Only 20 percent of the soybean seed sampls from a three-county survey could be classified as good seed. Weed seed and varietal contamination was high. Most soybean seed was homegrown or bought from a neighbor.
Knott, Oliver A.
"How Good is Iowa Soybean Seed?,"
Iowa Farm Science: Vol. 21
, Article 6.
Available at: https://lib.dr.iastate.edu/farmscience/vol21/iss1/6