Carlos Manoel Pedro Vaz

Bio: Carlos Manoel Pedro Vaz is an academic researcher from Empresa Brasileira de Pesquisa Agropecuária. The author has contributed to research in topics: Soil water & Water content. The author has an hindex of 26, co-authored 102 publications receiving 2486 citations. Previous affiliations of Carlos Manoel Pedro Vaz include University of Arizona & University of California, Davis.

Multifractal Characterization of Soil Particle-Size Distributions

Abstract: A particle-size distribution (PSD) constitutes a fundamental soil property correlated to many other soil properties. Accurate representations of PSDs are, therefore, needed for soil characterization and prediction purposes. A power-law dependence of particle mass on particle diameter has been used to model soil PSDs, and such power-law dependence has been interpreted as being the result of a fractal distribution of particle sizes characterized with a single fractal dimension. However, recent studies have shown that a single fractal dimension is not sufficient to characterize a distribution for the entire range of particle sizes. The objective of this study was to apply multifractal techniques to characterize contrasting PSDs and to identify multifracfal parameters potentially useful for classification and prediction. The multifractal spectra of 30 PSDs covering a wide range of soil textural classes were analyzed. Parameters calculated from each multifractal spectrum were: (i) the Hausdorff dimension, f(α); (ii) the singularities of strength, α; (iii) the generalized fractal dimension, D q ; and (iv) their conjugate parameter the mass exponent, τ (q), calculated in the range of moment orders (q) of between -10 and -10 taken at 0.5 lag increments. Multifractal scaling was evident by an increase in the difference between the capacity D 0 and the entropy D 1 dimensions for soils with more than 10% clay content, Soils with <10% clay content exhibited single scaling. Our results indicate that multifractal parameters are promising descriptors of PSDs. Differences in scaling properties of PSDs should be considered in future studies.

Evaluation of Standard Calibration Functions for Eight Electromagnetic Soil Moisture Sensors

Abstract: An increasing number of electromagnetic (EM) sensors are deployed to measure volumet ric soil water content (q) for agricultural, ecological, and geotechnical applications. While impedance and capacitance sensors generally operate at frequencies between 20–300 MHz, time domain-reflectometry (TDR) and-transmissometry (TDT) function in the GHz range. In general, lower frequency sensors are less expensive but more sensitive to confounding effects of salinity, temperature, and soil textural variations. To simplify sensor application, factory-supplied calibrations are often provided for different porous media types such as mineral, organic, and saline soils, or soilless-substrates. The objective of the presented study was to evaluate the performance of eight commercially available EM moisture sensing systems (TDR 100, CS616, Theta Probe, Hydra Probe, SM300, Wet2, 5TE, 10HS) in seven well-characterized and texturally varying soils using a standardized approach. The validity of factory supplied-calibration relationships was evaluated and the influence of soil prop erties on the EM responses for q measurements was observed. Results indicate that the factory-supplied calibration relationships for groups of mineral and organic soils in general performed well, but some inconsistences were identified and suggestions for improvement are discussed. Soil-specific calibrations from this study yielded accuracies of around 0.015 m 3 m −3 for 10HS, SM300, and Theta Probe, while lower accuracies of about 0.025 m 3 m −3 were found for TDR100, CS616, Wet2, 5TE, and the Hydra Probe. These results are based on mineral soils having a large variation in texture, electrical conductivities below 2 dS m −1 , organic matter below 10%, and specific surface areas of less than 50 m 2 g −1 . Abbreviations: CV, coefficients of variation; EC b , bulk electrical conductivity; EM, electromagnetic; MW, Maxwell–Wagner; ORG, organic soil; RMSD, root mean squared deviations; SCL, silty clay loam soil; TDR, time domain-reflectometry; TDT, time domain-transmissometry; TLO, transmission line oscillation

Simultaneous Measurement of Soil Penetration Resistance and Water Content with a Combined Penetrometer–TDR Moisture Probe

Abstract: and nutrient exploration have been obtained (Stelluti et al., 1998), and cone penetrometers have been used Soil mechanical impedance affects root growth and water flow, extensively in soil science studies to identify natural and controls nutrient and contaminant transport below the rooting and induced compacted layers (Henderson, 1989) or to zone. Among the soil parameters affecting soil strength, soil water content and bulk density are the most significant. However, field predict related soil properties (Ayers and Bowen, 1987). water content changes both spatially and temporally, limiting the Among the soil parameters that affect PR, soil water application of cone penetrometers as an indicator of soil strength. content and bulk density are the most significant (VazConsidering the presence of large water content variations within a quez et al., 1991). For example, Stitt et al. (1982) consoil profile and across a field and the large influence of water content ducted a comprehensive study of factors affecting PR on soil strength, there is need for a combined penetrometer‐moisture in coarse-textured soils in the Atlantic Coastal Plain, probe to provide simultaneous field water content and soil resistance and used stepwise regression to relate mechanical immeasurements. Such a probe was developed, which uses the time pedance to various measured soil properties. The highdomain reflectometry (TDR) technique to determine water content est correlation coefficients were found for a regression and its influence on soil penetration resistance. The coiled TDR moismodel that included soil water content, soil particle ture probe consists of two parallel copper wires, each 0.8 mm in roughness and bulk soil density. Shaw et al. (1942) condiameter and 30 cm long, coiled around a 5-cm-long polyvinyl chloride (PVC) core with a 3-mm separation between wires. Calibration curves cluded that soil moisture is the dominant factor influencrelating the soil bulk dielectric constant measured by the coiled probe ing the force required to push a penetrometer into the to water content were obtained in the laboratory for a Columbia soil, with PR increasing as the moisture content define sand loam (coarse-loamy, mixed, superactive, nonacid, thermic creased. In an experimental study by Henderson et al. Oxyaquic Xerofluvent), a Yolo silt clay loam (fine-silty, mixed, non- (1988) it was found that PR was only slightly affected acid, thermic Typic Xerorthent), and washed sand, and data were with a decrease of soil water content to ∪70% of field analyzed based on a mixing model approach. Subsequently, field ex- capacity. However, the PR increased exponentially with periments were conducted to measure simultaneously the penetration a further reduction of the water content of the sandy soil. resistance (PR) and water content along a soil profile. Results showed This study showed that PR increased with an increase of a detailed water content profile with excellent correlation with the bulk density across the whole measured water content gravimetric method, whereas the depth distribution of PR was similar range. However, because soil moisture varies both spato that of dry bulk density as determined from soil cores. tially and temporally and is only one of the soil variables related to PR, the utility of using PR to determine compaction effects is marginal. Moreover, interpretation of

Molecular Structure in Soil Humic Substances: The New View

Abstract: A critical examination of published data obtained primarily from recent nuclear magnetic resonance spectroscopy, X-ray absorption near-edge structure spectroscopy, electrospray ionization−mass spectrometry, and pyrolysis studies reveals an evolving new view of the molecular structure of soil humic substances. According to the new view, humic substances are collections of diverse, relatively low molecular mass components forming dynamic associations stabilized by hydrophobic interactions and hydrogen bonds. These associations are capable of organizing into micellar structures in suitable aqueous environments. Humic components display contrasting molecular motional behavior and may be spatially segregated on a scale of nanometers. Within this new structural context, these components comprise any molecules intimately associated with a humic substance, such that they cannot be separated effectively by chemical or physical methods. Thus biomolecules strongly bound within humic fractions are by definition humic...

Revista Brasileira de Ciência do Solo

Abstract: Resumen en: The aim of this study was a survey of the estimated costs of soil erosion, an issue of fundamental importance in view of the current worldwide discussion...

A conceptual model of organo-mineral interactions in soils: self-assembly of organic molecular fragments into zonal structures on mineral surfaces

Abstract: In this paper, we propose a structure for organo-mineral associations in soils based on recent insights concerning the molecular structure of soil organic matter (SOM), and on extensive published evidence from empirical studies of organo-mineral interfaces. Our conceptual model assumes that SOM consists of a heterogeneous mixture of compounds that display a range of amphiphilic or surfactant-like properties, and are capable of self-organization in aqueous solution. An extension of this self-organizational behavior in solution, we suggest that SOM sorbs to mineral surfaces in a discrete zonal sequence. In the contact zone, the formation of particularly strong organo-mineral associations appears to be favored by situations where either (i) polar organic functional groups of amphiphiles interact via ligand exchange with singly coordinated mineral hydroxyls, forming stable inner-sphere complexes, or (ii) proteinaceous materials unfold upon adsorption, thus increasing adhesive strength by adding hydrophobic interactions to electrostatic binding. Entropic considerations dictate that exposed hydrophobic portions of amphiphilic molecules adsorbed directly to mineral surfaces be shielded from the polar aqueous phase through association with hydrophobic moieties of other amphiphilic molecules. This process can create a membrane-like bilayer containing a hydrophobic zone, whose components may exchange more easily with the surrounding soil solution than those in the contact zone, but which are still retained with considerable force. Sorbed to the hydrophilic exterior of hemimicellar coatings, or to adsorbed proteins, are organic molecules forming an outer region, or kinetic zone, that is loosely retained by cation bridging, hydrogen bonding, and other interactions. Organic material in the kinetic zone may experience high exchange rates with the surrounding soil solution, leading to short residence times for individual molecular fragments. The thickness of this outer region would depend more on input than on the availability of binding sites, and would largely be controlled by exchange kinetics. Movement of organics into and out of this outer region can thus be viewed as similar to a phase-partitioning process. The zonal concept of organo-mineral interactions presented here offers a new basis for understanding and predicting the retention of organic compounds, including contaminants, in soils and sediments.