Relationship of Nitrogen Utilization Patterns with Soybean Yield and Seed‐Fill Period

Abstract

A positive relationship generally exists between duration of seed‐fill period (SFP) and seed yield in soybean [Glycine max (L.) Merr.], but exceptions have been reported. The objective of this research was to determine if differences in N2 fixation, N accumulation, or N remobilization could explain inconsistent relationships between duration of SFP and seed yield in soybean. Eight experimental soybean lines were selected, on the basis of differences in SFP and seed yield in previous experiments, to provide lines differing in (i) SFP and seed yield, (ii) SFP but not seed yield, and (iii) seed yield but not SFP. Field experiments were conducted at two locations in Delaware on a Matapeake silt loam (fine‐silty, mixed, mesic, typic Hapluduit) and on a Rumford loamy sand (coarse‐loamy, siliceous, thermic, typic Hapludult). Plant samples were taken at the beginning and at the end of SFP. Nitrogen fixation was determined by isotope dilution. Seed yields ranged from 229 to 290 g m−2; SFP ranged from 35 to 45 d. Nitrogen derived from N2 fixation ranged from 51 to 82%. Lines with short SFP remobilized more N and dry matter than lines with long SFP. Seed yields were not consistently associated with seed N concentration, N remobilized, total N2 fixed, vegetative biomass, dry matter remobilized, or N2 fixed prior to SFP. Yield was positively associated with dry matter production and N2 fixation rates during SFP. The duration of SFP is an important factor in defining yield potential, but the duration and rates of accumulation of N and C during this period determine how much of that potential will be realized.