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Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2017-09-04T17:31:07Z No. of bitstreams: 1 TESE_Viviane Figueiredo Souza versão final.pdf: 1973892 bytes, checksum: 8b1ac31fbe25c8a6584e68f8e3b8ff71 (MD5) / Made available in DSpace on 2017-09-04T17:31:07Z (GMT). No. of bitstreams: 1 TESE_Viviane Figueiredo Souza versão final.pdf: 1973892 bytes, checksum: 8b1ac31fbe25c8a6584e68f8e3b8ff71 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ / O nitrogênio (N) é um elemento imprescindível para todos os organismos do nosso planeta, entretanto o composto nitrogenado mais abundante, o gás dinitrogênio (N2), é assimilável apenas por poucos micro-organismos. Isso torna o N limitante, refletindo na sua disponibilização via mineralização de matéria orgânica (MO) e a nitrificação, que produzem amônio (NH4+) e nitrato (NO3-), respectivamente. Em solos, esses processos são regulados por fatores como conteúdo de MO e água no solo, pH e temperatura. Em ecossistemas florestais, tropicais e boreais, esses processos são muito relevantes e ainda pouco estudados, principalmente em áreas de floresta secundária sob influência de manejo. A mudança de uso do solo causa alterações na ciclagem e disponibilidade do N, nos fatores reguladores, e na emissão de óxido nitroso (N2O), um gás de efeito estufa. Padrões de recuperação florestal são bastante distintos entre diferentes florestas tropicais, como visto para floresta de Mata Atlântica e Amazônica, com taxas de mineralização em florestas jovens (10 anos) muito elevadas na Amazônia (20,9 μg N g-1 SWD d-1) e mais baixas na Mata Atlântica (3,2 μg N g-1 SWD d-1). Já a nitrificação teve um padrão semelhante, com baixas taxas em ambas as florestas jovens (0,6 6,8 μg N g-1 SWD d-1 na Mata Atlântica e Amazônia, respectivamente), o que indica uma ciclagem de N conservativa, evitando perdas via emissão de gás e lixiviação de NO3-. Entretanto, a emissão de N2O em área de restauração na Mata Atlântica foi maior do que na pristina (22 e 2,5 μg N2O-N g-1 SWD h-1, respectivamente) devido à maior temperatura do solo que estimula os processos microbianos produtores de N2O. Em termos de floresta pristina, a taxa de nitrificação foi bastante distinta entre a floresta de Mata Atlântica e Amazônica (0,08 e 15,9 μg N2O-N g-1 SWD h-1, respectivamente). Isso evidencia os diferentes fatores reguladores de cada região tropical, como regime de chuvas, composição vegetal, tipos de solo, etc. Em florestas boreais, foi visto que o conteúdo de MO e água do solo e o pH do solo são os principais reguladores, limitando a disponibilidade de N em florestas bem drenadas dominadas por coníferas, em comparação com florestas pouco drenadas dominadas por turfa. Dessa forma, verificamos que a mineralização e, principalmente, a nitrificação, são processos muito relevantes no controle de N, e mesmo em ecossistemas diferentes, os fatores reguladores muitas vezes são os mesmos. Isso evidencia a necessidade de mais estudos acerca da dinâmica do N nesses ambientes, principalmente em florestas em restauração / Nitrogen (N) is an essential element for all organisms; however, the most abundant nitrogen compound, dinitrogen (N2), is assimilable only by a few microorganisms. This makes N limiting, which reflects in its availability via organic matter (OM) mineralization and nitrification, which produce ammonium (NH4+) and nitrate (NO3-), respectively. In soils, these processes are regulated by factors such as OM and soil water content, pH and temperature. In forest ecosystems, tropical and boreal, these processes are very relevant and still poorly understood, especially in secondary forest previously deforested. The land use change causes alterations in cycling and availability of N, regulating factors, and emission of nitrous oxide (N2O), a greenhouse gas. Forest recovery patterns are quite distinct among different rainforests, as seen for Atlantic and Amazon rainforest, with very high levels of mineralization in young forests (10 years) in Amazonia (20.9 μg N2O-N g-1 SWD h-1) and low in the Atlantic Forest (3.2 μg N2O-N g-1 SWD h-1). Nitrification had a similar pattern between them, with low rates in both young forests (0.6 and 6.8 μg N2O-N g-1 SWD h-1 in the Atlantic and Amazon forest, respectively), indicating a conservative N cycling, avoiding losses through gas emission and NO3- leaching. However, the N2O emission in restoration area in the Atlantic Forest was higher than in pristine (22 and 2.5 μg N2O-N g-1 SWD h-1, respectively) due to the higher soil temperature, which stimulates microbial production of N2O. In terms of pristine forest, the nitrification rate was very different between the Atlantic forest and Amazonian forest (0.08 and 15.9 μg N2O-N g-1 SWD h-1, respectively), showing the different regulatory factors of each tropical region, such as rainfall regime, vegetal composition, soil types, etc. In boreal forests, OM, soil water content and soil pH were the main regulators, limiting the availability of N in conifer-dominated well-drained forests compared to peat-dominated poorly drained forests. In this way, we verified that mineralization and, mainly, nitrification are very relevant processes in the control of N, and even in extremely different ecosystems, the regulating factors are often the same. This evidences the need for more studies about N dynamics in these environments, especially in restoration forests

Submitted by Biblioteca de Pós-Graduação em Geoquímica BGQ (bgq@ndc.uff.br) on 2017-09-21T14:51:23Z No. of bitstreams: 1 Dissertação Renato de Aragão Ribeiro Rodrigues.pdf: 3393188 bytes, checksum: 62e4ebd43780efd96e9d6775d8d182f0 (MD5) / Made available in DSpace on 2017-09-21T14:51:23Z (GMT). No. of bitstreams: 1 Dissertação Renato de Aragão Ribeiro Rodrigues.pdf: 3393188 bytes, checksum: 62e4ebd43780efd96e9d6775d8d182f0 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Universidade Federal Fluminense. Instituto de Química. Programa de Pós-Graduação em Geoquímica, Niterói, RJ / Este trabalho apresenta fluxos de deposição atmosférica (úmida e seca) dos íons majoritários, relativos ao período de agosto 2004 a novembro de 2005, medidos em local próximo à Sede do Parque Nacional da Serra dos Órgãos, em Teresópolis. No período de janeiro a dezembro de 2005 foram medidas, quinzenalmente, em local próximo à sede, as emissões de óxido nitroso (N2O) no solo da floresta. E foram coletadas, semanalmente, amostras da água do rio Paquequer, em local próximo à entrada da sede Teresópolis. A água da chuva apresentou pH médio de 5,2 e os íons mais abundantes foram (em Xeq L-1) o amônio, sulfato e cloreto. Do total de enxofre (S) e nitrogênio (N) depositados, cerca de 90% estão associados à deposição úmida, e o restante à seca. Os fluxos de deposição total (úmida + seca) de SO4 2- e nitrogênio inorgânico (NO3 - e NH4 +) foram 295 mol ha-1 ano-1 (9,4 kg S ha-1 ano-1) e 824 mol ha-1 ano-1 (11,5 kg N ha-1 ano-1), respectivamente. Se assumirmos a mesma deposição nos 11000 ha do PARNASO, teremos uma deposição de 97 t de S e 117 t de N. Mais de 90% do sulfato depositado provêm da oxidação do dióxido de enxofre (SO2) na atmosfera e o restante dos aerossóis de sal marinho. Os fluxos de deposição de NH4 +, SO4 2- e NO3 - na água da chuva do PARNASO são superiores às verificadas em várias localidades do estado do Rio de Janeiro, como Parque Nacional do Itatiaia, Ilha Grande, Niterói e cidade do Rio de Janeiro, além de outras localidades do Brasil. Isso indica que o PARNASO, face à sua localização geográfica e à ação dos ventos do quadrante sul, atua como uma área receptora das emissões geradas, principalmente por queima de combustíveis fósseis e mudanças do uso da terra na Região Metropolitana do Rio de Janeiro. O fluxo médio de N2O na interface solo-atmosfera foi 3,1 Xg N m-2 h-1. A umidade do solo (traduzida pelos valores de precipitação) e a temperatura do solo se mostraram importantes fatores no controle do fluxo de N2O. As águas do Rio Paquequer apresentaram altos valores de NO3 - e SO4 2-. Esses valores provavelmente resultam da alta deposição atmosférica de N e S. A análise de cluster e a análise de componentes principais indicaram mais uma vez que a RMRJ exerce uma influência grande na qualidade da água mesmo em sistemas protegidos. / Wet and dry deposition fluxes of major ions were measured from August 2004 to November 2005 at the headquarters of Serra dos Órgãos National Park, in Teresópolis. In a forest site nearby, nitrous oxide (N2O) fluxes were measured at the soil surface from January to April 2005. Average rainwater pH was 5,2. The most abundant ions (in Xeq L-1) were ammonium, sulfate, and chloride. About 90% of the total sulfur (S) and nitrogen (N) were associated with wet deposition. The estimated total (wet + dry) deposition fluxes of sulfate and inorganic nitrogen (ammonium and nitrate) were 295 mol ha-1 ano-1 (9,4 kg S ha-1 ano-1) and 824 mol ha-1 ano-1 (11,5 kg N ha-1 ano-1), of which 70% is due to ammonium and the remainder to nitrate. More than 90% of the total sulfate were originated from oxidation of sulfur dioxide (SO2) in the atmosphere and the remaining from sea salt aerosols. The deposition fluxes of NH4+, SO42- e NO3- were bigger than in other sites of Rio de Janeiro state, like Itatiaia National Park, Ilha Grande, Niterói e Rio de Janeiro city. This indicates that PARNASO due its geographical localization and the actions of the wind from South quadrant actuate like a receptor area of the emissions from Rio de Janeiro Metropolitan Region (RJMR). The average N2O flux at the soil-atmosphere interface was 3,1 Xg N m-2 h-1, which was lower than other values found in forest soils of Rio de Janeiro state. The water from Paquequer river showed high values of NO3 - and SO4 2-. This values are probably due the high deposition of N and S. The Cluster analysis and the Principal Components Analysis showed that PARNASO is under the influence of the emissions from RJMR.

Pendant plusieurs siècles, le sol a été labouré pour contrôler le développement des mauvaises herbes, incorporer des résidus de culture et préparer le sol avant le semis. Après le développement des herbicides la nécessité de labourer a été posée et des systèmes de travail du sol réduit ont été introduits. Ces systèmes de travail du sol réduit ont deux caractéristiques : (i) le sol n'est plus labouré et, (ii) le sol est toujours complètement ou partiellement couvert avec des résidus de culture. Le passage du labour profond au semis-direct (un système de travail du sol réduit) induit des modifications dans la structure du sol et la localisation de la matière organique du sol (MOS) et des résidus de culture. Ceci entraîne des modifications dans le climat du sol (température et humidité) et certaines propriétés biologiques, chimiques et physiques du sol. La combinaison de toutes ces modifications a une influence importante sur les transformations de l'azote et du carbone dans le sol. Les objectifs de notre étude ont été de (i) quantifier les différences des stocks et de flux de carbone et de l'azote entre différents systèmes de travail du sol différenciés depuis 32 années dans un sol limoneux de grande culture du bassin Parisien et, (ii) expliciter les effets du climat du sol, de la structure et des propriétés biologiques et physiques du sol sur les différences de fonctionnement des cycles du carbone et de l'azote du sol. Cette étude a été essentiellement focalisée sur les variables qui ont un impact agronomique ou environnemental : carbone et azote organique du sol, dynamique de l'azote minéral du sol et les émissions de CO2 et N2O. Deux systèmes de travail du sol ont été étudiés : le labour (CT) et le semis-direct (NT). Ces systèmes de travail du sol ont été suivis sur des parcelles en rotation maïs-blé du site expérimental de Boigneville (91) en France. NT présente des stocks de carbone 5 à 15 % plus importants et des stocks d'azote 3 à 10% supérieurs à ceux mesurés pour CT, mais ces différences n'ont pas toujours été statistiquement significatives. Les concentrations de C et N diminuent avec la profondeur en NT alors qu'elles sont distribuées de façon homogène dans la couche labourée en CT. La différence de stock d'azote organique associé aux argiles et limons et la différence de stock d'azote associé à la matière organique particulaire (MOP) ont chacune expliqué 50 % de la différence de stock d'azote total entre les deux systèmes. 66 % de la différence du stock de carbone total du sol ont été explicités par la différence de stock de carbone présent dans la MOP (58 %) et les résidus de culture (8 %). Le carbone et l'azote additionnel dans NT se situe dans des agrégats. Nos résultats suggèrent que les stocks de C et N plus importants pour NT peuvent être attribués à (i) la formation de macroagrégats plus prononcée dans la couche 0-5 cm due à l'activité microbienne et aux stocks de MOS plus importants et, (ii) la meilleure protection de la MOS dans la couche 5-20 cm due à une porosité du sol plus faible et à l'absence de la destruction de la structure du sol par le travail du sol ou le climat. Les modalités de travail du sol n'ont pratiquement pas eu d'influence sur les dynamiques de l'eau et de nitrates dans le profil (0-120 cm) du sol. L'interprétation des données avec le modèle LIXIM a permis de calculer des vitesses de minéralisation comparables pour les 2 systèmes que celles-ci soient calculées avec une échelle de temps exprimée en jours calendaires ou en jours normalisés (à une température et une humidité du sol de référence). Ces résultats montrent que la fourniture d'azote minéral par le sol est similaire dans les différents systèmes de travail du sol étudiés à Boigneville. Par ailleurs, les émissions de N2O ont eu tendance à être plus élevées pour NT que pour CT. Les émissions de CO2 en absence de couvert végétal ont pu être plus importantes pour l'un ou l'autre des systèmes de travail du sol en fonction des conditions climatiques et de la localisation des résidus de culture. Le cumul des quantités de CO2 émis par NT a été significativement plus important que pour CT. Au cours d'une seconde partie du travail, nous avons cherché à montrer si les différences de stocks et de flux de C et N entre les différentes modalités de travail du sol étaient le résultat des modifications des conditions climatiques, de la localisation et des quantités de SOM et résidus de culture ou des propriétés biologiques ou physiques du sol. D'abord, nos résultats ont montré que la minéralisation potentielle du C et N en conditions contrôlées n'a pas été moins importante pour NT comparé à CT. Par ailleurs, la protection physique de la MOS contre la minéralisation du C et N a été évaluée par incubation d'échantillons de sol dont les structures entre 50 µm et 12.5 mm ont été progressivement détruites. Quatre zones structurales ont été considérées : zones avec une structure poreuse ou compacte pour CT et horizons 0-5 et 5-20 cm pour NT. Les résultats indiquent que la destruction de la structure de l'horizon 0-5 cm de NT induit une faible augmentation de la minéralisation de l'azote et pas d'augmentation pour la minéralisation du carbone. La protection de la MOS est en réalité la plus importante pour la couche 5-20 cm du NT. Ensuite, les différences de décomposition de la MOS entre CT et NT au champ ont été influencées par des différences de la température et de l'humidité du sol. Toutefois ces différences ont été souvent faibles et les conditions n'ont pas été systématiquement plus favorables pour la décomposition dans l'un ou l'autre des systèmes de travail du sol. Néanmoins, la distribution et la quantité de pluie et l'évaporation d'eau ont eu une influence importante sur la dynamique des flux de CO2. Les pluies induisent une réhumectation rapide des résidus de surface qui entraîne une augmentation importante des flux de CO2 pour NT par rapport à CT. Après les pluies, la teneur en eau des résidus de surface diminue rapidement ce qui limite sérieusement leur décomposition entraînant des émissions plus faibles pour NT comparé à CT. Finalement, les flux de C et N ont été simulés avec le modèle PASTIS. Les simulations ont montré que la quantité cumulée plus importante de CO2 émise par NT a résulté d'une décomposition plus importante des résidus de culture et pas d'une différence de décomposition des MOS. En réalité, la plus grande quantité des résidus de culture accumulée à la surface du sol dans NT fait plus que compenser la plus faible vitesse de décomposition des résidus en surface pour NT comparé avec la situation de résidus enfouis pour CT. En définitive, c'est la teneur en eau du mulch de résidus qui contrôle le plus l'amplitude de la différence de vitesse de décomposition des résidus entre CT et NT.

In recent times, as regulations and legislations for exhaust treatment have become more stringent, a major concern in the arena of environmental catalysis is to find new efficient and economical exhaust treatment catalysts. Chapter 1 is a review of the current status of various NOx abatement techniques and understanding the role of “auto-exhaust catalysts” involved therein. Chapter 2 presents the studies on synthesis of ionically substituted precious metal ions like Pd2+, Pt2+ and Rh3+ in CeO2 matrix and their comparative three-way catalytic performances for NO reduction by CO, as well as CO and hydrocarbon oxidation. Ce0.98Pd0.02O2- showed better catalytic activity than ionically dispersed Pt or Rh in CeO2. The study in Chapter 3 aims at synthesizing 1 atom% Pd2+ ion in TiO2 in the form of Ti0.99Pd0.01O2- with oxide ion vacancy. A bi-functional reaction mechanism for CO oxidation by O2 and NO reduction by CO was proposed. For NO reduction in presence of CO, the model based on competitive adsorption of NO and CO on Pd2+, NO chemisorption and dissociation on oxide ion vacancy fits the experimental data. The rate parameters obtained from the model indicates that the reactions are much faster over this catalyst compared to other catalysts reported in the literature. In Chapter 4 we present catalytic reduction of NO by H2 over precious metal substituted TiO2 (Ti0.99M0.01O2-, where M = Ru, Rh, Pd, Pt) catalysts. The rate of NO reduction by H2 depends on the reducibility of the catalysts. Chapter 5 presents the studies on reduction of NO by NH3 in presence of excess oxygen. 10 atom % of first row transition metal ions (Ti0.9M0.1O2-, where M = Cr, Mn, Fe, Co and Cu) were substituted in anatase TiO2 and TPD study showed that the Lewis and Bronsted acid sites are adsorption sites for NH3, whereas NO is found to dissociatively chemisorbed in oxide ion vacancies. The mechanism of the low temperature catalytic activity of the SCR and the selectivity of the products were studied to understand the mechanism by studying the by-reactions like ammonia oxidation by oxygen. A new catalyst Ti0.9Mn0.05Fe0.05O2- has shown low temperature activity with a broad SCR window from 200 to 400 °C and more selectivity than commercial vanadium-oxides catalysts. We attempted NO dissociation by a photochemical route with remarkable success. In Chapter 6 we report room temperature photocatalytic activity of Ti0.99Pd0.01O2- for NO reduction and CO oxidation by creating redox adsorption sites and utilizing oxide ion vacancy in the catalyst. The reduction of NO is carried out both in the presence and in the absence of CO. Despite competitive adsorption of NO and CO on the Pd2+ sites, the rate of reduction of NO is two orders of magnitude higher than unsubstituted TiO2. High rates of photo-oxidation of CO with O2 over Ti0.99Pd0.01O2- were observed at room temperature. In Chapter 7 the results are summarized and critical issues are addressed. Novel idea in this thesis was to see if both noble metal ions and base metal ions substituted in TiO2 and CeO2 reducible supports can act as better active sites than the corresponding metal atoms in their zero valent state.

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La major conscienciació actual dels problemes de pol·lució que acompanyen les pèrdues de N del sòl cap a l'atmosfera ha reorientat les investigacions cap a un coneixement més profund dels processos implicats en les emissions dels compostos nitrogenats que comporten un major perjudici des d'un punt de vista ecològic així com els seus principals factors reguladors. La creixent preocupació per l'increment de la concentració atmosfèrica de N2O és deguda a les seves interaccions amb la fotoquímica atmosfèrica i el balanç de radiació de la Terra ja que intervé en la destrucció de la capa estratosfèrica d'ozó, contribueix a l'efecte hivernacle i participa de la pluja àcida. Es considera que els sòls són la principal font de N2O atmosfèric. Al voltant del 90% d'aquestes emissions són d'origen biòtic; els principals processos implicats són la desnitrificació i la nitrificació. L'emissió del N2O produït a través d'aquests dos processos es caracteritza pels diferents nivells de regulació que presenta ja que depèn de la taxa dels processos, de la proporció de N canalitzada per cada procés cap a la producció de N2O i del seu consum dins el mateix sòl el qual està relacionat amb les dificultats en el transport cap a l'atmosfera. Això comporta una gran dificultat a l'hora d'aprofundir en el coneixement de les emissions de N2O del sòl cap a l'atmosfera i de la seva regulació. El desconeixement dels nivells d'emissió de N2O i de la importància de la desnitrificació així com de la seva regulació tant en sòls agrícoles com naturals de les nostres contrades és el principal punt de partida dels objectius d'aquest treball. / The current increased awareness of pollution problems that accompany the loss of soil N to the atmosphere has reoriented research towards a deeper understanding of the processes involved in emissions of nitrogen compounds that lead to greater damage from an ecological point of view as well as their regulatory factors. The growing concern over the increased atmospheric concentration of N2O is due to their interactions with atmospheric photochemistry and radiation balance of Earth as it participates in the destruction of the stratospheric ozone layer, the greenhouse effect and in acid rain. It is considered that the soils are the main source of atmospheric N2O. Around 90% of these emissions are of biotic origin, the main processes involved are nitrification and denitrification. The emissions of N2O produced via these two processes are characterized by different levels of regulation, as it depends on the rate of processes, the proportion of N channeled by each process to N2O production and consumption within the same soil which is related to difficulties in transport to the atmosphere. This entails a great difficulty to deepen the knowledge of soil N2O emissions to the atmosphere and its regulation. The ignorance of N2O emission levels and the importance of denitrification as well as their regulation in both natural and agricultural soils is the main starting point of the objectives of this work.

Made available in DSpace on 2014-07-29T16:24:16Z (GMT). No. of bitstreams: 1 Dissertacao Adriana R da Costa.pdf: 1069791 bytes, checksum: 743805ac385dad30c9c493e611823930 (MD5) Previous issue date: 2011-02-24 / The loss of nitrogen from the soil-plant system has economic and environmental repercussions, especially when nitrous oxide is emitted to the atmosphere. The aim of this study was to evaluate the emission of nitrous oxide (N2O) in the production system of irrigated commom beans under no-tillage, with brachiaria grass as cover plant (green manure), as affected by the application of different N sources. The experiment was conducted at Embrapa Rice and Beans, in a clayey Haplic Ferralsol. Six areas planted with common beans in no-till system, with sprinkler irrigation, center pivot, were evaluated in the fall/winter period of 2009. In each area (150 m2) a different source on N (treatments) was applied. The total area of the study was 1000 m2. The treatments were: no N (control), urea, ammonium sulfate (A.S.), urea + urease inhibitor (Ur.+Inhi.), urea combined with charcoal (Ur.+Car.), biological fixation nitrogen (B.F.N.), Cerrado (Cer). One hundred kg of N ha-1 was applied in all areas: 20% at sowing together with the seed at the same depth and 80% as top dressing, 25 days after planting. Periods, whose N2O fluxes were more important, were selected for more detailed study, including soil biological variables. The N2O concentration was determined by gas chromatography. Concurrently, soil moisture, temperature, water filled pore space (WFPS), pH and parameters related to the microbial biomass were also measured. The variables that influence soil N2O fluxes during the growing cycle of the bean are: the levels of nitrate in the soil, pH, moisture and WFPS, indicating conditions that favor the denitrification process. The highest emissions of N2O, occur in the following treatments: urea with urease inhibitor, biological nitrogen fixation and urea associated with charcoal, 70%, 36% and 32% higher then that observed in the control, respectively. The emission factors observed in this study are below the lowest levels suggested by IPCC (Intergovernmental Panel on Climate Change). After fertilization at sowing, the variables that control the emission of N2O are basal respiration, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), total organic carbon (TOC), soil moisture and WFPS. The charcoal combined with urea provides better conditions for microorganisms, increasing MBC and microbial quocient. After topdressing N2O fluxes are lower than at sowing, possibly due to higher N losses through volatilization or increased demand for N by the plant and consequent higher N uptake by plants. The ammonium sulfate source shows the highest N2O fluxes in this period. The variables that control N2O emission in this period are: MBN, pH, moisture and WFPS. During the senescence of the bean plants urea combined with urease inhibitor and biological fixation nitrogen are the treatments that most emitt N2O. The variables that controll the fluxes are soil temperature and TOC. / A perda de nitrogênio no sistema solo-planta tem repercussões econômicas e ambientais, especialmente quando óxidos de nitrogênio são emitidos para a atmosfera. O objetivo deste estudo foi avaliar a emissão de óxido nitrosos (N2O) em sistema de produção de feijoeiro comum irrigado em sistema plantio direto, sobre palhada de braquiária, com aplicação de diferentes fontes de nitrogênio (N), bem como as variáveis ambientais e do solo que condicionam esta emissão. O experimento foi conduzido na Embrapa Arroz e Feijão, num Latossolo Vermelho distrófico argiloso. Foram avaliadas seis áreas de cultivo de feijoeiro comum, em sistema plantio direto, sobre palhada de braquiária, irrigado por aspersão via pivô central, no outono/inverno de 2009. A área de cada tratamento foi de 150 m2. A área total do estudo foi de 1000 m2. Os tratamentos foram: Sem N (testemunha); Uréia; Sulfato de amônio (S.A.); Uréia tratada com inibidor de urease (Ur.+ Inib.); Uréia combinada com carvão vegetal (Ur.+Car.); Fixação biológica de nitrogênio (F.B.N.); Cerradão (Cer) como referência. Foram aplicados 100 kg ha-1 de N: 20% na linha de semeadura e 80% em cobertura, a lanço, 25 dias após plantio. Selecionaram-se períodos, cujos fluxos de N2O apresentaram maior relevância, para que fosse realizado um estudo mais detalhado, incluindo variáveis biológicas do solo. A concentração de N2O foi determinada por cromatografia gasosa. Concomitantemente, realizou-se amostragem de solo para verificação da temperatura, espaço poroso saturado por água (EPSA), pH e parâmetros referentes a biomassa microbiana. As variáveis de solo que mais influenciam os fluxos de N2O, durante o ciclo do feijoeiro, são os teores de nitrato no solo, pH e EPSA, cujas condições favorecem o processo de desnitrificação, no sistema de produção irrigada em plantio direto. As maiores emissões totais de N2O, ocorrem nos seguintes tratamentos: uréia com inibidor de urease, fixação biológica de nitrogênio e uréia associada ao carvão vegetal, sendo 70%, 36% e 32% maior que o observado na testemunha, respectivamente. Os fatores de emissão observados neste estudo estão abaixo dos menores níveis sugeridos pelo IPCC (Intergovernmental Panel on Climate Change). Após adubação no sulco, as variáveis que controlam a emissão de N2O são respiração basal, carbono da biomassa microbiana (CBM), nitrogênio da biomassa microbiana (NBM), carbono orgânico total (COT) e EPSA. O carvão vegetal combinado com uréia proporciona melhores condições aos microrganismos, elevando índices como o CBM e o quociente microbiano. Após a adubação de cobertura os fluxos de N2O são menores que na semeadura, talvez devido a maiores perdas de N por volatilização e maior demanda pela planta por N, sendo o sulfato de amônio a fonte que mais emitiu N2O. As variáveis que controlam a emissão de N2O neste período são o NBM, o pH do solo e o EPSA. No período de senescência do feijoeiro as fontes uréia combinada com inibidor de urease e a fixação biológica de nitrogênio são as que mais emitem N2O, sendo as variáveis que controlam este período de emissão, a temperatura do solo e o COT.

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A radio frequency (rf) quadrupole instrument, currently known as an Isobar Separator for Anions (ISA), has been integrated into an Accelerator Mass Spectrometry (AMS) system to facilitate anion–gas reactions before the tandem accelerator. An AMS Cs+ sputter source provided > 15 keV ions that were decelerated in the prototype ISA to < 20 eV for reaction in a single collision cell and re-accelerated for AMS analysis. Reaction based isobar suppression capabilities were assessed for smaller AMS systems and a new technique for gas–phase reaction studies was developed. Isobar suppression of 36S– and 12C3– for 36Cl analysis, and YF3– and ZrF3– for 90Sr analysis were studied in NO2 with deceleration to < 12 eV. Observed attenuation cross sections, σ [x 10^–15 cm^2], were σ(S– + NO2) = 6.6, σ(C3– + NO2) = 4.2, σ(YF3– + NO2) = 7.6, σ(ZrF3– + NO2) = 19. With 8 mTorr NO2, relative attenuations of S–/Cl– ~ 10^–6, C3–/Cl– ~ 10^–7, YF3–/SrF3– ~ 5 x 10^–5 and ZrF3–/SrF3– ~ 4 x 10^–6 were observed with Cl– ~ 30% and SrF3– > 90% transmission. Current isobar attenuation limits with < 1.75 MV accelerator terminal voltage and ppm impurity levels were calculated to be 36S–/Cl– ~ 4 x 10^–16, 12C3–/Cl– ~ 1.2 x 10^–16, 90YF3–/SrF3– ~ 10^–15 and 90ZrF3–/SrF3– ~ 10^–16. Using 1.75 MV, four 36Cl reference standards in the range 4 x 10^–13 < 36Cl/Cl < 4 x 10^–11 were analyzed with 8 mTorr NO2. The measured 36Cl/Cl ratios plotted very well against the accepted values. A sample impurity content S/Cl < 6 x 10^–5 was measured and a background level of 36S–/Cl < 9 x 10^–15 was determined. Useful currents of a wide variety of anions are produced in AMS sputter sources and molecules can be identified relatively unambiguously by stripping fragments from tandem accelerators. Reactions involving YF3–, ZrF3–, S– and SO– + NO2 in the ISA analyzed by AMS are described, and some interesting reactants are identified.