Journal Paper Digests

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Journal Paper Digests 2019 #14

  • Preparing a soil spectral library using the Internal Soil Standard (ISS) method: Influence of extreme different humidity laboratory conditions
  • In situ and laboratory soil spectroscopy with portable visible-to-near-infrared and mid-infrared instruments for the assessment of organic carbon in soils
  • Alternative approach to calculate soil hydraulic-energy-indices and -functions
  • Mapping LUCAS topsoil chemical properties at European scale using Gaussian process regression

Preparing a soil spectral library using the Internal Soil Standard (ISS) method: Influence of extreme different humidity laboratory conditions

Authors: Chabrillat, S; Gholizadeh, A; Neumann, C; Berger, D; Milewski, R; Ogen, Y; Ben-Dor, E

Source: GEODERMA, 355 13855-13855; DEC 1 2019

Abstract: Extensive efforts are currently being devoted to the establishment of soil spectral libraries on regional, national, continent-wide and global domains. In particular, a new development goes in the direction of global harmonized soil spectral databases that shall be acquired following common standards and procedures so that they can be merged with other soil spectral libraries. The choice of standards is important, especially with respect to their behaviors when laboratory conditions, such as humidity, change. In this study, we test the application and robustness of the Internal Soil Standard (ISS) spectral re-alignment procedure on an extended number of soil samples acquired at different laboratories. In particular, a focus is placed on the comparison between two standards Lucky Bay (LB) and Wylie Bay (WB), for their performance with different humidity laboratory conditions. LB and WB are almost pure quartz sands from Australia. For this, 71 soil samples from Israel with diff erent mineralogical background and variable soil organic matter contents are scanned at two laboratories. The scanning took place with different spectral measurement protocols and extreme diverse conditions in terms of laboratory humidity and moist. All scans are completed by the repeated scans of the two Australian white sands through all scan batches to harmonize the spectral measurements. Our results show that the ISS minimizes the visual spectral variation, aligns the minor and extreme systematic changes of the protocols, and makes them more stable. Furthermore, the LB and WB standards do not exhibit equal performance regarding to relatively dry and humid conditions. The WB standard provides more stable and satisfactory results in humid condition. However, the high performance of the LB sample in spectral correction is still observed, particularly in laboratories with lower moist. Accordingly, these analyses suggest that in the ISS re-alignment procedure, the WB sample i s more reliable to be used in humid laboratory condition.

In situ and laboratory soil spectroscopy with portable visible-to-near-infrared and mid-infrared instruments for the assessment of organic carbon in soils

Authors: Hutengs, C; Seidel, M; Oertel, F; Ludwig, B; Vohland, M

Source: GEODERMA, 355 13900-13900; DEC 1 2019

Abstract: Mid-infrared (MIR) spectroscopy has been established as a rapid and cost-efficient laboratory analysis technique for soil organic carbon (SOC) concentrations. Current portable, high-performance handheld MIR instruments have opened the opportunity to take the technique from the laboratory to the field. We tested the potential of handheld MIR spectroscopy for SOC estimation with field spectral data against parallel VIS-NIR measurements and further evaluated the impact of soil state (in situ, dried, ground) on the accuracy of SOC prediction models. MIR and VIS-NIR data were collected for a set of 90 soils from 90 agricultural loess sites in Central Germany in the field, (i) in situ on the soil surface, and in the laboratory, on (ii) dried and sieved (< 2 mm), and (iii) dried, sieved and ground sample material (similar to 10 mu m). Multivariate calibrations for SOC for each pre-treatment were evaluated with a repeated double cross-validation (rdCV) analysis and the Kennard-Stone (KS) calibration sampling approach. MIR calibrations were more accurate than VIS-NIR calibrations for samples measured under the same conditions in each case with lower RMSE values from 27 to 56% in the rdCV and from 15 to 61% in the KS approach. Sample pre-treatment in the laboratory had a pronounced effect on calibrations in the MIR as models developed on finely ground samples (R-rdCV(2) = 0.86, RMSErdCV = 0.11%) were more accurate than those for dried and sieved samples (R-rdCV(2) = 0.79, RMSErdCV = 0.13%), but differences in the VIS-NIR were negligible. SOC estimates with in situ MIR measurements were less accurate due to spectral variation induced by surface heterogeneity and soil moisture but compared favourably against VIS-NIR data (R-rdCV_MIR(2) = 0.63, RMSErdCV_MIR = 0.17% vs R-rdCV_VIS-NIR(2) = 0.39, RMSErdCV_VIS-NIR = 0.23%). Our findings show that portable MIR spectroscopy can achieve superior SOC calibrations to the VIS-NIR range with in situ data demonstrating its applicability for the on-the-go acquisition of spectral ! soil information in the field. Handheld MIR instruments thus have the potential to facilitate quantitative applications in proximal soil sensing, although with less accuracy than achievable with pre-treated samples in the laboratory.

Alternative approach to calculate soil hydraulic-energy-indices and -functions

Authors: Armindo, RA; Wendroth, O

Source: GEODERMA, 355 13903-13903; DEC 1 2019

Abstract: Soil physical quality (SPQ) is related to soil health and many studies have applied these indices manifesting soil structural behavior. A widely used hydraulic function in this analysis is the soil water retention curve (SWRC) and its integration holds important information, which reflects SPQ diversity. Usually, the SWRC is mathematically describing the relationship between volumetric soil water content (theta) and suction head (h) in the functions theta(h) and h(theta), in which h >= 0 and 0 < theta < 1. Geometrically, a logic way to describe the SWRC is applying the logarithm to the values of h to build the function theta(log(10)h) or log(10)h(theta), however, in this case the graph usually begins at h = 1, since log(10)(1) = 0. In several studies, the concept of the integral integral theta(h)dh [or integral h(theta)d theta] has been presented in the literature since 1978. Unfortunately, the integral integral log(10)h(theta)d theta should be used for h >= 1 in order to avo id negative results generated from the domain 0 < h < 1, which would be integrated to the final area under the SWRC. Furthermore, since the fitted values of the parameters of the Van Genuchten-Mualem (VGM) equation are different when functions theta(h) and theta(log(10)h) are used, results of water content at saturation (theta(s)), permanent wilting point (theta(pwp)) and field capacity (theta(fc)) are different as well, questioning the applicability of the integral integral log(10)h(theta)d theta. The objective of this study was to develop a novel approach to calculate hydraulic-energy indices and to improve their capacity to reflect SPQ differences. In this approach, the function theta(h) was parameterized in order to find results for theta(s), theta(pwp) and theta(fc). Then, the function theta(log(10)h) was parameterized to obtain results for theta(s-pF), theta(pwp-pF) and theta(fc-pF), which were tested against theta(s), theta(pwp) and theta(fc). A total of 72 SWRCs were analysed with both functions theta(h) and (log(10)h). Resul! ts showed that the limits of integration theta(s-pF), theta(pwp-pF) and theta(fc-F) remained the same by keeping the same ranges of available water and drainable porosity, as in the case when the function theta(h) was used. This new approach turned out more suitable than the original approach for calculating hydraulic-energy indices, because it was more sensitive to reveal SPQ differences.

Mapping LUCAS topsoil chemical properties at European scale using Gaussian process regression

Authors: Ballabio, C; Lugato, E; Fernandez-Ugalde, O; Orgiazzi, A; Jones, A; Borrelli, P; Montanarella, L; Panagos, P

Source: GEODERMA, 355 13912-13912; DEC 1 2019

Abstract: This paper presents the second part of the mapping of topsoil properties based on the Land Use and Cover Area frame Survey (LUCAS). The first part described the physical properties (Ballabio et al., 2016) while this second part includes the following chemical properties: pH, Cation Exchange Capacity (CEC), calcium carbonates (CaCO3), C:N ratio, nitrogen (N), phosphorus (P) and potassium (K). The LUCAS survey collected harmonised data on changes in land cover and the state of land use for the European Union (EU). Among the 270,000 land use and cover observations selected for field visit, approximately 20,000 soil samples were collected in 24 EU Member States in 2009 together with more than 2000 samples from Bulgaria and Romania in 2012. The chemical properties maps for the European Union were produced using Gaussian process regression (GPR) models. GPR was selected for its capacity to assess model uncertainty and the possibility of adding prior knowledge in the form of covaria nce functions to the model.The derived maps will establish baselines that will help monitor soil quality and provide guidance to agroenvironmental research and policy developments in the European Union.

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