Investigation of soil water infiltration at a scale of individual earthworm channels

Abstract

This study focused on the hydraulic efficiency of vertical earthworm channels (henceforth referred to as macropores or channels). The parameters selected for investigation were the rate of change in hydraulic soil conductivity in the channel walls due to compaction, the rate of this compaction, and the wall stability against running and stagnant water. We preferentially tested the variants for infiltration of water flowing from the soil horizons against gravity (e.g. from the level of installation of tile and controlled drainage). The details of influx and infiltration processes were examined both in the field and more thoroughly in the laboratory using an accurate continuous infiltrometer constructed at the Research Institute for Soil and Water Conservation (RISWC), Czech Republic. Both direct measurements and indirect evidence consisted of tests of individual natural macropores directly in the field, as well as tests of intact collected samples and artificial samples with variants of natural, artificially extruded, and cut out tubular macropores. We studied the processes occurring in macropores with diameters of ca. 5 mm and larger. In these particular conditions, we identified the apparent saturated hydraulic conductivity (K_s') of the soil horizons (including macropore-mediated vertical surface infiltration and preferential flow to soil followed by radial infiltration) most frequent as K_i (apparent saturated hydraulic conductivity affected by preferential flow or influx of water) from 50 to 200 cm/h. In some cases, saturated hydraulic conductivity of earthworm channel walls (K_sw) was reduced in the order of tens of percent compared with matrix K_s. The increase of bulk density of soil (ρ_d) in the macropore vicinity reached the maximum of 25%. The intensity of macropore wall erosion (i_er) ranged from 0 to 70 mg/min/dm².