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Processes at the soil-root interface shaping soil functions (Communication session)

EUROSOIL2020CONT-2347

EFFECTS OF COVER CROP ROOT TRAITS ON SOIL SHEAR STRENGTH

Matthieu Forster^{* 1}, Mathieu Lamandé^{2, 3}, Carolina Ugarte¹, Michel-Pierre Faucon¹

¹Unilasalle, Beauvais, France, ²Norwegian University of Life Sciences, Norway, ³Department of Agroecology - Soil Physics and Hydropedology, Aarhus University, Denmark

Content: Compaction induced by machinery in agriculture represents a major threat for soil functionality. Solutions exist to cope with compaction as reducing stress induced during traffic or improving soil resilience. Improving soil strength using roots could be part of the solution. Soil reinforcement by roots has been investigated to prevent landslides and improve riverbank stability. However, differences in soil and root properties, and in the rate and range of deformation exist between landslides or riverbank stability and traffic-induced compaction of agricultural soils. The objective of this study was to investigate the relationships between root traits of cover crops and soil shear strength

Three cover crop species presenting a contrasted root morphology were grown in controlled conditions (access to water, temperature, exposition to light, etc.) in pots containing a remoulded loamy sand: Secale cereale, Brassica napus and Vicia faba. Twelve pots were produced for each species. In addition, twelve pots were left unplanted as control condition. At the flowering stage of the plants, the pots were subjected to direct shear using a direct shear box. The direct shear tests were performed at a constant strain rate of 3 mm min^-1 for six specific normal loads of 25, 34, 44, 63, 83 and 93 kPa. Consequently, two shear tests per species per normal load were performed, giving twelve points for determination of the cohesion and angle of internal friction using the Mohr-Coulomb approach. Root characteristics were then measured as the length, the volume and the dry mass and compare to the root effects on soil strength.

The pots containing Vicia faba had a higher cohesion and angle of internal friction than the pots containing Secale cereale or Brassica napus. Cohesion and angle of internal friction were not significantly different for the pots containing Secale cereale, Brassica napus or the bare soil, indicating that the presence of roots did not necessarily increase soil shear strength. Vicia faba showed the largest root volume and root mass per soil volume. The results showed that soil shear strength was not related to the root length nor the presence of a tap root.

The root traits of Vicia faba indicated that soil reinforcement was due to the root volume per volume of soil provide by the whole root system. This exploratory study suggests the use of the root volume per soil volume as an indicator of soil reinforcement by roots of cover crops. More research is needed to generalize these preliminary results.

Disclosure of Interest: None Declared

Keywords: Compaction, Root traits, Soil resistance