Good Nitrogen Fixing Plants for Citrus, Thats Hardy in Zone 9B

New to this forum and permaculture, looking for a zone 9b hardy plant that does a good job at repairing the nitrogen content of the soil for my orange, lemon and pomegranate trees. I ordered some Erythrina herbacea (Coral Bean), I heard through a separate thread that this may be a good one but still unsure. Keep in mind I live where it gets to 120 degrees F.

Mimosa and broom are the common ones around here but they might be considered too invasive.

Traditionally, the locals will pee under citrus trees, ensuring each one gets a regular dose.  Your mileage might vary on the suitability of that approach though.