Marine microorganisms play a significant role in the cycling of nutrients in the open ocean through production, consumption, and degradation of organic matter (OM). Carbon (C), nitrogen (N), and phosphorus (P) are essential ingredients in every known recipe for life. However, the cycling of each of these elements proceeds at different rates such that the ratio of C:N:P can vary widely between particulate, dissolved, organic, and inorganic pools. To better understand the mechanisms controlling these transformations, this study investigated the bacterial remineralization of photosynthetically-derived organic matter derived from cultures of Trichodesmium IMS101, Thalassiosira weissflogii, Prochlorococcus MED4, and particulate material collected from the surface waters of an upwelling regime. Experiments were conducted at sea for a short duration (<6d) and in the laboratory for longer periods (<150 days). In all treatments, across experiments, we observed rapid and selective P remineralization independent of the type of organic material added. Full solubilization and remineralization of P typically occurred within a week. Conversely, N remineralization was slower, with only 39-45% of particulate N (PN) remineralized in shorter (6d) experiments and 55-75% of PN remineralized in <150d experiments. Nitrification was observed after 70-98 days depending on the remineralizing bacteria (isolated from either the Oregon coastal upwelling regime or the North Pacific Subtropical Gyre (NPSG). Notably, these events did not transform the full complement of ammonium to nitrate. This differential lability between N and P led to rapid changes in the N:P ratio of inorganic pools as organic matter was depolymerized by varying bacterial populations. The variable input of potentially limiting elements could have consequences for primary productivity and particle export. Finally, we observed that in short-term experiments with heterotrophic bacteria collected from the NPSG, the N:P ratio of remineralization (11 ± 2.2) was independent of the N:P of added organic material (5-23). This uniformity of inorganic ratios implies differential lability and N:P composition of residual semi-labile and refractory organic matter. Formation of refractory C and N rich organic matter, often termed the microbial pump, is a significant pathway for the transport and sequestration of elements in the aphotic zone of the ocean interior. The experimental results reported here suggest that differential supply of POM leads to rapid and preferential P remineralization, N:P remineralization independent of the N:P of added substrates, and variable N:P of residual organic matter. These findings help constrain our knowledge of elemental cycling in the marine environment. / Graduation date: 2013

The purpose of this study was to investigate the results of two long-term fertilization experiments on soil organic C, total N, and mineralizable N in the Jiangsu Province of People's Republic of China. The soil samples that received manure over the years contained more soil organic C, and total N than the inorganic fertilized samples. Soil organic C was closely correlated with total N and there were correlations between crop yields and soil organic C contents and between crop yields and soil total N contents. Plant-available N was estimated using biological and chemical tests. Mineralized N formed under anaerobic incubation was low except for those soil samples that received manure. Microbial biomass C and N were estimated using the chloroform fumigation-incubation method (CFIM) and fumigation-extraction procedures. Biomass measurements by CFIM were more precise and reliable than values obtained by fumigation-extraction. Treatment differences in biomass were not significant. Estimates of biomass C and N were influenced by the choice of the control soil and the period of incubation used by the CFIM. Unfumigated (10-20 d) control soils were found to be the best control for samples. Extraction of mineralized N using O.5M NaHCO$ sb3$ after incubation overestimated biomass N since this extraction was found to extract non-biomass N.

Many producers in North America are finding it profitable to make the transition from conventional farming to organic agriculture. Organic fertilisers may affect crop production and soil quality differently than inorganic fertilisers. The objectives of this study conducted in Ste.-Anne-de-Bellevue. Quebec were to examine crop yield, grain quality, soil fertility and microbial community parameters in wheat and corn agroecosystems receiving poultry manure or inorganic fertiliser. Wheat grain yield declined and corn grain yield did not increase with higher N rates, suggesting that increased N supply did not encourage grain production. Soil analyses demonstrated high inherent soil fertility at the study site, and fertilisation led to an environmentally undesirable increase in residual soil NO3 concentrations. Microbial biomass and respiration in corn agroecosystems were greater with poultry manure amendments than inorganic fertiliser, but not in wheat agroecosystems due to significant variation among field replicates. Phospholipid fatty acid analysis revealed significant differences between wheat and corn soil microbial community composition, but differences due to fertilisation were less evident. Further work is needed to uncover the relationships among N fertilisation, crop nutrition and soil microbiology in organic agroecosystems.

Manure and underseeded clover are sustainable N sources for spring wheat on gleysolic soils of the St. Lawrence lowlands. Farmers rely on little information to manage adequately, these alternatives to fertilizer N. This study documents in spring wheat red (Triticum aestivum L. cv Algot) (i) the agronomic value of (Trifolium pratense L. cv Arlington); (ii) the impacts of application time and underseeded clover an manure N recovery; (iii) the residual NO3-- in the soil profile that constitutes a potential risk of N transfer from soil to air and water associated to clover alone or combined with manures and, (iv) the use of a plant N availability index. A four year field experiment was established an a St. Urbain clay (Orthic Humic Gleysol) at St. Bruno de Montarville (45°33'N; 73°21'W) in 1993. Ammonium nitrate at 0 to 160 kg N ha--1, swine liquid manure (SLM) and dairy solid manure (DSM) were used either alone or in combination with clover ploughed down in fall as green manure. Manures were applied at pre-seeding, in post-emergence or after harvest. The impact of clover on wheat yield was related solely to an improved N nutrition. Clover supplied fertilizer N equivalents of approximately 30 kg ha --1 to the succeeding wheat crop. Clover combined with manures increased available N in the soil profile so that estimated recovery of manures N was strongly reduced in 1995. Apparent N recovery of SLM was higher than for DSM with values of 5% and 17% in 1994 and 1995 compared to 2 and 4% for DSM. Application time did not significantly affect manure N recovery. Limited risk of N transfer to water and air was associated with post-harvest manure application and underseeded red clover because those practices increased soil profile NO3-- in fall and the end of April. Fluxes of N estimated by NH4+ and NO3 -- sorbed in situ on ionic exchange membranes (IEMs) provided better monitoring of N released by added organic N sources than N extracted by 2M KCl and also were bette

[Truncated abstract] The principal aim of this thesis was to examine the response of the microbial community to the addition of small amounts (<50 μg C g-1 soil) of organic C substrates (‘trigger molecules’) to soil. This addition is comparative to indigenous soluble C concentrations for a range of soil types in Western Australia (typically measured between 20 and 55 μg C g-1 soil). Previously it has been reported that the application of trigger molecules to European soils has caused more CO2-C to be evolved (up to six fold) than was applied . . . Findings from this study indicated that there was an additional CO2 release (i.e. greater than the C added) on application of organic C substrates to some soil treatments. However, findings from this study indicate that the response of the microbial community to small additions of soluble C substrate is not consistent for all soil types and may vary due to greater availability of C, and supports the premise that microbial responses vary in a yet to be predicted manner between soil type and ecosystems. Differences in microbial response to the addition of soluble organic C are likely attributable to differences in soil attributes and environmental factors influencing both the diversity of microbes present and the frequency of food events. Theoretically, trigger molecules could also provide a possible control mechanism for microorganisms in arable farming systems. These mechanisms include stimulating either targeted pathogenic microorganisms that starve after depletion of a suitable substrate; or stimulating beneficial microorganisms to manipulate nutrient cycling, by targeting specific functional groups and altering mineralisation and immobilisation turnover rates.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.

Orientador: Ricardo Antonio Ferreira Rodrigues / Resumo: Dentre os desafios atuais da agricultura, estão a racionalização do uso da água, aumento da produtividade e redução das perdas de nutrientes. Para isso, deve-se avaliar técnicas de otimização ou redução da utilização da água, como o uso de cultivares mais adaptadas a estresses hídricos e, a aplicação de fertilizantes melhor aproveitados pelas plantas. Recentemente foi lançado no mercado o cultivar de arroz BRS Esmeralda que tem como características maior tolerância ao estresse hídrico e elevado potencial produtivo. Diante disso, o objetivo deste trabalho foi avaliar o efeito da variação hídrica e fontes de N em cultivares de arroz de terras altas sobre o teor de N foliar, desempenho agronômico, produtividade, qualidade industrial e qualidade fisiológica de sementes produzidas. O experimento foi desenvolvido na Fazenda de Ensino e Pesquisa da Unesp, campus de Ilha Solteira, localizada no município de Selvíria-MS e no laboratório de sementes em Ilha Solteira-SP, em 2013/14 e 2014/15. O tipo de solo é um LATOSSOLO VERMELHO Distrófico típico argiloso. O experimento foi realizado em duas etapas: produção em campo e avaliação da qualidade fisiológica das sementes produzidas. O delineamento experimental em campo foi o de blocos casualizados em esquema de parcelas sub-subdividas, sendo constituído de três variações hídricas nas parcelas (irrigação com a lâmina recomendada para o arroz + precipitação; irrigação com a lâmina de 75% da recomendada + precipitação; e sem irrigação + preci... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The rationalization of water use, the increase in productivity and the reduction of nutrient losses are among the current challenges of agriculture. For this, it is necessary to evaluate techniques of optimization or reduction of water use, such as the use of cultivars more adapted to water stresses, and the application of fertilizers better utilized by plants. Recently, the upland rice cultivar BRS Esmeralda, more tolerant to drought and with high productive potential, was released in the market. Thus, the objective of this study was to evaluate the effect of the hydric variation and nitrogen sources in topdressing in upland rice cultivars on the leaf nitrogen content, agronomic performance, yield, industrial quality and physiological quality of the seeds produced. The experiment was conducted at the Education and Research Farm of Unesp, Ilha Solteira campus, located in Selvíria-MS and in the seed laboratory in Ilha Solteira-SP, in 2013/14 and 2014/15. The soil of the area is a Dystrophic RED LATOSOL (Oxisol) with a clayey texture. The experiment was performed in two stages: field production and evaluation of the physiological quality of the seeds produced. The experiment conducted in the field consisted of randomized blocks in a split-split plot design, with three hydric variations as plots (irrigation with a recommended water depth for rice + rainfall; irrigation with 75% of the recommended water depth + rainfall; and without irrigation + rainfall – “rainfed”), two cultiv... (Complete abstract click electronic access below) / Doutor

Submitted by Claudia Rocha (claudia.rocha@udesc.br) on 2018-03-21T14:23:46Z No. of bitstreams: 1 PGCA17MA228.pdf: 726282 bytes, checksum: 40f271b726c358d9c09eb5ec50c81604 (MD5) / Made available in DSpace on 2018-03-21T14:23:46Z (GMT). No. of bitstreams: 1 PGCA17MA228.pdf: 726282 bytes, checksum: 40f271b726c358d9c09eb5ec50c81604 (MD5) Previous issue date: 2017-06-22 / Capes / Nitrogen (N) participates in several metabolic processes in the plant and is directly related to the accumulation of dry matter of the pasture, thus reflecting increases in the overall productivity of the system. In this sense, the Ncritical (lower concentration of N for a given species to perform its maximum growth potential) in multispecies pastures may change depending on the species that compose it. The objective of this work was to evaluate the NNI (Nitrogen Nutrition Index) in three perennial winter grasses (oatgrass - Arrhenatherum elatius, cocksfoot - Dactylis glomerata - and tall fescue - Festuca arundinacea) cultivated as monocultures or intercropped throughout the four seasons of the year. The experimental area was located in Lages, SC, containing 12 paddocks of 45 m2 each where the four treatments (the three pure cultivated species and the mixture) were distributed through a completely randomized design with three replicates. The cut height at each treatment was determined by the time the swards intercept 95% of the incident light during the vegetative stage of the pastures, being lowered by 50% of this height. Fertilization was carried out with the equivalent of 50 kg / N / ha every 40 days, totaling 450 kg of N / ha / year. The forage mass was determined in pre-cut, and thus evaluated the N contents in the forage mass and the N contents in the 10 cm of the upper part of the canopy for the species pure and individually for each species in the consortium. The Ncritical was estimated by the equation: Ncritical = 4,8 x W-0,32, where W is the mass of forage above the level of the soil. A second experiment was carried out with the objective of evaluating the effect of the management adopted on the N dilution curve, in which two methods were performed to determine the N dilution curve, one performed with the management adopted in the experiment (starting from a residual height of 10 cm) and another with the management proposed by the literature starting from the ground level. Statistical analyzes were performed using the MIXED procedure of the SAS statistical program (version 9.02) with 5% significance. Regression analyzes were performed using the SigmaPlot(R) statistical package. In general, the NNI actually observed did not reach the critical values (Experiment I), however, when corrected (disregarded the percentage of dead material in the sample) NNIs were satisfactory for all species at all times. Throughout the manuscript inferences are discussed on the ways to evaluate the INN in perennial pastures under lenient grazing, due to the changes in the dilution of nitrogen, due to the high percentage of dead material at the beginning of pasture growth. The height control was important in the coexistence of the species in the consortium, since it allowed the entrance of luminosity, decisive factor in the absorption of N / O nitrogênio (N) participa de diversos processos metabólicos na planta e está diretamente relacionado com o acúmulo de matéria seca do pasto, refletindo, assim, em aumentos em produtividade global do sistema. Neste sentido, o Ncrítico (menor concentração de N para que uma determinada espécie desempenhe seu máximo potencial de crescimento) em pastagens multiespecíficas pode mudar em função das espécies que o compõem. Dessa forma, o objetivo desse trabalho foi avaliar o INN (índice de nutrição nitrogenada) em três espécies perenes de inverno (Aveia perene - Arrhenatherum elatius-, Dáctilis - Dactylis glomerata- e Festuca - Festuca arundinacea) cultivadas puras e em consórcio ao longo das quatro estações do ano. A área experimental foi implantada em Lages, SC, contendo 12 piquetes de 45 m2 cada onde foram distribuídos os quatro tratamentos (as três espécies cultivadas puras e o consórcio entre elas) por meio de um delineamento inteiramente casualizado com três repetições. A altura de corte em cada tratamento foi determinada pelo momento em que os mesmos interceptarem 95% da luz incidente durante o estádio de desenvolvimento vegetativo dos pastos, sendo rebaixados em 50% desta altura. As adubações foram realizadas com o equivalente a 50 kg/N/ha a cada 40 dias, totalizando 450 kg de N/ha/ano. Foi determinada a massa de forragem em pré-corte, e, assim avaliados os teores de N na massa de forragem e os teores de N nos 10 cm da parte superior do dossel para as espécies puras e individualmente para cada espécie no consórcio. O Ncrítico foi estimado pela equação: Ncrítico = 4,8 x W-0,32, onde W é a massa de forragem acima do nível do solo. Foi realizado um segundo experimento, com o objetivo de avaliar o efeito do manejo adotado na curva de diluição do N, no qual foram executados dois métodos para determinar a de curva de diluição do N, uma realizada com o manejo adotado no experimento (partindo de uma altura residual de 10 cm) e outra com o manejo proposto pela literatura partindo do nível do solo. As análises estatísticas foram realizadas por meio do procedimento MIXED do programa estatístico SAS (versão 9.02) com 5% de significância. As análises de regressão foram realizadas utilizando-se o pacote estatístico SigmaPlot (R). De modo geral, os INN efetivamente observados não alcançaram os valores críticos (Experimento I), no entanto, quando corrigidos (desconsiderados os porcentuais de material morto da amostra) os INN foram satisfatórios para todas as espécies em todas as épocas. Ao longo do manuscrito inferências são discutidas sobre as formas de se avaliar o INN em pastos perenes sob pastejo leniente, devido às alterações na diluição do nitrogênio, consequência da alta porcentagem de material morto no início do crescimento dos pastos. O controle de altura foi importante na coexistência das espécies no consórcio, pois permitiu a entrada de luminosidade, fator decisivo na absorção de N

Magister Scientiae - MSc / Amorphous silicon nitride (a-SiN:H) thin films has a multitude of applications, stemming from the tunability of the material properties. Plasma enhanced chemical vapour deposition (PECVD) is the industrial workhorse for production of device quality a-SiN:H. However, this technique has drawbacks in terms of film quality, rooting from ion bombardment, which then results in undesirable oxidation. Hot wire chemical vapour deposition (HWCVD) has shown to be a viable competitor to its more costly counterpart, PECVD. A thin film produced by HWCVD lacks ion bombardment due to the deposition taking place in the absence of plasma. This study will focus on optimising the MVsystems ® HWCVD chamber at The University of the Western Cape, for production of device quality a-SiN:H thin films at low processing parameters. The effect of these parameters on the structural, optical and morphological properties was investigated, for reduction of production costs. The films were probed by heavy ion elastic recoil detection, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy, Xray diffraction, and ultraviolet visible spectroscopy. It was shown that silicon rich, device quality a-SiN:H thin films could be produced by HWCVD at wire temperatures as low as 1400 °C and the films showed considerable resistance to oxidation in the bulk.

Thesis (Ph. D.)--Joint Program in Oceanography (Massachusetts Institute of Technology, Dept. of Biology; and the Woods Hole Oceanographic Institution), February 2002. / Vita. / Includes bibliographical references (leaves 153-161). / I used direct measurements of nitrogen gas (N₂ fluxes and a ¹⁵N stable isotope tracer to determine the contribution of denitrification to salt marsh sediment N cycling. Denitrification in salt marsh tidal creekbottoms is a major sink for groundwater nitrate of terrestrial origin. I studied creekbottom denitrification by direct measurements of N₂ fluxes in closed chambers against a low-N₂ background. I undertook experiments and simulation modeling of sediment N₂ fluxes in closed chambers to optimize the key experimental parameters of this approach. Denitrification in these sediments was driven by the degradation of labile organic matter pools which are depleted during long incubations. Sediment thickness was the most important parameter controlling the required incubation time. Errors of up to 13% with gas headspaces and 80% with water headspaces resulted from headspace N2 accumulation and the resulting collapse of the sediment-water diffusion gradient. These errors could be eliminated by using headspaces of sufficient thickness. Headspace flushing to reduce ammonium accumulation did not affect denitrification rates, but caused transient disturbance of N₂ flux rates. Direct measurements of 0₂, C0₂, N₂, and inorganic N fluxes from the sediments of a salt marsh tidal creek were made in order to examine the interaction of denitrification with the carbon, oxygen, and N cycles. Organic carbon concentration and lability were the primary controls on metabolic rates. C0₂/N flux ratios averaged 6.1, indicating respiration driven by algal biomass. / (cont.) Allochthonous denitrification accounted for 39% of total sediment denitrification (2.7 mol N m⁻² yr⁻¹). 46% of remineralized ammonium was denitrified, while the contribution of autochthonous denitrification to 0₂ and C0₂ fluxes was 18% and 10%, respectively. A ¹⁵N-ammonium tracer was used to study competition between plants and nitrifying bacteria for remineralized ammonium. In undisturbed sediments of Spartina alterniflora, plant uptake out-competed nitrification-denitrification, with plant uptake accounting for 66% of remineralized ammonium during the growing season. Under N fertilization (15.5 mol m⁻² yr⁻¹), both plant N uptake and denitrification increased, but denitrification dominated, accounting for 72% of the available N. When plant uptake was hydrologically suppressed, nitrification-denitrification was stimulated by the excess N, shifting the competitive balance toward denitrification. / by Michael Robert Hamersley. / Ph.D.