Alfalfa pellets have an N-P-K of about 3-1-2. Primarily a source of nitrogen, alfalfa pellets also contain trace minerals and triacontanol, a plant growth stimulator.

-Deerslayer

Alfalfa Pellets or Meal are primarily used to increase organic matter in the soil but do offer nutrients and a high availability of trace minerals. (good bacterial food) As deerslayer stated they contain trianconatol, a natural fatty-acid growth stimulant.

I found, from this site, the more diverse your grains the more diverse the biology.

All feed grains will increase organic matter in the soil. Many people incorporate alfalfa into the soil prior to seeding. It is an excellent starter fertilizer The growth stimulator gives new grass plants a jump-start.

-Deerslayer