Nitrous oxide (N2O) emissions in response to increasing fertilizer addition in maize (Zea mays L.) agriculture in western Kenya

National and regional efforts are underway to increase fertilizer use in sub-Saharan Africa, where attaining food security is a perennial challenge and mean fertilizer use in many countries is <10 % of nationally recommended rates. Increases in nitrogen (N) inputs will likely cause increased emissions of the greenhouse gas nitrous oxide (N₂O). We established experimental plots with different rates of N applied to maize (Zea mays) in a field with a history of nutrient additions in western Kenya and measured N₂O fluxes. Fertilizer was applied by hand at 0, 50, 75, 100, and 200 kg N ha^?1 in a split application on March 22 and April 20, 2010. Gas sampling was conducted daily during the week following applications, and was otherwise collected weekly or biweekly until June 29, 2010. Cumulative fluxes were highest from the 200 kg N ha^?1 treatment, with emissions of 810 g N₂O–N ha^?1; fluxes from other treatments ranged from 620 to 710 g N₂O–N ha^?1, but with no significant differences among treatments. Emissions of N₂O during the 99-day measurement period represented <0.1 % of added fertilizer N for all treatments. Though limited to a single year, these results provide further evidence that African agricultural systems may have N₂O emission factors substantially lower than the global mean.     

Influence of electrolytes on the absorption of nitrogen oxide components N2O4 and N2O3 in aqueous absorbents

The influence of electrolytes, which are dissolved in the aqueous absorbent and do not react with nitrogen oxides, on the absorption kinetics of both these components was investigated experimentally. In addition to demineralized water, various salt solutions of different concentrations as well as sodium hydroxide solution were used as absorbents. The term H \documentclass{article}\pagestyle{empty}\begin{document}$ H\sqrt {k_1 D} $\end{document} for N₂O₄ and N₂O₃, which is important for the design of industrial absorbers, was determined as a function of composition and concentration of the absorbents. In the case of N₂O₄, the chosen measuring and evaluation methods permitted a separate determination of the rate constant k of the pseudo first order reaction and of the solubility H. The diffusion coefficient D of the gas in the absorbent can be obtained only by calculation. Experimental results showed that \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 4} } $\end{document} decreases with increasing ionic strength I, however, without a clear indication of any ion-specific effects. This decrease does not appear to be caused simply by a reduction in solubility (salting out effect), or in diffusion coefficient, but at least, to the same extent, through a decrease of the rate constant k with increasing electrolyte content in the absorbent. The measurements permitted the determination of the gas-based salting out parameter for N₂O₄. The investigations on the absorption of N₂O₃ in water and in an Na₂SO₄ solution showed no experimentally detectable influence of dissolved salts on \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 3} } $\end{document}. The numerical value of \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 3} } $\end{document} is six times that of \documentclass{article}\pagestyle{empty}\begin{document}$(H\sqrt {k_1 D} )\,_{{\rm N}_{\rm 2} {\rm O}_{\rm 4} } $\end{document}.     

Emission of ammonia (NH3), nitrous oxide (N2O) and methane (CH4) from a dairy hardstanding in the UK

Emissions of ammonia (NH₃), nitrous oxide (N₂O) and methane (CH₄) from uncovered yard areas (hardstandings) of a UK dairy farm were measured between October 1997 and August 1999. Measurements were concentrated after morning milking when the yard had been scraped, and at positions accounting for differences in slurry coverage and manure type. Over two seasons, the mean NH₃ emission from a number of season and position categories on the hardstanding were 0.27 g N m⁻² h⁻¹ in winter and spring, 0.45 g N m⁻² h⁻¹ in summer when the feeding/loafing area was not included, increasing to 1.51 g N m⁻² h⁻¹ when this area was included, and 5.0 g N m⁻² h⁻¹ for the feeding/loafing area alone. The feeding/loafing area was close to the slurry lagoon where excreta were continuously deposited and not scraped to the slurry lagoon, as was the rest of the hardstanding. A diurnal study of emissions in the summer showed a marked decrease with time after the yard was scraped following the first milking, with emissions increasing again after evening milking when fresh excreta were deposited. Nitrous oxide emissions were more variable than NH₃, with an order of magnitude difference between lowest and highest emissions measured at the same time. Mean N₂O emission rates were 3.3 μg N m⁻² h⁻¹ in winter and spring, 6.5 μg N m⁻² h⁻¹ in summer when the feeding/loafing area was not included, increasing to 7.8 μg N m⁻² h⁻¹ when this area was included, and 17.9 μg N m⁻² h⁻¹ for the feeding/loafing area alone. Large mean methane emissions were measured, 185 mg C m⁻² h⁻¹ in winter and spring, decreasing to 57.3 mg C m⁻² h⁻¹ in summer when the feeding/loafing area was not included, increasing to 72.9 mg C m⁻² h⁻¹ when this area was included, and 151.2 mg C m⁻² h⁻¹ for the feeding/loafing area alone. Therefore in summer, emissions measured directly from a dung pat [0–5 cm] that had not been scraped from the loafing area were much greater than from scraped hardstanding areas, but in winter there were still significant emissions from the remaining slurry post-scraping. The experimental design was not sufficient to elucidate the physico-chemical variables controlling the measured emissions, but the data were put into context by estimating the annual emission of these pollutant gases from this one dairy farm. These were estimated at 0.43 t NH₃-N y⁻¹, 0.3 kg N₂O-N y⁻¹ and 1.0 kg CH₄-C y⁻¹. Therefore, uncovered farmyard areas that regularly have excreta deposited on them are significant but previously unaccounted for sources of NH₃ loss, less so for N₂O and CH₄, and require further study to assess the significance of these emission sources within the UK and worldwide. This revised version was published online in August 2006 with corrections to the Cover Date.     

N2Desorption in the Isothermal Decomposition of N2O on Rh(110) at Low Temperatures

Transient N₂desorption was analyzed in an angle-resolved form while a constant N₂O flux was introduced to clean Rh(110) or an oxygen-modified one. Even at 60 K, the decomposition proceeded and the product N₂desorption collimated at either 65 ± 3° or 30 ± 1° off normal towards the [001] direction.     

Methane (CH4) and nitrous oxide (N2O) emissions from the system of rice intensification (SRI) under a rain-fed lowland rice ecosystem in Cambodia

The present field study investigated the effects of the system of rice intensification (SRI) on greenhouse gas emissions and rice yield, in the first field trial of its kind in Cambodia. The study was a 2 × 4 factorial design, including SRI and conventional management practices (CMP) with the following treatments: control, composted farmyard manure (FYM), mineral fertiliser (MF) and FYM + MF. The results indicated large seasonal variations of CH₄ patterns during the growing season with a peak emission of about 1,300 mg CH₄ m^?2 day^?1 under both production systems 2 weeks after rice transplanting. There was large temporal variability of CH₄ fluxes from morning to midday. Emission of N₂O was below the detection limit in both systems. Under each production system, the highest seasonal emission of CH₄ was under the FYM + MF treatment, namely 282 kg ha^?1 under CMP and 213 kg ha^?1 under SRI. Total CH₄ emission under SRI practices was reduced by 22 % in the FYM treatment, 17 % in the MF treatment and 24 % in the FYM + MF treatment compared to CMP. There was no effect of water management on CH₄ emission in the non-fertilized treatment. Grain yields were not significantly affected by the production system. Thus the yield-scaled global warming potential (GWP) was lower under SRI than CMP, namely 21 % in FYM and FYM + MF treatments, and 8 % in MF treatment. The application of mineral fertilisers moderately increased CH₄ emission but significantly increased rice yields, resulting in a significantly lower yield-scaled-GWP compared to farmyard manure.     

A new inorganic (carbon-free) chelate ring: SnO2N2. Eight-coordinated tin(IV) in Sn(O2N2Ph)4 and a self-assembled 20-membered macrocycle in [Me3Sn(O2N2Ph)]4

The reaction of cupferron (NH₄L, L=PhN(O)NO⁻) with tin(IV) and trimethyltin(IV) halides yields cupferronato complexes SnL₄ (1) and [Me₃SnL]₄ (2) which were characterised by FT-IR and FT-Raman spectroscopy. The first X-ray diffraction analysis of the complexes reveals a slightly distorted dodecahedral and trigonal-bipyramidal coordination of the central metal atoms in 1 and 2, respectively. The N-nitroso-N-phenylhydroxylaminato [PhN(O)NO⁻] ligand behaves as chelating in 1 and bridging in 2 leading to a novel five-membered chelate ring, SnO₂N₂ in 1 and an unprecedented 20-membered inorganic metallomacrocycle, Sn₄O₈N₈ in 2.     

Novel porphyrazines containing peripherally functionalized macrocyclic (N2O2, N2S2) units: Synthesis and characterization

Novel maleonitrile moieties were synthesized by cyclization of 2,3-bis[(2-pyridylmethyl)amino]-2(Z)-butene-1,4-dinitrile with 1,2-bis(2-iodoethoxy)-4-nitrobenzene or o-xylyenebis(1-chloro-3-thiapropane) under conditions of high dilution. A series of novel, free-base, magnesium and zinc porphyrazines bearing macrocyclic substituents in peripheral positions were prepared via Linstead macrocyclization reactions of different maleonitrile derivatives, 12-nitro-4,7-bis(pyridin-2-ylmethyl)-2,3,4,7,8,9-hexahydro-1,10,4,7-benzodioxa-diaza-cyclododecine-5,6-dicarbonitrile or 5,8-bis(pyridin-2-ylmethyl)-1,3,4,5,8,9,10,12-octa-hydro-2,11,5,8-benzodi-thiadiazacyclo-tetradecine-6,7-dicarbonitrile and the corresponding divalent metal salts. Pentanuclear copper(II) complexes were also prepared from the corresponding zinc(II) porphyrazine derivatives. The compounds were characterized by a combination of elemental analysis, FT-IR, UV–vis, ¹H NMR, ¹³C NMR and MS spectral data.     

Effect of ZrB2 and its oxide impurities (ZrO2 and B2O3) on hot-pressed Si3N4 ceramics at low temperature

Based on the previous work on Si₃N₄-ZrB₂, the addition of 2.5 vol.% ZrB₂ promoted α- to β-Si₃N₄ phase transformation, bimodal microstructure, and toughness and strength improvement after hot-pressing at 1500 °C. However, the mechanism needed to be further explored. In the present work, the effect of ZrB₂ and its oxide impurities (ZrO₂ and B₂O₃) on phase composition, microstructure and mechanical properties of Si₃N₄ ceramics with MgO-Yb₂O₃ additives were studied. Results showed that the addition of B₂O₃ had no influence on Si₃N₄ ceramics, whereas the addition of ZrO₂ inhibited the α- to β-Si₃N₄ phase transformation, formed an uniform equiaxed microstructure, and deceased the toughness and strength. The positive effect of oxide impurities can be eliminated. Based on the STEM analysis, the possible reason was that the addition of ZrB₂ led to the formation of Si-Mg-O-N-Yb-Zr-B liquid phase, and then promoted α- to β-Si₃N₄ phase transformation.     

Temperature-dependent transport properties of micro and nano-sized zinc cobalt oxide (ZnCo2O4) and zinc manganese oxide (ZnMn2O4) particles synthesized by a hydrothermal route

In the present work, a hydrothermal method has been adopted to synthesize micro (~150 nm), and nano (~20 nm) particles of Zinc based, cobalt, and manganese oxide structures, i.e., ZnCo₂O₄ (ZCO) and ZnMn₂O₄ (ZMO). These structures have been examined by X-ray diffraction, Field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. The effect of different reducing agents and solvents have been ascertained on the morphological and the crystalline nature of the samples. The highly crystalline and micron-sized particle formation has been observed with the usage of NaBH₄ as the reductant in the water solution, and a polycrystalline structure with nanosized particle formation has been found with NaOH as the reductant in the water and DMF solution. The electrical properties have been investigated between 100 Hz and 1 MHz by varying the temperature from 303 K to 513 K. The micro and nano sized particles of ZCO and ZMO have shown frequency dependence, thermally activated and relaxation-type dielectric behavior confirming the semiconducting nature. The variation of ac conductivity with frequency at different temperatures is according to Jonscher's power law for micro and nano sized particles of the ZCO and ZMO but supporting different conduction mechanisms. The conduction mechanism in microparticles and nano-particles is according to an overlapping-large polaron tunneling (OLPT) model, and the Non-overlapping small polaron tunneling (NSPT) model, respectively.     

Features of the synthesis of carbon nitride oxide (g-C3N4)O at urea pyrolysis

First from urea was synthesized carbon nitride oxide (g-C₃N₄)O which is formed in a vapor gas reactionary space and is deposited outside of a place of precursor localization. The reaction of urea conversion was investigated in an interval of temperatures 350–450 °С, but carbon nitride oxide is detected in the products of pyrolysis only at temperatures above 430 °С. Carbon nitride oxide is dissolved in water and at a reducing it by hydroquinone is formed reduced carbon nitride oxide consisting, as we believe, from azagraphene sheets.     

Influences of rare-earth oxide additives on the formation and properties of porous Si2N2O ceramic

Here we prepared porous silicon oxynitride (Si₂N₂O) ceramics by reaction sintering of SiO₂ and Si₃N₄ using five different rare-earth oxides (RE₂O₃, RE = Lu, Yb, Y, Sm, and La) as sintering aids. The influences of RE₂O₃ on the formation, densification, microstructure, and mechanical properties of Si₂N₂O ceramics have been investigated in detail. The results have indicated that with the increase in RE ionic radius, the formation temperature of Si₂N₂O decreases, and the densification process could be promoted by RE₂O₃ with larger RE³⁺ ionic radius. In addition, microstructures and mechanical properties are highly dependent on the RE₂O₃ additives. With the increase in RE³⁺ ionic radius, Si₂N₂O changes from platelike crystals to elongated crystals. The samples doped with La₂O₃ and Sm₂O₃ with elongated crystals exhibit higher flexural strength and higher Vickers hardness.     

One novel polynuclear complex [Cu2(bpc)2(N3)4Ca(H2O)2Na2(H2O)2]n having three different transition and non-transition metal centres

The complex [Cu₂(bpc)₂(N₃)₄Ca(H₂O)₂Na₂(H₂O)₂]_n (1) (bpc²⁻=2,2^′-bipyridyl-3,3^′-dicarboxylate) has been prepared and characterised by elemental analyses, spectroscopic and single crystal X-ray diffraction study. Single crystal X-ray analysis revealed a novel polynuclear complex containing three different metal centres such as an alkali metal (sodium), an alkaline earth metal (calcium) and a transition metal atom (copper) connected together by azide and carboxylato groups.     

Phase formation between La(Sr)Ga(Mg)O3 and Ce(La)O2 for solid oxide fuel cell applications

In strontium- and magnesium-doped LaGaO₃ (LSGM) electrolyte-based solid oxide fuel cells (SOFC), lanthanum-doped CeO₂ (LDC) is usually used as buffer layer material to prevent reactions between LSGM electrolyte and NiO-based anode. In literature, based on results for one particular LSGM composition, a fixed buffer layer composition of 40% La-doped ceria (LDC40) has been used even with electrolytes of different LSGM compositions. In this study, we report the results of a comprehensive study of phase formations between various LSGM and LDC compositions. Our results show that only one LSGM/LDC combination results in no additional phases. For the other combinations, at least one and often two additional phases, LaSrGaO₄ and LaSrGa₃O₇, result. Because LaSrGa₃O₇ has much lower conductivity, it is necessary to select combinations that avoid this phase. We propose that the combination that results in no additional phase should be considered favorably for SOFCs. For other LSGM compositions, LDC50 should be used as a buffer layer instead of LDC40 as is presently done in SOFC studies. Alternately, if LDC40 is preferred for buffer layer, then lower Sr content LSGM compositions should be used as electrolytes. These combinations are likely to lead to better long-term SOFC performance.     

An extension of the group contribution method for estimating thermodynamic and transport properties part II. Polyatomic gases (F2, Cl2, CS2, H2S, NO and N2O)

Earlier work on the group contribution method applied to the Kihara potential is extended to polyatomic gases for the calculation of second virial coefficients, viscosities and diffusivities of dilute gases with a single set of gas group parameters. Functional group parameters are evaluated from the simultaneous regression of second virial coefficient and viscosity data of pure gases. Parameters for gas groups (F₂, Cl₂, CS₂, H₂S, NO, nd N₂O) are found to provide good predictions of second virial cross coefficients, mixture viscosities and binary diffusion coefficients of gas-gas mixtures. Application of the model shows that second virial coefficient data can be represented with good results comparable to the values by means of the corresponding states model. The reliability of the present model in viscosity predictions is proved by comparison with the Lucas method. Predictions of binary diffusion coefficients are in excellent agreement with experimental data and compare well with values obtained by means of the Fuller method.     

Assessment of CH4 and N2O fluxes in a Danish beech (Fagus sylvatica) forest and an adjacent N-fertilised barley (Hordeum vulgare) field: effects of sewage sludge amendments

Fluxes of CH₄ and N₂O were measured regularly in an agricultural field treated with 280 g m⁻² of sewage sludge. In a nearby beech forest N₂O and CH₄ fluxes were measured in a well-drained (dry) area and in a wet area adjacent to a drainage canal. We observed brief increases of both CH₄ and N₂O emissions immediately following soil applications of digested sewage sludge. Cumulated values for CH₄ emissions over the course of 328 days after sludge applications indicated a small net source in sludge treated plots (7.6 mg C m⁻²) whereas sludge-free soil constituted a small sink (-0.9 mg C m⁻²). The CH₄ emission amounted 0.01% of the sludge-C. Extrapolated to current rates of sludge applications in Danish agriculture this amounts to 0.1% of the total agricultural derived CH₄. Sludge applications did not affect cumulated fluxes of N₂O showing 312 mg N₂O–N m⁻² and 304 mg N m⁻² with and without sludge, respectively. Four months after the sludge applications a significant effect on CO₂ and NO emissions was still obvious in the field, the latter perhaps due to elevated nitrification. Nitrous oxide emission in the beech forest was about six times smaller (45 mg N m⁻²) than in the field and independent of drainage status. Methane oxidation was observed all-year round in the forest cumulating to -225 mg C m⁻² and -84 mg C m⁻² in dry and wet areas. In a model experiment with incubated soil cores, nitrogen amendment (NH₄Cl) and perturbation significantly reduced CH₄ oxidation in the forest soil, presumably as a result of increased nitrification activity. Sludge also induced net CH₄ production in the otherwise strong CH₄ oxidising forest soil. This emphasises the potential for CH₄ emissions from sewage sludge applications onto land. The study shows, however, that emissions of N₂O and CH₄ induced by sewage sludge in the field is of minor importance and that factors such as land use (agriculture versus forest) is a much stronger controller on the source/sink strengths of CH₄ and N₂O. This revised version was published online in August 2006 with corrections to the Cover Date.     

Synthesis,characterizations, and crystal structure of a novel layered phosphonate: Zn2Cl[O3PCH2N(CH2CH2)2O][O3PCH2NH(CH2CH2)2O]

A novel layered zinc phosphonate, Zn₂Cl[O₃PCH₂N(CH₂CH₂)₂O][O₃PCH₂NH(CH₂CH₂)₂O] 1 has been synthesized by hydrothermal reaction at 180 °C and structurally characterized by single crystal X-ray diffraction as well as with infrared spectroscopy, elemental analysis and thermogravimetric analysis. The interconnection of Zn(1)O₄, Zn(2)O₂NCl and CPO₃ tetrahedra via corner-sharing forms a double layer structure with a channel system along b-axis direction. The result of connections in this manner is the formation of 8- and 16-atom windows that are parallel to one another and run in the a-axis direction. The morpholinyl groups of the ligands are orientated toward the interlayer space.     

The effect of lanthanum oxide (La2O3) on the structure and crystallization of poly(vinylidene fluoride)

Rare earth polymers, due to their excellent luminescence, fluorescence, laser protective, optical and magnetic properties, have attracted much research attention in recent years. However, little attention has been paid to the effect of rare earths on the structure and crystallization of polymers, which is of important significance in the development of functional polymers. X‐ray diffraction and differential scanning calorimetry were used to investigate the structure and crystallization behavior of a poly(vinylidene fluoride) (PVDF)/lanthanum oxide (La₂O₃) composite. The results showed that the degree of perfection, crystal size, crystallization rate and isothermal crystallization activation energy of PVDF in the composite decreased, compared with pure PVDF. The spherulite nucleation and growth for PVDF and PVDF composite were analyzed in detail using the Lauritzen‐Hoffman equation. The modified Avrami equation and the Mo equation were used to study the non‐isothermal crystallization kinetics. The addition of La₂O₃ did not change the crystal structure and nucleation process for PVDF, but it decreased markedly the crystal growth rate and led to the formation of unstable crystals. This was attributed to the fact that too much La₂O₃ prevented PVDF molecular chains from moving and arranging in an orderly manner into crystals. Copyright © 2010 Society of Chemical Industry