The use of sugarcane straw is a promising option to enhance bioenergy production. But the implications of straw removal for soil greenhouse gas (GHG) emission are not yet fully understood due to scarcity of studies under Brazilian conditions. Four field experiments were designed to assess soil N 2 O and CH 4 emissions derived from nitrogen (N) fertilization under scenarios of sugarcane straw removal in São Paulo state, Brazil. Our focus was also to derive the direct N 2 O emission factor (EF) that represents the regional conditions of sugarcane production, taking into account the data obtained from this study and those from the literature. In each field study, four straw removal rates (no removal (NR); low removal (LR)-removal of 5 Mg ha −1 ; high removal (HR)-removal of 10 Mg ha −1 ; and total removal (TR)-removal of 15 Mg ha −1) were arranged in a randomized block design. This study shows a clear evidence that CH 4 fluxes are very low for all assessed sites regardless of straw removal rates, indicating a predominance of CH 4 consumption by the soil. Cumulative N 2 O emissions ranged from 0.20 to 4.09 kg ha −1 year −1 and were significantly affected by straw removal in two sites, indicating that straw removal reduces N 2 O emissions. The average direct N 2 O EFs obtained from this study and from the literature were 0.28, 0.44, 0.70, and 0.56% for TR, HR, LR, and NR treatments, respectively, which are consistently lower than the EF of 1% suggested by the IPCC. Based on our regional-specific EF (Tier 2), the direct N 2 O emissions derived from N fertilization under scenarios of straw removal showed a reduction of at least 50% in relation to IPCC approach. Our findings are a step forward in providing regional-specific data to reduce the high level of uncertainty concerning N 2 O emission assessments of sugarcane ethanol in Brazil, but further studies are needed to evaluate how straw removal for bioenergy production and the associated changes in soil organic carbon stocks affect the GHG balance of sugarcane. Keywords Saccharum spp.. CH 4 emissions. N 2 O emissions. N 2 O emission factor. IPCC methodology. Tier 2. Crop residues
Sugarcane cultivation uses many chemical inputs to ensure good yields, which puts local water resources under pressure. Grey water footprint (GWF) is a widely used indicator of the volume needed to assimilate a pollutant load in a water body. However, the GWF relies on leaching runoff fractions, which are empirically determined. We hypothesize that these fractions might not represent the true magnitude of the Brazilian sugarcane environment and that management practices can further reduce this fraction loaded into the environment. In two field trials, we measure the herbicides and nitrate loaded into the environment through in situ measurements, determine their loss fractions, compare them with some empirical models, calculate the GWF, and estimate the potential for nitrate pollution attenuation with the adoption of split and incorporated nitrogen application. Both hypotheses are confirmed. For nitrate, our results suggest that the leaching runoff fraction used in most GWF studies is overestimated by about two times, impacting the GWF estimation for the Brazilian sugarcane environment. However, the same conclusion was not possible for herbicides due to the low diversity of the analyzed molecules. In addition, the fertilizer management application reduced the nitrate load on the environment, which the GWF did not necessarily detect.
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