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Influência da aplicação de rizobactérias e matéria orgânica na produção de alface em ar livre
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O setor hortícola em Portugal possui grande importância económica, sendo a alface um dos principais hortícolas cultivados. A União Europeia apresenta metas ambiciosas para a redução da aplicação de produtos fitofarmacêuticos e de adubos de síntese até 2030, com o intuito de tornar a sua agricultura mais sustentável. Neste contexto, o presente estudo procurou avaliar os efeitos da aplicação de um complexo de rizobactérias promotoras do crescimento vegetal (Azotobacter spp. e Azospirillum spp.) e de um adubo orgânico azotado na produtividade da cultura da alface produzida em ar livre, bem como nas propriedades químicas e biológicas do solo. O ensaio foi realizado em ar livre, numa exploração agrícola, durante duas plantações sucessivas. Definiram-se quatro modalidades experimentais, comparando a aplicação de rizobactérias e adubo orgânico de forma isolada e combinada e o controlo sem aplicação. Foram recolhidas amostras de solo ao longo das duas plantações para avaliação da atividade da enzima desidrogenase e para a realização de plaqueamento e posterior contagem de bactérias e fungos. Analisaram-se os principais indicadores químicos do solo para três das amostras recolhidas. Foram também colhidas e pesadas alfaces em cada uma das plantações para estimar a produtividade. Os resultados indicaram que a aplicação isolada de adubo orgânico originou um aumento significativo de produtividade comparativamente à modalidade de controlo, em ambas as plantações. No primeiro ensaio, a produtividade foi de 57,1 t/ha, 9% superior ao controlo, e no segundo, 60,4 t/ha, 16% superior. Não se conseguiu estabelecer nenhum efeito das rizobactérias na produtividade da alface. A atividade biológica do solo apresentou grandes variações ao longo do tempo e entre modalidades. O resultado mais evidente ocorreu no plaqueamento de bactérias, com 25 458 colónias contabilizadas ao longo de todo o ensaio na modalidade com adubo orgânico. Não se registou influência direta das rizobactérias.
The horticultural sector in Portugal holds significant economic importance, with lettuce being one of the most widely cultivated crops. The European Union has set ambitious targets to reduce the use of pesticides and synthetic fertilizers by 2030, aiming to make European agriculture more sustainable. In this context the present study aims to evaluate the effects of applying a complex of plant growth-promoting rhizobacteria (Azotobacter spp. and Azospirillum spp.) and an organic nitrogen fertilizer on the productivity of lettuce crops grown in open field, as well as on the chemical and biological properties of the soil. The trial was conducted under open field conditions on a commercial farm during two successive planting cycles. Four experimental treatments were established, comparing the isolated and combined application of rhizobacteria and organic fertilizer with a control group, without application. Soil samples were collected throughout both planting cycles to assess dehydrogenase enzyme activity and to perform plating and subsequent bacterial and fungal colony counts. The main soil chemical indicators were also analysed for three of the collected soil samples. Lettuce plants were harvested and weighed for each planting cycle to estimate productivity. The results showed that the isolated application of organic fertilizer led to a significant increase in productivity compared to the control in both planting cycles. In the first trial, productivity reached 57.1 t/ha, 9% higher than the control, and in the second, 60.4 t/ha, 16% higher. No clear effect of rhizobacteria on lettuce productivity was established. Soil biological activity exhibited considerable variation over time and between treatments. The most notable outcome was observed in bacterial plating, with 25,458 colonies counted throughout the trial in the organic fertilizer treatment. No direct influence of rhizobacteria was detected.
The horticultural sector in Portugal holds significant economic importance, with lettuce being one of the most widely cultivated crops. The European Union has set ambitious targets to reduce the use of pesticides and synthetic fertilizers by 2030, aiming to make European agriculture more sustainable. In this context the present study aims to evaluate the effects of applying a complex of plant growth-promoting rhizobacteria (Azotobacter spp. and Azospirillum spp.) and an organic nitrogen fertilizer on the productivity of lettuce crops grown in open field, as well as on the chemical and biological properties of the soil. The trial was conducted under open field conditions on a commercial farm during two successive planting cycles. Four experimental treatments were established, comparing the isolated and combined application of rhizobacteria and organic fertilizer with a control group, without application. Soil samples were collected throughout both planting cycles to assess dehydrogenase enzyme activity and to perform plating and subsequent bacterial and fungal colony counts. The main soil chemical indicators were also analysed for three of the collected soil samples. Lettuce plants were harvested and weighed for each planting cycle to estimate productivity. The results showed that the isolated application of organic fertilizer led to a significant increase in productivity compared to the control in both planting cycles. In the first trial, productivity reached 57.1 t/ha, 9% higher than the control, and in the second, 60.4 t/ha, 16% higher. No clear effect of rhizobacteria on lettuce productivity was established. Soil biological activity exhibited considerable variation over time and between treatments. The most notable outcome was observed in bacterial plating, with 25,458 colonies counted throughout the trial in the organic fertilizer treatment. No direct influence of rhizobacteria was detected.
Descrição
Dissertação de Mestrado, Engenharia Agronómica, 2025, Universidade de Lisboa, Instituto Superior de Agronomia.
Palavras-chave
adubo orgânico azotado Azospirillum Azotobacter Lactuca sativa produtividade organic fertilizer productivity