Nutrient Cycling in Agroecosystems最新文献

Urine patches from grazing cattle are hotspots of nitrous oxide (N₂O) emissions. The default IPCC emission factor for urine patches (EF_urine) is 0.77% for wet climates and 0.32% for dry climates. However, literature reports a considerable range of cattle urine EF values and urine characteristics used in experimental studies, revealing contrary results on the effects of urine patch characteristics and seasonal pattern. Therefore, we examined N₂O emissions and corresponding EF_urine values in relation to urine patch characteristics (urine N concentration, urine volume, patch area, urine composition) and environmental drivers (precipitation, water filled pore space, soil temperature). Ten artificial urine application experiments were performed from July 2020 to June 2022 on a pasture located in Eastern Switzerland. Urine N concentration, patch area, volume and urine N composition showed no significant effects on the EF_urine value (p > 0.05). EF_urine varied, however, strongly over time (0.17-2.05%). A large part of the variation could be predicted either by cumulative precipitation 20 days after urine application using a second order polynomial model (Adj. R² = 0.60) or average WFPS 30 days after urine application using a linear model (Adj. R² = 0.45). The derived precipitation model was used to simulate EF_urine weekly over the last 20 years showing no significant differences between the seasons of a year. The resulting overall average EF_urine was 0.67%. More field studies are needed across sites/regions differing in climate and soil properties to implement a country-specific EF₃ for Switzerland and to improve the quantification of N₂O emissions at the national scales.

In recent years, many peatlands in Europe have been rewetted for nature conservation and global warming mitigation. However, the effects on emissions of the greenhouse gas nitrous oxide (N₂O) have been found to be highly variable and driving factors are poorly understood. Therefore, we measured N₂O fluxes every two weeks over three years on pairs of sites (one drained, one rewetted) of three important peatland types in North-Eastern Germany, namely, percolation fen, alder forest and coastal fen. Additionally, every three months, sources of N₂O were determined using a stable isotope mapping approach. Overall, fluxes were under the very dry conditions of the study years usually small with large temporal and spatial variations. Ammonium concentrations consistently and significantly correlated positively with N₂O fluxes for all sites. Cumulative fluxes were often not significantly different from zero and apart from the rewetted alder forest, which was always a source of N₂O, sites showed varying cumulative emission behavior (insignificant, source, potentially sink in one case) among years. Precipitation was positively correlated with cumulative fluxes on all drained sites and the rewetted alder forest. Isotope mapping indicated that N₂O was always produced by more than one process simultaneously, with the estimated contribution of denitrification varying between 20 and 80%. N₂O reduction played a potentially large role, with 5 to 50% of total emissions, showing large variations among sites and over time. Overall, neither the effect of rewetting, water level nor seasonality was clearly reflected in the fluxes or sources. Emissions were concentrated in hotspots and hot moments. A better understanding of the driving factors of N₂O production and reduction in (rewetted) fens is essential and stable isotope methods including measurements of ¹⁵N and ¹⁸O as well as site preferences can help foster the necessary comprehension of the underlying mechanisms.

Supplementary information: The online version contains supplementary material available at 10.1007/s10705-022-10244-y.

During the last decades, Alnus viridis has expanded over former montane pastures and meadows, due to land use and abandonment. This nitrogen-fixing woody species has triggered negative agro-environmental impacts, such as nitrogen (N) leaching, soil acidification and a reduced biodiversity. The aim of this study was to estimate the N translocation from A. viridis-encroached areas to adjacent open pastures by Highland cattle. In 2019 and 2020, Highland cattle herds equipped with GPS collars were placed in four A. viridis-encroached paddocks across Italy and Switzerland. The N content was measured in A. viridis leaves, herbaceous vegetation, and cattle dung pats, which were collected throughout the grazing season. Using GPS locations and collar activity sensors, livestock activity phases were discriminated. The N ingested by cattle was estimated through the N content of herbaceous vegetation and A. viridis leaves of vegetation patches visited by cattle during 24 h before dung sampling (N_24H). The N content of herbaceous vegetation significantly increased with increasing A. viridis cover. The average N content in dung pats (31.2 ± 3.4 g.kg^-1 DM) was higher than average values from literature on grazing cattle. Moreover, it was positively related to the N_24H. Most of this N (29.5 ± 10.3 kg ha^-1 yr^-1) was translocated towards resting areas, which generally occurred on flat open pastures. Our results highlight the potential of Highland cattle to effectively translocate part of the ingested N from A. viridis-encroached towards targeted open areas, thus bringing new perspective for forage yield and quality improvement in the long-term.

Supplementary information: The online version contains supplementary material available at 10.1007/s10705-023-10282-0.