Emissions of nitrous oxide from arable organic and conventional cropping systems on two soil types

摘要

Conventional cropping systems rely on targeted short-term fertility management, whereas organic systems depend, in part, on long-term increase in soil fertility as determined by crop rotation and management. Such differences influence soil nitrogen (N) cycling and availability through the year. The main objective of this study was to compare nitrous oxide (NO) emissions from soil under winter wheat (Triticum aestivum L.) within three organic and one conventional cropping system that differed in type of fertilizer, presence of catch crops and proportion of N-fixing crops. The study was replicated in two identical long-term crop rotation experiments on sandy loam soils under different climatic conditions in Denmark (Flakkebjergeastern Denmark and Foulumwestern Denmark). The conventional rotation received 165-170kgNhap# in the form of NHNO, while the organic rotations received 100-110kgNhap# as pig slurry. For at least 11 months, as from September 2007, static chambers were used to measure NO emissions at least twice every calendar month. Mean daily NO emissions across the year ranged from 172 to 438og N mpo dp# at Flakkebjerg, and from 173 to 250og N mpo dp# at Foulum. A multiple linear regression analysis showed inter-seasonal variations in emissions (P <0.001), but annual NO emissions from organic and conventional systems were not significantly different despite the lower N input in organic rotations. The annual emissions ranged from 54 to 137mgNmpo, which corresponded to 0.5-0.8% of the N applied in manure or mineral fertilizer. Selected soil attributes were monitored to support the interpretation of NO emission patterns. A second multiple linear regression analysis with potential drivers of NO emissions showed a negative response to soil temperature (P =0.008) and percent water-filled pore space (WFPS) (P =0.052) at Foulum. However, there were positive interactions of both factors with NO-N, i.e., high NO emissions occurred during periods when high soil nitrate levels coincided with high soil temperature (P =0.016) or high soil water content (P =0.056). A positive effect (P =0.03) of soil temperature was identified at Flakkebjerg, but the number of soil samplings was limited. Effects of cropping system on NO emissions were not observed.