Root Growth of Astragalus mongholicus and A. membranaceus as Affected by Soil Compaction

Our previous field experiment showed that the soil hardness affects the root growth of Astragalus mongholicus (AO) and A. membranaceus (AE), and the taproot elongation of AE is more sensitive to hard soil than that of AO. In the present study, the effects of soil compaction on the root and shoot growth of AO and AE, and on the amounts of glycosides and dilute ethanol-soluble extract in taproot of AE were determined more precisely by using PVC tubes (length 80 cm and inside diameter 10.5 cm) of four levels of soil compacting. The soil penetration resistance above 10.0 kg cm^-2 did not affect shoot growth, but it significantly shortened the taproot length of both species, decreased the dry weight of taproot of AE, increased that of AO, as implied in the previous paper. Promotion of branching magnitude of 1st order lateral root was higher in AE. The amounts of astragalosides -I, -II, -III, -IV, total astragalosides and dilute ethanol-soluble extract in taproot of AE linearly increased as the soil compaction decreased, whereas those of isoflavonoids -III, -IV, -V and total isoflavonoids were the lowest in the least compacted soil plot, as implied in the previous field experiments. Astragali radix with uniform quality and less thick lateral roots should be obtained when the plants are grown in the field having soil penetration resistance < 10.0 kg cm^-2 .