Nutrição mineral em Eucalyptus globulus Labill: fertilização e exportação de nutrientes
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2012
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A adequada nutrição dos povoamentos de Eucalyptus globulus Labill. permite otimizar o seu crescimento, maximizando a produção de madeira para pasta e papel. Frequentemente, os solos florestais não possuem nutrientes em quantidades suficientes para satisfazer as necessidades do eucalipto, recorrendo-se à fertilização mineral.
Este trabalho pretendeu avaliar a resposta de um povoamento de eucalipto à fertilização mineral, relacionando-a com a nutrição e a absorção de nutrientes pelas plantas, mais especificamente: i) avaliar a resposta do eucalipto à adubação de manutenção; ii) quantificar a produção de biomassa; iii) conhecer a curva de absorção de nutriente ao longo do ciclo e exportação de nutrientes; iv) avaliar a concentração foliar e a análise de solo como indicadores do estado nutricional da planta e da fertilidade do solo e v) calcular o balanço de nutrientes no ecossistema florestal.
Verificou-se resposta positiva à adubação com N, K, B, Zn e Cu, obtendo-se no final do ciclo 31% de ganho no volume de madeira, 13% na produção de biomassa e maior acumulação de nutrientes nas plantas. A aplicação individual de N e K resultou num ganho de 11% e 19% no volume de madeira, respetivamente. Os resultados indicam que o povoamento responderia a pelo menos mais uma adubação, sendo provável que este tenha entrado em défice nutricional e/ou outros fatores possam ter afetado o crescimento das plantas. A adição de B proporcionou um acréscimo em volume de 34%, sugerindo a inclusão deste na formulação dos adubos de manutenção para suprir eventuais carências nutricionais.
Inicialmente mais de 50% dos nutrientes, exceto Fe, estavam acumulados na copa e no final mais de 60% no tronco. Verificou-se maior acumulação de Ca, seguido de K, N, Mg e P.
Relativamente à utilização do teor foliar e da análise do solo como indicadores do estado nutricional da planta e do solo, nem sempre foram obtidas relações positivas com as variáveis de produção. Destaca-se a relação positiva entre a concentração de N foliar e as variáveis de produção na fase jovem do povoamento, reflexo do investimento que as plantas fazem inicialmente na formação da biomassa foliar (r>0,85). No solo, foram obtidas relações positivas entre a concentração de K e B e as variáveis de produção na fase juvenil da planta, embora moderadas.
O balanço de azoto neste ecossistema florestal foi positivo, independente no cenário de exploração considerado. A adubação azotada sobrepôs-se sempre à exportação deste nutriente, minimizando o impacto do cultivo da espécie no inventário de nutrientes do sistema (180 kg ha-1 aplicados vs 128 kg ha-1 extraídos, cenário mais intensivo). Para potássio, o balanço entre entradas e saídas foi sempre negativo, indicando que para suprir as necessidades das plantas foi necessário recorrer à riqueza natural de K no ambiente. No cenário de exploração mais intensivo, são removidos 113 kg de K ha-1. Este fato demonstra a necessidade de reforçar a adubação potássica, para minimizar a exportação contínua deste nutriente do solo, evitando o seu empobrecimento e a perda de sustentabilidade do ecossistema de produção florestal.
Adequate nutrition of Eucalyptus globulus Labill. allows to optimize its growth, maximizing the production of wood for pulp and paper production. Often, forest soils don’t have nutrients in sufficient quantities to satisfy eucalyptus needs, being necessary to complement with mineral fertilization. In this study the objective was to evaluate the response of a eucalyptus stand to mineral fertilization, relating it with plant nutrition and nutrient uptake by plants, more specifically: i) evaluate the response of Eucalyptus to maintenance fertilization; ii) quantify biomass production; iii) determine nutrient absorption curve over the cycle and nutrient exportation; iv) evaluate foliar concentration and soil analysis as indicators of plant nutritional status and soil fertility and v) calculate nutrient balance in this forest ecosystem. Positive response to fertilization with N, K, B, Zn and Cu was obtained, with 31% of wood production gain at the end of the cycle, plus 13% of biomass production and higher accumulation of nutrients in plants. The individual application of N and K resulted in a gain of 11% and 19% in wood production, respectively. The results indicate that the stand would respond to at least one more fertilization probably resulting into nutritional deficit of plants and/or other factors have affected plants growth. Boron addition to the fertilization increased plants volume in 34%, suggesting that this nutrient should be included in the formulation of maintenance fertilizers to prevent eventual nutritional deficiencies. Initially more than 50% of the nutrients, except Fe, were accumulated on the crown and at the end of the growth cycle more than 60% were located in the stem. Higher accumulation in plants was obtained for Ca, followed by K, N, P and Mg. Relatively to the use of foliar concentration and soil analysis as indicators of plants nutritional status and soil fertility, not always positive relationships with production variables were obtained. Positive relationships between foliar N concentration and production variables were obtained in young stage of growth, reflecting the investment that plants make initially in the formation of leaf biomass (r> 0,85). For soil, positive relationships between the concentration of K and B and the production variables were obtained during the juvenile stage of growth, although moderate. Nitrogen balance in this forest ecosystem was positive, regardless of harvesting scenarios. Nitrogen fertilization was always superior exportation of this nutrient, minimizing the impact of the cultivation of this specie in the existing nutrient inventory in the system (180 kg ha-1 applied vs 128 kg ha-1 extracted, most intensive scenario). For potassium, the balance between inputs and outputs was always negative, indicating that to satisfy plant needs it was necessary to use natural richness of K in the environment. In the scenario with the most intensive harvesting, 113 kg K ha-1 are removed. This fact demonstrates the need to increase K fertilization, to minimize the continuous exportation of this nutrient from the soil, preventing its depletion and loss of sustainability of this forest production ecosystem.
Adequate nutrition of Eucalyptus globulus Labill. allows to optimize its growth, maximizing the production of wood for pulp and paper production. Often, forest soils don’t have nutrients in sufficient quantities to satisfy eucalyptus needs, being necessary to complement with mineral fertilization. In this study the objective was to evaluate the response of a eucalyptus stand to mineral fertilization, relating it with plant nutrition and nutrient uptake by plants, more specifically: i) evaluate the response of Eucalyptus to maintenance fertilization; ii) quantify biomass production; iii) determine nutrient absorption curve over the cycle and nutrient exportation; iv) evaluate foliar concentration and soil analysis as indicators of plant nutritional status and soil fertility and v) calculate nutrient balance in this forest ecosystem. Positive response to fertilization with N, K, B, Zn and Cu was obtained, with 31% of wood production gain at the end of the cycle, plus 13% of biomass production and higher accumulation of nutrients in plants. The individual application of N and K resulted in a gain of 11% and 19% in wood production, respectively. The results indicate that the stand would respond to at least one more fertilization probably resulting into nutritional deficit of plants and/or other factors have affected plants growth. Boron addition to the fertilization increased plants volume in 34%, suggesting that this nutrient should be included in the formulation of maintenance fertilizers to prevent eventual nutritional deficiencies. Initially more than 50% of the nutrients, except Fe, were accumulated on the crown and at the end of the growth cycle more than 60% were located in the stem. Higher accumulation in plants was obtained for Ca, followed by K, N, P and Mg. Relatively to the use of foliar concentration and soil analysis as indicators of plants nutritional status and soil fertility, not always positive relationships with production variables were obtained. Positive relationships between foliar N concentration and production variables were obtained in young stage of growth, reflecting the investment that plants make initially in the formation of leaf biomass (r> 0,85). For soil, positive relationships between the concentration of K and B and the production variables were obtained during the juvenile stage of growth, although moderate. Nitrogen balance in this forest ecosystem was positive, regardless of harvesting scenarios. Nitrogen fertilization was always superior exportation of this nutrient, minimizing the impact of the cultivation of this specie in the existing nutrient inventory in the system (180 kg ha-1 applied vs 128 kg ha-1 extracted, most intensive scenario). For potassium, the balance between inputs and outputs was always negative, indicating that to satisfy plant needs it was necessary to use natural richness of K in the environment. In the scenario with the most intensive harvesting, 113 kg K ha-1 are removed. This fact demonstrates the need to increase K fertilization, to minimize the continuous exportation of this nutrient from the soil, preventing its depletion and loss of sustainability of this forest production ecosystem.
Descrição
Dissertação de Mestrado em Engenharia Florestal
Palavras-chave
Eucalyptus globulus , Adubação , Nutrição vegetal , Produção de madeira , Floresta , Sustentabilidade