50 pounds at a time so I have done two sidedress applications in those spots, both before the corn is too tall to get through with my applicator. Most of my soil can hold at least #100 at a time though.

In theory soil will hold 10 lbs/N for each point of CEC. 

In practice, HERE, our soils have held 24 lbs of N.

HERE I know if enogh N is dumped on the soil it will take 7 years to show signs of nitrogen stress. 
Go to the East Texas  Sandy soils and the school solution says N plays out in 6 weeks. In practice, there, their nitrogen starts to play out in 3 weeks.