Do Weeds From Seeds or Regrowth in Coexistence Periods Alter Biochemical and Yield Characteristics of Soybeans?

The objective of this study was to evaluate changes in soybean secondary metabolism and soybean yield components when subjected to coexistence periods with volunteer corn and established horseweed (Conyza spp.) regrowth. Two field experiments were conducted in the agricultural years 2015/2016 and 2016/2017 at Passo Fundo University, Passo Fundo, Rio Grande do Sul, Brazil. Experiment I was conducted in the agricultural year 2015/2016 in order to establish periods of coexistence between soybean and corn. The treatments consisted of two soybean densities in the main plots (175,000 and 350,000 plants ha-1) and different periods of coexistence between soybean and corn in the subplots. Experiment II was conducted in the agricultural year of 2016/2017 in order to investigate the interference of regrowth horseweed during coexistence periods with soybean. The total phenols, flavonoids, saponins, soybean yield components and seed yields were evaluated. Volunteer corn that initiates growth after the V4 soybean stage and horseweed regrowth during cultivation do not adversely affect secondary metabolism, seed yield or soybean yield components.