Using undisturbed soil samples to study how rock fragments and soil macropores affect the hydraulic conductivity of forest stony soils: Some methodological aspects

Forest stony soils have rock fragments and many macropores, the latter arising mainly from the activity of soil fauna and plant root decay. We still lack knowledge about the hydraulic properties of this type of soil, especially when considering the influence of both factors - rock fragments and macropores - on the saturated hydraulic conductivity. This research aims to supplement the method we proposed before to test the hydraulic conductivity of undisturbed soil samples (Ilek and Kucza, 2014; Kucza and Ilek, 2016). We propose to enhance the method by taking into account the impact of rock fragments and macropores on the hydraulic conductivity of forest stony soils, particularly on the hydraulic conductivity of the medium conducting water in the soil, that is, soil matrix. We studied, using artificial samples, how rock fragments influence hydraulic conductivity. To test the enhanced method, we used 33 undisturbed samples taken from the top layers (0-12 cm) of forest stony soils. The results show that rock fragments in the soil can both increase and decrease the infiltration of water by the soil matrix. Rock fragments with diameters close to 20 mm had the least influence on water infiltration. Soil macropores in the samples always increased water infiltration. Empty macropores increased it from two to twenty-four times while filled macropores from three to five times. Our method gives the opportunity to study the hydraulic conductivity of macropores and their physical and chemical properties.