Ponded infiltration experiment is a simple test used for in-situ determination of soil hydraulic properties, particularly saturated hydraulic conductivity and sorptivity. It is known that infiltration process in natural soils is strongly affected by presence of macropores, soil layering, initial and experimental conditions etc. As a result, infiltration record encompasses a complex of mutually compensating effects that are difficult to separate from each other. Determination of sorptivity and saturated hydraulic conductivity from such infiltration data is complicated. In the present study we use numerical simulation to examine the impact of selected experimental conditions and soil profile properties on the ponded infiltration experiment results, specifically in terms of the hydraulic conductivity and sorptivity evaluation. The effect of following factors was considered: depth of ponding, ring insertion depth, initial soil water content, presence of preferential pathways, hydraulic conductivity anisotropy, soil layering, surface layer retention capacity and hydraulic conductivity, and presence of soil pipes or stones under the infiltration ring. Results were compared with a large database of infiltration curves measured at the experimental site Liz (Bohemian Forest, Czech Republic). Reasonably good agreement between simulated and observed infiltration curves was achieved by combining several of factors tested. Moreover, the ring insertion effect was recognized as one of the major causes of uncertainty in the determination of soil hydraulic parameters.
The idea of the present study is to describe the spatially varying particle size distribution (PSD) along intact aggregate surfaces with the laser diffraction method (LDM) of four silty-loamy and OC enriched horizons of a Dystric Cambisol from the Uhlířská catchment (Czech Republic) with the laser diffraction method (LDM). Besides, the comparability of the LDM with the sieve and pipette method (SPM), the reproducibility, and the effect of pretreatment on the particle size distribution derived by LDM were analysed. The laser diffraction method enables rapid and continuous particle size distribution measurements with required sample amounts of 0.1–0.2 g for each measurement compared to 5–20 g for SPM. The LDM-derived PSD’s can be directly compared with the standardised SPM-derived PSD’s by using regression analysis with coefficients of determination (r²) between 0.83 and 0.93. Sample pretreatment following standardised proceedings indicates a better comparability between the particle size distributions of both methods. Besides, the highest coefficients of variation of up to 78.6 and therefore the lowest reproducibility were found for the unpretreated PSD of the AE and Bs horizon. Thus, limited evaluability and reproducibility of soil material enriched in organic carbon (OC), used in the current study, needs further analysis. For spatial analysis of PSD’s along intact surfaces of soil aggregates and profiles, spatial data interpolation by inverse distance weighting (IDW), kriging, and triangulated irregular networks (TIN) can be used for detailed measuring, mapping, and spatial extension of the sand, silt, and clay fractions at unsampled locations using a set of samples of known locations. The information offers the possibility of comparing and verifying data obtained by non-invasive midinfrared spectroscopy and Vis–NIR spectroscopy by spatial extension for given soil aggregates and profiles.