Research in the 1990's in WI, MN, and IA tried to increase soybean yields by adding nitrogen to soybeans, preplant, and at vegetative and reproductive plant stages. Yield increases could not be consistently achieved and in some cases yields decreased. Many states do not recommend adding nitrogen to soybeans at any stage of development. Bill Cox's research in New York showed that nitrogen showed no economic advantage when applied at planting.

More recent studies have shown an advantage to nitrogen applications under certain conditions. Most researchers agree that almost 60% of the nitrogen used by soybeans comes from the symbiotic relationship with rizobia on its roots. The addition...