Eucalyptus sp. SEEDLING RESPONSE TO POTASSIUM FERTILIZATION AND SOIL WATER

MATÉRIA SECA E RELAÇÕES HÍDRICAS EM MUDAS DE Eucalyptus sp. EM FUNÇÃO DA FERTILIZAÇÃO POTÁSSICA E DA UMIDADE DO SOLO

ABSTRACT

A considerable portion of Brazil's commercial eucalypt plantations is located in areas subjected to periods of water deficit and grown in soils with low natural fertility, particularly poor in potassium. Potassium is influential in controlling water relations of plants. The objective of this study was to verify the influence of potassium fertilization and soil water potential (Ψw) on the dry matter production and on water relations of eucalypt seedlings grown under greenhouse conditions. The experimental units were arranged in 4x4x2 randomized blocks factorial design, as follow: four species of Eucalyptus (Eucalyptus grandis, Eucalyptus urophylla, Eucalyptus camaldulensis and hybrid Eucalyptus grandis x Eucalyptus urophylla), four dosages of K (0, 50, 100 and 200 mg dm-3) and two soil water potentials (-0.01MPa and -0.1 MPa). Plastic containers with 15 cm diameter and 18 cm height, with Styrofoam base, containing 3.0 dm3 of soil and two plants per container were used. Soil water potential was kept at -0.01MPa for 40 days after seeding. Afterward, the experimental units were divided into two groups: in one group the potential was kept at - 0.01MPa, and in the other one, at -0.10 MPa. Soil water potential was controlled gravimetrically twice a day with water replacement until the desired potential was reestablished. A week before harvesting, the leaf water potential (Ψ), the photosynthetic rate (A), the stomatal conductance (gs) and the transpiration rate were evaluated. The last week before harvesting, the mass of the containers was recorded daily before watering to determine the consumption of water by the plants. After harvesting, total dry matter and leaf area were evaluated. The data were submitted to analysis of variance, to Tukey's tests and regression analyses. The application of K influenced A, gs and the transpiration rate. Plants deficient in K showed lower A and higher gs and transpiration rates. There were no statistical differences in A, gs and transpiration rates in plants with and without water deficit. The addition of K reduced the consumption of water per unit of leaf area and, in general, plants submitted to water deficit presented a lower consumption of water.

Keywords:
potassium nutrition; eucalypt; water deficit, water relations

RESUMO

No Brasil, uma considerável porção dos plantios comerciais de eucalipto está localizada em regiões sujeitas a períodos de déficits hídrico (DH) e, normalmente, em solos de baixa fertilidade natural, particularmente pobres em K, o que pode comprometer o crescimento e as relações hídricas das plantas. Assim, este trabalho teve como objetivo verificar a influência da adubação potássica e do potencial de água do solo (Ψw) na produção de matéria seca e nas relações hídricas de mudas de eucalipto, em casa de vegetação. O experimento foi constituído de 32 tratamentos, compreendendo quatro espécies de eucalipto (Eucalyptus grandis, Eucalyptus urophylla, Eucalyptus camaldulensis e o híbridoEucalyptus grandis x Eucalyptus urophylla), quatro doses de K (0, 50, 100 e 200 mg dm-3 de K) e dois regimes de umidade do solo (-0,01MPa e -0,10 MPa), no delineamento em blocos casualizados, em esquema fatorial, com três repetições. Foram utilizados vasos de PVC, com fundo de isopor, contendo 3,0 dm3 de solo, com duas plantas por vaso. O Ψw foi mantido em -0,01MPa por 40 dias. Após, as unidades experimentais foram divididas em dois grupos, sendo o Ψw, em um deles, mantido a -0,01MPa e, no outro, a -0,10 MPa. O controle da umidade do solo foi feito gravimetricamente. Uma semana antes da colheita do experimento, foram avaliados o potencial da água da folha (Ψ), a taxa fotossintética (A), a condutância estomática (gs) e a taxa de transpiração. Durante a última semana de condução do experimento, a massa dos vasos foi anotada diariamente antes da colocação de água de modo a se determinar o consumo de água pelas plantas. Na colheita, as plantas foram coletadas e determinada a matéria seca. Também, foi determinada a área foliar. Os dados foram submetidos à análise de variância, a testes de Tukey e análises de regressão. A aplicação de K influenciou a A, a gs, a transpiração e a EUA. Plantas deficientes em K apresentaram menor A e maior gs e taxa de transpiração, com consequente menor EUA. Não houve diferenças estatísticas na A, gs e taxa de transpiração entre plantas com e sem DH. A adição de K diminuiu o consumo de água por unidade de área foliar e, em geral, plantas submetidas à DH apresentaram menor consumo de água.

Palavras-chave:
nutrição potássica; eucalipto; déficit hídrico; relações hídricas

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Publication Dates

• Publication in this collection
  Jan-Mar 2008