Fertilizer linked to greenhouse gas rise BERKELY, Calif., April 2 (UPI) -- Fertilizer use over the past 50 years is responsible for an increase of the major greenhouse gas nitrous oxide in the Earth's atmosphere, U.S. scientists say. Climate scientist confirmed the cause of the increased nitrous oxide was nitrogen-based fertilizer, which stimulates microbes in soil to convert nitrogen to nitrous oxide at a faster rate than normal, the University of California, Berkeley, reported Monday. The researchers used nitrogen isotope data to identify the fingerprint of fertilizer use in archived air samples from Antarctica and Tasmania. "Our study is the first to show empirically from the data at hand alone that the nitrogen isotope ratio in the atmosphere and how it has changed over time is a fingerprint of fertilizer use," study leader Kristie Boering, a professor of chemistry and of earth and planetary science, said. Boering and her colleagues obtained air samples from Antarctic ice, called firn air, dating from 1940 to 2005, and from an atmospheric monitoring station at Cape Grim, Tasmania, which has archived air back to 1978. A significant increase in atmospheric nitrous oxide began in the 1960s, the researchers said, when inexpensive synthetic fertilizer and other developments boosted food production worldwide. We are not vilifying fertilizer. We can't just stop using fertilizer," Boering said. But we hope this study will contribute to changes in fertilizer use and agricultural practices that will help to mitigate the release of nitrous oxide into the atmosphere.