If you are planting into a good stand of alfalfa, you might not need much or any extra nitrogen.
One year, I fall plowed down a heavy stand of alfalfa. In the spring, I sidedressed several different rates of 28%, from 125 units down to 0 units/acre.
I also planted one strip of corn without any starter.
At harvest, there was less than 5 bu/ac. difference in yield across the whole plot. The item of biggest interest was that the strip without starter fertilizer was a point or two higher in moisture, indicating that in that particular year, the starter gave the corn a quicker start in the early part of the year.
The strip with the highest rate of N was the wettest at harvest, with no significant difference in yield (1 -2 bu).
I don't know how no-tilling would affect the rate of release of the nitrogen that the alfalfa fixed. I think it would make a difference toward slowing it down.
That is my experience with utilizing nitrogen following legumes. I now give more credit to legumes preceding corn than I used to. But it is still scary and it's easy to put the N down for insurance. There is no consistant, accurate soil test for N in our cooler soils.
I should add that the field had a history of good cattle manure application, being covered every 2 years at about 12 tonnes per acre.