N2O emissions and nitrogen dynamics of winter rapeseed fertilized with different N forms and a nitrification inhibitor
Winter oilseed rape is one of the most important crops in Germany. However, due to intensive nitrogen (N) fertilization, nitrous oxide (N2O) emissions can occur, which may negatively affect the greenhouse gas (GHG) balance of biodiesel produced from rapeseed oil. Therefore, various field experiments were performed during 2013 to 2016 to investigate the influence of different N forms (ammonium sulphate nitrate and urea) as well as the use of a nitrification inhibitor (NI) on the harvest yields, N uptake, soil mineral nitrogen (SMN) dynamics and N2O emissions during the cultivation of winter rapeseed. At a N fertilization level of 220 kg ha−1 and seed yields of up to 6.0 Mg ha−1, the N2O-N emissions during the crop growing period were relatively low, i.e., within the range of 200 and 2300 g ha−1. The oil yield of the various N forms did not differ significantly. Concerning SMN dynamics, the nitrate values in the urea treatments were mostly lower than in the ammonium sulphate nitrate (ASN) plots. Although being on a relatively low level, the bulk of N2O emissions occurred between flowering and maturity of plants. N surpluses in plants fertilized with urea were highest, but in contrast these treatments showed the lowest measured N2O emissions within the fertilized plots. N2O-N emissions during the different seasons averaged 360 g ha−1 in the unfertilized control treatment. In the fertilized treatments, 770 g N2O-N emitted in the single schedule treatment with urea+NI, respectively 790 g ha−1 N2O-N in the urea+NI treatment with a split fertilization, moreover 1110 g ha−1 in the urea treatment without NI and 1450 g ha−1 in the plots fertilized with ammonium sulphate nitrate. The results show that the choice of the form of N and use of nitrification inhibitors at this site represent an approach for the abatement of nitrous oxide fluxes. This potential should be enhanced to fulfil the sustainability requirements of the European Union (EU RED) concerning the use of biofuels.
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