Have you ever used cover crops?
Cover crops are plants that are grown in order to cover a bare patch of ground, anytime it's not in use. Such as a backyard garden or an agricultural field. Cover crops help protect the land from loss of water and soil. There are different types of cover crops, and each have advantages and disadvantages.
If you choose a leguminous cover crop, such as vetch, clover, peas, alfalfa, or beans, the cover crop will add nitrogen to the soil. Many people use nitrogen fertilizers, but keep in mind that those types of fertilizers are salts. If you use a legume cover crop, you'll get organic matter plus nitrogen... and no salts added.
However, legumes do grow a bit slower than non-legume crops. This is actually because of their ability to produce nitrogen. Legume crops form a relationship with rhizobia bacteria in the soil, and it's actually the rhizobia bacteria which "fix" nitrogen from the atmosphere (breaking apart the devilishly strong triple bond), making it available it for the legume plant and other plants in the surround soil. In return, the plant provides some of its carbohydrates to the bacteria. So the legume plants often don't grow as fast as other plants because they're giving away...