Iowa State College experiments show that a lot of nitrogren can be cheaply produced by adding a legume seeding to the oats preceding corn. Research indicates every farmer could profitably make a legume seeding for green manure in every acre of oats in addition to meadow and rotation plantings.
Johnson, I. J.; Bartholomew, W. V.; and Fribourg, H. A.
"More Legumes for Green Manure = More Corn,"
Iowa Farm Science: Vol. 9
, Article 4.
Available at: https://lib.dr.iastate.edu/farmscience/vol9/iss3/4