Efecto de la aplicación de efluentes líquidos de tambo sobre la fertilidad del suelo y la productividad de Festuca arundinaceae

During the last 30 years, Uruguayan dairy farming sector has experienced a profound transition. The country went from being a net importer of dairy products to export 70% of its production. This transformation was the result of an intensification of the production process, which was not accompanied by planning for the adequate final disposal of the effluents generated. It is known that, if not properly managed, dairy effluents may have negative impacts on the environment, affecting soil, water courses and air quality. On the other hand, there is a global tendency towards dairy effluents valorization. Due to their nutrient loads, and consequently their potential positive effects on soil chemical, physical and biological properties, dairy effluents are beginning to be recognized as resources rather than as waste. Within this context, this thesis proposes to analyze the impact of the application of dairy effluents regarding their effects on soil properties and crop yield. In order to do so, an experiment was developed in Centro Regional Sur of Faculty of Agronomy where dairy effluents (both raw and treated in a lagoon system) were applied to a Festuca arundinaceae pasture. The methodology involved 4 effluent applications according to their N content in order to achieve an annual dose of 200 kg N/ha. The applications were in September 2019, November 2019, May 2020 and August 2020 before which effluents samples were taken to characterize them. Before each application, pasture cuts were made in order to evaluate its yield. The effects on soil properties were studied through samples taken after the last application and pasture cut, 1 year and 6 months after the sowing. Results obtained for the pasture yield and the soil characteristics were compared to those obtained for non-amended control and for urea fertilization. Dairy effluents proved to be highly variable during the course of the experiment, demonstrating the importance of doing chemical analyzes before their application so as to determine the adequate dose to apply depending on the crop requirements. The effluents characteristics also demonstrated the effectiveness of the lagoon system in reducing the effluent’s organic loads. Regarding the soil properties, no negative effects were observed as a result of the effluent application during the course of the experiment. Some positive effects were determined such as the increase in the organic carbon and potassium concentrations. The maximum pasture yield was obtained with the urea application. Still, there was a significant improvement in total pasture yield with the application of effluents in comparison to the control pasture yield. Therefore, dairy effluents may appear as a promising alternative, even though further and longer-term studies should be performed.