Abstract:Obsticals for recropping are especially severe in the production of Rehmannia glutinosa, a Chinese medicinal herb. It taks 8 to 10 years before one can replant a Rehmannia glutinosa to the same field where the crop had been grown. In this study, five different solvents were used to extract potential autotoxins from the soil samples taken from a major Rehmannia glutinosa production area in Jiao-zuo，Henan Province after harvesting the crop. Bioassy was conducted to test the inhibiton rate (IR) of the five soil extracts on Rehmannia glutinosa radicle growth. Soil extract that had the greatest IR was selected for a greenhouse growth study and various physiological and biochemical parameters were measured. Finally, HPLC analysis was used to compare soil extracts with root exudates, and ESI-MS analysis was used to identify the chemical compositions of the soil extracts. Bioassy results demonstrated that water and methanol extracted soil autotoxins had the greatest IR; by adding 0.5 g/mL concentration of soil extracts to a germination study, the IR to Rehmannia glutinosa radicle growth was 17% and 26% for water and methanol extracts, respectively, and the IR reached above 70% when the concentration was increased to 5.0 g/mL. Greenhouse study exhibited that methanol extracted soil autotoxins had resulted in (1) decreased root activities and chlorophyll contents，(2) decreased activities of SOD, CAT, and POD, (3) enhanced membranaceous peroxidation, and (4) decreased growth hormones contents. HPLC analysis showed very similar chromatograms between the methanol extracts and the root exudates. ESI-MS analysis detected six characteristic substances: vanillic acid, D-mannitol, 2\[4′-hydroxyphenyl\] -ethyl hexacosanoate, verbascoside, β-sitosterol, and daucosterol.