You can add other ingredients to the soup, for example green split peas, or root parsley if you have some (leaves as well as the root). You can also add spinach. I simply recommend to you to try the combinations that come to your mind :)
I also recommend to you this alternative recipe :
half of radish haulm, 150 gr of split peas, 2 medium zucchini, vegetable broth, garlic, oregano, bay leaf, 1 tsp of lemon confit paste with ginger. Perfect for a spring recipe :)
Also, you can serve your soup with small slices of bread with fresh cheese and radishes: cut a few slices of good bread, spread fresh cream or fresh cheese (cow, goat, sheep... or whatever you like!) on top, and arrange the radishes cut into thin slices. Sprinkle finely chopped chives on the toast.