soybean, BNF, nitrogen, genetic gain, seed weight


Genetic gain is characterized by comparing the performance of genotypes from a different year of release. Historic studies are useful to understand changes in yield-related traits that also contribute to yield potential. This study aims to quantify yield improvement for soybean through a set of seven genotypes with different years of release, and their respective numerical components, with a focus on final seed weight generation under two different nitrogen (N) conditions. Changes in biological N fixa­tion (BNF) were quantified during the seed-filling period (SFP). Non-linear models were fit to the data to characterize seed weight and BNF changes throughout the SFP. Genetic gain led to an overall yield increase of 0.49 bu/a/year mainly explained by increases in the seed number rather than seed weight. Nitrogen application increased yield equally across genotypes (P < 0.01), and final seed weight in all genotypes tested. Biological nitrogen fixation activity was reduced by 44% at the onset of the SFP, however, no N deficiencies were observed.


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