Resumen de Lixiviados en horticultura intensiva ornamental y su tratamiento mediante humedades artificales
Nurseries growing potted ornamental plants carry an important activity in the overall agricultural production in Catalonia. As a result of the activity developed and agricultural practices adopted by nursery growers (irrigation and fertilization methods) will eventually generate leachates containing nutrients from fertilizers, especially nitrates (NO3-). The final destination of the nursery leachates is frequently it discharges into the surrounding medium. For this reason, certain plant-growing areas causes non-point source NO3- pollution of the groundwater. Many cultural practices have been adopted by nursery growers to limit this type of pollution. The considerations described above highlight the need for studies evaluating the effect of agricultural practices on the leachates composition from outdoor crops and, if appropriate, propose an alternative to reduce NO3- in the same place of origin. Therefore, the objectives of the thesis are: - to identify fertilization methods and other agricultural practices adopted by nurseries growing potted ornamental plants in Barcelona and Girona, - to determine the effect of applying two fertilization methods on the leachates composition from two crops of potted ornamental plants, and - to assess the appropriateness of using horizontal subsurface-flow constructed wetlands (HSsH) for treating nursery leachates and optimize the denitrification process developed in them. Some experiments were carried out to meet these objectives. In the first experiment a survey was designed and conducted to the nursery growers of Barcelona and Girona. As a result of this work common fertilization methods were identified and two successive experiments were raised and conducted to answer the second objective. These experiments consisted on using the two standard fertilization strategies of nurseries (fertigation or controlled released fertilizers-FLC-) for two outdoor potted crops (a woody ornamental plant and other herbaceous ornamental plant) and different doses. Once leachates were characterized in terms of the different forms of N, four experiments were designed to meet the third objective. These consisted on treating nursery leachates by HSsH, an effective alternative to conventional technology in treating water with a high NO3- content. A first-order plug-flow kinetic model based on NO3- removal was used to design a pilot plant with HSsH, in which experiments were conducted. These were different in the type of carbon source (sodium acetate -AcNa- or methanol -Me-) and dose added to promote influent denitrification. The results related to the first goal showed that fertilization methods and other agricultural practices related to irrigation and leachates management are very different depending on the type of common crop in each province. Thus, in Girona, where woody crops are most frequent, growers usually apply FLC and use overhead irrigation. However, in Barcelona, where herbaceous crops in season are performed, growers usually apply nutrient solutions (NS) by continuous fertigation and use drip or micro-sprinkler irrigation systems.The application of FLC to the crop resulted in the acidification of the leachates respect of the application of SN by fertigation.The coincidence of high growing media temperatures and prolonged heavy rain events during one of the two crops, indicated a greater initial loss of N by leaching to the environment when FLC are applied and, consequently, a decrease of FLC longevity.The results related to the third goal showed that the design of the pilot plant with HSsH was suitable for treating nursery leachates. The denitrification rate was greatest applying AcNa to achieve a C:N-NO3- ratio of 3:1. However, the application of this ratio and AcNa involves the addition of carbon and sodium in excess of purified effluent, respectively. The quality of the effluent and the denitrification process were enhanced when Me is applied to reach C:N-NO3- ratio of 1:1.5.
