Search

The rapid, simple and accurate determination of soil quality indicators is fundamental for improvements in precision agriculture and consequently in production efficiency. The objectives of this study were to determine the organic matter (OM) and total organic carbon (TOC) concentrations in agricultural soil and to discriminate soil provenance by energy-dispersive X-ray fluorescence (EDXRF) combined with principal component analysis and partial least square regression. The conventional methods used for the determination of OM and TOC concentrations are the gravimetric and Walkley–Black methods, respectively. Figures of merit such as sensitivity, detection and quantification limits, accuracy and precision were evaluated. Samples were differentiated by their provenance, and the quality of the prediction model shows that EDXRF combined with multivariate analysis is a promising methodology to fulfil the lack of rapid and accurate analytical methods for the assessment of OM and TOC concentrations in agricultural soils. [ABSTRACT FROM AUTHOR]

Abstract: The atomic force microscopy (AFM) is a technique for direct three dimensional measurements of the mineral structure in nanometric scale. In the literature, there are studies which approach the characterization of surfaces in atomic scale through AFM, such as humic substances and minerals. However, the number of studies aiming to characterize the clay fraction minerals in soil using this technique is not representative. In this study, AFM was employed to characterize the clay fraction morphology and microtopography in the surface layer of a Rhodic Ferralsol in Brazil, and X-ray diffraction (XRD) together with the Rietveld Method (RM) to characterize and quantify the main minerals. Images analyzed presented particles from 3 to 25nm. Through XRD and RM mineralogical analysis, the minerals found in higher amounts from the most to the least were, gibbsite, kaolinite, hematite, anatase, goethite, magnetite, calcite, vermiculite and rutile. AFM images made it possible to identify, by observing the height and shape, the particles that corresponded to kaolinite, goethite and gibbsite. This study shows the potential of the AFM technique to measure clay in nanometric scale and the possible identification of minerals present in the clay fraction with the use of XRD and RM. [Copyright &y& Elsevier]

Liming can influence crop growth by altering pore geometry, pore size distribution and water retention characteristics in acid soils. The aim of this work is to determine liming effects on the soil structure based on analysis of water retention data using a cubic spline adjustment function. For that, the authors investigated the effect of three lime rates (0, 15 and 20 t ha-1) on soil water retention characteristics and pore size distribution of a silty-clay "Cambissolo Háplico Alumínico" (Dystrudept) located in the SE region of the Paraná State, Brazil. Soil cores were collected after 31 months of the experiment at 0-10 cm and 10-20 cm soil layers. Eleven matric potentials (from 0 to -7000 cm H2O) were employed to calculate soil water retention and pore size distribution curves. The pore size distribution curves revealed trimodal soil porosity with three distinct peaks. Equivalent pore diameters ranging from 9.18 µm to 13.18 µm separated structural and matrix domains. Small differences exist in the pore size distribution curves due to liming and between layers for all peaks. With no-till plus surface liming, the volume of large pores diminished at the two layers and the volume of small pores increased at the surface layer.