“One limiting factor is just how densely can corn plants grow in a given area of soil. If just a few more rows of plants per acre could be added the increase might be enormous.”
High stress hybrids and GMOS are being tested for more rows.
I know that the U of Illinois had planted a number of plots with 44,000 plants per acred but I have not found out how the yield turned out. The average in the US for farmers is 30,000 plants per acre and if they can get the High stress hybrids to work there could be a huge increase in yield.
I found some interesting info at this site:
www.uwex.edu/ces/crops/CornPlantDensity04.htm.