Soybeans and Biological Nitrogen Fixation: A review

A review of 60 studies reporting on biological N fixation (BNF) in soybean was done to study the limits to which BNF can satisfy plant N demand. This review confirmed that BNF could satisfy plant N demand up to 200 kg N/ha. The N-gap (plant N uptake minus fixed N) widened rapidly if plant N demand exceeded 370 kg N/ha, which suggested the need for additional N under conditions of high yield potential. The partial N balance (fixed N minus N removed in seeds) was negative on average but approached neutral or positive values when BNF contributed at least 58% of plant N uptake.