Reducing nitrous oxide emissions by changing N fertiliser use from calcium ammonium nitrate (CAN) to urea based formulations.

The accelerating use of synthetic nitrogen (N) fertilisers, to meet the world's growing food demand, is the primary driver for increased atmospheric concentrations of nitrous oxide (N2O). The IPCC default emission factor (EF) for N2O from soils is 1% of the N applied, irrespective of its form. However, N2O emissions tend to be higher from nitrate-containing fertilisers e.g. calcium ammonium nitrate (CAN) compared to urea, particularly in regions, which have mild, wet climates and high organic matter soils. Urea can be an inefficient N source due to NH3 volatilisation, but nitrogen stabilisers (urease and nitrification inhibitors) can improve its efficacy. This study evaluated the impact of switching fertiliser formulation from calcium ammonium nitrate (CAN) to urea-based products, as a potential mitigation strategy to reduce N2O emissions at six temperate grassland sites on the island of Ireland. The surface applied formulations included CAN, urea and urea with the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) and/or the nitrification inhibitor dicyandiamide (DCD). Results showed that N2O emissions were significantly affected by fertiliser formulation, soil type and climatic conditions. The direct N2O emission factor (EF) from CAN averaged 1.49% overall sites, but was highly variable, ranging from 0.58% to 3.81. Amending urea with NBPT, to reduce ammonia volatilisation, resulted in an average EF of 0.40% (ranging from 0.21 to 0.69%)-compared to an average EF of 0.25% for urea (ranging from 0.1 to 0.49%), with both fertilisers significantly lower and less variable than CAN. Cumulative N2O emissions from urea amended with both NBPT and DCD were not significantly different from background levels. Switching from CAN to stabilised urea formulations was found to be an effective strategy to reduce N2O emissions, particularly in wet, temperate grassland.

Using stable isotopes to follow excreta N dynamics and N2O emissions in animal production systems.

Nitrous oxide (N2O) is a potent greenhouse gas and the dominant anthropogenic stratospheric ozone-depleting emission. The tropospheric concentration of N2O continues to increase, with animal production systems constituting the largest anthropogenic source. Stable isotopes of nitrogen (N) provide tools for constraining emission sources and, following the temporal dynamics of N2O, providing additional insight and unequivocal proof of N2O source, production pathways and consumption. The potential for using stable isotopes of N is underutilised. The intent of this article is to provide an overview of what these tools are and demonstrate where and how these tools could be applied to advance the mitigation of N2O emissions from animal production systems. Nitrogen inputs and outputs are dominated by fertiliser and excreta, respectively, both of which are substrates for N2O production. These substrates can be labelled with 15N to enable the substrate-N to be traced and linked to N2O emissions. Thus, the effects of changes to animal production systems to reduce feed-N wastage by animals and fertiliser wastage, aimed at N2O mitigation and/or improved animal or economic performance, can be traced. Further 15N-tracer studies are required to fully understand the dynamics and N2O fluxes associated with excreta, and the biological contribution to these fluxes. These data are also essential for the new generation of 15N models. Recent technique developments in isotopomer science along with stable isotope probing using multiple isotopes also offer exciting capability for addressing the N2O mitigation quest.

Evidence for the production of NO and N2O in two contrasting subsoils following the addition of synthetic cattle urine.

Nitrogenous materials can be transferred out of the topsoil, either vertically to a greater depth, or in lateral pathways to surface waters, and they may also become transformed, with the potential of generating environmentally active agents. We measured the production of NO and N(2)O in two contrasting subsoils (70 to 90 cm): one poorly drained and the other freely drained and compared this with the topsoil (0 to 20 cm) of the corresponding soils. The soils were incubated aerobically in jars with subtreatments of either synthetic cattle urine or deionised water and sampled at intervals up to 34 days. (15)N-NO(3)(-) was used to determine the processes responsible for NO and N(2)O production. The headspace was analysed for the concentrations of N(2)O, NO and CO(2) and (15)N enrichment of N(2)O. The soil samples were extracted and analysed for NO(2)(-), NO(3)(-) and NH(4)(+), and the (15)N enrichment of the extracts was measured after conversion into N(2)O and N(2). The study demonstrated the potential for NO, N(2)O and NO(2)(-) to be generated from subsoils in laboratory incubations. Differences in these N dynamics occurred due to subsoil drainage class. In the freely drained subsoil the rates of NO and NO(2)(-) production were higher than those observed for the corresponding topsoil, with mean maximum production rates of 3.5 microg NO(2)(-)-N g(-1) dry soil on day 16 and 0.12 microg NO-N g(-1) dry soil on day 31. The calculated total losses of N(2)O-N as percentages of the applied synthetic urine N were 0.37% (freely drained subsoil), 0.24% (poorly drained subsoil), 0.43% (freely drained topsoil) and 2.09% (poorly drained topsoil). The calculated total losses of NO-N as percentages of the applied synthetic urine N were 1.53% (freely drained subsoil), 0.02% (poorly drained subsoil), 0.25% (freely drained topsoil) and 0.08% (poorly drained topsoil).

Nitrite formation and nitrous oxide emissions as affected by reclaimed effluent application.

The effect of irrigation with reclaimed effluent (RE) (after secondary treatment) on the mechanisms and rates of nitrite formation, N2O emissions, and N mineralization is not well known. Grumosol (Chromoxerert) soil was incubated for 10 to 14 d with fresh water (FW) and RE treated with 15NO3- and 15NH4+ to provide a better insight on N transformations in RE-irrigated soil. Nitrite levels in RE-irrigated soil were one order of magnitude higher than in FW- irrigated soil and ranged between 15 to 30 mg N kg(-1) soil. Higher levels of NO2- were observed at a moisture content of 60% than at 70% and 40% w/w. Nitrite levels were also higher when RE was applied to a relatively dry Grumosol (20% w/w) than at subsequent applications of RE to soil at 40% w/w. Isotopic labeling indicated that the majority of NO2 was formed via nitrification. The amount of N2O emitted from RE-treated Grumosol was double the amount emitted from FW treatments at 60% w/w. Nitrification was responsible for about 42% of the emissions. The N20 emission from the RE-treated bulk soil (passing a 9.5-mm sieve) was more than double the amount formed in large aggregates (4.76-9.5 mm in diameter). No dinitrogen was detected under the experimental conditions. Results indicate that irrigation with secondary RE stimulates nitrification, which may enhance NO3 leaching losses. This could possibly be a consequence of long-term exposure of the nitrifier population to RE irrigation. Average gross nitrification rate estimates were 11.3 and 15.8 mg N kg(-1) soil d(-1) for FW- and RE-irrigated bulk soils, respectively. Average gross mineralization rate estimates were about 3 mg N kg(-1) soil d(-1) for the two water types.

Gaseous nitrogen emissions and mineral nitrogen transformations as affected by reclaimed effluent application.

Irrigation with reclaimed effluent (RE) is essential in arid and semiarid regions. Reclaimed effluent has the potential to stimulate gaseous N losses and affect other soil N processes. No direct measurements of the N2 and N2O emissions from Mediterranean soils have been conducted so far. We used the 15N gas flux method in a field and a laboratory experiment to study the effect of RE irrigation on gaseous N losses and other N transformations in a Grumosol (Chromoxerert) soil. The fluxes of N2, N2O, and NH3 were measured from six Grumosol lysimeters following application of either fresh water or RE. The N fertilizer was applied either as 15NH4 or 15NO3. Only up to 0.3% from the applied N fertilizer was lost as N2O + NH3. Reclaimed effluent enhanced the losses of NH3, but did not affect those of N2O. Nitrification and denitrification were equally important to N2O production. Laboratory incubations were performed to both confirm the influence of the irrigation water type and to test the effect of moisture content. Significant quantities of N2 and N2O (up to 3.1% of the applied fertilizer) were emitted from saturated soils. Reclaimed effluent application did not induce higher N2O emissions, yet significantly more (approximately 33%) N2 was emitted from RE-irrigated soils. Denitrification contributed up to 75% of the N2O amounts emitted from saturated soils. Reclaimed effluent application inhibited nitrification in the Grumosol by 15 to 25% and induced NO2 accumulation in soils incubated at a field-capacity moisture content.

Effect of liquid manure on the mole fraction of nitrous oxide evolved from soil containing nitrate.

The same emission factor is applied to fertiliser N and manure N when calculating national N2O inventories. Manures and fertilisers are often applied together to meet the N needs of the crop, but little is known about potential interactions leading to an increase in denitrification rate or a change in the composition of the end-products of denitrification. We used the 15N gas-flux method in a laboratory experiment to quantify the effect of liquid manure (LM) application on the fluxes of N2 and N2O when the soil contained fertiliser 15NO3-. LM increased the mole fraction of N2O from 0.5 to 0.85 in the first 12 h after application. More than 94% of the N2O was from the reduction of NO3-, probably due to aerobic nitrate respiration as well as respiratory denitrification.

Nitrous oxide and dinitrogen emissions from soil under different water regimes and straw amendment.

In a laboratory study, soil amended with and without wheat straw (2.8 g kg(-1) soil) was incubated under 70% water holding capacity (WHC), continuously flooded and flooded/drained cycle conditions at 30 degrees C for 51 days. Dinitrogen and N2O evolution and ammonia volatilisation were measured during the incubation. Extractable NH4+-N and NO3--N were determined at the end of the incubation. Entrapped N2, N2O, and dissolved NH4+-N and NO3--N in drainage water were measured in the flooded/drained cycle treatment when the floodwater was drained. The results indicated that N loss through ammonia volatilisation was undetected in all treatments due to the low soil pH value (pHH2O= 5.87) and no air movement. The recovery of urea-15N as N2 was lowest in the continuously flooded treatments (0.75% and 0.96% with and without straw amendment, respectively), highest in the 70% WHC treatments (5.65% and 4.41%, respectively), and intermediate in the flooded/drained cycle treatments (1.79% and 2.65%, respectively). The recovery of urea-15N as N2O was in the same order as that of N2, negligible in the continuously flooded treatments, 0.01% and 0.07% in the flooded/drained cycle treatments, and 1.29% and 2.23% in the 70% WHC treatments, respectively. Peak N2O evolution rates were observed after the floodwater was drained but no substantial evolution was found after the soil was reflooded following drained periods. However, peak N2 evolution rates were observed after the onset of both drainage and re-flooding. Considerable quantities of N2 but no detectable N2O were entrapped in the flooded soil.

A spatial study of denitrification potential of sediments in Belfast and Strangford Loughs and its significance.

The C2H2 inhibition technique was employed to study seasonal denitrification potential rates in sediment slurries from tidal and subtidal sites in Belfast and Strangford Loughs, Northern Ireland. A comparison of denitrification rates obtained from this method with those obtained from the 15N-gas flux method generally showed good agreement. Depth profiles measured up to 1 m showed that denitrification decreased with depth, with highest values in the 0-5-cm fraction. For the Belfast Lough tidal system a multiple regression model was developed which explained 83% of the variation in denitrification potential. The independent variables were water content, sediment temperature, total oxidizable N in porewater and total organic N. The highest rate of denitrification potential, 2100 micromol N m(-2) h(-1), was found in areas where there was a high anthropogenic input of nutrients. Denitrification in sediments in both loughs can play a potentially significant role in removal of NO3- from the overlying water. In Belfast Lough the overall denitrification potential rate matched the external NO3-N inputs, whilst in Strangford Lough it exceeded it by sixfold, which suggests a potential to remove future additional anthropogenic inputs to the Lough.

Perturbed bioelectrical properties of the mouse cecum following hepatectomy and starvation: the role of bacterial adherence.

Previous work in our laboratory has demonstrated that bacterial adherence alone to the intestinal epithelium, as occurs following catabolic stress, significantly perturbs the normal electrophysiology of the cecal mucosa. The aim of this study was to further characterize these effects in the mouse cecum following hepatectomy and short-term starvation, and to define the role of bacterial adherence in this process. Groups of mice underwent a surgical hepatectomy and were either fed or starved during the postoperative period. Groups of controls underwent sham operations and were either fed or starved postoperatively. Electrophysiologic studies in Ussing chambers at 48 hours were performed. Bacterial adherence to the mucosa was assessed by culture and histologic staining. To determine the role of bacteria in the altered electrophysiologic response, ciprofloxacin decontamination studies were performed. Only mice subjected to both hepatectomy and starvation developed bacterial adherence of sufficient magnitude (>10(5) cfu/gm) to alter mucosal electrophysiology (short-circuit current and basal potential difference). Ciprofloxacin decontamination completely abrogated this effect. Ion replacement studies suggested that active sodium transport was primarily responsible for the observed changes in mucosal electrophysiology. Bacterial-epithelial cell interactions may be responsible for altered mucosal ion transport observed following operative catabolic stress and short-term starvation.

Dissimilatory nitrate reduction in anaerobic sediments leading to river nitrite accumulation.

Recent studies on Northern Ireland rivers have shown that summer nitrite (NO(inf2)(sup-)) concentrations greatly exceed the European Union guideline of 3 (mu)g of N liter(sup-1) for rivers supporting salmonid fisheries. In fast-flowing aerobic small streams, NO(inf2)(sup-) is thought to originate from nitrification, due to the retardation of Nitrobacter strains by the presence of free ammonia. Multiple regression analyses of NO(inf2)(sup-) concentrations against water quality variables of the six major rivers of the Lough Neagh catchment in Northern Ireland, however, suggested that the high NO(inf2)(sup-) concentrations found in the summer under warm, slow-flow conditions may result from the reduction of NO(inf3)(sup-). This hypothesis was supported by field observations of weekly changes in N species. Here, reduction of NO(inf3)(sup-) was observed to occur simultaneously with elevation of NO(inf2)(sup-) levels and subsequently NH(inf4)(sup+) levels, indicating that dissimilatory NO(inf3)(sup-) reduction to NH(inf4)(sup+) (DNRA) performed by fermentative bacteria (e.g., Aeromonas and Vibrio spp.) is responsible for NO(inf2)(sup-) accumulation in these large rivers. Mechanistic studies in which (sup15)N-labelled NO(inf3)(sup-) in sediment extracts was used provided further support for this hypothesis. Maximal concentrations of NO(inf2)(sup-) accumulation (up to 1.4 mg of N liter(sup-1)) were found in sediments deeper than 6 cm associated with a high concentration of metabolizable carbon and anaerobic conditions. The (sup15)N enrichment of the NO(inf2)(sup-) was comparable to that of the NO(inf3)(sup-) pool, indicating that the NO(inf2)(sup-) was predominantly NO(inf3)(sup-) derived. There is evidence which suggests that the high NO(inf2)(sup-) concentrations observed arose from the inhibition of the DNRA NO(inf2)(sup-) reductase system by NO(inf3)(sup-).

Accuracy and precision for measurements of the mass ratio 30/28 in dinitrogen from air samples and its application to the investigation of N losses from soil by denitrification.

Abstract In the 1950s Hauck introduced a special version of the (15)N dilution technique ((15)N flux method) for the determination of N losses from the soil by denitrification. Although this method is very useful and reliable its application has been rather infrequent up to now. This is mainly due to the need to measure the m/z 30 in addition to the usually measured m/z 28 and 29 for dinitrogen, because the (15)N in the enriched air sample taken from an enclosure (cover box) at the soil surface is nonrandom. The signal from the m/z 30 is very low and difficult to measure with sufficient precision because other species (e.g. NO) also having the m/z 30 often interfere with its measurement. In this study the accuracy and precision of an easy to use CF-IRMS with sample batch operation to measure the ratio 30/28 was investigated. The relative standard deviation (RSD = precision) from natural abundance up to 2 at.% was always <1%. After correction of the mass ratio 30/28 (R30), by means of a formula obtained by linear regression of theoretical R30 against measured R30, the accuracy of the abundance calculated from this corrected R30 was very high. From the achieved precision and assuming a cover box height of 10 cm (headspace volume of 7 1), and a collection time of 2 h, a limit of detection for N(2) losses by denitrification equivalent to 16 g N/ha*d or 6 kg N/ha*a can be estimated. The performance of the (15)N dilution method using the equipment and procedure described is demonstrated by means of results from an incubation experiment with [(15)N]nitrate-amended soils.