Seeding date, row spacing, and weed effects on soybean isoflavone concentrations and other seed characteristics

Abstract

Soybean [Glycine max (L.) Merr.] seeds contain isoflavones that may have positive impacts on human health. Field experiments were conducted in 2003/2004 in Québec, Canada to determine the effects of seeding date (late May and mid-June), row spacing (20-, 40- and 60-cm) and weeds (presence or absence) on soybean isoflavone concentrations and isoflavone yield. Total and individual isoflavone concentrations were determined by HPLC. Seed yield, and oil and crude protein (CP) concentrations were concurrently determined. Year, seeding date, and weeds affected total and individual isoflavone concentrations, while row spacing had no effect. Total isoflavone concentration was 84% greater in 2003 than 2004. Seeding in mid-June increased isoflavone concentration by 38%, compared with seed ing in May. The presence of weeds increased total isoflavone concentration by 9%. Year, row spacing, and weeds significantly affected seed yields. Seed yields were greatest in 2004, at 20- or 40-cm row spacing, and in the absence of weeds. Seeding date affected CP and oil concentrations. Greater CP concentration was observed with earlier seeding, the reverse was observed for oil. Weeds also affected CP and oil concentrations: higher CP and oil concentrations were observed in weedy and weed-free plots, respectively. Total isoflavone yield was affected by all factors evaluated. Isoflavone yield was greater in 2003 than 2004, with mid-June rather than late May seeding, when seeded at row spacing of 20- or 40- than 60-cm, and without weeds. Finally, negative correlations were observed between isoflavone concentrations and CP concentration and seed yield. It thus seems that certain agronomic practices may need to be tailored specifically to isoflavone production if concentrations in soybean are to be maximized. The negative correlations observed between isoflavone concentrations and other important seed characteristics warrant further research. Key words: Soybean, isoflavone, daidzein, genistein, glycitein, protein, oil, seed yield, weeds, row spacing, seeding date