Little, if any, fertilizer nitrogen is needed by legume seed crops. Measure soil pH, phosphorus, potassium, and boron with a soil test to determine need. Red Clover requires a soil pH above 6.0. Annually apply sulfur before mid-March with other nutrients, if they are needed.
Red Clover Western Oregon Fertilizer Guide
Crimson Clover, Vetch, Field Peas Western Oregon Fertilizer Guide