Calibration of time domain reflectometry technique using undisturbed soil samples from humid tropical soils of volcanic origin

Weitz, A.; Grauel, W. T.; Keller, Michael; Veldkamp, Edzo

doi:10.1029/96wr03956

Cited by 86 publications

(64 citation statements)

References 18 publications

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“…The singular behavior of h in function of P is illustrated in figure 2, which shows the enormous enhance of the radius sampled by TDR probes with a centesimal enhance of P. The theoretical value calculated with P = 0.99 agrees to the assumption of the "radius of the measured soil cylinder" by the TDR probes used in this study (Figure 1). There was also a large degree of agreement between results obtained from experiments conducted by Petersen et al (1995) and Weitz et al (1997) and theoretical values obtained by Knight et al's model to estimate the soil volume by the TDR technique.…”

Section: Probe Orientation and Soil Volume Evaluated By Tdrsupporting

confidence: 73%

“…The accuracy of θ TDR estimations found by Topp et al (1980) was 0.01 m m -3 . Herkelrath et al (1991) found values of about 0.02 m m -3 , Bohl & Roth (1994) 0.02 to 0.03 m m -3 for mineral soils and 0.03 to 0.07 m m -3 for organic soils, Jacobsen & Schjønning (1995) found a precision in the range from 0.01 to 0.18 m m -3 , and Weitz et al (1997) in the range from 0.02 to 0.52 m m -3 .…”

Section: Soil Characteristicsmentioning

confidence: 99%

“…Accuracy of empirical equations for the determination of θ θ θ θ θ Some significant differences between the empirical equations under study are shown in Weitz et al (1997) and Dasberg & Hopmans (1992). This underestimation is probably related to the anomalous behavior of the dielectric properties of water bound in colloidal particles (clay and organic matter) which induces a different dielectric behavior of such water molecules from those of free water (Bohl & Roth, 1994).…”

Section: Soil Characteristicsmentioning

confidence: 99%

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Sampling and TDR probe insertion in the determination of the volumetric soil water content

Teixeira

Schroth

Marques

et al. 2003

Rev. Bras. Ciênc. Solo

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Volumetric soil water content (theta) can be evaluated in the field by direct or indirect methods. Among the direct, the gravimetric method is regarded as highly reliable and thus often preferred. Its main disadvantages are that sampling and laboratory procedures are labor intensive, and that the method is destructive, which makes resampling of a same point impossible. Recently, the time domain reflectometry (TDR) technique has become a widely used indirect, non-destructive method to evaluate theta. In this study, evaluations of the apparent dielectric number of soils (epsilon) and samplings for the gravimetrical determination of the volumetric soil water content (thetaGrav) were carried out at four sites of a Xanthic Ferralsol in Manaus - Brazil. With the obtained epsilon values, theta was estimated using empirical equations (thetaTDR), and compared with thetaGrav derived from disturbed and undisturbed samples. The main objective of this study was the comparison of thetaTDR estimates of horizontally as well as vertically inserted probes with the thetaGrav values determined by disturbed and undisturbed samples. Results showed that thetaTDR estimates of vertically inserted probes and the average of horizontally measured layers were only slightly and insignificantly different. However, significant differences were found between the thetaTDR estimates of different equations and between disturbed and undisturbed samples in the thetaGrav determinations. The use of the theoretical Knight et al. model, which permits an evaluation of the soil volume assessed by TDR probes, is also discussed. It was concluded that the TDR technique, when properly calibrated, permits in situ, nondestructive measurements of q in Xanthic Ferralsols of similar accuracy as the gravimetric method.

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Section: Probe Orientation and Soil Volume Evaluated By Tdrsupporting

confidence: 73%

Section: Soil Characteristicsmentioning

confidence: 99%

Section: Soil Characteristicsmentioning

confidence: 99%

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Sampling and TDR probe insertion in the determination of the volumetric soil water content

Teixeira

Schroth

Marques

et al. 2003

Rev. Bras. Ciênc. Solo

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“…The 8-ha site was on a recent alluvial terrace derived primarily from volcanic material (21). The soil (eutric Hapludand) (22) was deep (Ͼ Ͼ4 m) and very well-drained and had high base cation saturation and high capacity to stabilize organic matter and retain P and water (30 -34% by volume of residual water content).…”

Section: Methodsmentioning

confidence: 99%

Competition from below for light and nutrients shifts productivity among tropical species

Ewel

Mazzarino

2008

Proc. Natl. Acad. Sci. U.S.A.

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Chance events such as seed dispersal determine the potential composition of plant communities, but the eventual assemblage is determined in large part by subsequent interactions among species. Postcolonization sorting also affects the ultimate composition of communities assembled by people for restoration, horticulture, or conservation. Thus, knowledge of the mechanisms controlling interspecific interactions in plant communities is important for explaining patterns observed in nature and predicting success or failure of utilitarian combinations. Relationships among species, especially those from studies of biological diversity and ecosystem functioning, are largely based on studies of short-lived, temperatezone plants. Extrapolation to perennial plants in the humid tropics is risky because functional relationships among large-stature species change with time. Shifts in competitive relationships among 3 life forms-trees, palms, and perennial herbs-occurred during 13 yr in experimental tropical ecosystems. In 2 cases the novel competitive mechanism responsible for the shift was reduction in crown volume, and therefore light-capturing capability, of overtopping deciduous trees by intrusive growth from below a palm. In a third case, complementary resource use developed between 2 evergreen life forms (overstory tree and palm), probably because of differential nutrient acquisition. Species-level traits and adequate time for shifts in interspecific relationships to emerge are crucial for predicting community trajectories.complementarity ͉ diversity ͉ ecosystem functioning ͉ fertile soil ͉ plant competition D esign of sustainable ecosystems, whether for biodiversity conservation, economic gain, or restoration of ecosystem services, involves the assembly of plant communities comprising species of high ecological combining ability (1, 2). That combining ability is determined by interspecific interactions and refers to the ways and degree to which common resources, particularly light, water, and mineral nutrients, are shared. Does the nature of plant interactions remain relatively constant over time? If not, prediction of combining ability will require either case-specific long-term observation or thorough understanding of the mechanisms involved.To examine the stability of plant interactions, and to reveal mechanisms driving any changes observed, we constrained the number of perennial life-form groups in simple experimental communities while varying the specific identity of 1 of them. The study site, a young alluvial terrace at La Selva Biological Station in the humid tropical lowlands of Costa Rica, was chosen because of its exceptionally fertile soil and warm, wet climate. By conducting experiments in an environment where plants experienced few abiotic constraints on growth we achieved results quickly and avoided the delays intrinsic to environments where plant growth is slow or where the ecological clock is reset annually.The life forms selected are among those most common in mature forest at La Selva (3) and character...

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“…No entanto, os resultados de Rothe et al (1997) indicam que a compactação do solo por ocasião da instalação das sondas pode causar alterações substanciais nas estimativas de umidade pela TDR, principalmente em elevados valores de umidade. Em solos vulcânicos caracterizados pela reduzida densidade e elevados teores de matéria orgânica, Weitz et al (1997) constataram que o modelo proposto por Topp subestimou θ em até 15 %. Malicki et al (1996), utilizando diferentes materiais porosos, inclusive solo, demonstraram que a densidade, assim como a porosidade, influenciam na relação entre Ka e θ e que os erros das estimativas foram contornados quando os efeitos dessas variáveis foram considerados na função de calibração.…”

Section: Introductionunclassified

Influência da densidade do solo na estimativa da umidade em um nitossolo vermelho distroférrico, por meio da técnica de TDR

Gonçalves

Trintinalha²,

Tormena

et al. 2011

Rev. Bras. Ciênc. Solo

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Calibration of time domain reflectometry technique using undisturbed soil samples from humid tropical soils of volcanic origin

Cited by 86 publications

References 18 publications

Sampling and TDR probe insertion in the determination of the volumetric soil water content

Sampling and TDR probe insertion in the determination of the volumetric soil water content

Competition from below for light and nutrients shifts productivity among tropical species

Influência da densidade do solo na estimativa da umidade em um nitossolo vermelho distroférrico, por meio da técnica de TDR

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