Nitrogen fixers Leguminous plants, such as clover and soybeans, can form a symbiotic relationship with certain soil bacteria called rhizobia. There they extract nitrogen from the air and change it into a form plants can use. It is common practice to coat seeds with the particular species of rhizobia that the legume prefers just prior to planting. This process is called inoculation. Most of our legume seed is raw, meaning it's not already inoculated.
Inoculants have a limited shelf life.
Therefore, it's best to buy fresh inoculant each season. In fact, soils with excessively high nitrogen can retard the nitrogen fixing ability of legumes. All plants liberate some nitrogen when they decompose, but legumes such as alfalfa, bell beans, cowpeas, field peas, soybeans and all the vetches create a net gain in soil nitrogen. Nurse crops A nurse crop assists the development of a slower maturing crop. For example, oats can be planted with clover to provide the clover with shelter from the wind, rain and sun.