Effect of nitrogen fertilization on yield component distribution and assimilate translocation of determinate and indeterminate soybean lines

Studies were conducted to compare the main‐stem and branch yield component distribution of two soybean Glycine max (L.) Merr.] lines differing in architecture and growth habit, and to relate the partitioning of carbon assimilates during pod filling and seed filling stages. An indeterminate line (MI) and a determinate line (MD) were planted in early May on a fine, mixed mesic Udic Haplustalf soil in southwestern France. For the N treatment, N fertigation was applied at the end of the vegetative phase and the early stages of reproductive growth. Pod production on branches was stimulated in response to N application for the determinate line, and N also enhanced the weight of seeds located on branches for both lines. At different stages during pod setting and seed filling, mid‐canopy‐level leaves were allowed to assimilate ¹⁴CO₂ and 24 h after exposure, radioactivity was measured in different organs and levels of the whole plant. ¹⁴C‐assimilates appeared to be preferentially transferred to the lower level of the main‐stem in MI and to the lower level and branches in the MD line. For N‐treated plants, radiocarbon accumulation was particularly marked in pods located on the lower level and on branches; this was consistent with the yield component distribution patterns seen at harvest.