Lysimeter-based full fertilizer 15N balances corroborate direct dinitrogen emission measurements using the 15N gas flow method

The $^{15}$N gas flux ($^{15}$NGF) method allows for direct in situ quantification of dinitrogen (N$_2$) emissions from soils, but a successful cross-comparison with another method is missing. The objectives of this study were to quantify N$_2$ emissions of a wheat rotation using the $^{15}$NGF method, to compare these N$_2$ emissions with those obtained from a lysimeter-based $^{15}$N fertilizer mass balance approach, and to contextualize N$_2$ emissions with $^{15}$N enrichment of N$_2$ in soil air. For four sampling periods, fertilizer-derived N$_2$ losses ($^{15}$NGF method) were similar to unaccounted fertilizer N fates as obtained from the $^{15}$N mass balance approach. Total N$_2$ emissions ($^{15}$NGF method) amounted to 21 ± 3 kg N ha− 1, with 13 ± 2 kg N ha− 1 (7.5% of applied fertilizer N) originating from fertilizer. In comparison, the $^{15}$N mass balance approach overall indicated fertilizer-derived N$_2$ emissions of 11%, equivalent to 18 ± 13 kg N ha− 1. Nitrous oxide (N$_2$O) emissions were small (0.15 ± 0.01 kg N ha− 1 or 0.1% of fertilizer N), resulting in a large mean N$_2$:(N$_2$O + N$_2$) ratio of 0.94 ± 0.06. Due to the applied drip fertigation, ammonia emissions accounted for < 1% of fertilizer-N, while N leaching was negligible. The temporal variability of N$_2$ emissions was well explained by the δ$^{15}$N$_2$ in soil air down to 50 cm depth. We conclude the $^{15}$NGF method provides realistic estimates of field N$_2$ emissions and should be more widely used to better understand soil N$_2$ losses. Moreover, combining soil air δ$^{15}$N$_2$ measurements with diffusion modeling might be an alternative approach for constraining soil N$_2$ emissions

The Spatial Distribution of the Microbial Community in a Contaminated Aquitard below an Industrial Zone

The industrial complex Neot Hovav, in Israel, is situated above an anaerobic fractured chalk aquitard, which is polluted by a wide variety of hazardous organic compounds. These include volatile and non-volatile, halogenated, organic compounds. In this study, we characterized the indigenous bacterial population in 17 boreholes of the groundwater environment, while observing the spatial variations in the population and structure as a function of distance from the polluting source. In addition, the de-halogenating potential of the microbial groundwater population was tested through a series of lab microcosm experiments, thus exemplifying the potential and limitations for bioremediation of the site. In all samples, the dominant phylum was Proteobacteria. In the production plant area, the non-obligatory organo-halide respiring bacteria (OHRB) Firmicutes Phylum was also detected in the polluted water, in abundancies of up to 16 %. Non-metric multidimensional scaling (NMDS) analysis of the microbial community structure in the groundwater exhibited clusters of distinct populations following the location in the industrial complex and distance from the polluting source. Dehalogenation of halogenated ethylene was demonstrated in contrast to the persistence of brominated alcohols. Persistence is likely due to the chemical characteristics of brominated alcohols, and not because of the absence of active de-halogenating bacteria

Fates of slurry-nitrogen applied to mountain grasslands: the importance of dinitrogen emissions versus plant N uptake

Intensive fertilization of grasslands with cattle slurry can cause high environmental nitrogen (N) losses in form of ammonia (NH3), nitrous oxide (N2O), and nitrate (NO3−) leaching. Still, knowledge on short-term fertilizer N partitioning between plants and dinitrogen (N2) emissions is lacking. Therefore, we applied highly 15N-enriched cattle slurry (97 kg N ha−1) to pre-alpine grassland field mesocosms. We traced the slurry 15N in the plant-soil system and to denitrification losses (N2, N2O) over 29 days in high temporal resolution. Gaseous ammonia (NH3), N2 as well N2O losses at about 20 kg N ha−1 were observed only within the first 3 days after fertilization and were dominated by NH3. Nitrous oxide emissions (0.1 kg N ha−1) were negligible, while N2 emissions accounted for 3 kg of fertilizer N ha−1. The relatively low denitrification losses can be explained by the rapid plant uptake of fertilizer N, particularly from 0–4 cm depth, with plant N uptake exceeding denitrification N losses by an order of magnitude already after 3 days. After 17 days, total aboveground plant N uptake reached 100 kg N ha−1, with 33% of N derived from the applied N fertilizer. Half of the fertilizer N was found in above and belowground biomass, while at about 25% was recovered in the soil and 25% was lost, mainly in form of gaseous emissions, with minor N leaching. Overall, this study shows that plant N uptake plays a dominant role in controlling denitrification losses at high N application rates in pre-alpine grassland soils.</p