Morphological and Pull-Out Mechanical Properties of Alfalfa Roots in the Seedling Stage

PurposeThe mechanical properties of plant roots in the early growth stage are not clear, which limits the application of plants in soil reinforcement and slope protection. Thus, this study tried to understand the structure and root pull-out resistance of plants in the early growth stage.MethodsMorphological investigation and pull-out tests of alfalfa (Medicago sativa L.) were carried out in two soil types (clay loam and loamy sand) at four soil bulk densities (1.1 g center dot cm-3, 1.2 g center dot cm-3, 1.3 g center dot cm-3, and 1.4 g center dot cm-3).ResultsThe morphological and mechanical characteristics of alfalfa were closely related to the growth days. Alfalfa root morphology parameters changed following linear with the growth days. The pull-out force increased in a power-law manner with the growth days while duration of pulling and total root pull-out length of alfalfa increased exponentially with the growth days. No remarkable effect of soil types was observed on the morphology and pull-out parameters of alfalfa. Root pull-out force was increased exponentially with the soil bulk density while pull-out length and during of pulling were decreased exponentially with the soil bulk density. The impact of soil bulk density on alfalfa morphology and root pull-out parameters seemed to be significant since the fourth week.ConclusionsIt is suggested that moderate soil bulk density is beneficial to both the growth and root pull-out resistance of alfalfa. Besides, attention should be paid to the physiological and mechanical immaturity of alfalfa in the early growth stage.