Nitrogen is essential to all life, yet most organisms do not have the ability to use atmospheric (molecular) nitrogen. However, some plants, called pulse crops—also known as legumes, such as peas or lentils—form a symbiotic relationship with nitrogen-fixing bacteria. Through this process of biological nitrogen fixation (BNF), pulse crops convert nitrogen into a biologically available form, fertilizing and rejuvenating the soil. In Montana, pulse crops are a growing market and an alternative to fallowing fields. This lesson explores the importance of nitrogen to life and the chemical process of BNF.