amount of sugarcane residue (straw) available for harvest and bioenergy production, but several questions about how those practices will affect field GHG fluxes. In this sense, we quantified GHG emissions associated with four straw harvest rates (12 [no removal]; 6 [moderate removal]; 3 [high removal] and 0 Mg ha−1 [total removal] of dry matter of straw left on the soil), with and without 100 L ha−1 vinasse + N-fertilizer [80 kg ha−1 (NH 4) 2 SO 4 ]. GHG fluxes were measured for 60 days using static chambers. Our results showed that total straw removal reduced CO 2 and N 2 O emissions by 15% and 25%, respectively. After vinasse and fertilizer additions, CO 2 emissions were 2.5-fold higher, and N 2 O were 5-fold higher, regardless of straw rates. In additional, synergic effect of vinasse + fertilizer and straw removal decreased 60% CH 4 uptakes. Direct N2O emission factor was estimated at 0.32%. Net GHG emissions induced by vinasse + fertilizer applied in the sugarcane plantation were 220 g m−2 CO 2 e (or 60 g m−2 C-equivalent), disregarding straw harvest rate. Therefore, we conclude that maintaining at least 6 Mg ha-1 of sugarcane straw in the field will result in a 'win-win situation' by mitigating GHG emissions, sustaining soil, and still saving part of the raw-material for bioenergy production. • Total removal reduced emissions associated with CO2 by 15% and N2O, by 15%. • Vinasse + fertilizer increase CO2 emissions in 2.5 times and N2O, 5 times, regardless of straw harvest rates. • Direct N2O emission factor was estimated at 0.32%. • Net GHG emissions induced by vinasse + N-fertilizer were 220 g m-2 CO2e disregarding straw harvest rate. • Straw harvest rate did not alter the GHG emission. [ABSTRACT FROM AUTHOR]

Abstract Straw dead stock is a key driver for crop residue management decisions regarding bioenergy production. Therefore, a field study was conducted to evaluate the sugarcane straw decomposition under different straw removal rates, characterize straw composition changes, and quantify the straw-derived C and N loss. Four sugarcane straw removal rates were evaluated: no removal (14.0 Mg ha−1 of DM), 25 (10.5 Mg ha−1 of DM), 50 (7.0 Mg ha−1 of DM) and 75% (3.5 Mg ha−1 of DM) of straw removal. Our results showed that straw removal rate had no effect on first year of straw deposition, but during the second year, the lowest decomposition was associated with higher straw removal rates. Dry mass loss was also approximately 25% higher in the second year than in the first. Furthermore, carbon and nitrogen loss were two- and threefold higher in the first year compared to the second year of deposition. Overall, cellulose and hemicellulose decreased by 13 and 7%, respectively, while lignin increased proportionally by 92% during the two year experiment. Our findings suggest that the most appropriate removal rate to maintain soil quality and meet the demands for energy production is 50% of the total straw deposited on the soil. Highlights • We tracked the sugarcane straw decomposition over two years under Brazilian conditions. • The lowest decomposition was associated with higher straw removal rates. • Straw removal did not impact the relative C and N losses. • The effects of removal rates on straw C:N ratio was site-specific. • C:N ratio, cellulose and hemicellulose content would be important predictors of decomposition changes. [ABSTRACT FROM AUTHOR]

The conversion of agricultural residues into biochar produces a material with agronomic and environmental benefits. Biochars have been found to positively or negatively affect soil greenhouse gas (GHG) emissions, with the variability being explained by differences in biochar properties and environmental conditions. This study evaluated the effect of soil moisture conditions on the emissions of GHGs from soils amended with different types of biochar. For that, we added biochars to a sandy soil and incubated the samples at 23 °C for 90 days under two moisture conditions. While CH 4 fluxes remained not significantly different from zero in all treatments, CO 2 effluxes were stimulated at higher soil moisture contents, though the stimulating effect varied with biochar type. Soils amended with biochars with a narrow C:N ratio showed a higher CO 2 efflux than soils amended with biochars with a wide C:N ratio. There were significant main effects of pyrolysis temperature and soil moisture conditions on the N 2 O fluxes from the treatments, however total N 2 O fluxes from biochar amended soils were overall not significantly different from the control due to treatment interactions. Our study indicates that the main effect of biochars on the GHG balances of soils is related to an increase in soil C stocks, with little short-term changes in soil CH 4 and N 2 O fluxes. Nevertheless, short-term increases in GHG emissions due to biochar addition to soils can be easily mitigated by use of biochars with high C:N ratios produced under high temperatures and by avoiding application to moist soils. [ABSTRACT FROM AUTHOR]

Sugarcane straw has been identified as an important feedstock to increase bioenergy production. However, changes in greenhouse gas (GHG) emissions due to straw removal are not yet understood. We hypothesized that partial straw removal changes decomposition rates and could change GHG fluxes. We performed a field experiment within the largest sugarcane-producing region of Brazil (São Paulo state) to assess GHG fluxes and straw decomposition. The treatments were: no-removal – 12 Mg ha −1 left on soil surface; medium removal – 6 Mg ha −1 ; high removal – 3 Mg ha −1 ; and total removal – bare soil. Static chambers were used to quantify GHG fluxes, and straw decomposition was measured using bottomless plastic boxes over a period of 180 days. Our findings showed that GHG were affected by the straw removal, although daily emissions were highly variable. Cumulative CO 2 and N 2 O emissions were 35–45% lower under bare soil compared to other removal; however under no removal the CH 4 uptake was 40% higher compared to bare soil. High straw decomposition was found in the no-removal, which decreased with the removal intensity. C released by straw decomposition was estimated between 0.5 and 3.1 Mg ha −1 . By analyzing the C balance in C equivalent (Ceq) between decomposition and emissions we estimated that about 3.5 Mg ha −1 of straw are necessary to neutralize GHG emissions from soil and straw decomposition. Finally, we suggest that medium straw (∼6 Mg ha −1 ) maintenance would be a suitable strategy to increase bioenergy production and preserves adequate soil cover, as well as offsetting losses in soil C stocks. [ABSTRACT FROM AUTHOR]

Cellulosic ethanol derived from sugarcane straw may have a significant role to play in the projected increase of Brazilian biofuel production for next years. However, some practical challenges, such as, defining how much and how to recover straw from the field still need to be overcome. Integrated sugarcane harvesting ( i.e . stalks plus straw) with straw separation at the processing site has shown greater cost-effectiveness. However, there is no published procedure to quantify the yield of sugarcane straw, to set up the harvester to collect only a specific portion of this straw or to verify the quantity of straw left in the field. We conducted four field trials in the southeast of Brazil to develop systematic field guidelines that describe how to estimate the yield of sugarcane straw, the harvester setup to vary the amount of straw left in the field and how to evaluate the overall performance of the operation. The results showed that these guidelines were efficient (r 2 ≥ 0.97, p < 0.01) and, therefore, can be incorporated into a standard protocol to help the sugarcane industry improve the efficiency of the sugarcane straw harvesting process for bioelectricity cogeneration and cellulosic ethanol production. [ABSTRACT FROM AUTHOR]