Hatcher said that if hydrochloric acid didn't significantly attack the nitrogen-15 enriched proteins in the laboratory, weaker forces of decomposition in the environment such as bacteria would be unlikely to release the nitrogen in nature.
He added that this process may be the same one that can cause farmland to lose its fertility over time. Farmers regularly fertilize with nitrogen to replace nutrients that crops take from the soil. They also till crops back into soil so that bacteria can break down the protein-rich plant remains and release the nutrients.
If humic acid is responsible for trapping nitrogen-bearing proteins in farmland, Hatcher says, the process would happen most often in watery areas such as rice farms. That would explain why rice paddies in southeast Asia have yielded less rice over the past few decades, despite the fact that farmers add nitrogen-rich fertilizer.
Hatcher said little of the nitrogen fertilizer ever reaches the rice plants. The fertilizer promotes the growth of algae, he explained, which absorb the nitrogen and eventually settle into the underwater sediment along with other decomposed plant matter. Humic acid can then absorb the proteins in the dead algae, trapping the nitrogen.