2O Emissions Research Articles

Nitrate leaching, direct and indirect nitrous oxide fluxes from sloping cropland in the purple soil area, southwestern China

This study provides a combined dataset on N loss pathways and fluxes from sloping cropland in the purple soil area, southwestern China. A lysimeter experiment was conducted to quantify nitrate leaching (May 2004–May 2010) and N 2O emission (May 2009–May 2010) losses. Nitrate leaching was the dominant N loss pathway and annual leaching fluxes ranged from 19.2 to 53.4 kg N ha −1, with significant differences between individual observation years ( P < 0.05). Direct N 2O emissions due to N fertilizer use were 1.72 ± 0.34 kg N ha −1 yr −1, which corresponds to an emission factor of 0.58 ± 0.12%. However, indirect N 2O emissions caused by nitrate leaching and surface runoff N losses, may contribute another 0.15–0.42 kg N ha −1 yr −1. Our study shows that nitrate leaching lowered direct N 2O emissions, highlighting the importance for a better understanding of the tradeoff between direct and indirect N 2O emissions for the development of meaningful N 2O emission strategies.

Modelling nitrous oxide emissions from grazed grassland systems

Grazed grassland systems are an important component of the global carbon cycle and also influence global climate change through their emissions of nitrous oxide and methane. However, there are huge uncertainties and challenges in the development and parameterisation of process-based models for grazed grassland systems because of the wide diversity of vegetation and impacts of grazing animals. A process-based biogeochemistry model, DeNitrification-DeComposition (DNDC), has been modified to describe N 2O emissions for the UK from regional conditions. This paper reports a new development of UK-DNDC in which the animal grazing practices were modified to track their contributions to the soil nitrogen (N) biogeochemistry. The new version of UK-DNDC was tested against datasets of N 2O fluxes measured at three contrasting field sites. The results showed that the responses of the model to changes in grazing parameters were generally in agreement with observations, showing that N 2O emissions increased as the grazing intensity increased.

Mechanisms of N 2O production in biological wastewater treatment under nitrifying and denitrifying conditions

Nitrous oxide (N 2O) is an important greenhouse gas and a major sink for stratospheric ozone. In biological wastewater treatment, microbial processes such as autotrophic nitrification and heterotrophic denitrification have been identified as major sources; however, the underlying pathways remain unclear. In this study, the mechanisms of N 2O production were investigated in a laboratory batch-scale system with activated sludge for treating municipal wastewater. This relatively complex mixed population system is well representative for full-scale activated sludge treatment under nitrifying and denitrifying conditions. Under aerobic conditions, the addition of nitrite resulted in strongly nitrite-dependent N 2O production, mainly by nitrifier denitrification of ammonia-oxidizing bacteria (AOB). Furthermore, N 2O is produced via hydroxylamine oxidation, as has been shown by the addition of hydroxylamine. In both sets of experiments, N 2O production was highest at the beginning of the experiment, then decreased continuously and ceased when the substrate (nitrite, hydroxylamine) had been completely consumed. In ammonia oxidation experiments, N 2O peaked at the beginning of the experiment when the nitrite concentration was lowest. This indicates that N 2O production via hydroxylamine oxidation is favored at high ammonia and low nitrite concentrations, and in combination with a high metabolic activity of ammonia-oxidizing bacteria (at 2 to 3 mgO 2/l); the contribution of nitrifier denitrification by AOB increased at higher nitrite and lower ammonia concentrations towards the end of the experiment. Under anoxic conditions, nitrate reducing experiments confirmed that N 2O emission is low under optimal growth conditions for heterotrophic denitrifiers (e.g. no oxygen input and no limitation of readily biodegradable organic carbon). However, N 2O and nitric oxide (NO) production rates increased significantly in the presence of nitrite or low dissolved oxygen concentrations.

Differences in nitrous oxide fluxes from red soil under different land uses in mid-subtropical China

Red soil may play an important role in nitrous oxide (N 2O) emissions due to its recent land use change pattern. To predict the land use change effect on N 2O emissions, we examined the relationship between soil N 2O flux and environmental determinants in four different types of land uses in subtropical red soil. During two years of study (January 2005–January 2007), biweekly N 2O fluxes were measured from 09:00 to 11:00 a.m. using static closed chamber method. Objectives were to estimate the seasonal and annual N 2O flux differences from land use change and, reveal the controlling factors of soil N 2O emission by studying the relationship of dissolved organic carbon (DOC), microbial biomass carbon (MBC), water filled pore space (WFPS) and soil temperature with soil N 2O flux. Nitrous oxide fluxes were significantly higher in hot-humid season than in the cool-dry season. Significant differences in soil N 2O fluxes were observed among four land uses; 2.9, 1.9 and 1.7 times increased N 2O emissions were observed after conventional land use conversion from woodland to paddy, orchard and upland, respectively. The mean annual budgets of N 2O emission were 0.71–2.21 kg N 2O-N ha −1 year −1 from four land use types. The differences were partly attributed to increased fertilizer use in agriculture land uses. In all land uses, N 2O fluxes were positively related to soil temperature and DOC accounting for 22–48% and 30–46% of the seasonal N 2O flux variability, respectively. Nitrous oxide fluxes did significantly correlate with WFPS in orchard and upland only. Nitrous oxide fluxes responded positively to MBC in all land use types except orchard which had the lowest WFPS. We conclude that (1) land use conversion from woodland to agriculture land uses leads to increased soil N 2O fluxes, partly due increased fertilizer use, and (2) irrespective of land use, soil N 2O fluxes are under environmental controls, the main variables being soil temperature and DOC, both of which control the supply of nitrification and denitrification substrates.

Fuel characteristics of wheat-based Dried Distillers Grains and Solubles (DDGS) for thermal conversion in power plants

For many years, the sole use of Dried Distillers Grains and Solubles (DDGS) has been as a feed for livestock, due to its high protein and fiber content. Recently there has been interest in DDGS as a power station fuel. In this study, DDGS produced from wheat has been studied for its fuel properties. Pyrolysis studies were conducted via Thermogravimetric Analysis (TGA) and pyrolysis gas chromatography–mass spectrometry (py GC–MS): the former was used to calculate the apparent first order kinetics while the latter helped to characterise pyrolysis products such as methoxyphenols and long chain fatty acids and esters. Fast heating rate chars were made, and nitrogen and sulphur partitioning between volatiles and chars are reported. In addition the chars were studied for their combustion behavior via Simultaneous Thermogravimetric Analysis with Mass Spectrometry detection (STA–MS) to study the conversion of char nitrogen and sulphur to different nitrogen and sulphur-containing species. In addition DDGS was combusted in a 50 kW fluid bed furnace, and the nitrogen species also monitored. DDGS is predicted to have a high alkali index that predicts high fouling tendency due to the high potassium and sodium contents in the ash. The phosphorus content in DDGS ash is also very high. Pyrolysis studies showed some oil evaporation/decomposition occurring at lower temperatures compared to decomposition of the lignocellulosic material. Nitrogen and sulphur partitioning showed that approximately 91% N and 94% S were given off as volatiles. The char was enriched with nitrogen but depleted in sulphur. Char combustion took place in two distinct stages indicating the presence of two types of chars, which yield selective evolution of S and N species during their combustion. Fluid bed combustion studies showed release of both HCN and ammonia during initial stages, when the bed is heating and the fuel undergoes devolatilisation. Steady-state combustion gave NO and N 2O emissions of 290 and 30 ppm respectively, with HCN and NH 3 emissions dropping to below 1 ppm. Agglomeration of the bed was avoided by keeping the combustion temperature below 900 °C

The potential to increase soil carbon stocks through reduced tillage or organic material additions in England and Wales: A case study

Results from the UK were reviewed to quantify the impact on climate change mitigation of soil organic carbon (SOC) stocks as a result of (1) a change from conventional to less intensive tillage and (2) addition of organic materials including farm manures, digested biosolids, cereal straw, green manure and paper crumble. The average annual increase in SOC deriving from reduced tillage was 310 kg C ± 180 kg C ha −1 yr −1. Even this accumulation of C is unlikely to be achieved in the UK and northwest Europe because farmers practice rotational tillage. N 2O emissions may increase under reduced tillage, counteracting increases in SOC. Addition of biosolids increased SOC (in kg C ha −1 yr −1 t −1 dry solids added) by on average 60 ± 20 (farm manures), 180 ± 24 (digested biosolids), 50 ± 15 (cereal straw), 60 ± 10 (green compost) and an estimated 60 (paper crumble). SOC accumulation declines in long-term experiments (>50 yr) with farm manure applications as a new equilibrium is approached. Biosolids are typically already applied to soil, so increases in SOC cannot be regarded as mitigation. Large increases in SOC were deduced for paper crumble (>6 t C ha −1 yr −1) but outweighed by N 2O emissions deriving from additional fertiliser. Compost offers genuine potential for mitigation because application replaces disposal to landfill; it also decreases N 2O emission.

Nitrous oxide emissions in response to ESN and urea, herbicide management and canola cultivar in a no-till cropping system

Environmentally Smart Nitrogen (ESN), a type of polymer-coated urea, synchronizes N release with crop demand to increase N use efficiency and potentially reduce N 2O emissions. This study investigated the effects of ESN and weed management on N 2O emissions from soil under a canola ( Brassica napus L.) no-till cropping system. The experiment was conducted from 2005 to 2008 at three sites: Lethbridge, Lacombe, and Beaverlodge, located in southern, central and northern Alberta, Canada. Treatments included a hybrid and an open-pollinated canola cultivar, with ESN and urea applied at 1 and 1.5 times (×) the recommended rate, and herbicide at 50 and 100% of registered in-crop application rates. Canola was grown in rotation with barley ( Hordeum vulgare L.) and both phases of crop rotation were present each year. The N 2O fluxes from soil were measured using vented static chambers at 2-week intervals during the growing season from 2006 to 2008. Except for a few occasions with higher fluxes from urea than ESN earlier in the growing season and higher fluxes from ESN than urea later on, N 2O fluxes were similar among all treatments for all three years and three sites. The N 2O fluxes also varied over the growing season, and peak flux occurred in response to rainfall events. Similarly, cumulative N 2O emissions, expressed as either per land area or per canola seed yield, over the three growing seasons were low (0.15–2.97 kg N ha −1 yr −1 or 0.05–1.19 g N kg −1 seed) for all treatments and sites, and unaffected by weed management or crop variety ( P > 0.05). The N 2O emission across the three sites from ESN averaged 20% lower ( P = 0.040) than from urea although the differences between fertilizer types or application rates were not significant ( P > 0.05) at each site. Elevated N 2O emissions (72% higher; P = 0.028) from 1.5 × ESN (0.83 kg N ha −1 yr −1 or 0.33 g N kg −1 seed) relative to 1 × ESN (0.26 kg N ha −1 yr −1 or 0.16 g N kg −1 seed) were only observed at Beaverlodge while emissions were similar ( P > 0.05) at the other two sites. The higher N 2O emissions at 1.5 × ESN at Beaverlodge were due to excess N accumulation in soil caused by unfavourable weather conditions that reduced canola N uptake and yield. Our results suggest that ESN fertilizer could reduce N 2O emissions in Alberta, Canada, but reductions will depend on rainfall events and canola N utilization.

Corrigendum to “Direct N 2O emissions following transition from conventional till to no-till in a cover cropped Mediterranean vineyard ( Vitis vinifera)” [Agric. Ecosyst. Environ. 141 (2011) 234–239

Corrigendum to “Direct N 2O emissions following transition from conventional till to no-till in a cover cropped Mediterranean vineyard ( Vitis vinifera)” [Agric. Ecosyst. Environ. 141 (2011) 234–239

Long-Term Application of Organic Manure and Mineral Fertilizer on N 2O and CO 2 Emissions in a Red Soil from Cultivated Maize-Wheat Rotation in China

Abstract A long-term field experiment was established to determine the influence of mineral fertilizer and organic manure on soil fertility. A tract of red soil (Ferralic Cambisol) in Qiyang Red Soil Experimental Station (Qiyang County, Hunan Province, China) was fertilized beginning in 1990 and N 2O and CO 2 were examined during the maize and wheat growth season of 2007–2008. The study involved five treatments: organic manure (NPKM), fertilizer NPK (NPK), fertilizer NP (NP), fertilizer NK (NK), and control (CK). Manured soils had higher crop biomass, organic C, and pH than soils receiving the various mineralized fertilizers indicating that long-term application of manures could efficiently prevent red soil acidification and increase crop productivity. The application of manures and fertilizers at a rate of 300 kg N ha −1 yr −1 obviously increased N 2O and CO 2 emissions from 0.58 kg N 2O-N ha −1 yr −1 and 10 565 kg C ha −1 yr −1 in the CK treatment soil to 3.01 kg N 2O-N ha −1 yr −1 and 28 663 kg C ha −1 yr −1 in the NPKM treatment. There were also obvious different effects on N 2O and CO 2 emissions between applying fertilizer and manure. More N 2O and CO 2 released during the 184-d maize growing season than the 125-d wheat growth season in the manure fertilized soils but not in mineral fertilizer treatments. N 2O emission was significantly affected by soil moisture only during the wheat growing season, and CO 2 emission was affected by soil temperature only in CK and NP treatment during the wheat and maize growing season. In sum, this study indicates the application of organic manure may be a preferred strategy for maintaining red soil productivity, but may result in greater N 2O and CO 2 emissions than treatments only with mineral fertilizer.

Denitrification on Andosols in an intensive dairy farming region of central Japan

Evaluation of denitrification capacities is necessary to develop a sustainable manure management system in order to reduce NO 3 − leaching and N 2O emissions from agricultural soils. Denitrification rates were measured using the acetylene inhibition technique on intact soil cores from eight Andosols under three different cropping systems in an intensive livestock catchment of central Japan. The N application rates ranged from 200 to 800 kg N ha −1 yr −1. The denitrification rates were highly variable across fields, and were influenced significantly by land uses and manure forms. Compared with upland fields, paddy rice fields had a greater denitrification rate up to 1380 and 85 mg N m −2 day −1 in the top 30-cm soil layer during flooding and non-flooding periods, respectively. In upland fields, the maximum value for the top 30-cm soils was 44 mg N m −2 day −1 and most of the rates were less than 10 mg N m −2 day −1. The greater denitrification rates were often associated with slurry application rather than composted dry manure. Overall, denitrification from Andosols in this study displayed a lower capacity than that of non-Andosols.

Greenhouse gas emissions and plant characteristics from soil cultivated with sunflower ( Helianthus annuus L.) and amended with organic or inorganic fertilizers

Agricultural application of wastewater sludge has become the most widespread method of disposal, but the environmental effects on soil, air, and crops must be considered. The effect of wastewater sludge or urea on sunflower's ( Helianthus annuus L.) growth and yield, the soil properties, and the resulting CO 2 and N 2O emissions are still unknown. The objectives of this study were to investigate: i) the effect on soil properties of organic or inorganic fertilizer added to agricultural soil cultivated with sunflower, ii) how urea or wastewater sludge increases CO 2 and N 2O emissions from agricultural soil over short time periods, and iii) the effect on plant characteristics and yield of urea or wastewater sludge added to agricultural soil cultivated with sunflower. The sunflower was fertilized with wastewater sludge or urea or grown in unamended soil under greenhouse conditions while plant and soil characteristics, yield, and greenhouse gas emissions were monitored. Sludge and urea modified some soil characteristics at the onset of the experiment and during the first two months but not thereafter. Some plant characteristics were improved by sludge. Urea and sludge treatments increased the yield at similar rates, while sludge-amended soil significantly increased N 2O emissions but not CO 2 emissions compared to the other amended or unamended soils. This implies that wastewater sludge increased the biomass and/or the yield; however, from a holistic point of view, using wastewater sludge as fertilizer should be viewed with concern.

Modelling nitrous oxide and carbon dioxide emission from soil in an incubation experiment

Nitrous oxide (N 2O), one of the primary green house gases (GHG), is an important contributor to the radiative forcing and chemistry of the atmosphere. Nitrous oxide emissions from soil are mainly due to denitrification. In this paper, we test sub-modules in the APSIM and DAYCENT models to simulate denitrification. The models were tested by comparison of predicted and measured N 2O emission from an incubation experiment using 8.2 L soil cores. The N gas sub-modules in DAYCENT were based on the leaky pipe metaphor, that is, total N gas emissions are proportional to N cycling and gas diffusivity in the soil determines the relative amounts of N gas species emitted. The same approach was added to APSIM to enable simulation of N 2O emission. The soil monoliths were irrigated three times during a two-week period and set on tension tables to control the suction at the base of each core. The results show that APSIM underestimates denitrification, whereas DAYCENT better predicted N 2O emission from denitrification. In contrast, predictions of CO 2 emissions were better from APSIM than DAYCENT. Modification to the temperature response for denitrification in APSIM improved the simulation significantly. The use of multiple soil layers in the simulations improved predictions, especially at low soil moisture content. Under these conditions, the layered approach better captures the impact of soil moisture distribution. Reducing the time step to hourly improve the prediction of N 2O peaks and the daily total emissions, but there were still temporal mismatches between simulated and observed values. The denitrification algorithms in DAYCENT, combined with APSIM simulated CO 2, together with an hourly time step and a layered approach, produced the best results. These results highlight the need for improvement to the APSIM denitrification sub-model.

The effects of site preparation practices on carbon dioxide, methane and nitrous oxide fluxes from a peaty gley soil

Summary The effects of site preparation practices (drainage, mounding and fertilization) on the fluxes from the soil surface of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) were studied on an organic-rich peaty gley soil at Harwood Forest, north-east England. Drained plots had significantly higher CO 2 fluxes but significantly lower CH4 fluxes compared with undrained plots, while N 2O emissions were not affected by drainage. Mounding caused significantly higher CH 4 emissions, while it significantly reduced N 2O emissions. Fertilization caused significant increases in emissions of CO2, CH4 and N2O. In terms of overall greenhouse warming potential, drainage and fertilization increased CO2-equivalent emissions by ~18−29 and 7−23 per cent, respectively, while mounding reduced CO2-equivalent emissions by ~8 per cent in year 1, but had no effect on emissions in year 2 of study. Soil temperature was the main environmental variable controlling CO2 emissions, while CH4 was controlled primarily by water table depth. Nitrous oxide emissions responded to changes in soil temperature and water table depth. In the short term, drainage and fertilization contributed to accelerating greenhouse gas emissions significantly, although their long-term effects are likely moderated by accelerating carbon accumulation in the tree biomass. Long-term studies are required to assess the cumulative impacts of site preparation practices during the whole rotation cycle.

Synthetic fertilizer management for China’s cereal crops has reduced N 2O emissions since the early 2000s

China has implemented a soil testing and fertilizer recommendation (STFR) program to reduce the over-usage of synthetic nitrogen (N) fertilizer on cereal crops since the late 1990s. Using province scale datasets, we estimated an annual reduction rate of 2.5–5.1 kg N ha −1 from 1998 to 2008 and improving grain yields, which were attributed to the balanced application of phosphate and potassium fertilization. Relative to the means for 1998–2000, the synthetic N fertilizer input and the corresponding N-induced N 2O production in cereal crops were reduced by 22 ± 0.7 Tg N and 241 ± 4 Gg N 2O–N in 2001–2008. Further investigation suggested that the N 2O emission related to wheat and maize cultivation could be reduced by 32–43 Gg N 2O–N per year in China (26%–41% of the emissions in 2008) if the STFR practice is implemented universally in the future.

N 2O emission from a partial nitrification–anammox process and identification of a key biological process of N 2O emission from anammox granules

Emission of nitrous oxide (N 2O) during biological wastewater treatment is of growing concern. The emission of N 2O from a lab-scale two-reactor partial nitrification (PN)–anammox reactor was therefore determined in this study. The average emission of N 2O from the PN and anammox process was 4.0 ± 1.5% (9.6 ± 3.2% of the removed nitrogen) and 0.1 ± 0.07% (0.14 ± 0.09% of the removed nitrogen) of the incoming nitrogen load, respectively. Thus, a larger part (97.5%) of N 2O was emitted from the PN reactor. The total amount of N 2O emission from the PN reactor was correlated to nitrite (NO 2 −) concentration in the PN effluent rather than DO concentration. In addition, further studies were performed to indentify a key biological process that is responsible for N 2O emission from the anammox process (i.e., granules). In order to characterize N 2O emission from the anammox granules, the in situ N 2O production rate was determined by using microelectrodes for the first time, which was related to the spatial organization of microbial community of the granule as determined by fluorescence in situ hybridization (FISH). Microelectrode measurement revealed that the active N 2O production zone was located in the inner part of the anammox granule, whereas the active ammonium consumption zone was located above the N 2O production zone. Anammox bacteria were present throughout the granule, whereas ammonium-oxidizing bacteria (AOB) were restricted to only the granule surface. In addition, addition of penicillin G that inhibits most of the heterotrophic denitrifiers and AOB completely inhibited N 2O production in batch experiments. Based on these results obtained, denitrification by putative heterotrophic denitrifiers present in the inner part of the granule was considered the most probable cause of N 2O emission from the anammox reactor (i.e., granules).

Impact of biochar application to a Mediterranean wheat crop on soil microbial activity and greenhouse gas fluxes

Biochar has been recently proposed as a management strategy to improve crop productivity and global warming mitigation. However, the effect of such approach on soil greenhouse gas fluxes is highly uncertain and few data from field experiments are available. In a field trial, cultivated with wheat, biochar was added to the soil (3 or 6 kg m −2) in two growing seasons (2008/2009 and 2009/2010) so to monitor the effect of treatments on microbial parameters 3 months and 14 months after char addition. N 2O, CH 4 and CO 2 fluxes were measured in the field during the first year after char addition. Biochar incorporation into the soil increased soil pH (from 5.2 to 6.7) and the rates of net N mineralization, soil microbial respiration and denitrification activity in the first 3 months, but after 14 months treated and control plots did not differ significantly. No changes in total microbial biomass and net nitrification rate were observed. In char treated plots, soil N 2O fluxes were from 26% to 79% lower than N 2O fluxes in control plots, excluding four sampling dates after the last fertilization with urea, when N 2O emissions were higher in char treated plots. However, due to the high spatial variability, the observed differences were rarely significant. No significant differences of CH 4 fluxes and field soil respiration were observed among different treatments, with just few exceptions. Overall the char treatments showed a minimal impact on microbial parameters and GHG fluxes over the first 14 months after biochar incorporation.

Assessing the potential for greenhouse gas mitigation in intensively managed annual cropping systems at the regional scale

We predicted changes in yields and direct net soil greenhouse gas (GHG) fluxes from converting conventional to alternative management practices across one of the world's most productive agricultural regions, the Central Valley of California, using the DAYCENT model. Alternative practices included conservation tillage, winter cover cropping, manure application, a 25% reduction in N fertilizer input and combinations of these. Alternative practices were evaluated for all unique combinations of crop rotation, climate, and soil types for the period 1997–2006. The crops included were alfalfa, corn, cotton, melon, safflower, sunflower, tomato, and wheat. Our predictions indicate that, adopting alternative management practices would decrease yields up to 5%. Changes in modeled SOC and net soil GHG fluxes corresponded to values reported in the literature. Average potential reductions of net soil GHG fluxes with alternative practices ranged from −0.7 to −3.3 Mg CO 2-eq ha −1 yr −1 in the Sacramento Valley and −0.5 to −2.5 Mg CO 2-eq ha −1 yr −1 for the San Joaquin Valley. While adopting a single alternative practice led to modest net soil GHG flux reductions (on average −1 Mg CO 2-eq ha −1 yr −1), combining two or more of these practices led to greater decreases in net soil GHG fluxes of up to −3 Mg CO 2-eq ha −1 yr −1. At the regional scale, the combination of winter cover cropping with manure application was particularly efficient in reducing GHG emissions. However, GHG mitigation potentials were mostly non-permanent because 60–80% of the decreases in net soil GHG fluxes were attributed to increases in SOC, except for the reduced fertilizer input practice, where reductions were mainly attributed to decreased N 2O emissions. In conclusion, there are long-term GHG mitigation potentials within agriculture, but spatial and temporal aggregation will be necessary to reduce uncertainties around GHG emission reductions and the delivery risk of the associated C credits.

Pulse emissions of N 2O and CO 2 from an arable field depending on fertilization and tillage practice

Nitrous oxide (N 2O) emissions from soil are characterized by strong emission pulses. Although several mechanisms are known to create them, pulses are difficult to predict. Currently there is no established systematic way to identify pulses from long-term static chamber measurement results. In this study we suggest a simple algorithm for pulse identification. The algorithm was applied on time series of N 2O and carbon dioxide (CO 2) fluxes from a field study on the long-term impact of fertilization and tillage practice. Between 4 and 9% of N 2O values were pulse values; 20–60% of total emission was emitted as pulses. Minimum tillage resulted in more pulses than plowing. In contrast, long-term averages of N 2O losses from nitrogen (N) fertilizer were similar (3–4%) for all management practices. N 2O emissions per crop yield for increased fertilization practice were double the values for reduced fertilization practice independent of tillage practice. CO 2 emission pulses were scarce and there was no significant effect of management practice on CO 2 pulse probability.

Urease inhibitor reduces N losses and improves plant-bioavailability of urea applied in fine particle and granular forms under field conditions

A field lysimeter/mini plot experiment was established in a silt loam soil near Lincoln, New Zealand, to investigate the effectiveness of urea fertilizer in fine particle application (FPA), with or without the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT – “Agrotain”), in decreasing nitrogen (N) losses and improving N uptake efficiency. The five treatments were: control (no N) and 15N-labelled urea, with or without NBPT, applied to lysimeters or mini plots (unlabelled urea), either in granular form to the soil surface or in FPA form (through a spray) at a rate equivalent to 100 kg N ha −1. Gaseous emissions of ammonia (NH 3) and nitrous oxide (N 2O), nitrate (NO 3 −) leaching, herbage dry-matter (DM) production, N-response efficiency, total N uptake and total recovery of applied 15N in the plant and soil varied with urea application method and with addition of NBPT. Urea with NBPT, applied in granular or FPA form, was more effective than in application without NBPT: N 2O emissions were reduced by 7–12%, NH 3 emissions by 65–69% and NO 3 − leaching losses by 36–55% compared with granular urea. Urea alone and with NBPT, applied in FPA form increased herbage DM production by 27% and 38%, respectively. The N response efficiency increased from 10 kg DM kg −1 of applied N with granular urea to 19 kg DM kg −1 with FPA urea and to 23 kg DM kg −1 with FPA urea plus NBPT. Urea applied in FPA form resulted in significantly ( P < 0.05) higher 15N recovery in the shoots compared with granular treatments and this was improved further when urea in FPA form was applied with NBPT. These results suggest that applying urea with NBPT in FPA form has potential as a management tool in mitigating N losses, improving N-response efficiency and increasing herbage DM production in intensive grassland systems.

Reduced iron induced nitric oxide and nitrous oxide emission

Formation of the greenhouse gas nitrous oxide in water treatment systems is predominantly studied as a biological phenomenon. There are indications that also chemical processes contribute to these emissions. Here we studied the formation of nitric oxide (NO) and nitrous oxide (N 2O) due to chemical nitrite reduction by ferrous iron (Fe(II)). Reduction of nitrite and NO coupled to Fe(II) oxidation was studied in laboratory-scale chemical experiments at different pH, nitrite and iron concentrations. The continuous measurement of both NO and N 2O emission showed that nitrite reduction and NO reduction have different kinetics. Nitrite reduction shows a linear dependency on the nitrite concentration, implying first order kinetics in nitrite. The nitrite reduction seems to be an equilibrium based reaction, leading to a constant NO concentration in the liquid. The NO reduction rate is suggested to be most dependent on reactive surface availability and the sorption of Fe(II) to the reactive surface. The importance of emission of NO and N 2O coupled to iron oxidation is exemplified by iron reduction experiments and several examples of environments where this pathway can play a role.