So much focus is put into fall food plots and mainly brassicas. Most food plotters have perennial food plots as well, which typically consist of clover blends and alfalfas. I hear so often how people's perennials are not long lasting and vigorous and there are reasons for this.
It's all about the roots
Most farmers know how to manage their legumes to keep the forages healthy and set up for the winter. The initial growth of perennial forage legumes after every cutting or clipping depends on energy reserves stored in the taproots and crowns of the plants. High energy reserves are important for fast regrowth, which results in higher yields. Substantial energy reserves are also needed for the development of cold hardiness, which allows the plant to persist during the winter and still have enough energy for good spring growth. Research has shown energy reserves are usually highest when the plant is in the full-bloom stage and usually lowest a short time after cutting, when the plant is growing rapidly. What this means to us in the fall is to clip early enough that the plant still has time to get good regrowth into a later growth stage, where root reserves are built up. We don't want to clip too early so that the forage becomes over mature "ripe" where the deer will not get good nutrition or utilization. Sept 15 should be the latest date to clip in many northern climates and sept 1 in areas in the far northern zones.
Fall Fertilizer Annually
Each ton of dry matter of alfalfa grazed, harvested or clipped removes 7 lbs of phosphorous and 48 lbs of potassium.
Each ton of dry matter grazed, harvested, clipped or removed 12 lbs phosphorous and 42 lbs of potassium.
So, if you have an alfalfa field with a yield of 6 ton of dry matter per acre, you'd need to get 288 lbs of potassium down to maintain soil potassium levels (48x6 )
A clover field that you remove 3 ton of dry matter per acre, you'd need to get 126 lbs of potassium down to maintain soil potassium levels.
If you use 0-0-60 potassium. You would need to use 126/.60 = 210 pounds of 0-0-60 potassium needed to fertilizer per acre per year. You could always split applications of fertilizer of perennial plots,, putting 1/2 down in the spring and 1/2 down in the fall.
In summary, you get out of what you put into the soil. It takes "groceries" every year so as to not "mine the soil."