We intend to use a marker-facilitated, fast-track, backcrossing scheme to create BNF- and BNF+ activity contrasts as two near-isogenic lines in five different high-yielding contemporary soybean backgrounds – one in each of five maturity groups 0, I, II, III, and IV that can be used in Nebraska and in the other NCSRP states for research aimed at better understanding the relationship between soybean yield potential and the existent routes of N uptake by soybean plants. This project will provide the genetic tools to better characterize the apparent decline in harvest index (and in seed yield) estimates at high-BNF activity. These tools will be available to researchers in the NCSRP states upon completion of this project and more importantly, the findings of future research using these genetic resources can have a profound impact on future soybean genetic improvement and field management practices.