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FAPESP BIOENERGY PROGRAM - BIOEN

The BIOEN Program aims to integrate comprehensive research on sugarcane and other plants that can be used as biofuel sources, thus assuring Brazil’s position among the leaders in the area of Bioenergy. Research includes from biomass production and processing to biofuel production and its impacts.
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Ecology and Sustainability of Biofuels

Evan H. DeLucia

 

Managing global climate change and obtaining a sustainable supply of clean energy represent two of the greatest challenges facing society. Biofuels, particularly those derived from plants, are touted as a way to meet these challenges. In many cases, large scale deployment of biofuel crops (feedstocks) represent a major change in current land use practices that potentially alters the biogeochemical cycles of carbon, nitrogen and water. A thorough understanding of the ecological consequences of the deployment of biofuel crops is essential for understanding their sustainability. We have established side-by-side experimental plots of four biofuel crops (maize, switchgrass, miscanthus, mixed prairie) to quantify their effects on biogeochemical processes. Initial results during the establishment phase suggest that second generation feedstocks (switchgrass, miscanthus, prairie) provide ecological benefits when planted in areas currently used for row crop agriculture (maize and soybean), including restoring soil carbon and reducing nitrogen losses to ground water. A review of life-cycle analyses that quantify the total energy and material costs of producing biofuels from plants revealed enormous inconsistencies but point to unacceptable economic and ecological costs of relying on ethanol production from maize, a so called first generation biofuel. While our initial results suggest that second generation biofuels have the potential to improve the ecology of agricultural landscapes, care must be taken to fully understand the consequences of removing land from grain production on world food security.

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Contributions of Land Use Change to the Greenhouse Gas Budget of Biofuels

Kristina J. Anderson-Teixeira

 

Mitigation of climate change through reduced greenhouse gas (GHG) emissions is a primary motivation for biofuel cultivation. It is therefore critical to quantify the uptake or release of GHG’s that occurs as a result of biofuel-associated land use change (delta GHG luc). We delineate the terms that contribute to delta GHG luc and show that current life cycle analyses of liquid biofuels fail to account completely for the GHG effects of land use change. To fully quantify delta GHG luc, we quantify the GHG values of pertinent ecosystem types in terms of both storage of materials that would be released as GHG’s upon land clearing and annual fluxes of CO2, CH4, and N2O. We show that delta GHG luc is substantial and generally underestimated in life cycle analyses, and that it will often determine whether or not GHG emissions can be reduced through biofuel cultivation.

One important element of delta GHG luc is the change in soil organic carbon (SOC) that occurs upon conversion of natural or agricultural land to biofuel crops. We assembled estimates of changes in SOC under corn with residue harvest, sugarcane, Miscanthus x giganteus, switchgrass, and restored prairie. We show that conversion of uncultivated land to biofuel agriculture results in significant SOC losses, which would counteract the benefits of fossil fuel displacement. Corn residue harvest consistently results in SOC losses, implying that its potential to offset C emissions may be overestimated. In contrast, SOC accumulates under all four perennial grasses, with SOC accumulation rates averaging <1 Mg ha-1 yr-1 in the top 30 cm. Thus, SOC sequestration under perennial grasses represents an additional benefit that has rarely been accounted for in life cycle analyses of biofuels.

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Variations in C stock and GHG  emissions in tropical and subtropical soils of Brazil

Urquiaga Segundo, Jantalia Claudia P., Alves Bruno J.R., Boddey Robert M.

 

In Brazil, conventional tillage (CT), based on ploughing the soil at least once a year, has contributed to soil degradation such that nowadays it is necessary to apply more agricultural inputs to maintain productivity. This phenomenon is related to the effect of soil disturbance provoked by tillage on stimulating the decomposition of soil organic carbon (SOC) and reducing other favorable physical and chemical soil properties. For these reasons the zero-tillage system (ZT) that preserves crop residues on the soil surface, and makes an important contribution to control soil erosion, is seen today not only as a means to promote sustainable agriculture, but also to mitigate the emission of CO2 to the atmosphere. Until a few years ago, there was a general consensus that where reduced or zero tillage had been adopted, SOM levels will increase with time, but recently, this consensus has been challenged by Baker et al. (2007) who suggested that the conclusion that the adoption of ZT stimulates soil C sequestration was probably an artefact of the fact that soil sampling in most studies had been limited to only 20 to 30 cm depth. However, recent studies in Brazil where soils were sampled to 80 or 100 cm depth, show conclusively that in medium to high productivity systems when the cropping system showed a positive N balance, soil C accumulation can reach or exceed 1 Mg ha-1 year-1 for at least 10 years, significantly higher when only the surface layers of the soil were sampled. For the system to have a positive N balance it is necessary that the external inputs of N to the system (fertiliser N and BNF) exceed the N exported in grain or lost by leaching or in gaseous forms. In these studies the N balances were positive because of the presence in the crop rotations of N2-fixing leguminous cover crops such as lupins, vetch or clover. In tropical pastures, significant C accumulation was only observed when the grass pasture showed good productivity or was associated with a legume pasture (e.g. S. guianensis). In the case of the sugar cane crop, the traditional pre-harvest burning (actually applied in 60% of Brazilian sugar cane area) had little affect on the stock of SOC. Under this condition roots of this crop contributed significantly replacement the natural losses of the original SOC, as demonstrated by 13C studies. It is important to point out that in the case of this crop almost 4.5 Mg C ha-1 @page { size: 8.5in 11in; margin: 0.79in } P { margin-bottom: 0.08in } --> are left in the soil profile each year. From this one may deduce that the sugar cane trash that is being burned in the field without any direct benefit to the crop, but contributing to CH4 emission, could be used in the co-generation of electrical energy in the same manner as residual bagasse is used in some modern mills. This process can contribute also to increase the actual high value of the sugar cane crop as a source of bioenergy. On the other hand, effective practices to increase the stock of SOC must be accompanied by the evaluation of its impact on the GHG emissions, since in many situations this can neutralize any positive advantage of the increase of SOC in the soil profile. This is especially important in the sugar cane crop used to produce ethanol where substituting pure gasoline results in avoided GHG emission of approximately 80%. Recent studies carried out in representative Oxisols and Ultisols have indicated that the emission factors for N2O vary from 4 to 6 times less than the proposed by the IPCC. This behaviour of Brazilian soils is associated with good drainage and high water evaporation rate which contribute to reduce the time that soils are water saturated, which is necessary for the production of N2O and CH4.

 

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