Sugar beet (cv. Ascend) was grown in fields of soft haplic andosols and dense dystric cambisols to compare root system formation in soils with different physical properties. These root systems were analyzed using the root-model method and root length density. Three root types were classified according to root diameter, which were, in descending order of root diameter: primary lateral root > secondary lateral root > tertiary lateral root. In haplic andosols topsoil, the secondary lateral root rather than the primary lateral root became the foundation of the root system and was also the parent root for lateral root production at the mid-growth stage (10-19 weeks after transplantation). The primary lateral root acted mainly as the conducting system at the late-growth stage (19-23 weeks after transplantation). In dystric cambisols topsoil, root length density of the primary lateral root increased at the mid-growth stage. Toward the late-growth stage, the primary lateral root acted as the parent root of the secondary lateral root and the tertiary lateral root. These results suggest that the primary lateral root developed as the foundation of the root system and functioned as the parent root until the mid-growth stage, which encouraged the development of the whole root system toward the late-growth stage. The increase in root weight was proportional to root total weight and root sugar content. The increase in root length density of the tertiary lateral root suggests that the tertiary lateral root is most important for water and nutrient absorption in sugar beet.

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