Canopy closure of Chinese milk vetch (Astragalus sinicus L.) onrice-Chinese milk vetch rotation system [Japanese]

摘要

Rice-Chinese milk vetch was cultivated by a rotation system from 1994 to 1997 to examine the effect of rice straw on the establishment and growth of Chinese milk vetch. Chinese milk vetch was sown in rice stands. Rice was sown under 2 different land preparation conditions; no-tillage (NT), i.e., sod-seeded, and tillage (TA), in which green Chinese milk vetch and rice straw from the previous year were incorporated into the soil. A poor establishment of Chinese milk vetch in the NT plot was observed only in 1996. The percentage of canopy closure of Chinese milk vetch in both treatments decreased year by year, especially in NT:40%, 15%, and 5% in 1995, 1996, and 1997, respectively. When rice straw was removed after rice harvest in the NT plot, the canopy closure of Chinese milk vetch was fairly recovered. The seedlings of Chinese milk vetch planted on soil collected from the NT plot showed poor growth, compared with those planted on soil collected from the TA plot. When rice straw was put on the soil surface, the seedling growth was inferior to that on the bare surface, especially the root growth. These results suggested that an allelopathic substance released from rice straw inhibited the establishment and growth of the seedlings of Chinese milk vetch.