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The Global ETD Search service is a free service for researchers
to find electronic theses and dissertations. This service is
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Networked Digital Library of Theses and Dissertations.
Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
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Showing 1 to 5 of 5 (0.048 seconds)Spelling suggestions: "subject:"derable crop"" "subject:"cobrable crop""
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Biological control of Chenopodium album by Ascichyta caulinaMendi, Ebrahim M. January 2001 (has links)
The overall aim of the research project was to evaluate the potential of the fungal pathogen <I>Ascochyta caulina</I> as a biological control agent against <I>Chenopodium album</I>, a major weed in arable crops. A number of isolates of <I>Ascochyta caulina</I> were evaluated but isolate W 90-1 from Holland proved to be the most promising candidate because of its high virulence. It was therefore selected for more detailed greenhouse and field studies into the environmental parameters required for infection and disease development. Results of these studies showed that in order to achieve the maximum infection, a temperature of between 20-30°C, a relative humidity of >95% for 24 h and a spore density of approximately of 1-2 x 10<sup>6</sup> spores per ml spore suspension were required. Mortality and plant necrosis levels after application of <I>A. caulina</I> decreased with plant age and treatment of <I>C. album</I> shortly after emergence or to juvenile plants (before 4-leaf growth stage) was most effective. The requirement for long periods of high relative humidity and the inability of <I>A. caulina </I>to cause satisfactory disease after the 4 leaf growth stage are the most important limiting factors for the development of <I>A. caulina</I> as a bioherbicide for <I>C. album. </I>A range of spore formulations was studied with the aim of reducing the requirement for long periods of high relative humidity for disease development. Studies indicated that disease development could be increased by incorporation of surfactants (Tween 80 or Sylgard) and nutrients (Czapek-Dox Broth and Yeast Extract) into inoculum suspension. Results of field trials indicated that if application were properly timed and optimum environmental conditions can be achieved the pathogen can give satisfactory control of the weed.
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Transport and attenuation of pesticides in runoff from agricultural headwater catchments : from field characterisation to modellingLefrancq, Marie 11 April 2014 (has links) (PDF)
Understanding pesticide transport is crucial to evaluate their ecological impact on ecosystems. Current knowledge on the spatial variability of pesticide deposition, the impact of erosion on pesticides export and the in situ pesticide degradation is very limited at the catchment scale. In this thesis, characterisation and modeling at two scales, the plot and catchment, were combined in two agricultural contexts. A formalism was developed to predict pesticide transport in runoff and was integrated in LISEM (LImbourg Soil Erosion Model). The results show that impermeable roads contributed to more than 40% to the overall load of fungicides exported via runoff from the vineyard. Pesticide partitioning between suspended solids and runoff water differed largely according to the molecules and the hydrological dynamics. The occurrence of degradation products and the enrichment of one enantiomer were observed suggesting the potential of chiral analyses for assessing biodegradation of chiral pesticides at such scale. Overall, the investigation demonstrated that combining different approaches enable a better understanding of pesticide transport.
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Transport and attenuation of pesticides in runoff from agricultural headwater catchments : from field characterisation to modelling / Atténuation et transport par ruissellement des pesticides dans les têtes de bassins versants agricoles : de la caractérisation sur le terrain à la modélisationLefrancq, Marie 11 April 2014 (has links)
Comprendre le transport des pesticides est crucial pour évaluer leur impact écologique. Les connaissances sur la variabilité spatiale des dépôts de pesticides, l'impact de l'érosion sur leur export et leur dégradation in situ restent très limitées à l'échelle des bassins versants. La caractérisation expérimentale et la modélisation ont donc été combinées à deux échelles, parcelle et bassin versant, dans deux contextes agricoles. Un formalisme a été développé pour prédire le transport des pesticides par ruissellement et a été intégré dans le modèle LISEM (LImbourg Soil Erosion Model). Les résultats montrent que les surfaces imperméables contribuent significativement à la masse exportée par ruissellement du vignoble. La partition des pesticides entre phase dissoute et particulaire diffère considérablement selon les molécules et le forçage hydrologique, et la présence de produits de dégradation et un enrichissement en R-métolachlore ont été observés ce qui souligne le potentiel des analyses énantiomériques pour évaluer la biodégradation des pesticides. Globalement, cette étude a démontré que la combinaison des échelles et des approches permet une meilleure compréhension du transport des pesticides. / Understanding pesticide transport is crucial to evaluate their ecological impact on ecosystems. Current knowledge on the spatial variability of pesticide deposition, the impact of erosion on pesticides export and the in situ pesticide degradation is very limited at the catchment scale. In this thesis, characterisation and modeling at two scales, the plot and catchment, were combined in two agricultural contexts. A formalism was developed to predict pesticide transport in runoff and was integrated in LISEM (LImbourg Soil Erosion Model). The results show that impermeable roads contributed to more than 40% to the overall load of fungicides exported via runoff from the vineyard. Pesticide partitioning between suspended solids and runoff water differed largely according to the molecules and the hydrological dynamics. The occurrence of degradation products and the enrichment of one enantiomer were observed suggesting the potential of chiral analyses for assessing biodegradation of chiral pesticides at such scale. Overall, the investigation demonstrated that combining different approaches enable a better understanding of pesticide transport.
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Plant communities in organic and conventional agriculture - comparing local, landscape and regional effects / Ackerwildpflanzengesellschaften in ökologischer und konventioneller Landwirtschaft - die Bedeutung von Standort, Landschaft und RegionGabriel, Doreen 03 February 2006 (has links)
No description available.
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Spinnen in Agrarlandschaften und die biologische Kontrolle von Getreideblattläusen / Spiders in agricultural landscapes and the biological control of cereal aphidsSchmidt, Martin H. 27 May 2004 (has links)
No description available.
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