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The intensification of agricultural production in the Mekong Delta has faced serious challenges with respect to increased use of agrochemicals and especially pesticides. The indiscriminate use of pesticide could potentially impact on the long-term food production, environmental and human health in the delta. The aim of this thesis was to investigate the negative side effects of the current use of pesticides on climbing perch (Anabas testudineus) in rice fields using brain acetylcholinesterase (hereafter referred to as AChE) activity as a biomarker. The empirical work, on which this thesis is based, includes structured questionnaires, laboratory and field experiments. First, a field survey using questionnaires was carried out to gain a better understanding of the current state of rice farming systems, the use of pesticides and attitude to pest management strategies among rice and rice-fish farmers, as well as to provide basic information for the set-up of the laboratory and field experiments. Secondly, laboratory studies were conducted to clarify if the selected insecticides applied alone and in mixtures caused negative side effects on climbing perch fingerlings. Thirdly, further toxicity studies were carried out, under rice field conditions, to further investigate the toxicity effects of the insecticides, applied alone, in mixtures and under sequential applications, on climbing perch fingerlings. The results showed that although there were a more selective use of pesticides and an increased awareness among farmers of the negative side effects of pesticides in 2007 as compared to 1999, the current use of pesticide in the Mekong Delta still cause many problems to the environment and human health. Chlorpyrifos ethyl (hereafter referred to as CPF) was found to cause a significant and more prolonged inhibition on the brain AChE activity in climbing perch than fenobucarb (hereafter referred to as F). The inhibition by the mixture of CPF and F were significantly higher than the inhibition by only F, but less prolonged and significant lower than the inhibition by only CPF. The results suggest that the combined effect from a mixture of F and CPF can create both additive effects initially and later antagonistic effects. CPF and F applied at concentrations used by farmers, either as separate doses, in a mixture or in sequential doses, decreased the brain AChE activity, growth and survival rates in climbing perch. The results demonstrate that brain AChE activity in climbing perch is a relevant biomarker for monitoring of exposure to, and sub-lethal impacts from organophosphates and carbamates under tropical conditions. The result also shows that 2-PAM re-activate the brain AChE activity, and can be used as an alternative method to assess the AChE inhibition level in organisms recently exposed to OP’s, in situation where it may be difficult to find unexposed individuals as controls. In conclusion, this thesis shows that the current use of pesticides in the Mekong Delta has a negative effect on climbing perch living in rice fields. It indicates that a sustained long-term food production in the Mekong Delta must be based on ecological principles, taking advantages of ecosystem biodiversity and productivity, and not through intensified use of pesticides. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Submitted. Paper 5: Submitted.</p>

The objective of this thesis was evaluate the efficiencies of the harvesting operation in rice fields, located in the region of Depressão Central do Rio Grande do Sul. As specific objectives, this study sought to determine and evaluate the following efficiencies: field, time, field pattern and cutter bar; to verify if there is difference between the areas with land level and without it; compare the field efficiency found on this study with the efficiency established by ASAE D497 4 (2009b); To evaluate the influence of the geometry of land leveling fields on field efficiency; listing the variables that have more correlation with the reduction of the efficiencies and indicate actions that may will optimize the efficiencies evaluated. In the summer of 2008/2009, 19 operations were evaluated, shared in six farms, A, B, C, D, E and F, being fifteen fields of them with land level and four without land level. The operation data were collected manually, through the use of stopwatch, a clip board to record observations and with a signal receiver of GPS (Global Positioning System), Garmin® brand, model GPSMAP® 60CSX. For helping to analyze and calculate the efficiencies, the following variables were determined: area and ratio length/width of the fields, average harvest speed, ratio distance/turning and time spent in the operation. The field efficiency was calculated through the methodology used by Grisso et. al. (2002), and have been found the average of 65,2%, that being within the variation proposed by ASABE D497.4 (2009b), the time efficiency was determinate based on the concept of Hunt (2001), have been determined a average of 75,7%, to field pattern efficiency, had been used the methodology of Perin (2008) and was observed a average of 72,0% and for calculate the cutter bar efficiency was used the equation proposed by Taylor et. al. (2001), and have been found the average of 86,5%. There was no significant difference, at 5% probability of error, between the two methods studied in this thesis (with land level or without it). The time spent in maneuvers and unloading were the most important factors that influenced the field and time efficiencies. The efficiencies of field pattern and the cutter bar had a high correlation between themselves and the variables ratio of length/width of the field and distance/turning. Making unloading with the combine in operation and if possible avoid turning in the corners of the fields, even if this make to loose in efficiency in the cutting bar, can increase the field efficiency. / O objetivo deste trabalho foi avaliar a eficiência da operação de colheita mecanizada em lavouras de arroz irrigado, localizadas na região da Depressão Central do Rio Grande do Sul. Como objetivos específicos, o trabalho buscou determinar e avaliar as eficiências de campo, de tempo, de trajeto e da barra de corte; verificar se existe diferença entre as duas modalidades de sistematização para as variáveis estudadas; comparar a eficiência de campo encontrada com a estabelecida pela ASAE D497.4 (2009b); Avaliar influência da geometria das lavouras sistematizadas com nivelamento da superfície do solo em nível sobre a eficiência de campo;elencar as variáveis que possuem maior correlação com a redução e o aumento das eficiências e indicar medidas que possam otimizar as eficiências avaliadas. Na safra 2008/2009, forram avaliadas 19 operações, divididas em 6 propriedades, A, B, C, D, E, e F sendo que 15 lavouras eram sistematizadas com nivelamento da superfície do solo em nível e 4 sistematizadas com nivelamento da superfície do solo em desnível. Os dados das operações foram coletados de forma manual, através do uso de caderneta de campo e cronômetro, e com um receptor de sinal de GPS (Global Positioning System), marca Garmin®, modelo GPSMAP® 60CSX. Para auxiliar na análise e calcular as eficiências, foram determinadas as seguintes variáveis: área e relação comprimento/largura (F/W) das lavouras, deslocamento médio, distância percorrida/manora (DP/M) e tempos envolvidos na operação. A eficiência de campo foi calculada através da metodologia utilizada por Grisso et al. (2002), e encontrouse um valor médio de 65,2%, localizado dentro da variação proposta pela ASABE D497.4 (2009b), a eficiência de tempo foi determinada com base no conceito de Hunt (2001), determinou-se um valor médio de 75,7%, para a eficiência de trajeto, seguiu-se a metodologia de Perin (2008) e observou-se um valor médio de 72,0% e para o cálculo da eficiência da barra, realizado pela equação proposta por Taylor et al. (2001), encontrou-se valor médio de 86,5%. Não houve diferença significativa, em nível de 5% de probabilidade de erro, entre as duas modalidades de sistematização. Os tempos gastos em manobras e descargas foram os fatores que mais influenciaram na eficiência de campo e de tempo. As eficiências de trajeto e da barra de corte tiveram alta correlação entre elas e com as variáveis relação comprimento/largura da lavoura e relação distância percorrida/manobra. Realizar as descargas com a colhedora em operação e evitar efetuar manobras nos vértices das lavouras, mesmo que se perca em eficiência da barra de corte, podem otimizar a eficiência de campo.

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