A research team from the Hefei Institutes of Physical Science of the Chinese Academy of Sciences has introduced a soil amendment called humic acid-modified bentonite (HAMB). This amendment effectively enhances a soil's ability to hold onto ammonium while significantly reducing harmful nitrogen losses.

These results were published in Journal of Soils and Sediments on January 14.

Nitrogen is essential for crop growth, yet retaining this valuable resource is a major challenge in agriculture. A significant portion of soil nitrogen is lost through two key pathways: ammonium leaching and ammonia volatilization. These losses waste agricultural inputs and threaten environmental quality and human health. Traditional soil systems often lack the capacity to retain sufficient ammonium.

In this study, researchers found that applying HAMB enhanced the soil's ammonium adsorption capacity while suppressing desorption. These beneficial effects lasted 6-7 months. Importantly, the amendment's impact extended vertically to subsoil layers below the application zone, which is key for reducing deep nitrogen leaching.

Over the course of a three-year field experiment, HAMB substantially reduced potential ammonium leaching and ammonia volatilization compared to untreated soils, demonstrating its strong, sustained ability to mitigate nitrogen loss.

Further analysis showed that HAMB significantly enhanced the soil's maximum ammonium adsorption capacity (Q_max) and buffering capacity for several months. These improvements were identified as the key factors driving long-term ammonium retention in soil.

This innovative soil amendment provides a promising strategy for improving nitrogen use efficiency and promoting more sustainable agricultural practices.

Placement of HAMB in the soil layers and the sampling time (Image by YANG Yang)