Greenhouse gas emissions in rapeseed cultivation need to be assessed realistically for mitigation
A network of eight partners, coordinated by the Thünen Institute of Climate-Smart Agriculture (Thünen-Institut für Agrarklimaschutz, hereafter TI), investigated greenhouse gas (GHG) emissions from the cultivation of rapeseed. The aim was to find out whether the emissions in the framework of climate protection agreements are estimated realistically for Germany. The result of the project: the nitrous oxide emission factor for GHG accounting in rapeseed is too high for German conditions.
Rapeseed is the most important energy crop for biofuel production in Germany. By far the highest GHG emissions in rapeseed cultivation are caused by field emissions of nitrous oxide and greenhouse gas emissions during the production of the required synthetic nitrogen fertilizer. These two emission sources should therefore be in the focus to ensure compliance with the requirements of the EU (RL EU 2015/1513). According to this regulation, biodiesel and other biofuels must save at least 60% of GHG emissions compared to fossil fuels since 1.1.2018. For the GHG balance, biofuel manufacturers can use EU Renewable Energy Directive (EU) default values or regionalized information on resources such as fertilizer and fuel. The studies by the TI project team have now demonstrated that these values are unrealistic for Germany. The estimated amount of nitrogen fertilizer is too low, and the nitrous oxide emission factor is too high: Instead of the assumed 34 kg nitrogen per tonne of rapeseed, 50 to 56 kg nitrogen per tonne of rapeseed are common practice. The N2O emission factor is not 1.0 percent, but only 0.6 percent of applied nitrogen fertilizer.
In addition, the researchers recommend replacing synthetic fertilizers with organic ones, for example, through digestates, which improved the GHG balance in the project when ammonia emissions were minimized. However, one potential problem is the risk of higher nitrogen surpluses. It is just as important to avoid nitrous oxide emissions and save energy in the production of synthetic fertilizers.
Source: idw (Informationsdienst Wissenschaft)
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