Richard J. Heck

Application of X-ray computed tomography to soil science: A literature review

The study of the spatial configuration of soil, in its complexity, requires an understanding of the interrelations and interactions between the diverse soil constituents, at various levels of organization. Investigations of the spatial arrangement of the mineral and organic components of soil have benefited from the development of techniques for structural analysis. X-ray computed tomography (CT) is a non-destructive and non-invasive technique that has been successfully used for three-dimensional (3D) examination of soil. Valuable information has been obtained by the application of CT for the description and quantitative measurements of soil structure elements, especially of soil pores and pore network features. In many studies, X-ray CT has been used to investigate the hydro-physical characteristics of the soil, in a functional and temporal manner. A dynamic approach has also been utilized in the evaluation of the biotic factor influence on soil. The analysis of soil solid phases, by X-ray CT, has been c...

A comparison of 2D vs. 3D thresholding of X-ray CT imagery

Non-destructive soil constituent analysis has advanced from resin impregnation of intact samples to the utilization of non-destructive imaging devices (i.e., CT scanners) for 3D composition. A difficulty of CT scanning is the finite resolution of such devices and the resulting non-definitive boundaries. Isolation of voxels that contain a single constituent (i.e., low variance voxels) allows for improved segregation of 3D data by histogram thresholding. The results from proposed 2D and 3D low variance voxel segmentation techniques were compared to establish whether or not 3D consideration should be used when analyzing CT and intact soil columns. It was determined that 2D processing in single orientation and as a multiplicative orthogonal process produced dissimilar results to 3D processed data. The authors encourage further exploration of 3D investigation in soil science, particularly related to soil composition and arrangement. Key words: Computed tomography, threshold, segmentation, soil, 3D

The magnetic susceptibility of soils in Kohgilouye, Iran

Soil magnetic susceptibility (MS) and Fe were examined for several soils on calcareous parent material, reflecting key climatic conditions and drainage classes in southwestern Iran (Kohgilouye Province). Alfisols, in the eastern and northern parts, contained more pedogenic (citrate dithionite extractable) Fe (up to 60 g kg-1 on a minerogenic basis; 70 % of total Fe, as determined by lithium tetraborate fusion) and poorly crystalline Fe (up to 6 g kg-1 ammonium oxalate extractable) than the Inceptisols in the southern parts. Soil MS (χlf) ranged from 5 to 120 × 10–8 m3 kg-1, with A horizons exhibiting greater values than B horizons, and Alfisols higher than other soils. Pedogenic enhancement of χlf corresponded with preferential leaching of diamagnetics (primarily carbonates), as well as weathering of primary paramagnetics and neoformation of antiferromagnetics. Frequency dependence of MS (χfd), indicating ultrafine superparamagnetics, followed trends similar to χlf. Sequential heating of well-drained samp...

Remote Sensing of Soil Moisture in Vineyards Using Airborne and Ground-Based Thermal Inertia Data

Thermal remote sensing of soil moisture in vineyards is a challenge. The grass-covered soil, in addition to a standing grape canopy, create complex patterns of heating and cooling and increase the surface temperature variability between vine rows. In this study, we evaluate the strength of relationships between soil moisture, mechanical resistance and thermal inertia calculated from the drop of surface temperature during a clear sky night over a vineyard in the Niagara region. We utilized data from two sensors, an airborne thermal camera (height ≈ 500 m a.g.l.) and a handheld thermal gun (height ≈ 1 m a.g.l.), to explore the effects of different field of views and the high inter-row temperature variability. Spatial patterns of soil moisture correlated more with estimated thermal inertia than with surface temperature recorded at sunrise or sunset. Despite the coarse resolution of airborne thermal inertia images, it performed better than estimates from the handheld thermal gun. Between-row variation was further analyzed using a linear mixed-effects model. Despite the limited spatial variability of soil properties within a single vineyard, the magnitudes of the model coefficients for soil moisture and mechanical resistance are encouraging indicators of the utility of thermal inertia in vineyard management.

Gypsum-saturated water to reclaim alluvial saline sodic and sodic soils

Inadequate management of soil and irrigation water contribute to soil degradation, particularly in the alluvial areas of Northeast Brazil, where salinity and sodicity are already common features. This study evaluates the effects of the addition of gypsum in the irrigation water on physical and chemical properties of soils with different levels of salinity and sodicity. Samples were collected at the Custodia irrigation area of Brazil, predominantly covered by alluvial soils. Leaching tests using simulated irrigation water classified as C3S1, and gypsum-saturated irrigation water were carried out in soil columns of 20 and 50 cm depth. Soil leaching with gypsum saturated water (T2) resulted in an increase in the amounts of exchangeable calcium and potassium, and in a decrease of soil pH, in relation to the original soil (T0), with significant statistical differences to the treatment using only water (T1). There was a reduction in the electrical conductivity, exchangeable sodium and exchangeable sodium percentage in both treatments (T1 and T2), with treatment T2 being more effective in the leaching of soil sodium. No changes of electrical conductivity, calcium and pH in depth were observed, but the 20 - 50 cm layer presented higher amounts of magnesium, sodium and exchangeable sodium percentage. Gypsum saturated water improved the hydraulic conductivity in both layers. The use of gypsum in the irrigation water improved soil physical and chemical properties and should be considered as an alternative in the process of reclamation of saline-sodic and sodic soils in Northeast Brazil.

Scaling of pores in 3D images of Latosols (Oxisols) with contrasting mineralogy under a conservation management system

The aim of this study was to evaluate the spatial and morphological configuration of the pore space in 3D images of Latosols with different mineralogy under a conservation tillage system in a coffee crop area. The visualisation and quantification of pore size distribution by data mining and spatial variability by semi-variogams were investigated in 3D images with 60-µm spatial resolution generated by X-ray CT scan (EVS/GE MS8x-130) in soil core samples collected at different depths of a kaolinitic Red-Yellow Latosol (RYL) and a gibbsitic Red Latosol (RL) from Brazil. Greater spatial variability occurred in the horizontal direction of the 3D image, a novel finding in this area of research. The pores detected were different between the Latosols studied, mainly at 0.20–0.34 m depth. The largest number (>4000) and volume (±30 mm3) of pores was found in the RL. The soil classes differed in 3D pore characteristics, and this aspect may be important in the characterisation of causes of pore variability. Sphericity was similar for both soils, with greater emphasis on pore classes with a diameter 15%).

Object-Based Method Outperforms Per-Pixel Method for Land Cover Classification in a Protected Area of the Brazilian Atlantic Rainforest Region

Abstract Conventional image classification based on pixels hinders the possibilities to obtain information contained in images, while modern object-based classification methods increase the acquisition of information about the object and the context in which it is inserted in the image. The objective of this study was to investigate the performance of different classification methods for land cover mapping in the vicinity of the Alto Ribeira Tourist State Park, a Brazilian Atlantic rainforest area. Two classification methods were tested, including i) a hybrid per-pixel classification using the image processing software ERDAS Imagine version 9.1 and ii) an object-based classification using the software eCognition version 5. In the first method, six different classes were established, while in the second method, another two classes were established in addition to the six classes in the first method. Accuracy assessment of the classification results presented showed that the object-based classification with a Kappa index value of 0.8687 outperformed the per-pixel classification with a Kappa index value of 0.2224. Application of the users knowledge during the object-based classification process achieved the desired quality; therefore, the use of inter-relationships between objects, superclasses, subclasses, and neighboring classes were critical to improving the efficiency of land cover classification.

Porosity analysis of two Acrisols by X-ray computed microtomography.

Porosity and void characteristics of two major Acrisols (Ferric Acrisol and a Ferri-Plinthic Acrisol) with contrasting pedogenic features from the humid forest zone of Ghana were studied by X-ray computed microtomography. Spatial variability of the porosity of the two Acrisols, as well as the volume of different classes of void size, shape, and orientation, was quantitatively determined. Variations in the void characteristics were interpreted in correlation with the pedogenic features of the two soils. The Ferri-Plinthic Acrisol, with more numerous roots, faunal burrows, and with smaller amounts of rock fragments than the Ferric Acrisol, exhibited a larger total pore volume. The greatest part of the pore volume in the two soils could be associated with the macrovoids class. There was a strong correlation between void size and shape. Regular voids corresponded in general to mesovoids of biogenic origin, especially in the surface horizons, whereas irregular and elongated voids were composed mostly of macrovoids. Void orientation was predominantly inclined, with the exception of the horizons where the root or fauna advancement was impeded by a dense subjacent horizon. Considering soil-vegetation relationships, the computed microtomography imagery showed that root development in the lower horizons of the Ferric Acrisol was probably impeded by Fe-Mn nodules; cultivation of Crotalaria juncea on this soil probably facilitated the root penetration in some of the denser zones within the profile. The Ferri-Plinthic Acrisol structure could be improved by the extensive root system of Chromolaena odorata, a self-established fast-growing perennial shrub. Management strategies of the two major soils need to take into account relevant information on pore distribution, morphology, and orientation.

Topolitossequências de solos do Alto Paranaíba: atributos físicos, químicos e mineralógicos

Little is known bout the pedogenetic differentiation in Alto Paranaiba, western Minas Gerais, Brazil, when materials with such a variety of chemical compositions as tufite, alkaline-ultramafic igneous rocks and carbonatites are compared, which are all found in this region. The purpose of this study was to characterize the physical, chemical and mineralogical properties of three representative soil topolitosequences of the Alto Paranaiba region. Therefore, 11 soil profiles were described and collected in the Serra do Salitre, Patrocinio and Coromandel counties, representing the influence of mafic-ultramafic bodies along the geological interface between Bambui and Araxa groups. Soil samples were routinely analyzed for physical and chemical properties, besides determinations of Fe, Al and Si after sulfuric extraction; Fe after extraction by DCB and oxalate; Fe, Ca, Mg, K, P, Ti, and other heavy metals after total digestion (triacid attack); and determination of the different components in the clay fraction by DRX. The Latosols (Oxisols) of the Alto Paranaiba are extremely weathered and have very low Ki and Kr indexes, indicators of soils with high iron and aluminum oxides contents, with no defined relationship with the underlying parent materials, indicating intense pedoturbation and mixture with alloctonous materials. The geochemical signatures of the ultramafic nature are the unusual high content of Cr, Ni, Mn, Fe, and Mg. The clay fraction mineralogy of the Latosols shows the coexistence of VHE, kaolinite, gibbsite, and anatase, indicating a polycyclic genesis of the minerals from the finer fraction and the high weathering degree. In the Cambisols, the current rapid desilification indicates the coexistence of gibbsite and iron oxides with smectites and illite because of the fast weathering in the silicon-poor mafic or alkaline-ultramafic rock substrates.

Separating near surface thermal inertia signals from a thermal time series by standardized principal component analysis

Principal component analysis has been applied to remote sensing data to identify spatiotemporal patterns in a time series of images. Thermal inertia is a surface property that relates well to shallow surface thermal and physical properties. Mapping thermal inertia requires quantifying surface energy balance components and soil heat flux, both of which are difficult to measure remotely. This article describes a method to map soil thermal inertia using principal component analysis applied to a time series of thermal infrared images and it also assesses how sensitive this method is to the time intervals between images. Standardized principal component analysis (SPCA) was applied to thermal infrared images captured at half-hour intervals during a complete diurnal cycle. Shallow surface thermal properties accounted for 45%, 82% and 66% of the spatiotemporal variation in surface temperature observed during the heating phase, cooling phase and over the total diurnal cycle respectively. The remaining 55%, 18% and 34% of the variation was attributed to transient effects such as shadows, surface roughness and background noise. Signals related to thermal inertia explained 18% of total variation observed in a complete diurnal cycle and 7% of variation in the cooling series. The SPCA method was found useful to separate critical information such as timing and amplitude of maximum surface temperature variation from delays related to differential heating induced by micro-topography. For the field conditions experienced in this study, decreased temporal resolution when sampling intervals were greater than an hour significantly reduced the quality of results.