Impact of potential bio-subsoilers on pore network of a severely compacted subsoil

Subsoil compaction is a major threat to soil quality. The use of bio-subsoilers has been proposed as a mitigation practice. There is, however, a paucity of knowledge on the effects of potential bio-subsoiling crops in alleviating severely compacted subsoil. X-ray Computed Tomography (CT) was used to assess the changes caused by different crops in the pore network of a severely compacted subsoil. The potential bio-subsoilers, chicory, lucerne, radish and tall fescue, with spring barley as reference, were grown for one year in undisturbed soil columns (empty set = 0.20 m, h = 0.50 m) with soil originating from a heavily compacted soil after mechanical impact. Soil columns were X-ray CT-scanned before and after the experiment. CT-pore soil characteristics were quantified by image analysis. Crop treatments affected the soil porosity differently on the studied soil. Radish and tall fescue did not show a significant impact on CT-derived pore characteristics at any depth. In the compacted layer, the macropore density, the branches number, and the number of pores (for volume sizes of < 100 mm(3) and diameter <= 1.5 mm) were larger for chicory and lucerne compared to barley (P < 0.05). Chicory and Lucerne appear to contribute to the development of a large number of complex-shaped pores. Differences in the CT-derived pore network indicate that chicory and lucerne are likely to perform better than the other crops when used as bio-subsoilers by creating a larger, more connected and complex pore network. Longer-term growth is needed to obtain a marked loosening effect in the compacted layer.