O sistema de cultivo mínimo é caracterizado por um conjunto de operações mínimas de preparo de solo em que a maior parte dos resíduos florestais é mantida sobre o solo, a fim de garantir as demandas de produção e a sustentabilidade produtiva do sistema. Diante disto, os objetivos deste estudo foram: i) Avaliar a influência da remoção total ou parcial dos resíduos florestais e da fertilização mineral na fertilidade do solo e na produtividade de madeira; ii) Quantificar a biomassa e o estoque de nutrientes na parte aérea, em uma rotação de cultivo, sob manejo de resíduos florestais e omissões de nutrientes na fertilização mineral; iii) Quantificar a influência do manejo de resíduos florestais e da fertilização mineral na deposição, acúmulo, decomposição e qualidade nutricional da serapilheira; iv) Quantificar a exportação de nutrientes via colheita de madeira e outros componentes florestais; v) Avaliar o potencial de produtividade de madeira, com base no balanço nutricional, sob diferentes cenários de manejo florestal. Foi instalado um experimento com diferentes manejos de resíduos florestais e fertilização. Os tratamentos foram divididos em dois grupos em que o primeiro consistiu em remoção total ou parcial dos resíduos florestais: copa (folhas e galhos), casca e serapilheira. O segundo grupo de tratamentos consistiu na omissão de nutrientes na fertilização mineral: N, P, K ou calagem. Durante a rotação de oito anos foram monitoradas a fertilidade do solo, ciclagem biogeoquímica de nutrientes, crescimento e estado nutricional das árvores. Os diferentes manejos dos resíduos florestais e fertilização mineral apresentaram pouca influência na fertilidade do solo, pois, os níveis de nutrientes no solo estavam adequados, devido à aplicação de fertilizantes minerais no momento da instalação do experimento. A remoção total ou parcial dos resíduos florestais não influenciou a produtividade de madeira. Contudo, no tratamento em que o K foi omitido na fertilização, houve redução de 50% na produtividade de madeira. A omissão de P na fertilização não afetou a produtividade de madeira na rotação de cultivo avaliada, porém este foi o nutriente mais limitante quanto ao número potencial de futuras rotações. A remoção total ou parcial dos resíduos florestais não influenciou na ciclagem biogeoquímica de nutrientes, porém omissão de K via fertilização reduziu em 60% a deposição anual deste nutriente o que afetou sua a ciclagem biogeoquímica. Os resultados deste estudo mostram que embora os resíduos florestais exerçam funções fundamentais na qualidade química do solo e na nutrição mineral das árvores, a inadequada fertilização do solo pode diminuir expressivamente o potencial produtivo do sítio florestal. / The minimal tillage system is characterized by practices of reduced soil management which retains most part of forest residues in the production site, aiming to supply the forest demand and the sustainability of the production system. The aims of this study are: i) Access the effect on soil fertility and site production of total and partial removal of harvest residues and mineral fertilization. ii) Quantify the biomass and nutrient rates in trees along one eucalypt rotation, under different residues management and mineral fertilization. iii) Quantify the effects of residues management and mineral fertilization on deposition, accumulation, decomposition and nutritional qualities of litter. iv) Quantify the nutrient exportation due to the harvest, considering steam and other parts. v) Access productivity potential according to the nutritional balance under different forest management cases. For this study an experimental site with different residues management and mineral fertilization was established. The treatments were separated in two groups. The first one included the treatments with total or partial removal of forest residues: canopy (leaves and stems), bark and litter. The second group of treatment included the omission of nutrients in mineral fertilizer: N, P, K or lime. During eight years rotation were monitored soil fertility, biogeochemical cycling of nutrients, growth and tree nutritional status. The different residues management and mineral fertilizations has showed minor effects on soil fertility once the nutrient rates on soil were suitable due to the mineral fertilization applied for site preparation. However, when the fertilization was carried out without K, reduction of 50% in growth was observed. The omission of P in fertilization did not affect the wood productivity during the forest rotation, but P was the most limiting nutrient for the potential number of future rotations. The biochemical nutrient cycling was not affected by total or partial removal of forestry residues. Annual deposition of K was 60% reduced when the nutrient was not applied by fertilization, which affected the nutrient cycling. The results of this study demonstrated that despite the benefits of forest residues retention on chemical proprieties of soils, the inadequate fertilization reduces expressively the productive potential of the site.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The quest for greater productivity and concern for sustainability, it makes the constant search for alternatives that obtain high productivity sustainably and nutrient cycling, biological nitrogen fixation and proper N fertilization some of these alternatives. In order to validate these alternatives aim with this work was to verify the influence of inoculation and nitrogen management in winter cereals, rates of decomposition of plant residues and its influence on the yield of grain and corn silage. The work consists of three chapters with the first entitled "effect of inoculation with Azospirillum brasilense and seed treatment in the initial development of four cultivars of wheat" which aims to assess the development and initial establishment of wheat cultivars subjected to treatment and inoculating seeds with Azospirillum brasilense bacteria. The second titled "inoculation, waste straw and nitrogen on grain yield and quality of corn silage " aims to evaluate the influence of applying Azospirillum brasilense associated with different levels of nitrogen on yield components and quality of silage corn in no-till crop residues on different system. The third "different decomposition of crop residues on different nitrogen rates and application Azospirillum brasilense" aims to obtain a characterization of the decomposition of the macronutrients of different crops / cultivars, under the influence of different nitrogen and inoculant application based Azospirillum. The different crop residues have different productivities as well as provide change in silage quality. The application of Azospirillum brasilense causes increase in corn yield, change in the initial development of wheat seedlings, as well as providing variation in the decomposition of plant residues. The use of seed treatment affects initial growth of wheat seedlings, however, they have a compensatory gain minimizing this effect. / A busca pela maior produtividade e a preocupação com a sustentabilidade, faz com que as seja constante a busca por alternativas que obtenham alta produtividade de forma sustentável sendo a ciclagem de nutrientes, a fixação biológica de nitrogênio e o uso adequado da adubação nitrogenada algumas dessas alternativas. A fim de validar essas alternativas objetivou-se com esse trabalho verificar a influência da inoculação e manejo do nitrogênio em cereais de inverno, taxas de decomposição dos resíduos vegetais e sua influência sobre as produtividades de grãos e silagem de milho. O trabalho consiste em três capítulos sendo o primeiro intitulado efeito da inoculação com Azospirillum brasilense e tratamento de sementes sob o desenvolvimento inicial de quatro cultivares de trigo o qual tem por objetivo avaliar o desenvolvimento e estabelecimento inicial de cultivares de trigo submetido ao tratamento de sementes e inoculação com bactérias de Azospirillum brasilense. O segundo intitulado inoculação, resíduos de palhada e doses de nitrogênio sob a produtividade de grãos e qualidade de silagem de milho tem por objetivo avaliar a influência da aplicação de Azospirillum brasilense associada a diferentes doses de nitrogênio nos componentes de rendimento e na qualidade de silagem de milho em sistema de plantio direto sobre diferentes resíduos culturais. O terceiro decomposição de diferentes resíduos culturais sobre diferentes doses de nitrogênio e aplicação de Azospirillum brasilense tem por objetivo obter uma caracterização da decomposição dos macronutrientes de diferentes culturas/cultivares, sob a influência de diferentes doses de nitrogênio e aplicação de inoculante a base de Azospirillum. Os diferentes resíduos culturais apresentam proporcionam diferentes produtividades assim como alteração na qualidade da silagem. A aplicação de Azospirillum brasilense proporciona aumento na produtividade de milho, alteração no desenvolvimento inicial de plântulas de trigo, assim como proporciona variação na decomposição de resíduos vegetais. O uso do tratamento de semente afeta o desenvolvimento inicial de plântulas de trigo, no entanto, as mesmas possuem ganho compensatório minimizando esse efeito.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / The study on nutrient cycling in plantation of eucalyptus provides alternative recovery and management avoiding having reduction in future productivity of plantations, contributing to sustainable management. The current study was conducted in the municipality of Alegrete, Rio Grande do Sul, Brazil, in an area belonging to the enterprise Stora Enso S/A. The objective was to assess biomass and nutrient dynamics in a stand of Eucalyptus urograndis in soil subjected to sand effects in southern Brazil. From an inventory, 12 trees were selected and sampled for the quantification of aboveground biomass. The root system was sampled through the excavation of four trees. For the sampling of the leaf litter produced, 16 collectors of 0,5 m² of useful area were installed for the evaluation of leaves, miscellany and thin branches (diameter less than or equal to 5 mm). In addition, sub-plots were installed for the collection of thick branches (diameter greater than 5 mm). The estimated total biomass was of 75 Mg ha-1, with the following distribution 5,5%; 10,2%; 7,7%; 61,2% and 15,4% in the leaves, branches, stem bark, stem wood and roots, respectively. The litterfall in the year was 8,1 Mg ha-1, having its peak between the months of November and December. The litter accumulation was 9,7 Mg ha-1. The amount of nutrients in biomass had the following magnitude of the macronutrients: Ca > K > N > Mg > S > P. The amount of biomass was micronutrients: Mn> Fe> B> Zn> Cu. The litterfall followed the order of the following fractions: leaves > thin branches > thick branches > miscellany. The Ca concentration was greater in thick branches and N was higher in the leaves. The lowest P concentration was observed in the thick branches. Regarding the micronutrients, values showed variations and presented the following order: Mn > Fe > B > Zn > Cu. The species showed good efficiency in using nutrients. Based on nutrient removal in different scenarios harvest of biomass, nutritional balance and potential number of rotations of the wood harvesting + stem bark of removes over 50% of all accumulated in above-ground biomass nutrients. Performing their harvest of commercial timber leaving residues on the soil itself contributes to nutrient cycling avoiding decreased productivity in the next rotation. / O estudo sobre a ciclagem de nutrientes em plantio de eucalipto prevê alternativas de recuperação e manejo evitando que haja diminuição de produtividade em futuros plantios, contribuindo para o manejo sustentável. O presente estudo foi realizado no município de Alegrete, Rio Grande do Sul. O objetivo foi avaliar a biomassa e os nutrientes em um povoamento de Eucalyptus urograndis aos 4,5 anos de idade, estabelecido em solo sujeito a arenização no sul do Brasil. A partir de um inventário, doze árvores foram selecionadas e amostradas para a quantificação da biomassa acima do solo. O sistema radicular foi amostrado através da escavação de quatro árvores, uma em cada classe. Para a amostragem da serapilheira produzida foram instalados 16 coletores de 0,5 m² de área útil para avaliação das frações folhas, miscelânea e galhos finos (diâmetro menor ou igual a 5 mm), além da instalação de sub-parcelas para coletas de galhos grossos (diâmetro maior que 5 mm). A biomassa total estimada foi de 75 Mg ha-1, com a seguinte distribuição 5,5%; 10,2%; 7,7%; 61,2% e 15,4% nas folhas, galhos, casca do tronco, madeira do tronco e raízes, respectivamente. A quantidade de macronutrientes na biomassa teve a seguinte magnitude: Ca > K > N > Mg > S > P. A quantidade de micronutrientes na biomassa foi: Mn > Fe > B > Zn > Cu. A produção de serapilheira anual foi de 8,1 Mg ha-1, tendo seu pico nos meses de novembro e dezembro. A serapilheira acumulada foi de 9,7 Mg ha-1. A serapilheira produzida seguiu a ordem das seguintes frações: folhas > galhos finos > galho grosso > miscelânea. A concentração de Ca foi maior no galho grosso e do N foi maior nas folhas. A menor concentração do P foi no galho grosso. Em relação aos micronutrientes verificou-se que foram mais presentes nas raízes. A espécie apresentou boa eficiência no uso dos nutrientes. Com base na remoção de nutrientes nos diferentes cenários de colheita da biomassa, balanço nutricional e número potencial de rotações, a colheita da madeira do tronco + casca do tronco, removeu acima de 50% de todos os nutrientes acumulados na biomassa acima do solo. Realizando a colheita apenas da madeira comercial deixando os resíduos da colheita sobre o solo contribui-se com a ciclagem de nutrientes evitando a diminuição da produtividade nas próximas rotações.

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<p dir="ltr">Excess nitrogen loading to surface waters and groundwater from intensive agriculture threatens human and ecosystem health and economic prosperity within and downstream of the Mississippi River Basin. Restoring wetlands and floodplains reduces nitrogen export, but nitrogen export from the Mississippi River Basin remains elevated. Engineering restored wetlands and floodplains to have higher areal denitrification rates is necessary to advance toward nitrogen reduction goals. Environmental controls of denitrification in restored ecosystems must be further investigated to determine under what conditions denitrification is highest and to link these optimal conditions to restoration approaches. Yet, restoration efforts to reduce nitrogen export may inadvertently increase phosphorus export and greenhouse gas emissions. We evaluated different restoration design approaches and identified environmental controls of denitrification, phosphorus release, and greenhouse gas production to advance knowledge of how floodplain and wetland restorations can be designed and managed to maximize denitrification while also constraining phosphorus release and greenhouse gas production. Comparisons of different restoration design approaches in the Wabash River Basin in Indiana, U.S.A., demonstrated that a hydrologically connected floodplain with row crop agriculture provides limited N treatment. Floodplain restorations that involved structural modifications to enhance hydrologic connectivity supported higher denitrification than restorations that only reestablished native vegetation. Investigations of the plot- and field-scale drivers of denitrification indicated that enhanced hydrologic connectivity and specific native wetland and prairie vegetation types were associated with soil conditions that supported high denitrification potential, mainly sufficient soil moisture and bioavailable organic matter. These same soil conditions were associated with increased risks of phosphorus release and greenhouse gas production. However, artificial flooding experiments showed that preventing prolonged flooding has a strong potential to reduce phosphorus export from floodplains with limited impacts on nitrogen treatment. Microcosm experiments with plant litter and wetland soils indicated that certain wetland vegetation types may reduce greenhouse gas production without sacrificing nitrogen removal capacity based on differences in plant biomass composition.</p>

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The Southern Appalachian hardwood forests contain a wide diversity of flora and fauna. Understanding processes that affect nutrient availability in these forests is essential for sound forest management. Three interconnected research projects regarding soil resource heterogeneity were designed to increase our understanding of this ecosystem. The objective of these projects were as follows: 1) to examine and quantify the role of decaying stumps in regards to total carbon (C) and nitrogen (N) pools and fine-root dynamics, 2) compare and contrast the use of ground-penetrating radar (GPR) vs. a soil auger for estimating soil depth and site quality and 3) to evaluate how eastern red-backed salamanders (Plethodon cinereus) affect N-availability. For the stump study, results show that decomposing stumps occupy approximately 1.2% of the total soil volume and constitute 4% and 10% of total soil N and C pools. Significant differences in N (p = 0.0114), C (p = 0.0172), microbial biomass C (p = 0.0004), potentially mineralizable N (p = 0.0042), and extractable NH4+ (p = 0.0312) concentrations were observed when compared to mineral soil horizons. In particular, potentially mineralizable N was 2.5 times greater in stump soil than the A-horizon (103 vs. 39 mg kg-1), 2.7 times greater for extractable NH4+ (16 vs. 6 mg kg-1) and almost 4 times greater for MBC (1528 vs. 397 mg kg-1). These measured properties suggest higher N-availability, organic matter turnover and N uptake in stump soil versus the bulk soil. 19% of the total fine root length and 14% of fine root surface area also occurred in the stump soil. The increased fine root length suggests higher concentrations of labile nutrient in the stumps since roots often proliferate in areas with higher nutrient availability. Significant differences occurred in N and C concentrations between all four decay classes and the A-horizon, which validated the use of this system and the need to calculate weighted averages based on the frequency and soil volume influenced by each decay class. In the GPR Study, depth estimations were shallower using a soil auger compared to estimates obtained using GPR across all plots (p = 0.0002; Figure 3.4). On a soil volume basis, this was equivalent to about 3500 m3 of soil per hectare unaccounted for using traditional methods. In regards to using soil depth as a predictor for site quality, no significant relationships were observed with soil depth estimations obtained from the auger (Table 3.3). On the other hand, depth measurements from GPR explained significant amounts of variation across all sites and by physiographic region. Across all sites, soil depth estimates from GPR explained 45.5% of the residual variation (p = 0.001; Table 3.3). When the data were stratified by physiographic region, a higher amount of variation was explained by the regression equations; 85% for the Cumberland Plateau (p = 0.009), 86.7% for the Allegheny Plateau (0.007) and 66.7% for the Ridge and Valley (p = 0.013), respectively (Table 4.2). Results from this study demonstrate how inaccurate current methods can be for estimating soil depth rocky forests soils. Furthermore, depth estimations from GPR can be used to increase the accuracy of site quality in the southern Appalachians. In the salamander study, no significant salamander density treatment or treatment by time effects were observed over the entire study period (p < 0.05). However, when the data were separated by individual sampling periods a few significant treatment by time interactions occurred: 1) during August 2006 for available NH4+ under the forest floor (i.e. horizontal cation membranes; p = 0.001), 2) August and 3) September 2006 for available NH4+ in the A-horizon (p = 0.026), and 4) May 2007 for available NO3- under the forest floor (p = 0.011). As a result of these trends, an index of cumulative N-availability (i.e. NH4+ and NO3-) under the forest floor and in the A-horizon was examined through the entire study period. Cumulative N-availability under the forest floor was consistently higher in the low- and medium-density salamander treatments compared to the high-density treatment. For cumulative N-availability in the A-horizon, a gradient of high to low N-availability existed as salamander density increased. Factors such as a prolonged drought in 2007 may have affected our ability to accurately assess the effects of salamanders on N-availability. We concluded that higher salamander densities do not increase N-availability. Implementing methodologies that accurately account for soil nutrient pools such as stump soil, physical properties such as depth and fauna such as salamanders, increase our understanding of factors that regulate site productivity in these ecosystems. As a result, landscape-level and stand-level management decisions can be conducted more effectively. / Ph. D.

Reindeer appear to have strong positive effects on plant productivity and nutrient cycling in strongly nutrient-limited ecosystems. While the direct effects of grazing on vegetation composition have been intensively studied, much less is known about the indirect effect of grazing on plant-soil interactions. This thesis investigated the indirect effects of ungulate grazing on arctic plant communities via soil nutrient availability and plant nutrient uptake. At high density, the deposition of dung alone increased plant productivity both in nutrient rich and nutrient poor tundra habitats without causing major changes in soil possesses. Plant community responses to dung addition was slow, with a delay of at least some years. By contrast, a 15N-urea tracer study revealed that nutrients from reindeer urine could be rapidly incorporated into arctic plant tissues. Soil and microbial N pools only sequestered small proportions of the tracer. This thesis therefore suggests a strong effect of dung and urine on plant productivity by directly providing nutrient-rich resources, rather than by stimulating soil microbial activities, N mineralization and ultimately increasing soil nutrient availability. Further, defoliation alone did not induce compensatory growth, but resulted in plants with higher nutrient contents. This grazing-induced increase in plant quality could drive the high N cycling in arctic secondary grasslands by providing litter of a better quality to the belowground system and thus increase organic matter decomposition and enhance soil nutrient availability. Finally, a 15N natural abundance study revealed that intense reindeer grazing influences how plants are taking up their nutrients and thus decreased plant N partitioning among coexisting plant species. Taken together these results demonstrate the central role of dung and urine and grazing-induced changes in plant quality for plant productivity. Soil nutrient concentrations alone do not reveal nutrient availability for plants since reindeer have a strong influence on how plants are taking up their nutrients. This thesis highlights that both direct and indirect effects of reindeer grazing are strong determinants of tundra ecosystem functioning. Therefore, their complex influence on the aboveground and belowground linkages should be integrated in future work on tundra ecosystem N dynamic.

Recent research using stable isotope analysis has shown a dependence on migrating or breeding populations of vertebrates as vectors for the transfer of marine-derived nutrients within coastal ecosystems. Sable Island, Nova Scotia, Canada supports numerous species of plants, a variety of seabird colonies (including common [Sterna hirundo] and Arctic [Sterna paradisaea] terns), the world’s largest grey seal (Halichoerus grypus) breeding colony, and a self-sustaining population of wild (feral) horses (Equus ferus caballus). I hypothesize that nitrogen cycling within this island ecosystem is highly influenced by the input of nutrients from seals and seabirds (‘biogenic vectors’), affecting primary production and potentially stabilizing higher trophic levels (i.e., horses). To examine this relation I developed a spatially-explicit isoscape for Sable Island through stable isotope analysis of nitrogen (δ15N) in samples (n = 282) of marram grass (Ammophila breviligulata). I incorporated significant variables (i.e., distance to vector colony and distance to shoreline, r2 = 0.41) into the final parsimonious interpolation model using universal co-kriging techniques. The greatest 15N enrichment occurred within the tips and along the perimeter of the island, coinciding with greater densities of grey seals, while the lowest values occurred within the centre of the island. I then identified individual contributions of seal-, tern- and horse-mediated transfer of marine-derived nutrients inland. Marram grass exhibited higher δ15N within seal (μ = 7.5‰) and tern (μ = 5‰) colonies, while horses and biogeochemical processes (i.e., volatilization, ammonification, etc.) most likely contributed to the homogeneity within the centre of the island (μ = 3.6‰). Due to the higher densities, wider distribution, and greater 15N enrichment of marram tissues, grey seals appear to be the most important vector species while seabirds have a more localized effect. The greater availability of N within vector colonies supplemented the local vegetation community, contributing to greater vegetation cover within colony boundaries. This relation had secondary effects on the horse population, which showed correspondingly higher horse δ15N values within the tips of the island (δ15N + 1.6‰) due to consumption of 15N enriched forage. I conclude that biogenic vector species promote nutrient transfer by establishing nutrient gateways which indirectly cause cascading effects throughout the food web.

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