Soil macroporosity in relation to subsurface drain location on a sloping clay field in humid climatic conditions
Alakukku, L. | Nuutinen, V. | Ketoja, E. | Koivusalo, H. | Paasonen-Kivekäs, M.
Macroporosity of soil and earthworm abundance in relation to the distance from subsurface drain lines were determined to investigate the effect of subsurface drainage on the spatial variation of clay soil structure. Our hypothesis was that soil macroporosity near a drain line location would be greater than the macroporosity at a midpoint between two drain lines where the groundwater table remains theoretically at a higher level. The experimental site was located on a post-glacial clay soil classified as a very fine Aeric Cryaquept (Vertic Cambisol). The area of the field was 1ha and the slope varied from 2 to 4%. Measurements of soil properties were carried out along four subsurface drain lines installed 50 years before soil sampling. In each drain line, vertical soil profiles were examined at different distances from the drain: (1) above the drain, (2) 2m from the drain, and (3) midway between two drains (6-7m from a drain). In each vertical profile, soil macroporosity, number of earthworm burrows and root channels, and saturated hydraulic conductivity (K sat) were determined in three soil layers to the depth of 50cm. In addition, the field saturated hydraulic conductivity (in situ) and the number and fresh mass of earthworms were determined. The results showed that the number of earthworm burrows was 44% (90 burrowsm⁻²) greater above a drain than at a distance of 6-7m from the drain. There was also an indication of higher earthworm density above the subsurface drains than between them. The other measures of soil physical properties were not clearly related to distance from the drain. One reason for the small differences in soil properties in relation to drain position was probably the groundwater level that in our clay field varied less in relation to drain location than was expected. Spatial variation of the investigated soil properties was mostly explained by the slope of the field. Even though the groundwater table was shallower at the downslope part compared with the upslope part of the field, the number of biopores, K sat and the number of earthworms clearly increased downslope.Show more [+] Less [-]