Comparing Macropore Exploration by Faba Bean, Wheat, Barley and Oilseed Rape Roots Using In Situ Endoscopy

Large-sized biopores in the subsoil can provide rapid access to deeper soil layers and potentially enhance nutrient acquisition. Besides site conditions, the extent of these effects depends on crop root architecture. The aim of this study was to compare barley (Hordeum vulgare L.), wheat (Triticum aestivum L.), oilseed rape (Brassica napus L.) and faba bean (Vicia faba L.) with respect to time of macropore entry, root soil contact and root hair formation. Crops were grown in columns with condensed subsoil and an artificial macropore. Root growth dynamics in the macropore were monitored with in situ endoscopy. After harvest, the share of roots in macropores was quantified. Oilseed rape had many vertical roots with root hairs contacting the pore wall and was the only crop with preferential root growth in macropores. Cereal roots were mostly crossing the pore horizontally, partially with root hairs and partially contacting the pore wall. Nearly all faba bean roots were crossing the pore without root-soil contact. Our results support the notion that the importance of biopores for crop root growth and resource acquisition depends on root architecture. Under the conditions of the study with sufficient water supply and therefore comparatively low penetration resistance, macropores were only marginally used by cereals and faba bean. Oilseed rape roots were apparently much more sensitive to mechanical impedance, and the pores were used more intensively.