[en] Modernization and intensification of agriculture have managed to increase crop yields at the rate demanded by a growing world population. Nevertheless, this fact has resulted in a variety of adverse impacts on the environment, which can put the future sustainability of agriculture at risk. In this respect, apart from the degradation of water quality due to the use/abuse of fertilizers and pesticides, the impact of these compounds on soil quality must be considered. Such impact depends, to a great extent, on the status of the soil microbial communities, since they are responsible for many of the processes that take place in the soil ecosystem. The main objective of this work was to study, under laboratory conditions, the potential impact of some of the fertilizers and pesticides currently used in the Vulnerable Zone of Vitoria-Gasteiz on its soil and water quality. During a study of a characteristic crop in such area (sugar beet, Beta vulgaris L.), we found that, despite the implementation of a Code of Good Agricultural Practices in the Vulnerable Zone, significant amounts of nitrates and pesticides (e.g., ethofumesate and difenoconazole) are still being leached. Additionally, we observed that the excess of nitrate present in groundwater from the Vulnerable Zone is mitigated, at least partially, by denitrifying microbial activity in the riparian zone of the Salburua wetland. This process, however, involves the emissions of great amounts of greenhouse gases (CO2 and N2O) and might be negatively affected by pesticide presence (e.g., deltamethrin). Furthermore, different pesticides (deltamethrin, ethofumesate, difenoconazole) applied to soil samples at field application rates led to changes, of limited and temporary character, on soil microbial communities, which were more pronounced for the fungicide difenoconazole. Pesticide effects were more accused as their concentration in soil increased. Finally, organic amendments (avicompost), as opposed to conventional synthetic fertilizers (NPK), enhanced pesticide degradation and mitigated their impact on soil quality. The application of organic amendments might help reduce nitrate losses by leaching.

[es] En la presente tesis se ha estudiado el impacto de diferentes fertilizantes y pesticidas utilizados en la Zona Vulnerable de Vitoria-Gasteiz en la calidad del suelo y las aguas de dicha zona. Se ha podido constatar que hoy en día siguen lixiviándose cantidades significativas de nitratos y pesticidas (e.g., etofumesato y difenoconazol) a las aguas de la Zona Vulnerable, durante el cultivo de remolacha azucarera (Beta vulgaris L.), muy característico de la zona de estudio. Se comprobó que el alto contenido en nitratos de las aguas subterráneas en la Zona Vulnerable es mitigado, al menos en parte, por la acción de la actividad microbiana desnitrificante que alberga la zona riparia del humedal de Salburua. Dicho proceso, sin embargo, supone la emisión a la atmósfera de importantes cantidades de gases de efecto invernadero (CO2 y N2O), y puede verse afectado negativamente por la presencia de pesticidas (e.g., deltametrina) en el medio.Por otra parte, hemos observado que diversos pesticidas (deltametrina, etofumesato, difenoconazol) aplicados en concentraciones similares a las dosis de aplicación en campo inducen cambios, de carácter limitado y transitorio, en las comunidades microbianas edáficas, siendo más significativos en el caso del fungicida difenoconazol. El efecto de los pesticidas fue más acusado a medida que aumentaba su concentración en el medio. Finalmente, encontramos que la aplicación de abonos orgánicos (avicompost), en lugar de los fertilizantes sintéticos tradicionales (NPK), además de mejorar la degradación de los pesticidas y disminuir el impacto de éstos sobre la calidad del suelo, podría ayudar a reducir las pérdidas de nitratos por lixiviación.