Effects of competition with weeds on growth, development and yield of soyabeans.

Two field experiments were carried out in the inland Zanderij area of Suriname to study competition between soyabeans and weeds. The crop was kept weed-free or without weed control for increasing periods of time after sowing. An analysis of the growth and development of a crop with weed control and of a crop without weed control was obtained by making observations at the end of each period of time with or without weed control. Uncontrolled weed growth concentrated mainly between the rows. Competition with weeds reduced ground cover and LAI of the crop, leading to a lower weight and yield. Plant density was not affected, but weed competition reduced the number of branches, inflorescences, and pods per plant. Timing of flowering was not influenced. Competition for water was inferred and competition for light seemed likely. Competition for nutrients was weak. Weeding in the period of pod initiation, i.e. around 45-70 days after sowing, appeared to be essential to avoid competition with weeds. A period of around 4 weed-free weeks after sowing was necessary to avoid yield reduction or too much weed growth at harvest. (Abstract retrieved from CAB Abstracts by CABI’s permission)