This study was conducted to investigate the effect of competition with various weed densities on crop plants in soybean fields. As the density of weed decreased, the biomass production of soybeans increased, and the soybean yield was also high in plots with low weed occurrence density. The weed species that were dominant in the field were Cyperus iria, Eclipta prostrata, Portulaca oleracea, Mollugo pentaphylla, Galinsoga parviflora, Acalypha australis, and Amaranthus retroflexus. The diversity of weeds was lower in the plot in which weed density was lowered. The hyperspectral reflectance by weed density was different not only in soybean but also in weeds and was affected by the time of the investigation. At 21 days after flowering (DAF) at which water requirement is high in soybean, the hyperspectral reflection was lower than that of weeds, and at 42 DAF, the hyperspectral reflection of weeds was lower than that of soybeans. The carotenoid indicators (CI), known to be related to water stress in plants, was higher than that of weeds at 21 DAF, and at the higher weed density, weeds are higher than soybeans, and it is estimated that the more weeds occur, the more weeds are superior to soybeans in competition for water. When comparing the pigment specific simple ratio (carotenoids) (PSSRc) related to carotenoid level by the weed densities, the index of soybean at the low weed density and medium density decreased at 42 DAF compared to the value at 21 DAF.
Figures & Tables
Fig. 1. Dry weight of total weeds and soybean plants according to the weed density in the soybean field (A: 21 days after flowering [DAF], B: 42 DAF).