Medium red clover can fix up to 100 pounds of nitrogen per acre! It's dense, matted foliage and thick roots are very effective at building organic matter too. Clover also draw nutrients that are below most root lines and draw them up closer to the surface, making them accessible to vegetable crops that follow.
Red clover is a perennial, and will not winter kill. Sow in spring, summer or fall, and mow to prevent seed set. In the following spring, after the first season, mow and incorporate well by hand or with mechanical cultivate. Also makes a great pasture crop.
Garden Pack: 1/8 pound, sows roughly 250 square feet
Homestead Pack: 1/4 pound, sows roughly 500 square feet
Farm Pack: 1 pound, sows 2,000 square feet