A replacement series experiment under greenhouse conditions was carried out to evaluate the effects of ferulic acid (4-hydroxy-3-methoxy-t-cinnamic acid) on soybean [Glicine max (L.) Merr. cv. Bragg] and redroot pigweed (Amaranthus retroflexus L.) plant density combinations. Soybeans and redroot pigweed were combined at 4:0, 3:2, 2:4, 1:6 and 0:8 plants per pot. Ferulic acid dosages used were zero, 500 and 1000 ppm. A randomized block design with four replications was used. The duration of the experiment was 33 days. For ferulic acid dosages of 500 and 1000 ppm, delays in soybean emergence of 2 and 3 days respectively were observed. Soybean plant height was increased at lower soybean: pigweed rates and at higher ferulic acid dosages; the opposite was observed in pigweed. Soybean shoot and root dry weights decreased as the number of soybeans plants increased, in contrast to pigweed. Higher doses of ferulic acid reduced shoot dry weight and relative total yield of pigweed. Intraspecific competition in pure stands was higher for soybeans than pigweed. Soybeans were more competitive than pigweed up to the harvest time at 33 days. Ferulic acid affected redroot pigweed competitiveness to a much higher degree than that of soybeans.
Glycine max; Amaranthus retroflexus; allelopathy; interference