Soil reinforcement potential of cultivated cardoon (Cynara cardunculus L.): First data of root tensile strength and density.

Plant roots play a key role in erosion control by increasing soil resistance to shear stress. Root tensile strength data have been published for natural systems, less is available on cultivated crops. Cardoon (Cynara cardunculus L.) is raising a growing interest as multipurpose crop for marginal lands. In this work we measured cardoon roots tensile strength, topsoil root area ratio, root length density and estimated soil reinforcement potential. Root samples were collected in late spring and at the beginning of fall and were subjected to tensile strength tests in laboratory. Tensile strength (σmax) ranged between 1.57 and 254.78 MPa, decreasing with by a power-law relationship with high determination coefficients (>0.75), with differences between summer and fall roots. We measured root length density (RLD) and root area ratio (RAR) in surface soil (top 5 cm) at different positions in the row and inter-row. RAR was used to calculate soil reinforcement potential (Cr = 1.2 * Σ σmax (kPa) * RAR (cm2 cm-2)). Average RLD was quite high 8.68 cm cm-3 with a mean value of 9.183 cm cm-3 on the row and 8.179 cm cm-3 on the inter-row, though differences between row and inter-row, were not significant. RAR was on average 0.017 cm2 cm-2. Average soil reinforcement was 194 kPa with values ranging from 67.34 kPa to 265 kPa. This is not to be interpreted as absolute reinforcement values, due to drawbacks of the simple model used, but they are useful for comparisons within the framework of crop choices. Cardoon produces a dense mat of fine roots that can contribute to increase soil cohesion, thus providing important ecosystem services.