Avaliação do estado nutricional azotado de pés-mãe de Eucalyptus globulus Labill. ssp. globulus com recurso a um medidor portátil de clorofila

Evaluation of nitrogen status of Eucalyptus globulus Labill. ssp. globulus mother plants with a portable chlorophyll meter

H. M. Ribeiro¹, E. Vasconcelos¹, A. Ramos² & J. Coutinho³

 

RESUMO

Com o objectivo de avaliar a possibilidade de utilizar as leituras do medidor portátil de clorofila SPAD 502 (leitura SPAD), como um indicador do estado nutricional azotado de pés-mãe de Eucalyptus globulus Labill. ssp. globulus (E. globulus) foi instalado, em 1999, um ensaio de fertilização azotada de pés-mãe desta espécie. Utilizaram-se 2 clones (HD161 e CN5) aos quais se aplicaram 5 soluções nutritivas com diferentes concentrações de azoto (50, 100, 200, 400 e 800 mg N L^-1). No primeiro ano os pés-mãe foram sujeitos a uma poda de formação. Nos dois anos seguintes (2000 e 2001) avaliou-se: o número de estacas produzidas por pé-mãe, o enraizamento das estacas obtidas, o teor de azoto na folha mais jovem completamente expandida e as leituras SPAD na mesma folha.

Os resultados obtidos indicam a ocorrência de uma relação assimptótica entre a disponibilidade de azoto e a leitura SPAD e a existência de uma relação linear, positiva e altamente significativa, entre o teor foliar de azoto (x) e as leituras SPAD (y): y=23,27+0,75x; r=0,94; n=150. Na avaliação da possibilidade de utilização da leitura SPAD como indicador do estado nutricional azotado dos pés-mãe, observou-se um bom ajustamento do modelo quadrático à relação entre as leituras SPAD e as “produções relativas” (estacas e enraizamento), com coeficientes de determinação elevados e idênticos aos obtidos com o teor foliar de azoto. Desta forma, nestas condições experimentais, a “qualidade” da avaliação do estado nutricional azotado, utilizando as leituras SPAD, foi idêntica à conseguida com o teor foliar de azoto, o que sugere a sua utilização, com bons resultados, como indicador do estado nutricional azotado de pésmãe de E. globulus.

 

ABSTRACT

With the aim of evaluating the use of the portable chlorophyll meter “Minolta SPAD 502” readings (SPAD readings) as an indicator of the nitrogen status of Eucalyptus globulus Labill. ssp. globulus (E. globulus) mother plants, a nitrogen fertilization experiment with this species was performed. Mother plants of two clones (HD 161 and CN5) of E. globulus were grown in an open-air nursery, in 12 L pots. Plants received 5 different nutrient solutions containing 50, 100, 200, 400 e 800 mg N L^-1. During 1999, mother plants were subjected to a formative pruning. During 2000 and 2001 the following parameters were evaluated: number of cuttings produced, rooting ability of the cuttings, nitrogen content of the youngest fully expanded leaf, and leaf SPAD readings.

Results obtained showed a significant asymptotic relationship between nitrogen availability and SPAD readings and a linear, positive and significant relationship between SPAD readings (y) and nitrogen leaf contents (x, g kg ^–1): y=23,27+0,75x; r=0.94; n=150. Results also showed a good fitting of quadratic model to the relationship between SPAD readings and the mother plants production (cuttings production and rooting ability of the cuttings). The determination coefficients (78%) were similar to those obtained when the model was adjusted to the relationship between leaf nitrogen and mother plants production (80%). Results indicate that, in this experiment, SPAD readings can be used to evaluate nitrogen status of E. globulus mother plants with a diagnostic “quality” similar to leaf nitrogen contents.

 

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¹ Inst. Sup. de Agronomia, DQAA, Tapada da Ajuda, 1349-017 Lisboa. Tel: 213 653 440 E-mail: henriqueribe@isa.utl.pt

² Instituto de Investigação da Floresta e Papel -RAIZ, Qta de S. Francisco, apartado 15, 3801-501 Eixo. E-mail: aramos@raiz-iifp.pt

³ D. Edafologia, UTAD, apartado 1013, 5000-911 Vila Real. E-mail: j_coutin@utad.pt