Characterisation of soil pore structure anisotropy caused by the growth of bio-subsoilers

Deep-rooting cover crops (tap-rooted plants and grasses) are suggested to enhance soil properties when used as bio-subsoilers in compacted soils. However, there is limited knowledge the impact of bio-subsoilers on anisotropy of the soil pore system of compacted zones. The objective of this study is to evaluate the impact of different biosubsoiler species on the anisotropy of the soil pore characteristics of a compacted sandy loam subsoil. The experimental treatments consisted of spring barley as control and chicory, lucerne and tall fescue as biosubsoilers. The soil samples were taken in both vertical and horizontal directions at 0.3-0.4 m depth. Air permeability (k(a)) and air-filled porosity (epsilon(a)) were quantified at-10,-30,-50,-100 and-300 hPa matric potential, and X-ray computed tomography (CT) scans were obtained for samples drained at-100 hPa. Results showed no significant treatment effect (p < 0.05) on k(a), the ratio of the non-Darcian to the Darcian air permeability (R), or the PO1 index (k(a)/epsilon(a)) in either vertical or horizontal directions. However, the factor of anisotropy of k(a), PO1 and R-ratio was significantly affected by chicory and lucerne (p < 0.05), indicating the creation of more vertically than horizontally oriented pores. The results from measured parameters were supported by CT image analysis as macropores connecting from end-to-end of the soil cores were mainly captured for vertically oriented samples by the CT scanner. Lucerne had significantly larger proportion of CT-macroporosity (~50%) and CT-total branch length (~40%) for vertically connected pore network as compared to spring barley (~20% for both parameters). This study suggests that the impact of growing bio-subsoilers on the anisotropy of the soil pore system of the studied compacted subsoil is species-dependent.

Automated summary

This study evaluates the impact of different bio-subsoiler species on the anisotropy of soil pore characteristics in a compacted sandy loam subsoil. The results indicate that chicory and lucerne bio-subsoilers significantly affect the anisotropy of the pores, creating more vertically oriented pores.