A slightly heavier, but naturally occurring, form of nitrogen acts as a yardstick in identifying the source of nitrate pollution in cave water, springs and streams. Nitrate is a form of nitrogen available to plants. ARS researchers have been measuring the nitrogen form, N-15, in nitrate removed from soil, water and mineral deposits in caves. Tracing nitrate back to its source helps the researchers understand nitrate pollution and recommend solutions to farmers. A year's data confirms earlier studies showing that nitrate with high N-15 levels comes from animal waste, while nitrate with low levels comes from commercial fertilizer.
Medium levels come from soil microbes.
Also, the first year's data indicate that during the winter, the main source of nitrate pollution is animal waste. Summer's main sources are commercial fertilizer and soil microbes. When scientists replaced a third of a nitrogen fertilizer with a blend of composts from sewage sludge and municipal trash, they found that tall fescue grass didn't miss the fertilizer. That's because compost nitrogen is a slow-release form that the grass uses more efficiently with less waste. So grass fertilized with compost took in as much nitrogen as more heavily fertilized grass.