Your test is showing nitrate-N. The N from your alfalfa is tied up as organic nitrogen, and will be released over time. 

When we rotate from alfalfa to corn, we use "book values" for the amount of nitrogen available from the alfalfa, as it is a "better" estimate than a soil test.  You might want to find out what recommendations Minn Extensions supplies for situations like this.  That is what I would do.

at least find out what Minn Ext recommends, and then factor that into your decision-making, whether you follow it to a "T" or not.