Abstract
We examined the effects of sowing time, sowing density, and timing of weeding on the growth of winged bean as a cover crop to reduce soil erosion and improve soil fertility and on weed control at a subtropical site. Winged bean was sown in March (spring), May, or July (summer) and harvested in November. Growth tended to be better with later sowing, with or without weed control. Periodic weeding of Bidens pilosa var. radiata was needed in the March- and May-sown crops, but it might be possible to grow winged bean without weeding if it is sown in July. In addition, increased sowing density in weeded plots tended to enhance crop growth. Soil coverage reached 90% at 7 weeks after sowing at the highest density (49 hills per plot). However, even so, crop production in unweeded plots was half and weed biomass was double the values in the weeded plots. In the presence of fertilizer (10 g N, P2O5, K2O m–2), crop growth was affected by neither the number nor timing of weedings. Crop growth decreased slightly at 6 to 8 weeks after sowing, when soil coverage increased, possibly because the plants were damaged by hand weeding. One weeding at 4 weeks after sowing reduced the weed biomass to less than 1/3 of that in the unweeded plots. These results show that to grow winged bean as a cover crop to control weeds in summer, it is necessary to weed once in the early growth stages.
