Certified GKH Gardening Expert
There could be a number of reasons for this. Usually, you will not feed any member of the legume family with any amount of nitrogen. They fix their own from the atmosphere and store it in root nodules. Fertilizing with nitrogen will end up with plants that burn up into a papery consistency and die.
The alternative, would be a fungal infection from overwatering. This is also common. To be safe, you will want to add dolomitic lime and wettable sulfur to the area to kill off anything lurking. These will contribute to the health of the plant, as well.
If you can include a photo, I will be better able to see what is going on.