xx, 65 leaves : graphs ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Agricultural Biochemistry, 1979

Thesis(M.S.)--Auburn University, 2006. / Abstract. Includes bibliographic references.

?rea de concentra??o: Biotecnologia e melhoramento gen?tico florestal. / Incluir a Companhia Energ?tica de Minas Gerais S.A. (CEMIG), Universidade Federal dos Vales do Jequitinhonha e Mucuri (UFVJM) e Funda??o de Amparo ? Pesquisa do Estado de Minas Gerais (FAPEMIG) como ag?ncias financiadoras. / Submitted by Jos? Henrique Henrique (jose.neves@ufvjm.edu.br) on 2017-12-18T17:15:46Z No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) lilian_almeida_brito.pdf: 1387334 bytes, checksum: b11b197308560b439026c5ce3e4ce1fc (MD5) / Approved for entry into archive by Rodrigo Martins Cruz (rodrigo.cruz@ufvjm.edu.br) on 2018-01-03T17:04:10Z (GMT) No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) lilian_almeida_brito.pdf: 1387334 bytes, checksum: b11b197308560b439026c5ce3e4ce1fc (MD5) / Made available in DSpace on 2018-01-03T17:04:10Z (GMT). No. of bitstreams: 2 license_rdf: 0 bytes, checksum: d41d8cd98f00b204e9800998ecf8427e (MD5) lilian_almeida_brito.pdf: 1387334 bytes, checksum: b11b197308560b439026c5ce3e4ce1fc (MD5) Previous issue date: 2017 / Herbicidas com baixo poder de sor??o podem deixar res?duos no ambiente pass?veis de contamina??o em cursos h?dricos. A passagem dos res?duos para os cursos h?dricos pode ser diminu?da ou mesmo anulada por camadas vegetadas, notadamente, em matas ciliares. Contudo, pouca informa??o existe sob os efeitos de herbicidas em esp?cies florestais, principalmente na fase inicial de desenvolvimento. Com esse prop?sito avaliou-se a sensibilidade das esp?cies Senegalia polyphylla (DC.) Britton & Rose (monjoleiro) e Senna macranthera (DC. Ex collad.) H.S. Irwin & Barnaby (fedegoso) a res?duos dos herbicidas ametryn, atrazine, hexazinone e 2,4-D. Para o primeiro cap?tulo adotaram-se doses correspondentes a 0; 12,5; 25 e 50% daquela comercialmente recomendada de ametryn, atrazine e hexazinone em esquema fatorial 3 x 4 x 2 (herbicidas x doses x esp?cies) com quatro repeti??es, conduzidos em blocos ao acaso em casa de vegeta??o com temperatura controlada. Avaliou-se emerg?ncia, ?ndice de Velocidade de Emerg?ncia (IVE), taxa de mortalidade, massa fresca e seca, altura, di?metro, n?mero de folhas, al?m de vari?veis fisiol?gicas obtidas com aux?lio de um analisador a gases no infravermelho (IRGA). No segundo cap?tulo foram instalados dois experimentos paralelos (um por esp?cie) delineados inteiramente ao acaso em esquema fatorial 2 x 4, correspondentes a duas fontes de 2,4-D (produto comercial DMA? ou auxina Sigma-Aldrich? P.A.) e quatro concentra??es (0; 0,1; 1 e 10 mg.L-1 de 2,4-D), com quatro repeti??es e oito r?plicas cada. As esp?cies foram avaliadas quanto ? germina??o, ?ndice de Velocidade de Germina??o (IVG), contamina??o, di?metro, massa fresca e seca. Como resultado, de maneira geral o monjoleiro se mostrou mais sens?vel aos herbicidas, todavia, demonstrou potencial fitorremediador para atrazine. A compara??o entre os tipos de 2,4-D revela que o herbicida n?o pode ser utilizado como regulador de crescimento em laborat?rio, potencialmente devido aos aditivos que apresenta. Por fim, os resultados apontam que o uso recorrente de herbicidas lixivi?veis pr?ximos a fragmentos florestais podem afetar a perpetua??o de esp?cies nativas por efeito delet?rio silencioso. Novas pesquisas precisam ser realizadas com outras esp?cies nativas a fim de conhecer os efeitos dessas e de outras mol?culas ao ecossistema em geral. / Disserta??o (Mestrado) ? Programa de P?s-Gradua??o em Ci?ncia Florestal, Universidade Federal dos Vales do Jequitinhonha e Mucuri, 2017. / Herbicides with low sorption capacity can leave residues without an environment liable to contamination in water courses. Passage from the residues to the watercourses can be reduced or even negated by layers vegetated, notably in riparian forests. However, scarce information exists about the effects of herbicides on forest species, especially in the early stages of development. For this purpose the sensitivity of the species Senegalia polyphylla (DC.) Britton & Rose (monjoleiro) and Senna macranthera (DC. Ex collad.) H.S. Irwin & Barnaby (fedegoso) to residues of the herbicides ametryn, atrazine, hexazinone and 2,4-D were evaluated. For the first chapter doses corresponding to 0, 12.5, 25 and 50% of that commercially recommended for ametryn, atrazine and hexazinone were adopted in a 3 x 4 x 2 factorial arrangement (herbicides x doses x species) with four replicates, conducted in randomized blocks under controlled temperature greenhouse. It was evaluated the emergence, Emergency Speed Index (IVE), mortality rate, fresh and dry mass, height, diameter, number of leaves, and physiological variables obtained with the aid of an infrared gas analyzer (IRGA). In the second chapter were installed two parallel experiments (one per species) completely randomly delineated in a 2 x 4 factorial scheme, corresponding to two sources of 2,4-D (commercial product DMA? or auxin Sigma-Aldrich? P.A.) and four concentrations (0; 0,1; 1 e 10 mg.L-1 of 2,4-D), with four repletitons and eight replicates each. The species were evaluated for germination, Germination Speed Index (IVG), contamination, diameter, fresh and dry mass. As a result, in general the monjoleiro showed to be more sensitive to herbicides, however, it demonstrated a phytoremediation potential for atrazine. The comparison between the 2,4-D types reveals that herbicide cannot be used as a growth regulator in the laboratory, potentially due to the additives it presents. Finally, the results indicate that the recurrent use of leachable herbicides close to forest fragments can affect the perpetuation of native species by a silent deleterious effect. New research is done for other native species to know the effects of other molecules on the ecosystem in general.

The risk associated with the application and co-occurrence of atrazine and sulfentrazone, two herbicides applied to a corn and soybean rotational field, was evaluated in the current study. Peak field concentrations were found in the soil matrix, with atrazine and sulfentrazone values of 144 ng/g dry weight (dw), and 318 ng/g dw, respectively; however, due to the physicochemical properties of the compounds, the two herbicides were also transported to field water matrices. The highest mean runoff water concentrations for atrazine and sulfentrazone were 4.72 µg/L and 10.3 µg/L, respectively. A direct spray event of atrazine to the runoff water sampler caused concentrations as high as 1.6 mg/L, effectively becoming a worst case scenario concentration. Individual and mixture laboratory bioassays were also conducted to determine the effects of atrazine and sulfentrazone on the survival of D. magna, and P. promelas. Sub-lethal effects including germination of L. sativa, and growth of P. promelas, S. capricornutum and L. minor were also evaluated. Results showed that S. capricornutum and L. minor were the most susceptible non-target species tested, and synergistic effects were observed for both species when equipotent mixtures were tested. Margin of safety of 10% (MOS10) values were calculated for each species using field concentrations and bioassay benchmark concentrations. Atrazine MOS10 values, calculated with environmental concentrations not including the direct spray event, were 0.83 and 0.10 for S. capricornutum and L. minor, respectively. The MOS10 value for sulfentrazone effects on S. capricornutum was 0.31, and effects on L. minor was 1.39. There was a slight risk to S. capricornutum and L. minor growth associated with exposure to atrazine and sulfentrazone in an agricultural field. Although the co-occurrence of atrazine and sulfentrazone was observed, and synergistic effects were observed in the equipotent binary mixture bioassays for S. capricornutum and L. minor, it is believed that there is minimal increase in risk potential due to the co-occurrence, because field concentrations do not proportionally mimic the concentrations that produced synergism in the plant species.

Uma alternativa para o destino dos resíduos urbanos é a reciclagem através da compostagem e vermicompostagem (produção de húmus). A falta de padrão de qualidade destes materiais tem prejudicado o desenvolvimento dessa alternativa, tendo prejuízos, produtores e consumidores. Neste trabalho procurou-se parâmetros que pudessem ser utilizados para padronização. Por Ressonância Paramagnética Eletrônica (EPR) as amostras com nível de radicais livres semiquinona de 1017 spin/g de amostra e 1018 spin/g de carbono, ou superior, indicaram melhor qualidade do produto, no que se refere ao grau de humificação. Com o objetivo de avaliar o potencial de sorção do húmus e seu possível efeito catalítico na degradação e fotodegradação do herbicida Atrazina (AT), realizou-se vários experimentos. Resultados de espectroscopia no Ultravioleta e Visível (UV-Vis) mostraram que, para pH\'s próximos do pKa da AT (1,68) o húmus possui similar efeito catalítico que ácidos húmicos e fúlvicos na degradação da AT. Em pH neutro não foi observado degradação da AT, mesmo para altas concentrações de húmus e longos períodos de interação (262 dias). A partir de dados de Polarografia de Pulso Diferencial (PPD) em conjunto com dados de UV-Vis, observou-se uma curva de sorção da AT com máximo (20%) em torno de pH 4,0, decaindo para menos de 5% de sorção para os demais pH\'s utilizados (2,0; 6,0; 7,0; 8,0 e 10,0). Dados de EPR não mostraram reações de transferência de elétrons entre a AT e o húmus. Assim, considerando a forma da curva de sorção, observada por PPD, o mecanismo de reação mais importante entre a AT e o húmus é via ligação hidrofóbica. Experimentos de fotodegradação da AT com luz UV-Vis (300-450 nm) mostraram maior eficiência no processo quando da presença do húmus. Isto ocorreu, provavelmente, devido a ação de agentes fotooxidantes da AT, formados a partir do húmus excitado pela radiação UV. Observou-se também, uma dependência com a concentração de húmus, sendo que, dentro do intervalo de 10 a 1800 mg houve maior fotodegradação da AT para valores em torno de 300 mg.L-1. / One alternative to disposal of urban residues is recycling through composts and earthworm composts (humus production). The absence of a quality standard of these materials however brings limitations to commercial development with damage to producers and consumers. In this work was proposed a strategic parameter to be used as standard. From Electron Paramagnetic Resonance (EPR) analysis samples of humus with level semiquinone free radicals of 1017 spin/g of sample and 1018 spin/g of carbon, or higher, indicated good quality of product, with adequate humification degree. Also were studied mechanisms of interaction between humus and the herbicide Atrazine (AT). The proposal was evaluate potential of AT sorption by humus and possible catalytic effect in the degradation and photodegradation of this herbicide. Data from Ultraviolet and Visible Spectroscopy (UV-Vis) showed that for pH\'s close to AT pKa (1.68) the humus showed catalytic effect in degradation of AT similar as those observed in literature with purified humic and fulvic acids. However for neutra1 pH\'s AT degradation was not observed even in the presence of high humus concentrations and long periods of interaction (262 days). Using Differential Pulse Polarography (DPP), combined with data of UV-Vis Spectroscopy, an AT sorption curve on humus was obtained showing a maximum value of 20% around pH 4.0, decreasing for less than 5% of sorption for other pH\'s analyzed (2.0; 6.0; 7.0; 8.0 and 10.0). Data from EPR gave no evidence of electron transfer reaction. So from the kind of sorption curve, obtained by DPP, the major mechanism of reaction between AT and humus was suggested to be hydrophobic bonding. Experiments of AT photodegradation using UV-Vis light (300-450 nm) showed larger efficiency of the process in the presence of the humus. This occurred probably due action of photo-oxidants on AT, originated from excitation of humus by the UV radiation. It was also observed, dependence with the humus concentration, and in the range 10 to 1800 mg.L-1 there was larger photodegradation of the AT for values around 300 mg.L-1.

Neste trabalho buscou-se produzir filmes de nanopartículas de dióxido de titânio e de nanopartículas de dióxido de titânio contendo o complexo sintetizado undecatungstofosfatomanganês(melamina) suportados em cela tubular de vidro borossiliacato e testar sua reatividade como fotocatalisadores frente à atrazina. Os ensaios de fotodegradação da atrazina foram realizados através de um reator fotocatalítico tendo como fonte de irradiação ultravioleta uma lâmpada de vapor de mercúrio de alta pressão de potência de 125 W desprovida do bulbo externo. A degradação da atrazina ocorrida nos experimentos de fotocatálise heterogênea foram acompanhados através da técnica de Espectroscopia de Absorção na Região do Ultravioleta e Visível (UV-vis) e para as amostras inicíais e finais de cada ensaio foram realizadas medidas de teor de Carbono Orgânico Total (TOC). Assim, foi possível estimar a porcentagem de degradação parcial e de mineralização da atrazina. As porcentagens de degradação obtidas para soluções contendo concentração inicial de 10 ppm de atrazina foram: no caso de filmes de nanopartículas de dióxido de titânio, obteve-se porcentagem de degradação parcial da atrazina de 42,2% a partir da análise de UV-vis e 21,8% de mineralização através da análise de TOC. Para o mesmo sistema após 72 horas, as porcentagens de degradação parcial chegaram a 71,5% a partir da análise de UV-vis e 55,5% de mineralização pela análise de TOC. Para o filme de nanopartículas de dióxido de titânio contendo undecatungstofosfatomanganês(melamina) através da técnica de UV-vis obteve-se uma degradação parcial da atrazina de 44,7% ao final de 12 horas e através da análise de TOC obteve-se 22,4% de mineralização. / In this work, films of titanium oxide nanoparticles and of titanium oxide nanoparticles containing the complex undecatungstophosphatemanganese(melamine) immobilized in a borosilicate glass cylindrical cell were prepared and their reactivity as photocatalyst for atrazine were tested. The photodegradation essays of atrazine were made in a phocatalytic reactor where the ultraviolet irradiation source was one mercury vapor lamp of 125 W without the external bulb. The atrazine degradation in heterogeneous photocatalysis experiments were checked by Ultraviolet and visible spectroscopy (UV-vis) and for first and last samples for each essay were made analysis of Total Organic Carbon (TOC). So, it was possible to estimate the percentage of the partial degradation and mineralization of atrazine. The partial degradation percentages obtained for solutions with initial concentration of 10 ppm of atrazine were: In the case for films of titanium oxide nanoparticles, the partial degradation percentage for atrazine was 42,2% in UV-vis analysis and 21,8% of mineralization obtained by TOC analysis. For the same system after 72 hours, the partial degradation percentages were 71,5% in UV-vis analysis and 55,5% of mineralization obtained by TOC analysis. For the film with titanium oxide nanoparticles containing the complex undecatungstophosphatemanganese(melamine), after 12 hours, the partial degradation of atrazine was 44,7% in UV-vis analysis and 22,4% of mineralization obtained by TOC analysis.

[pt] O aumento da população mundial e a demanda crescente de alimentos têm motivado o uso de grandes quantidades de pesticidas nas plantações para prevenir e combater pragas e assegurar maior produtividade. Por outro lado, preocupações sobre os impactos potenciais dos pesticidas na saúde humana têm estado presentes, já que o uso extensivo dessas substâncias leva a sua presença, juntamente com seus metabólitos, nos corpos d´água naturais. A atrazina é um herbicida de uso extensivo na agricultura brasileira, principalmente em culturas de milho, cana-de-açúcar e sorgo, frequentemente encontrado nas águas subterrâneas em muitos países, e foi selecionado para estudo. Neste trabalho, o processo de oxidação pelo ozônio foi utilizado para degradar a atrazina em solução aquosa. Foram estudados os aspectos cinéticos da reação e a eficiência da transferência de ozônio da fase gasosa para a fase líquida. Foi comprovado que a vazão de alimentação de oxigênio é um fator de significativa importância para a transferência de ozônio da fase gasosa para a fase líquida, assim como a agitação do sistema, sendo este último em menor proporção que o primeiro. A ozonização da atrazina foi estudada sob diferentes condições de pH e em presença de capturador de radical hidroxila. O processo desenvolve-se principalmente através de reação radicalar, mesmo em meio reacional ácido. A constante cinética da reação direta entre o ozônio e a atrazina foi 26,40 M(-1) s(-1). Após 10 minutos de ozonização da atrazina, a degradação do herbicida mostrou-se mais eficiente com valor de pH do meio reacional 10,3 que em valores de pH 6,3 e 2,8. / [en] The increase in world population and increasing demand for food has driven the use of large quantities of pesticides on crops to prevent and combat pests and ensure greater productivity. Moreover, concerns about potential impacts of pesticides on human health have been present since the extensive use of these substances leads to its presence, together with its metabolites in natural water bodies. Atrazine is a herbicide for used in the extensive Brazilian agriculture, especially in crops oz maize, sugar-cane and sorghum, often found in groundwater in many countries, and was selected for study. In this work, the oxidation process by ozone was used to degrade atrazine in aqueous solution. Kinetics aspects were studied for the degradation reaction and the efficiency of mass transfer of ozone from the gas phase to the liquid phase. It was verify that the flow of oxygen supply is a factor of significant importance for the mass transfer of ozone from the gas phase to liquid phase and the agitation of the system, the latter being lower in the first. The ozonation of atrazine was studied under different conditions of pH and presence of capturing hydroxyl radical. The process takes place mainly through radical reaction, ever in the acid reaction medium. The kinetic constant of direct reaction between ozone and atrazine was calculated 26.40 M(-1) s(-1). After 10 minutes of ozonation of atrazine, a degradation of the herbicide was more effective with pH of the reaction medium at pH 10.3 to 6.3 and 2.8.

Master of Science / Department of Agronomy / Johanna A. Dille / An opportunity for postemergence (POST) grass weed control has recently been approved with ALS-resistant grain sorghum, however, grass weed emergence timing and crop tolerance to grass competition are not well understood. To address the importance of POST application timing, a critical period of weed control (CPWC) for grass competition in grain sorghum was developed. Field experiments were established near Manhattan and Hays, KS in 2016 and 2017, and near Hutchinson, KS in 2017 to determine the CPWC. Each site provided a different grass species community. A total of ten treatments were included, with four treatments maintained weed-free until 2, 3, 5, or 7 weeks after crop emergence, four treatments receiving no weed control until 2, 3, 5, or 7 weeks after crop emergence, and two treatments were maintained weed-free or weedy all season. Treatments did not influence grain yield at Hutchinson because of a lack of season-long weed emergence. At Hays the CPWC began at crop emergence and ended 28 days later. At Manhattan the CPWC began 27 days after emergence and continued through grain harvest. The CPWC in grain sorghum depends on rainfall and competitive ability of the weed species. The start of the CPWC began when weeds emerged, thus a POST application should be targeted 14 to 21 days after emergence of grain sorghum. Emergence and development of large crabgrass, barnyardgrass, shattercane, and giant, green, and yellow foxtails were studied near Manhattan, KS after seeding on April 11, 2017. Barnyardgrass had the longest duration of emergence, beginning at 180 GDD after seeding and continuing through July. Large crabgrass had the shortest duration of emergence from 325 to 630 GDD after seeding. In general, all grasses began to emerge in late April and most species completed 90% emergence by early June. Grain sorghum is typically planted at this time, so grass weed control prior to planting is critical. Palmer amaranth is a troublesome weed in double-crop grain sorghum production fields in Kansas. The presence of herbicide-resistant populations limits options for weed management. Field experiments were conducted to evaluate 14 different herbicide programs for the management of atrazine-resistant Palmer amaranth in double-crop grain sorghum at Manhattan and Hutchinson, KS in 2016 and 2017. Programs included eight PRE only and six PRE followed by POST treatments. Programs that had very long chain fatty acid-inhibiting herbicides provided greater control of atrazine-resistant Palmer amaranth by three weeks after planting sorghum. Programs of PRE followed by POST provided greater control of both atrazine-resistant and -susceptible Palmer amaranth by eight WAP compared to PRE alone. These results illustrate the value of residual herbicides, as well as an effective postemergence application, in double-crop grain sorghum. Early season grass and Palmer amaranth control with the use of residual herbicides such as very long chain fatty acid-inhibitors provide a competitive advantage to grain sorghum. Utilizing weed emergence patterns to time effective POST applications, in unison with residual herbicides, will provide season-long weed control in Kansas grain sorghum fields.

Master of Science / Department of Biological & Agricultural Engineering / Philip L. Barnes / Wichita, Kansas water supply is derived from multiple sources. Unfortunately, these sources are not expected to meet the future needs of the population. This predicted water shortage led to the development of the Equus Beds Recharge Project, to investigate artificial recharge as a solution to meet future water demands. This project focuses on the Little Arkansas River as a source of this recharge water. The Kansas Department of Health and Environment set a daily 3[Mu]g/L standard for the recharged water as opposed to surface waters used directly for drinking water which can't exceed a yearly average atrazine concentration of 3[Mu]g/L. During 2005, five sub-watersheds within the Little Arkansas River watershed were instrumented to collect water quality samples and measure flow rate to calculate daily contaminant loadings. Three of the sub-watersheds used atrazine best management practices (BMPs) applied to grain sorghum while the remaining two sub-watersheds maintained existing farm practices. During 2007, monitoring continued and additional atrazine BMPs were applied to corn grown in the treated sub-watersheds. During both 2006 and 2007, water quality monitoring was used to examine water quality parameters throughout the entire watershed. Watershed-scale monitoring allowed for pollutant transport patterns to emerge both spatially and temporally and indicated potential sources of the pollutants. In this particular study, atrazine and sediment loss were the two most important water quality parameters. Results from this study showed that by using BMPs the concentration of atrazine was decreased by greater than 40% in 2006 when compared to the atrazine concentration from those areas without BMPs. A 5% reduction was seen in 2007, which was due to differences in precipitation and runoff between the two years. There was no reduction in sediment losses between the treated and untreated watersheds during 2006, leading to the conclusion that additional practices would be needed to reduce sediment losses as well as any pollutants associated with sediment loss (ex nutrients absorbed to the sediments). During 2007, sediment, nitrogen, and phosphorus were 66%, 60%, and 55% lower respectively in the treated versus untreated sub-watershed. These 2007 differences were related to rainfall pattern differences in the sub-watersheds.

Cases of atrazine damage to maize, and occasional reports of excessive residue persistence that caused injury to susceptible following crops, prompted research on factors which influence the bioactivity and persistence of the herbicide. Bioassays with several indicator species were conducted in the field and in glasshouses. Measurement of atrazine by chemical means was done in only three of the experiments. Maize seedlings were not more sensitive to atrazine when stressed by insufficient supplies of N, P , K, Ca or Mg. Neither high P supply nor phytotoxic P concentrations in maize seedlings lowered their tolerance to atrazine. These findings on the roles of certain nutrients in the tolerance of maize to atrazine concluded a series of investigations into damage reported in the field. No satisfactory evidence for the factors which rendered maize susceptible to atrazine in the field was ever found. Another investigation showed that atrazine threshold concentrations for certain susceptible species varied from soil to soil , indicating that differential availability of the herbicide for uptake by plants in different soils precludes the allocation of fixed atrazine threshold values to different crop species. Atrazine bioactivity and persistence varied considerably in a series of field experiments which were conducted to determine the order of importance of certain soil properties in the prediction of short- and long-term bioactivity. Soil organic matter content (% C) was the best predictor in both instances. Soil pH was a poor predictor of short-term bioactivity, but became more prominent with time. Organic matter, pH and P-reversion accounted for 35%, 19% and 14% of the variation in bioactivity measured six months after atrazine application in the field. In view of the variation in atrazine persistence, and therefore, the potential for variable carry-over from soil to soil, the applicability of the recropping interval recommended for dry beans and sunflower were investigated. It was concluded that the specification could be justified for sunflower only, but then only on certain soils. It is suggested that recropping intervals , which are recommended for certain crops after atrazine use in maize, be refined on the basis of differences in follow-up crop sensitivity to atrazine, and relationships between atrazine persistence and certain soil properties. Chemical analysis showed that soil type and soil water content had greater influences on atrazine persistence than temperature. Irrespective of soil type, the rate of atrazine breakdown was faster in soil at a water content of field capacity, and in water-logged soil (2x FC), than in air-dry soil. A bioassay technique was used to estimate the concentration of atrazine and/or its phytotoxic residues in a soil profile. Basically the same procedure was followed in an incubation study with 25 soils to develop the following regression model for prediction of atrazine half-life in soil: γ = -2.29 + I.77xl + 20.8Ix2, where γ is half-life in days; Xl = [soil pH(H2O)2<f and X2 = % C. The bioassay technique proved useful for estimating total amounts of atrazine and its phytotoxic residues in various soil type AFRIKAANS : Beskadiging van mielies deur atrasien, en sporadiese berigte van oormatige nawerking met gepaardgaande beskadiging van gevoelige opvolggewasse, het aanleiding gegee tot navorsing oor faktore wat die bio-aktiwiteit en nawerking van die onkruiddoder be'invloed, Biotoetse is met verskillende toetsplante in glashuis- en veldproewe uitgevoer. Bepaling van atrasien deur chemiese analise is in slegs drie proewe gedoen , Mieliesaailinge se verdraagsaamheid teenoor atrasien is nie deur tekorte aan N , P, K, Ca en Mg in die plante be'invloed nie, Nog hoe P-voorsiening, nog fitotoksiese Pkonsentrasies in saailinge, het hul weerstand teen atrasien verlaag, Hierdie bevindings oor die rol van sekere voedingselemente by die verdraagsaamheid van mielies teenoOT atrasien het 'n reeks ondersoeke na destydse skade in die veld afgesluit, sonder bevredigende verklarings vir die probleem, In'n ander ondersoek is gevind dat drumpelwaarde-konsentrasies van atrasien vir bepaalde gevoelige gewasplante van grond tot grond varieer. Differensiele beskikbaarheid van atrasien in grond sal dus die toekenning van 'n vaste drumpelwaarde aan 'n bepaalde gewasplant verhoed , Dieorganiese koolstofinhoud van grond was die belangrikste voorspeller van die kort- en langtermyn bio-aktiwiteit van atrasien in 'n reeks veldproewe. Die variasie in bioaktiwiteit wat ses maande na toediening van die doder deur organiese materiaalinhoud, pH en P-reversie verklaar is, was onderskeidelik 35% , 19% en 14%. Derhalwe het grond-pH , wat 'n swak voorspeller (l % van variasie) van die korttermyn-aktiwiteit van atrasien was, belangriker geraak met tyd. Die bio-aktiwiteit en nawerking van atrasien het aansienlik tussen lokaliteite verskil. Weens die varierende nawerking van atrasien in grond , en gevolglike verskille in die potensiele oordraging van atrasien na 'n volgende seisoen , is die toepasLikheid van die wagperiode wat vir droebone en sonneblom gestel word vervolgens ondersoek. Die voorgeskrewe wagperiode kon slegs vir sonneblom as toepaslik bevestig word , en dan slegs op sekere grondsoorte. Dit word voorgestel dat wagperiodes verfyn behoort te word op basis van verski lle tussen grondsoorte en die verdraagsaamheid van gewasplante teenoor atrasien. Met chemiese analise is bepaal dat grondsoort en -waterinhoud 'n belangriker effek op nawerking van atrasien as temperatuur gehad het. Vergeleke met die afbraaktempo in 11Igdroe grond het atrasien vinniger afgebreek in grond waar die waterinholld by veldkapasiteit was, asook wanneer dit twee keer hierdie hoeveelheid water bevat het. 'n Biotoetstegniek is gebruik vir skatting van atrasien- en/of fitotoksiese residu-konsentrasies in 'n grondprofiel. Basies dieselfde prosed lire is in 'n inkubasieproef met 25 gronde toegepas vir ontwikkeling van die volgende model vir voorspelling van die halfleeftyd van atrasien in grond: γ = -2.29 + l.77x1 + 20.8Ix2, waar γ halfleeftyd in dae is; x1 = [grond-pH(H20)]2 en x2 = % C. Die biotoetstegniek was effektief vir skattings van die totale hoeveelheid atrasien en fitotoksiese atrasienresidue in grond. / Thesis (PhD)--University of Pretoria, 2011. / Plant Production and Soil Science / unrestricted