Summary:

The aim of the study was to assess the root system distribution of two Catalpa species - Catalpa bignonioides and Catalpa ovata - grown in row plantings on light soil under subsurface drip irrigation. The soil profile method by Oskamp was used to analyse the vertical and horizontal root system structure, including root diameter classes. The experiment was conducted in a split-plot design with two irrigation treatments (W1 - irrigation at -40 kPa soil water tension; W2 - at -20 kPa) and compared with a non-irrigated control (W0). For both species, most roots were located within the 0-30 cm soil layer; however, C. ovata developed a deeper root system, reaching 60 cm under intensive irrigation (W2). Irrigation increased the number of fine roots (<1 mm), which dominated the root structure and accounted for more than 60% of all roots. Both species showed a clear response to the applied irrigation variants, with a stronger effect observed in C. ovata. The results confirm that subsurface drip irrigation promotes root development in the surface layer and increases the total number of roots, which may support tree survival and stability in light soils and water-deficient conditions.