How humans have disrupted nitrogen cycle

More and more, scientists are getting a better grip on the nitrogen cycle. They are learning about sources of nitrogen and how this element changes as it loops from the nonliving, such as the atmosphere, soil or water, to the living, whether plants or animals. Scientists have determined that humans are disrupting the nitrogen cycle by altering the amount of nitrogen that is stored in the biosphere. The chief culprit is fossil fuel combustion, which releases nitric oxides into the air that combine with other elements to form smog and acid rain. But it has been difficult to know precisely the extent to which such emissions have altered the nitrogen
balance.