Assessment of water and air permeability of chernozem supported by image analysis

• We analyze chernozem filtering abilities by laboratory tests and image analysis.
• We simulate pores lost during scanning of structure specimens by spike noise.
• We introduce morphometric indices of pore system connectivity.
• Saturated water conductivity is positively correlated with volumes of active pores.
• Air permeability is positively correlated with index of pore network growth rate.

We aimed at the assessment of water and air permeability of a Haplic Chernozem developed from loess. The laboratory permeability measurements were presented against a number of morphometric indices that characterize the pore system in this soil, and were obtained by computer-aided image analysis on the basis of large resin-impregnated soil opaque blocks. Two indices of soil pore connectivity are proposed, i.e. the index of soil pore network growth rate and the percolation number. Basic soil properties were evaluated (soil texture, TOC, carbonates, pH, particle and soil bulk density, total porosity). The saturated hydraulic conductivity, and soil water content, air capacity and permeability at −15.54 kPa and −9.81 kPa were measured. From the samples with preserved structure, resin-impregnated soil opaque blocks 8 cm × 9 cm in size were prepared and then used for morphological and morphometric structure analysis. The preliminary image analysis was made to find the best representation of the actual chernozem pore system. The images were modified by applying the morphological closing with or without the spike noise, which modelled tiny pores missed during scanning. Consequently, the macroporosity of the images approximated the air capacity at potentials −15.54 and −9.81 kPa. During the extended image analysis, we calculated: the index of soil pore network growth rate; the percolation number; the average cross-sectional size of the pore; the total length of pore path; the relative volume of pores overlapping the left and right, and the top and bottom image edge; the relative volume of pores connecting the left and right and the top and bottom edge of the image. The correlation coefficients between the parameters’ values obtained from image analysis and from laboratory permeability measurements were calculated.The water and air permeability and the air capacity of the chernozem decreased with depth into the soil pedon. With decrease in the saturated hydraulic conductivity, measured in the laboratory, there was a decrease in the relative volumes of pores overlapping the left and right and upper and lower edges of the image, obtained from image analysis. The air permeability was positively correlated with the index of pore network growth rate. Morphological and morphometric image analysis confirmed that the most important parameters determining the transport of fluids in the soil are continuity of the pore system and pore volume. Based on the results obtained from image analysis one can formulate qualitative conclusions concerning the water and air permeability of soil.

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