Short-term effects of biogas digestate and cattle slurry application on greenhouse gas emissions affected by N availability from grasslands on drained fen peatlands and associated organic soils

摘要

pstrongAbstract./strong A change in German energy policy has resulted in a strong increase in the number of biogas plants in Germany. As a consequence, huge amounts of nutrient-rich residues, the by-products of the fermentative process, are used as organic fertilizers. Drained peatlands are increasingly used to satisfy the huge demand for fermentative substrates (e.g., energy crops, grass silage) and the digestate is returned to the peatlands. However, drained organic soils are considered as hot spots for nitrous oxide (Nsub2/subO) emissions and organic fertilization is additionally known to increase Nsub2/subO emissions from managed grasslands. Our study addressed the questions (a) to what extent biogas digestate and cattle slurry application increase Nsub2/subO and methane (CHsub4/sub) fluxes as well as the mineral nitrogen use efficiency (NUEsubmin/sub) and grass yield, and (b) how different soil organic matter contents (SOMs) and nitrogen contents promote the production of Nsub2/subO. In addition NHsub3/sub volatilization was determined at one application event to obtain first clues with respect to the effects of soil and fertilizer types. The study was conducted at two sites within a grassland parcel, which differed in their soil organic carbon (SOC) and N contents. At each site (named Csuborg/sub-medium and Csuborg/sub-high) three plots were established one was fertilized five times with biogas digestate, one with cattle slurry, and the third served as control plot. On each plot, fluxes of Nsub2/subO and CHsub4/sub were measured on three replicates over 2 years using the closed chamber method. For NHsub3/sub measurements we used the calibrated dynamic chamber method. On an annual basis, the application of biogas digestate significantly enhanced the Nsub2/subO fluxes compared to the application of cattle slurry and additionally increased the plant N-uptake and NUEsubmin/sub. Furthermore, Nsub2/subO fluxes from the Csuborg/sub-high treatments significantly exceeded Nsub2/subO fluxes from the Csuborg/sub-medium treatments. Annual cumulative emissions ranged from 0.91 ?± 0.49 to 3.14 ?± 0.91 kg N hasupa??1/sup yrsupa??1/sup. Significantly different CHsub4/sub fluxes between the investigated treatments or the different soil types were not observed. Cumulative annual CHsub4/sub exchange rates varied between −0.21 ?± 0.19 and −1.06 ?± 0.46 kg C hasupa??1/sup yrsupa??1/sup. Significantly higher NHsub3/sub losses, NUEsubmin/sub and grass yields from treatments fertilized with biogas digestate compared to those fertilized with cattle slurry were observed. The total NHsub3/sub losses following the splash plate application were 18.17 kg N hasupa??1/sup for the digestate treatments and 3.48 kg N hasupa??1/sup for the slurry treatments (36 and 15% of applied NHsub4/subsup+/supa??N). The observed linear increase of 16 days' cumulative Nsub2/subOa??N exchange or annual Nsub2/subO emissions, with mean groundwater level and ammonium application rate, reveals the importance of site-adapted N fertilization and the avoidance of N surpluses in Csuborg/sub-rich grasslands./p.