As for a species....hairy vetch has many advantages but is rarely used in food plot mixes.
Advantages:
-high N fixation potential
-weed smother crop
-good for grazing
-pollinator/beneficial insect attraction
-generally fall planted in the south
Rates:
-for general purpose use 2-6 lb/ac in mixes with small grains
-for optimum weed smothering use 6-12 lb/ac in mixes with small grains