Nitrous oxide emissions from crop rotations including wheat, oilseed rape and dry peas

[摘要] Approximately 65% of anthropogenic emissions of N₂O, a potentgreenhouse gas (GHG), originate from soils at a global scale, and particularlyafter N fertilisation of the main crops in Europe. Thanks to their capacityto fix atmospheric N₂ through biological fixation, legumes can reduce Nfertilizer use, and possibly N₂O emissions. Nevertheless, thedecomposition of crop organic matter during the crop cycle and residuedecomposition, and possibly the N fixation process itself, could lead toN₂O emissions. The objective of this study was to quantify N₂Oemissions from a dry pea crop (Pisum sativum, harvested at maturity) and from thesubsequent crops in comparison with N₂O emissions from wheat andoilseed rape crops, fertilized or not, in various rotations. A fieldexperiment was conducted over 4 consecutive years to compare the emissionsduring the pea crop, in comparison with those during the wheat (fertilizedor not) or oilseed rape crops, and after the pea crop, in comparison withother preceding crops. N₂O fluxes were measured using static chambers.In spite of low N₂O fluxes, mainly due to the site's soilcharacteristics, fluxes during the crop were significantly lower for pea andunfertilized wheat than for fertilized wheat and oilseed rape. The effect ofthe preceding crop was not significant, while soil mineral N at harvest washigher after the pea crop. These results should be confirmed over a wider range of soil types.Nevertheless, they demonstrate the absence of N₂O emissions linked tothe symbiotic N fixation process, and allow us to estimate the decrease inN₂O emissions by 20–25% through including one pea crop in a three-yearrotation. On a larger scale, this reduction of GHG emissions at field levelhas to be added to the decrease due to the reduced production and transport of the Nfertilizer not applied to the pea crop.

[学科分类] 地球化学与岩石