climate, tile, fertilizer, and irrigation...

in that order.

if you dont have the climate to grow good corn dont even start.  if you do but your soils are poor... install tile... pattern tile... more for clay hills... every acre needs good drainage and to be able to breath...

next you need a good balanced fertilizer program and enough of it... a mixture between immediately avaliable and more steady fertilizers, making sure your soils are balanced and at the right ph...

and finially the last thing if everything else is done is irrigation as poorer soils are going to have a harder time holding water, irrigation will guarrantee water at the right times... 

making it cost effective is another thing because the goal is not to have the highest yield but to make the most money per acre with a long term plan to sustain that...

with higher prices and higher incomes some of these options may now be affordable...