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Proposta e avaliação de um protocolo de monitorização dos nitratos num olival de regadio
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Resumo(s)
O azoto (N) é um dos mais importantes nutrientes para o crescimento das plantas, podendo ser aplicado de forma incorreta e/ou excessiva. Este elemento pode atingir as massas de água através de diversos processos, originando a sua contaminação. Assim sendo, surge a necessidade de analisar o impacto das práticas de gestão das culturas na qualidade do solo e das águas superficiais. Em particular, torna-se crucial analisar o impacto da aplicação de fertilizante solúvel em água, ou seja, da fertirrega, na qualidade destes ecossistemas.
Este trabalho irá apresentar como caso de estudo um moderno olival de regadio na região do Alentejo, onde irão ser identificados os principais processos de perda de azoto para as massas de água superficiais e subterrâneas. Pretende, também, propor-se um esquema de monitorização, incluindo equipamentos e procedimentos, a adotar pela empresa gestora do olival. Nesse sentido, foram instalados equipamentos de monitorização da lixiviação e do escoamento superficial, nomeadamente cápsulas porosas abaixo e na zona das raízes das oliveiras (Olea europaea) para deteção da presença de nitratos (NO3-) na solução do solo e de eventuais fluxos para as águas subterrâneas. Procedeu-se também à avaliação dos débitos através da medição do volume de diversos gotejadores, por forma a aferir se a aplicação de nutrientes está a ser feita uniformemente.
Os resultados demonstram que, à exceção de um dia em que o débito dos gotejadores difere substancialmente do estipulado pelo fabricante, se verificam apenas diferenças pontuais no caudal dos diversos gotejadores. Sendo que essas incongruências apenas apresentaram repercussões diretas na concentração de nitratos da solução fertilizante e não na solução de solo, admite-se que estas foram compensadas em todos os casos. Em muitas das cápsulas porosas foi impossível recolher solução de solo e verificou-se um impacto visível das flutuações das unidades de fertilizante de azoto (UF N) fornecidas ao sistema nas concentrações encontradas na solução de solo. Relativamente às concentrações, de um modo geral, estas foram superiores em camadas mais profundas do solo e houve uma tendência para encontrar valores mais elevados no perfil do solo do que na água de rega, o que leva a crer que o solo tem o potencial de acumular nitratos proveniente de fertilizações anteriores. No que diz respeito ao protocolo é sugerido o aumento do número de pontos de amostragem, bem como a sua repetição num ano diferente do corrente, em que se verifique a ocorrência de precipitação.
Nitrogen (N) is one of the most important nutrients for plant growth and can be applied incorrectly and/or excessively. This element can reach water bodies through various processes, causing their contamination. Therefore, it arises the need to analyse the impact of crop management practices on the quality of soil and surface water arises. In particular, it becomes crucial to analyse the impact of water-soluble fertilizer application, i.e., fertigation, on the quality of these ecosystems. This work will present a case study of a modern and irrigated olive grove in Alentejo, where the main processes of N loss to surface and groundwater bodies will be identified. It is also intended to propose a monitoring scheme, including equipment and procedures, to be adopted by the olive grove management company. In that regard, leaching and surface runoff monitoring equipment was installed, specifically porous capsules below and in the root zone of the olive trees (Olea europaea) to detect the presence of nitrates (NO3-) in the soil solution and possible flows to groundwater. The flow rates were also evaluated by measuring the volume of several drippers, to assess whether the nutrient application is being done evenly. The results show that, except for one day when the flow rate of the drippers differed substantially from that stipulated by the manufacturer, there were only occasional differences in the flow rate of the different drippers. Since these inconsistencies only had direct repercussions on the nitrate concentration of the fertilizer solution and not on the soil solution, it is assumed that these were compensated in all cases. In many of the capsules it was impossible to collect soil solution and there was a visible impact of the fluctuations of the nitrogen fertilizer units (UF N) supplied on the concentrations found in the soil solution. Regarding the concentrations, in general, they were higher in deeper soil layers and there was a tendency to find higher values in the soil profile than in the irrigation water, which leads to believe that the soil has the potential to accumulate nitrates from previous fertilizations. As far as the protocol is concerned, it is suggested to increase the number of sampling points, as well as to repeat it in a year when precipitation occurs.
Nitrogen (N) is one of the most important nutrients for plant growth and can be applied incorrectly and/or excessively. This element can reach water bodies through various processes, causing their contamination. Therefore, it arises the need to analyse the impact of crop management practices on the quality of soil and surface water arises. In particular, it becomes crucial to analyse the impact of water-soluble fertilizer application, i.e., fertigation, on the quality of these ecosystems. This work will present a case study of a modern and irrigated olive grove in Alentejo, where the main processes of N loss to surface and groundwater bodies will be identified. It is also intended to propose a monitoring scheme, including equipment and procedures, to be adopted by the olive grove management company. In that regard, leaching and surface runoff monitoring equipment was installed, specifically porous capsules below and in the root zone of the olive trees (Olea europaea) to detect the presence of nitrates (NO3-) in the soil solution and possible flows to groundwater. The flow rates were also evaluated by measuring the volume of several drippers, to assess whether the nutrient application is being done evenly. The results show that, except for one day when the flow rate of the drippers differed substantially from that stipulated by the manufacturer, there were only occasional differences in the flow rate of the different drippers. Since these inconsistencies only had direct repercussions on the nitrate concentration of the fertilizer solution and not on the soil solution, it is assumed that these were compensated in all cases. In many of the capsules it was impossible to collect soil solution and there was a visible impact of the fluctuations of the nitrogen fertilizer units (UF N) supplied on the concentrations found in the soil solution. Regarding the concentrations, in general, they were higher in deeper soil layers and there was a tendency to find higher values in the soil profile than in the irrigation water, which leads to believe that the soil has the potential to accumulate nitrates from previous fertilizations. As far as the protocol is concerned, it is suggested to increase the number of sampling points, as well as to repeat it in a year when precipitation occurs.
Descrição
Mestrado em Engenharia Agronómica. Universidade de Lisboa, Instituto Superior de Agronomia
Palavras-chave
agricultura escoamento superficial fertirrega lixiviação qualidade da água agriculture runoff fertigation leaching water quality
Contexto Educativo
Citação
Sarmento, C.E.M. Proposta e avaliação de um protocolo de monitorização dos nitratos num olival de regadio. Lisboa: ISA-Universidade de Lisboa, 2022. Dissertação de Mestrado
Editora
Instituto Superior de Agronomia, Universidade de Lisboa