Effect of Row Spacing and Soybean Genotype on Mainstem and Branch Yield

Received for publication November 2, 2004. Partitioning of soybean [Glycine max (L.) Merr.] seed yield between mainstem and branch fractions across row widths and genotypes at recommended seeding rates is not well understood. A field experiment was conducted to evaluate the distribution of seed yield between mainstem and branch fractions of eight soybean genotypes grown in narrow (19 cm) and wide (97 cm) rows at recommended seeding rates. In contrast to adequate rainfall throughout the crop season in 2002, a lack of rainfall during reproductive development in 2003 caused differences in mainstem and branch yield components between years. Mainstem seed yields, averaged over years and genotypes, accounted for 45 and 69% of the total yield in wide and narrow rows, respectively. Mainstem seed yields, averaged over years and row widths, ranged from 62 to 142 g m^–2 among genotypes. Ranking of mainstem and branch yields among genotypes was stable over environments. Similarly, row width did not influence mainstem yields among genotypes, but genotype branch yields in wide rows were different from those in narrow rows. Branch seed yields in narrow rows, averaged over years, ranged from 14 to 57% of total seed yield while 47 to 74% of total seed yield was produced on branches in wide rows. This research demonstrates considerable differences exist in mainstem and branch yields among genotypes and that genotypes having superior branch yield should be selected for wide rows while mainstem yield should be used as a selection criteria for narrow rows.