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1.
Nitrous oxide emission from three soils was measured using a chamber technique. Treatments sampled were unfertilized soil, and soil fertilized with 60 or 80 kg N ha –1 of band-applied anhydrous ammonia ± nitrapyrin. The flux of nitrous oxide from unfertilized soil was very low (1.1 to 1.6 g N ha –1 day –1).Application of anhydrous ammonia caused a significant increase in the cumulative emission of nitrous oxide in two soils over 27 or 29 days compared with unfertilized soil. Fertilizer-induced loss of nitrous oxide was highest in a calcareous clay soil which had the highest nitrification rate and accumulated the highest concentration of nitrite within the fertilizer bands. Fertilizer-induced losses of nitrous oxide were < 0.05% of the applied fertilizer.Addition of nitrapyrin inhibited nitrification in all soils and reduced nitrite accumulation in the fertilizer bands. Nitrapyrin addition significantly reduced fertilizer-induced loss of nitrous oxide only in the calcareous clay soil. In the other soil, nitrapyrin had a lower bioactivity (relative inhibition of nitrification) which may have been due to its higher organic matter content.
Resumo Este trabalho constitui de uma avaliação da quantidade de óxido nitroso emitido por três solos. A emissão de óxido nitroso foi determinada em solos não fertilizados e onde a amônia-anidra (60 e 80 kg de N ha–1) foi aplicada, em bandas, com e sem nitrapyrin. O fluxo diário de óxido nitroso nos solos onde não se aplicou o fertilizante variou entre 1.1 e 1.6 g N ha–1. A aplicação da amônia-anidra causou um significativo aumento na emissão de óxido nitroso em dois solos. A emissão de óxido nitroso induzida pela aplicação do fertilizante foi mais alta em um solo calcáreo-argiloso. Foi neste solo onde a nitrificação ocorreu mais intensamente e um maior acúmulo de nitrito foi observado. As perdas de óxido nitroso induzidas pela aplicação da amônia-anidra foram menores do que 0.05% do fertilizante aplicado. A aplicação conjunta de nitrapyrin com o fertilizante inibiu parcialmente a nitrificação nos três solos e reduziu o acúmulo de nitrito nas bandas do fertilizante. A adição de nitrapyrin reduziu significativamente a emissão de óxido nitroso somente no solo calcáreo-argiloso. No outro solo, a inibição relativa da nitrificação (bio-atividade) foi a mais baixa observada. A baixa bio-atividade do nitrapyrin sugere um efeito causado pelo mais alto teor de matéria orgânica verificado neste solo. 相似文献
2.
Résumé Les ionènes de formule {[NMe 2(CH 2) 5NMe 2(CH 2)
n
]2I} p (avec Me=radical méthyl; n=3, 4, 5; et p le degré de polymérization) ont été préparés. Leur spectre RMN et IR est présenté et discuté. Associés à de l'iodure d'argent, ils donnent des composés conducteurs qui suivent la loi d'Arrhénius. Le système AgI-polydiiodure de N pentylène N propyléne tétraméthyl N, N, N, N diammonium possède à 25°C une conductivité maximale de 0.01 cm –1 pour une composition renfermant 80% en équivalent de AgI. Cette étude se place dans une perspective de mise au point de générateurs tout solide.
Ionenes with the formula {[NMe2(CH2)5NMe2(CH2)
n
]2I}p (where Me=methyl group;n=3, 4, 5; andp the degree of polymerization) have been prepared. Their NMR and IR spectra are shown and discussed. When these compounds are associated with silver iodide they give conducting compounds which obey the Arrhenius law. The highest conductivity of the AgI–N-pentylene, N-alkylene, N, N, N, N-tetramethyl diammonium polyiodide system, at 25°C, is 0.01 cm–1, corresponding to a compound containing 80% of AgI equivalent. This study has been carried out with the purpose of achieving solid generators. 相似文献
3.
In Japan, upland soils are an important source of nitrous oxide (N 2O) and nitric oxide (NO) gas emissions. This paper reports on an investigation of the effect of soil moisture near saturation on N 2O and NO emission rates from four upland soils in Japan of contrasting texture. The aim was to relate these effects to soil physical properties. Intact cores of each soil type were incubated in the laboratory at different moisture tensions after fertilisation with NH 4-N, NO 3-N or zero N. Emissions of N 2O and NO were measured regularly over a 16–20 day period. At the end of the incubation, soil cores were analysed for physical properties. Moisture and N fertiliser significantly affected rates of emissions of both N 2O and NO with large differences between the soil types. Nitrous oxide emissions were greatest in the finer-textured soils, whereas NO emissions were greater in the coarser-textured soils. Emissions of N 2O increased at higher moisture contents in all soils, but the magnitude of increase was much greater in finer-textured soils. Nitric oxide emissions were only significant in soils fertilised with NH 4-N and were negatively correlated with soil moisture. Analysis of soil properties showed that there was a strong relationship between the magnitude of emissions and soil physical properties. The importance of soil wetness to gas emissions was mainly through its influence on soil air-filled porosity, which itself was related to gas diffusivity. From the results of this research, we can now estimate likely effects of soil texture on emissions through the influence of soil type on soil aeration and soil drainage. This is of particular value in modelling N 2O and NO emissions from soil moisture status and land use inputs. 相似文献
4.
In a field experiment over three growing seasons, the potential benefits of planting berseem clover ( Trifolium alexandrinum L) with Westerwold Italian ryegrass ( Lolium multiflorum Lam.) were examined under irrigated continental Mediterranean conditions.Similar N rates (0, 30, 60, 90 and 120 kg N ha –1 cut –1) were applied to both pure Italian ryegrass stands and mixtures, each given three successive cuts. One previously unfertilized cut was performed in late winter. Species in the mixture were established at 50:50 seed ratio but the mean proportion of berseem clover was 14%. Mean winter survival of berseem was 87% but 88% of the plants had leaves damaged by the frost. Forage production varied with both N rate and cutting sequence in both the pure stand and the mixture but differences between the two types of swards were significant only at low levels of fertilizer N. Total DM production over the four cuts in plots with N applications of 0,90, 180, 270 and 360 kg N ha –1 a –1 were 7.14, 9.51, 11.66, 13.91 and 14.36 t DM ha –1 a –1 in pure stand, respectively. Corresponding values for the mixture were 8.80, 10.94, 12.90, 14.05 and 13.64 t DM ha –1 a –1. The mean response of Italian ryegrass in the range of 0–360 kg N ha –1 a –1 was 20 kg DM per kg N applied. The corresponding value for the mixture was 13 kg DM per kg N applied. At the berseem clover proportions reached in this work, N equivalence showed values of about 80 kg N ha –1 a –1. As rates of N increased from 0 to 120 kg N ha –1 cut –1, nitrogen concentration increased by 78%. In the applied range of N fertilizers, N0 3-N was not affected.
Résumé Dans un essai réalisé au cours de trois saisons agricoles, on a étudié le potentiel de 1'association du bersim avec le raygrass italien. Les cultures ont été emenées et irrigué dans des conditions continentales méditerranéennes. On a appliqué, aussi bien pour la culture pure du raygrass que pour l'association, une fertilisation azotée avec les doses suivantes (0, 30, 60, 90 et 120 kg N/ha/coupe) après chacune des trois coupes successives. Une autre coupe avant fertilisation a été faite à la fin de 1'hiver. Les proportions du bersim et du raygrass dans le mélange de graines étaient de 50:50. Cependant, dans la culture en association, les plantes du bersim n'étaient préentés qu'avec un 14 pourcent. 87% des plantes du bersim ont pu survivre en hiver, dont 88% avaient des feuilles endommagées par les gelées. La production d'herbe a été proportionnelle aux doses de fertilisation pour la culture pure et l'association. Néanmoins, différence entre les rendements de chacune de ces dernières était d'autant plus nette que les doses d'azote incorporées dans le sol étaient faibles. La production de la MS pour les quatre coupes dans les parcelles avec les applications de 0, 90, 180, 270 et 360 kg N ha–1 a–1 étaient de 7.14, 9.51, 11.66, 13.51, 14.36 tMS ha–1 a–1. Le rendement moyen du raygrass italien dans un intervalle de 0-360 kg N ha–1 a–1 a été de 20 kg MS par kg de N de fertilisation. Concernant le bersim, les valeurs équivalentes de N étaient de 1'ordre de 80 kg N ha–1 a–1. Au fur et à mesure que les doses de fertilisation azotée augmente de 0 à 120 kg ha–1 coupe, la concentration en azote augmente de 78%. Dans l'intervalle de la fertilisation azotée appliqué NO3 -N n'a pas été affectée. 相似文献
5.
Biogeochemical processes regulating cropland soil nitrous oxide (N 2O) emissions are complex, and the controlling factors need to be better understood, especially for seasonal variation after fertilization. Seasonal patterns of N 2O emissions and abundances of archaeal ammonia monooxygenase ( amoA), bacterial amoA, nitrate reductase ( narG), nitrite reductase ( nirS/ nirK), and nitrous oxide reductase ( nosZ) genes in long-term fertilized wheat–maize soils have been studied to understand the roles of microbes in N 2O emissions. The results showed that fertilization greatly stimulated N 2O emission with higher values in pig manure-treated soil (OM, 2.88 kg N ha ?1 year ?1) than in straw-returned (CRNPK, 0.79 kg N ha ?1 year ?1) and mineral fertilizer-treated (NPK, 0.90 kg N ha ?1 year ?1) soils. Most (52.2–88.9%) cumulative N 2O emissions occurred within 3 weeks after fertilization. Meanwhile, N 2O emissions within 3 weeks after fertilization showed a positive correlation with narG gene copy number and a negative correlation with soil NO 3? contents. The abundances of narG and nosZ genes had larger direct effects (1.06) than ammonium oxidizers (0.42) on N 2O emissions according to partial least squares path modeling. Stepwise multiple regression also showed that log narG was a predictor variable for N 2O emissions. This study suggested that denitrification was the major process responsible for N 2O emissions within 3 weeks after fertilization. During the remaining period of crop growth, insufficient N substrate and low temperature became the primary limiting factors for N 2O emission according to the results of the regression models. 相似文献
6.
In Italy, managed soils account for about 50% of annual national emissions of nitrous oxide (N 2O), thus the effect of agricultural practices on N 2O emissions must be studied in order to develop mitigation strategies. Soil N 2O emissions were measured in two field campaigns (2013–2014 and 2014–2015) on durum wheat in a Mediterranean environment to test the mitigation potential of reduced tillage and nitrogen (N) fertilization rate. N 2O emissions were measured with a fully-transportable instrument developed during the project LIFE?+?IPNOA “Improved flux Prototypes for N 2O emission reduction from Agriculture” and equipped with an infrared laser detector. Reducing tillage from ploughing to minimum tillage had no effect on average daily N 2O flux, while decreasing the N rate from 170 to 110 kg N ha ?1 reduced the average daily N 2O flux, without negatively affecting the grain yield. Furthermore, N 2O daily flux were positively correlated with soil water filled pore space, NO 3-N, and NH 4-N concentrations, and they were largely variable between the two field campaigns as a result of different environmental and management conditions (i.e.: rainfall, different amount of crop residues incorporated in soil). Overall, the innovative fully-transportable instrument performed well in the field and allowed us to conclude that decreasing the N fertilizer rate was a valuable option to mitigate N 2O emissions without negative effects on wheat productivity. 相似文献
7.
A laboratory experiment was conducted to determine whether applying controlled release nitrogen fertilisers could reduce nitrous oxide emissions from an andosol maintained at different water contents, compared with applying standard nitrogen fertiliser. The effect of the form of N applied (NH 4-N or NO 3-N) was also investigated. Soil was collected from an arable field and sub-samples were treated with controlled release or standard fertiliser, applied at a rate of 200 g N g –1 dry soil either as NH 4
+ or NO 3
–. The soils were maintained at 40%, 55%, 70% or 85% water filled pore space (WFPS) and incubated at 25 °C for 50 days. Gas samples were collected and analysed every 3–4 days and soil samples were analysed on five occasions during the incubation. Emissions of N 2O were much greater from ammonium sulphate than from calcium nitrate fertiliser, indicating that nitrification was the main source of the N 2O. Emissions at 85% WFPS were greater than at the lower water contents in all treatments. The use of controlled release NH 4-N fertilisers reduced and delayed the maximum peak of emissions, but at 55% and 70% WFPS this did not always result in lower total emissions. Emissions from the controlled release NO 3-N fertiliser were very low, but only significantly lower than from standard NO 3-N fertiliser at water contents below 85% WFPS. The results demonstrate that choosing the appropriate form of fertiliser in relation to expected soil moisture could significantly reduce N 2O emissions. Applying the fertiliser in a controlled-release form could further reduce emissions by reducing the length of time that fertiliser nitrogen is present in the soil and available for nitrification or denitrification. 相似文献
8.
Résumé Les films CdO de quelques microns d'épaisseur obtenus par pulvérisation réactive et par métallisationoxydation sont examinés du point de vue de leur hydratation en Cd(OH) 2 et de leur réduction à l'état de Cd métallique, en milieu potassique aqueux. Le coefficient de diffusion des molécules H 2O à travers Cd(OH) 2 est mesuré en suivant la résistance des films, et est estimé de l'ordre de 10 –10 à 10 –11 cm 2s –1 pour les deux types de préparation. Des oscillations de potentiel pendant la réduction à courant constant révèlent un mécanisme dû à la compétition entre la réduction de CdO, son hydratation en Cd(OH) 2, la réduction et la dissolution de Cd(OH) 2.
CdO films a few micrometers thick, which have been prepared by reactive spraying and by oxidation in air of evaporated cadmium, were examined with respect to their hydration into Cd(OH)2 and to their reduction into Cd metal in aqueous potash solution. The diffusion coefficient of H2O molecules through Cd(OH)2 was measured by monitoring the film resistance, and was found to be in the order of 10–10 to 10–11 cm2s–1 for both types of film. Oscillations of potential during the course of the reduction at constant current have unveiled a mechanism which is due to a competition between the reduction of CdO, its hydration into Cd(OH)2, the reduction and the dissolution of Cd(OH)2.
ERA au CNRS No. 468 Electrochimie des Dérivés Métallo-minéraux et Métallo-organiques. 相似文献
9.
Tropical soils are important sources of nitrous oxide (N 2O) and nitric oxide (NO) emissions from the Earths terrestrial ecosystems. Clearing of tropical rainforest for pasture has the potential to alter N 2O and NO emissions from soils by altering moisture, nitrogen supply or other factors that control N oxide production. In this review we report annual rates of N 2O and NO emissions from forest and pastures of different ages in the western Brazilian Amazon state of Rondônia and examine how forest clearing alters the major controls of N oxide production. Forests had annual N 2O emissions of 1.7 to 4.3 kg N ha -1 y -1 and annual NO emissions of 1.4 kg N ha -1 y -1. Young pastures of 1–3 years old had higher N 2O emissions than the original forest (3.1–5.1 kg N ha -1 y -1) but older pastures of 6 years or more had lower emissions (0.1 to 0.4 kg N ha -1 y -1). Both soil moisture and indices of soil N cycling were relatively poor predictors of N 2O, NO and combined N 2O + NO emissions. In forest, high N 2O emissions occurred at soil moistures above 30 water-filled pore space, while NO emissions occurred at all measured soil moistures (18–43). In pastures, low N availability led to low N 2O and NO emissions across the entire range of soil moistures. Based on these patterns and results of field fertilization experiments, we concluded that: (1) nitrification was the source of NO from forest soils, (2) denitrification was not a major source of N 2O production from forest soils or was not limited by NO- supply, (3) denitrification was a major source of N 2O production from pasture soils but only when NO 3- was available, and (4) nitrification was not a major source of 3 NO production in pasture soils. Pulse wettings after prolonged dry periods increased N 2O and NO 3- emissions for only short periods and not enough to appreciably affect annual emission rates. We project that Basin-wide, the effect of clearing for pasture in the future will be a small reduction in total N 2O emissions if the extensive pastures of the Amazon continue to be managed in a way similar to current practices. In the future, both N 2Oand NO fluxes could increase if uses of pastures change to include greater use of N fertilizers or N-fixing crops. Predicting the consequences of these changes for N oxide production will require an understanding of how the processes of nitrification and denitrification interact with soil type and regional moisture regimes to control N 2O and NO production from these new anthropogenic N sources. 相似文献
10.
This paper addresses three topics related to N 2O emissions from agricultural soils. First, an assessment of the current knowledge of N 2O emissions from agricultural soils and the role of agricultural systems in the global N 2O are discussed. Secondly, a critique on the methodology presented in the OECD/OCDE (1991) program on national inventories of N 2O is presented. Finally, technical options for controlling N 2O emissions from agricultural fields are discussed.The amount of N 2O derived from nitrogen applied to agricultural soils from atmospheric deposition, mineral N fertilizer, animal wastes or biologically fixed N, is not accurately known. It is estimated that the world-wide N 2O emitted directly from agricultural fields as a result of the deposition of all the above nitrogen sources is 2–3 Tg N annually. This amounts to 20–30% of the total N 2O emitted annually from the earth's surface. An unknown, but probably significant, amount of N 2O is generated indirectly in on and off farm activities associated with food production and consumption.Management options to limit direct N 2O emissions from N-fertilized soils should emphasize improving N-use efficiency. Such management options include managing irrigation frequency, timing and quantity; applying N only to meet crop demand through multiple applications during the growing season or by using controlled release fertilizers; applying sufficient N only to meet crop needs; or using nitrification inhibitors. Most of these options have not been field tested. Agricultural management practices may not appreciably affect indirect N 2O emissions. 相似文献
11.
Nitrous oxide (N 2O) is formed mainly during nitrification and denitrification. Inherent soil properties strongly influence the magnitude of N 2O formation and vary with soil types. A laboratory study was carried out using eight humid tropic soils of Malaysia to monitor NH 4
+ and NO 3
– dynamics and N 2O production. The soils were treated with NH 4NO 3 (100 mg N kg –1 soil) and incubated for 40 days at 60% water-filled pore space. The NH 4
+ accumulation was predominant in the acid soils studied and NO 3
– accumulation/disappearance was either small or stable. However, the Munchong soil depicted the highest peak (238 g N 2O-N kg –1 soil d –1) at the beginning of the incubation, probably through a physical release. While the Tavy soil showed some NO 3
– accumulation at the end of the study with a maximum N 2O flux of 206 g N 2O-N kg –1 soil d –1, both belong to Oxisols. The other six soils, viz. Rengam, Selangor, Briah, Bungor, Serdang and Malacca series, formed smaller but maximum peaks in an decreasing order of 116 to 36 g N 2O-N kg –1 soil d –1. Liming the Oxisols and Ultisols raised the soil pH, resulting in NO 3
– accumulation and N 2O production to some extent. As such the highest N 2O flux of 130.2 and 77.4 g N 2O-N kg –1 soil d –1 was detected from the Bungor and Malacca soils, respectively. The Selangor soil, belonging to Inceptisol, did not respond to lime treatment. The respective total N 2O formations were 3.63, 1.92 and 1.69 mg N 2O-N kg –1 soil from the Bungor, Malacca and Selangor soils, showing an increase by 49 and 99% over the former two non-limed soils. Under non-limed conditions, the indigenous soil properties, viz. Ca ++ content, %clay, %sand and pH of the soils collectively could have influenced the total N 2O formation. 相似文献
12.
In the following study N 2O emissions from 3 different grasslands and from 3 different arable lands, representing major agriculture areas with different
soil textures and normal agricultural practices in Belgium, have been monitored for 1 to 2 years. One undisturbed soil under
deciduous forest was also included in the study. Nitrous oxide emission was measured directly in the field from vented closed
chambers through photo-acoustic infrared detection. Annual N 2O emissions from the arable lands ranged from 0.3 to 1.5 kg N ha −1 y −1 and represent 0.3 to 1.0% of the fertilizer N applied. Annual N 2O emissions from the intensively managed grasslands and an arable land sown with grass were significantly larger than those
from the cropped arable lands. Emissions ranged from 14 to 32 kg N ha −1 y −1, representing fertilizer N losses between 3 and 11%. At the forest soil a net N 2O uptake of 1.3 kg N 2O-N ha −1 was recorded over a 2-year period. It seems that the N 2O-N loss per unit of fertilizer N applied is larger for intensively managed and heavily fertilized (up to 500 kg N ha −1) grasslands than for arable lands and is substantially larger than the 1.25% figure used for the global emission inventory.
Comparison of the annual emission fluxes from the different soils also indicated that land use rather than soil properties
influenced the N 2O emission. Our results also show once again the importance of year-round measurements for a correct estimate of N 2O losses from agricultural soils: 7 to 76% of the total annual N 2O was emitted during the winter period (October–February). Disregarding the emission during the off-season period can lead
to serious underestimation of the actual annual N 2O flux.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
13.
Although it is known that crops can directly emit N 2O, their contribution to the total N 2O emission from crop-soil systems under field conditions is not well understood. This study was conducted to study the contribution
of crops to total N 2O emission from soybean-soil and maize-soil systems in northeastern China. The effects of N fertilization on N 2O emission and NO
3
−
-N concentration in plants were also studied. The emission from crop-soil systems was measured with the closed chamber method,
whereas the direct emission from crops was measured with the soil surface-sealed method. The addition of fertilizer N significantly
increased the NO
3
−
-N concentration in crops and enhanced the N 2O emission from crop-soil systems and from crops alone. The amount of N 2O emitted directly from soybean plants accounted for 6 to 11% of the total soybean-soil emission. Similarly, the amount of
N 2O emitted directly from maize plants accounted for 8.5 to 16% of the total maize-soil emission. The proportion of the applied
N lost through direct N 2O emission from plants ranged from 0.19 to 0.34%, whereas the proportion of the applied N lost through N 2O emission from the crop-soil system ranged from 1.1 to1.9%. These results suggest that the use of chambers that do not include
plants may lead to an underestimation of the total N 2O emission from crop-soil systems.
This revised version was published online in November 2006 with corrections to the Cover Date. 相似文献
14.
Studies on emissions of nitrous oxide (N 2O) from agricultural soils mostly focus on fluxes between the soil and the atmosphere or are limited to the atmosphere in
the topsoil. However, in soils with shallow water tables, significant N 2O formation may occur closer to the groundwater. The aims of this study were (i) to determine the importance of subsoil N 2O formation in a sandy soil; and (ii) to obtain a quantitative insight in the contribution of subsoil N 2O to the overall losses of N 2O to the environment. We applied 15N labeled fertilizer at a rate of 5.22 kg 15N ha −1; 50% as Ca(NO 3) 2 and 50% as NH 4Cl, on a mesic typic Haplaquod seeded with potatoes ( Solanum tuberosum L.), and traced soil N 2O concentrations and fluxes over a one-year period. Throughout the year, total N 2O and the amount of 15N recovered in soil N 2O were highest in the subsoil, with a maximum concentration at 48 cm depth in mid-February of 19900 μl m −3 and 24 μg 15N m −3, respectively. The maximum concentration coincided with the highest water-filled pore space of 71%. The cumulative flux of
N 2O was 446 g N 2O-N ha −1, the recovery of 15N in this flux was 0.06%. During the summer, maximum fluxes followed high soil N 2O concentrations. During winter, no such relation was found. We concluded that the formation of N 2O was the highest in the subsoil, largely controlled by water-filled pore space rather than NO 3− concentration or temperature. Although high subsoil N 2O concentrations did not lead to high surface fluxes of N 2O in the winter, artificial draining may lead to high indirect N 2O emissions through supersaturated drainage water. 相似文献
15.
The DNDC model was used to estimate direct N 2O emissions from agricultural soils in Canada from 1970 to 1999. Simulations were carried out for three soil textures in seven soil groups, with two to four crop rotations within each soil group. Over the 30-year period, the average annual N 2O emission from agricultural soils in Canada was found to be 39.9 Gg N 2O–N, with a range from 20.0 to 77.0 Gg N 2O–N, and a general trend towards increasing N 2O emissions over time. The larger emissions are attributed to an increase in N-fertilizer application and perhaps to a trend in higher daily minimum temperatures. Annual estimates of N 2O emissions were variable, depending on timing of rainfall events and timing and duration of spring thaw events. We estimate, using DNDC, that emissions of N 2O in eastern Canada (Atlantic Provinces, Quebec, Ontario) were approximately 36% of the total emissions in Canada, though the area cropped represents 19% of the total. Over the 30-year period, the eastern Gleysolic soils had the largest average annual emissions of 2.47 kg N 2O–N ha –1 y –1 and soils of the dryer western Brown Chernozem had the smallest average emission of 0.54 kg N 2O–N ha –1 y –1. On average, for the seven soil groups, N 2O emissions during spring thaw were approximately 30% of total annual emissions. The average N 2O emissions estimates from 1990 to 1999 compared well with estimates for 1996 using the IPCC methodology, but unlike the IPCC methodology our modeling approach provides annual variations in N 2O emissions based on climatic differences. 相似文献
16.
In this study, we measured nitrous oxide (N 2O) fluxes from plots of fall-planted hairy vetch (HV, Vicia villosa) and spring-planted broadleaf vetch (BLV, Vicia narbonensis) grown as nitrogen (N) sources for following summer forage crabgrass ( Digitaria sanguinalis). Comparisons also included 60 kg ha ?1 inorganic N fertilizer for crabgrass at planting (60-N) and a control without N fertilizer. Each treatment had six replicated plots across the slope. Fluxes were measured with closed chamber systems during the period between spring growth of cover crops and first-cut of crabgrass in mid-July. HV had strong stand and aboveground biomass had 185?±?50 kg N ha ?1 (mean?±?standard error, n?=?6) at termination. However, BLV did not establish well and aboveground biomass had only 35?±?15 kg N ha ?1. Ratio vegetation index of crabgrass measured as proxy of biomass growth was highest in HV treatment. However, total aboveground biomass of crabgrass was statistically similar to 60-N plots. Fluxes of N 2O were low prior to termination of cover crops but were as high as 8.2 kg N 2O ha ?1 day ?1 from HV plots after termination. The fluxes were enhanced by large rainfall events recorded after biomass incorporation. Rainfall enhanced N 2O fluxes were also observed in other treatments, but their magnitudes were much smaller. The high N 2O fluxes from HV plots contributed to emissions of 30.3?±?12.4 kg N 2O ha ?1 within 30 days of biomass incorporation. Emissions were only 2.0?±?0.7, 3.4?±?1.3 and 1.0?±?0.4 kg N 2O ha ?1 from BLV, 60-N and control plots, respectively. 相似文献
17.
Grazed pastures contribute significantly to anthropogenic emissions of N 2O but the respective contributions of archaea, bacteria and fungi to codenitrification in such systems is unresolved. This study examined the relative contributions of bacteria and fungi to rates of denitrification and codenitrification under a simulated ruminant urine event. It was hypothesised that fungi would be primarily responsible for both codenitrification and total N 2O and N 2 emissions. The effects of bacterial (streptomycin), fungal (cycloheximide), and combined inhibitor treatments were measured in a laboratory mesocosm experiment, on soil that had received 15N labelled urea. Soil inorganic-N concentrations, N 2O and N 2 gas fluxes were measured over 51 days. On Days 42 and 51, when nitrification was actively proceeding in the positive control, the inhibitor treatments inhibited nitrification as evidenced by increased soil NH 4 + -N concentrations and decreased soil NO 2 ? -N and NO 3 ? -N concentrations. Codenitrification was observed to contribute to total fluxes of both N 2O (≥ 33%) and N 2 (≥ 3%) in urine-amended grassland soils. Cycloheximide inhibition decreased NH 4 + – 15N enrichment and reduced N 2O fluxes while reducing the contribution of codenitrification to total N 2O fluxes by ≥ 66 and ≥ 42%, respectively. Thus, given archaea do not respond to significant urea deposition, it is proposed that fungi, not bacteria, dominated total N 2O fluxes, and the codenitrification N 2O fluxes, from a simulated urine amended pasture soil. 相似文献
18.
Recent interests in improving agricultural production while minimizing environmental footprints emphasized the need for research on management strategies that reduce nitrous oxide (N2O) emissions and increase nitrogen-use efficiency (NUE) of cropping systems. This study aimed to evaluate N2O emissions, annualized crop grain yield, emission factor, and yield-scaled- and NUE-scaled N2O emissions under continuous spring wheat (Triticum aestivum L.) (CW) and spring wheat–pea (Pisum sativum L.) (WP) rotations with four N fertilization rates (0, 50, 100, and 150 kg N ha?1). The N2O fluxes peaked immediately after N fertilization, intense precipitation, and snowmelt, which accounted for 75–85% of the total annual flux. Cumulative N2O flux usually increased with increased N fertilization rate in all crop rotations and years. Annualized crop yield and NUE were greater in WP than CW for 0 kg N ha?1 in all years, but the trend reversed with 100 kg N ha?1 in 2013 and 2015. Crop yield maximized at 100 kg N ha?1, but NUE declined linearly with increased N fertilization rate in all crop rotations and years. As N fertilization rate increased, N fertilizer-scaled N2O flux decreased, but NUE-scaled N2O flux increased non-linearly in all years, regardless of crop rotations. The yield-scaled N2O flux decreased from 0 to 50 kg N ha?1 and then increased with increased N fertilization rate. Because of non-significant difference of N2O fluxes between 50 and 100 kg N ha?1, but increased crop yield, N2O emissions can be minimized while dryland crop yields and NUE can be optimized with 100 kg N ha?1, regardless of crop rotations. 相似文献
19.
The application of animal manure slurries to soils may cause high short-term emissions of nitrous oxide (N 2O). We performed studies on N 2O emissions varying the contents of NH 4-N and microbial available organic carbon (measured as biological oxygen demand, BOD) of cattle slurry. Additionally the effect
of slurry BOD on N 2O emissions at different soil water contents (35, 54, 71% water filled pore space, WFPS) was studied. Slurries from an anaerobic
digestion plant (digested slurry, BOD: 1.2 g O 2 l −1) or untreated slurry (BOD: 6.8 g O 2 l −1) were applied at 30 m 3 ha −1 and incubated at 20°C. The higher the WFPS the more N 2O was emitted independent from the type of slurry applied. At low and medium soil water contents, the digested slurry induced
significantly lower N 2O emissions than the untreated slurry. The N 2O emissions were directly correlated with the BOD content of the slurry ( R
2=0.61, P≤0.001). We also compared the effect of NH 4-N concentration and BOD on emissions from the slurries at 54% WFPS. Again the BOD had a significant influence on N 2O emissions but a reduction of NH 4-N had no effect on the amount of N 2O emitted. The microbially available organic carbon seems to determine the amount of N 2O emitted shortly after slurry application.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
20.
Résumé A l'interface Fe/H 2SO 4, 1 N (aéré ou non), et dans le domaine de potentiel (–0·95, –1·2 V/E.S.S.), nous avons trouvé que le courant cathodique mesuré sur une électrode à disque tournant varie avec la vitesse de rotation suivant une loi de la forme: I=A+B
1/2.
A peut être identifié au courant de réduction du proton solvaté mais dépend fortement de la teneur en oxygène de l'électrolyte. La composante diffusionnelle B
1/2 peut être identifiée à la réduction de l'oxygène dissous mais est très inférieure à celle relative à une surface uniformément réactive. Le blocage résultant est compatible avec l'analyse en fonction du potentiel de la corrélation entre A et B
1/2 en supposant la réaction suivante: Fe H adsFe H
ads
*
, où Fe H ads est un hydrogène adsorbé faiblement lié de courte durée de vie (qq. s) et Fe H
ads
*
est un hydrogène adsorbé fortement lié de longue durée de vie (qq.h). Le déblocage résulte de la réaction chimique H ads+1/4 O 21/2 H 2O.Dans le cadre classique du mécanisme de dégagement de l'hydrogène en deux étapes, nous avons montré que notre modèle d'interdépendance implique que l'étape limitant la vitesse soit celle de Tafel à faible surtension et celle d'Horiuti pour des tensions cathodiques plus élevées.
We found that at the 1 N Fe/H2SO4 (aerated or de-aerated) interface within the potential range (–0d95, –1.2 V/S.S.E.) the cathodic current measured on a rotating disc electrode varies with the rotation speed according to the relation:I=A+B1/2.
A can be assigned to the reduction of H+ but depends strongly on the oxygen concentration. On the other hand the diffusional componentB1/2 can be assigned to the reduction of dissolved oxygen but is much lower than that relative to a uniform reactive surface. The resulting blocking is consistent with the analysis as a function of the potential of the correlation betweenA andB1/2 by assuming the following reaction: Fe HadsFe H
ads
*
. Fe Hads and Fe H
ads
*
are adsorbed hydrogen low bonded with a short life time (a few s) and strong bonded with a long life time (a few h) respectively. The blocked surface is activated by the chemical reaction Fe Hads+1/4 O21/2 H2O+Fe.In the classic framework of the two-step hydrogen evolution mechanism, we demonstrated that our interdependence model implies that the rate determining step is the Tafel reaction at low overpotentials and the Horiuti reaction for the highest overpotentials. 相似文献
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