Thèses sur le sujet « Italian ryegra »

Questa tesi studia e valuta le tecniche agronomiche legate alla coltivazione del riso biologico nell'area del Nord Italia. Il finanziamento principale di questa tesi deriva dal progetto MIPAAF "Risobiosystems", iniziato nel 2017 e terminato nel 2020. Gli studi presentati sono collegati alla strategia europea di produzione alimentare sostenibile "Farm to Fork", che è il fulcro del Green Deal europeo per rendere i sistemi alimentari equi, sani e rispettosi dell'ambiente, incoraggiando l'espansione del settore dell'agricoltura biologica (Commissione europea 2020). Come riportato in letteratura, l'agricoltura biologica è in grado di ridurre l'impatto ambientale dell'agricoltura evitando l'uso di composti di sintesi (es. fertilizzanti, pesticidi) e favorendo pratiche (es. rotazione delle colture, leguminose, fertilizzanti organici, sovescio, verde pacciamatura.) in grado di aumentare lo stock di carbonio nel suolo e prevenire gli impatti ambientali indiretti dovuti alla produzione industriale di input (Acuna et al. 2018). Concentrandosi sul settore del riso, è stato osservato che il sistema organico è in grado di aumentare la capacità di stoccaggio del carbonio nel suolo (Komatsuzaki e Syuaib, 2010) e il contenuto di materia organica, facilitando la preparazione del suolo (Mendoza, 2004) e favorendo la successione ecologica e l'eterogeneità temporale delle comunità biologiche nel suolo (Martínez-Eixarch et al. 2017). Il lavoro di tesi una raccolta di articoli pubblicati o in corso di revisione, ogni capitolo riporta il mio contributo, e ogni connessione con altri lavori che sono stati avviati ed ancora in corso. Il capitolo I (https://doi.org/10.1016/j.agsy.2019.102739 ) rivela la mancanza di ricerca scientifica e informazioni sulla risicoltura biologica, soprattutto in Europa e in Italia. Lo studio presenta principalmente tre tecniche innovative di gestione delle erbe infestanti in risaia che possono essere considerate modelli adattabili nel loro contesto per la coltivazione del riso biologico. Questi modelli sono alla base di una lotta sostenibile contro i problemi ecologici e ambientali grazie al rigoroso divieto di sostanze chimiche come gli erbicidi. Nel lavoro emergono le metodologie la cui efficacia è stata ampiamente testata. In particolare la tecnica della “pacciamatura verde” utilizza colture di copertura (cover-crops) che controllano efficacemente le erbe infestanti grazie a quattro meccanismi principali. Il primo consiste nella parziale inibizione della germinazione delle erbe infestanti grazie alla competizione per l'acqua, i nutrienti e l'ombreggiamento, fenomeni causati dalla presenza di colture di copertura. La seconda consiste nell'effetto pacciamatura quando le cover-crops vengono sminuzzate o poste a terra con la semina del riso. Il terzo è rappresentato dai fenomeni di allelopatia che insorgono tra cover crops ed erbe infestanti (questo aspetto sarà approfondito nel Capitolo II, https://doi.org/10.3390/plants9030324 , https://doi.org/10.1007/s11356 -020-10140-4 ). Allo stesso tempo, il quarto meccanismo è legato all'accumulo di composti fitotossici a seguito della fermentazione provocata dall'acqua di immersione della risaia: l'ambiente anaerobico che si crea porta alla formazione di acidi organici come acido acetico, butirrico e propionico acido. L'allelopatia è un aspetto interessante offerto dalle piante in questa particolare agrotecnica. L'allelopatia generalmente produce e rilascia metaboliti secondari, generando effetti inibitori contro le specie vegetali vicine. La germinazione, la crescita e la riproduzione delle piante bersaglio possono così essere compromesse; questi aspetti sono stati approfonditi nel Capitolo II, partendo dall'esperienza degli agricoltori biologici. Lo studio mirava a definire l'azione inibitoria del Lolium multiflorum Lam., utilizzato come coltura di copertura prima della semina del riso nei confronti dell'Echinochloa oryzoides (Ard.) Fritsch è una delle principali infestanti del riso. Il Capitolo III si concentra sulla valutazione dell'impatto ambientale della coltivazione del riso biologico attraverso l'LCA considerando gli scenari produttivi e gli agrotecnici descritti nel Capitolo I. L'approccio LCA è stato adottato perché è largamente utilizzato per valutare l'impatto ambientale del processo agricolo. Tuttavia, da un punto di vista LCA, l'agricoltura biologica non è una risposta ovvia ai problemi ambientali perché LCA definisce la funzione del sistema studiato utilizzando una 'unità funzionale', che dovrebbe essere una misura precisa di ciò che il sistema offre ma non è in grado di considerare ad esempio effetti indiretti. Inoltre, studi LCA esprimono gli impatti per unità di un prodotto per impostazione predefinita. Tuttavia, l'agricoltura biologica generalmente emette meno inquinanti per unità di terra occupata rispetto all'agricoltura convenzionale (un approccio basato sulla superficie); può però avere impatti maggiori per unità di prodotto a causa delle sue rese inferiori per unità di superficie (van der Werf, 2020).
This thesis studies and evaluates the agronomical techniques associated with organic rice cultivation in the Northern Italy area. The study funding is from the Italian MIPAAF project "Risobiosystems", which started in 2017 and ended in 2020. The studies presented are connected to the European sustainable food production strategy "Farm to Fork," which is the core of the European Green Deal to make food systems fair, healthy and environmentally friendly, encouraging the expansion of the organic agriculture sector (European Commission 2020). As reported in the literature, organic farming is capable of reducing the environmental impact of agriculture by avoiding the use of synthetic compounds (e.g. fertilisers, pesticides) and by promoting practices (e.g. crop rotation, leguminous cultivation, organic fertilisers, green manure crops, green mulching.) able to increase the soil carbon stock, and prevent the indirect environmental impacts due to the industrial production of inputs (Acuna et al. 2018). Focusing on the rice sector, the organic system was observed able to increase the soil carbon storage capacity (Komatsuzaki and Syuaib, 2010) and organic matter content, facilitating the soil preparation (Mendoza, 2004) and promoting the ecological succession and temporal heterogeneity of the macrophyte communities into the soil (Martínez- Eixarch et al.; 2017). The thesis is a collection of articles published or under review associated with the organic rice production connected with Risobiosystems project results. Each paper explains my work and contribution, and each Chapter gave rise to new and ongoing studies. Chapter I (https://doi.org/10.1016/j.agsy.2019.102739) reveals the lack of scientific research and information about organic rice farming, especially in Europe and Italy. The studies mainly propose three different weed management techniques in the paddy field that can be considered models that can be standardised on farms specialising in their use. These models are the basis of a sustainable fight against ecological and environmental problems thanks to the strict avoidance of chemicals such as herbicides. Value is given to methodologies whose effectiveness has been widely tested. The green mulching technique uses cover crops that effectively control weeds thanks to four main mechanisms. The first consists of the partial inhibition of weeds' germination thanks to competition for water, nutrients, and shading, which are phenomena caused by the presence of cover crops. The second consists of the mulching effect when the crops are chopped or placed on the ground with rice sowing. The third is represented by the phenomena of allelopathy that arise between cover crops and weeds (this aspect will be further explored in Chapter II, https://doi.org/10.3390/plants9030324, https://doi.org/10.1007/s11356-020-10140-4 ). At the same time, the fourth mechanism is linked to the accumulation of phytotoxic compounds following the fermentation caused by the submersion water of the paddy field: the anaerobic environment that is created leads to the formation of organic acids such as acetic acid, butyric and propionic acid. Allelopathy is an interesting aspect offered by plants in this particular agrotechnical. Allelopathy generally produces and releases secondary metabolites, generating inhibitory effects against nearby plant species. The germination, growth and reproduction of target plants can thus be impaired; these aspects were deepened in Chapter II, starting from the organic farmers' experience. The study aimed to define the inhibitory action of Lolium multiflorum Lam., used as a cover crop before rice sowing against Echinochloa oryzoides (Ard.) Fritsch is one of the main rice weeds. Chapter III focuses on evaluating the environmental impact of organic rice cultivation through LCA considering the production scenarios and the agrotechnics described in Chapter I. The LCA approach was adopted because it is largely used to assess the environmental impact of the agriculture process. However, from an LCA viewpoint, organic agriculture is not an obvious answer to environmental problems because LCA defines the function of the studied system using a 'functional unit', which should be a precise measure of what the system delivers but is not able to consider for example indirect effects. Furthermore, LCAs express impacts per unit of a product by default. However, organic agriculture generally emits fewer pollutants per unit of land occupied than conventional agriculture (an area-based approach); it may have higher impacts per unit of product due to its lower yields per unit area (van der Werf, 2020).

Thesis (M.S.)--University of Missouri-Columbia, 2005.
The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file viewed on (July 14, 2006) Includes bibliographical references.

Master of Science
Department of Agronomy
Randall S. Currie
Mithila Jugulam
Italian ryegrass (Lolium perenne L. ssp. multiflorum (Lam.) Husnot), one of the problem weeds of the US, evolved resistance to multiple herbicides including glyphosate due to selection in Arkansas (AR). Glyphosate is a 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) inhibitor and amplification of EPSPS gene, the molecular target of glyphosate confers resistance to this herbicide in several weed species, including Italian ryegrass from AR. The objective of this study was to determine the expression of EPSPS gene and protein as well as distribution of EPSPS copies on the genome of glyphosate-resistant Italian ryegrass (ARR) using a known susceptible Italian ryegrass (ARS) from AR. EPSPS gene copies and expression of ARR and ARS were determined using quantitative PCR with appropriate endogenous controls. EPSPS protein expression was determined using Western blot analysis. Fluorescence in situ hybridization (FISH) was performed on somatic metaphase chromosomes to determine the location of EPSPS copies. Based on qPCR analysis, ARR plants showed a wide range of 12 to 118 EPSPS copies compared to a single copy in ARS. EPSPS gene expression correlated with the gene copy number in both ARR and ARS. Individuals with high EPSPS copies showed high protein expression in Western blot analysis. FISH analysis showed presence of brighter EPSPS signals, distributed randomly throughout the genome of ARR individuals compared to a faint signal in ARS plants. Random distribution of EPSPS copies was previously reported in glyphosate-resistant Palmer amaranth. Overall, the results of this study will help understand the origin and mechanism of EPSPS gene amplification in Italian ryegrass.

A growth room experiment compared seedling growth after nine weeks of two wheat genotypes in pure cultures and mixtures with Italian ryegrass at a low phosphorus (P) level and the P level recommended by soil testing. At the recommended P level in both pure and mixed culture, Mit, a semi-dwarf genotype, had a greater height, leaf area, tiller number, and dry weight of leaves, stems and roots than did Kharkof, a landrace. These results reflected the visual selection criteria for seedling vigor and tillering used in the initial development of the semi-dwarf cultivars. Field experiments compared total dry matter, calories, and percent crude protein and acid detergent fiber of oats, wheat, and ryegrass in pure culture and mixtures at four locations in central Texas at first clipping, second clipping, and unclipped. Although, forage yield was lower for the first clipping than the second clipping or the unclipped treatment, the first clipping had the best forage quality. There was a strong environmental influence on yield and quality. The best forage was pure wheat at College Station, pure ryegrass at Marlin, the wheat-ryegrass mixture at Temple, and pure oats at Thrall. Since Temple had the greatest yield of any site, the wheat-ryegrass mixture demonstrated the highest yield potential. The soil adsorption characteristics of halosulfuron was examined using six soils. Soil adsorption of halosulfuron appeared to be a function of organic matter. Low Kf,ads values indicated that a relatively high plant availability of halosulfuron could be available for plant uptake. Sorghum produced in soils with a low organic matter content may experience injury because of the high plant availability.

Italian ryegrass (Lolium multiflorum Lam.) is a competitive weed in small grain production areas throughout the northwestern and southeastern US. In small grains, Italian ryegrass has generally been controlled with postemergence treatments of diclofop, or diclofop-methyl, a member of the subfamily of the aromatic carboxylic acid family, the aryloxyphenoxypropionates. The first incidence of diclofop resistance in Italian ryegrass was reported in Virginia in 1995. Experiments to characterize diclofop resistance in several Virginia biotypes of Italian ryegrass included the following objectives: (1) evaluation of the presence of diclofop resistance in several Italian ryegrass biotypes collected across Virginia, (2) evaluation of alternative herbicide efficacy for diclofop resistant Italian ryegrass control, and (3) characterization of the aryloxyphenoxypropionate (APP) resistance mechanism in resistant Italian ryegrass biotypes. The response of 32 biotypes to diclofop collected from various locations statewide with varying histories of diclofop applications confirmed diclofop resistance in Virginian Italian ryegrass populations. At 4-times the label-recommended application rate, only 50% of biotypes previously exposed to diclofop in a cropping situation were adequately controlled versus 94% of the biotypes not previously treated with diclofop. Tralkoxydim provided the most effective control of four of the biotypes. No postemergence treatment effectively controlled one biotype previously exposed to diclofop applications. Effective preemergence herbicide treatments for Italian ryegrass control in the greenhouse included acetochlor (two formulations) and flufenacet plus metribuzin. In the field, flufenacet plus metribuzin resulted in excellent Italian ryegrass control, little crop injury, and acceptable barley yields. Acetyl-coenzyme A carboxylase (ACCase) assays and herbicide absorption, translocation, and metabolism studies were conducted to investigate resistant mechanism(s) to two APP herbicides, diclofop and quizalofop. ACCase assays indicated no differences in enzyme activity between the two biotypes of Italian ryegrass evaluated. Furthermore, no significant differences in the specific activity of ACCase were detected between the two biotypes in the absence of diclofop. [14C]Quizalofop-P absorption, translocation, and metabolism did not differ between resistant and susceptible Italian ryegrass biotypes. Lack of a significant biotype effect suggests that differential metabolism does not explain the differential response to diclofop treatments observed in the herbicide dose-plant response experiment.
Ph. D.

Orientador : Prof. Dr. Paulo César de Faccio Carvalho
Co-orientador : Prof. Dr. Gilles Lemaire
Tese (doutorado) - Universidade Federal do Paraná, Setor de Ciências Agrárias, Programa de Pós-Graduação em Agronomia. Defesa: Curitiba, 25/02/2015
Inclui referências
Área de concentração: Produção vegetal
Resumo: Sistemas integrados de produção agropecuária (SIPA) são reconhecidos por sua produção sustentável, tanto agrícola quanto pecuária, devido a melhor utilização dos recursos naturais. Diferentes combinações e proporções de espécies animais e vegetais em SIPA são responsáveis por produzir aproximadamente metade da produção mundial de alimentos. Nas regiões subtropicais do mundo, particularmente na América do Sul, a utilização do azevém anual (Lolium multiflorum Lam.) estabelecidos por ressemeadura natural em rotação com milho (Zea mays L.) e/ou soja (Glycine max L.), são amplamente difundido entre os produtores rurais. Em SIPA a prática de ressemeadura natural são considerados economicamente e ambientalmente mais vantajosos, uma vez que economiza gastos e energia (combustível fóssil). Sobre este arranjo em SIPA, diversas questões ainda não foram respondidas sob a influência das práticas de manejo sobre o estabelecimento do azevém anual proveniente de ressemeadura natural. Por exemplo as plantas de soja e milho tem diferentes estruturas de dosséis, que podem afetar o desenvolvimento inicial das plântulas de azevém anual. Outro ponto é o manejo do pastoreio em SIPA, particularmente o efeito dos diferentes método de pastoreio e intensidades de pastejo que podem afetar o crescimento do pasto. Uma vez que o manejo do pastejo pode restringir a seletividade animal (altas intensidades de pastejo e pastoreio rotativo), afetam negativamente o acúmulo da massa de forragem, densidade de perfilhos reprodutivos e produção de sementes. Entretanto, estudos sobre o entendimento das interações e complementariedades entre as fases lavoura e pastagens em SIPA é pouco abordado na literatura, principalmente com o azevém anual estabelecido por ressemeadura natural. A hipótese deste trabalho é que a rotação das culturas de verão (monocultura de soja ou rotação soja-milho) e diferentes manejos do pasto (método de pastoreio e intensidade de pastejo) afetam diferentemente o desenvolvimento e a resiliência do azevém anual em SIPA no curto e longo prazo. Para comprovar esta hipótese foram preparados três artigos com os seguintes objetivos: i) avaliar os efeitos das práticas de manejo, rotação de culturas, método de pastoreio e oferta de forragem afetam o restabelecimento dos pastos de azevém anual por ressemeadura natural e determinar se os pastos são capazes de restabelecer por mais de um ano sem a adição de sementes no solo. ii) avaliar o impacto da rotação de culturas de verão e o manejo do pasto na massa de forragem no inicio e no final da fase pastejo. iii) Analisar e modelizar a dinâmica do azevém anual em SIPA com uma base de dados histórica do ciclo de vida do pasto e determinar a resiliência sob diferentes práticas de manejo sob uma perspectiva de longo-prazo. Palavras chave: Sistemas mistos, intensidade de pastejo, método de pastoreio, soja, milho, resiliência.
Abstract: Integrated crop-livestock systems with no-till (ICLS) are recognized to sustained agriculture and livestock production by the efficiently use of natural resources. Different combinations and proportions of animal and plant species in ICLS are responsible for producing about half of the of the word's food. In subtropical regions of the world, mainly in South America, the utilization of Italian ryegrass (Lolium multiflorum Lam.) established by self-seed in rotation with maize (Zea Mays L.) or soybean (Glycine max L. Merril) is widely widespread. In ICLS, the harnessing of self-seeding is economically and environmentally advantageous because is capable to save money and energy (based on fossil fuel). In ICLS many question are unanswered about the Italian ryegrass established by self-seeding in face of different agricultural practices. For example soybean and maize have different canopy structures that can differently affect the pasture establishment phase. The grazing management in ICLS, particularly the effect of different stocking method and different grazing intensity can affect the dynamic of the pasture production. Since manage the pasture restricting the animal selection (i.e. higher grazing intensity and rotational stocking) affects negatively the herbage mass accumulation, the flowering structure and the seed production. However, the understanding of the interactions and of the complementarity between crops and pasture phases is poorly addressed in the literature, mainly in Italian ryegrass established by selfseeding. The hypothesis is that summer crop rotation (soybean monoculture or soybeanmaize) and the different grazing management (stocking methods and grazing intensities) affects differently the development and the resilience of Italian ryegrass in ICSL in short and long-term. To prove this hypothesis were prepared three articles with the following objective: i) to evaluate the effects of management practices, crop rotation, stocking method and herbage allowance on the re-establishment of Italian ryegrass pastures by self-seeding and determining if the pastures are able to establish themselves following a year without seed production. ii) to evaluate the impacts of summer crop rotation and grazing management on herbage mass at the beginning and at the end of grazing phase in ICLS. iii) to analyse and modelling the dynamics of Italian ryegrass in ICLS from an experimental database, based on a life-cycle basis to determine the resilience of different cropping systems in a long-term perspective. Key words: Mixed systems, grazing intensity, stocking method, soybean, maize, resilience.

Genótipos de azevém (Lolium multiflorum Lam.) diplóides e tetraplóides são cultivados como forrageira na produção animal, no entanto, quando sistemas de produção que envolve o plantio direto são estabelecidos após o cultivo da forrageira é comum a dessecação com o herbicida glyphosate. Portanto, é importante conhecer se existe suscetibilidade diferencial a este herbicida entre os genótipos. Desta forma, foi desenvolvida a presente pesquisa como o objetivo de avaliar o grau de tolerância dos genótipos diplóides e tetraplóides de azevém ao herbicida glyphosate em quatro estádios fenológicos de desenvolvimento. Para isso, foram instalados quatro experimentos, sendo um para cada estádio fenológico do azevém (duas folhas, quatro perfilhos, pré-florescimento e formação de grãos). Os tratamentos consistiram da combinação dos dois genótipos e seis doses do herbicida glyphosate (240; 480; 960; 1.920; 3.840 e 7.680 g e.a. ha-1), e uma testemunha sem aplicação de glyphosate, em delineamento experimental de blocos ao acaso, quatro repetições. Os parâmetros analisados foram porcentagem de controle e fitomassa seca das plantas. Os resultados foram submetidos à análise de variância e em seguida ajustados para modelo de curva de dose-resposta do tipo logística, sendo destes modelos calculados valores de controle correspondestes a 50, 80, 90 e 99%. As conclusões principais obtidas nesta pesquisa foram de que os genótipos de azevém diplóide e tetraplóide apresentam suscetibilidade diferencial ao herbicida glyphosate, sendo o genótipo tetraplóide mais tolerante ao herbicida. O grau diferencial de tolerância, medido pelo fator de tolerância (FT) diferencial entre os genótipos, expresso pelo valor médio dos quatro estádios fenológicos estudados, utilizando como base o controle de 50% das plantas pelo glyphosate foi de 1,6 vezes a dose de glyphosate no genótipo tetraplóide em relação ao genótipo diplóide. Os estádios fenológicos de desenvolvimento das plantas de ambos os genótipos estudados afetam o grau de tolerância ao glyphosate. De maneira geral, em estádios mais avançados de desenvolvimento fenológico dos dois genótipos a suscetibilidade do azevém é menor ao glyphosate, exceto para o estádio de préflorescimento, no qual a planta é mais suscetível que o estádio de quatro perfilhos, quando o parâmetro de análise é a dose necessária para controle de 50% das plantas. O parâmetro de análise de suscetibilidade fitomassa seca das plantas apresentou a mesma tendência diferencial entre os fenótipos diplóides e tetraplóides que o parâmetro porcentagem de controle visual.
Diploid and tetraploid genotypes of Italian ryegrass (Lolium multiflorum Lam.) are cultivated as forage crop for animal production, however, when cropping systems that involve no tillage is established after the forage cultivation it is common the dessecation with the herbicide glyphosate. However, it is important to know if there is differential susceptibility between the genotypes to the herbicide, in four phenological stages of development. Therefore, it was developed this research with the objective of evaluating the degree of tolerance of the diploid and tetraploid genotypes of Italian ryegrass to the herbicide glyphosate. For that, four experiments were installed being one for each of the Italian ryegrass phenological stages (two leaves, four tillers, pre-flowering, and grain formation). The treatments consisted of the combination of the two genotypes and six rates of glyphosate (240; 480; 960; 1.920; 3.840 and 7.680 g a.e. ha-1) and a check plot without glyphosate application, in randomized complete blocks design, four replications. The parameters that were analyzed were control percentage and dry biomass. Results were submitted to analysis of variance and subsequently adjusted to non linear model of logistic dose-response curves, and from these models control values were calculated at 50, 80, 90 and 99%. The main conclusions obtained in this research were that genotypes of Italian ryegrass presented differential susceptibility to the herbicide glyphosate. The differential degree of tolerance, measured by the tolerance factor (TF) between the biotypes, expressed by the mean value of the four development stages studied, using the 50% Italian ryegrass control, was 1.6 times more glyphosate rate for the tetraploid genotype compared to the diploid genotype. The phenological stages of development of both genotypes affected the tolerance degree to glyphosate. In general, the more is the advanced development stages of both biotypes, the lower is the susceptibility of Italian ryegrass to glyphosate, except for the stage of pre-flowering, in which the plant is less susceptible than the stage of four tillers, when the analyzed parameter is the rate necessary to control 50% of the plants. The parameter of analysis of susceptibility plant dry biomass presented the same tendency of differential control between the diploid and tetraploid genotypes than the visual control percentage.

Integrated weed management involves the utilization of weed biology principles to develop effective and economical control strategies. This research involved investigations of herbicide-based weed management programs in potato (Solanum tuberosum L.) and winter wheat (Triticum aestivum L.) as well as investigations of the biological characteristics of smooth pigweed (Amaranthus hybridus), a troublesome species in many crops. Sulfentrazone is an herbicide registered for use in soybean [Glycine max (L.) Merr.] and tobacco (Nicotiana tabacum L.) that may also have potential for use in potato. In field experiments, potato tolerance to preemergence (PRE) applications of sulfentrazone at rates up to 0.21 kg/ha was similar to that from the registered herbicides metribuzin, metolachlor, or metribuzin plus metolachlor PRE. Potato generally did not tolerate sulfentrazone applications to foliage. Sulfentrazone effectively controlled common lambsquarters (Chenopodium album L.) at rates as low as 0.11 kg/ha and also controlled several annual grasses at higher application rates, but was slightly less effective on jimsonweed (Datura stramonium L.) and ineffective on common ragweed (Ambrosia artemisiifolia L.). Potato tuber yield and grade from sulfentrazone PRE applications was similar to yield of potato treated with registered herbicides. Laboratory research was also conducted to determine the mechanism of sulfentrazone selectivity between potato (a tolerant species), common lambsquarters (a sensitive species), and jimsonweed (an intermediate species). After 48 h root exposure to [14C] sulfentrazone, absorption by common lambsquarters was nearly two-fold that of jimsonweed and three-fold that of potato. Both weed species also exhibited nearly a two-fold increase in sulfentrazone translocation from roots to shoots compared to potato. Since the site of action of sulfentrazone, protoporphyrinogen oxidase, is located in shoot tissue, translocation to shoots is essential for sulfentrazone toxicity. Therefore, the proposed primary mechanisms of selectivity between these species are differential root absorption and differential translocation. Experiments were also conducted to investigate the potential of the experimental herbicide AE F130060 03 for Italian ryegrass (Lolium multiflorum Lam.) control in winter wheat. In laboratory research, foliar absorption of AE F130060 03 in Italian ryegrass was at least three times that in wheat. Additionally, herbicide metabolism was greater in wheat, particularly in wheat treated with the herbicide safener AE F107892. In field experiments, AE F130060 03 was as effective as diclofop-methyl for control of diclofop-sensitive Italian ryegrass and more effective than diclofop-methyl and all other herbicides tested for control of diclofop-resistant Italian ryegrass. Although wheat injury from AE F130060 03 was greater than from other herbicides, wheat recovered and yields were not affected. Postemergence AE F130060 03 applications controlled Italian ryegrass from emergence until the end of tillering, but applications made to four- to five-tiller Italian ryegrass resulted in the least amount of new Italian ryegrass emergence following application. To further define the utility of AE F130060 03 in winter wheat, ten wheat cultivars adapted to Virginia were evaluated for tolerance to AE F130060 03. Biomass production between cultivars was not influenced by AE F130060 03 application in the greenhouse, although slight yield decreases due to herbicide application were found in FFR 518, Coker 9663, AgriPro Patton, and VA98W593 under weed-free conditions in the field. Greenhouse, growth chamber, and field experiments were also conducted to investigate growth and seed production of one imidazolinone-susceptible (S) and five -resistant (R1, R2, R3, R4, and R5) smooth pigweed biotypes. Although the S biotype produced more total biomass than four of the five R biotypes, R4 displayed a more rapid growth rate at 3 to 5 wk after planting and a faster germination rate than S and all other R biotypes. Seed production in R4 was similar to S and greater than in all other R biotypes. Early rapid growth in R4 did not translate into increased biomass accumulation compared to S at the conclusion of the experiments.
Ph. D.

Objetivou-se avaliar como diferentes estratégias de manejo do pasto de azevém anual interferem na produção animal, no consumo de forragem e na emissão de metano por ovinos em sistema de integração lavoura-pecuária (SILP) (Capítulo II). Já no Capítulo III objetivou-se avaliar as técnicas dos nalcanos e do nitrogênio fecal na estimativa do consumo de forragem por ovinos em pastos de azevém anual. Os experimentos foram conduzidos nos anos de 2011 e 2012 na Estação Experimental da UFRGS. Foram utilizados ovinos em um SILP de soja e milho no verão, em rotação com azevém anual no inverno. Para ambos os Capítulos (II e III) foram estudados dois métodos de pastoreio (contínuo e rotativo) e duas intensidades de pastejo (moderada e baixa; 2,5 e 5 vezes o potencial de consumo de matéria seca, respectivamente) em um delineamento de blocos casualizados com 3 repetições. Para o Capítulo II, no primeiro experimento os animais experimentais eram cordeiros, enquanto no segundo foram ovelhas em lactação. Os resultados indicaram que o ganho médio diário (GMD) dos cordeiros foi maior (P<0,05) no método de pastoreio continuo que no método de pastoreio rotativo, independente da intensidade de pastejo. O ganho de peso vivo por área (GPV) apresentou a mesma resposta em ambos os experimentos, com maior GPV na intensidade de pastejo moderada (P<0,05). No experimento 1, o consumo de matéria seca (CMS) foi maior para o método de pastoreio continuo, enquanto no experimento 2 não houve diferenças entre métodos e intensidades. As emissões de CH4 diárias por animal não diferiram entre tratamentos em ambos os experimentos (P>0,05), porém, quando expressas em g CH4 kg GPV-1 as emissões foram em média 15,33% maiores (P<0.05) para o método de pastoreio rotativo, independente da intensidade de pastejo. Os resultados afirmam que as emissões de metano por animal não são afetadas pelos tratamentos impostos. Porém, do ponto de vista de sistema o método de pastoreio contínuo o mais eficiente, por apresentar menor emissão de metano por kg de ganho de peso vivo, independente da intensidade de pastejo. Para o Capítulo III, foram utilizados apenas cordeiros. Utilizou-se a metodologia dos n-alcanos e do nitrogênio fecal, por meio de coleta total de fezes com o auxílio de bolsas coletoras. Na avaliação entre os n-alcanos, verificou-se melhores resultados quando utilizando o par C31:C32. Para a metodologia do nitrogênio fecal, as equações propostas por Wang et al. (2009) e por Azevedo (2011) foram as melhores (P<0,05). A técnica do nitrogênio fecal mostrou-se mais acurado do que o uso dos n-alcanos, que superestimou os valores de consumo.
The aim of this study was to evaluate how different management strategies of Italian ryegrass affects animal production, forage intake and methane emissions by sheep in integrated crop-livestock system (ICLS) (Chapter II). In Chapter III, we aimed to evaluate the techniques of n-alkanes and fecal nitrogen in estimating forage intake by sheep grazing on ryegrass. The experiments were conducted in 2011 and 2012 at the UFRGS Experimental Station. The ICLS soybeans and corn crops in summer, in rotation with grazed Italian ryegrass in winter. For both chapters (II and III) two stocking methods (continuous or rotational) and two grazing intensities (moderate and low, 2.5 and 5 times the potential dry matter intake, respectively) were studied in a randomized block design with three replications. In Chapter II, in the first experiment, the experimental animals were lambs, while in the second were lactating ewes. The results indicated that the average daily gain (ADG) of lambs was higher (P<0.05) in the continuous method than in rotational grazing method, regardless of grazing intensity. The live weight gain per area (LWG) showed the same response in both experiments, with higher LWG values in moderate grazing intensity (P<0.05). In experiment I, higher dry matter intake (DMI) values were obtained under continuous grazing, while in experiment II, there no differences between methods and intensities. CH4 emissions per animal and per day did not differ between treatments in both experiments (P>0.05), but when expressed in g CH4 kg-1 LWG emissions were, on average, 15.33% higher (P<0.05) for rotational grazing method, regardless of grazing intensity. Methane emissions per animal were not affected by the treatments applied. However, from system point of view, the continuous grazing method is more efficient, since lower methane emissions per kg of LWG, regardless of grazing intensity, were obtained. In Chapter III, were used only lambs. The methodologies of n-alkanes and fecal nitrogen, were applied through total collection with dung bags. In relation to n-alkanes, better results were obtained when using the pair C31:C32. For the methodology of fecal nitrogen, the equations proposed by Wang et al. (2009) and Azevedo (2011) were the best (P<0.05). The technique of fecal nitrogen proved to be more accurate than the use of n-alkanes, which overestimated the intake.

Field experiments were conducted in Virginia to evaluate the efficacy of AEF-130060 03 plus AEF-107892 applied postemergence (POST) for the control of Italian ryegrass [Lolium multiflorum (Lam)] in barley [Hordeum vulgare (L.)] in comparison to other herbicides currently registered for use in wheat [Triticum aestivum (L.)] and barley. Laboratory experiments were also conducted to evaluate absorption, translocation and metabolism of AEF-130060 03 plus AEF-107892 in wheat, barley, and Italian ryegrass with or without the addition of dicamba. AEF-130060 03 plus AEF-107892 was applied alone at three POST timings. All of these applications were effective in controlling Italian ryegrass. The third application timing of AEF-130060 03 plus AEF-107892 commonly resulted in lower yields than the first or second application timing, due to increased duration of Italian ryegrass competition, increased barley injury and insufficient time for barley recovery from this injury. In the field experiment, significantly greater barley injury was observed when AEF-130060 03 plus AEF-107892 was combined with 2,4-D and dicamba. Early postemergence (EP) treatments of AEF-130060 03 plus AEF-107892 provided control of Italian ryegrass equivalent to that of delayed preemergence (DPRE) applications of flufenacet plus metribuzin when rainfall was received. However, when rainfall was not received AEF-130060 03 plus AEF-107892 provided superior control. Because the efficacy of AEF-130060 03 plus AEF-107892 is not dependant on rainfall, it should provide more consistent control of Italian ryegrass than DP treatments. Laboratory experiments indicated that Italian ryegrass absorbed greater than 2.5, 2.0, and 1.5 times the amount of applied radioactivity at 24, 48, and 96 hours after treatment (HAT), respectively, than wheat or barley. Metabolism experiments indicated that quantity of parent compound in the three species was greatest in Italian ryegrass, followed by barley and then wheat. However, the sum total of metabolites was not different between species. A higher rate of metabolism of AEF-130060 03 plus AEF-107892 was also observed in wheat and barley than in Italian ryegrass. Thus, lower absorption of herbicide by wheat and barley, coupled with a more rapid rate of metabolism, most likely accounts for differential selectivity between these plant species. No differences in absorption, translocation or metabolism were observed within the three plant species due to the addition of dicamba. An additional experiment was conducted in 2000 and 2001 to evaluate the efficacy of preemergence (PRE) and EP applications of DPX-R6447 for the control of Italian ryegrass in wheat and barley in comparison to other herbicides currently registered for use in these crops. Barley and wheat injury and yield were similar with treatments of DPX-R6447 at rates below 176 g ai/ha and treatments of flufenacet plus metribuzin applied alone in both years. Consistent Italian ryegrass control with DPX-R6447 occurred only with rates of 176 g ai/ha or greater in both years. However, these rates resulted in variable injury in both wheat and barley between years. Rates higher than 176 g ai/ha of DPX-R6447 resulted in unacceptable barley and wheat injury. The lack of consistency with regard to barley and wheat injury could limit the utility of this compound in these crops. Field trials were conducted in Virginia to evaluate herbicide programs for control of Italian ryegrass in no-till corn [Zea mays (L.)] establishment. Herbicide programs using transgenic corn hybrids were compared to standard programs that utilize non-selective herbicides in combination with high rates of triazine herbicides. Italian ryegrass control and corn yields similar to those provided by standard programs could be attained through the use of paraquat plus atrazine, and glyphosate applied in combination with atrazine or rimsulfuron plus thifensulfuron-methyl. In glyphosate-tolerant corn, EP applications of glyphosate controlled Italian ryegrass, but yield did not differ from yields of corn treated with standard PRE applications of glyphosate plus atrazine. The use of glufosinate, imazethapyr plus imazapyr, or sethoxydim with appropriate herbicide-tolerant hybrids did not demonstrate potential for improved control of Italian ryegrass. Field experiments were also conducted to investigate the incidence and severity of maize chlorotic dwarf virus (MCDV) and maize dwarf mosaic virus (MDMV) in response to POST johnsongrass control in two corn hybrids. Recent observations have indicated a lack of virus-tolerance in glyphosate-tolerant corn hybrids in Virginia. The rapidity of virus disease development in corn resulting from application of glyphosate or nicosulfuron was also investigated. The virus-susceptible glyphosate-tolerant hybrid developed significantly higher levels of virus incidence three weeks after treatment than the virus-tolerant, non-transgenic hybrid, and virus incidence and severity increased throughout the duration of the growing season. Little or no disease incidence occurred in the virus-tolerant hybrid. The virus-susceptible hybrid exhibited significant increases in disease incidence in response to any herbicide treatment applied to johnsongrass-containing plots relative to the same treatment applied to weed free plots. Johnsongrass control with nicosulfuron or glyphosate caused similar disease incidence and severity in the virus-susceptible hybrid, regardless of application method. Results of these experiments indicated that growers' choice of hybrid should focus primarily on disease resistance rather than herbicide resistance.
Ph. D.

No Instituto de Zootecnia, Nova Odessa, SP, em uma pastagem de capim-aruana (Panicum maximum Jacq. cv. Aruana) utilizada com ovinos em sistema intensivo de produção (irrigação, adubação e lotação rotacionada), foram sobre-semeadas as espécies forrageiras de inverno: aveia preta (Avena strigosa Schreb cv. Comum), azevém anual (Lolium multiflorum Lam. cv. Comum) e trevo branco (Trifolium repens L. cv. Zapicán) com o objetivo de suprir o déficit e melhorar o valor nutritivo da forragem no período crítico do ano. A sobre-semeadura foi efetuada em 14/04/00 e 07/06/01 no primeiro e segundo anos do experimento, respectivamente. Nos dois anos (14/04/00 a 18/01/01 e 07/06/01 a 22/02/02) foram avaliados, em seis períodos de pastejo: massa total de forragem pré-pastejo, sua composição botânica e porcentagem de lâminas foliares, massa de forragem pós-pastejo, acúmulo de forragem (AF) e taxa média diária de acúmulo de forragem (TMDAF) em cada período de rebrotação, altura do dossel forrageiro pré e pós-pastejo, características químicas: proteína bruta (PB), fibra em detergente neutro (FDN), fibra em detergente ácido (FDA), lignina e digestibilidade “in vitro” da matéria seca (DIVMS), nas amostras da massa total de forragem e nas dos componentes botânicos (aruana, aveia preta e azevém) pré-pastejo. O delineamento experimental foi o de blocos completos casualizados (quatro), com duas repetições dentro do bloco e dois tratamentos: 1) capim-aruana exclusivo (AE) e 2) sobre-semeadura da mistura das três espécies forrageiras de inverno (MFI). Os blocos eram pastejados pelo mesmo lote de animais, em sequência, por dois a três dias, até atingir 10 a 15 cm. O trevo-branco não se estabeleceu em ambos os anos. No primeiro ano, a pastagem MFI apresentou maior massa total de forragem do que a pastagem AE no segundo período e na média dos seis períodos. A aveia apresentou a maior contribuição no segundo período e o azevém no terceiro. As pastagens com a MFI apresentaram maiores AF e TMDAF que as pastagens de AE no segundo, quinto e na média dos seis períodos. A PB da forragem na pastagem de capim-aruana exclusivo foi maior em relação à sobre-semeada no terceiro período de pastejo e semelhante nos demais. A PB dos componentes aveia e azevém, no terceiro período, foi menor em relação aos do primeiro e segundo. FDN, FDA e lignina da forragem no tratamento exclusivo foram mais elevados em relação aos do tratamento sobre-semeado, na média dos seis períodos. Aveia e azevém apresentaram FDN mais baixos nos períodos iniciais de crescimento, com aumento no último. A digestibilidade da forragem foi semelhante nos dois tratamentos, em todos os períodos de avaliação. No segundo ano, a massa total de forragem apresentou quantidades semelhantes entre as duas pastagens ao longo dos seis períodos e na sua média. A aveia esteve mais presente no primeiro período e o azevém no terceiro. Não houve diferença entre tipos de pastagem para AF e TMDAF em nenhum dos seis períodos, nem na sua média. Para o componente aruana a porcentagem de lâminas foi semelhante entre os dois tipos de pastagem e para a aveia e azevém, as menores porcentagens ocorreram no período final dos seus ciclos vegetativos, em ambos os anos. O teor de PB da massa total de forragem da pastagem de capim-aruana exclusivo foi maior que o da pastagem sobre-semeada, no quarto período mas semelhante nos demais e na média dos períodos. Os teores de PB da aveia e do azevém decresceram ao longo dos períodos de pastejo. Os teores de FDN, FDA, lignina e DIVMS da forragem foram semelhantes entre as duas pastagens na média e ao longo dos seis períodos, exceto para FDN no segundo período. A aveia e o azevém apresentaram os maiores teores de FDN, FDA e lignina no último período de pastejo. A DIVMS do azevém manteve-se constante nos dois primeiros períodos de pastejo diminuindo no último. Pastos de capim-aruana convenientemente adubados e irrigados, que recebam sobre-semeadura com espécies forrageiras de inverno, produzem mais forragem no período crítico mas com valor nutritivo semelhante em relação a pastos não sobre-semeados, nas condições do Estado de São Paulo. Pastos deste capim, não sobre-semeados, mas que recebam adubação e irrigação também apresentam boa produção e valor nutritivo nesta época.
At Instituto de Zootecnia, Nova Odessa, SP, in a pasture of aruanagrass (Panicum maximum Jacq. cv. Aruana), grazed by sheep in an intensive production system (irrigation, fertilization and rotational stocking), it was introduced a three winter forage species: black oat (Avena strigosa Schreb. cv. Common), italian ryegrass (Lolium multiflorum Lam. cv. Common) and white clover (Trifolium repens L. cv. Zapican) with the objective of increasing the forage supply and its nutritive value during the dry winter period. The mixture was broadcasted sown over the grass on 04-14-00 and 06-07-01 in two years of experiment. From 04-14-00 to 01-18-01 and 06-07-01 to 02-22-02 it was evaluated, in six annual grazing periods, the forage mass, its botanical composition and leaf blades percentage pre grazing, residual mass post grazing, forage accumulation (FA) and mean forage accumulation daily rate (MFADR) in each regrowth period and sward heigth pre and post grazing, the chemical characteristics: crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), lignin and in vitro dry matter digestibility (IVDMD) in the forage on offer and in its botanical components. The experimental design was a completely randomized block (four) with two replications within the block. The treatments were: 1) grass alone and 2) the grass oversown with the mixture of the winter forages. The blocks were grazed by the same group of sheep in sequence for two or three days until the sward height reached to 10-15 cm. The white clover did not establish. In the first year the oversown treatment presented higher total forage mass than the control in the second periods and in the mean of the six periods. The black oat presented higher contribution in the second period and italian ryegrass in the third. The oversown pastures presented higher FA and MFADR than the single aruanagrass pastures, in the second, fifth and in the mean of the six periods. The CP in the forage from the grass pasture alone was greater than the one of the oversown pasture in the third period, and similar in the others. Oat and ryegrass CP was lower in the third period than the ones of the first and second ones. NDF, ADF and lignin in the forage from the grass pasture alone were greater than the ones of the oversown pasture. Oat and ryegrass NDF was lowest in the initial growth periods, increasing in the final. Forage IVDMD from the two treatments were similar in all evaluation periods. In the second year, the total forage mass was similar in the two pasture treatments in all grazing periods and in their means. The black oat contribution was higher in the first period and the one of italian ryegrass in the third. The FA and the MFADR were similar in the two pasture systems. The leaf blades percentage of aruanagrass was similar in the two pastures in all periods and the ones of black oat and italian ryegrass were lower in the final period compared to the preceeding ones, in the two years. The CP in the forage from the grass pasture alone was greater than the one of the oversown pasture in the fourth period, and similar in the others. Oat and ryegrass CP decreased along the grazing periods. NDF, ADF, lignin and IVDMD of the forage from the two treatments were similar in all evaluation periods. Oat and ryegrass NDF, ADF and lignin were greater in the last grazing period. Ryegrass IVDMD from the first two periods were similar and decreased in the final. For the São Paulo State conditions, adequately fertilized and irrigated aruanagrass pastures, when oversown with winter annual forages, yield more than single aruanagrass ones during the dry winter period but with similar nutritive value. Single aruanagrass pastures when fertilized and irrigated present also good forage yields with good nutritive value during this time.

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior
It was evaluated the performance of beef heifers on grazing receiving different levels of supplement: 0,0; 0,3; 0,6 and 0,9% of live weight (LW), in black oats (Avena strigosa Schreb.) plus Italian ryegrass (Lolium multiflorum Lam.) pasture and exclusively in natural pasture engaged by Annoni grass (Eragrostis planna Nees) after the end of the cycle of these forages. On cultivated pasture it was evaluated the botanic composition and the diurnal ingestive behavior of beef heifers. The supplement utilized was a commercial ration (14% CP; 18,8% NDF; 78,2% TDN) daily supplied at 2 pm. The studied variables were the average daily gain (ADG), body condition (BC), stocking rate (SR), weight gain per area (WGA), total forage on offer (TFO), height, live weight:height relation at 12 and 18 month of age and efficiency of transformation of forage in animal product. On the diurnal ingestive behavior were determined: grazing time, rumination, idle, trough permanence, biting rate and bite weight, in four dates. In cultivated pasture the ADG did not differ between animals that received different levels of supplement and it was bigger to supplemented animals. At 12 month of age the BC, SR, WGA, TFO and height of the animals did not differ between the supplement levels. On supplemented animals it was necessary 8.8 kg of DM of grass to produce 1 kg of live weight. The supply of supplement for heifers in grazing of oats and ryegrass interfere in a positive way on life weight, body condition and life weight: height relation of these animals at 18 months of age. The supplement levels affected partially the diurnal ingestive behavior of animals, reducing grazing time, increasing idle time, interfering on trough permanence time, biting rate and bite weight (P<0.05). The rumination time was not affected by supplement levels (P>0.05). The botanic and structural composition of pasture is influenced by supplement levels utilized and it is related with the cycle of forages production (P>0.05).
Foi avaliado o desempenho de bezerras de corte em pastejo recebendo diferentes níveis de suplemento: 0,0; 0,3; 0,6 e 0,9% do peso vivo (PV), em pastagem de aveia (Avena strigosa Schreb.) mais azevém (Lolium multiflorum Lam.) e exclusivamente em campo nativo ocupado por capim Annoni (Eragrostis plana Nees), após o final do ciclo destas forrageiras. Na pastagem cultivada foi avaliada a composição botânica e o comportamento ingestivo diurno de bezerras de corte. O suplemento utilizado foi uma ração comercial (14% PB; 18,8% FDN; 78,2% NDT), fornecida diariamente às 14:00 h. As variáveis estudadas foram ganho médio diário (GMD), condição corporal (CC), carga animal (CA), produção animal por hectare (GPA), oferta de forragem total (OFT), altura, relação peso vivo:altura aos 12 e 18 meses de idade, e eficiência de transformação de Kg de forragem em produto animal. No comportamento ingestivo diurno foram determinados: tempo de pastejo, ruminação, ócio, permanência no cocho, taxa de bocada e peso de bocado, em quatro datas. Em pastagem cultivada o GMD não diferiu entre animais que receberam diferentes níveis de suplemento e foi maior para animais suplementados. Aos 12 meses de idade a CC, CA, GPA, OFT e altura dos animais não diferiram entre níveis de suplemento. Nos animais suplementados foram necessários 8,8 kg de MS do pasto para produzir 1 kg de peso vivo. O fornecimento de suplemento para novilhas em pastejo em aveia e azevém interfere de forma positiva no peso vivo, CC e relação peso vivo:altura destes animais aos 18 meses de idade. Níveis de suplemento afetaram parcialmente o comportamento ingestivo diurno dos animais, reduzindo o tempo de pastejo, aumentando o tempo de ócio, interferindo no tempo de permanência no cocho, na taxa de bocada e peso do bocado (P<0,05). Tempo de ruminação não foi afetado pelos níveis de suplemento (P>0,05). A composição botânica e estrutural da pastagem é influenciada pelos níveis de suplemento utilizados e está relacionada com o ciclo de produção das forrageiras.

Plant form is a compromise between resource gathering, reproduction and the tolerance to physical demands of the abiotic and biotic environment. In an agricultural field in addition to the natural factors causing stress, humans also introduce physical and mechanical stresses, and chemical pesticides into the environment. Many of these factors are hazardous, since they represent stresses to which plants are unable to develop defense mechanisms. However, weeds have persisted in the agricultural environment despite the efforts to eradicate them. They have adapted to environmental changes such as crop rotation and have developed tolerance to stressors like pesticides in very short periods of times (less than 10 years), much less time than normally expected for evolutionary responses to occur. Perhaps a key to why weeds persist in stress-dominated habitats is the way they compromise between yield and survival. The mechanisms that explain which process is relevant in the control of seed production or seedling growth relate to the ecophysiology of the individual plants. However, trade-offs between plants physiological functions will have implications at both population and community levels. Climate change, air pollution and water scarcity are examples of environmental stresses that particularly affect agriculture. Herbicides are a major technological tool for agriculture and are responsible, at least in part, for significant increases in crop production during the last quarter of the century. The research presented in this dissertation was developed to understand the extent that individual responses to multiple environmental stresses can be extrapolated to population-level responses in an annual weed species. The specific objectives were to assess (1) the impact of three anthropogenic stresses (herbicide, UVB light and ozone) and their interactions on individual Italian ryegrass ontogeny and reproduction and (2) the potential evolutionary effect of these stresses and combinations on changes in population size and structure over time. Plants were capable of growth and reproductive compensation under the studied stresses. Stress factors with similar biochemical mechanisms had different effects at the individual plant and population levels of organization. Compensation occurred at all levels of organization: as individuals modifying growth and allocation to different organs and as populations modifying birth, and death rates and density dependent responses. The ability to compensate sometimes decreased with the number of stress factors (e.g. herbicide and UVB). In other cases, compensation ability increased with the number of stress factors (e.g. ozone and herbicide).
Graduation date: 2004

At present, and more so in the future, irrigated agriculture will take place under water scarcity. Owing to the global expansion of irrigated areas and the limited availability of irrigation water, there is a need to optimize water production and use efficiency (WUE). In South Africa, annual ryegrass (Lolium multiflorum) is one of the most widely grown cool season pasture species under irrigation. It is mainly used in dairy farming enterprises. Shortages of water and nitrogen can, however, be limiting factors for the production of this pasture. By using appropriate irrigation and nitrogen management tools, water and nitrogen productivity of the pasture can be improved. The objective of this study was, therefore, to determine the effects of different water levels in combination with different N fertiliser applications on the growth rate and dry matter production, quality, water use and water use efficiency of annual ryegrass. For two seasons, the trial was conducted under a rain shelter on the Hatfield Experimental Farm of the University of Pretoria. Higher frequency of irrigation coupled with high nitrogen application significantly improved the dry matter yield. Canopy size influenced the LAI and FI which in turn affects the yield. The study showed that the treatments that were irrigated twice weekly and top-dressed with 60 kg N ha-1 after each cut consumed the most water, and this resulted in the production of higher yield, maintenance of the largest leaf area index and higher interception of the incoming solar radiation. The increase in these parameters may be due to the sufficient water and nitrogen fertiliser that induces rapid cell elongation as a result of higher water potential, higher turgor pressure and higher photosynthetic processes. As hypothesized, the decrease in the frequency of water application resulted in an increase in the DMC, digestibility, ME and CP values. Nitrogen application had an effect on the WU, as less water was used in the treatments that received no nitrogen. Highest KC value recorded was in the optimal range and this indicates that the treatments were not over-irrigated. As the irrigation interval increased, more water was depleted from the soil profile. Depletion rates increased as the season progressed but generally it was minimal in the frequently irrigated treatments. Increase in WUE was achieved by reducing the frequency of irrigation from twice a week to once a week without causing significant yield loss. A possible reason for the increase in the WUE by reducing the irrigation frequency could be ascribed in part to reduced evaporation from the soil resulting from the lower wetting frequency of the deficit irrigation treatments. Within the same irrigation frequency, higher WUE was achieved by alleviating a limiting factor, N fertiliser, in this case, through increases in dry matter production. The highest WUE was achieved by irrigating once every two weeks. However, in some treatments, the WUE was not improved with the reduction in the frequency of irrigation as the water saved was overshadowed by yield loss. In summary, it can be said that the hypotheses that pasture production will be positively associated with soil moisture content, water stress can improve the quality of the pasture, N fertiliser will increase the DM response to soil moisture content and WUE will increase by alleviating a limiting factor, N fertiliser in this case were accepted. A logical extension of this work would be to do the trial in an open field to analyze the effect of irrigation and nitrogen fertilization on the growth, yield and quality of the pasture and then extrapolate the results to other sites and soil types using models.
Dissertation (MSc(Agric))--University of Pretoria, 2011.
Plant Production and Soil Science
unrestricted

Italian ryegrass (Lolium perenne spp. multiflorum) is a common weed management problem in turfgrasses, cereals and non-crop areas in the United States. In Oregon, the number of populations with multiple-resistance continues to increase. To manage these resistant populations, the resistance patterns must be determined. In this study, five Italian ryegrass populations (CT, R1, R2, R3 and R4) from two cropping systems were studied for resistance patterns and mechanisms. The CT population is from a Christmas tree plantation and was resistant to at least six herbicides with four different mechanisms of action: atrazine, diuron (2.4-fold), glyphosate (7.4-fold), hexazinone (3.1-fold), imazapyr (1.8-fold), and sulfometuron. The resistant indices (RI) for sulfometuron and atrazine could not be calculated because 50% growth reduction for the CT population was not reached even with the highest rates applied, 17.6 kg ai ha⁻¹and 16 kg ai ha⁻¹, respectively, which are 16 times the recommended field application rates for this two herbicides. The CT population accumulated less shikimate than the S population. There were two mutations in the CT population, Trp591 to Leu in the ALS gene and Ser264 to Gly in the psbA gene, which explain the ALS and PII cross resistance, respectively. R1, R2, R3 and R4 were collected from annual cropping systems. All four populations were resistant to flufenacet. RIs for two populations, R2 and R4, were 8.4 and 5.9, respectively. R2 and R4 also were resistant to mesosulfuron-methyl, pinoxaden, quizalofop and clethodim. R4 was resistant to diuron, but R2 was not. An Asp-2078-Gly substitution in the ACCase gene was found in both R2 and R4 populations, while another Ile-2041-Asn substitution in the ACCase gene was found in the R4 population. These mutations explain the ACCase cross resistance in the R2 and R4 populations. The mechanisms for the glyphosate resistance in the CT population and the flufenacet resistance in R1, R2, R3 and R4 populations were not identified in this study. None of the five populations were resistant to the herbicide pyroxasulfone.
Graduation date: 2013

Italian ryegrass growth and production from positionally selective applications and sublethal rates of a nonselective herbicide were compared to growth and production when treated with diuron applied preemergence as a broadcast treatment and safened by activated carbon applied over the crop row. In the positionally selective treatments, herbicide spray was directed to leave an untreated zone over the crop row at planting. Growth analysis indicated no detectable differences when Italian ryegrass safened by directed spray was compared to Italian ryegrass safened by activated carbon. The major difference between systems was greater weed control in the crop row for carbon-safened treatments. The non-safened application superimposed sublethal diuron rates over Italian ryegrass and rattail fescue grown in varying densities and proportiors. Growth analysis of monoculture stands indicated differences due to planted density, species, and herbicide, whereas growth analysis of plants grown as space-planted individuals indicated difference due to species only. Diuron at the rates applied did not affect seed yield or above ground dry weight. Soil samples were taken in crop rows where diuron was applied as directed spray or broadcast spray safened by carbon. Samples were assayed and soil profile concentrations mapped. To assist future investigators' understanding of the role rainfall plays in herbicide movement from directed applications, elementary rainfall depth and occurrence models were examined. The Markov and mixed-exponential models adequately described rainfall occurrence and depth patterns for Corvallis, Oregon.
Graduation date: 1992

In traditional forage breeding programmes, breeders have spent decades improving the agronomic characteristics of grasses, such as herbage yield, persistence and resistance to diseases, without considering the nutrient requirements of the grazing animal. In an attempt to improve the nutritive value of Italian ryegrass, which is widely utilised for intensive dairy, lamb and beef production in South Africa, Enhancer ryegrass was developed from predominantly Italian types of Lolium multiflorum, with a minor Westerwolds component, by selecting for a higher concentration of total nonstructural carbohydrate (TNC) and lower moisture content than that currently available in commercial cultivars. The nutritional value of Enhancer was compared with Midmar ryegrass in a controlled environment study and in a grazing trial with weaned lambs; and with Dargle ryegrass in a grazing trial with Holstein dairy cows. Neutral detergent fibre, acid detergent fibre, lignin, nitrogenous compounds, mineral content and in vitro digestibility were also investigated as parameters of nutritive value. The anatomical features of Enhancer and Midmar were studied to determine possible structural differences. Weaned lambs grazed Enhancer and Midmar in an eight-paddock rotational grazing system, with 3.5 days spent in each paddock, allowing a 24.5 day regrowth period for the pastures. Holstein dairy cows grazed Enhancer and Dargle which were established on 16 and 19 hectare pastures, respectively. The n-alkane technique was used to estimate dry matter intake (DMI) in both grazing trials. Results from the controlled environment study suggest that the differences in the dry matter and TNC concentration of Enhancer are not positively linked to anti-quality factors associated with forage species, but can be attributed to genetic differences between the two grasses. Despite the significantly higher (P < 0.01) DMI of weaned lambs grazing Midmar compared with Enhancer, the lambs on Enhancer outperformed those on Midmar in terms of liveweight gain and carcass quality. The superior animal performance on Enhancer is likely due to an improvement in the readily digestible energy to protein ratio as a result of its significantly higher (P < 0.001) concentration of TNC compared with Midmar. Milk yield for cows grazing Enhancer in period 1 of the cross-over study was significantly higher (P < 0.05) than for cows grazing Dargle, despite the significantly lower (P < 0.05) DMI of animals on Enhancer. The higher TNC concentration relative to the true protein content of Enhancer would suggest that the protein metabolism in the rumen can be enhanced.
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 2003.

The aim of this study was to test the hypothesis that ryegrass and clover, when grown under optimal conditions in mixed stands, interact in response to available light energy. with other resources non-limiting, pasture yield is determined by the efficiency with which solar radiation is intercepted by canopies and converted into dry matter. The clover-ryegrass interaction under varying light regimes, as experienced in the canopies of these pastures, was studied by investigating the growth and production of ryegrass and clover in relation to light harvesting abilities and photosynthetic utilization of intercepted light. Pasture canopy structure and growth were studied under a four-weekly clipping treatment. The interception of photon flux density (PFD) in the pasture canopy was monitored diurnally and seasonally in mixed and mono cultures. Light use efficiency (C02 fixed/ unit absorbed PFD) as well as photochemical efficiency of photosystem II (Fv/Fm) were studied by monitoring CO2 assimilation rates and chlorophyll fluorescence respectively. The results obtained from this study indicated that interaction did occur between ryegrass and clover, cultivated in mixed pastures. The mixture was capable of more efficient light interception than the mono cultures, which resulted in higher productivity. Light interception abilities, as manifested in canopy architecture, and not physiological utilization of light energy, were found to govern the interaction between the two pasture components.
Thesis (M.Sc.)-University of Natal, Durban, 1993.