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.
We're basically at the tip of the iceberg. Next Hatcher and Zang will try the same experiment with humic acid from other locations, and see whether it can trap other molecules. This work was funded by the National Science Foundation. In a related future project, Hatcher plans to study whether humic acid traps nitrogen in forests.