Abstract
To assess the allelopathic effect of velvetbean (Mucuna pruriens var. utilis), the weed appearance and population in fields with continuous cropping of velvetbean and other crops were examined in spring. The effect of crude extracts of velvetbean leaves on the emergence and growth of some weeds and crops was also analyzed. The results obtained are summarized as follows
1. The weed population in fields after continuous cropping of velvetbean, upland rice, egg plant, and tomato plant was investigated in early spring. In the velvetbean plot, weed emergence was minimal, compared to the other plots, in which Cerastium glomeratum was the dominant weed (Table 1).
2. Weed emergence and growth in the soils of these plots were observed (Table 2). The weed population of the velvetbean plot was about 1/2 of that of the fallow plot and 1/4 of that of the plots with other crops. However weed growth was similar in these plots.
3. Emergence and growth of lettuce in the soils of these plots were observed during a two year period (Table 3). Although the emergence and hypocotyl length were not affected, radicle growth was reduced significantly in the plot with continuous cropping of velvetbean for 5 years. In the soil where velvetbean had been cultivated for one year, the growth of lettuce seedlings was not appreciably reduced.
4. The effect of crude methanol extracts of velvetbean leaves on the emergence and growth of some weeds and crops was analyzed (Table 4). At the concentration of 1, 000ppm, the growth of Cerastium glomeratum and lettuce was markedly reduced. It is considered that the presence of allelopathic chemicals may account for the small amount of weeds in the fields with continuous cropping of velvetbean.
