An analytical investigation was conducted to study the behavior of a bottom flange bearing beam-to girder connection subjected to patch loading. This connection would be useful with deep deck (thickness greater than 3 in.) composite slabs as well as with commonly used deck where floor-to-floor height needs to be minimized. Five girder specimens were loaded until yielding during the initial phase of the research. The analysis section consists of the yield line theory and finite element study that were used to develop a model to predict the collapse loads of the girder sections. These results from the model were then compared to the experimental loads. A design procedure utilizing the proposed model and future work recommendations are then presented. / Master of Science

SIMS est une technique d'analyse sensible de la surface. La probabilité d'ionisation dépend de l'état chimique de la surface. La génération des ions positifs est améliorée par le bombardement de la surface avec des éléments électronégatifs.Sur le NanoSIMS 50 de CAMECA, dont la configuration optique nécessite une polarité opposée entre ions primaires et secondaires, l'analyse des ions positifs se fait sous bombardement d'ions O-, générés dans un duoplasmatron. La faible brillance de la source en mode O- a comme conséquence une faible résolution latérale des analyses. Pour y remédier, nous avons étudié la possibilité de générer d’autres faisceaux d’ions primaires négatifs. Dans cet objectif, nous avons étudié la génération par duoplasmatron d'ions F-, Cl-, Br- et I- en fonction du champ magnétique, du courant d'arc et de la pression totale des gaz. Le courant d'ions et le diamètre du faisceau ont été mesurés afin de déterminer la brillance de la source en mode F-, Cl-, Br- et I-. Une brillance 5 fois plus élevée en mode F- qu'en mode O- a été déterminée.En utilisant les faisceaux F-, Cl-, Br- et I-, le rendement de pulvérisation, la concentration d'ions primaires implantés et le rendement utile ont été mesurés pour des semi-conducteurs et des métaux. Suite à une faible concentration en halogène à la surface des semi-conducteurs, résultant des processus de décapage, le rendement utile sous bombardement halogène était plus faible que sous bombardement O-. Pour les métaux (p.ex. Ni, Cu et Ag) par contre, une amélioration du rendement utile sous bombardement halogène jusqu'à deux ordres de grandeurs, comparé au bombardement O-, a été mesurée / Secondary Ion Mass spectrometry (SIMS) is a powerful surface analysis technique. The ionisation probability strongly depends on the chemical surface state. The generation of positive secondary ions can be enhanced by surface bombardment with electronegative elements.Due to the optical configuration of the CAMECA NanoSIMS 50, that necessitates an opposite polarity of incoming and ejected ions, analyses of positive ions are realized with primary O- ions, generated in a duoplasmatron ion source. As a consequence of the low O- brightness of the duoplasmatron source, the lateral resolution of the analyses on the NanoSIMS 50 is not satisfactory in the positive secondary mode. In this work, we studied the feasibility of different alternative negative primary ion beams. We investigated the possibility of F-, Cl-, Br- and I- ion generation with a duoplasmatron as a function of the source parameters, notably the magnetic field strength, the arc current and the total gas pressure. The ion current and the beam diameter were measured in order to determine the F-, Cl-, Br- and I- brightness of the source. A comparative study with the O- brightness demonstrates an increase of the F- brightness by a factor of 5.By using the F-, Cl-, Br- and I- bombardment, the sputtering yield, the concentration of implanted primary ions and the useful yield of different semi-conductor and metal samples were analysed. As a consequence of a low halogen concentration, related to etching effects, no enhancement of the useful yield could be noticed for the semi-conductors. For metals however (e.g. Ni, Cu and Ag), useful yield enhancements by up to a factor of 100 compared to the O- bombardment could be demonstrated

<p></p><p>It is estimated that in the United States, agronomic weeds are responsible for about 50% of crop yield loss, costing nearly $27 billion each year. As interest in cover crops across the Midwest increases, so does the need to understand when to terminate cover crops for maximum weed control while still maintaining crop yield. Field experiments were conducted in 2017 and 2018 in Indiana to evaluate the effect of cover crop termination timings on weed control, and corn and soybean yield. Cereal rye (<i>Secale cereale </i>L.) and canola (<i>Brassica napus </i>L.) were subjected to early- or late- termination utilizing glyphosate-, saflufenacil- or glufosinate-based burndown herbicide programs. In corn, cereal rye and canola reduced early season weed biomass by 58 to 67% compared to fallow (no cover crop) plots. Cereal rye and canola reduced horseweed (<i>Erigeron canadensis </i>L.) and giant ragweed (<i>Ambrosia trifida </i>L.) emergence by 42 to 50% compared to fallow plots. Early- and late- terminated cereal rye reduced corn yields by 55 to 67% (5,173 to 7,116 kg ha^-1) compared to canola or fallow plots. In soybean, cereal rye and canola reduced early season weed biomass by 73 to 88% compared to fallow plots. Cereal rye and canola reduced horseweed emergence in 2017 and 2018 by 16 to 67 % compared to fallow plots. In 2017, both cover crop and termination timing influenced giant ragweed emergence. Early- and late- terminated cover crop plots reduced giant ragweed emergence by 50 to 76% compared to fallow plots. In 2018, cover crop termination timing influenced soybean yield. Late-terminated plots reduced yields by 48% compared to early-terminated plots. Results from this study suggest that cereal rye and canola planted at these rates can be effective for weed suppression prior to corn and soybeans, however, yield loss in both corn and soybean is expected. </p><p>Reports from Indiana in 2015 suggested that growers planting canola as a cover crop were experiencing difficulties when terminating with glyphosate prior to corn and soybean production. This suggests the utilization of inadequate herbicide programs, or perhaps a seed contamination event containing glyphosate resistant canola. Field experiments were conducted in 2016 and 2017 to determine the most effective herbicide treatment for terminating glyphosate resistant canola in Indiana, and to quantify how these herbicide programs influence corn yield. Canola was planted in early September and herbicide treatments were applied in the spring three weeks before corn planting. Visual ratings of control and above-ground biomass reduction were collected 21 days after treatment (DAT). The highest control of canola occurred following the application of paraquat + saflufenacil + 2,4-D or metribuzin, resulting in 88 to 94% control. These control ratings are supported by applications with paraquat + saflufenacil + 2,4-D or metribuzin resulting in 88 to 97% biomass reduction. Auxin herbicides alone provided very poor control, less than 41% at both locations. In general, saflufenacil-containing herbicide treatments provided the highest control of canola compared to mesotrione or atrazine. Herbicide treatments had no effect on corn grain yield.</p><br><p></p>

To achieve food security and meet environmental requirements, the average rates of major crop yields in crops such as maize are expected to increase instead of expansion of cultivated areas. Maize crop has as main factors responsible for the low yields in Brazil the water and nitrogen (N) deficits. The concept of yield gaps is the difference between the maximum yield that can be achieved in a given place, limited by water (Yw) or not (Yp), and the average yields, observed under practical conditions (Ya). This concept is of great importance for characterizing the range of maximum yields and definemanagement strategies to its mitigation. Yield potential (Yp) is determined by conditions of temperature, solar radiation, photoperiod and genetic potential; to Water-limited yield (Yw) is added the water limitation imposed by crops on rainfed condition. In this study we aimed to characterize the variability of yield gaps related to environmental and management conditions; and to evaluate the economic and energy returns related to management of these yield gaps through the mechanical application of nitrogen fertilizer in six regions located in the South Central portion of the country in two periods of maize cultivation (1st and 2nd maize growing seasons). Yield gaps related to water restriction (CYg = Yp - Yw) and imposed by management conditions (MYg = Yw - Ya) were determined through aid of integrated models DSSAT system (Decision Suport System for Agrotechnology Transfer). The maize model (CSM CERES-MAIZE) was calibrated with cultivars trial data obtained for the last few years in all evaluated regions. In the 1st growing season, Yp was higher and Yw was higher and more variable than on 2nd growing season due to climate variability. The yield gaps relative to management were more limiting than the gaps relative to water deficit in almost all the evaluated regions. In both crops\' growing seasons, higher and lower MYg were found in two regions of Southern and Midwestern portion of the country, respectively. Although both regions presented high average yields (Ya), different environmental conditions determined the largest absolute differences between their rates of Yp, Yw and MYg. When assessing the profitability (R$ k g-1, MJ kg-1, R $ ha-1; MJ ha-1) of N application as MYg reduction strategy, the behavior of the variation in yields with increasing rate of N was observed. In general, the diminishing returns showed higher use efficiency (per harvested yield and per unit area) at lower N rates (20-80 kg ha-1). Economic and energy profits (regardless of their rate of change related to the increased application of cost) were found at higher N rates (90-400 kg ha-1), and this limit is directly influenced by local climate conditions. Local management of MYg can be more or less viable depending on the combination of environmental conditions and usual management conditions. In general, the cost of N application is higher in 2nd growing season due to most limiting climatic conditions, but regions with efficient management of yield gapswere alsofound in 2nd growing season / Para alcançar a segurança alimentar e atender necessidades ambientais, os índices médios de produtividade de importantes culturas na alimentação como a do milho devem aumentar em detrimento da expansão de áreas cultivadas. A cultura do milho possui como principais fatores responsáveis pelos baixos índices de produtividade no Brasil os deficits hídrico e de nitrogênio (N). O conceito de quebra de produtividade (yield gaps) é a diferença entre a máxima produtividade que pode ser atingida em dado local, seja ela limitada pela água (Yw) ou não (Yp), e a produtividade média observada em condições práticas (Ya). Esse conceito é de grande importância para caracterização de limites de alcance de máximas produtividades e definição de estratégias de manejo para mitigação dos mesmos. A produtividade potencial (Yp) é aquela determinada pelas condições de temperatura, radiação solar, fotoperíodo e potencial genético; à produtividade limitada pela água (Yw) adiciona-se a limitação hídrica imposta por cultivos em sequeiro. Nesse estudo buscou-se caracterizara variabilidade das quebras de produtividade referentes às condições ambientais e de manejo; bem como avaliar o retorno econômico e energético do manejo dessas quebras por meio da aplicação mecanizada de fertilizante nitrogenado em seis municípios localizados na região Centro-Sul do país nas duas épocas de cultivo da cultura do milho (safra e safrinha). Quebras de produtividade referentes à restrição hídrica (CYg = Yp - Yw) e impostos pelas condições de manejo (MYg =Yw - Ya) foram determinadas com auxílio da utilização do sistema de modelos integrados DSSAT (Decision Suport System for Agrotechnology Transfer).O modelo da cultura do milho (CSM CERES-MAIZE) foi calibrado com dados de ensaio de cultivares, obtidos para os últimos anos em todas as regiões avaliadas. Na 1ª safra, os indices de Yp foram mais altos e os indices de Yw foram mais altos e variáveis devido à variabilidade climática.A quebra de produtividade relativa ao manejo foi mais limitante do que a quebra relativa ao deficit hídrico em quase todos os municípios avaliados. Em ambas as safras de cultivo, maiores e menores MYg foram encontrados em dois municípios das regiões Sul e Centro-Oeste do país, respectivamente. Apesar de ambas as regiões apresentarem altas produtividades medias (Ya), diferentes condições ambientais determinaram as maiores diferenças absolutas entre seus indices de Yp, Yw e MYg. Ao avaliar a rentabilidade (R$ kg-1; MJ kg-1; R$ ha-1; MJ ha-1) da aplicação de N como estratégia de redução de MYg, observou-se o comportamento da variação dos rendimentos de produtividade com o aumento das doses de N. Em termos gerais, os rendimentos decrescentes apresentaram maior eficiência de uso do insumo (por massa colhida e por unidade de área) nas menores doses de N (20-80 kg ha-1). Lucros econômicos e energéticos (sem considerar sua taxa de variação com relação ao aumento do custo de aplicação) foram encontrados até doses mais altas de N (90-400 kg ha-1), sendo que esse limite é diretamente influenciado pelas condições climáticas locais. O manejo local dos MYg pode ser mais ou menos viável em função da combinação das condições ambientais e de manejo usual locais. Em termos gerais, o custo de aplicação de N é maior na 2ª safra devido às condições climáticas mais limitantes, porém municípios com manejo eficiente da quebra de produtividade foram encontrados mesmo nas condições de cultivo do milho safrinha.

A cultura do milho é uma das atividades agrícolas de maior importância no Brasil. O país é o terceiro maior produtor mundial e a produtividade média passou de 1800 kg ha-1 para 3000 kg ha-1 nos últimos 15 anos. A produção de grãos e a tolerância à seca são caracteres complexos e de difícil seleção e uma possibilidade para se aumentar a eficiência dos programas de melhoramento que visam o incremento da produção de grãos e a tolerância à seca seria através da seleção indireta para caracteres relacionados a elas como o stay-green e os componentes da produção. O presente trabalho teve por objetivo estudar os caracteres stay-green, produção de grãos e seus componentes em milho com a finalidade de reunir informações sobre a herança desses caracteres. Para tanto foi utilizada uma população obtida pelo cruzamento das linhagens L-14-04 B e L-08- 05 F, contrastantes para diversos caracteres. Progênies F2:3 derivadas desses cruzamento foram retrocruzadas com as linhagens parentais formando dois conjuntos com 250 progênies de retrocruzamento cada. Essas progênies foram avaliadas em até seis ambientes segundo o delineamento de látice simples 10x10 para os caracteres produção de grãos (PG), e seus componentes: comprimento de espiga (CE), diâmetro de espiga (DE), número de fileiras por espiga (NFi), número de grãos por fileira (NGF) e peso de 500 grãos (P500) e para o caráter relacionado a tolerância à seca stay-green (SG). Um mapa de ligação obtido com 177 marcadores SSR foi utilizado para mapear QTL para esses caracteres em cada uma das populações de retrocruzamento através da metodologia de mapeamento por intervalo composto expandido para múltiplos ambientes (mCIM). Os efeitos genéticos aditivos e de dominância para cada QTL mapeado foram obtidos por meio de contrastes entre os efeitos dos QTL mapeados nas duas populações de retrocruzamento. Foram mapeados 217 QTL para os sete caracteres avaliados sendo alguns desses de maior efeito, estáveis através dos diversos ambientes e co-localizados com QTL para outras características, o que os tornam bons candidatos para seleção assistida por marcadores moleculares. O grande número de QTL mapeados nesse estudo confirma não só a complexidade desses caracteres como também o poder de detecção do método de mapeamento (mCIM) e do delineamento utilizado nesse estudo (delinemento III). / Maize is one of the most important agricultural activities in Brazil. The country is the third largest world producer and the yield rose from 1800 kg ha-1 to 3000 kg ha-1 in the last 15 years. The grain yield and drought tolerance are complex traits, difficult to select. A possibility to increase the efficiency of breeding programs that aims to improve the grain yield and drought tolerance would be through indirect selection for traits related to them as the stay-green and yield components. The aim of this work was to study the characters stay-green, yield and its components in maize in order to gather information on the inheritance of these characters. For this purpose it was used a population obtained by crossing the lines L-14-04 B and L-08-05 F, contrasting to several traits. Progenies F2:3 from this cross were derived from backcrosses to the parental lines forming two sets of backcross progeny with 250 each. These progenies were evaluated in up to six environments according to the simple lattice design 10x10 for grain yield (PG), and their components: ear length (CE), ear diameter (DE), number of rows per ear (NFI), number of grains per row (NGF), weight of 500 grains (P500) and the drought tolerance related trait stay-green (SG). A linkage map obtained with 177 SSR markers were used to map QTL for these traits in each backcross population through the methodology of composite interval mapping expanded to multiple environments (mCIM). The additive and dominance genetic effects for each mapped QTL were obtained by means of contrasts between effects of QTL mapped in the two backcross populations. Two hundred seventeen QTL were mapped for seven traits evaluated, some of these are of mayor effect, stable through the various environments and co-located with QTL for other characteristics, what make them good candidates for molecular marker assisted selection. The large number of QTL mapped in this study confirms not only the complexity of these characters but also the detection power of the mapping method (mCIM) and of the design used in this study (design III).

A intensidade de pastejo pode ser reconhecida como primordial na formação do potencial produtivo da lavoura em sistemas integrados de produção agropecuária (SIPA). Neste estudo, objetivamos entender como diferentes intensidades de pastejo definem a produtividade da soja em SIPA. O trabalho está inserido em um protocolo experimental de longa duração iniciado em 2001, no estado do Rio Grande do Sul, Brasil. Os tratamentos são definidos durante a fase pastagem, arranjados em um delineamento de blocos completamente casualizados com três repetições em diferentes intensidades de pastejo por novilhos em pasto misto de azevém anual e aveia: pastejo intenso (P10), pastejo moderado (P20), pastejo moderado-leve (P30), pastejo leve (P40) e ausência de pastejo (SP) e ausência de pastejo (SP). A soja foi semeada após a saída dos animais e os dados coletadas durante a safra 2015/16. A inserção do animal não afetou a produtividade da soja (P=0,0570). Análises de cluster e discriminante foram utilizadas no estudo da variação na produtividade. O cluster hierárquico agrupou valores de produtividade em três grupos, alta (CA), intermediária (CI) e baixa (CB), baseado em suas similaridades. Os atributos químicos não foram limitantes da produtividade. O residual da pastagem exerceu papel central na construção do potencial produtivo (P<0,001). A maior população de plantas foi encontrada no CB (P<0,001), com número inferior de legumes por área, frente aos demais cluster (P<0,001). A plasticidade fenotípica da soja explica a compensação pela modificação da arquitetura do estande de plantas nos clusters CA e CI, resultando na maior formação de legumes por planta (P<0,05). Pela análise de cluster observou-se que o P10 não apresenta valores de alta produtividade ao contrário do SP que não possui valores de produtividade baixa. Quase metade dos valores observado no P40 são mais produtividade enquanto, o P20 e P30 tendem a apresentar maior homogeneidade na distribuição entre os clusters. A análise discriminante definiu parâmetros que mais explicam a variação entre os clusters Através da função stepwise encontramos cinco variáveis (residual da pastagem, fósforo, altura final - R8, nós por ramos, legumes por área) que explicam a maioria da variação. O modelo para predizer a produtividade da soja, a partir das variáveis explicativas avaliadas a campo selecionadas pela análise discriminante, demostrou a acurácia na predição da produtividade espacial, em sistemas integrados de produção agropecuária com diferentes intensidades de pastejo, sob plantio direto na palha. / Grazing intensity can be considered essential to the potential productivity of crops in integrated crop-livestock systems (ICLS). In this study, we aimed to understand how differents grazing intensity defines the subsequent productivity of soybeans in ICLS. The work forms part of a long-term experimental protocol dating from 2001 in Rio Grande do Sul state, Brazil. Treatments were defined during the pasture phase, arranged in a completely randomized block design with three replicates under different grazing intensities by steers on Italian ryegrass and black oat mixed pastures: intense grazing (G10), moderate grazing (G20), moderate-light grazing (G30), light grazing (P40), and an ungrazed control (UG). Soybean was planted after exit of the animals and data were collected during the 2015/16 season. The integration of animals did not affect soybean productivity (P=0.0570). Cluster and discrimination analyses were used to study variation in productivity. The cluster hierarchy returned three groups of productivity values: high (HC), intermediate (IC), and low (LC), based on their similarities. Chemical attributes were not limiting to productivity. Pasture residue played a central role in the determination of potential productivity (P<0.001). The greatest plant population was found in the LC (P<0.001), while more pods per plant were found in the HC and IC (P<0.001). This result is explained by the phenotypic plasticity of soybean, which allows it to compensate for lower plant population by modifying plant stand architecture. The cluster analysis revealed that G10 did not present high productivity values, as opposed to UG, which did not contain low productivity values. Nearly half of the values observed in G40 were more productive, while G20 and G30 tended to produce greater homogeneity in the distribution among clusters. A discrimination analysis defined the parameters that explain the greatest part of the variation among clusters. Using a stepwise function, we found five variables (pasture residue, phosphorus, final plant height at R8, nodes per branch, and pods per area) that explained most of the variation. The model to predict soybean productivity, using the explanatory field variables selected by the discrimination analysis, demonstrated accuracy in the prediction of spatial productivity in ICLS with different grazing intensities under no-till.

A cana-de-açúcar é uma das culturas de maior importância social, econômica e ambiental para o Brasil. Com o aumento da demanda de etanol pela frota crescente de veículos flexfuel e com preço atrativo do açúcar, a cultura vem se expandindo de forma desordenada no país. Assim como as demais culturas, a cana-de-açúcar é dependente das condições climáticas para seu desenvolvimento, as quais são os principais fatores de risco para a cultura. Sendo assim, o objetivo do presente estudo foi determinar o risco climático para a cultura da cana-de-açúcar em diferentes regiões brasileiras, com foco nas áreas de expansão, e estabelecer os benefícios de diferentes estratégias de irrigação complementar no incremento de produtividade. Para tanto, utilizou-se o modelo CSM-CANEGRO parametrizado para as condições brasileiras para simular a produtividade da cana-planta de 12 meses em 30 localidades de diferentes regiões do Brasil, com condições agroclimáticas distintas, empregando-se séries históricas de dados meteorológicos, de 1981 a 2010, e para três tipos de solos com diferentes características, em termos da capacidade de retenção de água. A partir dos valores estimados de produtividade potencial (PP) e atingível (PA) foram definidos dois cenários de risco climático de acordo com os níveis de eficiência climática (?), dada pela razão entre PA e PP, sendo um cenário otimista (? >= 0,65) e um conservador (? >= 0,45). Além disso, foram simulados cinco diferentes condições de irrigação complementar, com lâminas fixas de 30 mm e variando-se o número de irrigações, de zero (sequeiro) a cinco (150 mm no ciclo), durante a estação seca de cada localidade. Os resultados mostraram que mesmo com banco de dados meteorológicos restrito, foi possível caracterizar o clima das principais tradicionais e de expansão da cana-de-açúcar. O modelo CSM-CANEGRO apresentou bom desempenho em estimar a produtividade comercial da cana-de-açúcar em diferentes ambientes, com uma Raiz Quadrado do Erro Médio da ordem de 15 t ha-1. O modelo, ainda, foi capaz de simular o efeito dos diferentes tipos de solo e datas de plantio na produtividade potencial e atingível da cana-de-açúcar, o que possibilitou se caracterizar as diferenças nos riscos climáticos associados à cultura da cana-de-açúcar em diferentes regiões do Brasil. A região de maior risco climático foi Petrolina, PE, enquanto que as regiões de menores riscos foram aquelas em que as chuvas eram mais intensas, como em Recife, PE, e Araguaína, TO. Por meio das simulações considerando as diferentes estratégias de irrigação, foi possível se observar que a resposta da cana-planta de 12 meses à irrigação complementar depende da combinação entre lâmina aplicada, tipo de solo e data de plantio. Os maiores incrementos de produtividade se deram no solo de textura arenosa, já que nessas condições o déficit hídrico é maior. No entanto, na grande maioria das localidades analisadas, o incremento de produtividade médio para as lâminas aplicadas, de 30 a 150 mm, não passaram de 30%, sendo a única exceção a região de Petrolina, PE. / Sugarcane is a crop of major social, economic and environmental importance for Brazil. The increasing demand by ethanol for the national flex fuel cars and the attractive sugar prices in the international market is making this crop to expand in a disorderly manner in the country. As well as the other crops, sugarcane requires specific climatic conditions to develop and produce, which are the main source of risk for this crop. Based on that, the objective of this study was to determine the climatic risk for sugarcane crop in different Brazilian regions, mainly for the areas to where the crop is expanding recently, and to evaluate the benefits of different complementary irrigation strategies for yield increase. For that, the model CSM-CANEGRO, parameterized for Brazilian conditions, was used to simulate the 12-month plant cane crop yield for 30 locations in different regions of Brazil, with varied climates, using a historical climate series from 1981 to 2010 and three types of soils, with distinct soil water holding capacities. With the simulated potential (PP) and attainable (PA) yield data two scenarios of climatic risk were defined, according to the climatic efficiency (?), one optimistic (? >= 0.65), and other conservative (? >= 0.45). Besides, five different complementary irrigation scenarios were simulated, with a fixed irrigation depth of 30 mm, and with the number of irrigations ranging from zero (rainfed crop) to five (150 mm per cycle), during the dry season of each location. The results showed that even with restricted climate series was possible to characterize the climatic conditions of the traditional and expanding sugarcane areas. The CSM-CANEGRO presented a satisfactory performance to estimate the operational sugarcane yield in different environments, with a Root Mean Square Error of about 15 t ha-1. The crop model was also able to simulate the potential and attainable yield for different soil types and planting dates, which makes possible to characterize the climatic risks associated to the sugarcane crop in the different Brazilian regions. The region with the highest risk was Petrolina, PE, whereas the smallest risk was observed where the rainfall was more intense, as in Recife, PE, and Araguaína, TO. Based on the simulations with the different complementary irrigation strategies, it was possible to understand that the 12-month plant cane response to water depends on the combination among amount of water, soil type and planting date. The highest yield increments were observed in the sandy soils, since this is the condition where the water deficit is more intense. However, for the majority of the locations evaluated, the average yield increment for the irrigation depth applied, between 30 and 150 mm, were not greater than 30%, with the only exception for Petrolina, PE.

Modern maize hybrids exhibit higher yields, increased biomass production, stress tolerance and greater nitrogen (N) use efficiency. Increased biomass accumulation can influence nutrient uptake and lead to increased nutrient removal. Hybrids were tested at seeding rates (SR) of 74000 (low) and 148000 (supraoptimal) plants ha-1 and at N rates of 0 (deficient) and 390 (non-limiting) kg N ha-1. Plants were sampled at V7, V14, R3, R5 and R6 and separated into vegetative and reproductive fractions for determination of dry matter and N accumulation. Grain yield was harvested at R6. The high SR and high N treatment combination resulted in greatest biomass accumulation, crop growth rates, and N accumulation per hectare in both vegetative and grain tissues. The high SR and high N combination maximized grain yield at 20.6 Mg ha-1, essentially through an increase in kernels ha-1. High SR decreased kernel weight, even with high N. At the higher plant densities resulting from the high SR, however, average utilization of available N was enhanced. The results have implications for improved management practices under high input systems and providing insight to growers who incorporate variable seed and N rates.

Thesis (M.Sc. (Agronomy)) --University of Limpopo, 2013 / In South Africa, wheat ranks first among the winter cereal crops produced and plays an important role in the country’s economy. The study was conducted to evaluate different South African wheat cultivars under irrigation for quality and yield parameters in Limpopo province. A field experiment was conducted during 2011 winter growing season under irrigation at the University of Limpopo experimental farm (Syferkuil). Eight wheat cultivars namely: Olifants, CNR 826, SST 347, Baviaans, Duzi, Steenbrass, SST 356 and Krokodil were laid out in a randomized complete block design with four replications for evaluation of yield and quality. The results showed that the highest grain yield obtained was 2372 kg/ha by CNR 826, and the lowest 311 kg/ha by SST 347. Flour yield, break flour yield, flour protein and mixogram development time and water absorption were not significantly different among cultivars. The highest hectolitre mass was 75.13 kghl-1for CNR 826 and the lowest 72.20 kghl-1 for Olifants. The highest falling number obtained was 187.00 sec for SST 347 and the lowest was 81.50 sec for Steenbrass. Cultivars CNR 826, SST 347, Steenbrass and SST 356 showed a good potential on protein content but Krokodil, Olifants and Baviaans had poor protein contents at 9.63%, 9.73% and 10.24% respectively. These results showed that wheat cultivars evaluated were within the requirements of the grading systems of South Africa as regards hectolitre mass and protein content. All these cultivars did not reach the required grade of 220 seconds in falling numbers with Olifants (97.50 sec), CNR 826 (103.50 sec), SST 347 (187.00 sec), Baviaans (146.75 sec), Krokodil (139.50 sec), Steenbrass (81.50 sec) and Duzi (50.25 sec), but only SST 356 met the requirement for utility grade with164.50 seconds. Olifants, CNR 826, Krokodil and Steenbrass yielded above 1500 kgha-1thus showing good potential under Limpopo conditions. These cultivars could be included in future performance evaluations in Limpopo.

Meadow bromegrass (<i>Bromus riparius</i> Rehm.) is a recently introduced pasture grass in western Canada. Its leafy production and rapid regrowth have made it the most widely used grass species for pasturing beef animals in this region. As relatively little breeding work has been done on this species, there is little information on its breeding behaviour. The main objective of this study was to estimate genetic parameters and assess breeding methodologies for meadow bromegrass. Forty-four meadow bromegrass genotypes from the three available cultivars and forty half-sib (polycross (PX) and open-pollinated (OP)) and selfed (S1) progenies were evaluated for morphological and agronomic characters, and molecular (RAPD) markers. Genetic variation for total biological yield, head weight, seed yield, harvest index, height, growth habit, spread, and volume was significant in the OP and S1 tests. Genetic variation estimates for dry matter yield were negative (PX), not significant (OP), or moderate (S1). Estimated geneticvariation for quality traits and those characters which were visually evaluated was not significant, except for growth habit (OP and S1) and acid-detergent fiber (ADF) (S1). Among progeny lines, RAPD marker variation found in the half-sib progenies accounted for about 15% of the total variation. In the S1 test the variation among progeny lines was twice that of the half-sib progenies. Correlations between the different characters demonstrated that is possible to simultaneously improve both seed and forage yield. Since leafiness was found to be correlated with dry matter yield but not with seed yield it may be possible to simultaneously improve all three characters. Rankings of progenies by the half-sib tests for forage and seed yield were not changed by the use of the synthetic parental value (SVi) which includes information from selfed progeny. The PX progeny test did not discriminate parents as well as the OP and S1 tests, which may be due to non-random pollination in the polycross. The S1 progeny test showed the highest predicted response to selection, followed by the OP test. Heritability estimates from the OP and S1 tests for total biological yield, seed yield, harvest index, and height, were similar to those found in the clonal evaluation test. Therefore, a clonal evaluation test will provide sufficient information to choose parents for breeding an improved synthetic cultivar for these characters. Observed dissimilarity of ranking of progeny lines over progeny tests for some traits (head weight, seed yield, and harvest index) was due to discrepancies between the PX and OP tests. No differences in progeny line ranking among the progeny tests were observed for all other traits. Analysis of variance on marker frequency means showed that interaction between genotypes and progeny lines was also not significant.