1. Soybean Nitrogen Aquisition and Utilization

Because of its high seed protein concentration soybean has a huge nitrogen demand, about 350 IbdA for a 65-bu/A crop. The nitrogen is supplied by two acquisition systems that operate in tandem. In early season the plant uses soil nitrate; later its nitrogen is acquired largely through Nz fixation. On highly fertile, Midwestern soils nitrate utilization peaks at about R3 and then declines sharply. With heavy nitrogen fertilization peak nitrate utilization can be extended through R5, but ordinarily...