School of Environment, Tsinghua University, Beijing 100084, China.
School of Environment, Tsinghua University, Beijing 100084, China.
J Environ Sci (China). 2025 Apr;150:362-372. doi: 10.1016/j.jes.2024.01.042. Epub 2024 Feb 10.
As a widely used fertilizer, urea significantly promotes the leaching of dissolved organic nitrogen (DON) in soils and aggravates nitrogen contamination in groundwater. Clay minerals are considered the most important factor in retaining DON. However, the effect of urea on the retention of DON with different molecular weights by clay minerals is unknown. In this study, the retention of both low-molecular weight DON (LMWD) and high-molecular weight DON (HMWD) by clay minerals in the presence of urea was investigated. For this purpose, batch adsorption and soil column leaching experiments, characterization analysis (Fourier transform infrared spectroscopy X-ray diffraction, and X-ray photoelectron spectroscopy), and molecular dynamics simulations were carried out. Urea had a positive effect on the adsorption of LMWD, whereas a competitive effect existed for the adsorption of HMWD. The dominant interactions among DON, urea, and clay minerals included H-bonding, ligand exchange, and cation exchange. The urea was preferentially adsorbed on clay minerals and formed a complex, which provided more adsorption sites to LMWD and only a few to HMWD. The presence of urea increased the retention of LMWD and decreased the retention of HMWD in clay minerals. The retention capacity of LMWD increased by 6.9%-12.8%, while that of HMWD decreased by 6.7%-53.1%. These findings suggest that LMWD tended to be trapped in soils, while HMWD was prone to be leached into groundwater, which can be used to evaluate the leaching of DON from soil to groundwater.
作为一种广泛使用的肥料，尿素显著促进了土壤中溶解有机氮（DON）的淋失，并加剧了地下水的氮污染。粘土矿物被认为是保留 DON 的最重要因素。然而，尿素对不同分子量的 DON 被粘土矿物保留的影响尚不清楚。在本研究中，研究了尿素存在下粘土矿物对低分子量 DON（LMWD）和高分子量 DON（HMWD）的保留作用。为此，进行了批量吸附和土壤柱淋滤实验、特征分析（傅里叶变换红外光谱、X 射线衍射和 X 射线光电子能谱）和分子动力学模拟。尿素对 LMWD 的吸附有积极影响，而对 HMWD 的吸附则存在竞争作用。DON、尿素和粘土矿物之间的主要相互作用包括氢键、配体交换和阳离子交换。尿素优先吸附在粘土矿物上并形成复合物，这为 LMWD 提供了更多的吸附位点，而对 HMWD 只有少数吸附位点。尿素的存在增加了 LMWD 在粘土矿物中的保留，降低了 HMWD 的保留。LMWD 的保留能力增加了 6.9%-12.8%，而 HMWD 的保留能力则降低了 6.7%-53.1%。这些发现表明，LMWD 倾向于被截留于土壤中，而 HMWD 则容易淋滤到地下水中，这可用于评估 DON 从土壤向地下水的淋失。
