I could not find a nutrient analysis of corn ash. In fact, the nitrogen content of your ash may differ greatly from what a lab test produces for some other corn ash. The chemistry of the ash will depend greatly on the fuel source and the burning conditions.

However, I did check with Extension Soil Scientist Carl Rosen. Although he has not seen a nutrient analysis of corn ash, it is his opinion that most of the nitrogen would go off as gas during the combustion process and would not be a good source of nitrogen. We, therefore, do not recommend that you use it to replace your usual nitrogen lawn fertilizer.

More importantly, several sources (including Professor Rosen) said that corn ash is a liming agent (as is wood ash). Because typical Minnesota soils are neutral to alkaline, I would strongly suggest a soil test before using any ash on your lawn or in your garden.

You might consider working some of the ash into your compost heap. But even in this case, I wouldn't use too much because it will modify the compost pH, and you don't want to alter the heap's chemistry too drastically.

Here is a Web site that discusses burning corn, with a brief discussion of the ash:
http://burncorn.cas.psu.edu/