Submitted by Luciana Ferreira (lucgeral@gmail.com) on 2015-01-14T13:41:03Z No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Dieimisson Paulo Almeida - 2014.pdf: 687444 bytes, checksum: ffba4f6a346736510c1445ffdf08f783 (MD5) / Approved for entry into archive by Luciana Ferreira (lucgeral@gmail.com) on 2015-01-14T14:12:20Z (GMT) No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Dieimisson Paulo Almeida - 2014.pdf: 687444 bytes, checksum: ffba4f6a346736510c1445ffdf08f783 (MD5) / Made available in DSpace on 2015-01-14T14:12:20Z (GMT). No. of bitstreams: 2 license_rdf: 23148 bytes, checksum: 9da0b6dfac957114c6a7714714b86306 (MD5) Dissertação - Dieimisson Paulo Almeida - 2014.pdf: 687444 bytes, checksum: ffba4f6a346736510c1445ffdf08f783 (MD5) Previous issue date: 2014-02-15 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In areas where it works with no till is common to observe flaws in the burn down of cover crops and/or spontaneous vegetation, which can characterize the insufficient deposition of active ingredient of herbicides. The spray technology is the tool to be used in the planning and execution of burn down, to ensure that products with proven for weed control and coverage, effectiveness are efficiently deposited in biological targets. Two assays were carried out in order to evaluate the efficiency of herbicide applications. At the first it was evaluated the influence of classes drops (very fine droplets and very coarse droplets) and spray volumes (50, 100, 150 and 200 L ha-1) on the effectiveness of cover crop control with use of glyphosate and glyphosate + saflufenacil to control Urochloa ruziziensis and Conyza sp., respectively. The classes of droplets influence the control of Urochloa ruziziensis. The reduction on spray volume increased the possibility of sprouts on Conyza sp. On the second experiment it was investigated the efficiency of two spray application volumes (50 and 200 L ha-1) at different times of day (4:30, 10:30, 16:30 and 22:30 pm) on burn down of Urochloa ruziziensis and spontaneous vegetation. The efficacy of glyphosate in cover crops is not influenced by schedules of spray. / Em áreas onde se trabalha com Plantio Direto é comum observar-se falhas na dessecação das plantas de cobertura e/ou vegetação espontânea, o que pode caracterizar a deposição em quantidade insuficiente do ingrediente ativo do herbicida. A tecnologia de aplicação é a ferramenta a ser utilizada no planejamento e execução da dessecação, a fim de garantir que produtos com eficácia comprovada para o controle de plantas daninhas e de cobertura, sejam eficientemente depositados nos alvos biológicos. Visando maximizar a eficácia de herbicidas por meio de aplicações eficientes foram realizados dois experimentos. No primeiro foi avaliada a influência das classes de gotas (gotas muito fina e gotas muito grossa) e volumes de aplicação (50, 100, 150 e 200 L ha-1) no controle das coberturas vegetais, com uso de glyphosate e glyphosate + saflufenacil para controle de Urochloa ruziziensis e Conyza sp., respectivamente, no qual concluiu-se que as classes de gotas influenciam no controle de Urochloa ruziziensis e a redução do volume de aplicação aumenta a possibilidade de rebrotes de Conyza sp.. No segundo experimento avaliou-se a eficiência da aplicação em dois volumes de aplicação (50 e 200 L ha-1) em diferentes horários do dia (4:30, 10:30, 16:30 e 22:30 horas) na dessecação de Urochloa ruziziensis e vegetação espontânea. Conclui-se que a eficácia de glyphosate nas coberturas vegetais não sofre influência de horários de aplicação.

<p>Herbicide-resistant weed populations have become problematic throughout the Eastern Corn Belt, with 18 unique herbicide-resistant weed biotypes confirmed in Indiana alone. In response to these resistant populations, the agricultural chemical industry has responded by developing glyphosate-resistant crops paired with resistance to synthetic auxin herbicides such as dicamba and 2,4-D.</p><p>This research evaluates weed population shifts in cropping systems using row crops that are resistant to synthetic auxin herbicides. Identifying weed population shifts will allow future research to be targeted to weed species that would become more prevalent in cropping systems using synthetic auxin-resistant crops. The use of multiple sites of action will be needed in order to prevent weed shifts in both conventional and no-till corn-soybean production systems. Weed densities and species richness were reduced within field evaluations when six or more herbicide sites of action were implemented with residual herbicides in both corn and soybean years over a seven-year period. Additionally, soil seedbank weed densities and species richness were reduced within 2,4-D-resistant soybean production systems. Additional strategies other than the application of herbicides may be needed to manage weed populations in the future due to the high levels of herbicide-resistant weed populations in the Midwest.</p><p>Off-target movement of these synthetic auxin herbicides, has been a concern, and label-mandated buffer areas are required near sensitive areas. Investigation of whether cover crops can be an effective tactic in managing weeds in these label-mandated buffer areas was conducted. Cover crop utilization in buffer areas has not been investigated in Indiana. Additionally, termination timing is becoming more prominent as farm operators are increasingly terminating cover crops after planting. Our results demonstrate that using cover crops that utilize cereal rye and that are terminated at, or after the time of soybean planting will be beneficial in suppressing waterhemp, grasses, and sometimes horseweed within label-mandated buffer areas, but not for suppression of giant ragweed. However, delaying termination of cover crops can result in soybean yield reductions and caution should be used. Terminating cover crops with glyphosate and auxin and a residual herbicide was more effective than glyphosate alone, but would not be permitted within label-mandated buffer areas.L</p>

Soils provide many essential functions that support the world. With a decline in soil health, these functions also decrease in efficiency, and can threaten the health of billions of people around the world. Typically, soil health tests do not use biological indicators, however microbes drive and perform vital functions to increase soil health. One way to increase soil health is through the use of cover crops to reduce soil erosion during fallow periods, increasing soil organic matter, as well as collecting nutrients from soil into their biomass. These cover crops are then terminated through various methods such as herbicides, disk tillage, or no tillage. The termination method can have an impact on soil health, by chemically affecting soil microbes with herbicides, disturbing soil, microbial communities, and fungi with tillage, or creating residue barriers on the surface of soil such as with using roller crimping (no tillage). Fertilization can also affect soil health, controlling rates of nutrient turnover and decomposition through the needs of microbes for carbon and nitrogen. This study quantifies the effects of four termination methods and four fertilization treatments on soil biological indicators during one growing season of sweet corn. Plots that were not tilled and terminated using roller crimping showed highest rates of decomposition, as well as increased labile carbon pools to feed microbes slowly throughout the growing season. Microbial activity was also observed to respond to fertilization, as patterns in activity spiked directly after fertilization. This study informs agricultural land management by the usage of biological indicators to further support the use of cover crops to increase soil health along with using no-till termination methods. Root biomass contributions toward soil health was also investigated, and how they may be affected by tillage.

A utilização de herbicidas pode modificar a dinâmica do nitrogênio nos agroecossistemas e, como consequência, a disponibilidade do nutriente às plantas e microrganismos. Estas mudanças podem ocorrer devido às alterações fisiológicas ocasionadas nas plantas e/ou devido ao efeito dos herbicidas na atividade e composição da comunidade microbiana do solo, a qual tem funções importantes nas transformações do N no sistema. Neste contexto, objetivou-se com este trabalho de tese: 1- avaliar as perdas de nitrogênio do sistema solo-planta, sem distinção às vias de saída, após a aplicação de herbicidas em Pennicetum glaucum, Avena strigosa e Brachiaria ruziziensis; 2- avaliar a concentração de NH4 + na planta, a emissão de NH3 via foliar e a volatilização de NH3 pelo solo após aplicação de glyphosate em B. decumbens; 3 avaliar a exsudação de compostos nitrogenados por B. decumbens após aplicação dos herbicidas glyphosate, glufosinato de amônio e paraquat; e 4 avaliar a mineralização do N da palha de P. glaucum e A. strigosa dessecados com herbicidas e o aproveitamento do N proveniente da palha por plantas de milho. O herbicida glyphosate aumentou a concentração de NH4 + em plantas de B. decumbens e, como consequência, a emissão de NH3 via foliar em duas espécies de plantas do gênero Brachiaria. A volatilização de NH3 pelo solo não foi afetada pela utilização do herbicida glyphosate. As perdas de N do sistema solo-planta foram maiores após aplicação dos herbicidas glyphosate e glufosinato de amônio em P. glaucum, B. decumbens e B. ruziziensis. No entanto, em A. strigosa as perdas não foram afetadas por estas moléculas. Os herbicidas glyphosate e glufosinato de amônio modificaram a partição do N nas espécies estudadas, ocorrendo redução no conteúdo de N nas folhas. As perdas de N do sistema e a partição do N nas plantas não foram afetadas pelo herbicida paraquat, aplicado em B. ruziziensis e A. strigosa. A exsudação de compostos nitrogenados foi maior após aplicação dos herbicidas glyphosate, glufosinato de amônio e paraquat em B. decumbens. A mineralização do N de resíduos culturais de P. glaucum e A. strigosa foi reduzida pela dessecação destas espécies com os herbicidas glyphosate e glufosinato, sendo observado menor conteúdo de N proveniente do fertilizante no milho cultivado em solo com palha proveniente de plantas dessecadas. No entanto, a massa seca de grãos e das plantas de milho não foram afetadas pela utilização de herbicidas na dessecação das espécies utilizadas como cobertura. O carbono da biomassa microbiana e a conversão de amônio em nitrato foram menores no solo com palha de P. glaucum dessecado com herbicidas em relação à testemunha. Com base nos resultados obtidos neste trabalho de tese, conclui-se que os herbicidas glyphosate, glufosinato de amônio e paraquat podem afetar a dinâmica do N nos agroecossistemas, reduzindo a disponibilidade de N às plantas. Estes resultados apontam a necessidade de desenvolvimento de novas pesquisas, visando conhecer a real magnitude dos impactos causados pelo uso de herbicidas nos processos relacionados ao ciclo do nitrogênio. As informações obtidas neste trabalho de tese e pesquisas futuras relacionadas ao tema podem ser úteis para elaboração de estratégias de manejo que aumentem o aproveitamento do N pelas culturas e reduzam o impacto ambiental ocasionado pelo uso de fertilizantes e herbicidas. / Herbicide adoption might modify nitrogen dynamics in agroecossystems and, for consequence, nutrient availability for plants and microorganisms. These modifications may occur because of plant physiologic changes and/or due to herbicide effects on activity and composition of soil microbial community, which has important functions on system N modifications. In this context, thesis was developed with the following objectives: 1- Evaluating nitrogen losses in soilplant system, with no distinction to exit ways, after herbicide application in Pennicetum glaucum, Avena strigosa and Brachiaria ruziziensis; 2 Evaluating NH4 + plant concentration, NH3 emission by leaves and soil NH3 volatilization after herbicide application in B. decumbens; 3- Evaluating nitrogen compounds exudation by B. decumbens after the application of the herbicides glyphosate, ammonium-glufosinate or paraquat; and 4- Evaluating nitrogen mineralization of P. glaucum e B. decumbens straw previously desiccated with herbicides and N-straw usefulness by corn plants. Glyphosate increased NH4 + concentration in plants of B. decumbens and, by consequence, NH3 leaf emission in two plant species of Brachiaria genus. Ammonia volatilization from soil was not affected by application of the herbicide glyphosate. Nitrogen losses of the soil-plant system were larger after glyphosate and ammonium-glufosinate application on P. glaucum, B. decumbens and B. ruziziensis. However, for A. strigosa, the losses were not affected by herbicide application. The herbicides glyphosate and ammonium-glufosinate modified species N partition, reducing N amount in leaves. System nitrogen losses and N plant partition were not affected by the herbicide paraquat, applied on B. ruziziensis and A. strigosa. Nitrogen compounds exudation was higher after application of the herbicides glyphosate, ammonium-glufosinate or paraquat on B. decumbens. Nitrogen mineralization from crop residues of P. glaucum e A. strigosa was reduced by crop desiccation with the herbicides glyphosate and ammonium-glufosinate, being observed smaller N-fertilizer amount in corn grown in soil with straw of these covering crops. Thus, kernel dry mass and whole plant dry mass were not affected by herbicide application for P. glaucum e A. strigosa desiccation. Microbial biomass carbon and ammonium-nitrate conversion were smaller in soil covered with P. glaucum straw previously desiccated with herbicides when compared to the check. Based on the results reached in this thesis, one could conclude that glyphosate, ammonium-glufosinate and paraquat may affect nitrogen dynamics at agroecossystems, reducing N availability for crops. These results indicate the necessity for developing new researches, aiming to know the real magnitude of the impacts caused by herbicides in the processes of nitrogen cycle. The information obtained in the work and in future researches related to the theme might be useful for creating management strategies that increase N crop usefulness and reduce environmental impact caused by herbicide and fertilizer adoption.

Além dos aspectos relacionados à proteção do solo, as coberturas vegetais, vivas ou mortas, também contribuem para a redução da infestação de plantas daninhas no período da entressafra. Com o objetivo de analisar o potencial de espécies utilizadas como coberturas vegetais de inverno no manejo de plantas daninhas, conduziram-se dois ensaios em áreas pertencentes ao Departamento de produção Vegetal da ESALQ/USP, em Piracicaba SP, durante o ano de 2008. As espécies usadas como culturas de cobertura foram: Raphanus sativus L. (nabo forrageiro), Helianthus annuus L. (girassol), Avena strigosa Schreb (aveia preta), Avena bysantina L. (aveia amarela), Vicia sativa L. (ervilhaca) e Sorghum bicolor L. Moench (sorgo forrageiro), sendo que esta última espécie não foi utilizada em um dos ensaios. Realizaram-se nos dois ensaios estudos fitossociológicos, avaliações referentes à quantificação de massa seca produzida pelas coberturas, identificação e levantamento de plantas daninhas e avaliação da taxa de decomposição das coberturas. As comunidades de plantas daninhas apresentaram modificações em sua composição florística de acordo com o tipo de cobertura utilizado. D. horizontalis foi a principal espécie no primeiro ensaio, com os maiores valores de importância relativa acumulada, enquanto que G.parviflora se destacou no segundo ensaio. Verifica-se que o cultivo de culturas de cobertura durante a entressafra pode contribuir para a redução de infestação de plantas daninhas na cultura subseqüente. O girassol apresentou o melhor potencial de produção e quantidade de massa seca por hectare, no entanto as aveias, amarela e preta, demonstraram ser as coberturas com maior potencial de supressão de plantas daninhas. E estas mesmas espécies foram as que demoraram mais tempo para se decompor, apresentando tempo de meia vida superior ao das demais coberturas, ou seja, foram necessários, em média, 144 e 119 dias para a decomposição de metade da quantidade da fitomassa da aveia amarela e preta respectivamente. As coberturas de ervilhaca e nabo foram as cobeturas que apresentaram decomposição mais acelerada. / Besides contributing to aspects related to soil protection, the cover crops also contribute to the weeds suppression during the counter season. Aiming to analyze the potential of species used as winter cover crops in winter management, two experiments were set up in areas located at the Vegetal Production Departament at ESALQ/USP, in Piracicaba SP, during 2008. The cover crops used were: Raphanus sativus L. (oilseed radish), Helianthus annuus L. (sunflower) Avena strigosa Schreb (sand oat), Avena bysantina L. (red oat), Vicia sativa L. (common vetch) and Sorghum bicolor L. Moench (sorghum). The last cover crop mentioned was not used in the second area. A phytosociological study of weeds was made in both experimental areas. An evaluation of mass yield, weeds identification and collection and a decomposition rate evaluation were also performed. The weeds communities showed changes in their floristic composition according to the cover crop used. D. horizontalis was the most important species in the first area, showing high values of relative importance, whereas G.parviflora was the most important in the second one. The use of cover crops during counter season can contribute to reduce weed infestation in the subsequent crop. Sunflower was the cover crop wich produced the greatest amount of dry mass per hectare, however, the oat varieties showed the best ability to suppress weeds. Those were the species that took more time to decompose, showing a longer half life compared to the other cover crops, it is, It was required, on average, 144 and 119 days for the decomposition of half of sand oat and red oat mass, respectively. Common vetch and oilseed radish were the cover crops that showed the fastest decomposition.

Orientador: Jose Eduardo Cora / Banca: Maria Cristina Pessoa da Cruz / Banca: Carolina Fernandes / Resumo: A rotação de culturas em sistema de semeadura direta (SSD) promove vários benefícios ao sistema, pois os resíduos das culturas, ao se decomporem, podem alterar os atributos químicos do solo e, como conseqüência, influenciarem a cultura em sucessão. O presente trabalho teve como objetivo avaliar os efeitos de culturas de inverno nos atributos químicos do solo, no estado nutricional e na produtividade das culturas de soja, milho e arroz, cultivadas no verão em SSD. O experimento foi realizado no município de Jaboticabal, SP, em Latossolo Vermelho eutrófico. O delineamento experimental utilizado foi de blocos casualizados com três repetições no esquema em faixas. Os tratamentos foram constituídos pela combinação de quatro seqüências de culturas de verão (monoculturas de milho e de soja e as rotações soja/milho e arroz/feijão/algodão) com sete culturas de inverno (milho, girassol, nabo forrageiro, milheto, guandu, sorgo e crotalária). Após o manejo das culturas de inverno e antes da semeadura das culturas de verão do ano agrícola 2006/2007, foram coletadas amostras de solo nas camadas de 0-2,5; 2,5-5,0; 5-10; 10-20 e 20-30 cm. Nas amostras de solo, foram determinados: matéria orgânica (MO), pH, P (resina), K, Ca, Mg, H+Al e calculados CTC e V. Nas culturas de verão, coletaram-se amostras foliares para a determinação das concentrações foliares de N, P, K, Ca, Mg, S, B, Cu, Fe, Mn e Zn. A produtividade das culturas de verão foi avaliada. Foram observados no solo, maiores teores de P após nabo forrageiro e crotalária e menores teores de MO após milho, girassol e guandu no inverno. O SSD apresentou gradientes de fertilidade ao longo do perfil para todos os atributos químicos avaliados... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The crop rotation practice in no-tillage system promotes lots of benefits to the system. The crop residues can change the soil chemical attributes, consequentially influencing the performance of following crops. The objective of this work was to evaluate the effects of winter crops on the soil chemical attributes, nutritional state and yield summer crops (soybean, corn and rice) in no-tillage system. A field experiment has been carried out on a eutrophic Red Oxisol at Jaboticabal, SP, Brazil. A completely randomized block design with three replications was used, in strips. The treatments were the combination of four summer crops sequences (corn and soybean monocultures, rotation soybean/corn and rotation rice/bean/cotton) with seven winter crops (corn, sunflower, oilseed radish, millet, pigeon pea, sorghum and sunn hemp). After the winter crops management and before the summer crops sowing at the crop season 2006/2007, the soil was sampled at 0-2.5, 2.5-5.0, 5-10, 10-20 and 20-30 cm soil depths. Organic matter, pH, P, K+, Ca+2, Mg+2, H+Al were determined, and cation capacity exchange and bases saturation values were calculated in each soil samples. The N, P, K, Ca, Mg, S, B, Cu, Fe, Mn and Zn uptake were determined in summer crops. Also, the summer crops yield was obtained. In the soil, the oilseed radish and sunn hemp provide the highest P contents and corn, sunflower and pigeon pea provide the lowest organic matter contents. The no-tillage system showed gradient of fertility in the soil profile. The soybean (rotation soybean/corn) showed lower S uptake after corn and sorghum. The soybean (monoculture) showed higher N, P and S uptake after oilseed radish and sunn hemp. In the corn, Zn uptake were lower after oilseed radish. The oilseed radish and sunn hemp provides the highest soybean yield. In the corn, the highest yields were observed after oilseed radish, millet and pigeon pea. The sorghum provides suppressor effect on the rice yield. / Mestre

<div>The demand for customized farm management prescription is increasing in order to maximize crop yield and minimize environmental risks under a changing climate. One great challenge to modeling crop growth and production is spatial and temporal variability. The goal of this dissertation research is to use publicly available Landsat imagery, ground samples and historical yield data to establish methodologies to spatially quantify cover crop growth and in-season maize yield. First, an investigation was conducted into the feasibility of using satellite remote sensing and spatial interpolation with minimal ground samples to rapidly estimate season-specific cover crop biomass and N uptake in the small watershed of Lake Bloomington in Illinois. Results from this study demonstrated that remote sensing indices could capture the spatial pattern of cover crop growth as affected by various cover crop and cash crop management systems. Soil adjusted vegetation index (SAVI), enhanced vegetation index (EVI) and triangular vegetation index (TVI) were strongly correlated with cover crop biomass and N uptake for low and moderate biomass and N uptake ranges (0-3000 kg ha-1 and 0-100 kg N ha-1). The SAVI estimated cover crop biomass and N uptake were +/- 15% of observed value. Compared to commonly used spatial interpolation methods such as ordinary kriging (OK) and inverse distance weighting (IDW), using the SAVI method showed higher prediction R2 values than that of OK and IDW. An additional advantage for these remote sensing vegetation indices, especially in the context of diverse agronomic management practices, is their much lower labor requirements compared to the high density ground samples needed for a spatial interpolation analysis. </div><div>In the second study, a new approach using the multivariate spatial autoregressive (MSAR) model was developed at 10-m grid resolution to forecast maize yield using historical grain yield data collected at farmers’ fields in Central Indiana, publicly available Landsat imagery, top 30 cm soil organic matter and elevation, while accounting for yield spatial autocorrelation. Relative mean error (RME) and relative mean absolute error (RMAE) were used to quantify the model prediction accuracy at the field level and 10-m grid level, respectively. The MSAR model performed reasonably well (absolute RME < 15%) for field overall yield predictions in 32 out of 35 site-years on the calibration dataset with an average absolute RME of 6.6%. The average RMAE of the MSAR model predictions was 13.1%. It was found that the MSAR model could result in large estimation error under an extreme stressed environment such as the 2012 drought, especially when grain yield under these stressed conditions was not included in the model calibration step. In the validation dataset (n=82), the MSAR model showed good prediction accuracy overall (± 15% of actual yield in 56 site-years) in new fields when extreme stress was not present. The novel approach developed in this study demonstrated its ability to use elevation and soil information to interpret satellite observations accurately in a fine spatial scale. </div><div>Then we incorporated the MSAR approach into a process-based N transformation model to predict field-scale maize yield in Indiana. Our results showed that the linear agreement of predicted yield (using the N Model in the Mapwindow GIS + MMP Tools) to actual yield improved as the spatial aggregation scale became broader. The proposed MSAR model used early vegetative precipitation, top 30 cm soil organic matter and elevation to adjust the N Model yield prediction in 10-m grids. The MSAR adjusted yield predictions resulted in more cases (77%) that fell within 15% of actual yield compared to the N Model alone using the calibration dataset (n=35). However, if the 2012 data was not included in the MSAR parameter training step, the MSAR adjusted yield predictions for 2012 were not improved from the N Model prediction (average RME of 24.1%). When extrapolating the MSAR parameters developed from 7 fields to a dataset containing 82 site-years on 30 different fields in the same region, the improvement from the MSAR adjustment was not significant. The lack of improvement from the MSAR adjustment could be because the relationship used in the MSAR model was location specific. Additionally, the uncertainty of precipitation data could also affect the relationship. </div><div>Through the sequence of these studies, the potential utility of big data routinely collected at farmers’ fields and publicly available satellite imagery has been greatly improved for field-specific management tools and on-farm decision-making. </div>

<p>Arbuscular mycorrhizal fungi (AMF) are best known for their potential to help plants acquire nutrients, especially phosphorous. These microbes improve soil health by promoting soil aggregation and carbon sequestration, and further benefit plants by helping them withstand biotic and abiotic stress. Currently, there are 200 recognized species of AMF within the phylum Glomeromycota. Recent studies indicate that individual AMF species differ in the benefits they provide, with some even acting as parasites. Moreover, AMF community composition can be altered by soil and crop management practices, but the effect of these changes on the benefits conferred by AMF are still not well understood. Consequently, the goal of this study was to determine how two widely used crop management systems can alter the composition of AMF species, and affect the potential for these communities to promote the productivity and drought tolerance. To accomplish this goal, we collected AMF inoculum from a long-term crop systems trial comparing organic and conventional management for use in greenhouse trials where we subjected plants to drought. We collected AMF inoculum during mid-summer when differences between the two management systems were likely cause larger effects on AMF communities, and again in autumn after harvest to see if differences in AMF communities would persist. We determined AMF species composition using next generation sequencing. Results of this study confirm that soil-building practices commonly used in organic farming systems can improve soil health and increase the productivity of food-grade soybeans. They also demonstrate that AMF communities in Indiana croplands are highly diverse, and some of these taxa can improve soybean growth and help plants tolerate water stress. Although the overall diversity of AMF communities did not differ between the organic and conventional management systems in mid-summer, individual AMF taxa did differ between the systems, which were likely responsible for the greater tolerance to water stress observed when plants were amended with inoculum from the organic system. AMF communities present during autumn were significantly different between the two crop management systems, but did not result in differences in drought tolerance of soybeans, indicating that the loss of key AMF taxa in the organic system from the first relative to the second experiment was likely responsible. Finally, plants grown using inoculum from both crop management systems in autumn had greater tolerance to water stress than plants that received a AMF commercial inoculum. This provides further evidence that individual AMF species vary in the benefits they provide, and that the presence of a diverse consortium of AMF species is needed to optimize plant health and productivity in agricultural systems. Agricultural producers should consider incorporating soil-building practices that are commonly used in organic farming systems such as planting winter cover crops, to improve the health of their soil and enhance the productivity of their crops. <b></b></p> <br>

Além dos aspectos relacionados à proteção do solo, as coberturas vegetais, vivas ou mortas, também contribuem para a redução da infestação de plantas daninhas no período da entressafra. Com o objetivo de analisar o potencial de espécies utilizadas como coberturas vegetais de inverno no manejo de plantas daninhas, conduziram-se dois ensaios em áreas pertencentes ao Departamento de produção Vegetal da ESALQ/USP, em Piracicaba SP, durante o ano de 2008. As espécies usadas como culturas de cobertura foram: Raphanus sativus L. (nabo forrageiro), Helianthus annuus L. (girassol), Avena strigosa Schreb (aveia preta), Avena bysantina L. (aveia amarela), Vicia sativa L. (ervilhaca) e Sorghum bicolor L. Moench (sorgo forrageiro), sendo que esta última espécie não foi utilizada em um dos ensaios. Realizaram-se nos dois ensaios estudos fitossociológicos, avaliações referentes à quantificação de massa seca produzida pelas coberturas, identificação e levantamento de plantas daninhas e avaliação da taxa de decomposição das coberturas. As comunidades de plantas daninhas apresentaram modificações em sua composição florística de acordo com o tipo de cobertura utilizado. D. horizontalis foi a principal espécie no primeiro ensaio, com os maiores valores de importância relativa acumulada, enquanto que G.parviflora se destacou no segundo ensaio. Verifica-se que o cultivo de culturas de cobertura durante a entressafra pode contribuir para a redução de infestação de plantas daninhas na cultura subseqüente. O girassol apresentou o melhor potencial de produção e quantidade de massa seca por hectare, no entanto as aveias, amarela e preta, demonstraram ser as coberturas com maior potencial de supressão de plantas daninhas. E estas mesmas espécies foram as que demoraram mais tempo para se decompor, apresentando tempo de meia vida superior ao das demais coberturas, ou seja, foram necessários, em média, 144 e 119 dias para a decomposição de metade da quantidade da fitomassa da aveia amarela e preta respectivamente. As coberturas de ervilhaca e nabo foram as cobeturas que apresentaram decomposição mais acelerada. / Besides contributing to aspects related to soil protection, the cover crops also contribute to the weeds suppression during the counter season. Aiming to analyze the potential of species used as winter cover crops in winter management, two experiments were set up in areas located at the Vegetal Production Departament at ESALQ/USP, in Piracicaba SP, during 2008. The cover crops used were: Raphanus sativus L. (oilseed radish), Helianthus annuus L. (sunflower) Avena strigosa Schreb (sand oat), Avena bysantina L. (red oat), Vicia sativa L. (common vetch) and Sorghum bicolor L. Moench (sorghum). The last cover crop mentioned was not used in the second area. A phytosociological study of weeds was made in both experimental areas. An evaluation of mass yield, weeds identification and collection and a decomposition rate evaluation were also performed. The weeds communities showed changes in their floristic composition according to the cover crop used. D. horizontalis was the most important species in the first area, showing high values of relative importance, whereas G.parviflora was the most important in the second one. The use of cover crops during counter season can contribute to reduce weed infestation in the subsequent crop. Sunflower was the cover crop wich produced the greatest amount of dry mass per hectare, however, the oat varieties showed the best ability to suppress weeds. Those were the species that took more time to decompose, showing a longer half life compared to the other cover crops, it is, It was required, on average, 144 and 119 days for the decomposition of half of sand oat and red oat mass, respectively. Common vetch and oilseed radish were the cover crops that showed the fastest decomposition.

A utilização de herbicidas pode modificar a dinâmica do nitrogênio nos agroecossistemas e, como consequência, a disponibilidade do nutriente às plantas e microrganismos. Estas mudanças podem ocorrer devido às alterações fisiológicas ocasionadas nas plantas e/ou devido ao efeito dos herbicidas na atividade e composição da comunidade microbiana do solo, a qual tem funções importantes nas transformações do N no sistema. Neste contexto, objetivou-se com este trabalho de tese: 1- avaliar as perdas de nitrogênio do sistema solo-planta, sem distinção às vias de saída, após a aplicação de herbicidas em Pennicetum glaucum, Avena strigosa e Brachiaria ruziziensis; 2- avaliar a concentração de NH4 + na planta, a emissão de NH3 via foliar e a volatilização de NH3 pelo solo após aplicação de glyphosate em B. decumbens; 3 avaliar a exsudação de compostos nitrogenados por B. decumbens após aplicação dos herbicidas glyphosate, glufosinato de amônio e paraquat; e 4 avaliar a mineralização do N da palha de P. glaucum e A. strigosa dessecados com herbicidas e o aproveitamento do N proveniente da palha por plantas de milho. O herbicida glyphosate aumentou a concentração de NH4 + em plantas de B. decumbens e, como consequência, a emissão de NH3 via foliar em duas espécies de plantas do gênero Brachiaria. A volatilização de NH3 pelo solo não foi afetada pela utilização do herbicida glyphosate. As perdas de N do sistema solo-planta foram maiores após aplicação dos herbicidas glyphosate e glufosinato de amônio em P. glaucum, B. decumbens e B. ruziziensis. No entanto, em A. strigosa as perdas não foram afetadas por estas moléculas. Os herbicidas glyphosate e glufosinato de amônio modificaram a partição do N nas espécies estudadas, ocorrendo redução no conteúdo de N nas folhas. As perdas de N do sistema e a partição do N nas plantas não foram afetadas pelo herbicida paraquat, aplicado em B. ruziziensis e A. strigosa. A exsudação de compostos nitrogenados foi maior após aplicação dos herbicidas glyphosate, glufosinato de amônio e paraquat em B. decumbens. A mineralização do N de resíduos culturais de P. glaucum e A. strigosa foi reduzida pela dessecação destas espécies com os herbicidas glyphosate e glufosinato, sendo observado menor conteúdo de N proveniente do fertilizante no milho cultivado em solo com palha proveniente de plantas dessecadas. No entanto, a massa seca de grãos e das plantas de milho não foram afetadas pela utilização de herbicidas na dessecação das espécies utilizadas como cobertura. O carbono da biomassa microbiana e a conversão de amônio em nitrato foram menores no solo com palha de P. glaucum dessecado com herbicidas em relação à testemunha. Com base nos resultados obtidos neste trabalho de tese, conclui-se que os herbicidas glyphosate, glufosinato de amônio e paraquat podem afetar a dinâmica do N nos agroecossistemas, reduzindo a disponibilidade de N às plantas. Estes resultados apontam a necessidade de desenvolvimento de novas pesquisas, visando conhecer a real magnitude dos impactos causados pelo uso de herbicidas nos processos relacionados ao ciclo do nitrogênio. As informações obtidas neste trabalho de tese e pesquisas futuras relacionadas ao tema podem ser úteis para elaboração de estratégias de manejo que aumentem o aproveitamento do N pelas culturas e reduzam o impacto ambiental ocasionado pelo uso de fertilizantes e herbicidas. / Herbicide adoption might modify nitrogen dynamics in agroecossystems and, for consequence, nutrient availability for plants and microorganisms. These modifications may occur because of plant physiologic changes and/or due to herbicide effects on activity and composition of soil microbial community, which has important functions on system N modifications. In this context, thesis was developed with the following objectives: 1- Evaluating nitrogen losses in soilplant system, with no distinction to exit ways, after herbicide application in Pennicetum glaucum, Avena strigosa and Brachiaria ruziziensis; 2 Evaluating NH4 + plant concentration, NH3 emission by leaves and soil NH3 volatilization after herbicide application in B. decumbens; 3- Evaluating nitrogen compounds exudation by B. decumbens after the application of the herbicides glyphosate, ammonium-glufosinate or paraquat; and 4- Evaluating nitrogen mineralization of P. glaucum e B. decumbens straw previously desiccated with herbicides and N-straw usefulness by corn plants. Glyphosate increased NH4 + concentration in plants of B. decumbens and, by consequence, NH3 leaf emission in two plant species of Brachiaria genus. Ammonia volatilization from soil was not affected by application of the herbicide glyphosate. Nitrogen losses of the soil-plant system were larger after glyphosate and ammonium-glufosinate application on P. glaucum, B. decumbens and B. ruziziensis. However, for A. strigosa, the losses were not affected by herbicide application. The herbicides glyphosate and ammonium-glufosinate modified species N partition, reducing N amount in leaves. System nitrogen losses and N plant partition were not affected by the herbicide paraquat, applied on B. ruziziensis and A. strigosa. Nitrogen compounds exudation was higher after application of the herbicides glyphosate, ammonium-glufosinate or paraquat on B. decumbens. Nitrogen mineralization from crop residues of P. glaucum e A. strigosa was reduced by crop desiccation with the herbicides glyphosate and ammonium-glufosinate, being observed smaller N-fertilizer amount in corn grown in soil with straw of these covering crops. Thus, kernel dry mass and whole plant dry mass were not affected by herbicide application for P. glaucum e A. strigosa desiccation. Microbial biomass carbon and ammonium-nitrate conversion were smaller in soil covered with P. glaucum straw previously desiccated with herbicides when compared to the check. Based on the results reached in this thesis, one could conclude that glyphosate, ammonium-glufosinate and paraquat may affect nitrogen dynamics at agroecossystems, reducing N availability for crops. These results indicate the necessity for developing new researches, aiming to know the real magnitude of the impacts caused by herbicides in the processes of nitrogen cycle. The information obtained in the work and in future researches related to the theme might be useful for creating management strategies that increase N crop usefulness and reduce environmental impact caused by herbicide and fertilizer adoption.