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Revista Brasileira de Ciência do Solo

versão On-line ISSN 1806-9657

Resumo

SANTOS, Marcelo Rocha dos; ZONTA, João Henrique  e  MARTINEZ, Mauro Aparecido. Influence of sampling type on the dielectric constant and calibration of TDR probes. Rev. Bras. Ciênc. Solo [online]. 2010, vol.34, n.2, pp.299-308. ISSN 1806-9657.  http://dx.doi.org/10.1590/S0100-06832010000200003.

The technique of TDR (time-domain reflectometry) is an important tool for the study of soil water content. For a correct use of this technique, models that relate the volumetric water content in soil with the soil dielectric constant must be calibrated, considering the characteristics of each soil. The purpose of this study was to evaluate the influence of soil type and sampling form (disturbed and undisturbed samples) on the dielectric constant (Ka) of the soil and the performance of models to estimate the volumetric water content in soil (θ) by TDR. The soils were a Haplic Cambisol, an Oxisol and a Typic Quartzipsamment, with different textures. Disturbed and undisturbed Haplic Cambisol and Oxisol samples were collected, but only disturbed Typic Quartzipsamment samples, due to its low aggregation. Calibration was performed with probes consisting of three rods (effective length 0.10 m and resin length 0.05 m), spaced 0.017 apart and without resistor on the center rod, connected to a TDR 100 (Campbell Scientific) equipment. The Ka values, for a same è value, were affected by variation of the soil type, but not influenced by the type of soil sampling (disturbed or undisturbed). For the models tested to estimate è as a function of Ka, the cubic polynomial model fit the θ data determined by gravimetry best for the Typic Quartzipsamment and Haplic Cambisol, whereas for the Oxisol a linear model fit better.

Palavras-chave : reflectometry; water content; soil texture.

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