Alfalfa

The king of nitrogen fixation, especially in the upper Midwest and further west. Farther south I’ve heard reports of sunn hemp performing better.

Studies in Utah have grown 200bu/a corn without the addition of nitrogen simply by planting in alfalfa residue. Or an equivalent of 140lbs of N/acre, just through the atmospheric fixation of the root nodules.

This is the nitrogen equivalent of 20lbs of 15-15-15 on 1000sqft garden, easily enough for whatever intensive crops you have

If you haven’t tried building your soil through the use of legumes, I highly recommend giving it a try. Not only are the nutrients there, but they’re gradually released like a slow release fertilizer keeping the nutrients from washing down stream.

On top of that the organic matter will loosen the soil structure and greatly help water retention and aeration. Just cut a healthy stand of any legume, cowpeas are another great option in the south, and let it decay into the ground or churn it under. This would work just fine in a raised bed.

I’ve seen my potato yields benefit specifically from alfalfa residue churned under in this way.

And other organic matter can work for this but legumes will provide the most nitrogen. Some people will rake the leaves out of their yards every year and eventually that soil will be so poor the grass hardly grows. So when we talk about soil building we are doing the opposite, putting the nutrients back in, uncompacting the soil, correcting drainage and irrigation issues.

High in protein and excellent forage/hay. It’s a common ingredient in rabbit food. I’ve read in storeys guide to raising rabbits that alfalfa and oats can be a complete food source long term with some extremely old bunnies following that diet. That’s not advice, but I do raise my own rabbits and they love my alfalfa