Anchorage Mechanics of the Tap Root System of Winter-sown Oilseed Rape (Brassica napus L.)

The anchorage mechanics of mature winter-sown oilseed rape (‘Envol’) were investigated by combining a morphological and mechanical study of the root system with anchorage tests on real and model plants. Oilseed rape plants were anchored by a rigid tap root; the few laterals all emerged below the centre of rotation of the root system (approx. 30 mm below the soil surface). When plants were pulled over, the tap root bent and the top 30 mm moved in the soil towards the direction of pull, creating a crevice on the opposite side. The maximum anchorage moment was 2.9 ± 0.36 N m. Two main components of anchorage were identified: the bending resistance of the tap root and the resistance of the soil on the near side to compression. The relative importance of these components was determined by measuring both the bending resistance of the tap root, and the resistance of metal tubes of varying diameter, inserted to various depths in the soil, to being pulled over. These tests showed that the tap root bending moment at failure could account for around 40% of anchorage moment, while soil resistance could account for around 60%. The model tests on the tubes also help to shed light on the way in which the dimensions of tap roots will influence their anchorage capability.