Abstract: Soil compaction is one of soil restricting factors for greenhouse vegetable production. The effects of bulk density of 1.20（D1.20），1.35（D1.35）and 1.58 g ? cm-3（D1.58）in sandy loam on seedling growth and root architecture of tomato were investigated using soil columns in greenhouse. The results showed that leaf elongation rate，plant height，plant water content，fresh and dry weight，root to shoot ratios were negatively correlated with soil bulk density. Root surface area，root length density and root volume density also decreased significantly with increasing soil bulk density. High bulk density inhibited root penetration to deep soil，and consequently influenced root distribution，e.g. roots were confined to the top 6 cm soils in D1.58 treatment. In soil profile，the distribution of root mass，root surface area，root length density and root volume density decreased significantly with increasing soil bulk density. In root hair zone，root invagination and cell deformation occurred in outer cortex under D1.58，and the roundness（R）and eccentricity（e）of root transverse section increased significantly with increasing bulk density，which indicated that the ability of root uptake would decrease. It is concluded that a decrease in soil cultivation layer would inhibit root growth of the deep-root vegetables such as tomato plant.

Key words: tomato, soil bulk density, plant growth, root architecture