I doubt anyone can answer your question definitively without knowing how fertile or depleted your soil is.

If you have had a soil test you might be able to do the math considering that alfalfa pellets have 3% nitrogen and I expect the meal to be similar. However from what I read the nitrogen analysis of soil tests is not reliable due to the mobility of nitrogen in soil.

While alfalfa meal or pellets are a great garden fertilizer IMO they are better regarded as a soil amendment than a fertilizer as they improve the soil on several levels. Their value for me is that they are organic, contain micronutrients and a plant hormone that stimulates growth, work quickly but also have long term benefits in that they feed the worms thus providing worm castings for an extended period. Worm castings are known to be one of the best fertilizers.

I use a small handful (probably 1/4 cup) of alfalfa pellets in the planting hole of each perennial so you might use less than that amount per square foot as the meal is more condensed. You can always add more later but can't remove once added so I'd not add too much.

I've also broadcast the pellets over my iris bed and the results were seen very quickly in improved color and growth of leaves. So if you see leaves that are not as green as they might be you can judiciously add more.

The standard application rate for alfalfa meal (2-1-2) in a new planting area is one cup per 10 square feet or 3 cups per 1/2 cubic foot (raised bed soils).