Ag Engineering/Agronomy, Central Iowa and BioCentury Research Farms
Not all corn and soybeans are produced as bulk commodities. Some end-use customers such as processors of low-linolenic soybean oil, organic growers, and seed producers desire products with extremely low amounts or no commingled grain from other varieties or crops. Multiple sources of contamination from residual grain within on-farm equipment are possible, but the combine has the greatest number and size of cavities to harbor grain even after the unloading auger has emptied the grain tank.
Iowa State University
Hanna, H. Mark and Jarboe, Darren H., "Combine Cleanout for Identity-Preserved Grain Production" (2007). Iowa State Research Farm Progress Reports. 843.